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Software industry

2010-09-28T12:40:00Z

220.227.122.253: /* Vijay History */

{{globalize}}

The '''software industry''' includes businesses involved in the [[software development|development]], [[software maintenance|maintenance]] and [[software publisher|publication]] of [[computer software]] using any business model. The industry also includes software [[Service (economics)|service]]s, such as [[training]], [[software documentation|documentation]], and [[consultancy|consulting]].

==History ==
The word "software" had been coined as a prank by at least 1953, but did not appear in print until the 1960s.<ref>{{cite web |author= Paul Niquette |title= Softword: Provenance for the Word 'Software' |year= 1995 |url= http://www.niquette.com/books/softword/tocsoft.html }} adapted from ''Sophisticated: The Magazine'' ISBN 1-58922-233-4</ref>
Before this time, computers were programmed either by customers, or the few commercial computer vendors of the time, such as [[UNIVAC]] and [[IBM]].
The first company founded to provide software products and services was [[Computer Usage Company]] in 1955.<ref>{{cite journal |title= Recollections of the first software company |author= Elmer C. Kubie |journal= IEEE Annals of the History of Computing |work= Annals of the History of Computing |volume= 16 |issue= 2 |publisher= IEEE Computer Society |date= Summer 1994 |pages= 65–71 |doi= 10.1109/85.279238 }}</ref>
The software industry expanded in the early 1960s, almost immediately after computers were first sold in mass-produced quantities. Universities, government, and business customers created a demand for software. Many of these programs were written in-house by full-time staff programmers. Some were distributed freely between users of a particular machine for no charge. Others were done on a commercial basis, and other firms such as [[Computer Sciences Corporation]] (founded in 1959) started to grow. The computer-makers started bundling [[operating systems]] software and programming environments with their machines.

When [[Digital Equipment Corporation]] brought a relatively low-priced micro-computer to market, it brought computing within reach of many more companies and universities worldwide, and it spawned great innovation in terms of new, powerful programming languages and methodologies. New software was built for micro-computers, and others, including IBM, followed DECs example quickly, resulting in the IBM AS400 amongst others.

The industry expanded greatly with the rise of the personal computer in the mid-1970s, which brought computing to the desktop of the office worker. In subsequent years, it also created a growing market for games, applications, and utilities. DOS, [[Microsoft]]'s first operating system product, was the dominant operating system at the time.

In the early years of the 21st century, another successful business model has arisen for hosted software, called software as a service, or [[SaaS]]; this was at least the third time this model had been attempted. SaaS reduces the concerns about software piracy, since it can only be accessed through the Web, and by definition no client software is loaded onto the end user's PC.

== Software sectors ==
There are several types of businesses in the software industry. Infrastructure software, including operating systems, middleware and databases, is made by companies such as [[Microsoft]], [[IBM]], [[Sybase]], [[EMC Corporation|EMC]], [[Oracle Corporation|Oracle]] and [[VMWare]]. Enterprise software, the software that automates business processes in finance, production, logistics, sales and marketing, is made by [[Oracle Corporation|Oracle]], [[SAP AG]] , [[Sage]] and [[Infor]]. Security software is made by the likes of [[Symantec]], [[Trend Micro]] and [[Kaspersky]]. Several industry-specific software makers are also among the largest software companies in the world: [[SunGard]], making software for banks, [[BlackBoard]] making software for schools, and companies like [[Qualcomm]] or [[CyberVision]] making software for telecom companies.
Other companies do contract programming to develop unique software for one particular client company, or focus on configuring and customizing suites from large vendors such as SAP or Oracle.

== Leading companies: mindshare and marketshare ==
In terms of technology leadership, the software industry has long been led by IBM. However, Microsoft became the dominant PC operating system supplier. Other companies that have substantial mindshare (not: marketshare) in the software industry are SUN Microsystems, the developer of the Java platform (purchased by Oracle in 2009), Red Hat, for its open source momentum, and Google for its Google Docs. However in terms of revenues coming from software sales, the software industry is clearly dominated by Microsoft, since inception.Microsoft products are still sold in largest number across the globe.

== Size of the industry ==
According to market researcher DataMonitor, the size of the worldwide software industry in 2008 was US$ 303.8 billion, an increase of 6.5% compared to 2007. Americas account for 42.6% of the global software market's value. DataMonitor forecasts that in 2013, the global software market will have a value of US$ 457 billion, an increase of 50.5% since 2008.<ref>[http://www.infoedge.com/product_type.asp?product=DO-4959 DataMonitor - Abstract from Global Software Industry Guide - 2008]</ref>

== Business models the software industry ==

Business models of software companies have been widely discussed.<ref name="cusumano">Cusumano M. (2003) Finding Your balance in the Products and Service Debate, Communications of the ACM. Vol. 46:3</ref><ref name="ReferenceA">{{cite book
| title = Profit from Software Ecosystems: Business Models, Ecosystems and Partnerships in the Software Industry
| year = 2010
| publisher = BOD
| location = Norderstedt, Germany
| isbn = 3839169836
| author9 = Karl M. Popp and Ralf Meyer}}</ref> Network effects in [[software ecosystems]] networks of companies and their customers are an important element in the strategy of software companies.<ref name="ReferenceA"/><ref>{{cite book
| title = Software Ecosystem: Understanding an Indispensable Technology and Industry
| year = 2003
| publisher = MIT Press
| location = Cambridge, MA, USA
| isbn = 0262134322
| author9 = David G. Messerschmitt and Clemens Szyperski}}</ref>

== See also ==
* [[Computer software]]
* [[Software development]]
* [[Software publisher]]
* [[Software engineering]]
* [[World's largest software companies]]

== References ==
{{reflist}}

== External links ==
{{Wiktionary}}
* [http://www.siia.net/ Software and Information Industry Association website]
* [http://www.softwareceo.com/ SoftwareCEO] the largest online community of software executives in the world
* [http://www.softwaremag.com/ Software Magazine website]
* [http://www.siprofessionals.org/ Software Industry Professionals website]
* [http://www.sao.org/ Software Association of Oregon website]

[[Category:Software industry|*]]

[[ar:صناعة البرمجيات]]
[[es:Industria del software]]
[[it:Industria del software]]
[[no:Programvareselskap]]
[[pt:Indústria de software]]
[[ru:Индустрия программного обеспечения]]
[[simple:Software company]]
[[sv:Programvaruföretag]]
[[th:ซอฟต์แวร์เชิงพาณิชย์]]

About fracture mechanics

2009-04-11T11:59:18Z

220.227.77.227: /* R-curve */

'''Fracture mechanics''' is the field of [[mechanics]] concerned with the study of the formation of cracks in materials. It uses methods of analytical [[solid mechanics]] to calculate the driving force on a crack and those of experimental solid mechanics to characterize the material's resistance to [[fracture]].

In modern [[materials science]], fracture mechanics is an important tool in improving the mechanical performance of materials and components. It applies the [[physics]] of [[stress (physics)|stress]] and [[Strain (materials science)|strain]], in particular the theories of [[Elasticity (physics)|elasticity]] and [[plasticity (physics)|plasticity]], to the microscopic [[crystallographic defect]]s found in real materials in order to predict the macroscopic mechanical failure of bodies. [[Fractography]] is widely used with fracture mechanics to understand the causes of failures and also verify the theoretical failure predictions with real life failures.

==The need for fracture mechanics==
[[Image:Tay1.jpg|thumb|right|Tay Bridge Disaster (1879)]]

In many cases, failure of engineering structures through fracture can be fatal; one example is that of the [[Tay Rail Bridge disaster]] (right). Often disasters occur because engineering structures contain cracks—arising either during production or during service (e.g. from [[Fatigue (material)|fatigue]]). For instance, growth of cracks in pressure vessels due to crack propagation could cause a fatal explosion. If failure were ever to happen, we would rather it were by [[yield (engineering)|yield]] or by leak before break.

[[Image:CrackForceLines.gif|thumb|right|Internal [[force lines]] are denser in the crack tips]]

Since cracks can lower the strength of the structure beyond that due to loss of load-bearing area a material property, above and beyond conventional strength, is needed to describe the fracture resistance of engineering materials. This is the reason for the need for fracture mechanics—the evaluation of the strength of cracked structures.

==History==
===Griffith's energy relation===
[[Image:EdgeCrack2D.png|thumb|right|An edge crack (flaw) of length <math>a</math>in a material.]]

Fracture mechanics was invented during World War I by English aeronautical engineer, [[Alan Arnold Griffith|A. A. Griffith]], to explain the failure of brittle materials.<ref>{{Citation | last = Griffith | first = A. A. | author-link = Alan Arnold Griffith | title = The phenomena of rupture and flow in solids | journal = Philosophical Transactions of the Royal Society of London | series = A | volume = 221 | pages = 163–198 | year = 1921 | url = http://www.cmse.ed.ac.uk/AdvMat45/Griffith20.pdf}}.</ref> Griffith's work was motivated by two contradictory facts:

* The stress needed to fracture bulk [[glass]] is around {{convert|100|MPa|psi|abbr=on}}.
* The theoretical stress needed for breaking atomic bonds is approximately {{convert|10000|MPa|psi|abbr=on}}.

A theory was needed to reconcile these conflicting observations. Also, experiments on glass fibers that Griffith himself conducted suggested that the fracture stress increases as the fiber diameter decreases. Hence the uniaxial tensile strength, which had been used extensively to predict material failure before Griffith, could not be a specimen-independent material property. Griffith suggested that the low fracture strength observed in experiments, as well as the size-dependence of strength, was due to the presence of microscopic flaws in the bulk material.

To verify the flaw hypothesis, Griffith introduced an artificial flaw in his experimental specimens. The artificial flaw was in the form of a surface crack which was much larger than other flaws in a specimen. The experiments showed that the product of the square root of the flaw length (''a'') and the stress at fracture (''σ''f) was nearly constant, which is expressed by the equation:

:<math>\sigma_f\sqrt{a} \approx C</math>

An explanation of this relation in terms of linear elasticity theory is problematic. Linear elasticity theory predicts that stress (and hence the strain) at the tip of a sharp flaw in a linear [[elastic deformation|elastic]] material is infinite. To avoid that problem, Griffith developed a [[thermodynamic]] approach to explain the relation that he observed.

