组合加载下的疲劳破坏与裂纹扩展条件

Fatigue Failure and Crack Propagation under Combined Stresses

光滑试样的表面滑移和疲劳破坏是传统的疲劳问题,而疲劳裂纹的扩展属断裂力学的应用范畴.本文用局部应力观点讨论它们各自发生的条件,并说明相互间的区别和联系.在弯扭组合加载条件下,滑移门槛应力、疲劳极限以及裂纹扩展门槛应力的计算结果均与实验值符合较好.

The conditions and features of slipping, fatigue fracture of smooth specimens and crack propagation under combined stresses are discussed from the point of view of the local stress. The specimens used are made of carbon steel type SK-5. Analysis and experimental results show that, under various combinations of bending and torsion, the maximum shear stress (max) effects the slip initiation, while the fatigue fracture is dependent not just on max or max. For short cracks, LEFM is applicable provided that the nominal stress is smaller than the slip initiation threshold stress of the material. For cracks of about 0.05 mm or less in length, the propagation threshold stress is nearly equal to the fatigue limit of various deformation modes. Calculated results for slip initiation threshold stress, crack propagation threshold stress and fatigue limit are in good agreement with experimental ones.