冲击和非冲击疲劳载荷下过载对裂纹扩展的影响

对12CrNi3A 钢在冲击和非冲击疲劳栽荷下的过载裂纹扩展延迟效应研究表明:过载对随后裂纹扩展的影响不仅取决于过载力作用下的裂尖塑变,还取决于随后基载力作用下的裂尖塑变.过载对随后裂纹扩展的影响存在两个互为矛盾的方面:一是裂尖塑变损伤促进裂纹扩展;另一是产生残余压应力场和闭合效应延缓裂纹扩展,两方面共同作用结果才能最终决定对随后裂纹扩展的影响.实验结果还表明,冲击疲劳载荷下的过载延迟效应与过载力的冲击速度有关,相同条件下,冲击疲劳载荷下的延迟期 Nd 高于非冲击疲劳载荷;各种因素对过载延迟的影响程度在两种载荷制度下不相同.

EFFECTS OF OVERLOAD ON CRACK PROPAGATION BEHAVIOUR IN IMPACT AND NON-IMPACT FATIGUE

The overload retardation effects on crack propagation in impact and non-impact fa-tigue in low carbon alloy steel 12CrNi3A were studied.It is shown that the overload effect on crack propagtion depends not only on the plastic deformation zone at crack tip due to overload stress,but also depends on the plastic deformation zone due to uccessive baseline stress.The effects of overload on crack propagation are mainly controled by the two con- tradictory factors:(1) crack propagation is promoted by plastic deformation damage,(2)crack propagation is retarded by residual compressive stress field and crack closure.The resultant crack propagation behaviour due to overloading is controlled by both(1) and(2) . It is also shown that the overload retardation effect in repeatad impact is related to the loading rate.Retardation period Nd in impact fatigue is larger than that in non-impact fa-tigue.The effects of every factor influencing overload retardation is different from impact and non-impact