The growth of a crack requires the creation of two new surfaces and hence an increase in the [[surface energy]]. Griffith found an expression for the constant ''C'' in terms of the surface energy of the crack by solving the elasticity problem of a finite crack in an elastic plate. Briefly, the approach was:

* Compute the [[potential energy]] stored in a perfect specimen under an uniaxial tensile load.
* Fix the boundary so that the applied load does no work and then introduce a crack into the specimen. The crack relaxes the stress and hence reduces the [[elastic energy]] near the crack faces. On the other hand, the crack increases the total surface energy of the specimen.
* Compute the change in the [[free energy]] (surface energy − elastic energy) as a function of the crack length. Failure occurs when the free energy attains a peak value at a critical crack length, beyond which the free energy decreases by increasing the crack length, i.e. by causing fracture. Using this procedure, Griffith found that

:<math>C = \sqrt{\cfrac{2E\gamma}{\pi}}</math>

where ''E'' is the Young's modulus of the material and ''γ'' is the surface energy density of the material. Assuming ''E'' = 62 GPa and ''γ'' = 1 J/m2 gives excellent agreement of Griffith's predicted fracture stress with experimental results for glass.

===Irwin's modification of Griffith's energy relation===
[[Image:PlasticZone2D.png|400px|thumb|right|The plastic zone around a crack tip in a ductile material.]]

<blockquote>
''Griffith's work was largely ignored by the engineering community until the early 1950s. The reasons for this appear to be (a) in the actual structural materials the level of energy needed to cause fracture is orders of magnitude higher than the corresponding surface energy, and (b) in structural materials there are always some inelastic deformations around the crack front that would make the assumption of linear elastic medium with infinite stresses at the crack tip highly unrealistic.'' '''F. Erdogan (2000)'''<ref name=Erdogan00>E. Erdogan (2000) ''Fracture Mechanics'', International Journal of Solids and Structures, 27, pp. 171–183.</ref>
</blockquote>

Griffith's theory provides excellent agreement with experimental data for [[brittle]] materials such as glass. For [[ductile]] materials such as [[steel]], though the relation <math> \sigma_y\sqrt{a} = C </math> still holds, the surface energy (''γ'') predicted by Griffith's theory is usually unrealistically high. A group working under [[G. R. Irwin]]<ref name=Irwin57>Irwin G (1957), ''Analysis of stresses and strains near the end of a crack traversing a plate'', Journal of Applied Mechanics 24, 361–364.</ref> at the U.S. Naval Research Laboratory (NRL) during World War II realized that plasticity must play a significant role in the fracture of ductile materials.

In ductile materials (and even in materials that appear to be brittle<ref>Orowan, E., 1948. ''Fracture and strength of solids''. Reports on Progress in Physics XII, 185–232.</ref>), a [[plastic]] zone develops at the tip of the crack. As the applied [[Structural load|load]] increases, the plastic zone increases in size until the crack grows and the material behind the crack tip unloads. The plastic loading and unloading cycle near the crack tip leads to the [[dissipation]] of [[energy]] as [[heat]]. Hence, a dissipative term has to be added to the energy balance relation devised by Griffith for brittle materials. In physical terms, additional energy is needed for crack growth in ductile materials when compared to brittle materials.

Irwin's strategy was to partition the energy into two parts:
* the stored elastic strain energy which is released as a crack grows. This is the thermodynamic driving force for fracture.
* the dissipated energy which includes plastic dissipation and the surface energy (and any other dissipative forces that may be at work). The dissipated energy provides the thermodynamic resistance to fracture. Then the total energy dissipated is

:<math>G = 2\gamma + G_p</math>

where ''γ'' is the surface energy and ''G''p is the plastic dissipation (and dissipation from other sources) per unit area of crack growth.

The modified version of Griffith's energy criterion can then be written as

:<math>\sigma_f\sqrt{a} = \sqrt{\cfrac{E~G}{\pi}}.</math>

For brittle materials such as glass, the surface energy term dominates and <math>G \approx 2\gamma = 2 \,\, J/m^2</math>. For ductile materials such as steel, the plastic dissipation term dominates and <math>G \approx G_p = 1000 \,\, J/m^2</math>. For [[polymers]] close to the [[glass transition]] temperature, we have intermediate values of <math>G \approx 2-1000 \,\, J/m^2</math>.

=== Stress intensity factor ===
Another significant achievement of Irwin and his colleagues was to find a method of calculating the amount of energy available for fracture in terms of the asymptotic stress and displacement fields around a crack front in a linear elastic solid.<ref name="Irwin57" /> This asymptotic expression for the stress field around a crack tip is

:<math>\sigma_{ij} \approx \left(\cfrac{K}{\sqrt{2\pi r}}\right)~f_{ij}(\theta)</math>

where ''σ''ij are the Cauchy stresses, ''r'' is the distance from the crack tip, ''θ'' is the angle with respect to the plane of the crack, and ''f''ij are functions that are independent of the crack geometry and loading conditions. Irwin called the quantity ''K'' the ''[[stress intensity factor]]''. Since the quantity ''f''ij is dimensionless, the stress intensity factor can be expressed in units of <math>\text{Pa-}\sqrt{\text{m}}</math>.

=== Strain energy release rate ===
Irwin was the first to observe that if the size of the plastic zone around a crack is small compared to the size of the crack, the energy required to grow the crack will not be critically dependent on the state of stress at the crack tip.<ref name="Erdogan00"/> In other words, a purely elastic solution may be used to calculate the amount of energy available for fracture.

The energy release rate for crack growth or ''strain energy release rate'' may then be calculated the change in elastic strain energy per unit area of crack growth, i.e.,

:<math>G := -\left[\cfrac{\partial U}{\partial a}\right]_P = -\left[\cfrac{\partial U}{\partial a}\right]_u</math>

where ''U'' is the elastic energy of the system and ''a'' is the crack length. Either the load ''P'' or the displacement ''u'' can be kept fixed while evaluating the above expressions.

Irwin showed that for a [[fracture#Crack separation modes|mode I crack]] the strain energy release rate and the stress intensity factor are related by:
:<math>
G = G_I = \begin{cases} \cfrac{K_I^2}{E} & \text{plane stress} \\
\cfrac{(1-\nu^2) K_I^2}{E} & \text{plane strain} \end{cases}
</math>
where ''E'' is the [[Young's modulus]], ''ν'' is [[Poisson's ratio]], and ''K''I is the [[stress intensity factor]] in mode I. Irwin also showed that the strain energy release rate of a planar crack in a linear elastic body can be expressed in terms of the mode I, [[fracture#Crack separation modes|mode II]], and [[fracture#Crack separation modes|mode III]] stress intensity factors for the most general loading conditions.

Next, Irwin adopted the additional assumption that the size and shape of the energy dissipation zone remains approximately constant during brittle fracture. This assumption suggests that the energy needed to create a unit fracture surface is a constant that depends only on the material. This new material property was given the name ''[[fracture toughness]]'' and designated ''G''Ic. Today, it is the related quantity ''K''Ic which is called the fracture toughness and is now universally accepted as the defining material property in linear elastic fracture mechanics.

=== Limitations of linear elastic fracture mechanics ===
[[Image:TankerSchenectady.jpg|thumb|right|The [[S.S. Schenectady|S.S. ''Schenectady'']] split apart by [[brittle fracture]] while in harbor (1944)]]

But a problem arose for the NRL researchers because naval materials, e.g., ship-plate steel, are not perfectly elastic but undergo significant [[plastic deformation]] at the tip of a crack. One basic assumption in Irwin's linear elastic fracture mechanics is that the size of the plastic zone is small compared to the crack length. However, this assumption is quite restrictive for certain types of failure in structural steels though such steels can be prone to brittle fracture, which has led to a number of catastrophic failures.

Linear-elastic fracture mechanics is of limited practical use for structural steels for another more practical reason. Fracture toughness testing is very expensive and engineers believe that sufficient information for selection of steels can be obtained from the simpler and cheaper [[Charpy impact test]].{{Fact|date=May 2008}}

==Elastic-plastic fracture mechanics==
[[Image:Aircraft Crash.jpg|thumb|right|[[Vertical stabilizer]], which separated from the aircraft leading to a fatal crash(2001)]]

Most engineering materials show some inelastic behavior under operating conditions that involve large loads.{{Fact|date=June 2008}} In such materials the assumptions of linear elastic fracture mechanics may not hold, that is,
* the plastic zone at a crack tip may have a size of the same order of magnitude as the crack size
* the size and shape of the plastic zone may change as the applied load is increased and also as the crack length increases.

Therefore a more general theory of crack growth is needed for elastic-plastic materials that can account for:
* the local conditions for initial crack growth which include the nucleation, growth, and coalescence of voids or decohesion at a crack tip.
* a global energy balance criterion for further crack growth and unstable fracture.

=== R-curve ===
An early attempt in the direction of elastic-plastic fracture mechanics was [[G. R. Irwin|Irwin's]] '''crack extension resistance curve''' or '''R-curve'''. This curve acknowledges the fact that the resistance to fracture increases with growing crack size in elastic-plastic materials. The R-curve is a plot of the total energy dissipation rate as a function of the crack size and can be used to examine the processes of slow stable crack growth and unstable fracture. However, the R-curve was not widely used in applications until the early 1970s. The main reasons appear to be that the R-curve depends on the geometry of the specimen and the crack driving force may be difficult to calculate.<ref name="Erdogan00"/>
dfkjoop[ erow werfqo wdfkwm fwot rjtpert

=== J-integral ===
In the mid-1960s [[James R. Rice]] (then at [[Brown University]]) and G. P. Cherepanov independently developed a new toughness measure to describe the case where there is sufficient crack-tip deformation that the part no longer obeys the linear-elastic approximation. Rice's analysis, which assumes non-linear elastic (or monotonic [[deformation-theory]] [[plastic]]) deformation ahead of the crack tip, is designated the [[J integral]].<ref>{{Citation | last = Rice | first = J. R. | author-link = James R. Rice | title = A path independent integral and the approximate analysis of strain concentration by notches and cracks | journal = Journal of Applied Mechanics | volume = 35 | pages = 379–386 | year = 1968 | url = http://esag.harvard.edu/rice/015_Rice_PathIndepInt_JAM68.pdf}}.</ref> This analysis is limited to situations where plastic deformation at the crack tip does not extend to the furthest edge of the loaded part. It also demands that the assumed non-linear elastic behavior of the material is a reasonable approximation in shape and magnitude to the real material's load response. The elastic-plastic failure parameter is designated JIc and is conventionally converted to KIc using Equation (3.1) of the Appendix to this article. Also note that the J integral approach reduces to the Griffith theory for linear-elastic behavior.

