A viscoelastic analysis of the creep behaviour of a chopped strand mat E-glass fibre reinforced vinylester resin

The viscoelastic response of a chopped strand mat E-glass fibre reinforced vinylester resin has been studied over a wide range of applied stress levels. At low applied stress levels, the material exhibited a linear viscoelastic response well represented by Schapery's power law model with constant C and n terms. At higher stresses nonlinear behaviour was observed which apparently is caused by the multiplicity of complex local phenomena associated with and preceding damage development (plastic deformation of the matrix, interfacial slippage, fiber-matrix debonding). The limits of linear viscoelastic behaviour and of damage initiation - about 0.48% strain or 42 MPa - coincide for this material. However, for successful modelisation of uniaxial creep strain in the nonlinear range a modified power law is proposed which uses stress-dependent creep parameters C and n.