Orientation and Path Dependence of Formability in the Stress- and the Extended Stress-Based Forming Limit Curves

This article analyzes the formability data sets for aluminum killed steel (Laukonis, J. V., and Ghosh, A. K., 1978, “Effects of Strain Path Changes on the Formability of Sheet Metals,” Metall. Trans. A., 9, pp. 1849–1856), for Al 2008-T4 (Graf, A., and Hosford, W., 1993, “Effect of Changing Strain Paths on Forming Limit Diagrams of Al 2008-T4,” Metall. Trans. A, 24A, pp. 2503–2512) and for Al 6111-T4 (Graf, A., and Hosford, W., 1994, “The Influence of Strain-Path Changes on Forming Limit Diagrams of Al 6111 T4,” Int. J. Mech. Sci., 36, pp. 897–910). These articles present strain-based forming limit curves (ϵFLCs) for both as-received and prestrained sheets. Using phenomenological yield functions, and assuming isotropic hardening, the ϵFLCs are transformed into principal stress space to obtain stress-based forming limit curves (σFLCs) and the principal stresses are transformed into effective stress and mean stress space to obtain the extended stress-based forming limit curves (XSFLCs). A definition of path dependence for the σFLC and XSFLC is proposed and used to classify the obtained limit curves as path dependent or independent. The path dependence of forming limit stresses is observed for some of the prestrain paths. Based on the results, a novel criterion that, with a knowledge of the forming limit stresses of the as-received material, can be used to predict whether the limit stresses are path dependent or independent for a given prestrain path is proposed. The results also suggest that kinematic hardening and transient hardening effects may explain the path dependence observed in some of the prestrain paths.

Steady-State Thermal Simulation of Weld Applied to a Practical Axisymmetric Weldment

Steady-state Eulerian analysis on thermal simulation of welds using moving coordinates is known as a very computationally efficient method. This paper presents a method of Eulerian analysis that uses commercial computational fluid dynamics code. In order to show the practical availability of the Eulerian method, the method is applied to an analysis of a circumferential weld of a core shroud in a boiling water reactor. In this analysis, the double ellipsoidal power density distribution model proposed by Goldak, Chakravarti, and Bibby (1984, Metall. Trans. B, 15B, pp. 299–305) is applied for the weld heat source, the temperature dependency of thermal properties is considered, and the effect of latent heat is treated by enthalpy method. Comparison of the analyzed temperature histories at several locations on the surface of the weldment to the measured results shows that the numerical results reproduce the measured results well.

Modeling of Macrosegregation and Secondary Phase Precipitation During Solidification of Binary Alloys

A multiphase volume-averaged model describing macrosegregation in an alloy that solidifies by the formation and growth of a primary and a secondary solid phase has been formulated. The model is based on the work presented by Ni and Beckermann (Metall. Trans. 22B, 1991, p. 349), but is extended to account for secondary phase precipitation. A CFD model has been developed by implementation of the mathematical model in a commercial CFD code. Macrosegregation due to thermo-solutal convection in binary alloys with a stationary solid phase (primary and secondary solids) has been simulated. The predictions compare fairly well to experimental results and simulations previously reported in the literature.