[SY-G2] Finite element analysis of the effect of interfacial bubbles on performance of epoxy coatings under the alternating hydrostatic pressure
Coatings suffer dramatic deterioration and premature damage in the deep-sea environment, in sharp contrast to the good protective performance in typical marine environments. Hydrostatic pressure (HP), which varies with ocean depth, has pronounced impact on coating performance when compared with other factors, such as oxygen level and pH value. The idea that loss of wet adhesion is the first step towards coating failure seems to be raising some controversy, with some researchers suggesting that the loss of adhesion results from the pressure relief process in the experiment rather than from hydrostatic pressure itself. AHP decreased the protective properties of coatings more rapidly than HP via a “push-and-pull” effect, which promotes bubbles formation at the interface between coatings and base metal.
Compared to other simulation methods, the finite element method (FEM) is capable of providing a multi-physical field to solve complex engineering problems more effectively. The interface is most susceptible to corrosion and the coating failure can be affirmed when the corrosion products are visible on there.
In this study, we attempt to develop a model of the growth of a bubble and the change of the stress distribution at the coating/substrate interface under AHP by means of FEM. The results show that the impacts of alternating hydrostatic pressure and hydrostatic pressure on the interface were compared with a precondition of bubbles inducing the coating failure.
1. Hydrostatic pressure cannot mechanically destroy the coating/metal interface because it acts as a compressive stress on the dry bubbles. If the bubbles turn into wet, the pressure loaded on the bubble will disappear.
2. Alternating hydrostatic pressure can provide tensile stress on the wet bubbles during every immersion period, so it accelerates disbonding of the coating.
3. The maximum stress on the bottom of wet bubbles is able to be minimized to less than the stable adhesion value if the lag time is large enough. In this case, alternating hydrostatic pressure cannot accelerate disbonding any more. The lag time will be different if the period of alternating pressure is changed. Thus, the lag time of a coating should be considered when it is designed to serve under alternating hydrostatic pressure.
Compared to other simulation methods, the finite element method (FEM) is capable of providing a multi-physical field to solve complex engineering problems more effectively. The interface is most susceptible to corrosion and the coating failure can be affirmed when the corrosion products are visible on there.
In this study, we attempt to develop a model of the growth of a bubble and the change of the stress distribution at the coating/substrate interface under AHP by means of FEM. The results show that the impacts of alternating hydrostatic pressure and hydrostatic pressure on the interface were compared with a precondition of bubbles inducing the coating failure.
1. Hydrostatic pressure cannot mechanically destroy the coating/metal interface because it acts as a compressive stress on the dry bubbles. If the bubbles turn into wet, the pressure loaded on the bubble will disappear.
2. Alternating hydrostatic pressure can provide tensile stress on the wet bubbles during every immersion period, so it accelerates disbonding of the coating.
3. The maximum stress on the bottom of wet bubbles is able to be minimized to less than the stable adhesion value if the lag time is large enough. In this case, alternating hydrostatic pressure cannot accelerate disbonding any more. The lag time will be different if the period of alternating pressure is changed. Thus, the lag time of a coating should be considered when it is designed to serve under alternating hydrostatic pressure.