ANSYS中的物理量（如应力、应变及相对位移等）的正负号规定

1、应力向量{σ}的符号规定：拉应力和拉应变为正，压应力和压应变为负；剪应力基本与弹性力学规定相同（正向正向，负向负向）

The stress vector is shown in the figure below. The sign convention（符号规定） for direct stresses and strains used throughout the ANSYS program is that tension is positive and compression is negative. For shears, positive is when the two applicable positive axes rotate toward each other.

  http://s9/mw690/002UWa5Fgy6WiGA1yNW18&690

2、主应力σ1, σ2,  σ3：按几何大小排序，受压时主应力为负，最小的为σ3，受拉时为正，最大的为σ1

The three principal stresses are labeled σ1, σ2, and σ3 (output quantities S1, S2, and S3). The principal stresses are ordered so that σ1 is the most positive (tensile) and σ3 is the most negative (compressive).

http://s8/mw690/002UWa5Fgy6WiFxtYdVd7&690

3、应力强度 σI的符号规定：永远为正。

The stress intensity σI (output as SINT) is the largest of the absolute values of σ1 - σ2, σ2 - σ3, or σ3 - σ1. That is:

http://s16/mw690/002UWa5Fgy6WiHmpFEz2f&690
4、von Mises or equivalent stress σe：永远为正。

The von Mises or equivalent stress σe (output as SEQV) is computed as:

5、常用来模拟接触的弹簧单元COMBIN39的相对位移正负号规定：

(e.g., UX(J) - UX(I) - UORIG, etc.).
 UJ--Displacement of node J
 UORIG--Origin shift upon reversed loading（反复荷载引起的原点移位）

待续。。。。。