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The recent inclusion of painted plastic fascias/bumpers into automotive applications has necessitated the evaluation of potential in-service damagability. One failure mode that has been identified, that of friction-induced paint/substrate damage, has been simulated in a laboratory environment. Our goal was to evaluate the effects of coating attributes, both thermal and mechanical, on subsequent performance of painted thermoplastic olefin (TPO) materials. It was determined that the most significant parameters in the paint which contributed to damage were the glass transition temperature, the secant modulus at break, and the static coefficient of friction. This paper will discuss techniques and results used to reach these findings.

Damage to painted automotive plastics induced by Hertzian contact stresses continues to plague the material engineer involved in the design and selection of fascias, bumpers, body-side moldings, and the like. Studies conducted to determine the root cause of such failures have focused on the effects of paint and the role of friction in the compressive, tensile and shear failure of painted thermoplastic olefins (TPOs). The study described herein probes the effects of paint type on the compressive, tensile and shear damage resistance of painted TPO substrates. Coating variations, e.g., adhesion promoter and topcoat type, and their effect on damage type and damage sensitivity will be described. The apparatus utilized to impart the damage, SLIDO, and the variables studied affecting the damage, e.g., acceleration, velocity, temperature, and loading pressure, are also discussed.