==Fully plastic fracture mechanics==
If the alloy is so tough that the yielded region ahead of the crack extends to the far edge of the specimen before fracture, the crack is no longer an [[effective stress]] concentrator. Instead, the presence of the crack merely serves to reduce the load-bearing area. In this regime the failure stress is conventionally assumed to be the average of the yield and ultimate strengths of the alloy.

==Engineering applications==
The following information is needed for a fracture mechanics prediction of failure:
*Applied load
*Residual stress
*Size and shape of the part
*Size, shape, location, and orientation of the crack

Usually not all of this information is available and conservative assumptions have to be made.

Occasionally post-mortem fracture-mechanics analyses are carried out. In the absence of an extreme overload, the causes are either insufficient toughness (KIc) or an excessively large crack that was not detected during routine inspection.

==Short summary==
Arising from the manufacturing process, interior and surface flaws are found in all metal structures. Not all such flaws are unstable under service conditions. Fracture mechanics is the analysis of flaws to discover those that are safe (that is, do not grow) and those that are liable to propagate as cracks and so cause [[structural failure|failure]] of the flawed structure. Fracture mechanics as a subject for critical study has barely been around for a century and thus is relatively new. There is a high demand for engineers with fracture mechanics expertise—particularly in this day and age where engineering failure is considered 'shocking' amongst the general public.

==Appendix: mathematical relations==
===Griffith's crack theory: strain energy release rate===
For the simple case of a thin rectangular plate with a crack perpendicular to the load Griffith’s theory becomes:

:<math>G = \frac{\pi \sigma^2 a}{E}\,</math>                 (1.1)

where <math>G</math> is the strain energy release rate, <math>\sigma</math> is the applied stress, <math>a</math> is half the crack length, and <math>E</math> is the [[Young’s modulus]]. The strain energy release rate can otherwise be understood as: the rate at which energy is absorbed by growth of the crack.

However, we also have that:

:<math>G_c = \frac{\pi \sigma_f^2 a}{E}\,</math>                 (1.2)

If <math>G</math> ≥ <math>G_c</math>, this is the criterion for which the crack will begin to propagate.

===Irwin's modified Griffith crack theory: fracture toughness===
Eventually a modification of Griffith’s solids theory emerged from this work; a term called [[stress intensity]] replaced strain energy release rate and a term called [[fracture toughness]] replaced surface weakness energy. Both of these terms are simply related to the energy terms that Griffith used:

:<math>K_I = \sigma \sqrt{\pi a}\,</math>                 (2.1)

and

:<math>K_c = \sqrt{E G_c}\,</math> (for [[plane stress]])                 (2.2)

:<math>K_c = \sqrt{\frac{E G_c}{1 - \nu^2}}\,</math> (for [[plane strain]])                 (2.3)

where ''K''I is the [[stress intensity]], ''Kc'' the fracture toughness, and <math>\nu</math> is Poisson’s ratio. It is important to recognize the fact that fracture parameter ''K''c has different values when measured under plane stress and plane strain

Fracture occurs when <math>K_I \geq K_c</math>. For the special case of plane strain deformation, <math>K_c</math> becomes <math>K_{Ic}</math> and is considered a material property. The subscript I arises because of the different ways of loading a material to enable a crack to propagate. It refers to so-called "mode I" loading as opposed to mode II or III:

[[Image:Fracture modes v2.svg|thumb|The three fracture modes.]]

There are three ways of applying a force to enable a crack to propagate:

*'''Mode I crack''' – Opening mode (a [[tensile stress]] normal to the plane of the crack)
*'''Mode II crack''' – Sliding mode (a [[shear stress]] acting parallel to the plane of the crack and perpendicular to the crack front)
*'''Mode III crack''' – Tearing mode (a [[shear stress]] acting parallel to the plane of the crack and parallel to the crack front)

We must note that the expression for <math>K_I</math> in equation 2.1 will be different for geometries other than the center cracked plate, as discussed in the article on [[stress intensity]]. Consequently, it is necessary to introduce a [[dimensionless number|dimensionless correction factor]], ''Y'', in order to characterize the geometry. We thus have:

:<math>K_I = Y \sigma \sqrt{\pi a}\,</math>                 (2.4)

where ''Y'' is a function of the crack length and width of sheet given by:

:<math>Y \left ( \frac{a}{W} \right ) = \sqrt{\sec\left ( \frac{\pi a}{W} \right )}\,</math>                 (2.5)

for a sheet of finite width ''W'' containing a through-thickness crack of length 2''a'', or

:<math>Y \left ( \frac{a}{W} \right ) = 1.12 - \frac{0.41}{\sqrt \pi} \frac{a}{W} + \frac{18.7}{\sqrt \pi} \left ( \frac{a}{W} \right )^2 - \cdots\,</math>                 (2.6)

for a sheet of finite width ''W'' containing a through-thickness edge crack of length ''a''

===Elastic-plastic fracture mechanics theory===
Since engineers became accustomed to using ''K''Ic to characterise fracture toughness, a relation has been used to reduce ''J''Ic to it:

:<math>K_{Ic} = \sqrt{E^* J_{Ic}}\,</math>          where <math>E^* = E</math> for plane stress and <math>E^* = \frac{E}{1 - \nu^2}</math> for plane strain          (3.1)

The remainder of the mathematics employed in this approach is interesting, but is probably better summarised in external pages due to its complex nature.

==See also==
*[[AFGROW]] - Fracture mechanics and fatigue crack growth analysis software
*[[Fracture toughness]]
*[[fatigue (material)|Fatigue]]
*[[Peridynamics]] (a numerical method to solve fracture mechanics problems)
*[[Stress corrosion cracking]]
*[[Stress intensity factor]]
*[[Strain energy release rate]]

==References==
===Notes===
{{reflist}}

===Bibliography===
*C. P. Buckley, "Material Failure", Lecture Notes (2005), [[University of Oxford]].
*T. L. Anderson, "Fracture Mechanics: Fundamentals and Applications" (1995) CRC Press.

==External links==
*[http://www.efunda.com/formulae/solid_mechanics/fracture_mechanics/fm_intro.cfm eFunda – Fracture Mechanics]
*[http://hdl.handle.net/1813/3075 Fracture Mechanics Notes] by Prof. Alan Zehnder (from Cornell University)
*[http://imechanica.org/node/755 Nonlinear Fracture Mechanics Notes] by Prof. John Hutchinson (from Harvard University)
*[http://imechanica.org/node/903 Notes on Fracture of Thin Films and Multilayers] by Prof. John Hutchinson (from Harvard University)
*[http://www.seas.harvard.edu/suo/papers/17.pdf Mixed mode cracking in layered materials] by Profs. John Hutchinson and Zhigang Suo (from Harvard University)
*[http://www.mate.tue.nl/~piet/edu/frm/sht/bmsht.html Fracture Mechanics] by Prof. Piet Schreurs (from TU Eindhoven, Netherlands)
*[http://www.dsto.defence.gov.au/publications/1880/DSTO-GD-0103.pdf Introduction to Fracture Mechanics] by Dr. C. H. Wang (DSTO – Australia)
*[http://imechanica.org/node/2621 Fracture mechanics course notes] by Prof. Rui Huang (from Univ. of Texas at Austin)

[[Category:Fracture mechanics| ]]
[[Category:Glass physics]]

[[de:Bruchmechanik]]
[[es:Mecánica de la fractura]]
[[fa:مکانیک شکست]]
[[it:Meccanica della frattura]]
[[he:מכניקת השבר]]
[[ja:破壊力学]]
[[ru:Механика разрушения твёрдых тел]]
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[[sv:Brott (mekanik)]]
[[uk:Механіка руйнування]]
[[zh:断裂力学]]

Regulatory requirement

2009-01-05T04:36:31Z

220.227.67.171: /* Regulatory Review: New Drug Application (NDA) */

'''Regulatory requirements''' are part of the process of [[drug discovery]] and [[drug development]]. Regulatory requirements describe what is necessary for a new drug to be approved for marketing in any particular country. In the US, it is the function of the [[Food and Drug Administration]] (FDA) to establish these regulatory requirements. The [[European Medicines Agency]] (EMEA) and Japanese [[Japan Ministry of Health|Pharmaceuticals and Medical Devices Agency]] (PMDA) are also important regulatory authorities in drug development. These three agencies oversee the three largest markets for drug sales.

Historically, the various regulatory authorities have had their own methods for obtaining regulatory approval, however the rising cost of meeting the demands of differing regulations led to the establishment of an [[International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use]] (ICH) in an attempt to co-ordinate and synthesize international regulatory requirements. The first Conference was held in [[Brussels]] in 1991, followed by ICH 2 in [[Orlando, Florida]] in 1993, and ICH 3 in [[Yokohama]], Japan in 1995. The Fourth International Conference on Harmonisation, in July 1997, was once again in Brussels.

These systems of new drug approvals are extremely rigorous and costly. On average, it will cost a pharmaceutical company $359 million to get one new medicine from the laboratory to the pharmacist's shelf, according to a February 1993 report by the [[Congressional Office of Technology Assessment]]. It takes 12 years on average for an experimental [[approved drug|drug]] to travel from the laboratory to the medicine chest. Only five in 5,000 compounds that enter preclinical testing will actually progress into human clinical trials, and of these five, only one is likely to be approved by the regulatory authorities.

== Drug Discovery and Development ==
The process of [[drug discovery]] and development begins with improvements in the understanding of disease. Basic scientific research will identify new biological targets which may be amenable to chemical alteration (e.g., to inhibit or stimulate an important [[enzyme]], to alter a metabolic pathway, or to change cellular structure). [[New chemical entities]] (NCEs) can be produced through novel chemical synthesis or extracted from natural sources (plant, mineral, or animal). The number of compounds that can be produced based on the same general [[chemical]] structure (or "[[pharmacophore]]") can run into the millions.

