Cure shrinkage in the thermoset matrix is the major source of cure-induced defects in composite p... more Cure shrinkage in the thermoset matrix is the major source of cure-induced defects in composite parts for industrial applications. Thus its correct determination is very important to optimize the composite fabrication process. In general, volume chemical shrinkage of resin is tested and assuming it isotropic, rule of mixture or a homogenization technique is used to model the linear chemical shrinkage of composite. Some studies are also found in the literature on the measurement of linear chemical shrinkage of very small composite samples under atmospheric pressure. In the present article, a new setup is presented for the measurement of evolution of in-plane chemical shrinkage of thermoset laminated composite during curing. Using this setup, characterization of mass scale samples was done under pressure and heating ramp conditions. Degree of cure of composite during the test was determined using differential scanning calorimeter (DSC). Results show that chemical shrinkage in the comp...
In this paper, we present an application of fibres optic sensors to the studies of the Resin Tran... more In this paper, we present an application of fibres optic sensors to the studies of the Resin Transfer Molding process. We present in a first time our experiments devices. Then, two fibres optics sensors are described and their associated exploitation means too. Finally few experimental results are presented and described. So we show that it is possible to measure temperature, cure degree and material change with a simple sensor. With a more complicated one we can also measure curing reaction stress.
ABSTRACT The quality of thermoplastic parts strongly depends on their thermal history during proc... more ABSTRACT The quality of thermoplastic parts strongly depends on their thermal history during processing. Heat transfer modelling requires accurate knowledge of thermophysical properties and crystallization kinetics in conditions representative of the forming process. In this work, we present a new PvT apparatus and associated method to identify the crystallization kinetics under pressure. The PvT-xT mould was designed for high performance thermoplastics: high temperature (up to 400°C), high cooling rate (up to 200 K/min) and very high pressure (up to 200 MPa). Specific volume measurements were performed at a low cooling rate to avoid a thermal gradient. The crystallization kinetics under pressure can be identified for a wide range of cooling rates by an inverse method taking into account the thermal and crystallinity gradients. Since identification is based on volume variations, the proposed methodology is non-intrusive. Furthermore, the enthalpy released by the crystallization was measured during the experiment by a heat flux sensor located in the moulding cavity.
The crystallization of polymers is commonly restricted in between the equilibrium melting tempera... more The crystallization of polymers is commonly restricted in between the equilibrium melting temperature of crystals and the glass transition temperature. Study of the isothermal crystallization, close to the glass transition temperature, is complicated since nucleation and crystallization must be avoided during the approach of the temperature of interest. It requires cooling at a rate, which is distinctly higher than the maximum rate of nucleation. In fact, the cooling capacity of standard differential scanning calorimetry (DSC) is often insufficient to highly super cool the melt before onset of nucleation or ordering processes. For that reason, the Flash DSC 1 was used, where the cooling rate can reach more than 1000 Kelvin per second, which has allowed studying the isothermal crystallization kinetics in a large temperature range.
We report below about the control of processing of composite materials in particular carbon fibre... more We report below about the control of processing of composite materials in particular carbon fibre dyed into epoxy resin. In the aeronautic industry, structures made of such composite materials have a very high "mechanical property to weight" ratio and can for this reason successfully compete with metallic ones. Their utilisation is constantly increasing in this industry and this growth is
Composites Part A: Applied Science and Manufacturing, 2015
ABSTRACT In Liquid Composite Molding (LCM) processes the saturation of the reinforcement by the r... more ABSTRACT In Liquid Composite Molding (LCM) processes the saturation of the reinforcement by the resin may induce the creation of porosity in the preform affecting the final properties of the composite. The purpose of this work concerns the development of an experimental protocol and the associated modeling to identify the dynamic saturation curve during filling by taking advantage of sharp contrasts of thermal properties existing between dry and fully-saturated reinforcement. To identify saturation, several injections were performed with a laboratory RTM mold for which thermal design allows accurate control of heat transfer. Several heat flux sensors were used to identify the saturation curve. Sensitivity analysis proves the feasibility of the method. The results are compared with a conductometric method with good agreement. Evolution of residual voids identified for several flow rates are also consistent with those expected according to the capillary number.
