Modeling of Cyclic Ratchetting Plasticity, Part II: Comparison of Model Simulations With Experiments,"

The material constants of the new plasticity model proposed in the first part of the paper can be divided into two independent groups. The first group, c (,> and. r (l&gt

Shape memory behavior in Fe 3 Al-modeling and experiments

The Fe 3 Al alloy with D0 3 structure exhibits large recoverable strains due to reversible slips. Tension and compression experiments were conducted on single crystals of Fe 3 Al, and the onset of slip in forward and reverse directions were obtained utilizing high-resolution digital image correlation technique. The back stress provides the driving force for reversal of deformation upon unloading, resulting in a superelastic phenomenon as in shape memory alloys. Using density functional theory simulations, we obtain the energy barriers (GSFE -generalized stacking fault energy) for {1 1 0}〈1 1 1〉 and {1 1 2} 〈1 1 1〉 slips in D0 3 Fe 3 Al and the elastic moduli tensor, and undertake anisotropic continuum calculations to obtain the back stress and the frictional stress responsible for reversible slip. We compare the theoretically obtained slip stress magnitudes (friction and back stress) with the experimental measurements disclosing excellent agreement

Mechanical Oscillations in TiNi Under Synchronized Martensite Transformations Experimental Procedure

Mechanical vibrations in alloys with thermoelastic martensitic transformations have some specific features. The main one is the existence of damping peaks at temperatures of austenite<-*martensite transitions (Van Humbeeck, 1989; Naturally, experiments including fast phase transformations with the duration of a small fraction of the period of vibrations (when tpi, < T) do not allow correctly judging the internal friction as of material damping capacity. However, such experiments are interesting from the point-of-view of active control of vibrations by fast changes of the phase composition. When tph < T, the object under investigation must be considered as a solid with periodically varying strain, in which martensitic transformation occurs on some stages of the deformation. In TiNi-based alloys the transformation is accompanied with such phenomena of martensitic nonelasticity as shape memory, transformation plasticity, generation, or relaxation of stresses. In other words, it leads to a change of the stressedstrained state of the body. If such changes occur one or several times during one period of vibrations, they will necessarily influence the whole mechanical process and cause a variation of the amplitude and frequency of vibrations, level of damping. The result of such influence will certainly depend on what stage of a vibration period the transformation takes place, is it direct or reverse, etc. On the whole, the existing knowledge of martensitic nonelasticity allows us to state that an effective control of vibrations can be achieved by specially organized fast changes of the material structural state. This is confirmed by the results of the preliminary studies by The main goal of this work is the analysis of the influence of fast martensitic transformations on the unforced oscillations of a TiNi alloy wire torsional pendulum. Experimental Procedure The vibrating system under investigation was a torsional pendulum. The specimen used as a working body has been made of Ti-50at.%Ni wire with the length 400 mm and the diameter 0.5 mm. After annealing the alloy had the transformation temperatures Af, = 330 K, Mf = 320 K, A, = 355 K, Af = 370 K. At the room temperature the specimen had the structure of martensite. The upper end of the specimen was fixed in an unmovable conical grip and the lower end could rotate freely together with an attached beam with weights. The length of the beam and the mass of weights have been chosen because the frequency of pendulum vibrations was about 0.05 Hz. The beam was equipped with a transparent rim with scores. Pendulum rotation by one angular degree corresponded to an interval between the scores. The angle of rotation was measured by the number of scores which passed through an optical registration system consisting of a lamp, a collimator, and a photo-indicator. Heating of the specimen had been done by the passing of alternating current through the circuit: upper grip-specimensteel rod fastened to the lower grip and aligned along the pendulum axis-electrolyte (water solution of copper sulfate) -copper blade contact immersed into the electrolyte. The use of the electrolytic bath as part of the circuit allowed securing a reliable electric contact with the specimen and reduce friction to a minimum. Cooling of the specimen after the break of the current occurred by natural heat exchange with the air. The mean temperature was obtained by measuring the resistivity of 0.01 mm diameter copper wire coiled around the specimen on all its length. The deformation y of the specimen was calculated by the formula y = irip)/L, where r and L are radius and length of the specimen, tp is the rotation angle in radians. The initial angular deflection of the pendulum from equilibrium corresponded to 7o = 0.3% deformation. Martensitic transformation was provoked by heating of the specimen with 0.2 s impulses of 3.5 A current. During an impulse the specimen was transformed from martensitic state into an austenitic one. Synchronization of the impulses with the mechanical oscillations is illustrated by Heating impulses were applied at a frequency twice that of the vibrations and as one may see from the figure the specimen experienced the transition from martensite to austenite and back in the course of each semiperiod of the vibrations. The moment of time corresponding to the maximum deflection of the pendulum from equilibrium in each semiperiod was registered by the equipment (by the minimum of the angular speed of the beam) and in a specified delay time At a heating impulse was given

