Pracownicy

Streszczenie:
The quasi-static and high strain rate compressive behavior of Gum Metal with composition Ti-36Nb-2Ta-3Zr-0.3O (wt pct) has been investigated using an electromechanical testing machine and a split Hopkinson pressure bar, respectively. The stress–strain curves obtained for Gum Metal tested under monotonic and dynamic loadings revealed a strain-softening effect which intensified with increasing strain rate. Moreover, the plastic flow stress was observed to increase for both static and dynamic loading conditions with increasing strain rate. The microstructural characterization of the tested Gum Metal specimens showed particular deformation mechanisms regulating the phenomena of strain hardening and strain softening, namely an adiabatic shear band formed at ~ 45 deg with respect to the loading direction as well as widely spaced deformation bands (kink bands). Dislocations within the channels intersecting with twins may cause strain hardening while recrystallized grains and kink bands with crystal rotation inside the grains may lead to strain softening. A constitutive description of the compressive behavior of Gum Metal was proposed using a modified Johnson–Cook model. Good agreement between the experimental and the numerical data obtained in the work was achieved.

Streszczenie:
In recent decades, several novel Ti alloys have been developed in order to produce improved alternatives to the conventional alloys used in the biomedical industry such as commercially pure titanium or dual phase (alpha and beta) Ti alloys. Gum Metal with the non-toxic composition Ti–36Nb–2Ta–3Zr–0.3O (wt. %) is a relatively new alloy which belongs to the group of metastable beta Ti alloys. In this work, Gum Metal has been assessed in terms of its mechanical properties, corrosion resistance and cell culture response. The performance of Gum Metal was contrasted with that of Ti–6Al–4V ELI (extra-low interstitial) which is commonly used as a material for implants. The advantageous mechanical characteristics of Gum Metal, e.g. a relatively low Young's modulus (below 70 GPa), high strength (over 1000 MPa) and a large range of reversible deformation, that are important in the context of potential implant applications, were confirmed. Moreover, the results of short- and long-term electrochemical characterization of Gum Metal showed high corrosion resistance in Ringer's solution with varied pH. The corrosion resistance of Gum Metal was best in a weak acid environment. Potentiodynamic polarization studies revealed that Gum Metal is significantly less susceptible to pitting corrosion compared to Ti–6Al–4V ELI. The oxide layer on the Gum Metal surface was stable up to 8.5 V. Prior to cell culture, the surface conditions of the samples, such as nanohardness, roughness and chemical composition, were analyzed. Evaluation of the in vitro biocompatibility of the alloys was performed by cell attachment and spreading analysis after incubation for 48 h. Increased in vitro MC3T3-E1 osteoblast viability and proliferation on the Gum Metal samples was observed. Gum Metal presented excellent properties making it a suitable candidate for biomedical applications.

Słowa kluczowe:
Gum Metal, mechanical behavior, in vitro corrosion resistance, in vitro biocompatibility, implant applications

Streszczenie:
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.

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

Streszczenie:
The mechanical anisotropy of a multifunctional titanium alloy, Gum Metal, is investigated in this paper. The structural characterisation showed a strong <110> texture for Gum Metal, that is a result of the cold-swaging process applied during its manufacture. Gum Metal was treated as a transversally isotropic solid because of this texture. A significant difference from Young's moduli of the alloy was detected from the ultrasonic measurement of parallel and perpendicular directions to the alloy swaging direction. Samples of Gum Metal cubes were compressed in two different orientations. During the deformation process, two perpendicular walls of each sample were monitored by two visible range cameras for further two-dimensional digital image correlation analysis, this confirmed a strong plastic anisotropy in Gum Metal.

Słowa kluczowe:
gum metal, compression, mechanical anisotropy, digital image correlation, ultrasonic measurement, texture, titanium alloy, full-field deformation measurement

Streszczenie:
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.

Słowa kluczowe:
large strain, hyperelasto-viscoplasticity, gum metal, cyclic deformation

Streszczenie:
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.

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

Streszczenie:
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.

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

Streszczenie:
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.

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

Streszczenie:
This paper presents experimental and numerical results of a polyurethane shape memory polymer (SMP) subjected to cyclic tensile loading. The goal was to investigate the polymer yielding phenomena based on the effects of thermomechanical coupling. Mechanical characteristics were obtained with a testing machine, whereas the SMP temperature accompanying its deformation process was simultaneously measured in a contactless manner with an infrared camera. The SMP glass transition temperature was approximately 45oC; therefore, when tested at room temperature, the polymer is rigid and behaves as solid material. The stress and related temperature changes at various strain rates showed how the SMP yield limit evolved in subsequent loading-unloading cycles under various strain rates. A two-phase model of the SMP was applied to describe its mechanical response in cyclic tension. The 3D Finite Element model of a tested specimen was used in simulations. Good agreement between the model predictions and experimental results was observed for the first tension cycle.

