The effect of additively manufactured grooved cores on the crack growth and delamination resistance of CFRP/PLA sandwich structures

This research aimed to exploit the potential benefits of 3D printing in sandwich panels engineering by fabricating topographic core capable of promoting sandwich panel interlayer strength. The influence of surface grooves with varied patterns onto the 3D printed cores on the interlaminar adhesion and fracture behavior of composite sandwich panels was explored. In this study, light and biodegradable polylactic acid (PLA) polymer and fused deposition modeling (FDM) have been employed to make textured cores. Grooves of various designs, comprising 45º, 90º, and V patterns, were made on the cores to enhance the interfacial strength between the PLA cores and CFRP composite face sheets in the sandwich panels. The end notched flexure (ENF) samples of sandwich structures were prepared and undergone three-point bending under three different pre-crack tip locations to evaluate the interlaminar critical strain energy release rate. The presence and geometry of 3D printed grooves on the core significantly affected the mode II critical interlaminar fracture energy and the extent of unstable crack growth in the sandwich panels. The image analysis of fracture surfaces revealed the activation of fiber bridging mechanism and the prevalence of cohesive failure in the CFRP-PLA interface as a result of applying PLA textured cores. The printed core featured with the 45º grooves alignment and 0.5 mm grooves interval led to the least unstable crack growth and about 100% and 240% increases in cohesive fracture and fracture energy, respectively. The additive manufacturing offers further potential capabilities in fabricating light and textured cores of diverse 3D contours for advanced and robust sandwich structures. The additive manufacturing can also be integrated with the automated lay-up of composite laminates to fabricate a wide range of sandwich structures.