Prediction of creep performance during long-term storage of composite directors based on nonlinear viscoelasticity

In order to investigate the long-term storage creep performance of composite directors for multiple launch rocket systems, E-glass fiber reinforced epoxy matrix composite laminates were prepared and the 60/60-minute creep/creep-recovery tests were carried out at different stress levels. The master curves of long-term creep compliance were obtained by shifting the short-term creep compliance based on the superposition principle, and then the parameters of linear-transient creep compliance model were obtained by a curve fitting procedure. The functional relation between the Schapery’s nonlinear parameters and the average matrix octahedral shear stress was developed by an analytical procedure. Finite element method and the user-defined material subroutine (UMAT) are used to establish the long-term storage numerical analysis model of composite directors, and the creep deformation after 15-years stacking storage was predicted.