Abstract:The paper focuses on developing constitutive models for superplastic deformation behaviour of near-α titanium alloy (Ti-2.5Al-1.8Mn) at elevated temperatures in a range from 840 to 890 • C and in a strain rate range from 2 × 10 −4 to 8 × 10 −4 s −1 . Stress-strain experimental tensile tests data were used to develop the mathematical models. Both, hyperbolic sine Arrhenius-type constitutive model and artificial neural-network model were constructed. A comparative study on the competence of the developed models to predict the superplastic deformation behaviour of this alloy was made. The fitting results suggest that the artificial neural-network model has higher accuracy and is more efficient in fitting the superplastic deformation flow behaviour of near-α Titanium alloy (Ti-2.5Al-1.8Mn) at superplastic forming than the Arrhenius-type constitutive model. However, the tested results revealed that the error for the artificial neural-network is higher than the case of Arrhenius-type constitutive model for predicting the unmodelled conditions.

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The study presents an integrated approach for superplastic forming of Ti-6%Al-4%V titanium alloy. The flow behavior of the studied alloy was investigated using uniaxial constant strain rate tensile tests in a temperature range of 800-900 °C and a strain rate range of 3×10−4-3×10-3s-1. The obtained flow behavior was modeled using the simple Johnson-Cook (S J-C), modified Johnson-Cook (M J-C) and artificial neural network (ANN) models. An assessment study between the constructed models was performed in order to evaluate the predictability of each model. Standard statistical comparative quantities such as correlation coefficient (R), mean absolute relative error (AARE) and the root mean square error (RMSE) were used to ascertain the model viability. The S J-C model proved ineffectual in predicting the flow behavior of Ti-6%Al-4%V alloy. The M J-C and ANN models are able to successfully describe the flow behavior of the alloy. The validity of the model used for the simulation was ascertained by testing the predicted data with the constructed models at a temperature of 875 °C and a strain rate of 2×10-3s-1 using DEFORM 3D finite element simulation (FES). The obtained results from the FES were verified with the experimental results after superplastic forming process. The FES results show the possibility of using uniaxial tensile test data to simulate superplastic forming process of the Ti-6%Al-4%V titanium sheets.