Torsional Strain Research Articles

Electron Backscatter Diffraction Analysis of the Microstructure Fineness in Pure Copper Under Torsional Deformation

Torsional deformation is regarded a promising deformation procedure to prepare the gradient structural materials. Pure copper was subjected to large plastic strains in torsion. Electron backscatter diffraction analysis was used to explore the microstructure evolution. The observations demonstrate that both high-angle grain boundaries and misorientation increase with strain. The grains finer and more homogeneous. In addition, the microstructure within the shear band demonstrates a distinct preferred orientation. The crystal direction is parallel to the shear direction, and the crystal {111} inclines to the plane shear surface. A torsion-induced bar specimen includes a {011} brass texture, {011} Gaussian texture, and stronger {112} copper texture.

Experimental study on effect of reverse rotation on micro-hardness value of high-pressure torsion processed samples

Recently severe plastic deformation methods have became a great importance in manufacture of ultrafine-grained microstructures, in order of sub-microns and nanometers, and their great potential to improve significant deformation properties of the materials. High Pressure Torsion method namely HPT is the leadership of the severe plastic deformation methods in which metals are subjected to a compressive forces and simultaneously torsional straining. The HPT process is recognized in the last 20 years due to the opportunity for achieving exceptional grain refinement often to the nanometers range and remarkably high strength. In this research, the HPT apparatus to investigate the properties of the materials in various process parameters was designed and manufactured. One of the most advantages of the manufactured apparatus is the ability of implementing the reverse rotation and the rotational revolution control. In this study the effect of the applied reverse direction on gain size of the processed materials is innovatively studied. The surface response method was implemented to the experimental tests. The material used in the current study was the commercial cooper blanks with 10 mm diameters. All experiments were performed at a constant normal pressure of 6 GPa. The results of the experiments were compared in various applied revolutions and directions.

Unusual biaryl torsional strain promotes reactivity in Cu-catalyzed Sommelet-Hauser rearrangement.

A Cu-catalyzed Sommelet-Hauser dearomatization of dihydrophenanthridine and diazo compounds is reported for the synthesis of spiro-indolines. A spiro-structure with adjacent quaternary and tertiary carbon centers was constructed in one step as a single isomer. Increasing steric hindrance by introducing ortho-substituents dramatically improved substrate reactivity in this transformation.

Влияние пластической деформации в мартенситном состоянии на развитие эффектов сверхэластичности и памяти формы в сплавах на основе никелида титана

AbstractThe superelasticity and shape memory effects upon torsional straining of samples of the binary titanium nickelide based alloy with the B 19' martensitic phase structure have been investigated. It has been found that, in samples plastically strained during their loading up to a specified torsional strain of ~39%, the superelasticity value can attain 6.3%, which is comparable with the classical superelasticity effect. The superelasticity manifestation in the martensitic state upon torsion straining of the samples has been compared with the results of similar studies on tensile straining of the titanium nickelide-based alloy samples.

Резонансы пространственного распределения дислокаций при взаимодействии со структурным параметром порядка

AbstractThe interaction of a structural subsystem with dislocations under the superposition of an elastic torsion strain and an additional uniaxial spatially nonuniform time-constant pressure is studied. The analysis is carried out within of Landau’s phenomenological theory with refusal of the approximation of constant magnitudes of irreducible vectors. The rise of spatial resonances of the dislocation density in these conditions is shown.

Fracture analysis of high strain rate torsion samples of aluminium zinc magnesium copper alloy

Aluminium alloy T was subjected to Torsional Split Hopkinson Bar A Hollow thin wall cylindrical samples were twisted with an instant release of bar with stored toque generating strain rate in the range of s to s Few samples failed around highest strain rate in the range of s A hollow thin wall cylindrical sample failing under high strain torsion revealed a range of failure from brittle to ductile owing to material behaving differently at different strain rates along the circumference of fracture Brittle failure at high strain rates were typically flat with sheared precipitates and intermetallic inclusions Ductile failure showed elongated oval dimples typical of shear fracture and bypassed precipitates and intermetallic inclusions Sample bending crack splitting and crack diversion was also observed

Gradient residual strain and stress distributions in a high pressure torsion deformed iron disk revealed by high energy X-ray diffraction

High energy X-ray diffraction is used to investigate for the first time the distribution of residual X-ray elastic stresses inside a high pressure torsion (HPT) deformed iron disk with a diameter and thickness of ~30 and ~8mm, respectively. In the experiment, a dedicated conical slit system restricts the diffraction gauge volume in three dimensions to ~0.45mm3, which is then used to scan the bulk sample cross-section in a non-invasive manner. Pronounced residuals stress gradients with maximal tensile stresses of ~200MPa are observed along radial and tangential directions and are correlated to the deformation gradient arising from HPT.

