Responsive and sensing composites for impact mitigation and damage detection in soft body armors

Soft body armors, utilized to mitigate impact damage for the users, are typically composed of layered composites of high strength and toughness woven Kevlar fabrics. Recently, extensive attempts have been made to improve the impact mitigation performance of Kevlar body armor through the incorporation of stimulus-responsive smart materials. For instance, shear thickening or dilatant compounds have been used due to their viscosity changes in response to loading rate. One of the common shear thickening materials is polyborodimethylsiloxane (PBDMS). PBDMS polymer chains possess dynamic cross-links that can break and reform depending on the loading rate, transforming the material from a highly viscous gel to a rigid solid. In addition, nanomaterials have been demonstrated to be capable of effectively enhancing the mechanical properties of polymers and enabling sensing mechanical damages based on strain measurements. Therefore, to further enhance the impact protection performance of body armors, this work aims to develop a responsive and flexible composite with force sensing capabilities by incorporating CNTs and PBDMS with Kevlar fabrics. In particular, additive manufacturing procedures for fabricating the composite material system were developed. A series of mechanical experiments, including quasi-static and dynamic tests, have been conducted to characterize the mechanical performance of the PBDMS-coated Kevlar. In addition, the sensing performance of the CNT/PBDMS-Kevlar composites was evaluated via electromechanical tests. Overall, the PBDMS material system synthesized in this project exhibited dynamic crosslink-based shear stiffening behavior and can effectively reinforce the mechanical performance of Kevlar fabrics, especially under dynamic impact loads. In addition, CNTs and PBDMS were uniformly incorporated with the Kevlar fabrics, which demonstrated a promising approach to detect potential damage on soft body armors.