Anisotropic structure-induced in-plane heterogeneous compression behavior of 3D mesh fabric

Three-dimensional (3D) mesh fabric has been used in various cushioning applications; in this type of fabric, standing monofilaments absorb mechanical energy and allow airflow. Spacer monofilaments bend against the knitting direction and normally form triangle patterns. Such an anisotropic structure brings about in-plane heterogeneous compression behavior. This study is an investigation of this behavior of 3D mesh fabric under flatwise compression based on a full-size finite element model of 10 cm x 10 cm including 91 unit cells. It is found that in-plane heterogeneity is reflected in nonuniform compression load distribution across the fabric. The intermediate area, entirely surrounded and constrained by adjacent unit cells, has aggravating load nonuniformity throughout the compression process, owing to the increasing irregularity of monofilament deformation, resulting from increasing interactions of spacer yarns among unit cells. In contrast, fabric extremities are partially constrained. The anisotropic unit cell structure results in varying load distributions in compression. Walewise asymmetry causes an increasing load difference between walewise extremities in the linear elasticity and plateau stages. In the densification stage, walewise shrinkage accumulates to rearrange spacer yarns compactly; this adequately constrains walewise extremity unit cells, so the load difference is subtle. A certain coursewise symmetry results in equivalent loads between coursewise extremities in the linear elasticity stage, but a difference appears in the plateau stage because of the imperfect symmetry. Spacer yarns are dispersed in the densification stage, owing to coursewise expansion, which weakens the constraints on the coursewise extremities to further increase the load difference. Enhancing coursewise symmetry improves the synergy of monofilament deformation, reducing heterogeneity and extending the plateau stage.