Uniaxial Direction Research Articles

An Elastic Triboelectric Nanogenerator for Harvesting Random Mechanical Energy with Multiple Working Modes

AbstractBecause of the shortage of fossil energy and the rapid development of Internet of things nowadays, renewable and clean energy is becoming valuable and necessary. One renewable energy source, triboelectric nanogenerators (TENGs), has been proved to effectively harvest energy from vibration, walking, and even sphygmus. TENGs based on contact–separation mode are foremost and fundamental, and the input stimuli for TENGs are strictly limited by constant amplitude and uniaxial direction of motion, which limits many practical applications. Therefore, it is extremely meaningful to develop a kind of TENG to collect random energy, which ubiquitously exists in the ambient environment. Here, an elastic rubber is placed inside the structure of an elastic TENG (E‐TENG). With this novel structure, the output signals of the TENG are almost independent of the amplitude of the external stimuli due to the elasticity of rubber. Moreover, the E‐TENG shows good performance on angle detection without the limitation of the direction of stimuli. It is believed that the E‐TENG will contribute to developing next‐generation flexible TENGs and self‐powered sensors in the future.

Deformation mechanisms of mechanically induced phase transformations in iron

Effects of uniaxial tensile directions on the phase transformations in a nano-sized face centred cubic (fcc) crystal in iron were studied by molecular dynamics simulations. The results show that externally applied loading induced phase transformations from fcc phase to body centred cubic (bcc) phase, and variant selection took place depending on the tensile direction relative to the crystallographic orientation of the fcc crystal. For the loading along the close packed fcc plane, the uniaxial tensile direction perpendicular to the close packed direction led to the formation of flat-ellipsoid bcc nuclei composed of {0 1 1} twinning martensite, while that parallel to the close packed direction resulted in zigzag bcc plates with the {1 1 2} twinning sub-structure. When the tensile loading was perpendicular to the close packed fcc planes, a number of stacking faults as a result of the movement of Shockley partial dislocations appeared temporarily in the shape of “funnels”, which distorted the fcc lattices severely before it transformed into the bcc phase. The deformation mechanisms of the mechanically induced phase transformations through twinning or dislocations revealed in the present study may provide clues to develop iron or iron-based shape memory alloys with both high strength and good ductility.

Study of Peculiarities of the Microwave Absorption Spectrum of Nanocrystalline Thin Magnetic Films

Based on the micromagnetic model which takes into account the random distribution of the uniaxial magnetic anisotropy directions in crystallites of a nanocrystalline film, an effective method has been implemented for calculation of the magnetization dynamics in microwave fields. For a certain range of crystallite sizes, when the energy of the random magnetic anisotropy is comparable to the exchange energy, a significant change of the ferromagnetic resonance field, broadening of the resonance line, and the appearance of an asymmetry in the shape of the resonance curve were found. With an increase of the crystallite sizes, the resonance field first grows, then, it quickly decreases to its minimum, and then, it grows again to reach saturation. In this case, the steepness of the left slope of the broadening resonance curve first decreases faster than that of the right slope, leading to the symmetry breaking of the resonance curve shape, then, the curve becomes symmetrical again, and then, the steepness of the left slope becomes greater than that of the right slope.

Mechanically Tunable Bilayer Composite Grating for Unique Light Manipulation and Information Storage

AbstractComposite gratings play important roles in modern information technology. However, such gratings are generally based on the same structural pattern with limited types, and their structural parameters are difficult to tune, which greatly limit their application. A mechanically tunable composite grating in bilayer film, which orthogonally couples a sinusoidal phase grating and a rectangular phase grating, is developed here. The structural parameters of the grating can be well tuned by mechanically stretching or releasing the grating in the uniaxial direction. Naturally, this property allows tunable light manipulation: that is, a single incident laser beam can be split into a 2D diffraction beams array, and the intensity and propagation angle of each diffraction beam can be precisely controlled via mechanical manipulation of the grating. A theoretical model based on scalar diffraction theory that can quantitatively describe and accurately predict this light manipulation is further established. In addition, after treatment with an electron beam, the tunable structures can be immobilized, which enables the storage of information in the bilayer film. This work may open up new pathways for composite grating fabrication and further extend the applications of composite gratings in diverse fields.

