invariant of stress tensor

例句：

1. 1.The temperature invariant is a constant that does not change with time.
   温度不变量是一个不随时间变化的常量。
2. 2.The invariant of the stress tensor is the only one that can be calculated from the components of the stress tensor.
   应力张量的不变量为从应力张量的分量中唯一可以计算出来的。
3. 3.Invariants are used to describe the properties of materials and structures under different loading conditions.
   变分法用于描述材料和结构在不同加载条件下的性质。