Benoît Cosson

Optimization of the Thickness of PET Bottles during Stretch Blow Molding by Using a Mesh-free (Numerical) Method

Abstract The stretch-blow molding process of polyethylene terephthalate (PET) bottles generates some important modifications in the mechanical properties of the material. Considering, the process temperature (T > Tg) that is usually used, the material exhibits a very high viscosity and involves a strain hardening effect associated with the microstructure evolution. An anisotropic viscoplastic model coupled with induced properties, identified from experimental results of uniaxial and biaxial tensile tests previously published by Chevalier and Marco (2006), is presented in a first part of the paper. Secondly, we perform a numerical simulation to simulate the free inflation of a preform under an internal pressure with different parameters. Because the final strains are up to 300 to 400%, it generates important distortion of node distribution and we chose to use the mesh-free Constrained Natural Elements Method (C-NEM) for numerical simulation. The final goal is to use these simulations in order to fit the best parameter set leading to a quasi-homogeneous distribution of the thickness along the bottle. Homogeneous thickness implies homogeneous biaxial stretching and more uniform induced properties for the final bottle and this is an important industrial goal.

Numerical analysis of effective thermal conductivity of plastic foams

This study is dedicated to the development of a numerical finite-element solution to determine the effective thermal conductivity of extruded polymeric foam with different levels of open and closed porosity. The implemented numerical method is derived from periodic homogenization techniques used for the simulation of laser welding of composite materials. For a validation purpose, it was applied to the calculation of the effective thermal conductivity of polyethylene extruded foam for which the input data (density, cell size and distribution, porosity ratio, and extinction coefficient) were characterized experimentally. The computed results were compared with experimental data obtained by the transient plane source technique and analytical results derived from the literature. The deviation from the experimental data is five times lower than that of analytical methods. Moreover, the proposed numerical solution allows reaching higher porosity ratio and makes it possible to reduce the computation time while ensuring the same compactness ratio regardless of the calculation.

Numerical Simulation of Multi‐Axial Tensile Tests and Free Blowing of a PET Bottle Near Tg by the C‐NEM

The stretch‐blow moulding process of poly (ethylene terephthalate) bottles generates some important modifications in the mechanical properties of the material. Considering, the process temperature (T > Tg) that is usually used, the material has a very high viscosity and shows a strain hardening effect linked to the microstructure evolution. A simple visco‐plastic model has been identified from experimental results of uniaxial and biaxial tensile tests. In the present work, we first valid the identification method by a numerical simulation of the tensile tests considering heterogeneity due to the imposed boundary conditions and second, we use the numerical technique to simulate the free inflation of a preform under an internal pressure. The finite elements method has a poor efficiency in the stretch‐blow process, because the final material strain is up to 200%. This strain level generates element distortion and necessitates to often re‐mesh. In order to carry out simulations, with strain higher than 200%, ...

A method of measuring the effective thermal conductivity of thermoplastic foams

An inverse method for determining the in-plane effective thermal conductivity of porous thermoplastics was implemented by coupling infrared thermography experiments and numerical solution of heat transfer in straight fins having temperature-dependent convective heat transfer coefficient. The obtained effective thermal conductivity values were compared with previous results obtained using a numerical solution based on periodic homogenization techniques (NSHT) in which the microstructure heterogeneity of extruded polymeric polyethylene (PE) foam in which pores are filled with air with different levels of open and closed porosity was taken into account and Transient Plane Source Technique (TPS) in order to verify the accuracy of the proposed method. The new method proposed in the present study is in good agreement with both NSHT and TPS. It is also applicable to structural materials such as composites, e.g. unidirectional fiber-reinforced plastics, where heat transfer is very different according to the fiber...

Infrared welding process on composite: Effect of interdiffusion at the welding interface

In this study, the effects of the welding temperature field developed during the infrared assembly process on the joining properties of glass fibre reinforced polycarbonate/ unreinforced polycarbonate with carbon black were investigated. The temperature field and the contact time govern together the quality of the adhesion at the welding interface. The effect of the semi-transparent glass fibre reinforced polycarbonate composite / unreinforced polycarbonate composite with carbon black interface was quantified in term of quadratic distance of diffusion or diffusion depth through the welding interface. The microstructural characterizations were investigated in order to inspect the welding zones quality and to observe their failure modes. The diffusion theory has then been applied to calculate the variation of the quadratic distance of diffusion versus time at different locations. The complete self-diffusion is supposed occurring only at temperature above the polycarbonate glass transition temperature (140°C) and with a quadratic distance of diffusion superior to the mean square end-to-end distance.

Experimental and numerical analysis of laser beam transmission in continuous fiber thermoplastic composites

Thermoplastics composites offer the possibility to use welding techniques for joining, due to the ability of the polymer constituting the matrix to melt when exposed to sufficient thermal energy. Laser technology is a good alternative for continuous joining of thermoplastics composites structures. However, presence of continuous fibers at a high fiber volume fraction generates laser beam diffusion. Optimization of the process requires understanding of the physics involved during laser propagation through continuous fibres composite media. Therefore laser beam diffusion and absorption at the substrate interface is modelled using ray tracing technique. Variability of simulated weld seam can be studied by a close enough representation of the composite microstructure. This variability can also be reproduced using experimental techniques. The knowledge of material properties constituting the composite and on the fibrous architecture are then sufficient to demonstrate the limits of the laser welding process without using trial and error developments. This approach can thus be broadened to any other laser application on semi-transparent and non-homogeneous structures.Thermoplastics composites offer the possibility to use welding techniques for joining, due to the ability of the polymer constituting the matrix to melt when exposed to sufficient thermal energy. Laser technology is a good alternative for continuous joining of thermoplastics composites structures. However, presence of continuous fibers at a high fiber volume fraction generates laser beam diffusion. Optimization of the process requires understanding of the physics involved during laser propagation through continuous fibres composite media. Therefore laser beam diffusion and absorption at the substrate interface is modelled using ray tracing technique. Variability of simulated weld seam can be studied by a close enough representation of the composite microstructure. This variability can also be reproduced using experimental techniques. The knowledge of material properties constituting the composite and on the fibrous architecture are then sufficient to demonstrate the limits of the laser welding process wit...