Explanation

The stress that exists inside the materials and does not depend on the external load. According to the scope of action, it can be divided into micro inner stress and macro inner stress. There are various micro defects in crystal, such as point defect (vacancy, interstitial atom), line defect (dislocation) and plane defect (stacking fault, grain boundary and twin boundary). There is an internal stress field corresponding to the elasticity distortion caused by the surrounding materials. Due to the small range of such distortions, the range of internal stress action is called microscopic internal stress. Distortion also exists around the inclusion and the second phase, so micro internal stress can also be generated. After unloading the sample or component after uneven plastic deformation, there will be residual inner stress in it. This kind of residual stress has a large scope of action, which is called macro inner stress. Multiple surface processing techniques can generate high compressive residual stresses on the surface layer, while generating smaller tensile residual stresses inside the specimen. Weld can also produce residual stress. When the component is heated unevenly or the coefficient of thermal expansion of each part is different, thermal stress will be generated inside when the temperature changes, which is also a inner stress. During loading, both internal and external stresses act simultaneously. If the sign is opposite to the external stress, it can offset part of the external stress and play a good role. For example, the surface residual compressive stress can improve the fatigue life. The internal tensile stress can be superimposed with the external tensile stress, thereby promoting the failure and failure of the component.

Classification