Off-axis flexure test: A new method for obtaining in-plane shear properties

Off-axis three-point flexure test for unidirectional composites is proposed as a new method for obtaining in-plane shear modulus and in-plane shear strength. The method of determination of the in-plane shear modulus G _LT has been explained in a previous work where the displacement field of an off-axis flexure test was analyzed. In the present work, besides summarizing the calculation equations of G_LT, the condition of small displacements is analyzed. Otherwise, an error analysis is carried out in order to study the influence of the calculated value of G_LT on the other elastic parameters. Normal and shear stresses in the fiber-matrix interface change from point to point in the specimen depending on the fiber orientation angle and specimen geometry. A critical point of failure that depends on the fiber orientation angle is determined and optimum conditions for obtaining in-plane shear strength are discussed. Experiments for different fiber orientations and geometric conditions have been carried out for IM7/8552 epoxy matrix based carbon fiber reinforced unidirectional composite material.