Measurement and FEM of ice adhesion to the downstream pipe of an air cycle machine

Ice accretion on the downstream pipe of an air cycle machine can lead to pipe blockage and turbine blade damage, and therefore de-icing is needed. Most previous studies focused on ice shedding from flat surfaces, and average interface shear strength rather than the true shear strength was usually reported. Here, the debonding of the interface between ice and cylindric surfaces of an aluminium pipe (2024-T3) was studied trying to understand the mechanism of interface fracture and to obtain the true adhesive shear strength and fracture energy. Average adhesive strength was measured first in the scrape test and the result was used to calibrate the finite element analysis. A cohesive zone model (CZM) with bilinear traction-separation law was used to simulate the interface delamination. The true shear strength σcs and mode-II energy release rate Gcs were determined by matching the numerically predicted critical force to the measured force. The influence of shear strength and shear energy release rate on the critical force was also investigated. At the interface, both the damage factor and the peak shear stress were found progressing away from the edge as the pushing force increased. Parametric studies on the influence of the length of the interface was performed. The critical force first increased and then stabilised with the increase of the length, showing the same trend as that of a theoretical model which ignored the mode-I fracture.