Interaction between different internal length scales for strain localisation analysis of single phase materials

It is well known that both rate dependent and gradient-dependent constitutive models introduce internal length scales in dynamic initial value problems. As a result, numerical solutions of such initial value problems involving strain-softening no longer exhibit excessive mesh dependence. In this paper, the length scales included in a solid model which exhibits both above mentioned constitutive behaviours are discussed. The internal length scales derived from damping effects, which are typical for the viscoplastic models, and the wave length, obtained from the critical wave number for which the wave speed is not imaginary, are used together to give a prediction of the internal length scale of the combined model. The approach proposed here for prediction of the internal length scale is more general than commonly used procedures and permits to explain phenomena observed in viscoplastic and gradient dependent models. A one dimensional example is given to illustrate the theoretical findings.