A phenomenological constitutive law for the nonlinear viscoelastic behaviour of epoxy resins in the glassy state

Lorenzo Bardella

Department of Civil Engineering, University of Brescia, Via Branze, 38-25123 Brescia, Italy


We propose a constitutive model to describe the nonlinear viscoelasticity of epoxy resins in the glassy state. Experimental tests have shown that nonlinear viscoelasticity rules the cyclic behaviour of epoxy resins before the material strength is reached. The proposed model allows the simulation of this cyclic behaviour and, in particular, of the flex which characterises the stress–strain curve upon unloading. The consistent integration algorithm, based on the Central Difference Scheme, of the proposed constitutive law is given. As an example, the model is successfully used to numerically homogenize the cyclic behaviour of hollow sphere-filled epoxy resins (i.e., syntactic foams) by means of unit cell models.

Author Keywords: epoxy resins; nonlinear viscoelasticity; Eyring model; syntactic foams