Optimum Specimen Geometry for Accurate Tensile Testing of Superplastic Metallic Materials

Abstract

The high temperatures and large strain limits associated with superplastic materials amplify the possibility of the tensile test outcomes being sensitive to the shape and size of the specimen geometry. In spite of that, the disparities in the specimen geometries used throughout the numerous efforts on characterising this unique class of materials are rather astonishing. There is an urge to evaluate the dependency of a superplastic tensile test on specimen geometry, before a much-needed universally-adopted standard specimen can be designed; which is the main objective of this comprehensive experimental investigation. More than 20 geometries, covering multiple variations in gauge length, gauge width, grip length and grip width values, are tested at identical conditions, and the corresponding material behaviour is compared in terms of deformation uniformity, material flow and the extracted stress/strain curves. The results reveal the influences of each geometrical parameter, as well as their combined effects, and guide the selection of an optimum specimen geometry for accurate and unified tensile testing of superplastic metallic materials.

The Effect of Material Properties on the Accuracy of Superplastic Tensile Test

“…The distribution of strain and strain rate within the specimen volume, as well as the material flow from the grip section to the gauge region, was studied for more than 30 specimen geometries. As a result, the recommendations to specimen geometry consistent with the ones provided in [22] are suggested.…”

“…At the same time, the viscoplastic character of deformation results in material flow from the grip area to the gauge region, which significantly affects the results, making them dependent on the specimen geometry. These aspects have been discussed in the literature in recent decades [18][19][20][21][22][23].…”

“…Various experimental trials and solutions improving the accuracy of the superplastic tensile test can be found in [20][21][22]. The gripping and specimen geometry issues, as well as heat and temperature effects, were discussed in [20].…”

“…The stress-strain curves were corrected based on the evolution of the central cross-section area measured in the interrupted tests. An extensive experimental study, involving 24 different specimen geometries, was performed by Abu-Farha et al [22]. The amount of material flow from the grip area to the gauge region was analyzed as the main source of errors in the superplastic tensile test.…”