Process modeling of liquid composite molding processes
Doctoral thesis, 2020
The polymer matrix composites (PMCs) are carving out a niche amid the keen market competition to replace the other material counterparts, e.g., metals. Due to the low weight and the corrosion resistance, the PMCs are wildly utilized from aerospace to automobile industries, both in the sectors of civilian and defense. To obtain high-quality products at low cost, the composites industry continues seeking for numerical simulation tools to predict the manufacturing processes instead of prototype testing and trials. Regarding the attractive liquid composite molding (LCM) process, it provides the possibility to produce net shape parts from composites. The challenges are how to identify the primary physics of LCM processes and develop mathematical models to represent them. Models need to be both accurate and efficient, which is not easy to achieve.
To model LCM processes, we have one option that describes all physics at the macroscopic scale. The fundamental continuum mechanics principles, e.g., mass balance, momentum balance, energy balance, and entropy inequality, help us developing models. In this regard, the theory of porous media (TPM), which relies on the concept of volume fractions, can explain the problems of the saturated/unsaturated multi-phase materials. Darcy's law describes the relation between the flow velocity and the pressure gradient, without accounting for the dual-scale flow. The air and resin compose the homogenized flow at the infusion stage. The existence of the capillary pressure influences the flow front, which has been revealed in this thesis. The finite element method is employed to solve for the homogenized flow pressure, and the degree of saturation with the staggered approach, especially the Streamline-Upwind/Petrov-Galerkin (SUPG) method is implemented to eradicate the stability problem.
As to the fiber preform response, an assumption of shell kinematics is made to reduce the model from a full 3-D problem to a shell-like problem. Given this, an explicit formulation is obtained to express the normal directional stretch as a function of homogenized flow pressure. This model has been verified and validated by a resin infusion experiment. The model mimics the preform relaxation and lubrication mechanisms successfully and efficiently.
So far, the works mentioned above aimed at the isothermal infusion stage. However, resin flow development, heat transfer, and resin curing are strongly interrelated during the whole LCM process. The holistic simulation of both the infusion stage and the curing stage is carried out in this thesis. Finally, we propose a system of coupled models to help process engineers to design and control process parameters by using virtual numerical experiments instead of the traditional trial-and-error approach.
To model LCM processes, we have one option that describes all physics at the macroscopic scale. The fundamental continuum mechanics principles, e.g., mass balance, momentum balance, energy balance, and entropy inequality, help us developing models. In this regard, the theory of porous media (TPM), which relies on the concept of volume fractions, can explain the problems of the saturated/unsaturated multi-phase materials. Darcy's law describes the relation between the flow velocity and the pressure gradient, without accounting for the dual-scale flow. The air and resin compose the homogenized flow at the infusion stage. The existence of the capillary pressure influences the flow front, which has been revealed in this thesis. The finite element method is employed to solve for the homogenized flow pressure, and the degree of saturation with the staggered approach, especially the Streamline-Upwind/Petrov-Galerkin (SUPG) method is implemented to eradicate the stability problem.
As to the fiber preform response, an assumption of shell kinematics is made to reduce the model from a full 3-D problem to a shell-like problem. Given this, an explicit formulation is obtained to express the normal directional stretch as a function of homogenized flow pressure. This model has been verified and validated by a resin infusion experiment. The model mimics the preform relaxation and lubrication mechanisms successfully and efficiently.
So far, the works mentioned above aimed at the isothermal infusion stage. However, resin flow development, heat transfer, and resin curing are strongly interrelated during the whole LCM process. The holistic simulation of both the infusion stage and the curing stage is carried out in this thesis. Finally, we propose a system of coupled models to help process engineers to design and control process parameters by using virtual numerical experiments instead of the traditional trial-and-error approach.
