Effect of Seawater on Carbon Fiber Composite Facings and Sandwich Structures With Polymeric Foam Core

Abstract

This chapter provides a summary of author’s findings from the research sponsored by the United States navy in the past decade associated with the durability aspect of the sandwich structures with thin face sheets made of carbon fiber vinyl ester composite facings and a thick core section of closed cell polymeric foam core material. Exposure to sea environment and coupled effects with temperature change to ship structures over extended period of time often leads to degradation of its mechanical properties. In this research, vinyl ester based carbon fiber composite facings manufactured using VARTM approach are evaluated for the fiber and resin dominated properties and corresponding degradation in static, fatigue, and fracture behavior. The mechanical response of carbon fiber vinyl ester composites immersed in simulated sea water and coupled degradation effects from simultaneous exposure to low temperature are reported. H100 PVC foam core degradation was evaluated under tension and torsion tests. Interfacial delamination fracture response for the sandwich structures due to combined effects of seawater and low temperature effects are also investigated including the weight gain and associated expansional hygroscopic strains. The effect of confined and one sided sea water exposure on the cyclic fatigue behavior yielded failures under much lower number of cycles of loading when fatigued under immersed conditions surrounded by sea water than in air for tension-tension fatigue. Even with the condition of one sided sample face exposed to sea water, a considerable reduction in the fatigue life, corresponding to approximately 50% was observed. A detailed study on the compression response of these naval composite sandwich structures is ongoing and is also included here.