3D-woven Reinforcement in Composites

Abstract: Composites made from three-dimensional (3D) textile preforms can reduce  both the weight and manufacturing cost of advanced composite structures  within e.g. aircraft, naval vessels and blades of wind turbines. In this thesis composite beams reinforced with 3D weave are studied, which are intended for use as joining elements in a boltless modular design. In practice, there are a few obstacles on the way to realise the modular boltless design. There is lack of experimental data and more importantly, lack of experience and tools to predict the properties of composites reinforced with 3D-weaves. The novel material will not be accepted and used in engineering applications unless proper design methods are available. The overall aim of this thesis is to remedy these deficiencies by generating data, experience and a foundation for the development of adequate design methods. In Paper A, an initial experimental study is presented where the mechanical properties of 3D-weave reinforced composites are compared with corresponding properties of 2D-laminates. The conclusion from Paper A is that the out- of-plane properties are enhanced, while the in-plane stiffness and strength is reduced. In Paper B the influential crimp parameter is investigated and three analytical models are proposed. The warp yarns exhibit 3D crimp which had a large effect the predicted Young’s modulus as expected. The three models have different levels of detail, and the more sophisticated models generate more reliable predictions. However, the overall trends are consistent for all models. A novel framework for constitutive modelling of composites reinforced with 3D-woven preforms is presented in Papers C and D. The framework enables predictive modelling of both internal architecture and mechanical properties of composites containing 3D textiles using a minimum of input parameters. The result is geometry models which are near authentic with a high level of detail in features compared with real composite specimens. The proposed methodology is therefore the main contribution of this thesis to the field of composite material simulation. Paper E addresses the effect of crimp and different textile architectures on the mechanical properties of the final composite material. Both stiffness and strength decreases non-linearly with increasing crimp. Furthermore specimens containing 3D-woven reinforcement exhibit non-linear stress-strain behaviour in tension, believed to be associated with relatively early onset of matrix shear cracks.