Failure analysis of FRP laminates by means of physically based phenomenological models

The successive failure of different laminates subjected to a variety of loading conditions has been treated by a layer-by-layer failure analysis. Three sources of non-linearity are considered, namely material non-linearity due to microdamage, matrix cracking, and changes in fibre angle with increasing strains. In general there is good agreement between predictions and experimental results. Some disagreement is due to imperfections in certain tests, therefore, these tests should be repeated. Three categories of laminate configuration/loading condition can be distinguished: (I) laminates with 3 or more fibre directions with arbitrary loading conditions; (II) balanced angle ply laminates with stress ratios in accordance with netting analysis; (III) laminates with 2 fibre directions and loadings which are not in accordance with netting analysis. The analysis of category (I) is straight forward. Category (II) is sensitive to the stiffness degradation after the onset of matrix cracking. Category (III) fails at low stresses and large strains of the laminate due to a rapid deterioration. An intensive discussion is necessary to define a failure limit for category (III).For the detection of the different modes (A, B, C) of interfibre fracture (IFF), refined action plane related IFF-criteria developed by Puck on the basis of Mohrʹs and Hashinʹs considerations on brittle fracture are used. They provide much more information than has been reported from the experiments. Their unique ability to predict the inclination of the fibre parallel fracture plane is the key for assessing of the risk of delamination and local buckling due to a wedge effect which occurs when oblique fracture planes are exposed to high transverse compression.