Crack-Parallel Tension Effects on Fracture of Soft Knitted Polymer Composites deduced from Gap Tests via Microplane Triads

Abstract

Soft composites are increasingly used in wearable and soft robotic systems as advances in material architecture enable greater damage tolerance under large deformation. In these mesoscale architectures, the crack-parallel stresses bias geometric rearrangements of reinforcement fibers, modifying the crack initiation and growth beyond the opening-mode fracture.
Here, we introduce a tensile gap test to quantify how the crack-parallel stress affects the onset and trajectory of damage localization, as well as the load- and energy-based fracture responses. We also develop and experimentally validate a continuum model that captures nonlinear behavior and progressive damage of knitted composites, using an ensemble of oriented microplane triads aligned with the yarn direction, capturing the axial load-transfer mechanisms while incorporating the transverse and shear effects. Together, the experiments and the computational model provide a tool to predict fracture under realistic stress states and to guide the rational design of soft composites in engineering applications.