Abstract
The objective of this work was to understand the cracking of aluminum flame spray on an epoxy thermoset. In the experiments presented here, epoxy cylinders were uniformly coated with flame spray. The cylinders were put into a state of tensile stress by taking them to elevated temperatures and similarly put into a state of compression by taking them down to cold temperatures. Surface cracks on the outside of the cylinders were photographed and compared. The cylinders were cross-sectioned at room temperature to study how the aluminum surface cracks propagate into the epoxy. It was shown that thicker aluminum generates observable surface cracks at a lower temperature than a thinner coating does. The surface cracks cannot be seen at room temperature. However, some of the coating cracks propagate into the substrate and can be seen at room temperature when the cylinder is cross-sectioned. The substrate cracks tend to be deeper with a larger coating thickness. Similarly, cracks are deeper when the substrate with a given thickness is taken to higher temperature. Supplementary examples that contain the addition of a hard inclusion (copper strip) between the aluminum and epoxy substrate at elevated temperatures were discussed, as well as delamination of the aluminum film at cold temperature.
