Analysis of the validity of the three-point off-axis bending method

Several methods for determining in-plane shear properties of anisotropic materials (i.e. fibre reinforced composite materials and natural wood) based on flexural loading have been proposed. One of those methods is the off-axis flexural test that considers unidirectional composite materials subject to three-point bending loading. As a result of the anisotropic behaviour, unidirectional off-axis laminates subjected to flexure present a bending–twisting coupling that may cause, in the case of 3-point bending loading, a lift-off of the specimen on the fixture supports. Such specimen lift-off has been considered one of the critical features to be considered on the mentioned experimental method. Besides geometrical parameters, material elastic constants, as longitudinal, transversal and shear elastic moduli, influence the validity to use this method for characterising in-plane shear properties. On that sense, an analytical approach for studying the material conditions for which the application of the off-axis 3P-B test is adequate is presented.