State of the art methods to post-process mechanical test data to characterize the hot deformation behavior of metals

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.

Evaluation of barreling and friction in uniaxial compression test: A kinematic analysis

“…This equation represents a weighted average of equations A.1 and A.4 in [3], obtained from a static framework. It is important to note that this calculation should not incorporate instantaneous measurements unless ∆R is available at any instantaneous H, which is not possible by the currently available test rigs [2]; instead, the equation utilizes data from only the initial and final states to obtain a single parameter value, reducing equation 9 to the mean of equations A.1 and A.4 in [3] as follows, which is used for the further calculations in this investigation.…”

“…While it is straightforward to establish the relationship between the recorded compression force F and the average stress σ using CPM, this model does not account for barreling. To address this limitation, Avitzur's model is commonly employed instead [2]. Avitzur proposed a simplified approximation that makes certain assumptions; see, e.g., [1,3] for detailed information.…”

A comprehensive experimental and numerical study of foldover onset and growth during the barrelling compression test

“…One notes that the flow data library in all commercially available finite element programs relies on the simplistic solutions of the test. 4 Given the limitations in the available data post-processing/reduction techniques, the sets comply reasonably well in all cases which justifies the use of the virtual setup as the best available method to benchmark the data conversion techniques. show the BCT sample at its initial undeformed mesh (H = 16mm).…”

“…1,2 However, only a few indirect measurement methods exist with serious limitations. 3,4 The erroneous BCT based flow curves have been perceived in numerous published works as measured values rather than computed values. To find more reliable and detailed solutions to the test, much more theoretical-analytical developments on the 1 unwanted effects, for example, foldover and friction, are needed.…”

Enhancing Axisymmetric Compression Testing: Modeling and Addressing Flow Curve Errors

“…We note that concurrent measurement of B during the test requires an upgrade to the traditional ACT machines. [ 7 ] Therefore, to evaluate the effectiveness of the new developments, a set of reference flow curves and their virtual test data will be generated using dedicated finite element (FE) models of the test. These data will then be used by different models and solved for comparison.…”