Is the out-of-plane shear strength an independent property? A micromechanical perspective about a macromechanical question

For unidirectional laminae, five elastic properties and six strengths are usually required. The goal of this paper is to evaluate if the out-of-plane shear strength is really an independent property or if it is somehow related to the transversal tensile and compressive strengths. The analytical VSPKc micromechanical model is used to derive closed-form relations. Fiber-matrix interface failure due to normal and shear interface tractions is evaluated considering a perfectly brittle behavior. The proposed model is compared with four analytical models from the literature and their estimations are verified against six experimental data. The relations proposed obtained the best results compared with the experimental data, with an average error equal to 8.84%, while the error using the second-ranked model is 17.40%, indicating with good reliability that the out-of-plane shear strength is not an independent property.