Snap-buckling and failure studies on CFRP laminate with an embedded circular delamination under flexural loading

Carbon fiber reinforced polymer (CFRP) laminate having an embedded delamination may exhibit snap-buckling phenomenon under flexural loading, and its influence on the bending strength reduction and associated laminate failure mechanisms need to be understood for efficient structural design. In this paper, a multi-angle CFRP beam specimen with an embedded circular delamination is studied under four-point bending. Experimental techniques like digital image correlation and acoustic emission are used to evaluate the bending moment and strain at which the snap-buckling of sub-laminate occurs and the subsequent intra/inter-laminar failure propagation in the beam specimen. Detailed fractography studies are carried out on the post-failed specimens to get more insights on the various damage modes and failure mechanisms. Subsequently, a three-dimensional finite element framework is proposed for simulating the snap-buckling of the sub-laminate and the associated damage modes occurring within the laminate. Both cohesive zone and continuum damage mechanics models are used to simulate the delamination and fiber/matrix failures in the laminate, respectively. The sub-laminate buckling strain and damage evolution results predicted by the numerical simulations are compared with the experimental observations. Finally, the developed numerical model is used to understand the effect of various parameters like delamination size, shape, position, and stacking sequence on the flexural response of the delaminated laminate. The parametric studies provides new insights on the snap-buckling effect on failure response of the delaminated composite beam under flexural loading