Accuracy issues in modeling superplastic metal forming

Abstract

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Correlation of finite element analysis to superplastic forming experiments

“…Because the high temperature tensile test does not typically employ an extensometer, an FEA based coefficient refinement technique developed by Luckey [5] has been applied that accounts for both gage section shape and the influence of material flow from the grip section on the stress, strain and strain rate. The approach is consistent with the work of Friedman and Ghosh [12], Johnson et al [13] and Raman et al [11]. The coefficients applied represent the superplastic response for a range of strain rates (5 × 10 −4 to 3 × 10 −3 s −1 ) that are typical of strain rates from the automotive superplastic forming of aluminum [5].…”

New approach to gas pressure profile prediction for high temperature AA5083 sheet forming

“…Ifε t+ t max =ε tar , whereε tar is the required constant strain rate in the sheet, then Eq. (3) can be used to predict p t+ t via Johnson et al (1995) and Khaleel et al (1997) explained the need for using an average of a subset of elements with the highest strain rates instead of considering the maximum strain rate in the sheeṫε t max . The maximum strain rate may thus be localized due to local mesh refinement, time-step size, and contact conditions.…”

Optimum Specimen Geometry for Accurate Tensile Testing of Superplastic Metallic Materials

“…However, with the extreme temperatures and large plastic strains associated with superplastic materials, the viscoplastic behaviour causes unavoidable material flow from the grip region into the gauge region of the test specimen. This could be a major source of errors in the captured stress/strain behaviour [11,12], hence indicating the great potentials for unaccounted for effects by the specimen geometry that require investigation. At least, it is likely to challenge the accuracy of claims of extreme superplastic elongations, particularly those exceeding 5000% [13].…”

“…Of those to be mentioned is the team at PNNL, which conducted both FE simulations and experiments on few AA5083 tensile specimens, with various gauge length-to-width ratios, in order to investigate the end effects on strain rate within the gauge length of each specimen [11,12,17]. Their efforts concluded with an improved geometry that provides a constant strain rate in a major portion of the specimen's gauge.…”