Experimental study on mechanical property and stone-chip resistance of automotive coatings

Abstract

The damage of automotive coatings caused by stone impact is a problem that has attracted great attention from automotive companies and users. In this work, experiments were conducted to investigate the dynamic tensile properties and stone-chip resistance of automotive coatings. Four kinds of paint films and three typical coatings (single-layer electrocoat coating, single-layer primer coating, and multilayered coating) were used. Under dynamic tensile load using split Hopkinson tension bar (SHTB), the engineering stress-strain curves of the paint films at medium and high strain rates (from 50 to 600 s ^−1 ) were obtained. Results indicated that the mechanical properties of the paint films exhibited strong nonlinearity and strain-rate correlation. A modified anti-impact tester was used to complete repeatable single impact tests. The effects of some key parameters, i.e., impact velocity, impact angle, and paint film thickness, on the stone-chip resistance of coatings were systematically investigated. The influence of contact type under high-speed impact conditions was investigated as well. The surface morphologies of the coatings after impact were examined by scanning electron microscopy (SEM), and the failure mechanism of the coatings under normal/oblique impact was discussed. In all experiments, the paint films showed brittle fracture behavior.

Keywords

• automotive coating
• split hopkinson tension bar
• single impact test
• mechanical property
• stone-chip resistance