表面强化对A-100钢带孔构件疲劳性能的影响

Influence of local surface strengthening on fatigue properties of components with holes of an A-100 steel

对超高强度钢A-100带孔构件进行喷丸和孔挤压等表面强化处理,对比在相同试验条件下的疲劳性能,计算分析表面强化延寿增长系数和疲劳极限的提高幅度,获得了超高强度钢A-100带孔构件疲劳的应力集中特性与表面强化改性效果。结果表明,A-100超高强度钢具有很高的应力集中敏感性;表面强化可显著延长带孔构件的疲劳寿命和提高其疲劳极限,表面强化效果主要取决于表面强化层内的残余压应力;疲劳断口分析表明表面强化构件的疲劳源不再位于孔边而是在孔边与内部的过渡部位。由于孔挤压强化在引入较深残余压应力的同时还可以改善孔边的粗糙度,因此其强化效果优于喷丸强化。喷丸和挤压分别使疲劳极限提高了35%和38%,有效缓解了孔边应力集中对疲劳性能的不利影响。

Fatigue properties of an A-100 steel were investigated for machined,shot-peened and hole-cold expanded specimens,and the fatigue limits of the specimens were determined by stair-step method. The results show that fatigue properties of the A-100 steel are sensitive to stress concentration and residual compressive stress induced by local surface strengthening treatment. Therefore,the surface strengthening can prolong fatigue lives and improve fatigue limits of the steel due to beneficial residual compressive stress. It can also be found that fatigue crack is mainly initiated at the hole edges of the specimen surface for the unstrengthened components,while the fatigue crakcs are located at surface of the hole wall for strengthened parts. Cold hole expansion improves the fatigue properties more effective than shot peening due to deeper compressive residual stresses and better surface state after the hole expansion. The fatigue limit is increased by 35% and 38% after shot peening and cold hole expansion,respectively. Therefore,the local surface strengthening can effectively relieve the detrimental stress concentration effect.