First-principles study on substitution effects in Nd2(Fe, X)14B

We study the magnetic properties of the substitution effects in Nd2(Fe, X)14B (X = Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge) by first-principles calculations in order to understand which added elements have the ability to improve the coercivity of Nd–Fe–B magnets. By analyzing the formation energies of these systems and the magnetic anisotropy K1 of Nd atoms, we find that adding Mg, Ca, Sc, Cu, Zn, and Ga into Nd–Fe–B magnets is a useful approach to improve K1, a factor which is strongly related to the coercivity of Nd–Fe–B magnets. This anisotropy improvement is due to the fact that the substitution weakens the orbital coupling between 3d electrons and Nd 5d electrons, allowing the 5d electrons to extend in a uniaxial direction.

(Invited) Orientation Dependence of the Hole Ballistic Velocity in Si, Sige, and Ge Thin-Body Structures with Uniaxial Compressive Strain

Uniaxial compressive strain of p-MOSFETs has significantly improved p-MOS performance since it was introduced into high-volume manufacturing in Intel's 90-nm node. Further increases in compressive strain and the Ge fraction of the Si1-xGex channel at successive technology nodes have led to increased hole mobility (and, therefore, increased hole ballistic velocity) in p-MOSFETs over time. While the hole mobility improvement for uniaxial compressive strain along a [110] channel (with a (001) wafer surface) is widely known, the orientation dependence of uniaxial strain on the hole ballistic for arbitrary channel and surface directions has received less attention. In this talk, we use quantum-mechanical strain-dependent 6×6 k·p band-structure simulations to provide a comprehensive theoretical analysis of the impact of crystallographic orientation of the uniaxial strain, channel, and surface direction on the average hole ballistic velocity in thin-body structures of Si, SiGe, and Ge.

Experimental and modeling study of compressive creep in 3D-woven Ni-based superalloys

Micro-architectured Ni-based superalloy structures, with Ni-20Cr-3Ti-2Al (wt.%) composition and γ/γ′-microstructure, are created by a multi-step process: (i) non-crimp orthogonal 3D-weaving of ductile, 202 μm diameter Ni-20%Cr wires, (ii) gas-phase alloying with Al and Ti, (iii) simultaneous transient-liquid phase (TLP) bonding between wires and homogenization within wires via interdiffusion, (iv) solutionizing to create a single-phase solid solution, and (v) aging to precipitate the γ′ phase. The creep behavior of these 3D-woven γ/γ′ nickel-based superalloys is studied under uniaxial compression via experiments at 825 °C and via finite element (FE) analysis, using a 3D model of the woven structures obtained through X-ray micro-tomography. The creep strain rate for the woven Ni-based superalloy is higher than that for the bulk superalloy due to the lower solid volume fraction of the woven structure, while the creep exponents are identical. The compressive creep behavior is sensitive to the geometry of the woven structures: fewer wires perpendicular to the load and fewer bonds between wires cause lower creep resistance of the woven structure, due to a reduction in load transfer from the longitudinal wires (which are primarily load-bearing) and the perpendicular wires. Creep buckling of longitudinal wires drastically reduces creep resistance of the woven structure, confirming the importance of maintaining longitudinal wires vertical and parallel to the uniaxial compression direction. Finally, reducing wire cross-section, e.g., via oxidation, reduces creep resistance. The oxidation kinetics of the wire structures at 750, 825, and 900 °C displayed parabolic rate constants comparable to commercial Ni-based superalloys, but indicates that up to 35% of the wire cross-section is oxidized after 7 days at 825 °C, such that oxidation-resistant coatings are needed for long-term use in oxidative environment.