Twisting short dsDNA with applied tension

The twisting deformation of mechanically stretched DNA molecules is studied by a coarse grained Hamiltonian model incorporating the fundamental interactions that stabilize the double helix and accounting for the radial and angular base pair fluctuations. The latter are all the more important at short length scales in which DNA fragments maintain an intrinsic flexibility. The presented computational method simulates a broad ensemble of possible molecule conformations characterized by a specific average twist and determines the energetically most convenient helical twist by free energy minimization. As this is done for any external load, the method yields the characteristic twist-stretch profile of the molecule and also computes the changes in the macroscopic helix parameters i.e. average diameter and rise distance. It is predicted that short molecules under stretching should first over-twist and then untwist by increasing the external load. Moreover, applying a constant load and simulating a torsional strain which over-twists the helix, it is found that the average helix diameter shrinks while the molecule elongates, in agreement with the experimental trend observed in kilo-base long sequences. The quantitative relation between percent relative elongation and superhelical density at fixed load is derived. The proposed theoretical model and computational method offer a general approach to characterize specific DNA fragments and predict their macroscopic elastic response as a function of the effective potential parameters of the mesoscopic Hamiltonian.

Constitutive modeling of cyclic deformation of metals under strain controlled axial extension and cyclic torsion

The present work provides a formulation of a constitutive model for metals with the aim to simulate cyclic deformation under axial extension or compression assisted by cyclic torsional (or shearing) straining of specified amplitude and frequency. Such a mode of deformation was recently implemented in technological processes such as extrusion, forging and rolling, cf. Bochniak and Korbel (Eng Trans 47:351–367, 1999, J Mater Process Technol 134:120–134, 2003, Philos Mag 93:1883–1913, 2013, Mater Sci Technol 16:664–674, 2000). The constitutive model accounting for combined hardening (isotropic–kinematic) with both hardening and recovery effects is presented and calibrated for several materials: pure copper, aluminum alloy (2024), and austenitic steel. The experimental data are used to specify model parameters of materials tested, and next the cyclic response for different shear strain amplitudes is predicted and confronted with empirical data. The constitutive model is developed in order to simulate technological processes assisted by cyclic deformation.

Torsional vibrations with bit off bottom: Modeling, characterization and field data validation

A distributed model of a drill string is presented, with Coulomb stiction as a distributed source term, to investigate the effect of borehole inclination and borehole friction on the incidence of torsional vibrations along a drill-string. To isolate the effect of this distributed friction, only cases where the bit is off bottom and with no axial movement are considered, and consequently a purely torsional model is used. The model is used to study the stick slip limit cycle, as caused by distributed Coulomb friction, and the limit-cycle period and amplitude dependence on the friction parameters is derived. This enables the qualitative limit-cycle behavior to be characterized as inertia or stick dominated, and examples of this characterization is validated with the field data. For comparison, high frequency field data from two deviated wells from surface and downhole sensors are considered. Time-series are isolated where angular rotation is restarted after a connection, with the bit off bottom and before axial motion is re-initiated, to make the data consistent with the model assumptions. A close match is obtained between recorded and modeled downhole data, however, in some cases either the initial torsional strain in the drillstring is not known or axial motion is initiated, which violates model assumptions, causing a mismatch.

Calculation of flutter and dynamic behavior of advanced composite swept wings with tapered cross section in unsteady incompressible flow

ABSTRACTIn this study, the aeroelastic stability and response of a swept composite wing in subsonic incompressible flow are investigated. The wing is modeled as an anisotropic tapered thin-walled beam with the circumferentially asymmetric stiffness structural configuration to establish proper coupling between bending and torsion. The structural model considers a number of nonclassical effects, such as transverse shear, material anisotropy, warping inhibition, nonuniform torsion, rotary inertia and three-dimensional strain effects. The aerodynamic strip method based on two-dimensional Wagner function in unsteady incompressible flow is used. Following the analysis, the mass, stiffness and the damping matrices of the nonconservative aeroelastic system are formed such that the extended Galerkin method and the separation of variables method can be employed. As a result, the coupled and linear governing system of dynamic equations is obtained. Then, by transforming matrices into the state-space and state-vector forms, the problem under study is finally converted into an eigenvalue problem. The flutter and the divergence speeds for various layer configurations with different geometric and material properties and fiber orientations are obtained. By solving the aforementioned equations of motion in the time domain, the aeroelastic responses of the tapered swept composite wing are computed. The obtained results are compared with the available literature.

