应力强度因子（Stress Intensity Factors），是表征弹性材料的裂纹尖端应力、应变状态控制失稳扩展的参量，是断裂力学／破坏力学中极其重要的一个参量。

对应于三种不同的断裂模式，有三个不同的物理量：、、。

与应力强度因子相对应的表征弹塑性材料的裂纹尖端应力应变场的参量是断裂韧性J积分，J积分也按照断裂模式分为、、。

The stress intensity factor, , is used in fracture mechanics to predict the stress state ("stress intensity") near the tip of a crack caused by a remote load or residual stresses. It is a theoretical construct usually applied to a homogeneous, linear elastic material and is useful for providing a failure criterion for brittle materials, and is a critical technique in the discipline of damage tolerance. The concept can also be applied to materials that exhibit small-scale yielding at a crack tip.