Effect Of Reorientation Research Articles

Hot deformation characterization of lamellar Ti-43Al-2Si alloy fabricated by cold crucible continuous casting

In order to investigate the hot deformation behavior of lamellar Ti-43Al-2Si (at%, similarly hereinafter) alloy with equiaxed colonies prepared by cold crucible continuous casting, the isothermal compression tests were carried out at different temperatures in the range of 1100–1250 °C using the strain rates between 0.001 s−1 and 1 s−1 with true strain of 0.8. A constitutive equation at elevated temperature and three-dimensional processing map of this alloy were established based on flow stress data at different temperatures and strain rates. The microstructures depended on deformation condition were observed by optical microscope (OM), backscattered electron (BSE) and electron back-scattered diffraction (EBSD). It was found that the deformation activation energy (Q) varied with the deformation temperature and strain rate, and average value was 451.15 kJ/mol which was much larger than that of the powder metallurgy TiAl-based alloy but smaller than that of the well directionally solidified (DS) microstructure TiAl-based alloy. Based on the processing map, the appropriate hot working domain of this alloy without deformed cracks was determined to be within the temperature window from 1150 °C to 1250 °C and in the strain rate range of 0.001–0.01 s−1. The flow softening feature of the present alloy during deformation was noted and caused by synergetic effect of dynamic recrystallization (DRX), globularization and reorientation of lamellae. In addition, the Zener-Hollomom parameter played a key role on the DRX process.

Effect of spin reorientation on magnetocaloric and transport properties of NdAl2

We report the magneto-thermal and resistive properties of rare-earth dialuminide NdAl2, including spin reorientation transition. To this purpose, we used a theoretical model that considers the interactions of exchange and Zeeman, besides the anisotropy due to the electrical crystal field. The theoretical results obtained were compared to experimental data of the NdAl2 in single crystal and bulk forms. Explicitly, we have calculated the anisotropic variation of magnetic entropy with the magnetic field oriented along the three principal crystallographic directions: [100], [110], and [111] of NdAl2 single crystal, where a signature of the spin reorientation is observed in the [110] and [111] directions. Moreover, of magnetoresistivity we consider the applied magnetic field along the crystallographic directions [100] and [110]. In turn, for the polycrystalline form, the good agreement between theory and experiment confirms the presence of spin reorientation, which was predicted theoretically in magnetization curves.

Mechanical stress effect on leakage current in Bi3.25La0.75Ti3O12 thin films

Bi3.25La0.75Ti3O12 (BLT) ferroelectric thin films were prepared on Pt/Ti/SiO2/Si substrates by metalorganic decomposition method. Mechanical stress effect on leakage current was investigated. The results demonstrate that the leakage current increases with increasing electric field. Under mechanical tensile or compressive stress, the increase trend of the leakage current with electric field shows negligible change in low field region (below 75kV/cm), while that gets weakened in high field region (above 75kV/cm) compared with that at free state (zero stress). At a certain electric field (above 75kV/cm), the leakage current decreases with increasing tensile or compressive stress. The effect of domain reorientation induced by stress combined with the contribution from charge injected into films is found to be reasonable for the explanation of the leakage current in BLT thin films under different stress.

Effect of martensite reorientation and reorientation-induced plasticity on multiaxial transformation ratchetting of super-elastic NiTi shape memory alloy: New consideration in constitutive model

Experimental results show that the martensite reorientation and reorientation-induced plasticity play critical roles on the non-proportional multiaxial transformation ratchetting of super-elastic NiTi shape memory alloy (SMA) (Song et al., 2014b). In this paper, the multiaxial transformation ratchetting of the NiTi shape memory alloy is described by developing a new constitutive model in the framework of crystal plasticity. Besides the well-known inelastic mechanisms of NiTi shape memory alloys, such as the martensite transformation, martensite reorientation, transformation-induced plasticity and accumulated residual martensite, a new inelastic deformation mechanism, i.e., reorientation-induced plasticity is included in the proposed model to address its effect on multiaxial transformation ratchetting. The constitutive model is constructed in the single crystal scale and extended to a polycrystalline version by adopting an explicit scale-transition rule. By comparing the predicted results with the corresponding experimental ones, it is verified that the proposed model describes the non-proportional multiaxial transformation ratchetting of super-elastic NiTi shape memory alloy more reasonably by considering the martensite reorientation and reorientation-induced plasticity simultaneously.