Słowa kluczowe:
Shape memory polymer, Tension cyclic loading, Thermomechanical coupling, Yield limit, Thermoelastic effect, Constitutive model

Streszczenie:
Residues resulting from the manufacture of strontium ferrite magnets have been recycled for further use in magnet fabrication instead of disposal as waste. The quality of the recycled ferrite powder has been tested and compared to that of the new starting ferrite material. The magnetic properties of the recycled powder not only match those of the starting material acquired by the company for the production of magnets but exceed them. A coercivity value 3.5 times larger than that of the new starting ferrite powder, accompanied by a 25% increase in remanence, makes this material a new and improved ferrite product to re-enter the production chain in the factory with an extended applications range. This improvement is proven to be due to tuning of the morphology and microstructure through processing and subsequent heat treatment. The use of processing conditions in the same range as those typically used in the preparation of ferrite powders and magnets, in combination with the superior magnetic quality of the resulting powders, makes this method a suitable path to guarantee sustainability and an efficient use of resources in permanent magnet companies.

Słowa kluczowe:
Ferrites, Permanent magnets, Recovery, Recycling, Sustainability

Streszczenie:
The impact of ultra-short milling at liquid nitrogen temperatures on structural and magnetic properties of cobalt ferrite (CoFe2O4) powders has been explored for the first time. Cryomilling for only up to 9 min increases the coercivity of the isotropic powder from 139 to 306 kA/m (1.74–3.85 kOe) and results in its modifications comparable with milling for hours at room temperature. A thermal treatment of processed CoFe2O4 enables further optimization of powder magnetic properties and leads to a high value of energy product (13.5 kJ/m3) for the sample treated at 600 °C. Systematic studies, comprising analysis of structural and microstructural properties, based on synchrotron powder X-ray diffraction, scanning and transmission electron microscopy demonstrate the high efficiency of cryomilling in reduction of crystallite sizes and formation of lattice strain in the processed cobalt ferrite samples.

Słowa kluczowe:
Cryomilling, Cobalt ferrite, Magnetic properties

Streszczenie:
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.

Słowa kluczowe:
gum metal, thermomechanical coupling, nonlinear elasticity, yield point, infrared camera

Streszczenie:
This paper presents experimental and modeling results of the effects of thermomechanical couplings occurring in a polyurethane shape memory polymer (SMP) subjected to tension at various strain rates within large strains. The SMP mechanical curves, recorded using a testing machine, and the related temperature changes, measured in a contactless manner using an IR camera, were used to investigate the polymer deformation process at various loading stages. The effects of thermomechanical couplings allowed the determination of the material yield point in the initial loading stage, the investigation of nucleation and development of the strain localization at larger strains and the estimation of the effects of thermoelastic behavior during the unloading process. The obtained stress–strain and thermal characteristics, the results of the dynamic mechanical analysis and estimated values of the shape fixity and shape recovery parameters confirmed that the shape memory polymer (T g = 45°C) is characterized by good mechanical and shape memory properties, as well as high sensitivity to the strain rate. The mechanical response of the SMP subjected to tension was simulated using the finite element method and applying the large strain, two-phase model. Strain localization observed in the experiment was well reproduced in simulations and the temperature spots were correlated with the accumulated viscoplastic deformation of the SMP glassy phase.

Słowa kluczowe:
shape memory polymer, thermomechanical coupling, infrared camera, tension test, strain rate, strain localization, constitutive model

Streszczenie:
We report on a comparative study of high performance isotropic cobalt ferrite (CoFe2O4) powder processed by dry and surfactant assisted (wet) ball milling. Milling times as short as 1.5 min (dry) and 6 min (wet) have resulted in a 4-fold increase in coercivity, with a maximum achieved value above 318 kA/m (4 kOe). The use of surfactant is shown to be advantageous in the formation of a more homogeneous structure constituted by non-agglomerated and strained nanoparticles. A record (BH) max value of 18.6 kJ m −3 (2.34 MGOe) has been obtained for isotropic powder after post-processing annealing. This magnetic performance combined with the required short processing times and the unnecessary requirement of oxygen avoidance in the milling process, makes this CoFe2O4 powder a good candidate for permanent magnet applications.

