Nonlinear compression behavior of warp-knitted spacer fabric : effect of sandwich structure

Abstract

Compressibility of warp-knitted spacer fabrics is one of their important mechanical properties with regard to many special applications such as body protection, cushion and mattresses. Due to specific structural features of the fabric and a non-linear mechanical behavior of monofilaments, the compression properties of this kind of fabrics are very complicated. Although several studies have been performed to investigate their compression behavior, its mechanism has not well been understood yet. This work is concerned with a study of compression mechanism of a selected warp-knitted spacer fabric with a given sandwich structure. Both experimental and numerical methods are used to study the effect of the material's structure on the overall compression mechanism. Compression tests are conducted to obtain force-displacement relationships of the fabric. A micro-computed tomography system is used to analyze specimens under different levels of compression displacement to investigate the change in material's structure during the compression process. At the same time, finite element models are developed separately to simulate the initial geometric structure and the compression behavior of the fabric. Three finite element models based on beam elements are firstly developed to simulate the effect of manufacturing process on shapes of monofilaments within the fabric and to determine their morphologies, which are used to assemble a geometry part of the finite element model of the overall fabric. Then the finite-element model is developed using beam and shell elements to describe the compression behavior of the fabric by introducing the effect of its complex microstructure and real non-linear mechanical properties of the monofilaments. A comparison of the obtained experimental and CT data, and results of simulation is carried out, demonstrating a good agreement. With this study, a compression mechanism of the warp-knitted spacer fabric can be better understood.