Modeling of steady-state crack growth in shape memory alloys using a stationary method

Shape memory alloys experience phase transformation from austenite to martensite around crack tip. When the crack advances, martensitic transformation occurs at the tip and the energy that goes into this transformation results in stable crack growth like in the case of plastic deformation. In literature, steady-state crack growth in elasto-plastic materials with small scale yielding at the crack tip has been successfully modeled using stationary methods. In this work, Mode I steady-state crack growth in an edge-cracked Nitinol plate is modeled using a non-local stationary method (Moumni, 1995). The Zaki–Moumni (ZM) constitutive model is utilized for this purpose. The model is implemented in ABAQUS by means of a user-defined material subroutine (UMAT) to determine transformation zones around the crack tip. Steady-state crack growth is first simulated without considering reverse transformation to calculate the effect of transformation on stress distribution in the wake region, then reverse transformation is taken into account. The effect of reorientation of martensite near the crack tip as a result of non-proportional loading is also studied. The stress distribution and the phase transformation region are compared to results obtained for the case of a static crack.

Classical simulations of heavy-ion fusion reactions and weakly-bound projectile breakup reactions

Heavy-ion collision simulations in various classical models are discussed. Heavy-ion reactions with spherical and deformed nuclei are simulated in a classical rigid-body dynamics (CRBD) model which takes into account the reorientation of the deformed projectile. It is found that the barrier parameters not only on the initial orientations of the deformed nucleus, but also on the collision energy and the moment of inertia of the deformed nucleus. Maximum reorientation effect occurs at near- and below-barrier energies for light deformed nuclei. Calculated fusion cross-sections for 24Mg + 208Pb reaction are compared with a static-barrier-penetration model (SBPM) calculation to see the effect of reorientation. Heavy-ion reactions are also simulated in a 3-stage classical molecular dynamics (3S-CMD) model in which the rigid-body constraints are relaxed when the two nuclei are close to the barrier thus, taking into account all the rotational and vibrational degrees of freedom in the same calculation. This model is extended to simulate heavy-ion reactions such as6Li + 209Bi involving the weakly-bound projectile considered as a weakly-bound cluster of deuteron and 4He nuclei, thus, simulating a 3-body system in 3S-CMD model. All the essential features of breakup reactions, such as complete fusion, incomplete fusion, no-capture breakup and scattering are demonstrated.

Experimental study of a textural transition in liquid crystals under shear stress induced by surface friction

Results of a study of the optical response of liquid crystals with helical supramolecular structure to surfacefriction-induced shear stress in aerodynamic experiments are reported. The effect of re-orientation of molecules from confocal (light-scattering) to planar (selectively reflecting light) texture is considered. The textural transition is examined by the spectral and colorimetric methods. Dependences of the reflection spectra of the formed planar texture on time and on the mean shear-stress level were obtained. It is shown that the dependence of the texture transition time on the shear-stress level can be approximated, in a logarithmic scale, with a linear dependence; this allows using the effect for flow diagnostics.

Modelling of Enhanced Photoinduced Reorientation of Nematic Liquid Crystal Molecules in Twisted Geometry: Monte Carlo Approach

Recently the effect of photoinduced molecular reorientation of nematic liquid crystal molecules originating from dispersed gold nanoparticles (NP) in twisted geometry above the Freedeericksz threshold was reported experimentally via optical Kerr effect studies [1]. In this paper we work out the Monte Carlo approach suitable for modelling of this effect using standard Lebwohl–Lasher–Rapini model with an additional term responsible for photoinduced molecular reorientation. The influence of local electric field enhancement on transmission coefficient is studied for chosen cases.

Microstructure of free-standing epitaxial Ni–Mn–Ga films before and after variant reorientation

We investigate the effect of stress-induced reorientation on the martensitic microstructure of free-standing epitaxial Ni–Mn–Ga films. Scanning electron microscopy and high-resolution transmission electron microscopy reveal that the films exhibit coexisting phases of 14 M and NM martensite after release from the MgO(1 0 0) substrate. After superplastic straining the film by 12% by applying tensile stress along a [0 0 1] direction of the Ni–Mn–Ga unit cell, the corresponding crystal structure is identified to be detwinned NM martensite.

