Particle-Based Geometric and Mechanical Modelling of Woven Technical Textiles and Reinforcements for Composites

Technical textiles are increasingly being engineered and used in challenging applications, in areas such as safety, biomedical devices, architecture and others, where they must meet stringent demands including excellent and predictable load bearing capabilities. They also form the bases for one of the most widespread group of composite materials, fibre reinforced polymer-matrix composites (PMCs), which comprise materials made of stiff and strong fibres generally available in textile form and selected for their structural potential, combined with a polymer matrix that gives parts their shape. Manufacturing processes for PMCs and technical textiles, as well as parts and advanced textile structures must be engineered, ideally through simulation, and therefore diverse properties of the textiles, textile reinforcements and PMC materials must be available for predictive simulation. Knowing the detailed geometry of technical textiles is essential to predicting accurately the processing and performance properties of textiles and PMC parts. In turn, the geometry taken by a textile or a reinforcement textile is linked in an intricate manner to its constitutive behaviour. This thesis proposes, investigates and validates a general numerical tool for the integrated and comprehensive analysis of textile geometry and constitutive behaviour as required toward engineering applications featuring technical textiles and textile reinforcements. The tool shall be general with regards to the textiles modelled and the loading cases applied. Specifically, the work aims at fulfilling the following objectives: 1) developing and implementing dedicated simulation software for modelling textiles subjected to various load cases; 2) providing, through simulation, geometric descriptions for different textiles subjected to different load cases namely compaction, relaxation and shear; 3) predicting the constitutive behaviour of the textiles undergoing said load cases; 4) identifying parameters affecting the textile geometry and constitutive behaviour under evolving loading; 5) validating simulation results with experimental trials; and 6) demonstrating the applicability of the simulation procedure to textile reinforcements featuring large numbers of small fibres as used in PMCs. As a starting point, the effects of reinforcement configuration on the in-plane permeability of textile reinforcements, through-thickness thermal conductivity of PMCs and in-plane stiffness of unidirectional and bidirectional PMCs were quantified systematically and correlated with specific geometric parameters. Variability was quantified for each property at a constant fibre volume fraction. It was observed that variability differed strongly between properties; as such, the simulated behaviour can be related to variability levels seen in experimental measurements. The effects of the geometry of textile reinforcements on the aforementioned processing and performance properties of the textiles and PMCs made from these textiles was demonstrated and validated, but only for simple cases as thorough and credible geometric models were not available at the onset of this work. Outcomes of this work were published in a peer-reviewed journal [101]. Through this thesis it was demonstrated that predicting changes in textile geometry prior and during loading is feasible using the proposed particle-based modelling method. The particle-based modelling method relies on discrete mechanics and offers an alternative to more traditional methods based on continuum mechanics. Specifically it alleviates issues caused by large strains and management of intricate, evolving contact present in finite element simulations. The particle-based modelling method enables credible, intricate modelling of the geometry of textiles at the mesoscopic scale as well as faithful mechanical modelling under load. Changes to textile geometry and configuration due to the normal compaction pressure, stress relaxation, in-plane shear and other types of loads were successfully predicted. During simulation, particles were moved randomly until a stable state of minimum strain energy in the system was reached; as particles moved upon iteration, the configuration of fibres in the textile changed under constant boundary conditions. Then boundary conditions were altered corresponding to strains imposed on the textile, and the system was iterated again towards a new state of minimum strain energy. The Metropolis algorithm of the Monte Carlo method was adopted in this specific implementation. The method relies on a statistical approach implemented in computational algorithms. In addition to geometrical modelling, the proposed particle-based modelling method enables the prediction of major elements of the constitutive behaviour of textiles and textile reinforcements. In fact, prediction of the constitutive behaviour is integral to the prediction of the meso-scale geometry. Simulation results obtained from the proposed particle-based modelling method were validated experimentally for yarns, single-layer textiles and multi-layer textiles undergoing compaction. Validation work showed that the particle-based modelling method replicates reality very faithfully, and it also showed the suitability of including Gutowski's function along with Hertz' function for representing lateral compaction of yarns. The procedure and results were accepted in final form for publication in a peer reviewed journal [104]. The capability of the proposed particle-based modelling method towards replicating the time-dependent relaxation and reconfiguration of woven textiles subjected to compaction loading was investigated. The capability, which was demonstrated for single and double-layers of plain woven textiles, is intrinsic to the modelling method. The method is unique in the fact that in contrary to work previously reported in the literature, it models the compaction and the relaxation seamlessly in the same simulations and environment. This work is being finalised towards submission for publication in a peer reviewed journal [103]. The proposed particle-based modelling method was also used for modelling in-plane shear in woven textiles. Simulation results were validated experimentally for a single-layer plain woven textile. Validation work showed that the particle-based modelling method reproduces experimental data and published trends very well. A novel algorithm for modelling friction was introduced, leading to results being obtained from a significantly less computationally demanding procedure in these simulations. This work was submitted for publication in a peer reviewed journal [102]. Finally the thesis discusses early work towards the application of the method to carbon fibre fabrics through the description of expansion algorithm (EA) to be used in modelling textiles made of yarns featuring very large numbers of fibres. Furthermore, additional modelling work is presented towards further manufacturing process involving technical textiles, namely textile bending and punching. The latter part is presented as early steps towards future work