In the present work, the Virtual Fields Method is used to extract from one single mechanical test the whole set of material parameters governing nonlinear constitutive equations of a unidirectional compsite material. The displacement fields at the surface of a rectangular coupon submitted to a shear/bending loading are measured by the grid method. Strain fields are derived from displacement fields using polynomial fitting. The strain fields are then processed by the Virtual Fields Method to retrieve the five constitutive parameters: the four linear elastic orthotropic stiffnesses and a softening parameter driving the nonlinearity.