Abstract
In this paper, mechanical tests aimed at characterizing the plastic anisotropy of a commercially pure α-titanium sheet are presented. Hemispheric and elliptic bulge tests conducted to investigate the forming properties of the material are also reported. To model the particularities of the plastic response of the material the classical Hill [1] yield criterion, and Cazacu et al. [2] yield criterion are used. Identification of the material parameters involved in both criteria is based only on uniaxial test data, while their predictive capabilities are assessed through comparison with the bulge tests data. Both models reproduce qualitatively the experimental plastic strain distribution and the final thickness of the sheet. However, only Cazacu et al. [2] yield criterion, which accounts for both the anisotropy and tension-compression asymmetry of the material captures correctly plastic strain localization, in particular its directionality. Furthermore, it is shown that accounting for the strong tension-compression asymmetry in the model formulation improves numerical predictions regarding the mechanical behavior close to fracture of a commercially pure titanium alloy under sheet metal forming processes.
Highlights
Titanium and its alloys have outstanding mechanical properties such as moderate weight, high ductility and high strength, exceptional corrosion resistance, and excellent high-temperature properties
It was reported that commercially purity (CP) and HP titanium materials display strength differential effects, in uniaxial compression the flow stress and strength are higher than in uniaxial tension
The Cazacu et al [2] yield criterion, which accounts for the tension-compression asymmetry of the plastic behavior captures correctly the plastic strain localization and its orientation
Summary
Titanium and its alloys have outstanding mechanical properties such as moderate weight, high ductility and high strength, exceptional corrosion resistance, and excellent high-temperature properties. It was reported that CP and HP titanium materials display strength differential effects, in uniaxial compression the flow stress and strength are higher than in uniaxial tension. These strength differential effects are attributed mainly to mechanical twinning. Previous studies have shown that classic plasticity models, such as J2 plasticity, or Hill [1] yield criterion cannot accurately describe the plastic behavior of titanium materials. Hill [1]’s criterion accounts for anisotropy, it cannot predict accurately the tension-compression asymmetry of HP-titanium [3].
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