Biological [[Screening]] and Pharmacological Testing: these are studies to explore the pharmacological activity and therapeutic potential of compounds. These tests involve the use of animals, isolated [[cell culture]]s and tissues, [[enzyme]]s and cloned receptor sites as well as computer models. If the results of the tests suggest potential beneficial activity, then related compounds, each a unique structural modification of the original compound are tested to see which version of the molecule produces the highest level of pharmacological activity and demonstrates the most therapeutic promise, with the smallest number of potentially harmful biological properties.

Pharmaceutical Dosage Formulation and Stability Testing: The process of turning an active compound into a form and strength suitable for human use. A pharmaceutical product can take any one of a number of [[Effective dose|dosage]] forms (e.g., liquid, tablets, capsules, ointments, sprays, patches) and dosage strengths (e.g., 50. 100, 250, 500 [[milligrams]].) The final formulation will include substances other than the [[active ingredient]], called excipients. Excipients are added to improve the taste of an oral [[Product (business)|product]], to allow the active ingredient to be compounded into stable tablets, to delay the drug's absorption into the body, or to prevent bacterial growth in liquid or cream preparations. The impact of each on the human body must be tested.

[[Toxicology]] and Safety Testing: Tests to determine the potential risk a compound poses to man and the environment. These studies involve the use of animals, tissue cultures, and other test systems to examine the relationship between factors such as dose level, frequency of administration, and duration of exposure to both the short- and long-term survival of living organisms. Tests provide information on the dose-response pattern of the compound and its toxic effects. Most toxicology and safety testing is conducted on new molecular entities prior to their human introduction, but companies can choose to delay long-term [[toxicity]] testing until after the therapeutic potential of the product is established.

== Regulatory Review: ==
An [[Investigational New Drug]] (IND) Application is filed with the Food and Drug Administration prior to human testing. The IND application is a compilation of all known information about the compound, including how it is manufactured. It also includes a description of the clinical research plan for the product and the specific protocol for phase 1 human clinical trials. Unless the FDA specifically objects, the IND is automatically allowed after 30 days and [[clinical trials]] can begin.

===Phase 1 Clinical Evaluation===
The first testing of a new compound in human subjects, for the purpose of establishing the tolerance of healthy human subjects at different doses, defining its pharmacological effects at anticipated therapeutic levels, and studying its [[absorption (pharmacokinetics)|absorption]], distribution, [[metabolism]], and excretion patterns in humans ([[ADME]]).

===Phase 2 Clinical Evaluation===
A controlled [[clinical trial]] of a compound's potential usefulness and short term risks is conducted. A relatively small number of patients, usually no more than a few hundred, are enrolled in phase 2 studies. While a Phase 1 trial has the objective of determining safety and tolerability of a new drug, Phase 2 trials determine whether the drug actually works, and the effective dose.

===Phase 3 Clinical Evaluation===
In this phase a controlled and uncontrolled clinical trial of a drug's safety and effectiveness in hospital and outpatient settings is done. Phase 3 studies gather precise information on the drug's effectiveness for specific indications, determine whether the drug produces a broader range of adverse effects than those exhibited in the small study populations of phase 1 and 2 studies, and identify the best way of administering and using the drug for the purpose intended. If the drug is approved, this information forms the basis for deciding the content of the product label. Phase 3 studies can involve several hundred to several thousand patients.

Development for manufacturing, quality control, engineering, and manufacturing design activities take place to establish a company's capacity to produce a product in large volume. Procedures are developed to ensure chemical stability, batch-to-batch uniformity, and overall product quality.

[[Bioavailability]] studies are conducted on healthy volunteers to document the rate of absorption and excretion from the body of a compound's active ingredients. Companies conduct bioavailability studies both at the beginning of human testing and just prior to marketing to show that the formulation used to demonstrate safety and efficacy in clinical trials is equivalent to the product that will be distributed for sale. Companies also conduct bioavailability studies on marketed products whenever they change the method used to administer the drug (e.g., from injection or oral dose form), the composition of the drug, the concentration of the active ingredient, or the manufacturing process used to produce the drug.

== Regulatory Review: New Drug Application (NDA) ==
An application to the FDA for dfgfghfmbn approval to market a new drug. All information about the drug gathered during the drug discovery and development process is assembled in the [[New Drug Application]] (NDA). During the review period, the FDA may ask the company for additional informvbgjgyf ation about th e produc t or seek gfhf clarification of the data contained in the application.

== Post approval ==
Research experimental studies and surveillance activities undertaken after a drug is approved for marketing. Clinical trials conducted after a drug is marketed (referred to as phase 4 studies in the United States) are an important source of information on as yet undetected adverse outcomes, especially in populations that may not have been involved the premarketing trials (e.g., children, the elderly, pregnant women) and the drug's long-term [[morbidity]] and mortality profile. Regulatory authorities can require companies to conduct Phase 4 studies as a condition of market approval. Companies often conduct post-marketing studies in the absence of a regulatory mandate.

==See also==
*[[Regulation of therapeutic goods]]
*[[GxP]]
*[[Nuremberg Code]]
*[[Declaration of Geneva]]
*[[Declaration of Helsinki]]
*[[EudraLex]]
*[[World Medical Association]]
*[[Belmont Report]]
*[[Uppsala Monitoring Centre]]
*[[Council for International Organizations of Medical Sciences]] (CIOMS)
*[[Clinical Data Interchange Standards Consortium]]

==External links==
*[http://www.access.gpo.gov/cgi-bin/cfrassemble.cgi?title=199821 FDA Code of Federal Regulations Title 21] - FDA CFR Title 21 - Food and Drugs
*[http://www.fda.gov/oc/gcp/preambles/52fr/52fr.html IND Rewrite Regulations] (FDA Title 21 CFR Parts 312, 314, 511, and 514)
*[http://pharmacos.eudra.org/F2/eudralex/index.htm Eudralex] - The Rules Governing Medicinal Products in the European Union
*[http://www.pmda.go.jp/index-e.html Pharmaceuticals and Medical Devices Agency] (PMDA)
*[http://www.wma.net/e/policy/c18.htm Declaration of Tokyo] - ethical code
*[http://www.fdaregulatory.org FDA Requirements Assistance and Library] - Papers regarding FDA Code of Federal Regulations Predicate Rules

[[Category:pharmacology]]
[[Category:clinical research]]
[[Category:Pharmaceuticals policy]]

[[ru:Специалист по клиническим исследованиям]]

University of Delhi

2008-10-20T10:57:19Z

220.227.97.99:

{{Unreferenced|date=September 2008}}

{{Infobox University
|name = University of Delhi
|image= [[Image:Delhiuniversity.jpg|Delhi University Logo]]
|motto = निष्ठा धति: सत्यम्
|established = 1922
|type = [[Public university|Public]]
|free_label = Vice Chancellor
|free = Deepak Pental
|city = [[Delhi]]
|country = [[India]]
|affiliations = [[University Grants Commission (India)|UGC]]
|campus = [[urban area|Urban]]
|website= [http://www.du.ac.in www.du.ac.in]
}}

The '''University of Delhi''' '''(DU)''' is a [[Central University (India)|central university]] located at [[Delhi]], [[India]] and is funded by [[Government of India]]. Established in 1922, it is one of the premier universities of the country and is known for its high standards in teaching and research.{{weasel-inline}} It offers courses at the undergraduate and post-graduate levels in most subjects.

The [[Vice-President of India]] is the Chancellor of the University of Delhi. The University has a distinguished alumni body and faculty. It is especially known for its faculties in Science, Economics, English and [[Hindustani]] Classical Music.{{weasel-inline}}

==Faculties==
# [[Arts]]
# [[Ayurvedic]] & [[Unani]] Medicine
# Commerce & Business Studies
# Education
# Int. Disp. & Applied Sciences
# [[Faculty of Law, University of Delhi|Law]]
# Main University
# [[FMS Delhi]] - Management Studies
# [[Mathematical Sciences]]
# [[Medical]] Sciences
# [[Music]] & [[Fine Arts]]
# [[Science]]
# [[Social Sciences]]
# [[Technology]]
# [[Undergraduate]] Courses

==Hostels in University of Delhi==
# Gwyer Hall
# Jubilee Hall
# Mansarovar Hostel
# P. G. Men's Hostel
# D. S. Kothari Hostel
# V. K. R. V. Rao Hostel
# International Students House
# Meghdoot Hostel
# University Hostel for Women

==Faculty of Science==
# [[School of Environmental Studies]]
# [[Department of Physics and Astrophysics]]
# [[Botany Department]]
# [[Zoology Department]]
# [[Chemistry Department]]
# [[Anthropology Department]]
# [[Geology Department]]

