UC San Diego

Carbon Fiber-Reinforced Polymer (CFRP) composites with epoxy matrices offer many advantages over conventional materials in terms of high strength-to-weight and high stiffness-to-weight ratios, design flexibility, corrosion resistance, and electromagnetic shielding for naval vessels in marine environments. However, the risk of fire and related structural degradation represent a challenge to the structural assessment of high performance composite structures. The accurate assessment of the deterioration and degradation of a composite structure subjected to elevated temperatures is vital in the planning for maintenance of mission critical components. In this research, carbon/epoxy composite materials have been thermally aged at nine (9) different temperatures for up to 72 hours of ageing time. In order to determine the residual mechanical properties of the specimens exposed to elevated temperatures, tensile, flexure, off-axis shear, and short beam shear tests were conducted in accordance with ASTM test procedures. In addition, the viscoelastic behavior and dynamic properties of these composites at varying ageing times and temperatures were found using Dynamic Mechanical Thermal Analysis (DMTA) and Differential Scanning Calorimetry (DSC). ThermoGravimetric Analysis (TGA) was performed to analyze the characteristics of thermal decomposition and Scanning Electron Microscopy (SEM) images were taken to investigate failure mechanisms such as interfacial debonding, delamination, and fiber fracture. Since polymer composite used in marine environments can easily be exposed to moisture related to high relative humidity and immersion, degradation mechanisms related to moisture were investigated on specimens immersed in seawater and deionized water for 72 weeks after exposure to selected regimes of elevated temperature using gravimetric analysis, SEM and short beam shear test. Finally, well-established prediction models such as Arrhenius rate model, Time- Temperature Superposition model and Weibull statistical strength model were used with experimental data to estimate characteristic associated with long-term service life