Multiple Delaminations Growth in Composite Laminates under Compressive Cyclic Loading in Post-Buckling

Abstract

Due to discontinuity of mechanical properties in composite laminates, failure occurs in different damage mechanisms. Delamination growth of adjacent layers is a major failure mechanism in laminates with various layup configurations. Pre existing delamination may initiate in composite laminate before use, due to impact in assembly and fabrication process. Cyclic compressive loading may cause delamination growth due to both post-bucking behavior and fatigue nature of loading. In this paper, a 3D mixed-mode interface element model has been developed to simulate the growth of multiple delaminations under compressive cyclic loading. For this purpose, the presented model should be able to handle the geometry nonlinearity of post-buckling and material nonlinearity of cohesive zone constitutive law under cyclic loading at interfaces. Because of mixed-mode condition of stress field at the delamination-front of post-buckled laminates, a mixed-mode bilinear constitutive law has been used as user material in this model. Paris Law has been used to relate the energy release rate to the fatigue crack growth in cohesive zone. A composite laminate with pre-existing delamination under buckling load, available from the literature has been reproduced with the present approach. Finally, laminates containing multiple delaminations in various interface layers have been analyzed under compressive fatigue loading. It is shown that the pre-existing delamination with more depth from the surface of laminate causes more initial static and fatigue delamination growth rate.