Thermoelastic effects on mixed-mode delamination growth emanating from circular holes in laminated FRP composites

This paper deals with the thermoelastic effects on mixed-mode delamination growth behaviour emanating from circular holes in laminated Fiber-Reinforced Polymeric (FRP) composites. Two sets of full three-dimensional analyses have been performed (one with the thermal residual stresses developed while curing the laminate and the other without thermal residual stresses i.e., with mechanical loading only) to calculate the displacements and interlaminar stresses along the annular shaped delaminated interface responsible for delamination onset and propagation. Modified Crack Closure Integral (MCCI) method based on the concept of linear elastic fracture mechanics has been followed to calculate the three modes of Strain Energy Release Rates (SERR). The strain energy release rate components GI, GII and GIII along the annular shaped delamination front due to thermal residual stresses developed while curing the laminate (i.e., cooling from an elevated temperature of thermosetting to the room temperature) and the subsequent mechanical loading have been obtained by superimposing their respective effects. Numerical calculations are carried out for multi-layered cross-ply and angle-ply glass/epoxy FRP composite laminates and the strain energy release rate plots demonstrate large asymmetries along the delamination front due to the interaction of residual curing stresses and superimposed mechanical loading. It is observed that the residual curing stresses have the effect of enhancing the behaviour of delamination growth. On subsequent mechanical loading this can be a potential source of causing premature failure due to the superimposed thermomechanical effects.