渗碳及渗碳喷丸齿轮轮齿弯曲疲劳极限的定量分析

QUANTITATIVE ANALYSES ON BENDING FATIGUE LIMITS OF TEETHOF CARBURIZED AND SHOT-PEENED GEAR SPECIMENS

跳出学科分工的局限性,对以齿轮为例的表面强化零件的表象疲劳极限进行综合分析。采用20CrMnTi钢制备三点弯曲小试样及齿轮试样。试样都经过同样的渗碳(并淬火及低温回火)处理,其中一半试样再经过表面喷丸强化。为了对比,还有一组小试样经过伪渗碳处理。测定了小试样表面层的残余压应力场。利用升降法确定了5×106周、应力比0.05条件下小试样和齿轮试样轮齿的弯曲疲劳极限载荷,并对各组试验中疲劳寿命最长的断口进行分析。建立有限元模型,并利用ANSYS软件计算齿轮根部的应力场。利用“疲劳源形成和疲劳极限的微细观过程理论”及“表面和内部疲劳极限”的概念对试验结果进行定量分析,并探讨根据小试样疲劳极限确定复杂零件(如齿轮)疲劳极限载荷的方法,以及表面强化工艺优化的问题。

Apparent fatigue limits of surface hardened machine parts (gears, for examples) are quantitatively studied according to comprehensive considerations to overcome the limitations caused by science divisions. Small specimens for three-point-bending fatigue test, as well as gear specimens made of low-carbon steel 20CrMnTi are carbunzed (and then quenched and low temperature tempered), and half of them were then shot-peened. Another group of small specimens used for com-parison is pseudo-carburized. Compressive residual stress fields in the surface region of small specimens are determined. Fa-tigue tests are carried out on a high-frequency machine. The fatigue limit loads of the three-point bending specimens and the teeth of gear specimens at 5×106 cycles and stress ratio=0.05 are determined. The fracture surfaces of the specimens with longest fatigue lives in each groups are studied under SEM Stress fields near the tooth root of gear specimens are calculated by using a finite-element method and the ANSYS software. The relationships between the fatigue limits of small specimens and the critical fatigue loads of gear specimens under both condi-tions are analyzed according to a 'micro-meso-processes theory for fatigue source formation' and a concept of 'surface / inter-nal fatigue limits of metals' developed. A method for calcula-tion of critical fatigue load of complex machine parts according to the fatigue limit determined with small specimens, as well as a judgment for optimization of surface hardening technology, is proposed.