Study of inverse magnetostrictive effect in metallic glasses Fe80−xCoxP14B6

The paper presents the possibility to build a tension gauge capable to discriminate different kinds of deformations: compression and twisting (induced by torsion strain) based on the magnetoelastic effect in new metallic glasses Fe80−xCoxP14B6. Applied loads increase coercive field Hc, saturation induction Bs and rectangularity of magnetic hysteresis loop. For example, hysteresis loop traced for 1 mm narrow, 50 cm long and 30 μm thick Fe40Co40P14B6 straight ribbon subjected to longitudinal stress of 346 MPa shown increased Bs from 1.24 to 1.7 T and squareness from 0.55 to 0.88 compared to unloaded specimen. For twisting, on the contrary, both squareness and coercive field vary whereas the value of Bs remains unchanged.

Effect of dislocations on the structural order parameter in a crystal upon torsional strain

The interaction of the structural subsystem with dislocations upon applying an elastic torsional strain has been studied. The consideration is performed in the terms of the Landau phenomenological theory with the refusal from the approximation that the irreducible vector magnitudes are constant. It is shown that additional spatial amplitude and frequency oscillations related to the change in the magnitudes of the structural order parameter and the dislocation density appear.

The anterior process of the malleus in extant Lagomorpha (Mammalia).

The anterior anchoring of the malleus of 30 extant species of Lagomorpha (rabbits, hares, pikas) has been studied on the basis of histological serial sections and µCT-scans. It is shown that former studies of Oryctolagus, Lepus, and Ochotona are incomplete, because the rostral part of the processus anterior of the malleus is always lacking due to damage of this extremely delicate structure. Our study shows that in perinatal stages of Leporidae the praearticulare develops a prominent processus internus that fits into a groove at the ventral side of the tegmen tympani; this "tongue and groove"-arrangement may act as a hinge. In adult stages, the rostral end of the praearticulare fuses synostotically with the medial process of the ectotympanic. Torsional strain produced by rotation around the axis of the middle ear ossicles at sound transmission must, therefore, be experienced by the extremely thin but highly elastic bony pedicle of the processus internus praearticularis. The free ending processus anterior of a late fetal Ochotona shows a short processus internus praearticularis, which does not articulate with the tegmen tympani. During postnatal development the middle ear of Ochotona becomes considerably remodelled: not only does excessive pneumatization of the tegmen tympani and tympanic cavity wall occur, but the short processus anterior is fused synostotically to a bone trabecula of the tegmen tympani meshwork. The thin and elastic bone bridges are not equivalent in Leporidae and Ochotonidae, that is, they must have evolved convergently. Fleischer's classification with Oryctolagus possessing a "freely mobile type" of middle ear ossicles cannot be supported by our observations. The same holds true for Ochotona, which does not represent a "freely mobile type" either. Thus, we suggest for the lagomorph middle ear ossicles a new category: the "bone elasticity type."

Probing Competitive and Co-operative Hydroxyl and Ammonium Hydrogen-Bonding Directed Epoxidations.

The diastereoselectivities and rates of epoxidation (upon treatment with Cl3CCO2H then m-CPBA) of a range of cis- and trans-4-aminocycloalk-2-en-1-ol derivatives (containing five-, six-, and seven-membered rings) have been investigated. In all cases where the two potential directing groups can promote epoxidation on opposite faces of the ring scaffold, evidence of competitive epoxidation pathways, promoted by hydrogen-bonding to either the in situ formed ammonium moiety or the hydroxyl group, was observed. In contrast to the relative directing group abilities already established for the six-membered ring system (NHBn ≫ OH > NBn2), an N,N-dibenzylammonium moiety appeared more proficient than a hydroxyl group at directing the stereochemical course of the epoxidation reaction in a five- or seven-membered system. In the former case, this was rationalized by the drive to minimize torsional strain in the transition state being coupled with assistance from hydrogen-bonding to the ammonium moiety. In the latter case, this was ascribed to the steric bulk of the ammonium moiety disfavoring conformations in which hydrogen-bonding to the hydroxyl group results in direction of the epoxidation to the syn face. In cases where the two potential directing groups can promote epoxidation on the same face of the ring scaffold, an enhancement of epoxidation diastereoselectivity was not observed, while introduction of a second, allylic heteroatom to the substrate results in diminishment of the rate of epoxidation in all cases. Presumably, reduction of the nucleophilicity of the olefin by the second, inductively electron-withdrawing heteroatom is the dominant factor, and any assistance to the epoxidation reaction by the potential to form hydrogen-bonds to two directing groups rather than one is clearly unable to overwhelm it.

