## 6 Finite Element Simulations  
A finite element analysis was set up to simulate the curing behavior and to predict the temperature developments of the cast block during curing. The program for finite element simulations was Abaqus 6.14-1 from Dassault Systemes Simulia Corp. All units of the used variables were stated in SI units. A mesh size of 0.005 was used for the simulations.  
For the material properties the temperature dependent thermal conductivity (see Section 5.2), the specific heat (see Section 7.2) and the density at room temperature were used.  
No mechanical boundary conditions were applied since a heat transfer problem was simulated. An appropriate initial temperature and degree of cure value was applied to all nodes of the mesh (see detailed description below). To simulate convective heat transfer in air on the surface of the body, a surface film condition interaction was implemented in the model. The sink temperature and film coefficient were chosen appropriately, dependent on the simulated conditions (see below).  
The simulation of the generation of heat due to curing is done with the HETVAL user subroutine. The routine was used in connection with the conversion in each nodal point as solution dependent variable. To initialize the solution dependent variable the SDVINI user subroutine was utilized which is called once at the start of the simulation. The HETVAL user subroutine reads the temperature and degree of cure in each nodal point. Then it calculates the progress of \(\alpha\) during the last time step according to Equation (1). The heat generated per cubic meter and time for the given step is then calculated according to Equation (2). The FLUX(1) variable of the HETVAL subroutine is set to this value. Abaqus is then able to calculate the distribution of the heat without further input.  
A complete list of all input parameters is given in Table 1 in Appendix D.  
Since the experiment consisted of two steps (mixing in bucket and the actual experiment in the mold) these two needed to be simulated. First the mixing in the bucket with the buckets geometry and 29,757 elements was modeled to determine the initial degree of cure for the simulations of the actual experiment. For this simulation the initial node temperature was set to 303 K, since the resin was pre-heated, and the surrounding temperature was 296 K. The (surface) film coefficient was set to 10 W/m per K, due to the fact that the heat transfer coefficient for convection in air with a low velocity is ca. 10 W/m per K [74]. The initial conversion was set to zero. The core temperature of the bucket-simulation was the control parameter to determine the initial degree of cure to be used in the block-simulation. When the core reached a temperature of 314 K (the very first temperature measurement), the conversion of said bucket-core was used as initial value for \(\alpha\) in the simulations of the block. The mixing process itself was not modeled.  
Secondly the actual experiment was simulated with a block of 20 \(\times\) 20 \(\times\) 6 cm\({}^{3}\) and 19,200 elements. The initial temperatures at the nodes were set to 314 K (the first measured temperature value) and the initial degree of cure was set to the value determined in the bucket-simulation. The surrounding temperature was set to 303 K but for the film coefficient a value of 20 W/m per K was used.  
were the mean total heat value and the activation energy for low conversions. Again, since the data was available for us, we did not reject these two minor differences, since this allowed us to easily get slightly better simulations. This will be discussed in the appropriate sections.