Probabilistic failure prediction of SCS-6/Ti-15-3 MMC ring

Two parameter Weibull analysis was used to predict the fracture strength an d fatigue life of an SCS-6/Ti-15-3 metal matrix composite (MMC) ring from c oupon samples. Two methods were used. One method was to calculate an effect ive volume for an idealized ring on the basis of a theoretical approximatio n of the stress distribution. Fracture strength and fatigue life of the cou pon samples wee then scaled to the effective volume of the ring. The other method used finite-element analysis (FEA) to determine a stress distributio n in the actual, geometrically imperfect ring. The total ring reliability w as then determined by multiplying the element reliabilities. Experimental f racture strengths were obtained for two MMC rings, each having an O.D. of 1 76.5 mm (6.95 in.) and I.D. of 146.0 mm (5.75 in.) and a 15.2 mm (0.60 in.) width. The median value of the experimental ring fracture strength data ws 173.1 MPa (25.1 ksi). Fracture strength predictions by the effective-volum e and finite-element methods were 5 and 17 percent lower than the experimen tal value, respectively. The effective-volume and finite-element methods pr edicted ring fatigue lives of 2700 and 4800 cycles, respectively, at a 50 p ercent probability of failure and 154.4 MPa (22.4 ksi) maximum ring interna l pressure. No ring fatigue data were available for comparison.