Injection molding is the most widely used process in the plastic industry. In the case of semi-cr... more Injection molding is the most widely used process in the plastic industry. In the case of semi-crystalline polymer, crystallization kinetics impacts directly the quality of the piece, both on dimensional and mechanical aspects. The characterization of these kinetics is therefore of primary importance to model the process, in particular during the cooling phase. To be representative, this characterization must be carried out under conditions as close as possible to those encountered in the process: high pressure, high cooling rate, shearing, and potential presence of fibers. However, conventional apparatus such as the differential scanning calorimeter do not allow to reach these conditions. A PVTalpha apparatus, initially developed in the laboratory for the characterization of thermoset composites, was adapted to identify the crystallization kinetics. The aim of the presented study is to demonstrate the feasibility of the identification. This device allows the molding of a circular sample of 40 mm diameter and 6 mm thick by controlling the applied pressure on the sample and the temperature field on its surfaces. This mold is designed such as heat transfer is 1D within the thickness of the sample. It is equipped with two heat flux sensors to determine the average crystallization rate through the thickness and a displacement sensor for the determination of the volume change. The heat transfer problem between the polymer and the molding cavity is modeled by using a 1D conduction problem with a moving boundary, in which the control volume is a uniform temperature disk with a variable volume, and coupled to a crystallization kinetic model. An inverse method is used to identify the parameters of the crystallization kinetic model by minimizing an objective function based on the difference between the evolutions of the experimental and computed volume of the sample. The first validation of this methodology was to compare the kinetic parameters identified with this apparatus with those obtained from DSC experiments, i.e. without additional pressure and at low cooling rates. A good agreement was obtained between both methods. A second validation was to compare experimental and computed temperatures at the center of the plastic part. In this case also, a very good agreement was found. The feasibility of the methodology is now demonstrated. The device is being adapted to increase the level of applied pressure as well as the cooling rate to achieve injection conditions.
Volume 2: Applied Fluid Mechanics; Electromechanical Systems and Mechatronics; Advanced Energy Systems; Thermal Engineering; Human Factors and Cognitive Engineering, 2012
ABSTRACT This chapter contains sections titled: Specific Heat Thermal Conductivity Thermogravimet... more ABSTRACT This chapter contains sections titled: Specific Heat Thermal Conductivity Thermogravimetric Analysis of Rubber/Epoxy Systems Kinetic Study from TGA References
Cure shrinkage in the thermoset matrix is the major source of cure-induced defects in composite p... more Cure shrinkage in the thermoset matrix is the major source of cure-induced defects in composite parts for industrial applications. Thus its correct determination is very important to optimize the composite fabrication process. In general, volume chemical shrinkage of resin is tested and assuming it isotropic, rule of mixture or a homogenization technique is used to model the linear chemical shrinkage of composite. Some studies are also found in the literature on the measurement of linear chemical shrinkage of very small composite samples under atmospheric pressure. In the present article, a new setup is presented for the measurement of evolution of in-plane chemical shrinkage of thermoset laminated composite during curing. Using this setup, characterization of mass scale samples was done under pressure and heating ramp conditions. Degree of cure of composite during the test was determined using differential scanning calorimeter (DSC). Results show that chemical shrinkage in the comp...
In this paper, we present an application of fibres optic sensors to the studies of the Resin Tran... more In this paper, we present an application of fibres optic sensors to the studies of the Resin Transfer Molding process. We present in a first time our experiments devices. Then, two fibres optics sensors are described and their associated exploitation means too. Finally few experimental results are presented and described. So we show that it is possible to measure temperature, cure degree and material change with a simple sensor. With a more complicated one we can also measure curing reaction stress.
ABSTRACT The quality of thermoplastic parts strongly depends on their thermal history during proc... more ABSTRACT The quality of thermoplastic parts strongly depends on their thermal history during processing. Heat transfer modelling requires accurate knowledge of thermophysical properties and crystallization kinetics in conditions representative of the forming process. In this work, we present a new PvT apparatus and associated method to identify the crystallization kinetics under pressure. The PvT-xT mould was designed for high performance thermoplastics: high temperature (up to 400°C), high cooling rate (up to 200 K/min) and very high pressure (up to 200 MPa). Specific volume measurements were performed at a low cooling rate to avoid a thermal gradient. The crystallization kinetics under pressure can be identified for a wide range of cooling rates by an inverse method taking into account the thermal and crystallinity gradients. Since identification is based on volume variations, the proposed methodology is non-intrusive. Furthermore, the enthalpy released by the crystallization was measured during the experiment by a heat flux sensor located in the moulding cavity.
