大功率多缸柴油机曲轴疲劳强度评估方法

以某型大功率柴油机作为研究对象,采用ADAMS/Engine建立了多缸柴油机曲柄连杆机构多体动力学模型,计算得到了曲轴的工作载荷.通过建立曲轴的整体三维有限元模型,将主轴承对主轴颈的支撑边界定义为接触对以模拟实际的约束状态,并将动力学计算所得一个周期内的曲柄销载荷历程曲线离散为16个载荷点,并按照发火次序,组合得到了16个载荷工况以模拟曲轴上的交变载荷,载荷的施加采用函数分布的形式模拟滑动轴承的压力分布,通过非线性有限元分析得到曲轴的应力应变结果.在此基础上,利用曲轴材料性能数据绘制了曲轴Goodman疲劳强度曲线,自编后处理分析程序得到了曲轴上所有节点的疲劳强度安全系数.结果表明:材料为42CrMo的整体曲轴满足结构疲劳强度要求,油孔处和过渡圆角处的疲劳强度安全系数相对较小,采用Goodman疲劳曲线计算的最小疲劳强度安全系数为5.04.分析结果与曲轴实际失效位置一致.

Evaluation Method of Crankshaft Fatigue Strength for High Power Multi-cylinder Diesel Engine

Taking the crankshaft of high power diesel engine as the research object ,the multi-body dynamics model of crank and connecting rod mechanism was established with ADAMS/Engine software and the working load of crankshaft was calculat-ed .The 3D finite element model of whole crankshaft was established and the supporting boundaries of main bearing on main journal were defined as the contact pair to simulate the actual restriction .The load curve of crank pin in one period was sampled as 16 discrete points ,which were reconstructed as load conditions according to the firing order to simulate the alternating load of crankshaft .The loads were applied to simulate the pressure distribution of sliding bearing in the form of function .Nonlinear finite element analysis was then used to obtain the stress and strain results .Furthermore ,the fatigue curve of Goodman was drawn with the performance data of crankshaft material and the fatigue strength safety factors of all crankshaft joints were cal-culated by using self-developed post-processing analysis program .The result shows that 42CrMo crankshaft can meet the struc-tural fatigue strength requirements .The fatigue strength safety factor of oil hole and fillet is relatively small and the minimum fatigue strength safety factor of Goodman is 5 .04 .The analysis results are consistent with the failure position of the crank-shaft .