A Study on Chipping Failure of Automotive Coatings

By utilizing a high-speed photographic machine, we successfully observed the very moment that the coated films got destructed by so-called “chipping.” A high-speed steel ball was shot onto multiple coating films, when the impact energy was consumed for an extremely short time, i.e. about 1/1000 second and the energy has caused film destructions and/or detachment between film layers and/or vibration absorption. There was a good correlation in destruction of coated films between the high-speed steel ball impact test and the conventional gravel impact test, the latter of which is commonly employed for evaluation of chipping resistance. Moreover, for a prediction of chipping resistance by viscoelastic property of coated dry films, the observation of high-speed film deformation was very effective as a means of chipping analysis. The relaxation spectrum, being obtained from frequency-temperature variance in dynamic viscoelasticity measurement, was highly correlative to anti-chipping performance.