Resin transfer molding (RTM) is a widely used technique for the manufacturing of composite parts.... more Resin transfer molding (RTM) is a widely used technique for the manufacturing of composite parts. A proper selection of process parameters is the key to yield successful molding results and obtain a good part. During composite consolidation, resin cure, also called chemical conversion, plays a decisive role on the final mechanical properties of the part. The modeling of resin kinetics and the evolution of composite properties during cure are crucial for process optimization. In this paper, the curing of a thermosetting polyester resin is studied by differential scanning calorimetry (DSC). A semiempirical autocatalytic model is developed to describe the kinetics of the chemical reaction. The model accounts for the maximum degree of polymerization as a function of cure temperature and induction time, i.e., the time required to attain total inhibitor degradation.The evolution of mechanical properties during resin cure for two glass-polyester composites is also studied with a dynamical mechanical thermal analyzer (DMTA) and a thermomechanical analyzer (TMA). Given that for a low chemical conversion, the elastic properties of the resin remain low, an initial degree of polymerization called after gel point (AGP) is introduced in the analysis of the mechanical properties during cure. A normalized elastic modulus is defined from the value at AGP, taken as a reference. The normalized elastic modulus is then compared to the polymerization degree. For pure resin samples, the logarithm of chemical conversion is found to be almost linearly related to the logarithm of the elastic modulus. Based on this comparison, a thermochemical model is proposed to describe the evolution of mechanical properties during the cure of composite samples with different fiber volume fractions.The viscoelastic behavior is also determined by performing stress relaxation tests with the DMTA. Resin specimens are tested for different cure states below the glass transition temperature, and master curves of stress relaxation during cure are constructed by applying the time-temperature superposition principle. The measurements depict the relaxation modulus of polyester resins as sharply affected by the degree of polymerization. Based on the experimental data, a relaxation modulus is modeled in a thermorheologically simple manner using exponential and power laws. Finally, a linear volume change model is constructed based on the TMA measurements of thermal expansion and resin shrinkage. The volume changes resulting from composite expansion-contraction and resin polymerization shrinkage are modeled as a function of temperature and degree of polymerization.The purpose of this work is to develop appropriate models of chemo- and thermomechanical behaviors of glass-polyester composites during cure. A resin cure kinetics model is developed by adding the glass transition effects to the J.L.B. model. For the mechanical properties, two new models are presented to account for the elastic and viscoelastic behaviors of the resin and the composite. Finally, the coefficients of the volume changes model are measured to account for the composite thermal expansion-contraction and resin chemical shrinkage. These models will be used in future investigations for thermal and curing optimization of composites processed by resin transfer molding.
Liquid Composite Molding (LCM) regroups a number of manufacturing techniques of polymer composite... more Liquid Composite Molding (LCM) regroups a number of manufacturing techniques of polymer composites based on the impregnation of dry fibrous reinforcements by a liquid resin. It involves several complex phenomena: fibre impregnation, resin gellification and cure, thermal and rheological variations, etc. The combination of such phenomena and the wide range of processing parameters often lead to non-optimum, sometimes inappropriate, processing setups. In this work, an approach is proposed to assist manufacturing specialists in reducing process development time and improving process robustness. A software interface was developed to enable users to define and quickly compare different processing scenarios. Using fuzzy logic inference and different levels of mathematical simplification, the proposed software is able to sketch the moldability diagram of the part and perform basic process optimizations. One original feature of the proposed approach consists of integrating into the optimization loop the feedback of process engineers which helps in correcting the numerical solution. An application example is conducted in order to demonstrate the capabilities of the approach for understanding process behaviour.
Resin transfer molding (RTM) has become one of the most widely used processes to manufacture medi... more Resin transfer molding (RTM) has become one of the most widely used processes to manufacture medium size reinforced composite parts. To further enhance the process yield while ensuring the best possible quality of the produced parts, physically based optimization procedures ...
A major issue in Liquid Composite Molding Process (LCM) concerns the reduction of voids formed du... more A major issue in Liquid Composite Molding Process (LCM) concerns the reduction of voids formed during the resin filling process. Reducing the void content increases the quality of the composite and improves its mechanical properties. Most of modeling efforts on process simulation of mold filling has been focused on the single phase Darcy’s law, with resin as the only phase, ignoring the formation and transport of voids. The resin flow in a partially saturated region can be characterized as two phase flow through a porous medium. The mathematical formulation of saturation in LCM takes into account the interaction between resin and air as it occurs in a two phase flow. This model leads to the introduction of relative permeabilities as a function of saturation. The modified saturation equation is obtained as a result, which is a non-linear advection-diffusion equation with viscous and capillary phenomena. In this work, a flux limiter technique has been used to solve a modified saturation equation for the LCM process. The implemented algorithm allows a numerical optimization of the injected flow rate which minimizes the micro/macroscopic void formation during mold filling. Some preliminary numerical results are presented here in order to validate the proposed mathematical model and the numerical scheme. This formulation opens up new opportunities to improve LCM flow simulations and optimize injection molds.
