Flexural Properties of 3D Braided Jute/Epoxy Composite Honeycombs

Abstract

An integrated molding composite honeycomb has been proposed, in which a seamless, 3D braided natural fiber cellular fabric serves as the reinforcement, with epoxy resin as the matrix. Three-point bending behaviors of the honeycomb, taking account of the effects of joint wall length and opening angle, were investigated. The fracture mechanisms during bending were monitored using 3D Digital Image Correlation. The validated Finite element model was developed and used to perform a parametric analysis identifying the effect of material Young's modulus and geometric variations on the flexural stiffness. The results reveal that fracture occurs at the junction of the joint wall and the free wall, characterized by shear-type failure and structural geometry parameters significantly affect flexural performance. Decreasing the joint wall length from 55 to 4 mm in 90° honeycombs reduced the maximum load by approximately 26% and the flexural stiffness (P/y) by about 55%, accompanied by an increase in maximum deflection. Conversely, for specimens with a 17 mm joint wall, increasing the opening angle from 60° to 120° decreased the maximum load and P/y by approximately 32% and 55%, respectively, while the flexural deflection gradually increased. The knowledge generated from this study is key in design and performance evaluation of 3D braided composite honeycomb cores for sandwich structures, which is crucial for enhancing the out-of-plane bending resistance of sandwich structures.