Fatigue Studies on Urea Assembly Adhesives

Abstract

Abstract Assembly adhesives made of “cold-setting,” urea-formaldehyde, synthetic resins, are employed in the fabrication of wooden aircraft such as gliders and motor-driven airplanes. Adhesives so used are frequently subjected to vibrating loads which induce alternating stresses in the glue; of these shear, in the plane of the glue, and direct tension, perpendicular to the glue line, are the two which are most likely to bring about failure. It is well known that most materials fail under alternating stresses smaller in magnitude than the static stresses required to cause failure, and synthetic-resin assembly adhesives are no exception. Little has been known quantitatively, however, respecting the behavior of such adhesives under alternating stresses. In this paper are presented the results of researches into the failures to be expected in glue joints of this kind, particularly the nature of the failure, cycles of stress to failure at various amplitudes and stresses, and the probable “fatigue limit” of such an assembly. Tests were carried out at room temperatures on an assembly adhesive representative of those employed in aircraft fabrication.