Didier Delaunay

Determination of Temperature Variable Properties of Composite Materials: Methodology and Experimental Results

In the present article we discuss a method for the determination of temperature variable properties of composite materials. The method involves thermophysical properties (specific heat and thermal conductivity) and rate of cure. The method is general and based on the combined analysis of heat transfer in thin and thick pieces of material. A simulation model is then developed to predict the cure response and heat transfer that occur in composite material during fabrication. It is validated by experimental results obtained with an epoxy resin/glass fiber composite.

Estimation of thermal conductivity of thermoplastics under moulding conditions: an apparatus and an inverse algorithm

The thermal conductivity of thermoplastics is measured under moulding conditions (high pressure and high temperature). A specific apparatus has been designed and is described. A parameter estimation method is used for the experimental data processing. It is based on the resolution of a 1-D non-linear inverse conduction problem. The optimisation algorithm developed to solve the problem, is efficient and stable. Confidence intervals of the estimated parameters take into account errors both in the temperature measurements and in the parameters of the model. Heat capacity is estimated from calorimetric measurements, error analysis on the estimated conductivity is discussed, especially in the phase change interval. Numerical validation and experimental examples are presented.

Thermal conductivity of unidirectional reinforced composite materials-experimental measurement as a function of state of cure

The thermal conductivity of a thermosetting polymeric matrix-based composite material is a thermophysical parameter, which varies significantly during the transformation of the matrix. These variations have a considerable effect on heat transfers within a thick piece in the process and therefore on transformation kinetics of the polymer. In order to address the analysis method used to determine the parameter variations according to both temperature and state of cure of the transformation, the experimental device developed by the authors is first described. Then, the results, experimentally obtained by inverse heat conduction with a composite of Fiberglas® and epoxy resin, are compared with those given by an effective thermal conductivity model.

Heat Transfer and Crystallization Modeling during Compression Molding of Thermoplastic Composite Parts

We present in this paper, the coupling of heat transfer to the crystallization of composite in a closed mold. The composite is based on thermoplastic resin (low viscosity PA 66) with glass fiber (50% volume fraction). In order to realize this coupling, an accurate characterizationof thermo physical properties in process conditions, especially in the molten and solid state is needed. In addition, theidentification of the parameters of crystallization kinetics is required. Therefore, we present the methods that were used to study the thermo physical properties as the thermal conductivity, heat capacity and the specific volume. Moreover, the kinetic of crystallization was estimated over a large temperature range by using Flash DSC and classical DSC. In order to validate the measurements, the whole process was modeled by finite elements. The model includes the resolution of the strong coupling between the heat transfer and crystallization. Finally, the experimental and numerical results were compared.

Estimation of effective thermal conductivity tensor from composite microstructure images

The determination of the effective thermal properties of inhomogeneous materials is a long-standing problem of continuously interest. The impressive number of methods developed to measure or estimate the thermal properties of composite materials clearly exhibits the importance given to their knowledge. Homogenization models are a cheap way to determine or predict them. Many different approaches of homogenization were developed, but the last advances are credited to numerical methods. In this study, a new computational model is developed to estimate the 2D thermal conductivity tensor and the thermal main directions of a pure carbon/epoxy unidirectional composite. This tool is based on real composite microstructure.

Implementation of an inverse method for identification of reticulation kinetics from temperature measurements on a thick sample

Abstract The aim of this article is to identify a reaction function involved in a model of vulcanization by using experimental study on thick pieces of rubber. The methods of determination of the parameters of the model are described, the inverse method is explained, results are given and commented on.

Analysis and Control of Heat Transfer in an Industrial Composite Mold in RTM Polyester Automotive Process

A composite mold was developed to manufacture pieces by the resin transfer molding process. This mold can be instrumented with different sensors which allows us to obtain great amounts of information during realistic conditions of production. The main features of the mold, as well as the used metrology, are detailed. The results of different experiments and the influence of temperature on the molding are presented. The experimental heat fluxes are compared to the predictions of a kinetic model. A thermal optimization of the curing cycle is proposed.

Optimization of the Incident IR Heat Flux upon a 3D Geometry Composite Part (Carbon/Epoxy)

The main purpose of this study is to cure a 3D geometry composite part (carbon fiber reinforced epoxy matrix) using an infrared oven. The work consists of two parts. In the first part, a FE thermal model was developed, for the prediction of the infrared incident heat flux on the top surface of the composite during the curing process. This model was validated using a reference solution based on ray tracing algorithms developed in Matlab®. Through the FE thermal model, an optimization study on the percentage power of each infrared heater is performed in order to optimize the incident IR heat flux uniformity on the composite. This optimization is performed using the Matlab® optimization algorithms based on Sequential Quadratic Programming and dynamically linked with the FE software COMSOL Multiphysics®. In a second part, the optimized parameters set is used in a model developed for the thermo-kinetic simulations of the composite IR curing process and the predictions of the degree of cure and temperature distribution in the composite part during the curing process.

Experimental Determination and Modeling of Thermal Conductivity Tensor of Carbon/Epoxy Composite

In this study, the effective thermal conductivity tensor of carbon/epoxy laminates was investigated experimentally in the three states of a typical LCM-process: dry-reinforcement, raw and cured composite. Samples were made of twill-weave carbon fabric impregnated with epoxy resin. The transverse thermal conductivity was determined using a classical estimation algorithm, whereas a special testing apparatus was designed to estimate in-plane conductivity for different temperatures and different states of the composite. Experimental results were then compared to modified Charles & Wilson and Maxwell models. The comparison showed clearly that these models can be used to accurately and efficiently predict the effective thermal conductivities of woven-reinforced composites.

A New PvT Device for the Thermoplastics Characterization in Extreme Thermal Conditions

In this work, we present an apparatus associated to a methodology that is able to determine simultaneously and according to temperature (up to 400°C) the specific volume (up to 200MPa), the thermal conductivity and the temperature function of the crystallization kinetics. The PvT-XT is a home-built device that is able to impose and quantify 1D heat transfer through the radius of a sample. This apparatus controls the applied pressure on the sample while measuring its volume variations. The associated moving boundary model takes into account the temperature and crystallinity gradients. Specific volume is determined from direct measurement whereas inverse methods are used to estimate the thermal conductivity and the crystallization kinetics (with cooling rates up to 200K/min). Specific volume measurements are compared with literature results and exhibit a very good agreement. Thermal conductivity identified in the present paper is also very close to literatures values. Finally identification of kinetic function values is consistent with previous studies.