The Effect of Long Term Hygrothermal Aging by Immersion on Carbon/Epoxy Composites Exposed to the Heat Sources for Naval and Marine Applications

Abstract

Fiber-Reinforced Polymer (FRP) composites have many advantages over conventional materials in terms of high strength-to-weight and stiffness-to-weight ratios, design flexibility and enhanced service life. Due to these advantages, FRP composites are used in many different fields such as Construction, Electric/power generation, Marine, Corrosion/infrastructure, transportation and so on. Most researches of FRP composites were focused on the applications used in ground field. However, in Navy, marine composite materials are increasingly being used in diverse applications: Submarine, Autonomous Underwater vehicle, Unmanned Surface vehicle and Payloads in Naval vessel. It is known that polymer composites are very sensitive and are friendly to water or moisture in any forms. Moisture in polymer composites often causes degradation by swelling and hydrolysis. Especially, if polymer composites will be immersed in water and seawater, faster degradation can be caused by water uptake than any other moisture environments. While general investigations regarding water uptake are concentrated on the composite materials cured in ambient temperature, the immersion effects of polymer composites exposed to elevated temperatures were studied because underwater applications of composite materials can be exposed to the various heat sources. For example, fires on naval vessels and underwater vehicles can be started by any number of causes such as electrical faults and ignition of flammable gases or liquids. Accordingly, immersion effects must be studied on marine composite materials exposed to various temperatures in order to evaluate service life in an underwater environment. This study investigated the water uptake, diffusion coefficient, and Short beam shear (SBS) for Interlaminar Shear Strength(ILSS), delamination between fiber and resin using test specimens exposed to the elevated temperatures. The specimens were immersed for a definite period of time (~one and a half years) in seawater and deionized water (DI water) to compare both degradation mechanisms.