Effects of Stacking Sequence on the Impact Resistance of Carbon Fiber Reinforced Thermoplastic Toughened Epoxy Laminates

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Abstract
Few comprehensive studies on the effects of stacking sequence and rein forcement form (unidirectional versus woven) have been published to date and much of the available data is contradictory. In the present study, instrumented impact tests were used to characterize such effects for carbon fiber reinforced thermoplastic toughened epoxy laminates. Impact resistance was characterized in terms of load and energy parameters measured during penetration tests. These parameters were related to damage in the lami nates by conducting rebound tests followed by ultrasonic imaging and microscopy. The results clearly demonstrated a relationship between the onset of damage and the first peak in the load versus deflection plots obtained in the penetration tests. No major effects of stacking sequence or reinforcement form were apparent in terms of the energy required for the onset of damage in the laminates. Energy to maximum load was found to be highly de pendent on stacking sequence. Substitution of woven reinforcement for unidirectional tape in a quasi-isotropic layup resulted in a substantial decrease in the energy to maximum load. The results in terms of peak load showed similar trends. No effects of stacking se quence or reinforcement form were observed in terms of energy after peak load. It is ap parent from this work that stacking sequence and reinforcement form can have significant effects on impact resistance particularly at higher impact energies.