Abstract
Materials engineering and science rely heavily on the indirect measurement of plastic stress and strain by post-processing of mechanical test data, including tension, torsion, and compression test. There is no consensus among researchers regarding the best test or the post-processing theory nor do adequate standards exist on the characterization methods. The tests are typically performed as customized tests, discrepancies exist in the flow curves obtained by different methods and the chosen mechanical test. More critically, the curves are dominantly treated (perceived) as a set of measured data rather than calculated values. The plasticity-based calculated flow curves and their gradients are, in turn, the basis for several second-tier indirect measurements, such as stacking fault energy and recrystallization. Such measurements are quite prone to errors due to oversimplified post-processing of the tests’ data and can only be experimentally verified in a qualitative or in an average fashion. Therefore, their findings are highly restricted by the limitations of each test, data type and post-processing method, and should be used carefully. This review examines some of the most commonly used data conversion methods and some recent developments in the field followed by recommendations. It will highlight the need to develop test rigs that can provide new data types and to provide advanced post-processing techniques for the indirect measurement.
Highlights
Industrial metal forming processes are way too expensive to be designed and optimized via trial and error
In the last 70 years, thermo-mechanical processing in the metal forming industry has developed from a skillsbased approach, relying on trial-and-error developments, to a scientific one, thanks to mathematical modeling and computational analysis to control and optimize its processes and to transfer the results from bench-scale physical simulations to real industrial production
Contrary to other traditional flow stress tests, there is no standard or commonly used procedure currently available to convert the measured raw high rates data to the flow curves; discrepancies exist in the results reported by different research groups, with different samples
Summary
Industrial metal forming processes are way too expensive to be designed and optimized via trial and error. The method relies on simulation of the test and the Avitzur barrelling model[73] and calculation of its barrelling parameter based on the method of Ebrahimi and Najafizadeh[85]; the latter has been shown to have serious limitations.[86,88] The laboratory simulation can lead to general insights into the likely microstructure evolution processes in commercial rolling, but outside of plate rolling it is generally necessary to make simplifications to the strain rate and thermal history of the sample
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