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说明：  機械應力，變形和變形速率之間的關係可能??非常複雜，儘管如果數量足夠小，線性近似在實踐中可能是足夠的。超過材料的某些強度極限的應力將導致永久變形（例如塑性流動，破裂，空化）或甚至改變其晶體結構和化學組成。 在某些工程分支中，術語壓力有時會在寬鬆的意義上用作“內部力量”的同義詞。例如，在桁架的分析中，它可以指作用在樑上的總牽引力或壓縮力，而不是力除以其橫截面的面積。(The relation between mechanical stress, deformation, and the rate of change of deformation can be quite complicated, although a linear approximation may be adequate in practice if the quantities are small enough. Stress that exceeds certain strength limits of the material will result in permanent deformation (such as plastic flow, fracture, cavitation) or even change its crystal structure and chemical composition. In some branches of engineering, the term stress is occasionally used in a looser sense as a synonym of "internal force". For example, in the analysis of trusses, it may refer to the total traction or compression force acting on a beam, rather than the force divided by the area of its cross-section.)