Yarn-level numerical simulation based on micro-CT reconstruction for the stentering process of warp-knitted three-dimensional mesh fabric

Three-dimensional mesh fabrics of one-piece spacer structure are an essential component of automotive seat ventilation systems due to their excellent cushion and ventilation performance. The mesh structure is manufactured by stretching across the width of as-knitted structure with closed surfaces in a coupled thermo-mechanical stentering and heat-setting process. This paper presents a numerical study to examine the effect of stentering on the mesh structure and yarn architecture of a typical three-dimensional mesh fabric by establishing a finite element model based on micro X-ray computed tomography reconstruction at the yarn level. The finite element model is verified with the global and local deformation of the mesh during the stentering process. The evolution of the yarn architecture in the stentering process is demonstrated and quantitatively analyzed in terms of curvature and torsion. Three-dimensional mesh fabrics of different mesh sizes and thicknesses after stentering at different ratios are also simulated to study their compression properties. The numerical and experimental results showed that stentering opens the meshes and simultaneously shortens, widens and thins the fabric. The meshes are unevenly distributed across the width, and the intermediate meshes are more open and uniform than the two selvage meshes. To obtain a three-dimensional mesh fabric with uniform and symmetrical meshes, the as-knitted fabric should be stretched coursewise to be wider than 2 times and narrower than 2.6 times its initial width. Stentering disperses, lengthens, tilts, bends and twists the spacer monofilaments, thereby broadening the compression plateau stage and decreasing the compression resistance.