Finite Element Simulations for Investigating the Effects of Specimen Geometry in Superplastic Tensile Tests

Abstract

Characterizing the behavior of superplastic materials is largely based on the uniaxial tensile test; yet the unique nature of these materials requires a particularly tailored testing methodology, different to that used with conventional materials. One of the crucial testing facets is the specimen geometry, which has a great impact on the outcome of a superplastic tensile test, as a result of the associated extreme conditions. And while researchers agree that it should take a notably different form than the typical dog-bone shape; there is no universal agreement on the specimenÕs particular size and dimensions, as evident by the disparities in test specimens used in the various superplastic testing efforts found throughout the literature. In view of that, this article is dedicated to understanding the effects of specimen geometry on the superplastic behavior of the material during tensile testing. Deformation of the Ti6Al4V titanium alloy is FE simulated based on a multitude of specimen geometries, covering a wide range of gauge length, gauge width, grip length, and grip width values. The study provides key insights on the influences of each geometrical parameter as well as their interactions, and provides recommendations on selecting the specimenÕs proportions for accurate and unified tensile testing of superplastic materials.

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

“…These FE meshes are presented in Figure 1b. Based on the information provided in [23], the friction coefficient between the specimen and the grip shoulders was considered to be equal to 0.4. The grip was simulated as a rigid body, moving along the Y-axis with an increasing velocity (v) to maintain the constant target strain rate ( .…”

“…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].…”

“…Simulations can be used to predict the distributions of strain and strain rate within the specimen volume and study how these distributions are affected by the material properties or the specimen geometry. A comprehensive numerical investigation aimed to study the effect of specimen geometry in tensile testing of Ti6Al4V alloy at 900 • C was provided by Nazzal et al [23]. 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.…”

Submerged Friction Stir Back Extrusion of AZ31 Magnesium Alloy

“…This happens due to the frictional heat generated from the metal-on-metal contact that softens the material and aids in tube formation. FSBE can be applied to many lightweight metal alloys such as Magnesium and Aluminum that have been utilized in environmental benign manufacturing processes [7][8][9][10][11][12][13][14][15][16][17]. The produced tubes have the potential to be used in multiple industries such as automotive and aeronautics for its superior properties.…”

Finite element modeling of superplastic co-doped yttria-stabilized tetragonal-zirconia polycrystals

“…On the other hand, Kim et al (1996) combined a strain rate controlling function in their model that could control the pressure to maintain the maximum strain rate near a target value during analysis and obtain the optimal pressure-time relationships for the SPF process under the prerequisite that the material did not crack. Similarly, for research on SPF problems that simulate superplastic alloys as non-Newtonian viscous flow materials using an elastic-viscoplastic constitutive model, Chandra (1988) and Nazzal et al (2011) incorporated grain growth evolution; Abu-Farha and Khraisheh (2007) incorporated both grain and void growth evolutions; Chen et al (2001), Hassan et al (2003), Li et al (2004), and Yenihayat et al (2005) combined the strain rate controlling capability, and Ding et al, (1995), Huh et al (1995), Lin (2003), Nazzal et al (2004), Tao and Keavey (2004), and Nazzal and Khraisheh (2008) joined microstructure evolutions and the strain rate controlling capability together within their models.…”