Two new mathematical models to predict the flow stress at hot deformation

Based on both linear and non-linear estimations of work hardening rate versus strain curves, two mathematical models have been developed to predict the flow curves under hot working conditions up to the peak. The models were tested for a mechanically alloyed Al6063/0.75Al2O3/0.75Y2O3 nanocomposite under different hot forming conditions. The predicted results from both models are found to be in accord with the experimental flow stress curves. However, the linear model (with an average error of 0.81%) predicted the flow stress more accurate than the non-linear model (with an average error of 1.94%).Comment: Written in spring of 2012, as an independent work. 19 Pages, 13 Figures, 3 Appendice

Flow curve approximation using Avitzur's model for barreling compression test

The combination of the Cylindrical Profile Model (CPM) and Avitzur's model is commonly used to determine flow stress curves in material testing using compression test. In this process, stress is corrected for friction using Avitzur's model and the average strain is calculated from CPM. This study proposes a method for estimating strain based on Avitzur's model. The presented case studies demonstrate the impact of this strain correction on the flow curves. The results show that increasing friction leads to higher strain values at the center of the sample due to barreling. The proposed method provides a more accurate interpretation of compression test results

Evaluation of coefficient of friction in bulk metal forming

In this study an upper bound analysis for cylindrical "Barrel Compression Test" (BCT) is developed. BCT method is a very simple method which can be utilized in order to evaluate quantitatively the coefficient of friction by means of just one cylindrical specimen in an upsetting test. The method is checked by a series of finite element method (FEM) simulations and by means of the results of FEM simulations the method is modified.Comment: A self report. 20 Pages, 2 Tables, 2 Figure

Revisiting the Common Practice of Sellars and Tegart’s Hyperbolic Sine Constitutive Model

The Sellars and Tegart’s hyperbolic sine constitutive model is widely practiced in describing stress–strain curves of metals in hot deformation processes. The acceptance of this phenomenological model is owed to its versatility (working for a wide range of stress values) and simplicity (being only a function of strain, strain rate, and temperature). The common practices of this model are revisited in this work, with a few suggestions to improve its results. Moreover, it is discussed that, with the progress of data-driven models, the main reason for using the Sellars and Tegart’s model should be to identify reliable activation energies, and not the stress–strain curves. Furthermore, a piece of code (Hot Deformation Fitting Tool) has been created to automate the analysis of stress–strain curves with various models.</p