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Puck's action plane failure criteria have already proven their capability in the first and second world-wide failure exercises (WWFE-I and WWFE-II). However, Puck and his co-workers have only recommended inclination parameters for GFRP/Epoxy and CFRP/Epoxy. These UD composites generally have high transverse compressive-to-tensile strength ratios YC/YT, and are regarded by them as intrinsically brittle materials. Therefore, Puck's inter fibre fracture (IFF) criteria might not be directly applied to other types of UD composites with low YC/YT ratios. In particular, Puck's original IFF criteria will result in unrealistic predictions if YC/YT is extremely low. In the present study, Puck's original IFF criteria are extended to all types of UD composite materials to solve the problem. Composites are divided into three categories, namely semi-brittle materials, brittle materials, and intrinsically brittle materials. Depending on the material category, three different algorithms are proposed for determination of the two parameters in Puck's IFF criteria, namely the resistance of the action plane against transverse tensile stressing, R ⊥ A t , as well as the inclination parameter of contour lines of the fracture body, p ⊥ ⊥ . The present criteria are theoretically evaluated for composites with low YC/YT ratios, while the predictions of the present criteria are compared with the test results of composites with high YC/YT ratios such as thermoset GFRP and CFRP. Theoretical and experimental assessment demonstrates the reasonableness of the extension of Puck's IFF criteria.

A micro-macro mechanical finite element model is developed for the prediction of the ultimate strength and failure modes of Composite-Metal-Weld (Comeld) joints. A micromechanical finite element model is firstly proposed, based on the periodic RVE technique, to gain the equivalent stiffness and strength of the protrusion layer by FEM. A suitable unit cell model, which can represent the protrusion layer through applying a unified periodical displacement boundary condition, has been established according to the geometric distribution of protrusions on the metal surface. With the predicted equivalent properties of the protrusion layer which can be considered as a new homogenized material layer in the global model, failure modes and ultimate strength of three different Comeld joints subjected to static tensile loads are predicted numerically. A good agreement between the experimental and simulated results shows correctness and effectiveness of the developed micro-macro mechanical method for predicting the load bearing capacity of Comeld joints. Moreover, Comeld parameters like the density and height of protrusions and the lap size of joints need to be adjusted to achieve higher joint strength.

An improved analytical method is presented to predict the damage area of composite laminates induced by low velocity impact, which avoids expensive nonlinear three-dimensional FEM analysis. The key point of the proposed method is the definition and analysis of the initial interlaminar shear strength for the prediction of the interlaminar shear failure due to impact. The initial interlaminar shear strength is predicted by a micromechanical model based on Eshelby’s equivalent inclusion method. The simplified energy-balance model and quasi-static assumption are used to estimate the maximum contact force. In addition, an approximate solution is proposed for the bending of a clamped symmetric angle-ply laminated rectangular plate subjected to a central concentrated force. Finally, the above techniques are combined to formulate a methodology predicting the impact induced damage area. The analytical results agree well with the test data.

An investigation has been conducted to predict the tensile and compressive strengths of fiber-dominated composite laminates with notches. Research shows that the strength of a notched fiber-dominated laminate can be evaluated from the failure prediction for the 0° plies in the laminate. On the basis of this study and the frequently used ‘characteristic length’ concept, a lay-up-independent failure criterion, the load-bearing ply-failure criterion (LBPF), is proposed, which relates the laminate strength to the failure of the principle load-bearing ply. Two characteristic lengths are obtained for tension and compression, respectively. Results indicate that, in most cases, the two characteristic lengths are properties of a composite material system, regardless of laminate configurations. Once these two parameters are estimated from preliminary tests on notched multidirectional laminates of the material, they can be used to predict the notched strength of fiber-dominated laminates of the same material. Good consistency is observed between test results and predictions.