Finite element simulation and experimental study on mechanical behavior of 3D woven glass fiber composite sandwich panels

Abstract

The results of finite element simulation followed by an experimental study are presented in order to investigate the mechanical behavior of three-dimensional woven glass-fiber sandwich composites using FE method. Experimental load–displacement curves were obtained for flatwise compressive, edgewise compressive, shear, three-point bending and four-point bending loads on the specimens with three different core thicknesses in two principal directions of the sandwich panels, called warp and weft. A 3D finite element model is employed consisting of glass fabric and surrounding epoxy resin matrix in order to predict the mechanical behavior of such complex structures. Comparison between the finite element predictions and experimental data showed good agreement which implies that the FE simulation can be used instead of time-consuming experimental procedures to study the effect of different parameters on mechanical properties of the 3D woven sandwich composites.

Introduction

Sandwich structures are increasingly used in structural applications where materials with high mechanical strength and stiffness at low specific weight are required. Thermal and acoustic insulation, high energy absorption and low cost are some other benefits of sandwich materials which make them more suitable than isotropic materials for many advanced constructions in marine, aerospace, automotive and building industries. Despite all mentioned benefits, the connection between the skin and core is one of the major weak spots in traditional sandwich materials which could cause damage initiation during impact, shear and bending loads [1], [2]. Although some techniques have been used to improve the skin–core debonding problem [3], [4], each method is likely to enforce some restrictions and extra cost during the production process. High skin–core debonding resistance of 3D woven sandwich composites established a new era in the field of sandwich structures which is very beneficial in increasing their lifetime and damage tolerance. This kind of sandwich composite is a fabric woven out of a glass yarn and consists of two parallel deck-layers bonded together by vertical threads, called piles. These piles are woven into deck-layers thus forming an integral sandwich structure. According to the core geometry, two principal material directions could be considered; warp and weft which both are shown in Fig. 1. Velvet weaving technique is the method which is used to produce these fabrics. The idea of using velvet weaving techniques to produce these fabrics first was given in 1985 in both Belgium (Katholieke Universiteit Leuven) and Germany (University of Stuttgart and MBB) in order to be used in the composite sandwich structures [5], [6].

van Vuure et al. [7] compared the drum-peel strength of 3D woven glass fiber sandwich composites with a variety of sandwich materials. Their results reveal that the skin–core debonding resistance of 3D woven sandwich materials is much higher than other commercial sandwich materials. Some researchers investigated the mechanical properties and failure mechanisms of 3D woven sandwich composites using experimental methods [8], [9], [10]. Zheng et al. [11] used 3D woven panels in hierarchical lattice panels. They showed that such structure has much better energy absorption capability than metallic stretching-dominated lattice truss materials and ordinary honeycombs. Fan et al. [12] designed multilayered panels by stacking monolayers panels. Their tests revealed a great improvement in energy absorption capacity compared to monolayer 3D woven sandwich panels. Studies on the effect of adding foam to the core of 3D woven composite revealed a large synergistic effect on mechanical properties, fatigue and impact behavior [13], [14], [15], [16], [17]. Corigliano et al. [18] modeled 3D woven composite filled with syntactic foam in the core as a sandwich to predict the bending behavior of such materials. Although their finite element simulation showed good agreement with the experimental results, the mechanical properties of the core and the facesheets should be obtained from experiments, to be used as input to the finite element program. van Vuure et al. [19] performed a detailed modeling of 3D woven composites to predict the core shear modulus and compression modulus using a linear elastic finite element analysis and compared the results with experimental data. Their simulation showed acceptable predictions for the core shear modulus in warp direction, but the results for weft direction shear modulus and for panel compressive modulus were not accurate.

Considering the core structure of 3D-fabric sandwich composites, the mechanical behavior of such materials highly depends on several parameters such as thickness of the sandwich, pile diameter, skins thickness, resin content, the angle of the piles and the fabric pattern. Since many factors influence the mechanical behavior of these complex structures, numerical modeling plays an important role in their development.

The main objective of this research is to provide a finite element approach to predict the mechanical behavior of 3D woven composite structures under different loads with high accuracy. The 3D structure of the glass fabric and the surrounding epoxy resin matrix are modeled using CATIA program, separately. The finite element simulation is performed using ABAQUS package. Besides, an experimental study on the basic mechanical properties of 3D-fabric sandwich composites on the basis of related ASTM test standards were performed and the predictions by finite element model are compared with the experimental results.