Institute of Fundamental Technological Research

Mechanical behavior of a multifunctional titanium alloy Gum Metal was investigated by conducting tensile tests at various strain rates and applying digital image correlation (DIC) technique. Stress–strain curves confirmed low Young's modulus and high strength of the alloy. The determined values of yield strength had a tendency to increase, whereas the elongation to the specimen rupture tended to decrease with increasing strain rate. True stress versus strain curves were analyzed using selected lengths of virtual extensometer (VE) placed in the strain localization area. When the initial length of the VE was the same as the gauge length, work hardening was observed macroscopically at lower strain rates, and a softening was seen at higher strain rates. However, the softening effect was not observed at the shorter VE lengths. Evolution of the Hencky strain and rate of deformation tensor component fields were analyzed for various strain rates at selected stages of Gum Metal loading. The DIC analysis demonstrated that for lower strain rates the deformation is macroscopically uniform up to the higher average Hencky strains, whereas for higher strain rates the strain localization occurs at the lower average Hencky strains of the deformation process and takes place in the smaller area. It was also found that for all strain rates applied, the maximal values of Hencky strain immediately before rupture of Gum Metal samples were similar for each of the applied strain rates, and the maximal local values of deformation rate were two orders higher when compared to applied average strain rate values.

titanium alloy, gum metal, strain rate sensitivity, strain localization, digital image correlation, full-field deformation analysis

A hyperelastic-viscoplastic model of Gum Metal is presented. The model is formulated in the large strain framework. The free energy function is postulated consisting of the hyperelastic and viscoplastic components. Original extension of the Neo-Hooke model with a power law component is proposed for hyperelasticity, which enables to describe a relatively large non-linear elastic regime observed for the alloy. Viscoplastic strain follows the Perzyna-type law with an overstress function. The model is implemented into the finite element method and used to simulate the Gum Metal response in multiple tension loading-unloading cycles. The results are compared with experimental outcomes. Good accordance of the simulation results and the available experimental data is obtained.

large strain, hyperelasto-viscoplasticity, gum metal, cyclic deformation

The research concerns investigation of yielding and developing of the strain localization in new β-Ti alloy characterized by unique elastic-plastic properties, named Gum Metal. The alloy was subjected to tension on testing machine at three various strain rates up to rupture. Digital image correlation and infrared thermography were applied to analyze the experimental results. Strain distributions were determined on the basis of digital image correlation algorithm. The related temperature variations were found in contactless manner using infrared thermography. Mechanical and the corresponding thermal data were used to study the Gum Metal large nonlinear reversible deformation and localization effects.

gum metal, tension, large nonlinear elastic deformation, thermomechanical couplings, temperature change, digital image correlation

Effects of thermomechanical couplings were studied in a new beta Ti alloy by IR and DIC techniques. The obtained stress-strain curves confirmed low Young’s modulus and high strength of the alloy. The determined values of yield strength increases and values of elongation till rupture decreases with increasing strain rate. It was found, by using fast and sensitive infrared camera, that the large limit of the Gum Metal reversible nonlinear deformation originates from mechanisms of dissipative nature, probably exothermic stress-induced transition of α" nanodomains.

titanium alloy, gum metal, strain rate, infrared camera, temperature change, DIC

This paper presents results of investigation of multifunctional beta-Ti alloy Gum Metal subjected to tension at various strain rates. Digital image correlation was used to determine strain distributions and stress-strain curves, while infrared camera allowed for us to obtain the related temperature characteristics of the specimen during deformation. The mechanical curves completed by the temperature changes were applied to analyze the subsequent stages of the alloy loading. Elastic limit, recoverable strain, and development of the strain localization were studied. It was found that the maximal drop in temperature, which corresponds to the yield limit of solid materials, was referred to a significantly lower strain value in the case of Gum Metal in contrast to its large recoverable strain. The temperature increase proves a dissipative character of the process and is related to presence of w and a” phases induced during the alloy fabrication and their exothermic phase transformations activated under loading. During plastic deformation, both the strain and temperature distributions demonstrate that strain localization for higher strain rates starts nucleating just after the yield limit leading to specimen necking and rupture. Macroscopically, it is exhibited as softening of the stress-strain curve in contrast to the strain hardening observed at lower strain rates.

gum metal, yield limit, thermomechanical coupling, infrared thermography, digital image correlation, strain localization

Results of initial investigation of thermomechanical couplings in innovative β-Ti alloy called Gum Metal subjected to tension are presented. The experimental set-up, consisting of testing machine and infrared camera, enabled to obtain stress–strain curves with high accuracy and correlate them to estimated temperature changes of the specimen during the deformation process. Both ultra-low elastic modulus and high strength of Gum Metal were confirmed. The infrared measurements determined average and maximal temperature changes accompanying the alloy deformation process, allowed to estimate thermoelastic effect, which is related to the alloy yield point. The temperature distributions on the specimen surface served to analyse strain localization effects leading to the necking and rupture.

gum metal, thermomechanical coupling, nonlinear elasticity, yield point, infrared camera

Effects of thermomechanical couplings were studied in a new beta Ti alloy by IR and DIC techniques. The obtained stress-strain curves confirmed low Young’s modulus and high strength of the alloy. The determined values of yield strength increases and values of elongation till rupture decreases with increasing strain rate. It was found, by using fast and sensitive infrared camera, that the large limit of the Gum Metal reversible nonlinear deformation originates from mechanisms of dissipative nature, probably exothermic stress-induced transition of alpha" nanodomains.

