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In the crack growth prediction models, the effect of variable amplitude loading is taken into account by different ways. One of them the Newman's model is used very often, but in its original form it is not able to take into account the effect of specimen thickness. The new modification which involves the specimen thickness is presented. The study of variable thickness impact is based on the FEanalysis of M(T) specimen. The variability of constrained factor α was analysed for several load levels and specimen thicknesses. The value of α is governed by the ratio of thickness B versus plastic zone size rp. The effect of overloads on the plastic zone and relevant constraint factor value is analysed as well. During loading, it was found, that the constraint factor value is lower after overloads than when creating monotonic plastic deformation on the same load level in a large part of the cycle. The influence of thickness effect based on different α value after overload was successfully implemented into the strip yield model. Simulation of crack growth taking into account the thickness of the specimen under variable amplitude loading shows similar behaviour like the experimental data.

The interlaminar properties of a bond joint of stacked layers in a carbon fibre-reinforced composite with a thermoplastic matrix were evaluated under static loading. The un-precracked tension specimen with an external reinforcing layer was analysed in detail in the area of a bond joint. A detailed finite element method (FEM) analysis was performed to evaluate the influence of the bond joint shape on the interlaminar cohesive forces, which are simulated using the cohesive zone model (CZM). Simple lap and tapered joints were analysed. Continuum and shell elements were utilized in the FEM analysis, and the delamination results obtained using both solutions were compared to each other; however, no significant influence of the bond joint shape on the delamination onset was observed. The FEM analysis was supported using an experimental test on an un-precracked specimen made from prepreg with a carbon fibre fabric and a polyphenylene sulphide (PPS) matrix.

Impact by foreign objects is a concern for most composite structures, requiring attention in damage threat assessment. The purpose is to identify impact damage severity and detectability for design and maintenance. Barely visible impact damage (BVID) requires special treatment due to the difficulties in detecting it by any visual inspection method. BVID can reduce the load-carrying capability of a composite structure and, therefore, it can cause severe damage. The low-velocity impact causing BVID in a composite panel was studied via a numerical method using finite elements (FEs) with the explicit dynamic integration method. A ply-by-ply three-dimensional model with cohesive zone behavior of interaction was created, enabling a detailed study of material degradation through composite thickness. Two cases with double impact and with no impact were analyzed. Impacts directed near the hole's edge caused delamination and ply degradation. Subsequently applied shear loading shows the impact influence on the strength of the panel. The numerical results confirm a decrease in the strength of the composite panel after impact, as expected, but differences in displacement behavior were also observed. According to the FE solution, buckling appears in regions of impact before rupture, while test results reported rapid failures in the compression zone and tension zone, independently, in two stages. On the other hand, the FE results of the non-impacted panel show two independent failures, as observed experimentally. As a result, the unrealistic buckling is attributed to a decrease in element stiffness during impact. In conclusion, the final strength of the impacted panel was predicted by the FE solution sufficiently. The BVID modelling approach presented in this study is useful in the case of small-scale models such as a flat panel. The research has received funding from the European Union's Seventh Framework Programme for Research, Technological Development and Demonstration within CANAL (CreAting NonconventionAl Laminates) project under grant agreement number 605583.