Experimentally Characterizing Shear Strength of Structural Adhesives With Varying Surface Preparations

Structural epoxy is a commonly used adhesive in aerospace grade manufacturing due to its ease of use, bond strength, and resistance to extreme temperatures. The strength of the epoxy bond in shear is impacted by multiple factors including surface preparation and materials. This paper presents an experiment to test different surface preparations with the goal of reliably adhering materials together. The purpose of these tests was to experimentally characterize the shear strength of bonds in flight hardware undergoing aerodynamic forces of Georgia Tech Experimental Rocketry (GTXR) vehicles, a project team of the Ramblin’ Rocket Club (RRC) at the Georgia Institute of Technology. The specific materials tested were woven fiberglass laminate (G10), steel, aluminum, and Formlabs Rigid 10K Resin in three different combinations. All pairings underwent three different surface preparations: dry sanding, wet sanding, and epoxy wet sanding. Additionally, each combination was tested with both JB Kwik Weld and Proline 4500. The specimens underwent a single lap shear test loaded in tension on an Instron load frame. The experimental shear strength of each specimen was calculated and compared against the values provided by manufacturers. The experimental shear strengths were similar to the values provided and proved wet sanding to be the best surface preparation for these combinations. The results of this experiment will aid in future manufacturing of GTXR vehicles by ensuring that the best process is chosen for all bonds between flight components flying at supersonic speeds.