Composites Part A-applied Science and Manufacturing, 2005
Resin transfer molding (RTM) is a widely used manufacturing technique of composite parts. Proper ... more Resin transfer molding (RTM) is a widely used manufacturing technique of composite parts. Proper selection of processing parameters is critical in order to produce successful molding and to obtain a good part. Notably, when thermosetting resins are processed, the shrinkage that results from resin polymerization increases the complexity of the problem. Numerical prediction of internal stresses during composite manufacturing has
Resin transfer molding (RTM) is a widely used technique for the manufacturing of composite parts.... more Resin transfer molding (RTM) is a widely used technique for the manufacturing of composite parts. A proper selection of process parameters is the key to yield successful molding results and obtain a good part. During composite consolidation, resin cure, also called chemical conversion, plays a decisive role on the final mechanical properties of the part. The modeling of resin kinetics and the evolution of composite properties during cure are crucial for process optimization. In this paper, the curing of a thermosetting polyester resin is studied by differential scanning calorimetry (DSC). A semiempirical autocatalytic model is developed to describe the kinetics of the chemical reaction. The model accounts for the maximum degree of polymerization as a function of cure temperature and induction time, i.e., the time required to attain total inhibitor degradation.The evolution of mechanical properties during resin cure for two glass-polyester composites is also studied with a dynamical mechanical thermal analyzer (DMTA) and a thermomechanical analyzer (TMA). Given that for a low chemical conversion, the elastic properties of the resin remain low, an initial degree of polymerization called after gel point (AGP) is introduced in the analysis of the mechanical properties during cure. A normalized elastic modulus is defined from the value at AGP, taken as a reference. The normalized elastic modulus is then compared to the polymerization degree. For pure resin samples, the logarithm of chemical conversion is found to be almost linearly related to the logarithm of the elastic modulus. Based on this comparison, a thermochemical model is proposed to describe the evolution of mechanical properties during the cure of composite samples with different fiber volume fractions.The viscoelastic behavior is also determined by performing stress relaxation tests with the DMTA. Resin specimens are tested for different cure states below the glass transition temperature, and master curves of stress relaxation during cure are constructed by applying the time-temperature superposition principle. The measurements depict the relaxation modulus of polyester resins as sharply affected by the degree of polymerization. Based on the experimental data, a relaxation modulus is modeled in a thermorheologically simple manner using exponential and power laws. Finally, a linear volume change model is constructed based on the TMA measurements of thermal expansion and resin shrinkage. The volume changes resulting from composite expansion-contraction and resin polymerization shrinkage are modeled as a function of temperature and degree of polymerization.The purpose of this work is to develop appropriate models of chemo- and thermomechanical behaviors of glass-polyester composites during cure. A resin cure kinetics model is developed by adding the glass transition effects to the J.L.B. model. For the mechanical properties, two new models are presented to account for the elastic and viscoelastic behaviors of the resin and the composite. Finally, the coefficients of the volume changes model are measured to account for the composite thermal expansion-contraction and resin chemical shrinkage. These models will be used in future investigations for thermal and curing optimization of composites processed by resin transfer molding.
Liquid Composite Molding (LCM) regroups a number of manufacturing techniques of polymer composite... more Liquid Composite Molding (LCM) regroups a number of manufacturing techniques of polymer composites based on the impregnation of dry fibrous reinforcements by a liquid resin. It involves several complex phenomena: fibre impregnation, resin gellification and cure, thermal and rheological variations, etc. The combination of such phenomena and the wide range of processing parameters often lead to non-optimum, sometimes inappropriate, processing setups. In this work, an approach is proposed to assist manufacturing specialists in reducing process development time and improving process robustness. A software interface was developed to enable users to define and quickly compare different processing scenarios. Using fuzzy logic inference and different levels of mathematical simplification, the proposed software is able to sketch the moldability diagram of the part and perform basic process optimizations. One original feature of the proposed approach consists of integrating into the optimization loop the feedback of process engineers which helps in correcting the numerical solution. An application example is conducted in order to demonstrate the capabilities of the approach for understanding process behaviour.
Resin transfer molding (RTM) has become one of the most widely used processes to manufacture medi... more Resin transfer molding (RTM) has become one of the most widely used processes to manufacture medium size reinforced composite parts. To further enhance the process yield while ensuring the best possible quality of the produced parts, physically based optimization procedures ...
A major issue in Liquid Composite Molding Process (LCM) concerns the reduction of voids formed du... more A major issue in Liquid Composite Molding Process (LCM) concerns the reduction of voids formed during the resin filling process. Reducing the void content increases the quality of the composite and improves its mechanical properties. Most of modeling efforts on process simulation of mold filling has been focused on the single phase Darcy’s law, with resin as the only phase, ignoring the formation and transport of voids. The resin flow in a partially saturated region can be characterized as two phase flow through a porous medium. The mathematical formulation of saturation in LCM takes into account the interaction between resin and air as it occurs in a two phase flow. This model leads to the introduction of relative permeabilities as a function of saturation. The modified saturation equation is obtained as a result, which is a non-linear advection-diffusion equation with viscous and capillary phenomena. In this work, a flux limiter technique has been used to solve a modified saturation equation for the LCM process. The implemented algorithm allows a numerical optimization of the injected flow rate which minimizes the micro/macroscopic void formation during mold filling. Some preliminary numerical results are presented here in order to validate the proposed mathematical model and the numerical scheme. This formulation opens up new opportunities to improve LCM flow simulations and optimize injection molds.
Composites Part A-applied Science and Manufacturing, 2005
Resin transfer molding (RTM) is a widely used manufacturing technique of composite parts. Proper ... more Resin transfer molding (RTM) is a widely used manufacturing technique of composite parts. Proper selection of processing parameters is critical in order to produce successful molding and to obtain a good part. Notably, when thermosetting resins are processed, the shrinkage that results from resin polymerization increases the complexity of the problem. Numerical prediction of internal stresses during composite manufacturing has
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