## 五种力的作用效果

### 力(force)和应力(stress)的区别

There are five fundamental types of loading: compression压缩, tension拉伸, shear剪切, torsion扭转, and bending弯曲. 参考

### 应力-应变曲线(Stress–strain curve)

(1)  线性弹性阶段，遵循胡克定律，斜率为杨氏模量。此阶段的结束恰好是塑性变形的开始，该点的应力即为屈服强度(屈服应力)。
(2)  应变硬化阶段，对应的应力范围大小，大于屈服强度，小于极限强度。极限强度就是曲线的最高点对应的应力大小。这个区域一开始的应力不随应变变化，有短暂的水平之后，继续呈现应力增大应变增大的趋势。
(3)  颈缩阶段，也就是应力超过极限强度后，材料的某一段的截面积明显比平均截面积小。应力在截面积较小的区域很容易集中，因此颈缩会自我增强，让应力更集中，正反馈使得材料很快断裂。

Moment of Inertia and Polar Moment of Inertia are both the quantities expressing a body’s tendency to resist changes when certain torque is being applied.

Moment of Inertia is often refereed as mass moment of inertia or the angular mass. It is the measure of an object’s resistance against the angular acceleration. The resistance being done here is against the rotation rate when certain torque is applied.

On the other hand, Polar Moment of Inertia is a measure of a body’s ability to resistance against the torsion when torque is being applied. It is utilized to calculate the angular displacement of a body subjected to torque.来自