Abstract
The oil industry is interested in drilling for oil in the ocean at depths of 2000 m and greater. In order to do this in a cost effective manner, the use of composites as risers is under investigation. Presently, the long-term effects of seawater on composites are unknown. These effects must be determined before composites are used in offshore applications. In an effort to understand the failure scenario and to determine the effects of seawater on composites, a program has been developed to determine the interfacial strength (normal to the fiber) of an interlayer hybrid composite which has been exposed to seawater for two different lengths of time. Specimens were tested in transverse tension in an environmental scanning electron microscope. The specimens were tested in the as-received condition, after they reached saturation, and eight months after they reached saturation. Observations revealed that damage initiated at the boundary of resin rich regions regardless of the conditioning process. Analytical results obtained using linear superposition to determine the stress at the fiber/matrix interface revealed several interesting things. For example, as moisture is added to a composite, the hydrothermal residual stresses in an inhomogeneity change from tensile to compressive. Assuming a constant interfacial strength, this should make it more difficult to initiate damage in conditioned specimens. As this was not the case, moisture appeared to have a slight degrading effect on the interfacial strength. However, as the damage tried to grow outside of resin rich regions, moisture actually helped to arrest the damage growth, causing the mechanical stress to give transverse cracking to increase with increased moisture content and with increased aging time-
Wood, Catherine Ann (1996). Determining the effect of seawater on the interfacial strength of an interlayer E-glass-graphite/epoxy composite using observations of transverse cracking made in-situ in an environmental SEM. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1996 -THESIS -W665.