Thermal stresses develop during the solidification of a casting due to non-uniform cooling of the casting part. These stresses are driven by thermal gradients, expansion and contraction of metal and its interaction with the mold. Engineers are interested in studying thermally induced stresses and the resulting deformations to gain insights in to the integrity of the part. The Thermal Stress Evolution (TSE) model in FLOW-3D is one such tool that allows casting engineers to study this phenomenon.
In this Flow Science Report, the stresses predicted by the TSE model are validated with experimental results. Several key aspects of the modeling process are discussed to demonstrate the capabilities while also accounting for the limitations of the model.
Pokorny et al. studied stresses developed during cooling of a binary Magnesium-Aluminum alloy and compared simulations results with measurements from experiments. In the current study, stresses measured for Mg-9 wt. pct. Al alloy without hot tear published by Pokorny et al (1) were compared to the stresses obtained using FLOW-3D.
In the reference paper, measurements from specially designed experiments were extracted for the evolution of temperature and contraction forces during solidification and cooling of a restrained rod-shaped casting in a steel mold. These experiments were carried out for several initial mold temperatures. For this study, results for the mold temperature of Tmold = 773K (500°C) were used for comparisons. The absence of hot tear made this an ideal candidate for evaluation of the TSE model in FLOW-3D.
Hot tearing is not modeled in FLOW-3D due to the lack of a fracture model for the mush during the solidification phase. This is also true for the simulation results presented in the reference paper and consequently the stresses were over-predicted compared to the experimental measurements. The coupling of the stress model with the feeding flow and macrosegregation calculations is also important in accurately predicting stresses in the presence of hot tear (1).
Gandharv Kashinath and Melissa Carter, “Validating the Thermal Stress Evolution Model,” Flow Science Report 09-16, June 2016, Copyright Flow Science