Residual Stress Development in Marine Coatings Under Simulated Service Conditions

Abstract

This chapter explains the residual stress development in marine coating under simulated service condition. The chapter illustrates that residual stress development in AA coatings is similar to that observed by Croll who also found that the residual stress in thermoplastic coatings reached an equilibrium value that was independent of the thickness and that the thickest coatings took the longest time to reach equilibrium. Tensile stresses form as the result of the volumetric shrinkage that accompanies the loss of solvent. The residual stresses in AB thermoset coatings are also tensile but shows greater scatter in magnitude. The highest residual stresses observed in this study have been caused by differential thermal contraction between coating and substrate. A temperature change similar to that between a dry dock in a warm climate and the open sea gives stresses of 4 MPa and a significant fraction of the failure strength. Other sources of residual stress are complex and are probably highly specific to the coating composition. When using bi-layered coatings the changes in stresses were moderated somewhat and it appears that a significant and beneficial reduction in the stress magnitude can be achieved by appropriate combination of thicknesses of the two layers.