The effect of uniaxial and torsional strains on the Density of States of Single Walled Carbon Nanotubes

In this paper we investigate the effect of uniaxial and torsional strains on the Density of States (DOS) of single walled Carbon nanotubes (SWCNTs). We employ the nearest neighbor and the third nearest neighbor π-TB (Tight Binding) models for our investigation. It is shown that uniaxial and torsional strains in some cases of metallic SWCNTs not only open a band gap but also effectively increase the DOS of SWCNT. It is also shown that, the mentioned types of strain have different effects on the DOS of chiral SWCNTs; in some types, they increase the DOS at the band edges while in other types they decrease it at the band edges.

Effects of torsional deformation on the microstructures and mechanical properties of a CoCrFeNiMo0.15 high-entropy alloy

The effects of torsional deformation on the microstructures and mechanical properties of a CoCrFeNiMo0.15 high-entropy alloy have been investigated. The torsional deformation generates a gradient microstructure distribution due to the gradient torsional strain. Both dislocation activity and deformation twinning dominated the torsional deformation process. With increasing the torsional equivalent strain, the microstructural evolution can be described as follows: (1) formation of pile-up dislocations parallel to the trace of {1 1 1}-type slip planes; (2) formation of Taylor lattices; (3) formation of highly dense dislocation walls; (3) formation of microbands and deformation twins. The extremely high deformation strain (strained to fracture) results in the activation of wavy slip. The tensile strength is very sensitive to the torsional deformation, and increases significantly with increasing the torsional angle.

Age-related differences in left ventricular structure and function between healthy men and women

Objectives: Cardiovascular function generally decreases with age, but whether this decrease differs between men and women is unclear. Our aims were twofold: (1) to investigate age-related sex differences in left ventricular (LV) structure, function and mechanics, and (2) to compare these measures between pre- and postmenopausal women in the middle-aged group.Methods: Resting echocardiography was performed in a cross-sectional sample of 82 healthy adults (14 young men, 19 middle-aged men, 15 young women, 34 middle-aged women: 15 premenopausal and 19 postmenopausal). Two-way ANOVAs were used to examine sex × age interactions, and t-tests to compare pre- and postmenopausal women (α < 0.1).Results: Normalized LV mass, stroke volume and end-diastolic volume were significantly lower in middle-aged than young men, but this difference was smaller between middle-aged and young women. Peak systolic apical mechanics were significantly greater in middle-aged men than in middle-aged women, but not between young men and women. Postmenopausal women had significantly lower LV relaxation and mechanics (torsion, twisting velocity and apical circumferential strain rates) compared with middle-aged premenopausal women.Conclusion: Our cross-sectional findings suggest that the hearts of men and women may age differently, with men displaying greater differences in LV volumes accompanied by differences in apical mechanics.

Sequence-Dependent Self-Assembly and Structural Diversity of Islet Amyloid Polypeptide-Derived β-Sheet Fibrils

Determining the structural origins of amyloid fibrillation is essential for understanding both the pathology of amyloidosis and the rational design of inhibitors to prevent or reverse amyloid formation. In this work, the decisive roles of peptide structures on amyloid self-assembly and morphological diversity were investigated by the design of eight amyloidogenic peptides derived from islet amyloid polypeptide. Among the segments, two distinct morphologies were highlighted in the form of twisted and planar (untwisted) ribbons with varied diameters, thicknesses, and lengths. In particular, transformation of amyloid fibrils from twisted ribbons into untwisted structures was triggered by substitution of the C-terminal serine with threonine, where the side chain methyl group was responsible for the distinct morphological change. This effect was confirmed following serine substitution with alanine and valine and was ascribed to the restriction of intersheet torsional strain through the increased hydrophobic interactions and hydrogen bonding. We also studied the variation of fibril morphology (i.e., association and helicity) and peptide aggregation propensity by increasing the hydrophobicity of the peptide side group, capping the N-terminus, and extending sequence length. We anticipate that our insights into sequence-dependent fibrillation and morphological diversity will shed light on the structural interpretation of amyloidogenesis and development of structure-specific imaging agents and aggregation inhibitors.

Spider dragline silk’s surprising twist

The arachnid threads respond to torsional strain in a strikingly different fashion from conventional fibers. The arachnid threads respond to torsional strain in a strikingly different fashion from conventional fibers.