Creation of individual few-layer graphene incorporated in an aluminum matrix

3D-networks of few-layer graphene (FLG) platelets at grain boundaries, sandwiched between thin amorphous Al2O3 layers, were fabricated by spark plasma sintering (SPS) of graphene oxide (GO)/Al mixed powders. The GO was prepared by a modified Hummers’ method, and was thermally reduced to FLG simultaneously during SPS densification. Subsequent plastic flow of the Al matrix during the hot extrusion process caused the destruction of this structure, rearranged the FLG platelets individually into the uniaxial direction, and made them incorporate in the Al matrix. Observations by high-resolution transmission electron microscopy proved the existence of a direct-contact interface between the FLG and the Al matrix without any interfacial compounds, and revealed that the Al matrix featured a fairly low dislocation density. Consequently, the mechanical strength of Al matrix was noticeably enhanced by FLG incorporation, agreeing with the potential strengthening effect predicted by the load transfer mechanism.

Raman studies of MoS2 under strain at different uniaxial directions

Raman spectra of bulk and few layers MoS2 under strain at different uniaxial directions have been measured. MoS2 samples, encapsulated in between polyethylene terephthalate (PET) of octadecagonal shape and a layer of polymethlmethacrylate (PMMA), were bended in order to apply uniaxial tensile strain along different directions of MoS2. For bulk MoS2, the Raman shift rates of the E12g and A1g modes (the change of the Raman peak position versus strain level) were very small and almost the same for strains applied along different directions. On the other hand, the Raman shift rates of few layers MoS2 were larger than those in bulk MoS2. In addition, they also exhibited distinctive anisotropic strain responses. On the basis of our results, we believe that the armchair and zigzag directions of the exfoliated MoS2 might be determined by monitoring the variation of Raman shifts of the E12g and A1g modes in different strained directions of MoS2.

Effects of strain energy on the recrystallization within narrow metallization

Elastic strain energy within materials due to recrystallization of grains with a specific orientation, or texture, can be calculated through the use of Eshelby inclusions, where a recrystallized grain can be treated as an elastically anisotropic inclusion in an elastically isotropic matrix. The evolution of texture that minimizes elastic strain energy is shown to be dependent on the specific strain state. The interaction strains generated by this elastic incompatibility and corresponding strain energy have been derived for grains with cubic symmetry for general forms of the applied strain tensor. For uniaxial and isotropic, biaxial strain tensors, the interaction strain tensor and corresponding elastic strain energy density are proportional to the orientation parameter, Γ, which relates the Miller indices of the recrystallized grain to the loading direction: either parallel to the uniaxial strain direction or perpendicular to the plane in which isotropic biaxial strain is applied. It is rigorously proven that for elastically isotropic inclusions, corresponding to Γ = 1/5, the interaction strain is zero. Although blanket films often possess an isotropic, biaxial stress state, metallization trenches can exhibit a combination of normal and shear strain components, particularly near the trench corners. It is shown that in cases where shear is present, the resulting elastic strain energy can be lowered by the development of (110) texture despite its higher surface energy, as has been observed in thin films and interconnect trenches. These results suggest that shear strain can play an important role in the evolution of texture in narrow, metallization structures.

