THE INFLUENCE OF MATRIX MICROSTRUCTURE AND TIC REINFORCEMENT ON THE CYCLIC RESPONSE AND FATIGUE BEHAVIOR OF 2219-AL

The low-cycle and high-cycle fatigue behavior and cyclic response of n aturally aged and artificially aged 2219/TiC/15p and unreinforced 2219 Al were investigated utilizing plastic strain-controlled and stress-c ontrolled testing. The cyclic response of both the reinforced and unre inforced materials was similar for all plastic strain amplitudes teste d except that the saturation stress level for the composite was always greater than that of the unreinforced material. The cyclic response o f the naturally aged materials exhibited cyclic hardening and, in some cases, cyclic softening, while the cyclic response for the artificial ly aged materials showed no evidence of either cyclic hardening or sof tening. The higher ductility of the unreinforced material made it more resistant to fatigue failure at high strains, and thus, at a given pl astic strain, it had longer fatigue life. It should be noted that the tensile ductilities of the 2219/TiC/15p were significantly higher than those previously reported for 2XXX-series composites. During stress-c ontrolled testing at stresses below 220 MPa, the presence of TiC parti cles lead to an improvement in fatigue life. Above 220 MPa, no influen ce of TiC reinforcement on fatigue life could be detected. In both the composite and unreinforced materials, the low-cycle and high-cycle fa tigue lives were found to be virtually independent of matrix microstru cture.