Inelastic response and stability of titanium alloy tubes under cyclic bending

The response and stability of titanium alloy tubes:subjected to cyclic bend ing are presented in this paper. The curvature-ovalization measurement appa ratus, designed by Pan et al.((1)), is used for conducting the present curv ature-controlled experiments. It is observed from the moment-curvature curv e that the titanium alloy tube is cyclically harden and becomes steady afte r a few cycles for symmetric curvature-controlled bending. However, from th e ovalization-curvature curve, the ovalization of the tube cross-section in creases in a ratchetting manner with the number of cycles. Owing to the pro gressive accumulation of the ovalization of the tube cross-section during t he cyclic bending, the titanium alloy tubes buckle-eventually. Theoretical formulation, proposed by Kyriakides and Shaw((2)), is used for investigatin g the relationship between the magnitude of the controlled curvature range and the number of cycles to produce buckling. Good agreement between the ex perimental and theoretical results is achieved. Furthermore, experimental d ata of the titanium alloy tubes from present study are compared with the ex perimental results of 6061-T6 aluminum and 1018 steel tubes tested by Kyria kides and Shaw((2)). It is shown that for similar outer diameter/wall thick ness ratio, the stronger metal tube exhibits a shorter number of cycles to produce buckling.