Abstract
Anisotropic creep behavior of unidirectional T800H/3631 carbon/epoxy composite under constant and variable loading conditions at 100℃ is examined. First, constant-stress creep tests in tension are performed on plain coupon specimens with four kinds of fiber orientations θ=10, 30, 45 and 90°. Then, creep deformation of off-axis specimens subjected to a single step change, either with an increase in stress or a partial decrease in stress, is measured to observe effects of the load histories on the off-axis tensile creep behavior of the unidirectional composite. Off-axis creep recovery behavior after completely removing the creep stress for each of the five-hour tensile creep tests is also observed. Off-axis creep behavior is clearly observed for all fiber orientations. Creep rate rapidly disappears under a constant stress condition. Transient creep with a rapid hardening to terminate creep is dominant. Temporal creep softening is caused by stress changes. Creep strain transiently recovers after partial unloading, and this implies a development of internal stress. Creep strain does not completely recover after unloading, and so an irrecoverable creep strain has been developed. A viscoplasticity model that considers the nonlinear kinematic hardening and its accelerated change over a certain range of viscoplastic strain is developed, and applied to simulation of the off-axis creep behavior observed. The proposed model succeeds in adequately describing the off-axis creep behavior of the PMC employed under constant and variable stress conditions.