Dynamic regulation of canonical TGF beta signalling by endothelial transcription factor ERG protects from liver fibrogenesis

The role of the endothelium in protecting from chronic liver disease and TGFβ-mediated fibrosis remains unclear. Here we describe how the endothelial transcription factor ETS-related gene (ERG) promotes liver homoeostasis by controlling canonical TGFβ-SMAD signalling, driving the SMAD1 pathway while repressing SMAD3 activity. Molecular analysis shows that ERG binds to SMAD3, restricting its access to DNA. Ablation of ERG expression results in endothelial-to-mesenchymal transition (EndMT) and spontaneous liver fibrogenesis in EC-specific constitutive hemi-deficient (ErgcEC-Het) and inducible homozygous deficient mice (ErgiEC-KO), in a SMAD3-dependent manner. Acute administration of the TNF-α inhibitor etanercept inhibits carbon tetrachloride (CCL4)-induced fibrogenesis in an ERG-dependent manner in mice. Decreased ERG expression also correlates with EndMT in tissues from patients with end-stage liver fibrosis. These studies identify a pathogenic mechanism where loss of ERG causes endothelial-dependent liver fibrogenesis via regulation of SMAD2/3. Moreover, ERG represents a promising candidate biomarker for assessing EndMT in liver disease

Hardening by slip-twin and twin-twin interactions in FeMnNiCoCr

© 2018 Acta Materialia Inc. To enhance strain hardening of alloys beyond levels accessible by forest hardening slip-twin interactions and twin-twin interactions have been proposed. The high entropy alloy FeMnNiCoCr constitutes a prominent example of exceptionally pronounced strain hardening instigated by profuse slip-twin/twin-slip and twin-twin interaction at cryogenic temperatures. In the current study, we perform uniaxial straining experiments on single crystals at 77 K. The Tension crystal shows the potential ease of twin progression for slip-twin interaction (softening) in contrast to the difficulty for twin advancement in Tension, Tension and Compression cases (hardening). The corresponding self and latent hardening coefficients derived from the data reveal that slip-twin latent moduli are much smaller than twin-twin latent moduli. Unlike previous undertakings, this study demonstrates a novel approach to assess latent hardening where plastic straining is implemented in a monotonic fashion and primary and latent systems operate simultaneously. To predict the flow stress depending on crystal orientation and as a function of strain a numerical model is proposed using the obtained hardening moduli. It emerges that the magnitude of residual Burgers vectors originating from twin-related reactions can explain the experimental hardening/softening trends. These results hold considerable promise for a quantitative description of strain hardening in metals and alloys.status: publishe

Ultrahigh tensile transformation strains in new Ni50.5Ti36.2Hf13.3 shape memory alloy

We report on unprecedented transformation strains exceeding 20% in tension for Ni50.5Ti36.2Hf13.3 shape memory alloy (SMA). The strain measurements were made at multiscales utilizing advanced digital image correlation. The display of excellent strain reversibility in shape memory (isothermal deformation between Mf and Af), isobaric thermal cycling (between Mf and Af), and superelasticity experiments (deformation above Af) confirms a wide range of functionality. The ultrahigh strains in [111] orientation exceed the lattice deformation theory predictions possibly pointing to contributions from mechanical twinning effects. The high strength levels and large strains result in very high work outputs compared to other SMAs

Twinning-induced strain hardening in dual-phase FeCoCrNiAl0.5 at room and cryogenic temperature

A face-centered-cubic (fcc) oriented FeCoCrNiAl0.5 dual-phase high entropy alloy (HEA) was plastically strained in uniaxial compression at 77K and 293K and the underlying deformation mechanisms were studied. The undeformed microstructure consists of a body-centered-cubic (bcc)/B2 interdendritic network and precipitates embedded in 〈001〉-oriented fcc dendrites. In contrast to other dual-phase HEAs, at both deformation temperatures a steep rise in the stress-strain curves occurs above 23% total axial strain. As a result, the hardening rate associated saturates at the unusual high value of ~6 GPa. Analysis of the strain partitioning between fcc and bcc/B2 by digital image correlation shows that the fcc component carries the larger part of the plastic strain. Further, electron backscatter diffraction and transmission electron microscopy evidence ample fcc deformation twinning both at 77K and 293K, while slip activity only is found in the bcc/B2. These results may guide future advancements in the design of novel alloys with superior toughening characteristics.status: publishe

Shape memory functionality under multi-cycles in NiTiHf

The functionality of NiTiHf (25%Hf) shape memory alloy (SMA) was studied under isobaric temperature cycling experiments. Both the local and overall strains, determined with digital image correlation (DIC), displayed excellent stability and no measurable unrecovered elongation. The external stress levels were higher than 250 MPa and transformation temperature was 420 °C which exceeds other NiTi based alloys, demonstrating the outstanding potential of the NiTiHf alloys