Stress Yield Strength
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When working on designs, I often encounter problems related to stress and strength. As a beginner, I have forgotten a lot of what I learned in school. What exactly is stress, and how is it calculated? What is yield strength? What is the relationship between stress and yield strength?
You can check Baidu’s explanations at http://baike.baidu.com/view/170203.htm, http://baike.baidu.com/view/72126.htm, and http://baike.baidu.com/view/625885.htm. These three links correspond to Baidu’s pages on stress, yield strength, and yield stress respectively. This post was last edited by wode*aohei on 2009-4-3 at 09:26
Stress refers to the force per unit area, and its units are Pa and MPa. To understand yield strength, one must first know what yield is. Let me explain it to you. During the loading of a material, at the beginning, its deformation is proportional to the magnitude of the load; this stage is known as the proportional stage (elastic stage). When the load reaches a certain level, something happens: with the load remaining constant (or with only slight changes in stress), the deformation changes significantly. This phenomenon is called yield. The minimum stress at the yield stage becomes the yield limit. The yield limit divided by the safety factor is what you referred to as the yield strength. At the design stage of components or structures, strength analysis is often conducted to prevent plastic deformation. One of the criteria for this analysis is that the maximum normal stress should not exceed the material’s yield strength, in order to ensure safety. The above is for reference only; to gain a detailed understanding, one can consult materials on mechanics of materials and mechanical design.