Probabilistic Failure Prediction of SCS-6/Ti-15-3 MMC Ring

Abstract

Two parameter Weibull analysis was used to predict the fracture strength and fatigue life of an SCS-6/Ti-15-3 metal matrix composite (MMC) ring from coupon samples. Two methods were used. One method was to calculate an effective volume for an idealized ring on the basis of a theoretical approximation of the stress distribution. Fracture strength and fatigue life of the coupon samples were then scaled to the effective volume of the ring. The other method used finite-element analysis (FEA) to determine a stress distribution in the actual, geometrically imperfect ring. The total ring reliability was then determined by multiplying the element reliabilities. Experimental fracture strengths were obtained for two MMC rings, each having an O.D. of 176.5 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 was 173.1 MPa (25.1 ksi). Fracture strength predictions by the effective-volume and finite-element methods were 5 and 17 percent lower than the experimental value, respectively. The effective-volume and finite-element methods predicted ring fatigue lives of 2700 and 4800 cycles, respectively, at a 50 percent probability of failure and 154.4 MPa (22.4 ksi) maximum ring internal pressure. No ring fatigue data were available for comparison.