Northeast Asia

2009-06-15T07:08:17Z

124.82.46.107:

'''Northeast Asia''', sometimes Northeastern Asia, is a [[subregion]] of [[Asia]] that can be defined any of four ways:

1. The region bounded roughly by the Great Wall in the South, Lake Baikal in the West, the tundra in the North, and the Pacific Ocean in the East. This conception of the region draws attention to cultural and linguistic connections between the [[Mongols]], the [[Manchus]], the [[Koreans]] and other indigenous ethnic groups in the region, and to the contestation over the region between [[China]], [[Russia]] and [[Japan]] since the 17th century.

2. The far eastern peninsula of the Asian continent, now entirely within [[Russia]], especially in the context of its anthropological, biological and geological connections across the [[Bering Strait]] with [[Alaska]].

3. [[Japan]] and [[Korea]]. This usage was adopted by the United States [[State Department]] in 1945 and is used by the [[Association for Asian Studies]].

4. [[China]], [[Japan]] and [[Korea]]. This somewhat general usage is synonymous with the most common meaning of the term [[East Asia]] but has been adopted in response to the extension of the meaning of East Asia in diplomatic circles to include [[Southeast Asia]] and sometimes, though not very accurately even [[India]], e.g. the [[East Asian Summit]].

India, Bangladesh, Nepal Bhutan and Pakistan (grouping based on ethnic and religio-cultural similarities i.e. Hinduism, Buddhism as well as the Dravidian phenotype) however would be clearer defined with the term [[West Asia]] with East Asia referring to [[ASEAN]] +3 which encompasses North East Asia AND South East Asia.

5. In [[ASEAN+3]] these countries [[China]], [[Japan]] and [[Korea]] are considered the '+3' portion of the grouping of [[ASEAN]] and are nations and cultures strongly influenced by Confucian Philosophy. North East Asians are fair with yellow tinted skin. The [[ASEAN]] [[South East Asian]] archipelago region, also [[Nusantara]], is distinct and typified by brown skinned Khmer-Austronesian Animist peoples who have nominally adopted into Middle Eastern Muslim cultures. Countries such as [[Brunei]], [[Borneo]], [[Phillipines]], [[Indonesia]] and [[Malaysia]] are considered part of South East Asia.

Between these two regions is [[Indo-China]], which consists of [[Burma]], [[Cambodia]], [[Laos]], [[Thailand]], [[Vietnam]], nominally Animist-Buddhist regions, skin colouration varying between that of the three regions, [[North East Asia]], [[West Asia]] and [[South East Asia]]; caused from both climate and interracial mixing from proximity to both regions.

{{Asia-stub}}

[[de:Nordostasien]]
[[gan:東北亞]]
[[ja:北東アジア]]
[[zh-yue:東北亞]]
[[zh:东北亚]]

About fracture mechanics

2007-11-17T03:09:10Z

124.82.166.189:

{{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]], 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|left|thumb|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|left|thumb|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|left|thumb|[[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.

== 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 theory emerged from this work; a term called [[stress intensity]] replaced strain energy release rate and a term called [[fracture toughness]] replaced surface 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]]
[[uk:Механіка руйнування]]
[[zh:断裂力学]]

JavaScript/Basics

2007-05-02T14:19:16Z

124.82.178.121: /* First Lesson */

== Learning Basic JavaScript ==

What you should know - HTML/XHTML

Basics - 
• JavaScript is the most popular web page scripting language and is suppported by almost every browser. 
• It adds interactivity to your web pages. 
• You can use only the tools all ready on your computer with out the need to download any software. 
• It is easy and fun

== First Lesson ==

Open up your text editor of choice and create a basic page. Now I am going to teach you how to write on your webpage using JavaScript. 

<html> 
<body> 
<script type="text/javascript"> 
document.write("Hello World!") 
</script> 
</body> 
</html> 

As you can see JavaScript is added directly into your HTML by adding the <script> tag. You dont have to understand exactly how that worked, I'm about to explain. What you do need to know is this <script type"text/javascript"> tells the borwser that what ever you write between the that tag and the comsing </script> tag is JavaScript. 
 
Now You also need to know this JavaScript is case sensitive. What that means is what ever you type must be in capitilized the way it should be. For example if you wrote <ScRiPt TyPe="TeXt/JaVaScRiPt"> not only would you waste alot of time, your browser would also have no idea what you did.
 
You are probably wondering when im going to explain the rest of what you did. Well, document.write is the JavaScript standered way of writing. You declaired where you wanted to be mesing with by typing document, then you told what you wanted to do on the document, also known as giving the command, with .write, then you told the the bowser what to do with the command, and in this case what to write with ("Hello World")
 
These are the absolute essentials to understand for starting JavaScript.
 
--[[User:Xora K Joken|Xora K Joken]] 19:18, 3 April 2007 (UTC)

[[Category:Java]]
[[Category:Basics]]

IdeaWazaWiki - User contributions [en]

Northeast Asia

About fracture mechanics

JavaScript/Basics