Application of multiaxial fatigue criterion in critical plane to determine lifetime of composite laminates

This paper analyzes the results of fatigue tests of samples made of composite laminate. These samples were cut out from a previously produced laminate with different fiber-orientated layers at different angles. Thus, various variants of the complex stress state were obtained for the ma-terial with anisotropic properties. The samples cut out at 0 degrees angle was taken as a reference point for the calculations. In order to perform the calculations, three popular stress criteria used in the case of statics were modified: maximum stress, Azzi-Tsai-Hill and Norris. Then, it was proposed to apply to the analysis of fatigue life of composites the fatigue criteria known from the analysis of isotropic materials, defined in the critical plane. The definition of the critical plane was consid-ered as the plane in which the maximum normal stress or maximum shear stress occurs - obtaining two different versions. As a result of the calculations, it turned out that the best compliance of the calculations with the experiment was obtained using the criterion defined in the critical plane determined by the shear stresses, where the normal and shear stresses were included in it as the sum of their linear combination with weighting factors.