Process modeling of liquid composite molding processes
Doctoral thesis, 2020
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.
Liquid composite molding
Porous media theory
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
A Shell Model for Resin Flow and Preform Deformation in Thin-walled Composite Manufacturing Processes
International Journal of Material Forming,; (2020)p. 1-15
Modeling and Experimental Validation of the VARTM Process for Thin-Walled Preforms
Polymers,; Vol. 11(2019)
D. Wu, R. Larsson, B. Blinzler, A preform deformation and resin flow coupled model including the cure kinetics and chemo-rheology for the VARTM process
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), 2014-01-01 -- 2017-12-31.
Areas of Advance
C3SE (Chalmers Centre for Computational Science and Engineering)
Innovation and entrepreneurship
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4752
Chalmers University of Technology
Opponent: Prof. Sylvain Drapier, Ecole de MINES Saint-Etienne, France