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Role of Microstructure and Sea Water Confinement on Damage Evolution of Vinyl Ester Based Carbon Fiber Marine Composites

A fundamental study on the damage evolution of composite materials being considered by US Navy made of T700 based carbon fiber fabric (12k tows and plane weave) and vinyl ester resin (Derakane 510A) using VARTM process is presented utilizing high-resolution X-ray computed tomography, 3-D Digital Image Correlation integrated with mechanical testing systems. Panels of approximately 1.5 m x 1.5 m are manufactured using VARTM and coupon samples are obtained from various orientations. The deformation behavior of matrix dominated samples having [±45]2S orientation with the fiber dominated samples of [0/90]2S typically show large changes in damage evolution with increased deformation. A time aged (dry) and saturated sample are then subjected to controlled rate of strain loading monotonically with several unload-reload loops to evaluate the accumulated plastic strain (damage) as a function of stress amplitude. Damage is quantified using surface strain variations along the gage length of a deforming sample using a high resolution three-dimensional digital imaging correlation system. The surface deformation data obtained from 3DDIC is then considered synergistically with the variation of microstructural features obtained from high-resolution X-ray micro-tomography. The experimental techniques developed for this study are then utilized to evaluate the effect of sea environment on the damage behavior of marine composites for tensile monotonic loading conditions and fatigue loading. The motivation of the current study is to identify failure modes applicable for naval carbon fiber reinforced polymer composites and for developing future material systems with a targeted microstructure that can minimize accumulation of damage from repeated loading, blast, and impact conditions under harsh naval environment. Additive manufacturing techniques can realize the prospect of printing carbon fiber reinforced composites with target microstructure.