某V型柴油机机体瞬态动力学分析与疲劳寿命预测

Transient Dynamics Analysis and Fatigue Life Prediction of V Type Diesel Engine Block

对某高强化V型柴油机运动机构进行多体系统动力学分析,将获取的动态工作载荷应用于有限元瞬态动力学分析,计算了机体在激振力作用下的动态响应,得到了结构的应力-时间历程。研究结果表明:V型柴油机机体隔板一点处应力变程由不同侧气缸的最高燃烧压力所引起且隔板上对称位置的应力分布趋势大致相反。根据该机体的材料和受力特点,应用临界面法预测了机体上若干位置的疲劳寿命,认为机体肩胛的圆角处由于受到典型的拉压载荷作用,易发生疲劳破坏。相关的样机台架试验表明:按照考核工况谱测试,经过387h试验,机体第二横隔板左侧产生裂纹。预测结果与试验结果相吻合,证明该计算的正确性。

Transient dynamics analysis of a V type heavy duty diesel engine block was carried out using the dynamic load data attained from the multi-body dynamics analysis of engine moving mechanisms. The stress-time history of the structure was gained by calculation of the block dynamic response under excitation condition,and it showed that stress varying magnitude at node in the block diaphragm was caused by the explosion exciting force of opposite side cylinder, and the stress distributions at symmetrical points in diaphragms exhibited inverse shape roughly. In consideration of the block material and the stress state, the critical plane method was used to predict fatigue life at several key points of the block. It is found that the fillet of the block scapular is liable to fatigue damage under typical tensile-compressive load. Bench tests show that there appears a fracture at left side of the second diaphragm after running 387 hours in the evaluating condition spectrum,just as indicated by the prediction.