Improvement of Fatigue Life and Dynamic Strength of an Engine Mounting Bracket Using Experimental and Numerical Approaches

The engine mounting bracket is one of the most sensitive parts of an automobile that is used to connect the engine to the body of the vehicle. Under operating conditions, it is subjected to static, cyclic, and exceptional loads. Since this part is generally manufactured by the casting method, the casting-induced defects can affect its service life. In this study, an engine mounting bracket was first subjected to an experimental static load test, the results of which showed the absence of defects. The endurance limit was then measured experimentally using the high-cycle fatigue test. According to the results of the staircase-Locati fatigue test, the relative mean resistance load was obtained as 1.24 with a relative scatter of 0.07 which fell in the unsafe operating region of the engine mounting bracket. Therefore, a finite element analysis was conducted to determine the critical regions on the part and modify its geometric shape to improve its performance. The crack onset and growth regions obtained in the fatigue tests agreed well with the critical areas identified in the finite element analysis. After modifying the geometric shape and eliminating production defects, several experimental tests were performed to evaluate the endurance limit. The results showed that an increase of only 0.9% in the mass of the engine mounting bracket, decreased stress concentration up to 37%. The relative mean resistance load was increased up to 1.33 with a relative scatter of 0.06, which provided safe performance in the vehicle operating condition. Finally, the modified bracket passed the dynamic load test without any crack and loosening of the screws during the assembly process.