Settings for the Domain ODEs and DAEs interface, which solves for the degree of cure. Pay special attention to how the units are set up. We now need to add one more interface to solve for the degree of cure, and this is done via the Domain ODEs and DAEs interface, as shown below. This feature implements the right-hand term from Equation 1 based upon the time derivative of the degree of cure. The endothermic effect of the curing is accounted for via a volumetric heat source, -rho0*H_r*d(alpha,t), as shown above. The absorption of heat due to the material curing is modeled via the Heat Source feature. A Heat Flux boundary condition at the other end of the domain applies 10 kW/m 2 due to the heating of the mold. The Heat Transfer in Solids interface solves for the temperature distribution over time, starting with the specified initial temperature along with a Thermal Insulation boundary condition on one end. Our modeling domain is simply a 5-mm-long 1D interval, with the material properties as shown above. The Global Parameters define a set of representative material properties of a thermoset. Let’s now look at how to set up this model in COMSOL Multiphysics, starting with the definitions of a few Global Parameters defining the properties of our representative thermoset material. Where the Arrhenius equation defines the temperature-dependent reaction rate, with A being the frequency factor, E_a being the activation energy, R as the universal gas constant, and n as the order of the reaction. Assuming no flow, the equation governing heat transfer in the thermoset precursor is: Our model will compute the variation in time of the temperature, T, and the degree of cure, \alpha, of the thermoset from the centerline to the mold wall. Schematic of a mold with a thermoset curing inside and the equivalent model for temperature and degree of cure. Since the material is heated uniformly and at a known rate on both sides, we can exploit symmetry to only model one half of the material. A thin-walled part, such as the radio cabinet shown earlier, can be reasonably modeled with a one-dimensional model through the thickness. During heating and curing, the material does not move around inside the mold, and for simplicity, we won’t consider any filler materials. We will look at simulating curing during a transfer molding process, wherein the material is loaded into a mold and then heated, as shown in the schematic below. Modeling Thermal Curing in COMSOL Multiphysics Let’s now look at how to implement such a model in COMSOL Multiphysics. If this is so, then you can develop a very simple model to predict the curing based upon the temperature. Now, depending upon the exact manufacturing process, the precursor material might not move around or flow significantly during the curing step. Carbon fiber and fiberglass composites, for example, bond relatively strong but flexible fibers together using a relatively rigid thermoset matrix. Additional filler materials are often added to improve the properties of the final product. These precursors are put into a mold and heated under high pressure. Licensed under CC BY-SA 2.0, via Wikimedia Commons.īakelite and other thermosets come in various precursor forms, such as powders and thick viscous liquids. The material was used in a variety of early consumer products, such as telephones and radio cabinets.Ī Bakelite radio cabinet. Bakelite is a very hard material that is resistant to many chemicals, is a good electrical insulator, and has an attractive surface finish. Bakelite, one of the first thermosets, is often credited as kicking off the polymer industry. This chemical reaction can be due to heat, light, or the addition of a chemical catalyst. Thermosets are a class of polymer materials that undergo an irreversible chemical reaction, causing the polymer chains to cross-link and form a rigid material. Thermal curing is very easy to model within the core functionality of COMSOL Multiphysics, as we will show in this blog post. You can often assume that the material does not flow during curing, which simplifies the analysis. This process is relevant, for example, when a precursor resin is heated and hardens during the manufacturing of composites. Thermal curing is the process of temperature-induced chemical change in a material, such as the polymerization of a thermoset resin.
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