Metallurgical Examination of a Diaphragm - Lockup Clutch Piston

摘要

A metallurgical examination was performed on a diaphragm - lockup clutch piston which experienced cracking around the inside diameter. The study required reviewing the manufacturing procedures, analyzing the service conditions and determining the operating stresses induced on the part in service. The extent of cracking was verified by using magnetic particle testing. Material identification and characterization was accomplished by performing mechanical testing, chemical analysis, and metallographic techniques. Scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS) was used to examine features of the material and the fracture surface. Finally, a mechanics analysis was included in order to calculate an approximation of the actual operating stresses, the critical stress-intensity factor (KIC) for the material, the stress-intensity factor (KI) under observed conditions, and the possible crack propagation rates under actual loading. Measurements of the residual stress were also taken utilizing X-ray diffraction.