Failure Analysis of an Ambulance Cathode Ray Tube Monitor Bracket

Abstract

An aluminum alloy ambulance monitor bracket that fractured in-service was analyzed to determine the mode, mechanisms, and causes of its failure. After visual inspection, cause-and-effect analysis was conducted to identify all the possible factors that may have contributed to failure. The bracket arm was investigated using macro- and micro-fractography, chemical analysis, optical microscopy, and hardness testing to assess the failure characteristics and material properties. Finally, simulations were conducted with SolidWorks® to evaluate the component loading and stress distributions that led to fracture. The failure of the bracket was attributed to long-term, low stress amplitude, unidirectional dynamic bending high-cycle fatigue of the bracket arm, applied by the monitor weight in conjunction with vehicular vibrations while driving. Failure was most likely caused by: (1) the unsatisfactory surface condition of the arm produced by thermal cutting, including large inclusions, jagged edges, and a heat-affected zone; (2) the poorly designed component geometry, which promoted a stress concentration at the point of failure; and (3) the inadequate material strength, given the component geometry and applied cyclic stress requirements. Several options for improved component reliability were recommended.