MICROMECHANICS ANALYSIS AND LIFE PREDICTION OF TITANIUM MATRIX COMPOSITES

The response of a unidirectional SCS-6/Ti-6Al-4V composite is evaluate d under a range of isothermal fatigue (IF) and thermomechanical fatigu e (TMF) conditions. Both processing and thermomechanical test conditio ns are simulated using a cylinder in cylinder code, FIDEP, which treat s the fiber as thermoelastic while the matrix is characterized using a recent version of the Bodner-Partom constitutive law. Computed stress es and strains in the constituents are obtained after 10 cycles of loa ding and are used as input into a new and simpler version of a life fr action model. Applied stress at temperature and computed matrix strain s are used for the time-dependent and matrix fatigue terms in the mode l, respectively. Cyclic stress-strain behavior of the matrix material is also computed and used, together with fatigue life data, to identif y the governing mechanisms and to explain the observed trends in fatig ue life as a function of frequency and applied stress level. Compariso ns of fatigue behavior with that of SCS-6/Timetal 21S illustrate diffe rences when tested under nominally similar conditions.