Experimental Construction and Validation of Revised Drucker–Prager Model Using Finite Element Method for Moisture Condensation Zone in Bentonite-Bonded Silica Sand

For predicting casting deformation by FEM (finite element method) thermal stress analysis, this paper experimentally constructed and validated the Drucker–Prager (DP) model and its revised model (RDP) for the condensation zone of bentonite-bonded sand molds. The condensation zone has been known as a remarkably low-strength region in the mold, and its mechanical response should be dominant to the casting deformation. To construct the models through uniaxial and triaxial compression tests, the test pieces reproducing the condensation zone were prepared by permeating water vapor through a test piece of bentonite-bonded sand. The constructed models were then applied to the FEM stress analysis of the triaxial test to validate them by comparing the analytical stress–strain curves with the experiment. The experimental stress–strain curve after permeating water did not show any distinct yielding point; however, the analytical curve with the original DP model clearly exhibited a yielding point due to the yield criterion of the model. The distinct yielding criterion should be essentially fatal to reproduce the stress–strain relationship of the condensation zone. Contrarily, the RDP model reproduced the experimental curve with less than 10 % error and was found to be advantageous for modeling the smooth stress–strain relationship of the condensation zone.