Development of a multigrid finite difference solver for benchmark permeability analysis

A finite difference solver, dedicated to flow around fibre architectures is currently being developed. The complexity of the internal geometry of textile reinforcements results in extreme computation times, or inaccurate solutions. A compromise between the two is found by implementing a multigrid algorithm and analytical solutions at the coarsest level of discretisation. Hence, the computational load of the solver is drastically reduced.\ud This paper discusses the main features of the 3D multigrid algorithm implemented as well as the implementation of the analytical solution in the finite difference scheme. The first tests of the solver on the permeability benchmark lithographic reference geometry are discussed.\ud Several tests were performed to assess the accuracy and the reduction in calculation time. The methods prove to be both accurate and efficient. However, the code is developed in Matlab© and hence is relatively slow. A C++ code is currently under development to achieve acceptable calculation times

Electrical Conductivity Characterisation of Stochastic Zigzag Paths in Unidirectional C/PAEK

Induction welding has emerged as a promising technology for fusion bonding of carbon fibre reinforced thermoplastic composites. The process relies on the generation of eddy currents, induced by an alternating electromagnetic field, within a composite susceptor. The eddy current density and the resulting heat generation is directly influenced by the electrical conductivity of the carbon fibrenetwork, making accurate measurement of this orthotropic electrical property crucial for physics-based process simulations. The present study focuses on the characterisation of the in-plane transverse electrical conductivity in unidirectionally reinforced PAEK composites using the six-probe method. Theinvestigation specifically addresses the stochastic nature of the conductive paths within the fibre networks by considering the effects of the specimen dimensions and the uniformity of the current density field. The conductivity data obtained within this study is found to be consistent with earlier characterisation efforts that employed a different analysis technique. The agreement serves as a reliable validation of the methodology used in the previous study and provides valuable insights for future research in the field of electrical characterisation. <br/

Laser Assisted Fibre Placement of Thermoplastic Composites:From the theory behind Disney movies to aircraft

Poster presentation at the 26th Engineering Mechanics Symposium, hosted by the Graduate School on Engineering Mechanics. Prize won for best submission in the poster contes

Transverse squeeze flow of fibre reinforced thermoplastic composites

Transverse squeeze flow is one of the deformation mechanisms that govern the forming of molten fiber reinforced thermoplastic composites. It is typically described by a transverse bulk viscosity, dictating the resistance against the flow of the combined constituents. In this work, the squeeze flow method was used to characterize the transverse viscosity of carbon fiber reinforced low-melting PAEK at three different compression rates. The experiments were recorded with a camera and the video images were analyzed to obtain the flow fields. A power law fluid model was fitted to the logged data, but found to be unable to describe the material behavior at all compression rates. Moreover, the video analyses indicated discrepancies between the observed specimen deformations and those predicted by the model. Future studies need to focus on the description of the squeeze flow behavior of UD C/LM-PAEK by different models (viscous, viscoelastic), using video-captured deformations for numerical fitting of the models.</p

Towards the combination of automated lay-up and stamp forming for consolidation of tailored composite components

A process route is proposed where automated lay-up is followed by stamp forming for the manufacturing of load carrying components of thermoplastic composite. The focus is on rapid lay-up, rather than in situ consolidation, while the final consolidation quality and shape are achieved by stamp forming. An experimental study offers improved understanding of the relation between blank preconsolidation quality and final quality and the role of the prepreg. Two C/PEEK prepregs are processed into blanks by ATL and AFP and subsequently stamp formed. The consolidation quality of the stamped blanks was characterized by C-scans, micrographs and density measurements, while the mechanical performance was evaluated based on flexural tests. The results demonstrate the key role of the prepreg, especially thickness variations, in the consolidation process, but also that high quality laminates can be obtained

Stress analysis of bias extension specimens

The Bias Extension test is commonly used for material characterisation in shear, providing essential input to composites forming simulations. Specimens of different sizes are used, with some preference for the minimum length-to-width ratio of 2. A static equilibrium analysis is presented to derive the forces and stress distribution in a test specimen of this minimum aspect ratio. The stress distribution is shown to depend on two variables, while usually only one (the pulling force) is measured. The central region of relatively longer specimens is generally subject to non-homogeneous boundary conditions, causing non-uniform deformations which can hamper accurate material characterisation. In addition, the analysis demonstrates that the major part of the pulling force is carried by the outer fibres, further emphasizing the need for critical preparation and evaluation of bias extension testing if high accuracy characterisation is needed