Effects of layup angle and ply thickness on matrix crack interaction in contiguous plies of composite laminates

Matrix microcracking behaviors in constrained plies adjacent to a cracked ply are highlighted. Quasi-static tension tests of [0/θ/90]s and [0/θ2/90]s laminates with θ=30, 45 and 60° were conducted in order to investigate effects of the ply thickness and the intersecting angle of the cracked plies on the crack development in the adjacent plies. Matrix cracks developed along the fiber direction were the dominant damages observed in 30° plies of [0/θ2/90]s laminates, whereas a high density form of matrix microcracking was mainly observed in θ° plies of the other laminates. The difference of the matrix cracking behaviors in the adjacent plies among laminate configuration is characterized by calculating energy release rates associated with θ° ply crack growth in the presence of 90° ply cracks using finite element analysis. It is clarified that microcracking in plies adjacent to a cracked ply is susceptible to formation in the cases of thin θ° ply thickness and small intersecting angles of the cracked plies.