Preloaded composite panels under high velocity impact

Composite structures due to their low strain to failure are regarded as a brittle material and are susceptible to possible impact damage during manufacture, maintenance and in use. This paper describes the influence of tension, compression and hybrid preload on E-glass/polyester composite plates under high velocity impact loading in a velocity range of 185 to 235 m/s. Six layered, E-glass plain weave woven roving [0/90]6 composite panels were made by hand layup method. An innovative preloading apparatus, which is patented with number IRI-83450 was developed to apply the preloading in uniaxial and biaxial directions. This device was used simultaneously with a gas gun to conduct high velocity impact tests. A spherical hard body projectile was used in the impact tests. Uniaxial tension, uniaxial compression and biaxial tension and compression preload were applied to each specimen. To assess the strain rate sensitivity of the material concern under different preloading, three different impact velocities were used. Result showed, the ballistic resistance of the samples with the different preloading condition decreased compared to no preload case. Less variation was observed in exit velocities in the upper impact velocity range test (235 m/s) conducted for all boundary conditions used. A significant increase in the rate of change of residual velocity was observed for the impact velocity of 185.3 m/s compared with that of higher impact velocities tested. Delamination and fiber fracture constituted the major fracture modes followed by matrix fracture.

Field-induced uniaxial and biaxial nematic phases in the Maier–Saupe–Zwanzig (MSZ) lattice model

ABSTRACTWe report detailed statistical mechanics calculations to analyse the field-temperature phase diagram of a fully connected Maier–Saupe–Zwanzig (MSZ) lattice model for the nematic transitions in liquid-crystalline systems. If the field is applied along the uniaxial direction, with positive anisotropy, there is a first-order boundary between distinct uniaxial paranematic phases, which ends at a simple critical point. For negative values of the anisotropy, the first-order boundary becomes continuous at a tricritical point, and the transition is between field-induced uniaxial and biaxial structures. This elementary MSZ lattice model provides a way to systematically regain all of the main features of earlier phenomenological and model calculations. Due to the simplicity of the calculations, critical and tricritical points, as well as critical lines, can be located analytically, which leads to a possibility of comparisons with values for real experimental systems. Also, we formulate a generalised six-state MSZ model, which takes into account intrinsic molecular biaxiality, and perform calculations to determine the location of the critical point in the field-temperature phase diagram.

Deformation-induced anisotropy of uniaxially prestrained steel sheets

This article investigates the macroscopic behavior of uniaxially pre-strained large-scale DP780 and CHSP45R sheet specimens. A novel grip system was designed for the pre-straining of the large tensile specimens. After this first loading, the uniformly strained gauge-section of the large-scale specimen was machined to smaller standard specimens. After pre-strain, further uniaxial tension tests at 45° and 90° from the pre-tensile direction, compression test and in-plane biaxial tension tests at 1:1, 2:1 and 1:2 force ratios were conducted. The flow curves and the instantaneous r-values of the pre-strained steel in the aforementioned uniaxial loading directions were compared with their monotonic response. In addition, the pre-strained compression test was incorporated to the π-plane at several incremental offset strains.The yield function- and isotropic hardening-based homogeneous anisotropic hardening (HAH) model (Barlat et al., 2014) was selected to predict the material response after non-linear strain path change. The Swift law characterized the isotropic hardening, while the Yld2000-2d anisotropic yield function (Barlat et al., 2003a) represented the yield locus. All the coefficients of the distortional plasticity model were manually determined and validated with an optimization algorithm. The HAH-predictions of the pre-strained flow curves and yield loci at several offset strains were in reasonable agreement with the experimental data, while the instantaneous r-value evolution was qualitatively well captured.

An Omnidirectionally Stretchable Photodetector Based on Organic-Inorganic Heterojunctions.

Omnidirectionally stretchable photodetectors are limited by difficulties in designing material and fabrication processes that enable stretchability in multiaxial directions. Here, we propose a new approach involving an organic-inorganic p-n heterojunction photodetector comprised of free-standing ZnO nanorods grown on a poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate transport layer coated on a three-dimensional micropatterned stretchable substrate containing bumps and valleys. This structure allows for efficient absorption of stretching strain. This approach allows the device to accommodate large tensile strain in all of the directions. The device behaves as a photogated p-n heterojunction photodetector in which current modulation was obtained by sensing the mechanisms that rely on photovoltage and photogating effects. The device exhibits a high photoresponse to UV light and reliable electrical performance under applied stretching in uniaxial and omniaxial directions. Furthermore, the device can be easily and conformally attached to a human wrist. This allowed us to investigate the response of the device to UV light during human activity.

