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Prediction of the deformation during shape casting by FEM (finite element method) thermal stress analysis has been desired. For such prediction, validated constitutive models are essential for both the casting alloy and the mold. In this paper, two fatal defects in the modified Cam-Clay (MCC) model, which has conventionally been employed for a green sand mold, are clarified. The aim of this paper is to concurrently resolve these defects by a new yield criterion. The defects were those that cause an unreal distinct yielding and dilatancy peak on the stress-strain curve, which was clarified by comparing the true stress-strain curves obtained in the experiment and the FEM stress analysis of a triaxial compression test. A device capable of measuring the true stress during vertical compression was newly developed for the triaxial experiment. These defects inevitably led the MCC model to overestimate the mold strength by approximately 200% of the experimental value. This paper provides a new yield criterion, which employs an additional yield surface with the Drucker-Prager inherent surface, to rectify these defects of the MCC model. As a result of the stress analysis of the triaxial test with the new criterion, the smooth stress-strain curve with neither a peak nor a distinct yielding was reproduced. The calculated compressive stress traced the experimental value with less than a 15% error. Therefore, the new criterion should remarkably improve the accuracy of calculating the mold strength in the FEM thermal stress analyses during casting when compared to the MCC model. [Display omitted] • Modified Cam-Clay model of a green sand mold is constructed and validated. • An original triaxial test device is developed to validate the model experimentally. • Defects of the model that cause overestimation of the mold strength are clarified. • The defects are distinct yielding and dilatancy regardless of sand filling degree. • To resolve both of the two defects, a new yield criterion is proposed and validated. [ABSTRACT FROM AUTHOR]

This study investigated the influence of the solid cohesion, f s c , on the viscous properties (m -value and k -value in the Norton law) for aluminum alloys during partial solidification. In the previous study of Haaften (Mater. Sci. Eng. A, 336 (2002), 1–6), a constitutive model taking into account f sc was proposed as ε ˙ = k (T) (σ / f sc (θ,T)) n (=1/ m), where θ referred to the dihedral angle at the solid/liquid interface. However, even though it is well known that the m -value decreases with the decreasing temperature in the semi-solid state, the model defined the m -value as a constant to the temperature. Therefore, m = f(f sc) and k = g(f sc) during solidification were clarified in this study. The viscous properties were obtained by tensile tests during partial solidification for Al-5mass%Mg and Al-2mass%Cu alloys. As a result, it was found that the change in the m -value of 0 ≤ f sc < f sc|eut.st was expressed by the following linear rule-of-mixtures: m = m solid (f sc / f sc|eut.st) + m liquid (1– f sc / f sc|eut.st), where f sc|eut.st is f sc at the beginning of the eutectic solidification, while m solid and m liquid are the m -values just below the solidus temperature and at f sc = 0, respectively. The increase in f sc due to the eutectic solidification hardly affected the change in the m -value and such a value was equivalent to m solid. On the contrary, the change in the k -values was found to obey the Arrhenius equation rather than be controlled by f sc. It is suggested that regardless of the aluminum alloy composition, the viscous properties of partial solidification can be determined using the these relationships. [ABSTRACT FROM AUTHOR]

This study investigated the influence of the solid cohesion, f s c , on the viscous properties (m -value and k -value in the Norton law) for aluminum alloys during partial solidification. In the previous study of Haaften (Mater. Sci. Eng. A, 336 (2002), 1–6), a constitutive model taking into account f sc was proposed as ε ˙ = k (T) (σ / f sc (θ,T)) n (=1/ m), where θ referred to the dihedral angle at the solid/liquid interface. However, even though it is well known that the m -value decreases with the decreasing temperature in the semi-solid state, the model defined the m -value as a constant to the temperature. Therefore, m = f(f sc) and k = g(f sc) during solidification were clarified in this study. The viscous properties were obtained by tensile tests during partial solidification for Al-5mass%Mg and Al-2mass%Cu alloys. As a result, it was found that the change in the m -value of 0 ≤ f sc < f sc|eut.st was expressed by the following linear rule-of-mixtures: m = m solid (f sc / f sc|eut.st) + m liquid (1– f sc / f sc|eut.st), where f sc|eut.st is f sc at the beginning of the eutectic solidification, while m solid and m liquid are the m -values just below the solidus temperature and at f sc = 0, respectively. The increase in f sc due to the eutectic solidification hardly affected the change in the m -value and such a value was equivalent to m solid. On the contrary, the change in the k -values was found to obey the Arrhenius equation rather than be controlled by f sc. It is suggested that regardless of the aluminum alloy composition, the viscous properties of partial solidification can be determined using the these relationships. [ABSTRACT FROM AUTHOR]