The design of lightweight and high-performance components used in numerous applications requires accurate prediction of the mechanical behavior of titanium Ti6A14V alloys. Generally, the mechanical behavior of these alloys exhibits complex features due to strength differential effects and distortional hardening. Considerable efforts, focusing mainly on modeling a part until fracture, have been devoted to advance the available models for finite element simulation of titanium alloys. These approaches take into account the sensitivity of the alloy yield strengths to both the temperature and strain rates. According to the existing literature, constitutive models can be identified based on uniaxial loading and/ or biaxial loading. Nonetheless, accurate prediction of large deformation behavior in titanium alloys have remained a challenge.
In recent research, Professor Víctor Tuninetti from Universidad de La Frontera, Dr. Gaëtan Gilles from Siemens Company, Prof. Paulo Flores from Universidad de Concepción, Gonzalo Pincheira from Universidad de Talca, Professor Laurent Duchêne and the Vice Dean of Research Anne-Marie Habraken from the Engineering School of University of Liège studied the mechanical behavior of Ti6A14V alloys until fracture based on three plasticity models. These models were assessed by comparing their respective finite element predictions with the obtained experimental results i.e. loads and displacement of field subjected to different stress triaxiality values. The main objective was to determine the most suitable plasticity model for designing bulk Ti6A14V parts. Their research work is currently published in the journal, Meccanica.
Briefly, their experiment comprised of both tensile and compression tests. The former was performed on round bars with V-notches, through-holes or radial notches while the later was performed on elliptical cross-section samples. The three models included the advanced orthotropic yield criterion CPB06 with distortional hardening, anisotropic Hill’48 yield criterion with distortional hardening and the classical Hill’48 yield locus with Voce isotropic hardening.
Results show satisfactory predicted plastic behavior of the CPB06 model attributed to the minimized the global. Even though the Hill model provided lower load errors in tensile tests, it was not effective in the global evaluation due to significant error observed in the compression state. Furthermore, the predicted plastic behavior of the isotropic Hill’48 model has shown to be only satisfactory for positive stress triaxilities. This poor performance was attributed to its inability to describe the strength differential effects of the alloy.
The authors demonstrated the significant impact of distortion hardening on the quality of global model predictions. For instance, the numerical simulations results show clearly that none of the models could be used for perfect prediction of both the measured loads and sample shapes. It was worth noting that the microscopic observations like the texture and crystal plasticity have a considerable influence on the evolution of yield locus of Ti6A14V alloys and thus should be taken into consideration during modeling. Additionally, accurate Voce law based on true stress-strain identification should be used in modeling of the post-necking behavior especially in cases involving large strains.
In a nutshell, the study insights highlight the impact of mechanical features such as hardening, plastic anisotropy and tension-compression asymmetry on the prediction of the post-necking deformation behavior in Ti6A14V alloys and why they should be taken into account during modeling for more authentic results. Based on the findings of the research, Professor Víctor Tuninetti in a statement to Advances in Engineering noted that his research will advance the prediction of damage and fractures of high performance titanium alloys.
Tuninetti, V., Gilles, G., Flores, P., Pincheira, G., Duchêne, L., & Habraken, A. (2019). Impact of distortional hardening and the strength differential effect on the prediction of large deformation behavior of the Ti6Al4V alloy. Meccanica, 54(11-12), 1823-1840.