The main idea behind “Quilted Stratum Process” (QSP ® ) is to create a flat blank made of unidirectional/woven thermoplastic prepreg patches instead of using uniformly shaped prepreg stack as is the case with standard thermostamping process. Thus, using QSP ® ; one can manufacture components with complex geometries by using nearly rectangular patches while still maintaining a short cycle time similar to the standard thermostamping process. The use of near-rectangular patches results in a significant material saving which is a necessity for a sustainable product development. During standard thermostamping and/or QSP ® ; the consolidation phase plays a key role in the strength and quality of the final product. This becomes even more important in the case of unidirectional thermoplastic prepregs where mechanisms such as transverse squeeze flow can impact not only the in-plane dimensions of the prepreg but also the fibre orientations within the prepreg. This work presents a unified modeling approach that combines a novel pinching shell element, a new elasto-plastic constitutive model for pinching shell in order to provide a unified solution to simulate both forming and consolidation-flow using a shell-based approach. This unique unified approach of simulating forming and consolidation provides a set of additional outputs such as the through-thickness stress, final deformed shape of the plies including the squeeze flow effect and the changes in the orientation of fibres within the plies during and after the process. This work finally demonstrates how this information can help the manufacturers to design better tooling based on the outcomes of the numerical process simulation in order to achieve a desired product quality. Additionally, one can also steer the final fibre orientation which results from the initial position of the patch, its forming and squeeze flow.

“Quilted Stratum Process” (QSP®) is a new process developed by CETIM, Ecole Centrale de Nantes and their partners which is in the category of thermoplastic composite forming. Unlike the conventional thermoforming process, a QSP® preform stack consists of several discontinuous plies. Due to the inability of using the blank-holders in this process, these discontinuous patches can experience large sliding and/or rotation. Thus, the mechanisms occurring at ply-ply interfaces, especially the interply adhesion are important and should be considered in the process simulation. A penalty based, semi-empirical contact model is proposed and implemented in the industrial code of Altair RADIOSSTM in order to model interply adhesion. This model allows sliding of plies over long distance while providing a finite adhesive strength before delamination and it has resulted in a significant improvement in the prediction of the final positions and orientation of the discontinuous patches in QSP® simulation. The model requires minimal characterization making it suitable for industrial applications.

"Quilted StratumProcess" (QSP®) is a unique process in the category of thermoplastic composite formingwith the objective to locally strengthen the composite parts by strategically stacking discontinuous UD/woven prepregs while maintaining the short cycle time of about one minute. Interply adhesion plays an important role in QSP® due to the presence of resin-rich layer at the ply-ply interface, inability to use blank holders for prepreg patches and high temperature of forming process where the resin is in melt state. Without modeling interply adhesion in the numerical simulation, plies could delaminate without any resistance which is unrealistic and it also results in incorrect final positions of the plies. Thus, a penalty based, semi-empirical contact model for interply adhesion has been developed and implemented in the industrial finite element code of Altair RADIOSSTM. This model allows large sliding of plies while providing a finite maximum interply adhesive stress before delamination. With this semi-empirical model, the final positions of the plies is predicted with better accuracy. Mots Clés : Formage, préimprégnés thermoplastiques, patchs, modélisation adhésion interplis, simulation numérique

Cells rely on an interplay of subcellular elements for motility and migration. Certain regions of motile cells, such as the lamellipodium, are made of a complex mixture of actin monomers and filaments, which polymerize at the front of the cell, close to the cell membrane, and depolymerize at the rear. The dynamic actin turnover induces the so-called intracellular retrograde flow, and it is a fundamental process for cell motility. Apart from some comprehensive mathematical models, the computational modelling of actin treadmilling has been based on simpler biophysical models. Here, we adopt a highly detailed theoretical model of the actin treadmilling process and develop a coupled unsteady finite element formulation. We clearly describe the structure and implementation of the coupled problem within the finite element method. Our numerical results show an excellent correlation with experimental results from literature and with previous models. We include time dependent effects and convective transport terms, which expose puzzling dynamics in the retrograde flow. We propose several biological scenarios to analyze the behavior of the actin treadmilling along space and time. We observed response times of the main density variables in the order of seconds. Compared with previous analytical solutions, which make assumptions related to convective transport, transient dynamics, and actin fluxes, the generic solution can have significant influence on the retrograde flow. All together, our results unveil a promising applicability of classical finite element methods to derive an in silico testing platform for the actin treadmilling processes in motile cells, which could allow for an extension to other biophysical effects.