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对扭转试样进行喷丸和预应变,经强化后试样的对称扭转疲劳极限比磨削态提高20～30％。 断口分析表明,在疲劳极限水平附近运转的扭转疲劳断裂是由正应力引起的,断口与轴线成45°。喷丸试样的硬度分布曲线表明,在表下一定深度存在软化区,而裂纹萌生的位置比软化区更深。 喷丸后扭转疲劳极限提高的主要原因是残余压应力的作用。在喷丸前或后进行预应变均使疲劳极限下降。这和预应变时造成的损伤或在夹杂周围造成裂纹有关,它使疲劳寿命降低。
Shot peening and pre-straining of the torsional specimen were performed, and the symmetrical torsional fatigue limit of the specimen was increased by 20-30% compared with the ground state after strengthening. Fracture analysis shows that the torsional fatigue fracture operating near the fatigue limit level is caused by normal stress and the fracture is at 45 ° to the axis. The hardness distribution curve of shot peening shows that there is a softening zone at a certain depth under the table, while the crack initiation position is deeper than the softening zone. The main reason for the increase of torsional fatigue limit after shot peening is the effect of residual compressive stress. Pre-strain before and after shot peening both reduced the fatigue limit. This is pre-strain caused by damage or inclusions around the cause of the crack, it reduces the fatigue life.