Biaxial tensile behavior of spunbonded nonwoven geotextiles

Geotextiles can be successfully employed for any geotechnical application when they are able to sustain pre-defined levels of tensile stresses. The biaxial tensile test has an advantage over other tensile test methods in that it does not allow “necking” during deformation which simulates the operational conditions of geotextiles under confined stresses. In this study, the model for uniaxial tensile behavior of nonwovens has been modified to investigate the biaxial tensile behavior of spunbonded geotextiles. The model has included the effect of fiber re-orientation, stress-strain behavior of constituent fibers, and physical characteristics of nonwovens when the geotextile specimen is laterally constrained. A comparison is made between predicted and experimental stress-strain curves obtained from previous work ( Bais-Singh and Goswami, 1998). Theoretical findings of biaxial tensile behavior obtained using the layer theory are also critically discussed. In addition, it has been revealed that fiber re-orientation is a key factor in translating the random spunbonded nonwoven geotextiles to anisotropic structures under defined biaxial tensile stresses.

Thermal orientation effect in a nematic liquid crystal

The system of equations describing the thermal orientation effect in nonchiral liquid crystals, which was observed earlier, is proposed and substantiated. The effect of the director reorientation under the action of the temperature gradient is in many ways analogous to the Freedericksz transition in electric or magnetic fields. The angle of deviation of the director from the initial position is determined by the square of the temperature gradient. The effect is observed for a nematic liquid crystal, initially uniformly oriented, and is not accompanied by macroscopic fluxes of the medium under stationary conditions.

Suspended carbon nanotube nanocomposite beams with a high mechanical strength vialayer-by-layer nano-self-assembly

The fabrication and characterization of single-walled carbon nanotube(SWCNT) composite thin film micropatterns and suspended beams prepared bylithography-compatible layer-by-layer (LbL) nano-self-assembly are demonstrated.Negatively charged SWCNTs are assembled with a positively chargedpolydiallyldimethylammonium chloride, and the composite thin film is patterned by oxygenplasma etching with a masking layer of photoresist, resulting in a feature size of2 µm. Furthermore, the SWCNT nanocomposite stripe pattern with a metal clamp on both endsis released by etching a sacrificial layer of silicon dioxide in the hydrofluoric acid vapor.I–V measurement reveals that the resistance of SWCNT nanocomposite film decreases by 23%upon release, presumably due to the effect of reorientation of CNTs caused by thedeflection of about 50 nm. A high Young’s modulus is found in a range of 500–800 GPabased on the characterization of a fixed–fixed beam using nanoindentation. This value ismuch higher than those of the other CNT–polymer composites reported due toorganization of structures by self-assembly and higher loading of CNTs. The stiffCNT–polymer composite thin film micropattern and suspended beam have potentialapplications to novel physical sensors, nanoelectromechanical switches, other M/NEMSdevices, etc.

Polarization Transfer Solid-State NMR for Studying Surfactant Phase Behavior

The phase behavior of amphiphiles, e.g., lipids and surfactants, at low water content is of great interest for many technical and pharmaceutical applications. When put in contact with air having a moderate relative humidity, amphiphiles often exhibit coexistence between solid and liquid crystalline phases, making their complete characterization difficult. This study describes a (13)C solid-state NMR technique for the investigation of amphiphile phase behavior in the water-poor regime. While the (13)C chemical shift is an indicator of molecular conformation, the (13)C signal intensities obtained with the CP and INEPT polarization transfer schemes yield information on molecular dynamics. A theoretical analysis incorporating the effect of molecular segment reorientation, with the correlation time τ(c) and order parameter S, shows that INEPT is most efficient for mobile segments with τ(c) < 0.01 μs and S < 0.05, while CP yields maximal signal for rigid segments with τ(c) > 10 μs and/or S > 0.5 under typical solid-state NMR experimental conditions. For liquid crystalline phases, where τ(c) < 0.01 μs and 0 < S < 0.3, the observed CP and INEPT intensities serve as a gauge of S. The combination of information on molecular conformation and dynamics permits facile phase diagram determination for systems with solid crystalline, solid amorphous, anisotropic liquid crystalline, and isotropic liquid (crystalline) phases as demonstrated by experiments on a series of reference systems with known phase structure. Three solid phases (anhydrous crystal, dihydrate, gel), two anisotropic liquid crystalline phases (normal hexagonal, lamellar), and two isotropic liquid crystalline phases (micellar cubic, bicontinuous cubic) are identified in the temperature-composition phase diagram of the cetyltrimethylammonium succinate/water system. Replacing the succinate counterion with DNA prevents the formation of phases other than hexagonal and leads to a general increase of τ(c).

