Analysis of nonlinearly viscoelastic behavior of adhesive bonds

The purpose of this paper is to provide a theoretical framework to study the nonlinear viscoelastic behavior of adhesive layers. The stress-strain behavior of the adhesive material in shear is assumed to have a nonlinear elastic part and a linear viscoelastic part, i.e., σ_yx=f(ε_yx)+K_mε_yx. To measure f(ε_yx) and K_m by an ultrasonic technique, it is proposed to prestress the adhesive layer in the nonlinear range and to superimpose a small amplitude ultrasonic signal. The reflected field is used to obtain the wave speed and hence df(ε_yx)/dε_yx as a function of the pre-stress. The viscoelastic parameter is obtained from the amplitude decay. By repeating this procedure for various values of prestress and using numerical integration, the stress-strain behavior of the adhesive layer can be reconstructed.