Resin cure
Porous media theory
Process modeling
Polymer composites
Liquid composite molding
Fabric composites
Author
Da Wu
Chalmers, Industrial and Materials Science, Material and Computational Mechanics
Homogenized free surface flow in porous media for wet-out processing
International Journal for Numerical Methods in Engineering,; Vol. 115(2018)p. 445-461
Journal article
A Shell Model for Resin Flow and Preform Deformation in Thin-walled Composite Manufacturing Processes
International Journal of Material Forming,; Vol. 13(2020)p. 1-15
Journal article
Modeling and Experimental Validation of the VARTM Process for Thin-Walled Preforms
Polymers,; Vol. 11(2019)
Journal article
A preform deformation and resin flow coupled model including the cure kinetics and chemo-rheology for the VARTM process
International Journal of Material Forming,; Vol. 14(2021)p. 421-434
Journal article
Whenever you decide to buy a new pair of skis, have you asked why they are so expensive? When you ride your fantastic carbon road bike, are you curious to know how the bike is made? To answer these questions, we need to explore the topic of the manufacturing of polymer composite materials.
Composite materials are the most advanced and adaptable engineering materials known to man. They are only a few decades old, but the evolution of composites and manufacturing process is rapid. All manufacturing techniques aim to bind fiber reinforcements together with polymer matrices. The matrix gives the composite shape, appearance, and durability. At the same time, the fiber reinforcement carries the structural loads to provide stiffness and strength. Any successful composite manufacturing process boils down to how to control temperatures and pressures throughout the process. Sufficient pressure can force the matrix to fill out the entire fiber bed, and the right temperature held for a suitable period will stabilize the dimensions of composites. Due to the flexible combinations of pressures and temperatures, it is very difficult to tell if one process is good. The balance between high properties and low costs challenges all manufacturers. The trial-and-error approach is avoided, but the virtual numerical experiment is emerging. To develop a good numerical solution, we need to understand the physical mechanism and build mathematical models for the selected process.
In this thesis, we define the problem of the liquid composite molding process and formulate the problem as mathematical equations through fundamental continuum mechanics. We also made assumptions to simplify the problem. Once the model is developed, we verify and validate the model. By using the proposed model, we can run simulations on computers to mimic the real manufacturing process of polymer composites. Now, you may answer the questions asked at the beginning by yourself, if you run our model with some settings and clicks.
Composite materials are the most advanced and adaptable engineering materials known to man. They are only a few decades old, but the evolution of composites and manufacturing process is rapid. All manufacturing techniques aim to bind fiber reinforcements together with polymer matrices. The matrix gives the composite shape, appearance, and durability. At the same time, the fiber reinforcement carries the structural loads to provide stiffness and strength. Any successful composite manufacturing process boils down to how to control temperatures and pressures throughout the process. Sufficient pressure can force the matrix to fill out the entire fiber bed, and the right temperature held for a suitable period will stabilize the dimensions of composites. Due to the flexible combinations of pressures and temperatures, it is very difficult to tell if one process is good. The balance between high properties and low costs challenges all manufacturers. The trial-and-error approach is avoided, but the virtual numerical experiment is emerging. To develop a good numerical solution, we need to understand the physical mechanism and build mathematical models for the selected process.
In this thesis, we define the problem of the liquid composite molding process and formulate the problem as mathematical equations through fundamental continuum mechanics. We also made assumptions to simplify the problem. Once the model is developed, we verify and validate the model. By using the proposed model, we can run simulations on computers to mimic the real manufacturing process of polymer composites. Now, you may answer the questions asked at the beginning by yourself, if you run our model with some settings and clicks.
A shell theory based on two-phase porous media for process modeling of structural composites
Swedish Research Council (VR) (2013-3907), 2014-01-01 -- 2017-12-31.
Subject Categories
Mechanical Engineering
Materials Engineering
Metallurgy and Metallic Materials
Areas of Advance
Production
Infrastructure
C3SE (Chalmers Centre for Computational Science and Engineering)
Driving Forces
Innovation and entrepreneurship
ISBN
978-91-7905-285-0
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4752
Publisher
Chalmers
Opponent: Prof. Sylvain Drapier, Ecole de MINES Saint-Etienne, France