Słowa kluczowe:
Milling, Nanopowders, Powders, Coercive force, Surfactants

Streszczenie:
Synthesis of nanocrystalline Co-ferrite powders with tunable magnetic properties is demonstrated by using co-precipitation and a novel ultrafast milling route. Milling times as short as a few minutes are re- ported for the first time to be sufficient to refine microstructure and to induce microstrain, and act efficiently, providing a 5-fold increase in coercivity. This is achieved with no compositional change during processing, but exclusively through microstructural modification. The efficiency of this process and its feasible scalability pave the way for development of Co-ferrite powders for permanent magnet applications.

Streszczenie:
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.

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

Streszczenie:
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.

Słowa kluczowe:
infrared thermography, thermomechanical behavior, gum metal

Streszczenie:
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.

Streszczenie:
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.

Słowa kluczowe:
Gum metal, nonlinear elasticity, thermomechanical couplings

Słowa kluczowe:
Gum Metal, Multifunctional Ti-based Alloy, Cyclic Compression, Infrared Thermography

Słowa kluczowe:
Gum metal, Titanium alloy, Tensile loading, Digital Image Correlation

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

Słowa kluczowe:
Mechanical Anisotropy, Ti alloy, Gum Metal, Ultrasound Measurement, Digital Image Correlation

Słowa kluczowe:
Gum Metal, EBSD, ultrasonic measurement

Streszczenie:
Experimental investigation of mechanical anisotropy in a multifunctional beta titanium alloy Gum Metal under compression is reported. Non-destructive and destructive techniques were used to analyze unique mechanical behavior of the alloy. Structural characterization showed a strong <110> texture of Gum Metal, which is a result of cold-swaging applied during its fabrication [1]. Due to this kind of texture Gum Metal can be treated as transversally isotropic solid. Ultrasonic measurements determined elastic constants with high accuracy. A significant difference between Young's moduli of the alloy calculated for parallel and perpendicular directions to the alloy swaging direction was demonstrated. Compression of Gum Metal cube samples with two orientations was conducted on a testing machine. Two perpendicular walls of each sample were monitored by two visible range cameras during the deformation process for further 2-dimensional digital image correlation (DIC) analysis. Strong mechanical anisotropy of Gum Metal was confirmed by a detailed analysis of the stress vs. strain curves and strain distributions.

Streszczenie:
In this work, mechanical properties of a β-Ti alloy Gum Metal (Ti–23Nb–0.7Ta–2.0Zr–1.2O at.%, free of cytotoxic content), which was fabricated at Toyota Central Research&Development Laboratories, Inc., were investigated. It was confirmed that Gum Metal is characterized by a low Young's modulus (around 60 GPa), high strength (over 1000 MPa) and a large range of reversible deformation, which are important features in the context of potential implant applications. Moreover, a comprehensive assessment of biocompatibility was realized. Properties of Gum Metal were contrasted with those of Ti-6Al-4V (ELI) which was taken as reference. Surface conditions, such as topography, roughness and structural composition, were analyzed. Evaluation of biocompatibility for the alloys was performed by cell attachment and spreading analysis after predefined cell culture periods. Gum Metal presented excellent properties, what makes it a goodcandidate for implant applications.

Słowa kluczowe:
Gum Metal, titanium alloy, biocompatibility, implant applications

Streszczenie:
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.

Słowa kluczowe:
gum metal, titanium alloy, tension test, strain rate, thermomechanical coupling

Streszczenie:
Preliminary results of mechanical behavior of Gum Metal compressed along the swaging direction during cyclic loading were presented. The unique mechanical performance of Gum Metal - low Young’s Modulus and high strength were confirmed. During the cyclic loading the curves profiles change significantly with each cycle and reveal a clearly pronounced yield points for the 4th and further cycles. Compression tests along perpendicular direction to the swaging one will be considered for our future research.

Słowa kluczowe:
Gum Metal, polycrystal, compression loading, cyclic loading, digital image correlation

Streszczenie:
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.

Słowa kluczowe:
Gum Metal, cyclic loading, infrared camera, thermomechanical coupling

Słowa kluczowe:
Gum metal, biomedical application, superelastic properties

Streszczenie:
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.

Słowa kluczowe:
Gum metal, Titanium alloy, Superelastic nonlinear properties, strain rate

Streszczenie:
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.

Słowa kluczowe:
Gum metal, cyclic loading, titanium alloy, thermomechanical behavior