Thermal load effects on aluminum light alloy plates with epoxy coatings

When the assembling of hull structure is completed, the sides of metal motor yachts are usually affected by bumps and hollows coming from welding plates to each other and plates to frames. These defects, normally tolerated on merchant ships, cannot be accepted on superyachts for which the external surface must be smooth and glossy. For this reason the surface finishing is achieved by a long and delicate process of filling, fairing and painting. The final result of this process is very important for the yacht aesthetics as the general appearance of the vessel depends on the external painting. As a matter of fact the quality of painting depends mainly on the undercoat preparation to assure an adequate grip and, most of all, a perfect smooth and faired surface. Despite accurate preparation and painting, surface conditions can undergo undesired alteration because of excessive heating due, as an example, to a long exposure to solar radiation. While stresses do not reach significant values because of the relatively low intensity of thermal loads, strains could still cause very slight surface distortions and undulations which are perceived by human eye as a surface defect. The phenomenon becomes particularly evident if the surface is painted with a dark colour. In this paper an investigation on the influence of temperature on the stress and strain distribution of aluminium light alloy plates coated by filler layers of different kind and thickness is reported. The study has been performed by FEM structural analyses calibrated by experimental measurements performed on laboratory specimens. This work represents the continuation of a research begun some time ago with the measurement of temperatures on yacht hulls exposed to solar radiation in different conditions.