喷丸对H13钢单边带缺口试样疲劳裂纹扩展行为的影响

喷丸工艺通过改变试件的表面形貌、微观组织及残余应力等表面完整性可以影响裂纹的萌生和扩展;对于存在缺陷的试件,喷丸的作用机制和影响结果有所不同。采用白光干涉仪、SEM、XRD及显微硬度计等对单边带缺口的H13钢薄板试样喷丸前后的表面完整性进行了测定。并借助原位SEM开展了系列裂纹扩展试验,分析了喷丸对试样疲劳寿命、裂纹扩展速率以及疲劳断口特征的影响。研究结果表明,虽然残余压应力诱发裂纹闭合,但由于喷丸后表面粗糙度的大幅提高增强了缺口效应,表面加工硬化使得韧性有所降低,以及残余应力在加载过程中发生松弛等因素,喷丸后单边带缺口试样的裂纹萌生过程缩短,疲劳寿命降低,且裂纹扩展速率的变化较小。喷丸前后疲劳断口形貌均为准解理特征,喷丸后断口近表面处的撕裂棱特征消失。

Effects of Shot Peening on Fatigue Crack Propagation Behavior of Single Notched H13 Steel Specimens

Shot peening process affects the crack initiation and propagation of specimens by changing surface integrity, such as surface topography, microstructure and residual stress. For notched specimens, the influencing mechanism of shot peening on their fatigue properties are different. The surface integrity of single notched H13 steel specimens before and after shot peening were measured by a white-light interferometer, SEM, XRD and a microhardness tester. A series of crack propagation experiments were carried out with in-situ SEM, and the effect of shot peening on the fatigue life, crack propagation rate and fatigue fracture were investigated. Results show that the sharp increase of surface roughness enhances the notch effect and the work hardening near surface results in toughness decrease after shot peening though the residual compressive stress induces the crack closure. Stress relaxation also occurs during loading process. The above effect caused by shot peening shortens the crack initiation process, reduces the fatigue life, and slightly changes the crack propagation rate of the single notched H13 steel. The fracture morphologies of H13 steel are mainly quasi cleavage. The tear ridges on the edge of fracture surface disappear after shot peening.