Question

请问各位大侠，什么是stress/strain?什么是normal stress/shear stress?不胜感激！！！

其实是具体的一段英文，但是因为本人非工程专业，实在是难以理解。原文如下，希望高手指点一二。
The strict definition of stress and strain is beyond the purpose of the present article and may be found elsewhere 14.
However, in its simplest definition, in a monodimensional structure (such as a string/spring pair), stress (or tension) may
http://erj.ersjournals.com/cgi/content/full/22/47_suppl/15S（第 3／19 页）2006-6-4 23:38:18
Physical and biological triggers of ventilator-induced lung injury and its prevention -- Gattinoni et al. 22 (47 Supplement): 15S -- European Respiratory Journal
be defined as the force per unit area which develops in a structure as a reaction to an applied external force of the same
entity but opposite direction, i.e. n= F/ S, where n is stress, F change in force and S the reference surface to which
the force is applied. This internal force, cutting the structure by an ideal surface, may be resolved into three components,
one of which is normal to the plane (normal stress) and two of which are tangential (shear stresses). The deformation of
the structure (if any) due to the applied force is called strain. In the simplest monodimensional structure under traction,
strain is defined as the ratio of the change in length of the structure ( L) to its length in the resting position (L0), i.e. =
L/L0, where is strain. Indeed, stress and strain are the natural response of a structure to an applied force. In the lung,
during mechanical ventilation, stress and strain are periodically changing variables characterised by maximal and minimal
values (end-inspiratory and end-expiratory PL for stress, and end-inspiratory and end-expiratory lung volume (EELV)
for strain) at a given frequency and amplitude (difference between maximal and minimal value).

Answer 1

我不是学英语的，帮你把关键部分意译一下吧。

“stress（或tension）”定义为单位面积上的力大小，该力是因为外力作用在物体上，而物体要产生基尘反作用而产生迹锋模的，其大小跟外力相同，但是大小相反。stress定义为：dF/dS，实际上就跟压强差不多了。

stress可以分解为三个方向，其中一个方姿缓向跟参考面垂直，另外两个方向跟参考面平行（其实这是废话，任何的矢量都能沿x,y,z分解）

在一维情况下，strain则是物体受力后的长度改变与原来长度的比值。具体来说，如果L是物体受力后长度改变的大小，L0是原来的长度，那么strain＝L/L0