MMC Life System Development (Phase 1)--A NASA/Pratt & Whitney Life Prediction Cooperative Program

摘要

Metal-matrix composites (MMC's), typically consisting of a titanium alloy matrix and ceramic reinforcement, are generally held as leading candidate materials for tomorrow's aircraft engines. Recognizing this, NASA Lewis Research Center and Pratt & Whitney Division of United Technologies Inc. entered into a four-year cooperative effort, hoping to lay the foundations of knowledge that will make these materials more reliable and ultimately less exotic. The four-year study, which began in January 1988, had several objectives: assessing life and fracture prediction methods; determining the actual fracture strength and lives of 6-in. diameter MMC rings made from a titanium alloy designated SiC (SCS-6)/Ti15V-3Cr-3Al-3Sn: and evaluating different means of nondestructive evaluation (NDE). Chosen for its extensive data base this material represents the MMC's that would be used in an aircraft engine but is not the specific grade. Five separate fracture and life prediction analysis methods were applied and compared with each other and with fracture data of the rings. Manufacturing defects inherent in the rings prevented the researchers from conducting planned cyclic tests. Fatigue predictions ranged from 1000 to 15000 cycles. Fracture predictions were less scattered, ranging from 25 to 40.1 ksi. Low-resolution x-ray computed tomography proved an effective NDE evaluation tool. The result of the various studies together with a material data base, are presented.