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Thermomechanical fatigue (TMF) damage mechanism and life maps are generated for unidirectional SCS-6/Timetal 21S undergoing repeated uniaxial loadings oriented along the fiber direction. The maps show the constant life contours as well as the dominant damage mechanisms as a function of maximum cyclic temperature and maximum applied cyclic stress. The maps are constructed using models that describe the individual damage mechanisms. Presently, the damage models include time, temperature, and stress-temperature phasing dependencies but are limited to repeated uniaxial loadings with constant amplitudes and positive stress ratios. Both in-phase and out-of-phase TMF maps are constructed with maximum cyclic temperatures ranging from 300‡ to 900‡C and maximum applied cyclic stresses ranging from 0 to 2000 MPa. The temperature range, stress ratio, and cycle period (500‡C, 0.1, 3 min., respectively) are held constant. In addition, maps are generated for isothermal fatigue using the same stress ratio and cycle period. The maps are useful for giving the overall picture of the TMF behavior over a wide range of stress and temperature combinations. The connection between TMF and isothermal fatigue is illustrated.
metal matrix composites, titanium matrix, silicon carbide fibers, thermomechanical, fatigue, elevated temperature, micromechanics
Assistant professor, Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA