Damage morphology and force-deflection curves for impact loading of thick multilayer organic protective coating systems

The response of organic coatings to mechanical impact is crucial to their corrosion protection performance, particularly under offshore conditions. The paper categorizes and discusses four different types of response during the high-energy (3 to 20 J) impact of a falling ball-shaped weight on 14 multilayer organic offshore coating systems. The response types include plastic deformation, brittle (compressive) crushing, radial crack formation, and lateral delamination. Threshold and transition conditions are analyzed based on contact mechanics relationships. For the first time, complete force-deflection curves for this type of coating are recorded with an instrumented impact tester. The curves feature four characteristic points, namely a first local force maximum (F_FS), the respective deflection at this force level (δ_FS), a maximum force (F_max), and the respective deflection at this maximum force (δ_max). These characteristic parameters are discussed in terms of coating system composition. Empirical equations for these parameters as well as for the damage size are derived. The results offer opportunities to quantitatively rank organic coatings with respect to their impact resistance.