旋翼扭力臂孔多轴疲劳准则及挤压强化效果评估

Multi-axial fatigue criteria and extrusion-strengthening evaluation of helicopter rotor’s torsional arm hole

扭力臂组件是直升机旋翼系统中的重要部件之一,在飞行过程中,其承受着复杂高频振动及交变载荷,所以紧固孔连接处易发生疲劳破坏。为了改善扭力臂孔的疲劳性能,通过三维非线性接触有限元对扭力臂进行力学行为分析。基于Smith-Waston-Topper(SWT)准则,对扭力臂孔的裂纹萌生位置及疲劳寿命进行预测,并分析孔挤压工艺对扭力臂孔疲劳寿命的影响。结果表明:SWT损伤准则可以成功预测疲劳裂纹萌生位置和寿命;扭力臂孔的疲劳破坏属于I型破坏,且裂纹萌生处有三维裂纹源;随着挤压量的增加,扭力臂孔的疲劳寿命基本呈现出增大的趋势,最后趋于稳定;把扭力臂孔破坏点位置作为挤出端,寿命提升效果最好;孔面残余压应力有益于延长疲劳裂纹萌生寿命。挤压强化多轴疲劳预测方法可以为扭力臂寿命预测和优化设计提供理论依据。

As one of the most important parts of the helicopter rotor system,the torsional arm is subjected to complex highfrequency vibration and alternating loads in service,so its fastener hole is prone to fatigue-led failure.In this article,in order to improve the torsional arm hole’s fatigue performance,the mechanical behaviors of the torsional arm are simulated by means of the three-dimensional non-linear finite-element method.Based on the Smith-Watson-Topper(SWT)criteria,efforts are made to predict the torsional arm’s position of crack initiation and fatigue life,as well as to explore the effect of the extrusion process on the torsional arm’s fatigue life.The results show that:thanks to the SWT damage criteria,the torsional arm’s position of crack initiation and fatigue life are predicted successfully;the fatigue-led failure of the torsional arm hole belongs to the Mode I fracture,and there are three-dimensional crack sources at the position of crack initiation;with the ever-growing extrusion,the fatigue life extends basically,and finally it tends to be stable without any growth;with the fracture position as the extruding end,the torsional arm hole witnesses its life improvement to the best;the ever-growing residual pressure stress on the hole surface helps to extend the fatigue life.Therefore,this method provides theoretical basis for life prediction and optimization design of torsional arms.