THERMOMECHANICAL FATIGUE BEHAVIOR OF AN ANGLE-PLY SCS-6 TI-15-3 METAL-MATRIX COMPOSITE

The response of the continuous-fiber-reinforced metal-matrix composite SCS-6/Ti-15-3 with orientation [+/-45](2s) was investigated under fat igue conditions. Three temperature and load profiles were used to char acterize the metal-matrix composite, namely: isothermal fatigue (IF) a t 427 degrees C, in-phase thermomechanical fatigue (IP-TMF) from 149 d egrees C to 427 degrees C, and out-of-phase thermo-mechanical fatigue (OP-TMF) from 149 degrees C to 427 degrees C. At high stress levels (a bove 400 MPa) the [+/-45](2s) laminate displayed in-phase, out-of-phas e, and isothermal fatigue lives which were all within 1000 cycles. At these high stress levels the laminate exhibited the most detrimental f atigue response when subjected to the in-phase TMF profile. The IP-TMF and IF curves displayed equivalent fatigue lives at stress levels bel ow 400 MPa. At these lower stress levels (below 400 MPa) the OP-TMF li ves were approximately a factor of two lower than the IP-TMF and IF li ves. Mechanical strain measurements, Young's modulus calculations, mic romechanical analysis, acetate edge replication, metallography, and fr actography were all employed to explain the damage mechanisms and thei r effects on the fatigue life of the laminate. The initial mode of dam age for all specimens tested at all load-temperature profiles was fibe r-matrix interfacial failures. Matrix plasticity, matrix cracking, fib er rotation, and fiber failures were evident at all applied stress lev els in IP-TMF, OP-TMF, and IF. The degree of each of these mechanisms was dependent on both the applied stress level and the temperature pro file.