Titanium alloy, Gum Metal, strain rate, infrared camera, temperature change, DIC

This paper presents an investigation of strain localization phenomena during tension of a β-Ti alloy Gum Metal that can deform reversibly to large strains (around 2%). Digital image correlation (DIC), with the especially developed PAN algorithm at IPPT, and infrared thermography were used to determine strain and the related temperature distributions with high accuracy. The analysis of strain and temperature distributions showed that the increase in the strain rate affects both the onset and development of the strain localization process.

infrared thermography, thermomechanical behavior, gum metal

This work presents results of experimental investigation of recoverable deformation of a β-Ti alloy Gum Metal inspected by infrared (IR) thermography. To this end, a flat specimen of Gum Metal was subjected to cyclic tension with an increasing strain on a testing machine and was simultaneously monitored by a fast and sensitive IR camera. The IR measurements determined an average temperature accompanying the alloy deformation process for subsequent tension cycles and allowed to estimate thermoelastic effect, which is related to the alloy yield point. Thermomechanical couplings accompanying the loading-unloading cycles were analyzed for estimating the range of reversible deformation from mechanical and thermal perspectives as well as discussed in the view of Lord Kelvin's formula.

Results of investigation of thermomechanical couplings in innovative β-Ti alloy (Gum Metal) subjected to tension are presented. The experimental set-up, consisting of testing machine and infrared camera, enabled to obtain stress-strain curves with high accuracy and correlate them to estimated temperature changes of the sample during the deformation process. Both ultra-low elastic modulus and high strength of Gum Metal were confirmed. The infrared measurements determined average and maximal temperature changes accompanying the alloy deformation process, allowed to estimate thermoelastic effect, which is related to the alloy yield point. The temperature distributions on the sample surface served to analyze localization effects leading to the sample necking and rupture.

Gum metal, nonlinear elasticity, thermomechanical couplings

Gum Metal, cyclic loading, infrared camera, thermomechanical coupling, rupture

Advanced material, Titanium alloy, Gum Metal, Superelasticity, High Strength, Tension, Infrared Camera, DIC

Gum metal, Titanium alloy, Tensile loading, Digital Image Correlation

Mechanical characteristics obtained by MTS testing machine and digital image correlation (DIC) algorithm as well as the related temperature changes in a new B-Ti alloy - Gum Metal, subjected to tension in a wide spectrum of the strain rates, are presented The fast and sensitive infrared camera ThermaCam Phoenix allowed estimating temperature changes accompanying the specimen deformation process in contactless manner. The obtained mechanical curves confirm an ultra-low elastic modulus and high strength of Gum Metal. Furthermore, it was presented how the stress-strain characteristics change from hardening to softening depending on the strain rate. The thermoelastic effect, estimated by the IR technique was discussed according to the Gum Metal yield point.

gum metal, titanium alloy, tension test, strain rate, thermomechanical coupling

Results of investigation of mechanical properties and the related temperature changes in a β-Ti alloy, Gum Metal, subjected to tension in a wide spectrum of the strain rates are presented. The stress-strain curves have been obtained by MTS testing machine while fast and sensitive infrared camera Phoenix Flir Co. allowed estimating temperature changes accompanying the specimen deformation process. The obtained mechanical curves confirm an ultra- low elastic modulus and high strength of Gum Metal. The yield point was estimated with high accuracy basing on the thermoelastic effect measured by the advanced infrared technique. Furthermore, it was observed that the stress-strain characteristics change from hardening to softening beyond the Yield point depending on the strain rate applied.

Gum metal, Titanium alloy, Superelastic nonlinear properties, strain rate

Gum Metal, a new multifunctional titanium alloy combining high elasticity of rubber and strength of metal, has been mechanically and thermomechanically tested. The subsequent tension deformation cycles have been conducted. At the strain rate of 10-2s-1 and step of 0.005 - 37 loading-unloading cycles until rupture were performed. Comparison of stress and temperature changes vs. strain for 2nd, 20th and 36th loading-unloading cycles is discussed.

Gum Metal, cyclic loading, infrared camera, thermomechanical coupling

This work presents thermomechanical characterization of a new multifunctional class of β-Ti alloy called Gum Metal subjected to cyclic tensile loading. Being developed in the Toyota Central R&D Laboratory (CRDL), Gum Metal has attracted remarkable attention due to its exceptional properties, i.e. low elastic modulus, high strength, nonlinear elastic deformation, excellent cold workability as well as Invar- and Elinvar-like behavior. Typical composition of Gum Metal is Ti-Nb-Ta-Zr-O, where oxygen content plays a key role. Its fabrication route consists of powder metallurgy forging method with subsequent cold working usually up to 90% in area reduction. The latter is critical for the unique mechanical performance but deformation mechanisms occurring in Gum Metal are unconventional and still unclear.

Gum metal, cyclic loading, titanium alloy, thermomechanical behavior

Gum metal, biomedical application, superelastic properties

Initial results of effects of thermomechanical couplings in the β-Ti alloy, Gum Metal, subjected to tension are presented. An MTS testing machine allows obtaining stress-strain curves with high accuracy, while fast and sensitive infrared camera allows estimating temperature changes of the sample during the deformation process. The obtained mechanical characteristics confirm an ultra-low elastic modulus and high strength of the Gum Metal. The infrared measurements enable to indicate average or maximum temperature change accompanying the alloy deformation process, to estimate thermoelastic effect, related to the yield point in solids, whereas the temperature distribution on the sample surface enables to investigate localisation effects, leading to the sample necking and rupture.

Gum Metal, Titanium alloy, Elastic properties, Nonlinear elasticity, thermomechanical couplings, infrared camera