Dynamic analysis of loads and stresses in connecting rods

Automobile internal combustion engine connecting rod is a high volume production component subjected to complex loading. Proper optimization of this component, which is critical to the engine fuel efficiency and more vigorously pursued by the automotive industry in recent years, necessitates a detailed understanding of the applied loads and resulting stresses under in-service conditions. In this study, detailed load analysis under service loading conditions was performed for a typical connecting rod, followed by quasi-dynamic finite element analysis (FEA) to capture stress variations over a cycle of operation. On the basis of the resulting stress-time histories, variation of stress ratio, presence of mean and bending stresses, and multi-axiality of stress states in various locations of the connecting rod under service operating conditions were investigated. It was found that even though connecting rods are typically tested and analyzed under axial loading and stress state, bending stresses are significant and a multiaxial stress state exists at the critical regions of connecting rod. A comparison is also made between stresses obtained using static FEA which is commonly performed and stresses using quasi-dynamic FEA. It is shown that considerable differences in obtained stresses exist between the two sets of analyses.