汽车悬架簧早期疲劳断裂原因的试验研究

采用同一种55CrSi钢但抗拉强度相差7%的两种钢制成的弹簧,虽经过同一台喷丸机床喷丸强化处理,但在疲劳抽检试验时发现,强度稍高的簧达到了规定的疲劳断裂寿命(N=4×105cycles)要求,而强度稍低者的疲劳断裂寿命为N=2.6×105cycles。制造者认为,材料的抗拉强度偏低是导致发生早期疲劳断裂的主要原因。但是通过本文完成的大量试验及其分析表明,由于弹簧在线生产中喷丸强度的偏低、喷丸工艺欠稳定、以及喷丸质量监控的缺乏等所导致的组织结构强化效应的降低,是发生早期纵向切断型(LSF)模式疲劳断裂的主要原因。这一分析结果表明,弹簧的喷丸强化工艺不良,是导致发生早期疲劳断裂的主要原因。由此可见,只有正确地认识和恰当地运用喷丸强化工艺中的"显微组织结构强化机制",才有可能有效地避免弹簧发生早期纵/横向切断型(LSF/TSF)模式的疲劳断裂,从而制造出具有高疲劳断裂抗力的NTF模式疲劳断裂的弹簧。

Investigation on early fatigue fracture for automobile suspension springs

55CrSi steel with different tensile strength levels by different treatment were used to manufacture automobile suspension springs.The springs were processed on same shot peening machine with identical procedure supplied by different manufacturerers.The experimental results exhibit significant difference in the fatigue(LSF) life,namely the one is N=4×105 cycles the other is N=2.6×105 cycles.It is considered that the lower tensile strength of the spring should be responsible for its early longitudinal shear fatigue(LSF) fracture.However,the analysis based upon a great number of test results reveals that the instability of shot peening operation,the un-proper shot peening intensity as well as the poor quality control of the shot peening,all of which produce the lower effects of microstructure strengthening,are the inevitable consequence resulting in the early longitudinal fatigue fracture.Only if the manufacturerer correctly recognizes "the microstructure strengthening mechanism " in shot peening process,it could be avoided effectively to produce the suspension springs with early fatigue fracture for both longitudinal and transverse shear fracture(LSF/TSF) modes,and manufacture the suspension springs with high fatigue fracture resistance by normal tensile fracture mode.