Inhomogeneous shear of orthotropic incompressible non-linearly elastic solids: singular solutions and biomechanical interpretation

We present a detailed study of rectilinear shear deformation in the framework of orthotropic nonlinear elasticity, under Dirichlet and mixed-boundary conditions. We take a slab made of a soft matrix, reinforced with two families of extensible fibers. We consider the case where the shear occurs along the bissectrix of the angle between the two privileged directions aligned with the fibers. We show that if the two families of parallel fibers are mechanically equivalent, then only smooth solutions are possible, whereas if the mechanical differences among the two families of fibers is pronounced, then strain singularities may develop. We determine the precise conditions for the existence of such singular solutions for the standard reinforcing orthotropic model. We then extend our findings to some orthotropic models of interest in biomechanical applications, and we discuss the possible relevance of the singular solutions to biomechanics.