Tensile behaviour of nonwoven structures: comparison with experimental results

Nonwoven structures have been recently explored for numerous novel applications ranging from composites to scaffolds. The tensile property of nonwovens is a pre-requisite and indeed, one of the main parameters to determine their performance for such applications. In the first part, a modified micromechanical model describing the tensile behaviour of thermally bonded nonwovens was proposed by incorporating the effect of fibre re-orientation during the deformation (Rawal et al., J Mater Sci 45:2274, 2010). In this study, an attempt has been made to compare the theoretical and experimental stress–strain curves of thermally bonded and spunbonded nonwoven structures. These theoretical findings have been obtained from the most popular analytical tensile models of nonwovens available in the literature in addition to our modified tensile model. Poisson’s ratio has also been determined experimentally in order to predict the stress–strain behaviour of nonwoven, and its relationship with longitudinal strain has clearly distinguished between the randomly and preferentially orientated types of structures. In thermally bonded nonwovens, the tensile strength in various test directions is computed through pull-out stress and a comparison is made with the experimental results.

Tensile behaviour of thermally bonded nonwoven structures: model description

Nonwovens are complex three-dimensional anisotropic structures and consisting of fibres orientated in certain directions, which are bonded by thermal, chemical, mechanical entanglement or a combination of these techniques. Thermally bonded are further classified in two categories, i.e. through-air and calendared nonwoven structures. In this study, a modified micromechanical model describing the tensile behaviour of thermally bonded nonwovens is proposed by incorporating the effect of fibre re-orientation during the deformation. The anisotropic behaviour of through-air bonded structures is demonstrated through theoretical stress–strain curves and the relationship between the fibre re-orientation and fabric strain is also analysed. Furthermore, the failure criterion of thermally bonded nonwovens is analysed using pull-out behaviour of fibres in the system. A parametric study revealing the dependencies of various structural and geometrical characteristics of fibres on pull-out behaviour of fibres in thermally bonded nonwovens is also discussed.

Bidirectional Multiple Cracking Tests on High-Performance Fiber-Reinforced Cementitious Composite Plates

This article describes how an experimental program was conducted to investigate the effects of simultaneous opening-sliding of multiple cracks on the behavior of high-performance fiber-reinforced cementitious composites (HPFRCCs). For this purpose, 12 HPFRCC plates were tested in bending and under two constitutive principal stress directions. To facilitate reorientation of the stress fields, the plates were precracked and then sawed with certain orientations. Finally, the plates were retested in bending to failure. The results showed that the change in principal stress direction had a substantial effect on macroscopic plate behavior, as marked by reductions in strength and initial stiffness. The effect of stress field reorientation on the cracking pattern was, however, minimal. Regardless of the orientation of the new principal stress direction to that of precracking, a somewhat orthogonal crack pattern always appeared. To characterize the mechanisms involved, the relationship within the constant moment span of each plate is presented and discussed.

Investigation of domain pinning fields in ferromagnetic GaMnAs films using angular dependence of the planar Hall effect

The dependence of the planar Hall effect (PHE) in ferromagnetic GaMnAs films on the direction of the applied magnetic field was used to determine domain pinning fields in this material. The investigation was carried out by measuring the effect of reorientation of magnetization from one easy axis to another on the value of PHE as the magnetic field of fixed strength was rotated over 360 ∘. This process was repeated at several field strengths, and the PHE results were analyzed using Cowburn’s model of magnetic free energy, from which domain pinning fields of Δ E [ 1 ̄ 10 ] / M = 27.5 ± 0.3 Oe and Δ E [ 1 ̄ 1 ̄ 0 ] / M = 38.0 ± 0.7 Oe were obtained for the Ga 0.94Mn 0.06As film used in this study. These values of pinning fields agree with those obtained in earlier studies where the magnetization reversal was investigated by sweeping the magnetic field. We show that the present approach of rotating a fixed field provides a simpler and more elegant way for studying domain pinning fields in a ferromagnetic film.

