is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. The poly ethylene terephthalate near the glass transition temperature highlights a strongly non linear elastic and viscous behaviour when biaxially stretched at high strain rates representative of the injection stretch blow moulding process. A non linear visco-hyperelastic model, where characteristics are coupled to the temperature, has already been identified from equi-biaxial tension experimental results. The weak form of the mechanical part of the model is presented and implemented into a finite element code developed in the Matlab environment and validated by comparing numerical simulation of equibiaxial testing with the analytical solution in the isothermal case. Considering the thermal aspects, an experimental study, where PET sheets are heated using infrared (IR for short) lamps is also presented. The modeling of the IR radiation of the sheet helps to identify the thermal properties of the PET. The thermal model is then implemented in the finite element code, coupled to the 2D viscoelastic model. A discussion is made to justify the accuracy of the assumption made on homogeneity of the temperature field through the thickness. The simulation of the 2D plane stress equibiaxial test shows the important influence of the thermal aspects and the coupled thermo-mechanical software is used to quantify the selfheating phenomenon in the case of the biaxial elongations of PET sheets at high strain rates.

Homogeneous nucleation rate measurements of 1-butanol in helium: A comparative study of a thermal diffusion cloud chamber and a laminar flow diffusion chamberThe influence of buoyant convection on the operation of the upward thermal diffusion cloud nucleation chamber J. Chem. Phys. 111, 8013 (1999); 10.1063/1.480274 Two-dimensional transport and wall effects in the thermal diffusion cloud chamber. II. Stability of operation J. Chem. Phys. 106, 624 (1997); 10.1063/1.473401 Two-dimensional transport and wall effects in the thermal diffusion cloud chamber. I. Analysis and operations criteriaThe formation of clouds resulting from the homogeneous condensation of vapor phase diluted in a background or carrier gas was studied numerically. The effect of the background gas on the nucleation process in a cloud chamber heated from below is discussed. The computations were performed using 1-propanol as the condensable gas and helium, hydrogen, nitrogen, and argon, respectively, as carrier gases. Results of the simulation conducted show that large differences appear in the cloud formation when operating with hydrogen or helium, and with argon or nitrogen for which the onset of convective motions are predicted. Therefore, the isothermal patterns and streamlines are similar to those obtained in the case of Rayleigh-Bénard instabilities. The influence of the thermal Rayleigh number on the nucleation process is also considered, and it is shown that supersaturation isolines exhibit complex distortions for supercritical thermal Rayleigh numbers. As a consequence, only small zones of important nucleation rate are observed.

Initial heating conditions and temperature effects (heat transfer with air and mould, self-heating, conduction) have important influence during the ISBM process of PET preforms. The numerical simulation of infrared (IR) heating taking into account the air convection around a PET preform is very time-consuming even for 2D modelling. This work proposes a simplified approach of the coupled heat transfers (conduction, convection and radiation) in the ISBM process based on the results of a complete IR heating simulation of PET sheet using ANSYS/Fluent. First, the simplified approach is validated by comparing the experimental temperature distribution of a PET sheet obtained from an IR camera with the numerical results of the simplified simulation. Second, we focus on the more complex problem of the rotating PET preform heated by IR lamps. This problem cannot be modeled in 2D and the complete 3D approach is out of calculation possibilities actually. In our approach, the IR heating flux coming from IR lamps is calculated using radiative laws adapted to the test geometry. Finally, the simplified approach used on the 2D plane sheet case to model the air convection is applied to the heat transfer between the cylindrical preform and ambient air using a simple model in Comsol where only the preform is meshed. In this case, the effect of the rotation of the preform is taken into account in the radiation flux by a periodic time function. The convection effect is modeled through the thermal boundary conditions at the preform surface using the heat transfer coefficients exported from the simulations of the IR heating of a PET sheet with ANSYS/Fluent. The temperature distribution on the outer surface of the preform is compared to the thermal imaging for validation.

of the convection and radiation heat transfers during the infrared heating of PET sheets and preforms Nomenclature. AbstractInitial heating conditions and temperature effects have important influence during the ISBM process of PET preforms. The numerical simulation of infrared (IR) heating taking into account the air convection is very time-consuming even for 2D modelling. This work proposes a simplified approach of the coupled heat transfers in the ISBM process based on the results of a complete air convection and IR heating simulation of PET sheet using ANSYS/Fluent. First, the simplified approach is validated by comparing the experimental temperature distribution of a PET sheet obtained from an IR camera with the numerical results of the simulation. Second, we focus on the PET preform heated by IR lamps. This problem cannot be modelled in 2D and the complete 3D approach is out of calculation possibilities actually. In our approach, the IR heating flux coming from IR lamps is calculated using radiative laws adapted to the test geometry. Finally, the simplified approach used on the 2D plane sheet case to model the air convection is applied to the heat transfer between the preform and ambient air using a simpler model in Comsol where only the preform is meshed.The temperature distribution on the outer surface of the preform is compared to the thermal imaging for validation.

Effects of temperature: initial heating conditions or self heating during the process, are very important during the injection stretch blow moulding (ISBM) process of PET bottles. The mechanical characteristics of the final products, which are mainly controlled by the final thickness and the orientation of the molecular chains, depend strongly on the process temperature. Modelling the heat transfer during the ISBM process is therefore necessary. In the first part of this paper, an experimental study is presented in order to measure the initial temperature distribution and to identify the thermal properties of the PET. An infrared camera has been used to determine the surface temperature distribution of the PET sheets which are heated by infrared (IR) lamps. The Monte Carlo method is used to identify the parameters best fit from the temperature evolution. In the second part, a thermo-viscohyperelastic model is used to predict the PET behaviour, taking into account the strain rate and temperature dependence. A finite element approach implemented in matlab is used to achieve the numerical simulation.