Instabilities in bimetallic layers

The analysis of the thickness fluctuations in the extrusion process of bimetallic tubes has motivated the present work. For an orthotropic, incrementally-linear solid, the possibility of non-uniform solutions near the bimaterial interface is investigated by assuming an initial perturbation along the interface. The bifurcation equation for the problem is established and firstly solved numerically to obtain a critical strain in terms of a corresponding wavenumber. Then the bifurcation equation is solved for strains above the critical strain in order to analyse the growth of the perturbation, by means of an instability parameter introduced in the analysis. A set of values for several selected parameters of the process and three constitutive equations are considered in the computations. Their influence in the stability of the process is discussed in detail.