Analysis Of Damage Characteristic Of Carbon Woven Fabric/Epoxy Laminates Subjected To Simulated Lightning Strike Under Specific Environments

Carbon fiber reinforced polymer (CFRP) composites have been widely used in aerospace industry for decades due to their high specific stiffness and strength, high fatigue resistance, environmental adaption and design flexbility. With the emergence of various affordable carbon fibers and cost-effective manufacturing process, the applications of CFRP composites have been also widely used in automotive, sports and civil infrastructures. In recent years, the support of smart grid and green, sustained energy utility in China and worldwide has attracted an increase interest in the potential replacement of large amount of electrical products by composite structures in the electric power industry, to overcome their inherent defects and increase reliability. As one may easily see most of the structures in electric power industry often work outdoor all year round, lightning strike damage to the composite structure is one of the primary issues which need to be addressed before the use of composite materials broadly spreads into the power industry. Therefore, following research areas have been conducted to study the damage characteristics of composite materials subjected to lightning strike.Unidirectional carbon woven fabric and epoxy have been selected as reinforcement and matrix to fabricate standard unidirectional coupons to measure their longitudinal, transverse and in-depth mechanical properties, electrical conductivities and reaction kinetics parameters. The accuracy of these data has been evaluated, which provide a solid foundation to the following experimental and numerical analysis.This paper experimentally investigates the damage characteristics of two stacking sequenced carbon woven fabric/epoxy laminates subjected to three different level of simulated lightning strike. The mechanical properties of post-lightning specimens are then studied. Observations show that three types of lightning strike damage have formed. With the increase of strike intensity, different behavior has been shown for these three damage forms. Meanwhile, stacking sequence has significant influence on the area of internal delamination. SEM shows that the resin/fiber interfacial bonding is severely damaged by a thermal-mechanical effect due to lightning strike infliction. For both of the two stacking sequenced specimens, the residual modulus and strength decrease with the increase number of lightning strike. However, failure mechanics are quite different for the two kinds.This paper. in the first time, investigates the effect of hygrothermal aging on the damage behavior of the above two stacking sequenced carbon woven fabric/epoxy laminates subjected to simulated lightning strikes. The mechanical properties of post-lightning specimens exposed to the dry and moisture environments are then studied, respectively. Results show that hygrothermal aging significantly increases three types of lightning strike damage. While, the influence of stacking sequence on the damage forms is decreased. SEM results show that the fiber/matrix interfacial bonding is severely degraded by moisture. Meanwhile, hygrothermal aging has a great influence on the residual strength and in the first time discovered that it has a brittle effect in the strength of the tested specimen. The stacking sequence also governs the effect of hygrothermal aging on the mechanical performance of the composite specimens.This paper also studies the damage characteristics of a special designed carbon/glass hybrid woven fabric/epoxy laminate subjected to lightning strike damage, both in the dry and moisture condition. Compared to the carbon fabricated counterparts, three different damage forms have shown for the hybrid laminate. Moisture can greatly degrade bonding strength between the carbon fiber layer and surface fiberglass layer. When lightning strike is introduced, the fiberglass damage, carbon fiber damage and internal delamination damage all enlarged, even triggers total debonding between the fiberglass and carbon layer.Finally, this paper builds a comprehensive framework to simulate lighning strike damage on the composite structure using Abaqus. Temperature field, electrical field, stress field and pyrolysis field can be evaluated during the strike infliction. Based on the pyrolysis results calculated from the lightning strike simulation, this paper firstly integrated LaRC failure criterion into progressive failure damage mechanics to develop a new model to evaluate the residual mechanical performance of composite structure subjected to lightning strike. The calculated results are in good agreement with experimental ones. The proposed method has a bright application prospect in the area of composite damage tolerance.