Effects of Low Cycle Loading on Shear Stressed Adhesive Bondlines

Abstract

Adhesively bonded thick adherend model joints were cyclically loaded on squarewave and sinusoidal modes. Durind the cycling loading,the real shear strains of the bondlines and, for the first time, the failure strains were quantitatively measured by use of a special shear strain extensometer. The analysis of bondline strains of a modern structural adhesive indicates dependence on time, shear stress and cycle frequency, and suggests a strengthening of the adhesive in the bondline under cyclic loads. A linear viscoelasticity can be expected only at very low bondline shear stresses. At higher stresses, residual strains build up to a critical level and exceeding this level causes failure of the bondline. Adhesive material properties obtained in the present study provide a guide to allowable shear stresses or strains to design cyclically loaded adhesively bonded structures.