Material fall-off, or the process of material spalling, refers to the phenomenon of certain materials breaking or crumbling under certain conditions, such as high temperatures or mechanical stress. This can be a challenging aspect to consider in the calculation of temperature distribution in materials using finite element method, particularly in the case of gypsum boards (Sultan, 1996a).

Two main approaches have been proposed to address the issue of material fall-off in these calculations. The first approach involves sequentially removing material as the calculation progresses when the fall-off criterion is met. This can be a time-consuming process but allows for accurate simulation of material fall-off as it occurs. The second approach involves dynamically changing the conductivity of the material as the calculation proceeds, with the assumption that the material's conductivity will decrease as it approaches the fall-off criterion (Cherif et al., 2021; Ferreira et al., 2018a). However, this approach has been associated with inaccuracies due to numerical instabilities (Gernay et al., 2015). When the material's properties are changed suddenly, it can cause problems in the calculations, leading to inaccuracies in the results.

To address these issues, Joakim Sandström developed an open source finite element software called VGP, VärmeGenomströmningsProgram, (Sandström, 2022). VGP employs an explicit approach, which allows for the accurate simulation of material fall-off without the risk of numerical instabilities. By using relatively small time-steps, it is possible to avoid these instabilities and achieve reasonable results. According to the results of this study, there is a negligible difference in considering material fall-off using VGP versus dynamically removing materials, making VGP an efficient method to use while still providing accurate results.