Transversely isotropic material: nonlinear Cosserat versus classical approach

We consider a specific case of unidirectional reinforced material under applied tensile load. The reinforcement of the material is inclined with 45A degrees to the direction of the tensile resultant. Different approaches are discussed: one experiment and three computational models. Two models use the classical Cauchy continuum theory whereas the third computational model is based on a Cosserat continuum. It is well known that test specimen with inclination between unidirectional reinforcement and tensile direction show, besides Poissons effect, additional deformation perpendicular to the load direction. The classical transversely isotropic continuum theory predicts this deformation as typical S-shape. In the Cosserat continuum the orientation of the inner structure is incorporated. Thus, structural parameters influence the deformation. With the proposed geometrically non-linear Cosserat model classical and non-classical behaviour can be modelled. In the non-classical case, the transverse deformation is not described by one S-shape but by multiple S-shaped modes. The additional rotational parameters in the Cosserat continuum are responsible for the non-classical behaviour which is due to non-symmetric strain.