Applying physical science principles to mid-substance Achilles tendinopathy and the relationship to eccentric lengthening exercises.

Mid-substance Achilles tendinopathy is common in the active population. Eccentric (lengthening) exercises are known to be effective in alleviating the clinical condition. To better understand mid-substance Achilles tendinopathy and the response to lengthening exercises physical science principles of elasticity are applied. We apply elastic motion laws to the spring-like tendon as well as the normal and pathological adaptation seen with this common injury. We will validate important assumptions of the spring-like behavior of the tendon and then apply these findings to the injured and rehabilitating states. Our analysis considers that the tendon can be viewed as being spring-like with elasticity principles being applicable and the force exerted on the tendon during lengthening is primarily in a uniaxial direction. This applied lengthening force results in tendon mechanical and structural adaptation. Injury, and ultimately the clinical condition, occurs when the applied force exceeds the ability of the tendon to normally adapt. Morphological changes of the injured tendon are an attempt by the body to make the tendon more compliant. Lengthening exercises can be assessed as achieving this task with an improvement of tendon compliance. Physical science analysis proposes that the preferred rehabilitation tendon pathway is to try and decrease tendon stiffness to allow for more tendon lengthening. The body's morphological alterations of the pathological tendon are also consistent with this approach. For mid-substance Achilles tendinopathy, this adaptation of decreased stiffness ultimately increases the tendons ability to withstand applied force during lengthening.

Experimental and numerical investigations of the anisotropic deformation behavior of low-density polymeric foams

Low-density porous materials and foams have been widely used for a variety of applications, such as light structural components, impact energy absorption, thermal insulation and sound absorption. The macroscopic deformation of such materials is strongly dependent on their inherent micro-cellular structure. This study investigated the compressive anisotropic deformation behavior of low-density polymeric foam by using X-ray computed tomography (CT) and the finite element method (FEM) in order to understand both the microscopic and macroscopic deformation behavior. The foams used in this study have a closed cell structure, with pores that are elliptical in shape. Three different types of expansion ratios were employed. The porosities of these materials were 93.5, 95, and 96%. From the observations using the X-ray CT method, the averaged pore heights were 1 mm and the aspect ratios were 2, 2.5, and 2.25, respectively. The foam demonstrated anisotropic deformation, dependent on the uni-axial compression direction. It was found that the deformation rigidity in the longitudinal direction was larger than that in the transverse direction. By using the X-ray CT method in situ, the microscopic deformation behavior when subjected to compressive loading was observed. Deformation and collapse of pores was observed for both directions during the loading. In conjunction with this, FEM computations were carried out to elucidate how such pore geometry undergoes elastoplastic deformation and leads to macroscopic deformation behavior. The FEM-created three-dimensional spatial structures were based on elongated rhombic dodecahedrons. It is revealed that the FEM computation shows relatively good agreement with the experimental results. Thus, our experimental and computational models may be useful for microstructural design using anisotropic cellular materials.

Lattice stability and the effect of Co and Re on the ideal strength of Ni: First-principles study of uniaxial tensile deformation**Project supported by Beijing Municipality Science and Technology Commission, China (Grant No. D161100002416001) and the National Key R&D Program of China (Grant No. 2017YFB0701502).

Using first-principles density functional calculations, lattice stability of γ-Ni under [001], [110], and [111] uniaxial tensions and the effect of alloying elements Co and Re on the uniaxial tensile behavior of γ-Ni were studied in this paper. With elastic constants and phonon spectra calculations, we examined the mechanical stability and phonon stability of Ni during the uniaxial tensions along the three characteristic directions. The results show that the mechanical stability and phonon stability of a lattice occurs before the maximum stress–strain point under the [001] and [111] tension, respectively. The effects of Co and Re on the ideal tensile strength of γ-Ni show a significant directivity: Co and Re have little effect on the stresses in [001] and [111] directions, but increases the ideal strength of the system in the weakest uniaxial tensile direction. Moreover, the strengthening effect of Re is significantly better than that of Co. By further analyzing electronic structure, it is found that the effect of alloying elements on the uniaxial tensile behavior of γ-Ni comes from their interactions with host atoms.

