A method for determining material parameters includes applying a character grid over a planar sample, clamping the planar sample in a frame in accordance with directions of orthotropy of the planar sample; collecting a first set of data that describes a first position of the character grid; applying predetermined normal and shear stresses to the planar sample thereby bringing the planar sample into a deformed state and changing the position of the character grid; collecting a second set of data that describes a second position of the character grid, determining a relative position change of the character grid by correlating the collected first set of data and the second set of data; determining a relative displacement and a current distortion state of the planar sample; determining a deformation equilibrium of the deformed state of the planar sample; and calculating the material parameters from the deformation equilibrium.