Tensile and compressive damage assessment of a novel sandwich composite structure made of Kevlar/flax/epoxy hybrid laminates

This is a study to quantify damage progression of a new Kevlar/flax/epoxy (KFE) hybrid composite made with 12 layers of pure flax fiber fabric sandwiched between 4 layers of pure Kevlar fiber weave. There were four versions of the composite: 0° unidirectional, 0°/90° cross-ply,  ± 45° angle-ply flax fibers, and Kevlar fibers-only as the control. Composite plates were subjected to progressive load-unload levels in tension and compression until failure and were evaluated for stiffness degradation, permanent strain, and crack density. Unidirectional KFE laminates exhibited less damage accumulation compared to cross ply and angle ply configurations. Damage progression and failure of KFE hybrids mainly involved cracks through flax fiber bundles and at flax fiber/epoxy interfaces. The reported data are useful for damage-limited design structures made from a combination of natural and synthetic fibers.