非对称循环交变动载荷下惰轮裂纹扩展研究

Study on crack propagation of idler gear under asymmetric cyclic dynamic load

摘要

惰轮轮齿的两工作齿廓依次与主、从动轮的轮齿工作齿廓交替接触啮合使轮齿承受非对称循环交变载荷，齿根处拉、压应力状态交替出现，致使其裂纹扩展行为复杂。通过等效离散化将惰轮两工作齿廓的啮合过程模拟为等效移动载荷依次在两工作齿廓的离散点上加载，考虑闭合效应下拉、压应力状态交替变化引起的影响，提出了非对称循环交变载荷下惰轮裂纹扩展仿真方法，分别在准静态和动态载荷情况下开展惰轮裂纹扩展研究。结果表明：相比于拉应力受载状态，拉、压应力交变受载状态下压应力会延缓齿根应力强度因子K_Ⅰ增长，使裂纹前缘开裂角θ增大，且随着裂纹扩展压应力的影响逐渐减小，当压应力失效时K_Ⅱ显著下降，使有效应力强度幅值ΔK_eq显著增大，导致裂纹扩展寿命降低；相比于准静态载荷，动态载荷会促进K_Ⅰ增长，使裂纹前缘开裂角θ减小，使有效应力强度幅值ΔK_eq显著增大，导致裂纹扩展寿命降低。

Abstract

The two working tooth profiles of the idler gear tooth engage alternately with the tooth working profiles of the driver and driven gears，resulting in the gear tooth being subjected to the asymmetric cyclic alternating load. This leads to alternating tensile and compressive stress state at the tooth root，making the crack propagation behavior complex. By employing the concept of discrete equivalence，the meshing process of the two working tooth profiles of the idler gear is simulated as an equivalent moving load successively applied at discrete points on the two working tooth profiles. The effects caused by the alternating tensile and compressive stress state with the closure effect are considered. Consequently，a simulation method for crack propagation of the idler gear under the asymmetric cyclic dynamic load is proposed，and investigations are carried out under quasi-static and dynamic loading conditions. Compared with the tensile stress state，the compressive stress delays growth of the root stress intensity factor K_Ⅰ and increases the crack initiation angle θ at the crack tip in the alternating tensile and compressive stress state. However，as the crack propagates，the influence of the compressive stress gradually decreases. When the compressive stress fails，K_Ⅱ decreases significantly. The compressive stress results in a higher effective stress intensity amplitude ΔK_eq and reduced crack propagation life. Compared with the quasi-static load，the dynamic load accelerates growth of K_I and reduces θ，leading to a higher ΔK_eq and a shorter crack propagation life.

关键词

非对称循环 / 动态载荷 / 惰轮 / 裂纹扩展 / 有限元

Key words

asymmetric cycle / dynamic load / idler / crack propagation / finite element

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基金资助

国家自然科学基金资助项目(52105040)

国家自然科学基金资助项目(52075001)

国家自然科学基金资助项目(52105082)