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本文研究了喷丸残余应力场在疲劳加载初期的静载松弛现象及机理,并对最佳喷丸残余应力场进行了探讨。试验结界表明,残余应力在疲劳过程中的静载松弛是工件表层材料剧烈塑性变形的结果。残余应力的静载松弛会使晶界、相界等障碍物处形成一定数量的微裂纹,给工作表层材料带来损伤,降低疲劳裂纹的形核寿命。为了避免疲劳初期由于残余应力的静载松弛所造成的损伤,在喷丸后采用应力松弛低温回火工艺,预先降低残余应力场中的最大残余压应力值,建立最佳残余应力场。这种通过热激活的方式使残余应力发生的松弛属子非损伤性松弛,因而能够有效地提高材料在S—N曲线上的较高交变应力区的疲劳寿命。
In this paper, the static relaxation phenomenon and mechanism of the residual stress field of shot peening in the early stage of fatigue loading are studied, and the optimum residual stress field of shot peening is discussed. The experimental ensemble shows that the static relaxation of residual stress in fatigue process is the result of severe plastic deformation of workpiece surface material. Static stress relaxation will make the grain boundary, phase boundary and other obstacles at the formation of a number of micro-cracks, the work of the surface layer of material damage, reduce fatigue crack nucleation life. In order to avoid the damage caused by the static relaxation of the residual stress in the early stage of fatigue, stress relaxation and low temperature tempering process was used to reduce the maximum residual compressive stress in the residual stress field in advance and establish the optimal residual stress field. This thermal activation mode relaxes the relaxation genesis of the residual stress, which can effectively improve the fatigue life of the material in the high alternating stress region on the S-N curve.