Energy-based criterion of elastic limit states in fibre-reinforced composites

The paper deals with elastic limit states of fibre reinforced composites. In particular a single lamina of orthotropic symmetry is considered. An energy-based criterion proposed by J. Rychlewski [1, 2, 3] is specified for plane state of stress, which occurs in the considered lamina. The Rychlewski criterion was specified by calculation of the limit elastic energy densities with use of the experimental results obtained in the simple strength tests. It was shown that the condition for limit curve in biaxial state of stress, resulting from Rychlewski criterion, to be convex and bounded is equivalent to the condition that the elastic energy is positive. This conditions can be used for verification of validity of experimental parameters of elasticity and strength, which are obtained in mechanical tests applied for comosites. The known criteria of Tsai-Hill and Tsai-Wu are also identified for the same experimental data. It is visible that the differences between the discussed criteria are much larger for biaxial states of stress than for tension or compression of the lamina.