The crystallization of polymers is commonly restricted in between the equilibrium melting tempera... more The crystallization of polymers is commonly restricted in between the equilibrium melting temperature of crystals and the glass transition temperature. Study of the isothermal crystallization, close to the glass transition temperature, is complicated since nucleation and crystallization must be avoided during the approach of the temperature of interest. It requires cooling at a rate, which is distinctly higher than the maximum rate of nucleation. In fact, the cooling capacity of standard differential scanning calorimetry (DSC) is often insufficient to highly super cool the melt before onset of nucleation or ordering processes. For that reason, the Flash DSC 1 was used, where the cooling rate can reach more than 1000 Kelvin per second, which has allowed studying the isothermal crystallization kinetics in a large temperature range.
We report below about the control of processing of composite materials in particular carbon fibre... more We report below about the control of processing of composite materials in particular carbon fibre dyed into epoxy resin. In the aeronautic industry, structures made of such composite materials have a very high "mechanical property to weight" ratio and can for this reason successfully compete with metallic ones. Their utilisation is constantly increasing in this industry and this growth is
Composites Part A: Applied Science and Manufacturing, 2015
ABSTRACT In Liquid Composite Molding (LCM) processes the saturation of the reinforcement by the r... more ABSTRACT In Liquid Composite Molding (LCM) processes the saturation of the reinforcement by the resin may induce the creation of porosity in the preform affecting the final properties of the composite. The purpose of this work concerns the development of an experimental protocol and the associated modeling to identify the dynamic saturation curve during filling by taking advantage of sharp contrasts of thermal properties existing between dry and fully-saturated reinforcement. To identify saturation, several injections were performed with a laboratory RTM mold for which thermal design allows accurate control of heat transfer. Several heat flux sensors were used to identify the saturation curve. Sensitivity analysis proves the feasibility of the method. The results are compared with a conductometric method with good agreement. Evolution of residual voids identified for several flow rates are also consistent with those expected according to the capillary number.
Injection molding is the most widely used process in the plastic industry. In the case of semi-cr... more Injection molding is the most widely used process in the plastic industry. In the case of semi-crystalline polymer, crystallization kinetics impacts directly the quality of the piece, both on dimensional and mechanical aspects. The characterization of these kinetics is therefore of primary importance to model the process, in particular during the cooling phase. To be representative, this characterization must be carried out under conditions as close as possible to those encountered in the process: high pressure, high cooling rate, shearing, and potential presence of fibers. However, conventional apparatus such as the differential scanning calorimeter do not allow to reach these conditions. A PVTalpha apparatus, initially developed in the laboratory for the characterization of thermoset composites, was adapted to identify the crystallization kinetics. The aim of the presented study is to demonstrate the feasibility of the identification. This device allows the molding of a circular sample of 40 mm diameter and 6 mm thick by controlling the applied pressure on the sample and the temperature field on its surfaces. This mold is designed such as heat transfer is 1D within the thickness of the sample. It is equipped with two heat flux sensors to determine the average crystallization rate through the thickness and a displacement sensor for the determination of the volume change. The heat transfer problem between the polymer and the molding cavity is modeled by using a 1D conduction problem with a moving boundary, in which the control volume is a uniform temperature disk with a variable volume, and coupled to a crystallization kinetic model. An inverse method is used to identify the parameters of the crystallization kinetic model by minimizing an objective function based on the difference between the evolutions of the experimental and computed volume of the sample. The first validation of this methodology was to compare the kinetic parameters identified with this apparatus with those obtained from DSC experiments, i.e. without additional pressure and at low cooling rates. A good agreement was obtained between both methods. A second validation was to compare experimental and computed temperatures at the center of the plastic part. In this case also, a very good agreement was found. The feasibility of the methodology is now demonstrated. The device is being adapted to increase the level of applied pressure as well as the cooling rate to achieve injection conditions.
Volume 2: Applied Fluid Mechanics; Electromechanical Systems and Mechatronics; Advanced Energy Systems; Thermal Engineering; Human Factors and Cognitive Engineering, 2012
ABSTRACT This chapter contains sections titled: Specific Heat Thermal Conductivity Thermogravimet... more ABSTRACT This chapter contains sections titled: Specific Heat Thermal Conductivity Thermogravimetric Analysis of Rubber/Epoxy Systems Kinetic Study from TGA References
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