Bio-Inspired Laminates of Different Material Systems

Helicoidal laminates mimicking the laminar structure of the exoskeleton of crustaceans have been reported to resist higher out-of-plane loads than the common cross-ply and quasi-isotropic fiber-reinforced laminates. Some have reported that smaller inter-ply angle improves strength of helicoidal laminates but others have reported the opposite. A few important material parameters that dictate the failure mechanism of helicoidal laminates have recently been proposed based on proof-of-concept carbon fiber-reinforced laminates, which is not the best material system to benefit from a helicoidal configuration. This study investigates the out-of-plane loading performance of helicoidal laminates with various inter-ply angles, ply thicknesses, and materials. Result shows that the failure mechanism is dictated by the competition between spiraling matrix split and delamination followed by fiber breakage regardless of the laminate material system. Spiraling matrix split resistance decreases as pitch (ratio of inter-ply angle to ply thickness) and matrix toughness decreases. This study provides guidelines for the optimization of helicoidal laminates. Coexistence of spiraling matrix split and fiber damage is often seen on the failed laminate with the highest peak load. The optimal inter-ply angle provides the optimal spiraling matrix split resistance; so, neither spiraling matrix split nor fiber/delamination damage becomes dominant. Since resistance to spiraling matrix split decreases as pitch or matrix toughness decreases, the optimal inter-ply angle will increase for laminates with weaker matrix or thicker plies and vice versa.

Comparative Evaluation of Quasi-Static Indentation Behaviour of Glass Fiber Reinforced (GFRP) and Carbon Fiber Reinforced (CFRP) Laminates

A comparative study of Quasi Static Indentation (QSI) conduct of Glass Fiber Reinforced Laminates (GFRP) and Carbon Fiber Reinforced Laminates (CFRP) of different thicknesses is made in this work. QSI tests are performed as per ASTM Standard D 7766M using custom – built Digital Flexural test equipment with dedicated fixture which provides constraint from all the four sides. A hemispherical Indentor of 12.5 mm diameter made from hardened steel is used to indent the specimens at a speed of 25 mm/minute. The damage area at different stages of QSI are assessed using ultrasonic ‘A’ scan and macroscopic inspection. The influences of thickness and type of laminate on the QSI parameters such as peak load at fracture, energy absorbed till fracture and maximum deflections are determined. It is found that the initial stiffness and the energy required for complete fracture is significantly more in case of CFRP as compared to GFRP laminate.Key words: QSI, GFRP, CFRP, Energy, Peak load, Initial Stiffness.

Interlaminar Toughening of Epoxy Carbon Fiber Reinforced Laminates: Soluble Versus Non-Soluble Veils

This work describes the evaluation of different interlaminar veils to improve the toughening of epoxy/carbon fiber composites manufactured by resin infusion. Three commercial veils have been used in the study: two electro spun thermoplastic nanofiber (Xantulayr® from Revolution Fibres) with different areal weight, and one micro carbon fibers veil (Optiveil® from TFP). Two laboratory made veils were also manufactured by electrospinning commercial polyethersulfone (PES) tougheners (Virantage by Solvay). The veils were selected to be either soluble or non-soluble in the epoxy resin matrix during curing. The solubility was analyzed by scanning electron microscopy and dynamic mechanical analysis testing on the cured laminates. The fracture energy was evaluated by double cantilever bending (DCB) testing under Mode I loading. The insoluble thermoplastic nanofibers showed the highest toughening efficiency, followed by the soluble nanofiber veils. The carbon fiber based veil showed no toughness improvement.