A unified creep-plasticity model suitable for thermo-mechanical loading

An experimentally based unified creep-plasticity constitutive model was implemented for 1070 steel. Accurate rate and temperature effects were obtained for isothermal and thermo-mechanical loading by incorporating deformation mechanisms into the constitutive equations in a simple way

Twin nucleation in Fe-based bcc alloys - Modeling and experiments

We develop an analytical expression for twin nucleation stress in bcc metal and alloys considering generalized planar fault energy and the dislocations bounding the twin nucleus. We minimize the total energy to predict the twinning stress relying only on parameters that are obtained through atomistic calculations, thus excluding the need for any empirical constants. We validate the present approach by means of precise measurements of the onset of twinning in bcc Fe-50at% Cr single crystals showing excellent agreement. The experimental observations of the three activated slip systems of symmetric configuration in relation to the twinning mechanism are demonstrated via transmission electron microscopy techniques along with digital image correlation. We then confirm the validity of the model for Fe, Fe-25at% Ni and Fe-3at% V alloys compared with experiments from the literature to show general applicability

Twin migration in Fe-based bcc crystals: Theory and experiments

We establish an overall energy expression to determine the twin migration stress in bcc metals. Twin migration succeeds twin nucleation often after a load drop, and a model to establish twin migration stress is of paramount importance. We compute the planar fault energy barriers and determine the elastic energies of twinning dislocations including the role of residual dislocations (br) and twin intersection types such as 1 1 0, 1 1 3 and 2 1 0. The energy expression derived provides the twin migration stress in relation to the twin nucleation stress with a ratio of 0.5-0.8 depending on the resultant residual burgers vector and the intersection types. Utilizing digital image correlation, it was possible to differentiate the twin nucleation and twin advancement events experimentally, and transmission electron microscopy observations provided further support to the modelling efforts. Overall, the methodology developed provides an enhanced understanding of twin progression in bcc metals, and most importantly the proposed model does not rely on empirical constants. We utilize Fe-50at.%Cr in our experiments, and subsequently predict the twin migration stress for pure Fe, and Fe-3at.%V from the literature showing excellent agreement with experiments. © 2014 Taylor & Francis

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

Mitochondrial carrier homolog 1 (Mtch1) antibodies in neuro-Behçet's disease

Cataloged from PDF version of article.Efforts for the identification of diagnostic autoantibodies for neuro-Behcet's disease (NBD) have failed. Screening of NBD patients' sera with protein macroarray identified mitochondrial carrier homolog 1 (Mtch1), an apoptosis-related protein, as a potential autoantigen. ELISA studies showed serum Mtch1 antibodies in 68 of 144 BD patients with or without neurological involvement and in 4 of 168 controls corresponding to a sensitivity of 47.2% and specificity of 97.6%. Mtch1 antibody positive NBD patients had more attacks, increased disability and lower serum nucleosome levels. Mtch1 antibody might be involved in pathogenic mechanisms of NBD rather than being a coincidental byproduct of autoinflammation. © 2013 Elsevier B.V