Mechanical Behaviour of Steel Plates with Epoxy Coatings Exposed to Thermal Loads

At the end of structure assembling sides of yacht hulls are usually affected by bump and hollows coming from welding plates each other and plates to frames. This defect, normally tolerated on merchant ships, cannot be accepted on yachts for which the external surface must be smooth and glossy. In case of GRP vessels surface finishing comes from the external layer of gelcoat; in case of steel and aluminium vessels 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 just depends on the external painting. For the most part of people painting is simply perceived as the color of a product; as a matter of fact the quality of painting depends mainly by the bottom 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 exposition to solar radiation. This can cause very slight surface distortions and undulations which however, by human eyes, is perceived as a surface defect. The phenomenon is amplified if the surface is painted with a dark color, and this is the trend of today superyachts for which blue, dark green or black hulls are becoming always more frequent. In this paper an investigating of the influence of temperature on the mechanical behavior of steel 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 specimens. This work represents the continuation of a research begun one years ago with the measurement of temperatures on yacht hulls exposed to sun radiation in different conditions.