Papers by Keyword: Off Axis Loading

Abstract: A macromechanics constitutive model to describe the anisotropic creep behavior of unidirectional composites under off-axis loading conditions is developed with a particular emphasis on accurate prediction of temporal creep softening due to stress variation. A viscoplasticity model that takes account of a combined isotropic and kinematic hardening is adopted as a base for this formulation, and the evolution equation of the kinematic hardening variable is elaborated to enhance the accuracy of prediction of the transient creep softening due to stress variation. Validity of the modified kinematic-hardening viscoplasticity model is evaluated by comparing with the experimental results on unidirectional T800H/3631 carbon/epoxy composites. It is demonstrated that the proposed model can adequately describe the off-axis creep behavior of the unidirectional CFRP laminate under constant and variable stress conditions.

Abstract: Off-axis tensile behavior of two grades of hybrid laminates, GLARE-2 and GLARE-3, made of unidirectional glass/epoxy laminae (GFRP) and aluminum (Al) alloy sheets is examined for various fiber orientations, and the differences in mechanical properties between the unidirectional and cross-ply hybrid laminates are quantified. The problem of accurately describing the nonlinear deformation of GLARE laminates under off-axis loading conditions is revisited, and the effect of local nonlinear deformation in the constituent GFRP layers on the overall inelastic behavior of GLARE laminates subjected to inclined tensile loading is elucidated by means of elastic-plastic finite element (FE) analyses.

Abstract: Off-axis creep recovery behavior after complete unloading during creep at a constant stress is examined for a unidirectional T800H/3631 carbon/epoxy composite laminate at high temperature. Creep and creep recovery tests are performed on plain coupon specimens with four kinds of fiber orientations: 10, 30, 45 and 90°. It is observed that the creep strain appeared at a high stress does not completely recover after full removal of the creep stress, indicating that an irrecoverable creep strain has developed under the prior constant stress loading. Variable stress creep simulations are attempted using the modified kinematic hardening model for homogenized anisotropic inelastic composites in which an accelerated change in kinematic hardening over a certain range of viscoplastic strain is considered. Comparison with experimental results demonstrates that the proposed model can adequately describe the off-axis creep and creep recovery behaviors of the unidirectional composite system under constant and variable stress conditions.