Damage to brittle coating layer with compliant substrate from concentrated loads

Abstract

The mechanics of contact-induced damage in brittle layers on soft support substrates are of interest for their relevance to lifetime-limiting failures of technological laminate systems in concentrated loading. The results of experiments model bilayer that enable in situ viewing during loading with simple concentrated loads (spherical indenters) and yet simulate the essential features of damage in a wide range of engineering layer structures are described. The experiments reveal a competition between damage modes-cone cracks at the top (near-contact) brittle-layer surfaces and laterally-extending radial cracks at the lower surfaces. Hertzian loading superposed tangential loads shows slight shift of critical load point and value and it represents that tangential loads are secondary issue. The effect of slow crack growth is demonstrated in brittle coating on supporting substrate. The critical loads for radial crack depend sensitively on adhesive thickness and modulus. Delamination at the interface in poorly bonded specimens greatly reduces the critical loads of radial cracking.