疲劳近门槛值区裂纹扩展模式变化的试验研究  

Experimental Research on Fatigue Crack Growth Modes Transition in Near-threshold Regime

作　　者：朱明亮[1] 轩福贞[1] 安春香[2] 

机构地区：[1]华东理工大学机械与动力工程学院,上海200237 [2]上海汽轮机有限公司,上海200240

出　　处：《压力容器》2009年第8期7-10,31,共5页Pressure Vessel Technology

基　　金：国家863高技术资助项目(2006AA04Z413);教育部新世纪优秀人才计划项目(NCET-06-0414)

摘　　要：利用扫描电镜观察疲劳门槛值区试样的裂纹表面形貌,研究了疲劳门槛值区裂纹扩展模式的分布,分析了裂纹扩展模式的变化对疲劳裂纹扩展速率da/dN的影响。结果表明,断口形貌存在面型断裂(沿晶或穿晶)(Faceted Fracture,FF),面型断裂分数(Percentage of Faceted Fracture,PFF)最大值出现在循环塑性区尺寸接近原始奥氏体晶粒直径时。通过比较循环塑性区尺寸与晶粒尺寸,随着应力强度因子幅值ΔK的降低,裂纹先以辉纹型模式扩展,在PFF达到最大值后,裂纹以晶体学模式扩展。辉纹型模式扩展时,PFF的变化对da/dN影响不大;晶体学模式扩展时,由于FF诱发裂纹闭合,从而降低da/dN。The distribution of fatigue crack propagation modes in the near - threshold regime was investigated by employing scanning electric microscopy to explore crack surface appearance in fatigue threshold test samples. The effect of fracture modes transition on fatigue crack growth rate da/dN was analyzed. Results show that faceted fracture was found on the fracture surface and maximum percentage of faceted fracture （PFF） existed when cyclic plastic zone equals to the prior austenitic grain size. By comparing the cyclic plastic zone and the grain size, it concludes that with the stress intensity factor range AK decreasing, crack growth is first dominated by striation - mode of advance and changes into crystallographic - mode of growth at the maximum PFF. In the Striation - mode of advance region, changes of PFF have little influence on da/dN while in the crystallographic - mode of growth region, faceted fracture can induce crack closure which can decrease da/dN.

关 键 词：疲劳门槛值 裂纹扩展模式 断口形貌 沿晶断裂 

分 类 号：TG115.5[金属学及工艺—物理冶金]