A consolidation process model for film stacking glass/PPS laminates

The applied pressure, processing temperature and holding time influence the\ud consolidation of thermoplastic laminates. A model to optimise the processing\ud parameters is proposed. The influence of heating rate, processing temperature and pressure is investigated. Short textile impregnation times, in the order of seconds, are predicted. The model is validated in an experimental programme

Towards a process simulation tool for the laseer assisted tape placement process

A combined optical and thermal model for the laser assisted tape placement process is presented. The optical model adopts a ray tracing procedure, based on the Fresnel equations, to predict the incident heat flux on the tape and substrate near the nip-point. The heat flux distribution is subsequently used in a one-dimensional thermal model to predict the temperature distribution in the tape and substrate. The results demonstrate that for small incident laser angles a part of the laser light is reflected at the surface, which significantly influences the temperature distribution in the nip-point. The presented model allows, with a weld strength and consolidation model, optimization of the processing parameters

A state-rate model for the transient wall slip effects in ply-ply friction of UD C/PAEK tapes in melt

Ply-ply slippage is one of the key deformation mechanisms occurring during hot press-forming of thermoplastic composite laminates. Advanced forming simulations, required for defect-free manufacturing, rely on accurate constitutive models for these deformation mechanisms. In this work, we propose a relative simple, yet accurate, transient model to describe the start-up friction response of UD C/PAEK tapes. The model combines a White–Metzner viscoelastic fluid with a state-rate model for the evolution of wall slip near the fiber–matrix interface, describing the disentanglement of surface polymer chains followed by the settlement of these chains in a new equilibrium state. This allows prediction of the stress growth at start-up and the transition from peak to steady-state friction, from smooth to sharp with increasing sliding rate, as well as the magnitude of the peak and steady-state friction. We obtained a good correlation between the modeled and measured friction response for different sliding rates

Textile impregnation with thermoplastic resin - models and application

One of the key issues of the development of cost-effective thermoplastic composites for the aerospace industry is the process quality control. A complete, void free impregnation of the textile reinforcement by the thermoplastic resin is an important measure of the quality of composites. The introduction of new, more thermal resistant and tougher polymers is accompanied by a large number of trial and error cycli to optimise the production process, since the polymer grade strongly influences the processing conditions. Therefore, a study on the impregnation is performed. Thermoplastic manufacturing processes are often based on pressure driven, transverse impregnation, that can be described as a transient, non-isothermal flow of a non-Newtonian fluid, where a dual scale porosity is assumed for the reinforcement's internal geometry. Meso- and micro scale models of isothermal flow revealed a limited sensitivity to the process conditions at the bundle scale for high pressure processes such as plate pressing, with an increasing sensitivity for lower pressures as apply for autoclave processes. The process conditions are significant for the quality of impregnation at filament scale. Specific combinations of pressure, viscosity and bundle compressibility can lead to void formation inside the bundles, as confirmed by microscopic analysis. The methodology developed has been translated to a ready-to-use design tool for the implementation of new polymers

Modeling anisotropic friction in triaxial overbraiding simulations

Triaxial overbraiding is a highly intricate textile manufacturing process that involves interlacing yarns in three directions, enhancing reinforcement of the final composite compared to biaxial braids. Predictive process simulation is a cost-effective approach to optimizing the manufacturing process. Previous research on biaxial overbraiding simulations indicates that yarn-yarn friction has a significant effect on the braid angle and convergence zone length. This study presents an extended yarn interaction model; it utilizes a fast frontal approach and a Eulerian on Lagrangian method to simulate the complex interlacing of multiple yarns in triaxial overbraiding, including yarn-yarn and yarn-ring friction. Experiments were conducted to evaluate the effect of UD yarn tension on the convergence zone length and braid angle, and to validate the simulations. The model validation shows that a recently proposed anisotropic yarn-yarn friction model predicts braid angle more accurately than an isotropic friction model

A mesoscopic model for inter-yarn friction

Friction between yarns is a crucial phenomenon in fabric manufacturing processes, and it becomes more complex when using lubrication agents to improve processing. This work presents an experimental investigation of the frictional behaviour of different combinations of yarns under dry and wet conditions, as occurring in overbraiding processes. The experiments were designed to maintain a constant yarn tension, and subsequently also a constant normal force and contact area during the test. Both the inter-yarn angle and the normal force significantly influence the friction coefficient. The additional contribution of the capillary force results in consistently higher friction coefficients for the water-lubricated yarns compared to the dry yarns. An anisotropic friction model is proposed to capture the influence of the inter-yarn angle, normal force, and capillary effects observed during the experiments. The model shows that the friction follows Amontons’ friction at high external normal forces and Howell’s friction at moderate normal forces

On crystallisation and fracture toughness of poly(phenylene sulphide) under tape placement conditions

Fibre reinforced thermoplastic tapes are subjected to high heating and cooling rates during the tape placement process. Such high cooling rates can significantly inhibit the crystallisation of the thermoplastic polymer and thereby affect its mechanical properties, such as strength or toughness. In the present work, the crystallisation of poly(phenylene sulphide) (PPS) subjected to high cooling rates was investigated using a fast scanning calorimeter. The PPS was found to be unable to crystallise when subjected to cooling rates higher than 20°C s−1. The influence of the degree of crystallinity on fracture toughness was investigated using an essential work of fracture approach. The amount of plastic work during the fracture process was found to decrease after moderate annealin

Prediction of the in-plane permeability and air evacuation time of fiber-placed thermoplastic composite preforms with engineered intertape channels

The two main void removal mechanisms during vacuum-bag-only (VBO) consolidation of thermoplastic composites are through-thickness diffusion and in-plane air evacuation. The automated fiber placement (AFP) process allows for the creation of preforms with an engineered intertape channel network by deliberately introducing spacing between the tapes that can facilitate air evacuation during the VBO consolidation. However, it is unclear what dimensions of the intertape channels allow for effective in-plane air evacuation. The current research presents a predictive simulation tool to optimize the intertape channel dimensions for effective in-plane air evacuation. An analytical method is developed to calculate the in-plane permeability tensors of the composite preform with uniform intertape channel dimensions. In addition, a more elaborate mesoscale method is developed that estimates the in-plane permeability tensor of the engineered intertape channel network based on the distributions in intertape channel dimensions. Finally, a finite difference model is implemented to calculate the time required for air evacuation as a function of the in-plane permeability tensors of the preform and its in-plane dimensions. The results from the models indicated that in-plane air evacuation through the engineered intertape channel network is quick, and it takes only a few minutes to evacuate 99% of the air from large preforms like fuselage panels