Viscoplastic analysis of the off-axis rate-dependent inelastic behavior of unidirectional AS/PEE

Using the finite element program generator (FEPG), the three-dimensional viscoplasticity model is introduced into this finite element automatic generating system. The corresponding element subroutine is developed, which is verified by comparing the finite element computing results with the experimental ones. With the generated procedure the monotonic tensile stress-strain curves are obtained under the strain rate of 0.1 s(-1) for the off-axis angles 5, 10, 15, 30, 45, 60 75, and 90, respectively. The above stress versus strain curves show marked nonlinearity for the off-axis angles in the range 10 degrees < theta < 60 degrees. Furthermore, in order to observe the rate-dependent nonlinear stress-strain behavior for unidirectional thermoplastic composites of different off-axis angles, we have acquired the stress-strain curves under the strain rate of 1 x 10(-5), 1 x 10(-3), and 0.1 s(-1) from which we can conclude that the unidirectional AS4/PEEK composites have distant rate-dependent behavior when the stress extends some values which are different especially for the off-axis angles.