钝缺口试样疲劳短裂纹形成与扩展

对两种晶粒尺寸的中碳钢钝缺口试样进行了对称拉疲劳试验，应用复型方法观察了疲劳理解纹沿缺口根部的早期形成与扩展过程；测量了表面裂纹形状随裂纹长度的变化规律。结果表明，试样的破坏是由形成于缺口根部表面的短裂纹扩展、裂纹间连接形成穿透裂纹，穿透裂纹扩则引起的。

SHORT FATIGUE CRACK INITIATION AND PROPAGATION IN BLUNT NOTCHED SPECIMENS

Completely reversed uniaxial cyclic tests were carried out using single edge notched specimens of a medium carbon steel with two different grain sizes.The processes of early crack development at the notch surface were observed by the replication method.The variation of the shape of cracks with the crack length was investigated.It was shown that the failure of the specimen was caused by the growth of the short cracks which initiated from the surface of notch root.The initiation life of short cracks are less than 10 % of the fatigue life,and the short crack growth life before which the through thickness crack has not initiated is less than 80 % of the fatigue life.The shape of short cracks is related to the crack length.The shorter the crack is,the larger will be the fluctuations of a/c .When the crack length is larger than the critical length,the value of a/c is about 1.5.