Investigating the mode II critical strain energy release rate of glass/epoxy laminated composites reinforced with polyvinyl alcohol interlayer

Owing to the increasing demand in the industry for materials possessing favorable mechanical properties and a high strength-to-weight ratio, the utilization of laminated composites has seen a surge in popularity. Nevertheless, laminated composite materials are susceptible to delamination because of their inadequate out-of-plane strengths and poor adhesion at the interface of composite laminated layers. This research aimed to enhance the mode II critical strain energy release rate in glass/epoxy laminated composites by using the inter-layering method and polyvinyl alcohol as the interlayer. To achieve this purpose, end-notch flexure samples (ENF) were fabricated using the hand lay-up technique. The experimental results indicate that the presence of a polyvinyl alcohol interlayer led to a significant increase of 177% in the initiation fracture toughness and 36% in the propagation fracture toughness. The reason for this is to increase the adhesion between the composite layers and reduce their tendency to slide relative to each other. Furthermore, the examination of the fracture surface of ENF samples demonstrated that the utilization of the interlayer induced a transition in the failure mechanism from adhesive failure to cohesive failure, thereby generating a rougher fracture surface in comparison to the neat sample. It is important to note that examining the crack growth resistance curve and comparing the strain energy release rate obtained from the CCM and CBBM methods demonstrated a favorable agreement.