Failure of coatings over joints and gaps: finite-element models

Painting over joints and the narrow gaps around fasteners is extremely common. When the joint or gap is stressed, the gap opens and the coating over it is subject to very large strains that may immediately or eventually cause it to fail and thus permit corrosion, etc. Improving the design or selection of coatings to overcome this problem requires quantification of the imposed elongation of the coating. A simple coated butt joint geometry, in tension and in bending, is modeled by finite-element analysis to examine how coatings of different modulus respond to the opening of a joint, particularly showing regions where strain distributions may provoke failure. More loci of possible initial failure occur when the gap is filled by a material that is different from the coating over the gap because there is an added interface.