Time-Dependent Mechanical Response of Ice Adhesion on Aluminum Substrates

Ice adhesion on aerospace-relevant materials is both complex and not well understood. Measuring such adhesion and understanding the underlying physics involved require reliable testing techniques that can yield multifaceted data sets. The latter includes the surface morphology, that is, roughness, and its spatial correlation structure, resolving substrate-induced strain, and direct mechanical testing of adhesion. As part of a continuing investigation of ice adhesion on a relevant surface, we performed time-dependent stress ramps on aluminum surfaces. The temperature range explored, from -20 to -7 °C, allowed spontaneous icing and ice morphologies, namely, below or above -15 °C. Additionally, we characterized the spatial correlation surface roughness maps of the specimens. Our novel test protocol yields reproducible and high-precision results when compared with alternative methods reported throughout the literature. The stress-ramp test data using the proposed protocol show that the apparent average critical stress (proportional to the adhesion strength) depends on both stress-ramp rate and temperature. More specifically, the adhesion strength is higher for higher stress rates and increases with decreasing temperature. The stress-ramp test yields the full span of the time-dependent adhesive behavior of ice and particularly the upper bound. Additional stress-concentration analysis is needed to correct for this effect and thereby yield the critical stress rather than the average value produced by our procedure. The results in this work should aid to improve our understanding of ice adhesion mechanisms.