Local Structural Effects and Related Dynamics in Supercritical Ethanol. 2. Hydrogen-Bonding Network and Its Effect on Single Reorientational Dynamics

The local hydrogen-bonding (HB) network and its possible interconnection with the single reorientational dynamics in pure supercritical (sc) ethanol have been systematically investigated by employing molecular dynamics simulation techniques. The results obtained reveal a nonlinear density dependence of the calculated average number of hydrogen bonds n(HB), similar to that of the calculated coordination numbers N(c), signifying also the interrelation between the local HB network and the local density augmentation in sc ethanol. Additionally, the HB dynamics were investigated in terms of several appropriate time correlation functions. The results obtained reveal that the density dependence of HB dynamics has some similarities with local density and residence dynamics, corresponding to very short length scales. Moreover, the effect of mutual reorientation on HB dynamics seems to be more important than that of mutual diffusion. Finally, the reorientational dynamics of several intramolecular vectors of ethanol have been systematically studied. From the results obtained, we may observe that the dynamics of several reorientational modes in the molecule exhibit significant differences between them. Furthermore, the effect of the HB state of each molecule on these dynamics has also been studied, revealing significant differences, especially in the case of the dynamics of HB free molecules.

Gravity and tectonic patterns of Mercury: Effect of tidal deformation, spin‐orbit resonance, nonzero eccentricity, despinning, and reorientation

We consider the effect of spin‐orbit resonance, nonzero eccentricity, despinning, and reorientation on Mercury's gravity and tectonic pattern. Large variations of the gravity and shape coefficients from the synchronous rotation and zero eccentricity values,J2/C22= 10/3 and (b−c)/(a−c) = 1/4, arise because of nonsynchronous rotation and nonzero eccentricity even in the absence of reorientation or despinning. Reorientation or despinning induces additional variations. The large gravity coefficientsJ2= (6 ± 2) × 10−5andC22= (1 ± 0.5) × 10−5estimated from the Mariner 10 flybys cannot be attributed to Caloris alone since the required mass excess in this case would have caused Caloris to migrate to one of Mercury's hot poles. Similarly, a large remnant bulge due to a smaller semimajor axis and spin‐orbit resonance can be dismissed since the required semimajor axis is unphysically small (&lt;0.1 AU). Reorientation of a large remnant bulge recording an epoch of faster rotation (without significant semimajor axis variations) can explain the large gravity coefficients. This requires initial rotation rates ≳20 times the present value and a positive gravity anomaly associated with Caloris capable of driving ∼10°–45° equatorward reorientation. The required gravity anomaly can be explained by infilling of the basin with material of thicknesses ≳7 km or an annulus of volcanic plains emplaced around the basin with an annulus width ∼1200 km and fill thicknesses ≳2 km. The predicted tectonic pattern due to these despinning and reorientation scenarios, including some radial contraction, is in good agreement with the lobate scarp pattern observed by Mariner 10. We also predict that lobate scarps will follow a NE–SW orientation in the eastern hemisphere and a positive gravity anomaly (of a few hundred mGal) associated with Caloris.

Adsorption layer characteristics of Triton surfactants: 4. Dynamic surface tension and dilational visco-elasticity of micellar solutions

The presence of micelles in the solution accelerates the adsorption dynamics of Tritons at the solution/air interface, depending on the micelle dissolution rate. Micellar solutions (at CMC and up to about 10× CMC) are studied by maximum bubble pressure tensiometry and oscillating bubble profile tensiometry. The dynamic surface tensions in the time range between 0.1 ms up to 50 s are analysed by a diffusion controlled mechanism. At very short times the effect of molecular reorientation of the Triton molecules at the surface is observed. The dilational elasticity data at low frequencies (0.005–0.2 Hz) provide good agreement with a respective model assuming a very fast micelle dissolution. While for Triton X-45 and X-100 a quantitative agreement with existing theories is observed, the results for Triton X-165 and X-405 agree only qualitatively. This discrepancy is obviously due to the respective composition of the technical surfactants and a quantitative understanding would require an accurate knowledge on the sample composition.