==Colleges under the University of Delhi[http://www.imconfuzed.com/du]==
<div style="-moz-column-count:2; column-count:2;">
*[[Acharya Narendra Dev College]]
*[[Aditi Mahavidyalaya]]
*[[Ahilyabai College of Nursing]]
*[[Amar Jyoti Institute of Physiotherapy]]
*[[Atma Ram Sanatan Dharma College]]
*[[Ayurvedic & Unani Tibbia College]]
*[[Bhagini Nivedita College]]
*[[Bharati College]]
*[[Bhaskraycharya College of Applied Sciences]]
*[[Bhim Rao Ambedkar College]]
*[[College of Arts]]
*[[College of Pharmacy]]
*[http://www.imconfuzed.com/colleges/CVS College of Vocational Studies]
*[http://www.imconfuzed.com/colleges/DRC Daulat Ram College]
*[[Deen Dayal Upadhayay College Delhi College of Arts & Commerce]]
*[http://www.imconfuzed.com/colleges/dcac]
*[[Delhi College of Engineering]] (Faculty of Technology)
*[[Delhi School of Economics]]
*[[Department of East Asian Studies, University of Delhi]]
*[[Deshbandhu College]]
*Deshbandhu College (Evening)
*[[Dyal Singh College]]
*Dyal Singh College (Evening)
*[[Faculty of Management Studies]]
*[http://www.imconfuzed.com/colleges/gargi Gargi College]
* [[Hans Raj College]]
*[http://www.imconfuzed.com/colleges/Hindu Hindu College]
*[[Indira Gandhi Instt.of Phy. Edu. & Sports Sciences]]
*[http://www.imconfuzed.com/colleges/ip Indraprastha College for Women]
*[[Institute of Home Economics]]
*[[Institute of Physically Handicapped]]
*[[Janki Devi Memorial College]]
*[http://www.imconfuzed.com/colleges/JMC Jesus & Mary College]
*[http://www.imconfuzed.com/colleges/kalindi Kalindi College]
*[[Kamala Nehru College]]
*[[Keshav Mahavidyalaya]]
*[http://www.imconfuzed.com/colleges/KMC Kirori Mal College]
*[[Lady Harding Medical College]]
*[[Lady Irwin College]]
*[http://www.imconfuzed.com/colleges/lsr Lady Shri Ram College for Women]
*[[Lakshmi Bai College]]
*[[Maharaja Agrasen College]] [http://www.macdu.com MAC]
*[[Maharishi Valmiki College of Education]]
*[[Maitreyi College]]
*[[Mata Sundri College for Women]]
*[[Maulana Azad Medical College]]
*[[Miranda House]]
*[[Moti Lal Nehru College]]
*Moti Lal Nehru College (Evening)
*[[Nehru Homeopathic College]]
*[[Netaji Subhas Institute of Technology]] (Faculty of Technology)
*[[Pannalal Girdharlal Dayanand Anglo Vaidic College]]
*Pannalal Girdharlal Dayanand Anglo Vaidic College (Evening)
*[[Rajdhani College]]
*[[Rajkumari Amrit Kaur College of Nursing]]
*[[Ram Lal Anand College]]
*Ram Lal Anand College (Evening)
*[http://www.imconfuzed.com/colleges/ramjas Ramjas College]
*[[Sri Guru Tegh Bahadur Khalsa College]]
*[[Sri Guru Nanak Dev Khalsa College]]
*Sri Guru Tegh Bahadur Khalsa College (Evening)
*[[Satyawati College]]
*Satyawati College (Evening)
*[[School of Open Learning]]
*[[Shaheed Bhagat Singh College]]
*Shaheed Bhagat Singh College (Evening)
*[[Shaheed Rajguru College of Applied Sciences for Women]] [http://www.rajgurucollege.org]
*[[Shaheed Sukhdev College of Business Studies]]
*[[Sherubtse College]]
*[[Shivaji College]]
*[http://www.imconfuzed.com/colleges/SRCC Shri Ram College of Commerce]
*[[Shyam Lal College]]
*Shyam Lal College (Evening)
*[[Shyama Prasad Mukherjee College]]
*[[Sri Aurbindo College]]
*Sri Aurbindo College (Evening)
*[[Sri Guru Gobind Singh College of Commerce]]
*[http://www.imconfuzed.com/colleges/venky Sri Venkateswara College]
*[http://www.imconfuzed.com/colleges/stephans St. Stephen's College, Delhi]
*[[Swami Shraddhanand College]]
*[[University College of Medical Sciences]]
*[[Vivekanand College]]
*[[Zakir Husain College]]
*Zakir Husain College (Evening)

</div>

==Former Vice Chancellors==

# Hari Singh Gaur 1922-1926
# Moti Sagar 1926-1930
# Abdur Rehman 1930-1934
# Ram Kishore 1934-1938
# Maurice Gwyer 1938-1950
# S.N. Sen 1950-1953
# G.S. Mahajani 1953-1957
# V.K.R.V. Rao 1957-1960
# N.K. Sidhanta 1960-1961
# C.D. Desh Mukh 1962-1967
# B.N. Ganguli 1967-1969
# K.N. Raj 1969-1970
# Sarup Singh 1971-1974
# R.C. Mehrotra 1974-1979
# Gurbakhsh Singh 1980-1985
# Moonis Raza 1985-1990
# Upendra Baxi 1990-1994
# V.R. Mehta 1995-2000
# Deepak Nayyar 2000-2005
# Deepak Pental 2005-...

{{IndianCentralUniv}}

==External links==
*[http://www.du.ac.in/ Official Website].
*[[Du beat]] [http://www.dubeat.com/ Student's Newspaper]
*[http://www.imconfuzed.com/du Information On Delhi University].

[[Category:Central universities in India|Delhi]]
[[Category:Universities and colleges in Delhi]]
[[Category:Educational institutions established in 1922]]
[[Category:University of Delhi alumni]]
[[Category:University of Delhi]]
[[Category:Cloud computing users]]

[[ar:جامعة دلهي]]
[[de:University of Delhi]]
[[ml:അണ്ണാമലൈ സര്‍വകലാശാല]]
[[ja:アンナーマライ大学]]
[[ta:தில்லிப் பல்கலைக்கழகம்]]
[[zh:德里大學]]

About fracture mechanics

2008-02-27T07:19:01Z

220.227.64.170: /* Engineering applications of fracture mechanics */

{{refimprove||date=June 2006}}

'''Fracture mechanics''' is a method for predicting failure of a structure containing a crack. It uses methods of analytical [[Solid mechanics]] to calculate the driving force on a crack and those of experimental [[Solid mechanics]] to characterize the material's resistance to fracture.

In modern [[materials science]], fracture mechanics is an important tool in improving the mechanical performance of materials and components. It applies the [[physics]] of [[stress (physics)|stress]] and [[Strain (materials science)|strain]], in particular the theories of [[Elasticity (physics)|elasticity]] and [[plasticity (physics)|plasticity]], to the microscopic [[crystallographic defect]]s found in real materials in order to predict the macroscopic mechanical failure of bodies. [[Fractography]] is widely used with Fracture Mechanics to understand the causes of failures and also verify the theoretical failure predictions with real life failures.

== The need for fracture mechanics ==
[[Image:Tay1.jpg|thumb|right|Tay Bridge Disaster (1879)]]

In many cases, failure of engineering structures through fracture can be fatal; one example is that of the [[Tay Rail Bridge]] disaster (left). Often disasters occur because engineering structures contain cracks - arising either during production or during service (e.g. from [[Fatigue (material)|fatigue]]). For instance, growth of cracks in pressure vessels due to crack propagation could cause a fatal explosion. If failure were ever to happen, we would rather it were by [[yield (engineering)|yield]] or by leak before break.

Since cracks can lower the strength of the structure beyond that due to loss of load-bearing area a material property, above and beyond conventional strength, is needed to describe the fracture resistance of engineering materials. This is the reason for the need for fracture mechanics - the evaluation of the strength of cracked structures.

== The history of fracture mechanics ==
=== Griffith's energy relation ===
Fracture Mechanics was invented during World War I by English aeronautical engineer, [[Alan Arnold Griffith|A.A.Griffith]], to explain the failure of brittle materials. Griffith was faced with the problem that theoretical calculations showed that the stress at the tip of a sharp crack approaches infinity. Accordingly, any structure containing a crack should fail, no matter how small the crack or how light the load. To solve this dilemma, Griffith developed a thermodynamic approach. He assumed that growth of a crack requires creation of surface energy, which is supplied by the loss of strain energy accompanying the relaxation of local stresses as the crack advances. Failure occurs when the loss of strain energy is sufficient to provide the increase in surface energy.

=== Irwin's modification of Griffith's energy relation ===
[[Image:TankerSchenectady.jpg|thumb|right|The S.S.Schenectady split apart by [[brittle fracture]] while in harbor (1944)]]

Griffith’s work was ignored for over twenty years until a group under [[G.R. Irwin]] at the U.S. Naval Research Laboratory (NRL) took it up during World War II. Irwin and his colleagues developed a modified form of Griffith's approach; they reformulated it in terms of stress, rather than energy. Their work resulted in a new materials property, [[fracture toughness]], which is denoted KIc, and is now universally accepted as the defining property of fracture mechanics.

But a problem arose for the NRL researchers because naval materials, e.g. ship-plate steel, are not perfectly elastic but undergo [[plastic deformation]] at the tip of a crack violating the underlying assumption of the theory. Linear-elastic fracture mechanics is of limited practical use for structural steels for two other reasons:

(1) Fracture toughness testing is very expensive and sufficient information for selection of steels can be obtained from the simpler and cheaper [[Charpy impact test]]

(2) If a part's response to load is sufficiently close to linear-elastic that KIc can be measured, there is little plastic relaxation at the crack tip and the steel will be [[brittle]]. Structural steels, in particular, can be prone to brittle fracture, which has led to a number of catastrophic failures.

== Elastic-plastic fracture mechanics ==
[[Image:Aircraft Crash.jpg|thumb|right|[[Vertical stabilizer]], which separated from the aircraft leading to a fatal crash(2001)]]

In the mid-1960s J.R. Rice (then at Brown University) developed a new toughness measure to describe the case where there is sufficient crack-tip deformation that the part no longer obeys the linear-elastic approximation. Rice's analysis, which assumes non-linear elastic deformation ahead of the crack tip, is designated the [[J integral]]. This analysis is limited to situations where plastic deformation at the crack tip does not extend to the furthest edge of the loaded part. It also demands that the assumed non-linear elastic behavior of the material is a reasonable approximation in shape and magnitude to the real material's load response. The elastic-plastic failure parameter is designated JIc and is conventionally converted to KIc using Equation (3.1) of the Appendix to this article. Also note that the J integral approach reduces to the Griffith theory for linear-elastic behavior.
thats all.

== Fully plastic fracture mechanics ==
If the alloy is so tough that the yielded region ahead of the crack extends to the far edge of the specimen before fracture, the crack is no longer an effective stress concentrator. Instead, the presence of the crack merely serves to reduce the load-bearing area. In this regime the failure stress is conventionally assumed to be the average of the yield and ultimate strengths of the alloy.

== Engineering applications of fracture mechanics ==
The following information is needed for a fracture mechanics prediction of failure:
*Applied load
*Residual stress
*Size and shape of the part
*Size, shape, location, and orientation of the crack

Usually not all of this information is available and conservative assumptions have to be made.

Occasionally post-mortem fracture-mechanics analyses are carried out. In the absence of an extreme overload, the causes are either insufficient toughness (KIc) or an excessively large crack that was not detected during routine inspection.
hi i am mohan

== Short summary ==
Arising from the manufacturing process, interior and surface flaws are found in all metal structures. Not all such flaws are unstable under service conditions. Fracture mechanics is the analysis of flaws to discover those that are safe (that is, do not grow) and those that are liable to propagate as cracks and so cause [[structural failure|failure]] of the flawed structure. Fracture mechanics as a subject for critical study has barely been around for a century and thus is relatively new. There is a high demand for engineers with fracture mechanics expertise - particularly in this day and age where engineering failure is considered 'shocking' amongst the general public.

