Design and Development of Auxetic Polymeric Textile Composites for Enhanced Impact Resistance

Abstract

Textiles including fibers, yarns and fabrics with unique characteristics are ubiquitous in our daily lives, standing fit in the design specifications for the proposed tasks. Fibres and yarns developed with Negative Poisson’s Ratio (NPR) is an area of intense current research interest due to their ability for application in high performance textiles (e.g., military, sports, etc.). Braided helically wrapped yarns with NPR effect had been fabricated with simple methodology which were subsequently used for development of Auxetic woven fabrics. The chances of slippage of wrap component from core was minimized due to development of yarns with this unique interlacement braiding technology. The geometrical and auxetic behaviour of these braided helical structure were analyzed for two different combination of monofilament cores including elastomeric Polyurethane (PUR) and Polyester cord with similar combination of wrap materials including multifilament Ultra-high molecular weight polyethylene (UHMWPE) and Polyethlene terephthalate (PET) fibres for various sets of braid angles. Investigation towards NPR effect of the applied braided configuration at seven different angles, 9°, 11°, 13°, 17°, 19°, 21° and 23° respectively, revealed that the NPR of the Auxetic yarns entirely depends on selection of braid angle and core and wrap materials. The core with higher elasticity showed higher extent of NPR ratios (e.g., PU elastomer compared with polyester); lower wrap angle and lower braiding speed also exhibited higher NPR values. Evaluation at a strain rate of 50% generated the maximum NPR value of -1.70 for PUR core braided at an angle of 9°. The mechanical response of 2D woven auxetic fabrics (AF) having stable structure with various weave patterns was studied in detail. Several mechanical properties of Matt and Twill designed 2D woven AF were compared. Semi-automatic loom was used to develop AFs with multifilament UHMWPE yarn in warp direction and auxetic yarn that was braided at lowest angle of 9° having combination of core PUR and wraps UHMWPE and PET yarns in weft loading direction. Auxetic effect of AFs was analyzed to study its various mechanical characteristics such as tensile strength, low and high velocity impact energy absorption, puncture resistance, in-plane, and out-of-plane auxeticity. The impact absorption energy of 3.33 Nm was found for Matt fabric while for Twill fabric it was 1.38 Nm. Higher auxetic effect having NPR value of -5.5 was found for Twill fabric compared to Matt fabric having NPR value of approximately -1. Twill fabric showed good puncture resistance properties compared to Matt fabric. Unique mechanical properties were exhibited by Twill and Matt geometrical constructions that had potential in protective textiles applications like shielding helmets, bullet proof vests, cut resistance gloves, blast curtains, and puncture tolerant elastomeric composites. Laminated composites developed from the two types of fabrics with Linear low-density polyethylene (LLDPE) used as matrix, were investigated for mechanical properties such as tensile, flexural and impact characteristics and auxetic effects. The comparison of energy absorption of two types of layered composites revealed that matt composites had energy absorbing capacity of 197 Nm while twill composite had 133 Nm. The detail study of deformation mechanisms concluded that matt composite samples observed better energy absorption capabilities due to back-cone formation, shear plugging effect, fibre disentanglement and frictional effects compared to the twill composites samples. These deformation mechanisms presumably played key roles in enhancement of auxeticity of the composites.