A REVIEW OF THERMOMECHANICAL FATIGUE DAMAGE MECHANISMS IN 2 TITANIUM AND TITANIUM ALUMINIDE MATRIX COMPOSITES

Combined load and temperature cycling could limit the durability of continuous fibre reinforced titanium matrix composites. The fatigue life and damage induced by combining load and temperature cycling in several different ways were examined in two representative 0-degrees unidirectional titanium and titanium aluminide matrix composites. Load and temperature were sequentially cycled and simultaneously cycled in thermomechanical fatigue tests. Sequential and simultaneous thermomechanical fatigue tests in which maximum tensile loads occurred at minimum temperature had comparable lives and damage, associated with environment-assisted surface cracking. Sequential and simultaneous thermomechanical fatigue tests in which maximum loads occurred at maximum temperature each had different lives and damage, primarily because of differences in the extent of matrix-relaxation-induced load shedding from the matrix to the fibres. These general results applied to both titanium matrix composite systems.