== Appendix: Mathematical relations ==
=== Griffith's crack theory: strain energy release rate ===
For the simple case of a thin rectangular plate with a crack perpendicular to the load Griffith’s theory becomes:

:<math>G = \frac{\pi \sigma^2 a}{E}\,</math>                 (1.1)

where <math>G</math> is the strain energy release rate, <math>\sigma</math> is the applied stress, <math>a</math> is half the crack length, and <math>E</math> is the [[Elastic modulus|Young’s modulus]]. The strain energy release rate can otherwise be understood as: the rate at which energy is absorbed by growth of the crack.

However, we also have that:

:<math>G_c = \frac{\pi \sigma_f^2 a}{E}\,</math>                 (1.2)

If <math>G</math> ≥ <math>G_c</math>, this is the criterion for which the crack will begin to propagate.

=== Irwin's modified Griffith crack theory: fracture toughness ===
Eventually a modification of Griffith’s solids theory emerged from this work; a term called [[stress intensity]] replaced strain energy release rate and a term called [[fracture toughness]] replaced surface weakness energy. Both of these terms are simply related to the energy terms that Griffith used:

:<math>K_I = \sigma \sqrt{\pi a}\,</math>                 (2.1)

and

:<math>K_c = \sqrt{E G_c}\,</math> (for [[plane stress]])                 (2.2)

:<math>K_c = \sqrt{\frac{E G_c}{1 - \nu^2}}\,</math> (for [[plane strain]])                 (2.3)

where ''K''I is the [[stress intensity]], ''K''c the [[fracture toughness]], and <math>\nu</math> is [[Poisson ratio|Poisson’s ratio]]. It is important to recognise the fact that fracture parameter ''K''c has different values when measured under plane stress and plane strain

Fracture occurs when ''K''I ≥ ''K''c. For the special case of plane strain deformation, ''K''c becomes ''K''Ic and is considered a material property. The subscript I arises because of the different ways of loading a material to enable a crack to propagate. It refers to loading via Mode I - the most common form of loading:

[[Image:Fracture modes.svg|right|frame|The three fracture modes.]]
There are three ways of applying a force to enable a crack to propagate: 
* '''Mode I crack''' - Opening mode (a [[tensile stress]] normal to the plane of the crack)
*'''Mode II crack''' - Sliding mode (a [[shear stress]] acting parallel to the plane of the crack and perpendicular to the crack front)
*'''Mode III crack''' - Tearing mode (a [[shear stress]] acting parallel to the plane of the crack and parallel to the crack front)

We must note that the expression for ''K''I in Eq (2.1) will be different for geometries other than the center cracked plate, as discussed in the article on [[stress intensity]]. Consequently, it is necessary to introduce a [[dimensionless number|dimensionless correction factor]], ''Y'', in order to characterise the geometry. We thus have:

:<math>K_I = Y \sigma \sqrt{\pi a}\,</math>                 (2.4)

where ''Y'' is a function of the crack length and width of sheet given by:

:<math>Y \left ( \frac{a}{W} \right ) = \sqrt{\sec\left ( \frac{\pi a}{W} \right )}\,</math>                 (2.5)

for a sheet of finite width ''W'' containing a through-thickness crack of length 2''a'', or

:<math>Y \left ( \frac{a}{W} \right ) = 1.12 - \frac{0.41}{\sqrt \pi} \frac{a}{W} + \frac{18.7}{\sqrt \pi} \left ( \frac{a}{W} \right )^2 - \cdots\,</math>                 (2.6)

for a sheet of finite width ''W'' containing a through-thickness edge crack of length ''a''

=== Elastic-plastic fracture mechanics theory ===
Since engineers became accustomed to using ''K''Ic to characterise fracture toughness, a relation has been used to reduce ''J''Ic to it:

:<math>K_{Ic} = \sqrt{\frac{E J_{Ic}}{1 - \nu^2}}\,</math>                 (3.1)

The remainder of the mathematics employed in this approach is interesting, but is probably better summarised in external pages due to its complex nature (refer to the Useful Websites section).

== References ==
*C. P. Buckley, "Material Failure", Lecture Notes (2005), [[University of Oxford]]
*T. L. Anderson, "Fracture Mechanics: Fundamentals and Applications" (1995) CRC Press.

== See also ==
*[[fatigue (material)|Fatigue]]
*[[Stress corrosion cracking]]
*[[Stress intensity factor]]

== External links ==
*[http://www.efunda.com/formulae/solid_mechanics/fracture_mechanics/fm_intro.cfm eFunda - Fracture Mechanics]
*[http://www2.umist.ac.uk/material/research/intmic/features/charpy/notes.htm UMIST - Charpy Impact Test]
*[http://www.engin.brown.edu/courses/EN175/Notes/Failure_Plasfrac/Failure_Plasfrac.htm Brown University Engineering - Mathematical Relations]
*[http://dspace.library.cornell.edu/handle/1813/3075 Fracture Mechanics Notes from Cornell University]

[[Category:Mechanical engineering]]
[[Category:Structural engineering]]
[[Category:Materials science]]
[[Category:Continuum mechanics]]

[[de:Bruchmechanik]]
[[ja:破壊力学]]
[[ru:Механика разрушения твёрдых тел]]
[[sv:Brott (mekanik)]]
[[uk:Механіка руйнування]]
[[zh:断裂力学]]

About fracture mechanics

2008-02-27T07:12:53Z

220.227.64.170: /* Elastic-plastic fracture mechanics */

{{refimprove||date=June 2006}}

'''Fracture mechanics''' is a method for predicting failure of a structure containing a crack. It uses methods of analytical [[Solid mechanics]] to calculate the driving force on a crack and those of experimental [[Solid mechanics]] to characterize the material's resistance to fracture.

In modern [[materials science]], fracture mechanics is an important tool in improving the mechanical performance of materials and components. It applies the [[physics]] of [[stress (physics)|stress]] and [[Strain (materials science)|strain]], in particular the theories of [[Elasticity (physics)|elasticity]] and [[plasticity (physics)|plasticity]], to the microscopic [[crystallographic defect]]s found in real materials in order to predict the macroscopic mechanical failure of bodies. [[Fractography]] is widely used with Fracture Mechanics to understand the causes of failures and also verify the theoretical failure predictions with real life failures.

== The need for fracture mechanics ==
[[Image:Tay1.jpg|thumb|right|Tay Bridge Disaster (1879)]]

In many cases, failure of engineering structures through fracture can be fatal; one example is that of the [[Tay Rail Bridge]] disaster (left). Often disasters occur because engineering structures contain cracks - arising either during production or during service (e.g. from [[Fatigue (material)|fatigue]]). For instance, growth of cracks in pressure vessels due to crack propagation could cause a fatal explosion. If failure were ever to happen, we would rather it were by [[yield (engineering)|yield]] or by leak before break.

Since cracks can lower the strength of the structure beyond that due to loss of load-bearing area a material property, above and beyond conventional strength, is needed to describe the fracture resistance of engineering materials. This is the reason for the need for fracture mechanics - the evaluation of the strength of cracked structures.

== The history of fracture mechanics ==
=== Griffith's energy relation ===
Fracture Mechanics was invented during World War I by English aeronautical engineer, [[Alan Arnold Griffith|A.A.Griffith]], to explain the failure of brittle materials. Griffith was faced with the problem that theoretical calculations showed that the stress at the tip of a sharp crack approaches infinity. Accordingly, any structure containing a crack should fail, no matter how small the crack or how light the load. To solve this dilemma, Griffith developed a thermodynamic approach. He assumed that growth of a crack requires creation of surface energy, which is supplied by the loss of strain energy accompanying the relaxation of local stresses as the crack advances. Failure occurs when the loss of strain energy is sufficient to provide the increase in surface energy.

=== Irwin's modification of Griffith's energy relation ===
[[Image:TankerSchenectady.jpg|thumb|right|The S.S.Schenectady split apart by [[brittle fracture]] while in harbor (1944)]]

Griffith’s work was ignored for over twenty years until a group under [[G.R. Irwin]] at the U.S. Naval Research Laboratory (NRL) took it up during World War II. Irwin and his colleagues developed a modified form of Griffith's approach; they reformulated it in terms of stress, rather than energy. Their work resulted in a new materials property, [[fracture toughness]], which is denoted KIc, and is now universally accepted as the defining property of fracture mechanics.

But a problem arose for the NRL researchers because naval materials, e.g. ship-plate steel, are not perfectly elastic but undergo [[plastic deformation]] at the tip of a crack violating the underlying assumption of the theory. Linear-elastic fracture mechanics is of limited practical use for structural steels for two other reasons:

(1) Fracture toughness testing is very expensive and sufficient information for selection of steels can be obtained from the simpler and cheaper [[Charpy impact test]]

(2) If a part's response to load is sufficiently close to linear-elastic that KIc can be measured, there is little plastic relaxation at the crack tip and the steel will be [[brittle]]. Structural steels, in particular, can be prone to brittle fracture, which has led to a number of catastrophic failures.

== Elastic-plastic fracture mechanics ==
[[Image:Aircraft Crash.jpg|thumb|right|[[Vertical stabilizer]], which separated from the aircraft leading to a fatal crash(2001)]]

In the mid-1960s J.R. Rice (then at Brown University) developed a new toughness measure to describe the case where there is sufficient crack-tip deformation that the part no longer obeys the linear-elastic approximation. Rice's analysis, which assumes non-linear elastic deformation ahead of the crack tip, is designated the [[J integral]]. This analysis is limited to situations where plastic deformation at the crack tip does not extend to the furthest edge of the loaded part. It also demands that the assumed non-linear elastic behavior of the material is a reasonable approximation in shape and magnitude to the real material's load response. The elastic-plastic failure parameter is designated JIc and is conventionally converted to KIc using Equation (3.1) of the Appendix to this article. Also note that the J integral approach reduces to the Griffith theory for linear-elastic behavior.
thats all.

== Fully plastic fracture mechanics ==
If the alloy is so tough that the yielded region ahead of the crack extends to the far edge of the specimen before fracture, the crack is no longer an effective stress concentrator. Instead, the presence of the crack merely serves to reduce the load-bearing area. In this regime the failure stress is conventionally assumed to be the average of the yield and ultimate strengths of the alloy.

