# A Numerical Investigation of Delamination Response of CNT/Epoxy Film Interleaved Composite
###### Abstract  
In this study, numerical modeling through the cohesive zone theory was performed to simulate the end notch flexure (ENF) test with same conditions of the experimental results of previous study that investigated the effect of a carbon nanotube (CNT)/epoxy film in carbon fiber reinforced polymer (CFRP) composite through the mode II interlaminar fracture toughness of a non-interleaved, epoxy film interleaved, CNT/epoxy film interleaved CFRP laminate specimen. The effect of the presence of CNT/epoxy film interleave on a composite laminate was modeled. The influence of the interleave cohesive parameters was studied to link the parameters to the material strength and energy release rate. Cohesive parameter identification was performed by matching the initial loading and the damage evolution phase by dividing the cohesive zones into cohesive front and remaining cohesive zones. This is because, when modeling with a single cohesive zone, the critical load point that causes delamination or the curve after load drop do not match the experimental values. Results showed that the divided cohesive zone model is in good agreement with the experimental results and that there is a clear relationship between the cohesive energy of the interface and CNT/epoxy film parameters. d 2022 2022 2022 2022 2022 20222 2022 2022 20222 2022 20222  
to investigate the difference in the fracture strengths between a nanomodified laminate interface and the corresponding non-modified material. In their study, [PERSON] et al. numerically simulated double-cantilever beam (DCB) and end notch flexure (ENF) tests on CFRP composites, which has been performed in a previous study. Several configurations of nanofibrous mats have been fabricated to investigate the effect of interleaving. It was observed that the cohesive zone parameters were corresponding to the effect of nanofiber diameter, nanolayer thickness, and nanofiber orientation on the delamination behavior of the composite [5]. [PERSON] et al. performed cohesive modeling using ABAQUS. A pre-softening zone was proposed ahead of softening zone. In this pre-softening zone, the initial stiffness and strength gradually decrease [6]. [PERSON] et al. studied the effect of element size on force-displacement behavior in the DCB test. It shows that element size should be less than 1 mm. It is explained that this greatly affects the accuracy of the solution [7]. In addition, there are studies on the numerical modeling of delamination through cohesive zone modeling [8; 9; 10; 11; 12]. Carbon fiber reinforced polymer (CFRP) composites have high strength, stiffness, and low weight. The manufacturing techniques of CFRP composites have been developed. Thus, they substitute the existing metal materials in the aerospace, military, automotive, and sporting goods gradually. Compared with metal materials, composite laminates are attracting attention in various industries in that they can reduce the processing cycle and enhance in-plane direction properties while making products lighter according to advances in binders and prepregs. However, in composite laminates, resin-rich areas exist between layers, resulting in inferior properties of through the thickness (or out-of-plane) direction compared to the properties of in-plane direction. Due to these characteristics, improper lamination, incomplete curing, and external impact during the process become crack seeds and delamination occurs. This failure is often considered fatal because it is often not visible from the outside. There are many studies that have aimed to improve interlaminar mechanical properties of fiber reinforced composites. Bucky paper interleaves made from carbon nanofibers improved interlaminar shear strength and mode-II interlaminar fracture toughness of composites [13]. Multi-walled carbon nanotubes (MWCNT) were grown on carbon fibers and single-walled carbon nanotubes were dispersed into matrix to enhance the interlaminar shear strength [14].