An automated method for counting propagating matrix tunnelling cracks for use in mechanical testing of Glass Fibre Reinforced Plastic (GFRP) laminates under quasi-static and fatigue loading is

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., "Fatigue damage evolution in GFRP laminates with constrained off-axis plies", Composites Part A, http://dx.doi. org/10.1016/j.compositesa.2017. method with a data mining approach and applying these to large data sets obtained during fatigue tests. It is shown that for a constant stress level, the stochastic nature of off-axis crack initiation and crack growth is accurately modelled by the Weibull distribution, with the distribution parameters being efficiently derived using the developed approach. The data-rich characterisation provides new insight in the crack density evolution process for VA and C-T loading, as well as derived Weibull distribution parameters in combination with the classical S-N curves and Paris' Law relationship.Hence, providing an improved approach that includes the stochastic and deterministic information for physically based modelling of crack density evolution for fatigue loading.Glud, J.A., Dulieu-Barton, J.M., Thomsen, O.T. and Overgaard, L.C.T., "Fatigue damage evolution in GFRP laminates with constrained off-axis plies", Composites Part A, http://dx

This paper investigates the behavior of woven prepreg plies being placed on a weakly double curved mold by a robot. It is essential that the draped configuration is free from wrinkles. The baseline is a virtual draping environment that can plan and simulate robot draping sequences. It consists of a kinematic mapping algorithm for obtaining target points for the grippers on the mold surface. A simple motion planner is used to calculate the trajectories of the grippers. Here, two conceptually different draping strategies are employed. Finally, the two generated draping sequences are simulated using a transient, non-linear finite element model and compared w.r.t. their predicted wrinkle formations. Material data are obtained by means of tension, bias-extension and cantilever tests. The numerical examples show that the virtual draping environment can aid in developing the automatic draping system but that the generation of feasible draping sequences is highly path dependent and non-trivial.

A cohesive finite element implemented as a user programmable feature (UPF) in ANSYS Mechanical is presented. Non-standard post-processing capabilities compared to current available cohesive elements in commercial finite element software packages have been defined and implemented. A description of the element formulation and the post-processing options are provided. Simulation studies are presented which serves to verify the implementation and compare the performance to ANSYS INTER205 cohesive element. The results show that the implemented element performs better in terms of ability to converge to a solution and requires fewer iterations to converge in the incremental Newton-Raphson solution procedure used. Additionally, a sensitivity study about the typical remedy to obtain convergent solutions having coarse meshes by lowering the onset traction is conducted. The study brings new insight to the effect of lowering the onset traction and recommendations of practical usage in case of coarse meshes are outlined.

A model to predict off-axis crack evolution in multidirectional laminates subjected to multiaxial loading is proposed. The model applies multi-scale stress and local fracture mechanics analyses to distinguish between two microscopic damage mechanisms, which govern the damage evolution, as well as determining the magnitude of the damage evolution rate associated with each microscopic damage mechanism. The multi-scale analysis is based on the GLOB-LOC off-axis crack damage model, which is extended to include substantial new capabilities such as the influence of crack face sliding interaction and prediction of variations in the stress field due to the local crack density. The extension of the GLOB-LOC model introduces physically based multiaxial fatigue criteria for off-axis crack initiation and mixed-mode off-axis crack propagation. The extended GLOB-LOC model is implemented and it is demonstrated that good predictions are obtained for the damage evolution under various multiaxial stress conditions. Furthermore it is shown that the model only requires input from two different multiaxial stress states to obtain the material parameters for a given FRP ply.

A model for the off-axis crack propagation in laminated fibre reinforced polymer composites subjected to multiaxial fatigue loadings is presented. On the basis of several observations reported in the literature, the crack propagation phenomenon can be seen as the result of a series of micro-scale events occurring ahead of the crack tip within a process zone. The mixed mode loading condition defines the type of the micro-scale events which occur in the process zone and lead to fatigue crack propagation. Based on this evidence and by using a multiscale approach to determine the micro-scale stress fields in the matrix, two simple parameters are defined for predicting the crack growth rate through a Paris-like law. By extracting the proposed

The data published with this paper is obtained during fatigue testing of a unidirectional non-crimp fabric based glass fibre composite by means of ex-situ X-ray CT and in-situ transilluminated white light imaging experiments. The data experimentally shows the damage initiation and progression under fatigue loading both in terms of off-axis cracks in the thin supporting backing fibre bundles and fibre fractures in the load carrying fibre bundles. X-ray CT data comparing the loaded and unloaded state of damage regions by means of a tension clamp solution are also published with this paper.