== Engineering applications of fracture mechanics ==
The following information is needed for a fracture mechanics prediction of failure:
*Applied load
*Residual stress
*Size and shape of the part
*Size, shape, location, and orientation of the crack

Usually not all of this information is available and conservative assumptions have to be made.

Occasionally post-mortem fracture-mechanics analyses are carried out. In the absence of an extreme overload, the causes are either insufficient toughness (KIc) or an excessively large crack that was not detected during routine inspection.

== Short summary ==
Arising from the manufacturing process, interior and surface flaws are found in all metal structures. Not all such flaws are unstable under service conditions. Fracture mechanics is the analysis of flaws to discover those that are safe (that is, do not grow) and those that are liable to propagate as cracks and so cause [[structural failure|failure]] of the flawed structure. Fracture mechanics as a subject for critical study has barely been around for a century and thus is relatively new. There is a high demand for engineers with fracture mechanics expertise - particularly in this day and age where engineering failure is considered 'shocking' amongst the general public.

== Appendix: Mathematical relations ==
=== Griffith's crack theory: strain energy release rate ===
For the simple case of a thin rectangular plate with a crack perpendicular to the load Griffith’s theory becomes:

:<math>G = \frac{\pi \sigma^2 a}{E}\,</math>                 (1.1)

where <math>G</math> is the strain energy release rate, <math>\sigma</math> is the applied stress, <math>a</math> is half the crack length, and <math>E</math> is the [[Elastic modulus|Young’s modulus]]. The strain energy release rate can otherwise be understood as: the rate at which energy is absorbed by growth of the crack.

However, we also have that:

:<math>G_c = \frac{\pi \sigma_f^2 a}{E}\,</math>                 (1.2)

If <math>G</math> ≥ <math>G_c</math>, this is the criterion for which the crack will begin to propagate.

=== Irwin's modified Griffith crack theory: fracture toughness ===
Eventually a modification of Griffith’s solids theory emerged from this work; a term called [[stress intensity]] replaced strain energy release rate and a term called [[fracture toughness]] replaced surface weakness energy. Both of these terms are simply related to the energy terms that Griffith used:

:<math>K_I = \sigma \sqrt{\pi a}\,</math>                 (2.1)

and

:<math>K_c = \sqrt{E G_c}\,</math> (for [[plane stress]])                 (2.2)

:<math>K_c = \sqrt{\frac{E G_c}{1 - \nu^2}}\,</math> (for [[plane strain]])                 (2.3)

where ''K''I is the [[stress intensity]], ''K''c the [[fracture toughness]], and <math>\nu</math> is [[Poisson ratio|Poisson’s ratio]]. It is important to recognise the fact that fracture parameter ''K''c has different values when measured under plane stress and plane strain

Fracture occurs when ''K''I ≥ ''K''c. For the special case of plane strain deformation, ''K''c becomes ''K''Ic and is considered a material property. The subscript I arises because of the different ways of loading a material to enable a crack to propagate. It refers to loading via Mode I - the most common form of loading:

[[Image:Fracture modes.svg|right|frame|The three fracture modes.]]
There are three ways of applying a force to enable a crack to propagate: 
* '''Mode I crack''' - Opening mode (a [[tensile stress]] normal to the plane of the crack)
*'''Mode II crack''' - Sliding mode (a [[shear stress]] acting parallel to the plane of the crack and perpendicular to the crack front)
*'''Mode III crack''' - Tearing mode (a [[shear stress]] acting parallel to the plane of the crack and parallel to the crack front)

We must note that the expression for ''K''I in Eq (2.1) will be different for geometries other than the center cracked plate, as discussed in the article on [[stress intensity]]. Consequently, it is necessary to introduce a [[dimensionless number|dimensionless correction factor]], ''Y'', in order to characterise the geometry. We thus have:

:<math>K_I = Y \sigma \sqrt{\pi a}\,</math>                 (2.4)

where ''Y'' is a function of the crack length and width of sheet given by:

:<math>Y \left ( \frac{a}{W} \right ) = \sqrt{\sec\left ( \frac{\pi a}{W} \right )}\,</math>                 (2.5)

for a sheet of finite width ''W'' containing a through-thickness crack of length 2''a'', or

:<math>Y \left ( \frac{a}{W} \right ) = 1.12 - \frac{0.41}{\sqrt \pi} \frac{a}{W} + \frac{18.7}{\sqrt \pi} \left ( \frac{a}{W} \right )^2 - \cdots\,</math>                 (2.6)

for a sheet of finite width ''W'' containing a through-thickness edge crack of length ''a''

=== Elastic-plastic fracture mechanics theory ===
Since engineers became accustomed to using ''K''Ic to characterise fracture toughness, a relation has been used to reduce ''J''Ic to it:

:<math>K_{Ic} = \sqrt{\frac{E J_{Ic}}{1 - \nu^2}}\,</math>                 (3.1)

The remainder of the mathematics employed in this approach is interesting, but is probably better summarised in external pages due to its complex nature (refer to the Useful Websites section).

== References ==
*C. P. Buckley, "Material Failure", Lecture Notes (2005), [[University of Oxford]]
*T. L. Anderson, "Fracture Mechanics: Fundamentals and Applications" (1995) CRC Press.

== See also ==
*[[fatigue (material)|Fatigue]]
*[[Stress corrosion cracking]]
*[[Stress intensity factor]]

== External links ==
*[http://www.efunda.com/formulae/solid_mechanics/fracture_mechanics/fm_intro.cfm eFunda - Fracture Mechanics]
*[http://www2.umist.ac.uk/material/research/intmic/features/charpy/notes.htm UMIST - Charpy Impact Test]
*[http://www.engin.brown.edu/courses/EN175/Notes/Failure_Plasfrac/Failure_Plasfrac.htm Brown University Engineering - Mathematical Relations]
*[http://dspace.library.cornell.edu/handle/1813/3075 Fracture Mechanics Notes from Cornell University]

[[Category:Mechanical engineering]]
[[Category:Structural engineering]]
[[Category:Materials science]]
[[Category:Continuum mechanics]]

[[de:Bruchmechanik]]
[[ja:破壊力学]]
[[ru:Механика разрушения твёрдых тел]]
[[sv:Brott (mekanik)]]
[[uk:Механіка руйнування]]
[[zh:断裂力学]]

Archive:Fanboy

2007-07-13T09:31:11Z

220.227.121.36: /* Background */

'''Fanboy''' is a term used to describe an individual (usually male, though the feminine version '''fangirl''' may be used for females) who is utterly devoted to a single fannish subject, or to a single point of view within that subject, often to the point where it is considered an [[obsession]]. Fanboys remain loyal to their particular obsession, disregarding any factors that differ from their point of view. Fanboys are also typically aggressive and hateful towards the opposing brand or competition of their obsession regardless of its merits or achievements.

== Background ==
Fanboys are attributed with a sycophantic devotion to the creators and principles behind a work with which they are currently enthralled. Fanboys are noted for a very emotional attachment to their chosen subject, often taking negative remarks about it as a personal attack. They will readily engage in debates, but will fall back on emotional responses when challenged on facts. For example, a fanboy may go out of his way to point out negative and often untrue statements about their obsession's rivals. Fanboys are often hostile towards critical review of their chosen subject.

As electronic entertainment gained popularity, the term became increasingly applied to [[video game]] and [[television]] addicts. As a result, a subculture emerged which readily labeled itself as "fanboys." Within this group, more effort is taken to fit in with a perceived standard, resulting in a more outgoing attitude, even among those with insecurities. This outgoing stance is often felt to be abrasive by those not involved in the culture as deeply.

More recently, especially in the [[video game industry]], fans of a particular video game console manufacturer have begun exhibiting slavish devotion to their brand of choice. An example would be a "Microsoft Fanboy", one who holds devotion to the company Microsoft. In the video game industry, fanboy dubbing can also occur in video game titles, such as Halo. Another example would be a "Sony Fanboy," one who holds devotion to the company Sony, and only likes such games as "Metal Gear Solid."

A Prime example of the Microsoft fanboy is Sanas_Thirtu of Gfaqs, who believes Halo is the greatest game ever and hates the PS3.

==History of fanboys and the term==
The term "fanboy" is most commonly associated with adolescent and teen males but can be applicable to any age or sex. it is often used in a derogatory manner by other, less obsessed fans. An example of an individual who fits this criteria and description would be [[sanas_thiritu]] (creator of the giant metal camel topic of the Halo 3 board, as well as many other worthwhile mentions, including immortal Forerunner Dragons and Glass armor. And don't forget that NOTHING in the future has wires exposed. He knows.)

The term originated in [[comic book]] circles to describe someone immersed in the fictional worlds of comics and the culture of comics fandom. Common subjects of reverence by fanboys are [[TV show]]s, [[film|movie]]s, [[music]], [[anime]], [[comic book]]s, [[Star Trek]] ("[[Trekkies]]"), [[Star Wars]], [[car]]s, [[video game console]]s, [[video games]], [[operating system]]s, [[MMORPG]]s, [[Computer Hardware|hardware]] and [[software]] companies.

Popular depictions of Fanboy stereotypes include the [[Comic Book Guy]] on ''[[The Simpsons]]'' and columnist [[Larry Groznic]] from the satirical newspaper ''[[The Onion]]''.

In the songs of the fannish [[parody]] [[musician]] [[Luke Ski]], many characters proudly consider themselves ''fanboys.''

The earliest published uses of the word "fanboy" have been dated to 1982. One reference is to the cover of the "Official Underground and Newave Comix Price Guide". On this cover page are sketched overweight, overzealous comic book collectors wearing T-shirts that state "Fanboys of America," and are describing the extreme measures they would go to, including moving to San Francisco, to preserve their comics.

Also published in 1982, a comic strip appeared in Jim Engel and Chuck Fiala's "Fandom Confidential" comic. In the strip, Jim and Chuck met comic artist/writer [[John Byrne]] and collapsed into "mindless paroxysms of adoration." The John Byrne character responded that they were "a couple of fanboys in bondage" (a play on words referring to a [[List of Monty Python’s Flying Circus episodes#10. E. Henry Thripshaw.27s Disease|Monty Python sketch]] in which an Elizabethan era character reads what she claims to be a new Shakespeare work called "Gay Boys in Sanas". [http://www.byrnerobotics.com/FAQ/listing.asp?ID=7&T1=Miscellaneous+Questions#154] Another early use is in a smart-alec editorial reply by "[[Ambush Bug]]" to a letter in his comic in [[1985]].

