Failure Analysis of the Rear Axles in a Sports Utility Vehicle (SUV)

Abstract In a rollover accident, both rear axles of a Sports Utility Vehicle (SUV) were fractured adjacent to the wheel-mounting flange. The purpose of this paper is to describe the methodology and experimental techniques used in determining whether one or both axles failed prior to the accident, and thus contributing to the accident, or whether both axles failed as a result of the rollover and the ensuing impact with the highway. Scanning Electron Microscopy (SEM) technique was used to obtain detailed characteristics of the fracture surface on both axles. Through-thickness hardness profile of the axles was determined using incremental micro-hardness measurements in order to assess the depth of case hardening in both axles. Impact, tensile and fatigue specimens were machined from the remaining parts of the failed axles and were tested to destruction using standard impact (Izod), tensile and fatigue tests. The fracture surface characteristics of the test specimens were compared to those of the failed axles in order to isolate the mode of failure. Based on the results of the above tests, the history of the repair work performed on the rear wheel bearings and the physical evidence of various marks and damages remaining on the vehicle’s body, it was determined that one of the rear axles failed prior to the rollover, while the other occurred as a result of the rollover and ensuing impact with the highway.