The effect of humidity on composite lap joints and an electrochemical study of coatings and galvanic systems

This dissertation presents a study of the effect of humidity on the static and dynamic strength of adhesive composite lap joints and an electrochemical study of coatings on metals and galvanic couples.; The effect of humidity on the static and impact strength of composite lap joints was studied by bonding steel to carbon fiber using a commercially available two-part epoxy. The quasi-static strength of the joints was measured using an INSTRON machine and the dynamic strength was determined with a Split-Hopkinson Pressure Bar Apparatus.; Baseline failure data was performed on unexposed specimens. The remaining joints were placed in a saltwater humidity chamber to determine the effects of simulated seawater on the adhesive joint strength over time. Joints were removed from the chamber at 250, 500, 1000, and 2000-hour intervals and tested to failure to determine the joint strength. The static and dynamic strength was measured as a function of exposure to determine the effect of humidity. It was determined that initial bond quality, as well as exposure time, is a major factor in joint strength.; Electrochemical Impedance Spectroscopy (EIS) was used to investigate single and galvanic couples of mild steel, stainless steel, and aluminum. In addition to bare metals, testing was performed on metals coated with polyurethane, electroplated aluminum, or an aluminum/titanium ceramic. The goals were to develop analytic models to predict the effectiveness of future coatings on metals and to investigate whether EIS could measure the effect of coupling a more anodic metal to a more cathodic metal in seawater.; This study determined EIS cannot discern between two coupled materials and measures the open circuit potential and corrosion current of the more anodic metal. Modeling the coatings was made impossible due to high rates of coating failure and software limitations. Although models from the EIS data were not developed, the open circuit potential and final impedance values of the coated systems may yield a valuable prediction tool.