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- Erosion; Simulation; Polyurethane; Protective Films; Sand; Angularity
Among many useful properties of elastomers, one is their ability to absorb energy by deforming to large strains without fracturing. This property combined with their good adhesion to substrates makes them suited as adhesive films and coatings for protection against impact damage. An example of practical significance is the erosion of helicopter rotor blades where the protection of leading edge is often achieved by mounting a film or applying a coat of polyurethane. Although this is a workable solution, there is currently little knowledge as to the durability of this elastomeric film/coat under impact of hard and angular particles such as sand. A deformation and failure analysis that deals with the angularity of the erodents and captures the local mechanisms responsible for erosion damage in elastomers is the sine qua non. The present endeavor tries to address these issues by considering a polyurethane layer on a quasi-rigid substrate, impacted by hard particles at velocities and angles of attack given by pre-specified distributions. A novel method is devised to address the angularity issue. A series of finite-element calculations are performed on the coating layer-substrate systems subjected to different velocities, incidence and angularity of the impacting erodents. An elasto-plastic material constitution with isotropic hardening is employed in the simulations and material parameters representative of polyurethane are used for the coat. Initial parametric deformation analyses provided an adequate qualitative estimate of erosion parameters. Incorporation of a stress based fracture criterion enabled a quantitative measure of material removal due to erosion to be achieved. The simulation results show good match with experimental trends of target mass loss as obtained under normal and inclined loadings with angular erodents. The current simulation framework has sufficient capability and versatility to incorporate more enriched polymer-models and advanced fracture criteria in the future, thereby allowing parametric studies toward selection of materials and coat-layer thicknesses thus predicting the erosion mass loss as accurately as measured by experiments.