==Subjects of obsession==
Some current examples of brands and products which have fanboy supporters:
*The competing gaming systems [[Playstation 3]], [[Wii]], [[Xbox 360]] and [[PC]].
*The operating systems [[Microsoft Windows]], [[Mac OS X]] and [[Linux]].
*The internet web browsers [[Mozilla Firefox|Firefox]], [[Internet Explorer]] and [[Opera (internet suite)|Opera]].
*The various technology companies: [[Google]], [[Sony]], [[Apple Computer|Apple]], [[Microsoft]], [[Nintendo]].
*The computer microprocessor companies [[Advanced Micro Devices|AMD]] and [[Intel Corporation|Intel]].
*The competing [[DVD]] successor formats [[Blu-ray Disc|Blu-ray]] and [[HD DVD]].
*The competing handheld video game consoles the [[Nintendo DS]] and the [[PlayStation Portable]].
*The various [[MP3]] players, notably the [[iPod]] and the [[Zune]].

==Media==

===People===
*[[sanas_thiritu]]' ''Fanboy''

===Comic Book===
*[[Sergio Aragonés]]' ''Fanboy''
*[[Galactic Storm]] ''Fanboy''

===Television===
*''[[The Simpsons]]'''s [[Comic Book Guy]] refers to himself as a fanboy.
*''[[Freakazoid!|Freakazoid]]'''s [[freakazoid!#Other characters|Fan Boy]]
*''[[King of the Hill]]'''s [[Hank Hill]] is a fanboy of [[propane]].

===Radio/Podcasts===
*[[Fanboy Radio]] - [http://fanboyradio.com]
*[[Fanboy TV]] - [http://www.fanboy.tv]
*Drooling FanBoy - [http://droolingfanboy.com]
*ifanboy - [http://www.ifanboy.com]
*[[The Fanboy Smackdown Podcast]] - [http://www.fanboysmackdown.com]
*[[The Opie and Anthony Show]] - [http://www.opieandanthony.com]

===Webcomics===
*Fanboy Almanac (webcomic) - [http://fanboyalmanac.com Fanboy Almanac]
*[http://www.ngeb.net/fanboys Fanboys web comic]
*[http://www.fogclub.net F.O.G.Club web comic]
*[http://www.fanboysonline.com Fanboys!! Beyond Geekdom!!! (webcomic)]
*[http://www.fanboys-online.com Fanboys-Online]
*[http://www.megatokyo.com M3g4Toky0]

==See also==
* [[Addiction]]
* [[Cyberstalking]]
* [[Editor war]]
* [[Anorak (slang)|Anorak]]
* [[Astroturfing]]
* [[Otaku]]

== External links ==
* [http://www.urbandictionary.com/define.php?term=fanboy Urban dictionary: fanboy]
* [http://www.netjak.com/review.php/1013 Dissecting the Fanboy Mind] - A discussion of the fanboy behavior in regards to video games.
* [http://palgn.com.au/article.php?id=6463 The trial of the Fanboy] - A criticism of the fanboy concept and overusage of the term.
[[Category:Fandom]]
[[Category:Anime and manga terminology]]

[[de:Fanboy]]

Archive:Fanboy

2007-07-13T07:48:45Z

220.227.121.36: /* People */

'''Fanboy''' is a term used to describe an individual (usually male, though the feminine version '''fangirl''' may be used for females) who is utterly devoted to a single fannish subject, or to a single point of view within that subject, often to the point where it is considered an [[obsession]]. Fanboys remain loyal to their particular obsession, disregarding any factors that differ from their point of view. Fanboys are also typically aggressive and hateful towards the opposing brand or competition of their obsession regardless of its merits or achievements.

== Background ==
Fanboys are attributed with a sycophantic devotion to the creators and principles behind a work with which they are currently enthralled. Fanboys are noted for a very emotional attachment to their chosen subject, often taking negative remarks about it as a personal attack. They will readily engage in debates, but will fall back on emotional responses when challenged on facts. For example, a fanboy may go out of his way to point out negative and often untrue statements about their obsession's rivals. Fanboys are often hostile towards critical review of their chosen subject.

As electronic entertainment gained popularity, the term became increasingly applied to [[video game]] and [[television]] addicts. As a result, a subculture emerged which readily labeled itself as "fanboys." Within this group, more effort is taken to fit in with a perceived standard, resulting in a more outgoing attitude, even among those with insecurities. This outgoing stance is often felt to be abrasive by those not involved in the culture as deeply.

More recently, especially in the [[video game industry]], fans of a particular video game console manufacturer have begun exhibiting slavish devotion to their brand of choice. An example would be a "Microsoft fanboy", one who holds devotion to the company [[Halo]]. In the video game industry, fanboy dubbing can also occur in video game titles, such as [[Metal Gear Solid]]. An example of an individual who fits this criteria and description would be [[sanas_thiritu]] (creator of the giant metal camel topic of the Halo 3 board).

==History of fanboys and the term==
The term "fanboy" is most commonly associated with adolescent and teen males but can be applicable to any age or sex. it is often used in a derogatory manner by other, less obsessed fans.

The term originated in [[comic book]] circles to describe someone immersed in the fictional worlds of comics and the culture of comics fandom. Common subjects of reverence by fanboys are [[TV show]]s, [[film|movie]]s, [[music]], [[anime]], [[comic book]]s, [[Star Trek]] ("[[Trekkies]]"), [[Star Wars]], [[car]]s, [[video game console]]s, [[video games]], [[operating system]]s, [[MMORPG]]s, [[Computer Hardware|hardware]] and [[software]] companies.

Popular depictions of Fanboy stereotypes include the [[Comic Book Guy]] on ''[[The Simpsons]]'' and columnist [[Larry Groznic]] from the satirical newspaper ''[[The Onion]]''.

In the songs of the fannish [[parody]] [[musician]] [[Luke Ski]], many characters proudly consider themselves ''fanboys.''

The earliest published uses of the word "fanboy" have been dated to 1982. One reference is to the cover of the "Official Underground and Newave Comix Price Guide". On this cover page are sketched overweight, overzealous comic book collectors wearing T-shirts that state "Fanboys of America," and are describing the extreme measures they would go to, including moving to San Francisco, to preserve their comics.

Also published in 1982, a comic strip appeared in Jim Engel and Chuck Fiala's "Fandom Confidential" comic. In the strip, Jim and Chuck met comic artist/writer [[John Byrne]] and collapsed into "mindless paroxysms of adoration." The John Byrne character responded that they were "a couple of fanboys in bondage" (a play on words referring to a [[List of Monty Python’s Flying Circus episodes#10. E. Henry Thripshaw.27s Disease|Monty Python sketch]] in which an Elizabethan era character reads what she claims to be a new Shakespeare work called "Gay Boys in Sanas". [http://www.byrnerobotics.com/FAQ/listing.asp?ID=7&T1=Miscellaneous+Questions#154] Another early use is in a smart-alec editorial reply by "[[Ambush Bug]]" to a letter in his comic in [[1985]].

==Subjects of obsession==
Some current examples of brands and products which have fanboy supporters:
*The competing gaming systems [[Playstation 3]], [[Wii]], [[Xbox 360]] and [[PC]].
*The operating systems [[Microsoft Windows]], [[Mac OS X]] and [[Linux]].
*The internet web browsers [[Mozilla Firefox|Firefox]], [[Internet Explorer]] and [[Opera (internet suite)|Opera]].
*The various technology companies: [[Google]], [[Sony]], [[Apple Computer|Apple]], [[Microsoft]], [[Nintendo]].
*The computer microprocessor companies [[Advanced Micro Devices|AMD]] and [[Intel Corporation|Intel]].
*The competing [[DVD]] successor formats [[Blu-ray Disc|Blu-ray]] and [[HD DVD]].
*The competing handheld video game consoles the [[Nintendo DS]] and the [[PlayStation Portable]].
*The various [[MP3]] players, notably the [[iPod]] and the [[Zune]].

==Media==

===People===
*[[sanas_thiritu]]' ''Fanboy''

===Comic Book===
*[[Sergio Aragonés]]' ''Fanboy''
*[[Galactic Storm]] ''Fanboy''

===Television===
*''[[The Simpsons]]'''s [[Comic Book Guy]] refers to himself as a fanboy.
*''[[Freakazoid!|Freakazoid]]'''s [[freakazoid!#Other characters|Fan Boy]]
*''[[King of the Hill]]'''s [[Hank Hill]] is a fanboy of [[propane]].

===Radio/Podcasts===
*[[Fanboy Radio]] - [http://fanboyradio.com]
*[[Fanboy TV]] - [http://www.fanboy.tv]
*Drooling FanBoy - [http://droolingfanboy.com]
*ifanboy - [http://www.ifanboy.com]
*[[The Fanboy Smackdown Podcast]] - [http://www.fanboysmackdown.com]
*[[The Opie and Anthony Show]] - [http://www.opieandanthony.com]

===Webcomics===
*Fanboy Almanac (webcomic) - [http://fanboyalmanac.com Fanboy Almanac]
*[http://www.ngeb.net/fanboys Fanboys web comic]
*[http://www.fogclub.net F.O.G.Club web comic]
*[http://www.fanboysonline.com Fanboys!! Beyond Geekdom!!! (webcomic)]
*[http://www.fanboys-online.com Fanboys-Online]
*[http://www.megatokyo.com M3g4Toky0]

==See also==
* [[Addiction]]
* [[Cyberstalking]]
* [[Editor war]]
* [[Anorak (slang)|Anorak]]
* [[Astroturfing]]
* [[Otaku]]

== External links ==
* [http://www.urbandictionary.com/define.php?term=fanboy Urban dictionary: fanboy]
* [http://www.netjak.com/review.php/1013 Dissecting the Fanboy Mind] - A discussion of the fanboy behavior in regards to video games.
* [http://palgn.com.au/article.php?id=6463 The trial of the Fanboy] - A criticism of the fanboy concept and overusage of the term.
[[Category:Fandom]]
[[Category:Anime and manga terminology]]

[[de:Fanboy]]