Cu substituted CeCo5: New optimal permanent magnetic material with reduced criticality

A comprehensive theoretical prediction using a mechanism of site substitution confirms the crucial role of Cu in enhancing the capabilities of CeCo5 as a competitive magnet with its known high coercivity. A remarkable enhancement of magnetic anisotropy energy (MAE) of 3.09 meV/f.u. and 2.94 meV/f.u. without significant decrease of magnetic moment is found for 10% and 5% Cu substitution at 2c sites of the hexagonal lattice. Calculations predict the increment of coercivity and magnetocrystalline anisotropy (1.6 times) compared to pristine CeCo5. The exceptional enhancement in MAE is due to the formation of asymmetric charge hybridization among the Cu (2c) and Co (both 2c and 3g) sites along the uniaxial direction. Because of this asymmetric charge distribution environment, the intrinsic behavior of Ce adjacent to Cu changes abruptly making them more uniaxial and magnetically enhanced creating mixed valence states. For these calculations, we have employed the full-potential augmented plane wave method in conjunction with spin orbit coupling.

Statistical study of ductility-dip cracking induced plastic deformation in polycrystalline laser 3D printed Ni-based superalloy

Ductility-dip cracking in Ni-based superalloy, resulting from heat treatment, is known to cause disastrous failure, but its mechanism is still not completely clear. A statistical study of the cracking behavior as a function of crystal orientation in a laser 3D-printed DL125L Ni-based superalloy polycrystal is investigated here using the synchrotron X-ray microdiffraction. The dislocation slip system in each of the forty crystal grains adjacent to the 300 μm long crack has been analyzed through Laue diffraction peak shapes. In all these grains, edge-type geometrically necessary dislocations (GNDs) dominate, and their dislocation line directions are almost parallel to the crack plane. Based on Schmid’s law, the equivalent uniaxial tensile force direction is revealed normal to the trace of the crack. A qualitative mechanism is thus proposed. Thermal tensile stress perpendicular to the laser scanning direction is elevated due to a significant temperature gradient, and thus locations in the materials where the thermal stress exceeds the yield stress undergo plastic deformation mediated by GND activations. As the dislocations slip inside the crystal grains and pile up at the grain boundaries, local strain/stress keeps increasing, until the materials in these regions fail to sustain further deformation, leading to voids formation and cracks propagation.

Evaluation of the mechanical anisotropy and the deformation mechanism in a multi-pass friction stir processed Al-Zn-Mg-Cu alloy

Multi-pass friction stir processing (MP-FSP) can produce extensive bulk nanostructured areas in various metallic materials, such as the Al 7075 alloy (Al-Zn-Mg-Cu), providing fine and highly misoriented grains. This allows obtaining superplastic deformations by the activation of grain boundary sliding (GBS) mechanism at certain strain rate and temperature window, crucial for performing a further superplastic forming (SPF). The superplastic performance of the MP-FSP Al 7075 alloy in two uniaxial testing directions was evaluated and compared to that of a single pass FSP (SP-FSP), reporting a mechanical anisotropy in the MP-FSP attributed to the heterogeneous crystallographic orientation distribution along the transverse testing direction. The operative deformation mechanism was determined by uniaxial tensile test and small punch test (SPT), the former a test with biaxial with radial symmetry. GBS was corroborated as the main operative deformation mechanism in the SP-FSP and MP-FSP, reporting high strain rate superplasticity in the temperature range 350–400°C at 10−2s−1, and maximum elongation values between 290–540% at 400°C depending on the testing direction. The Al 7075 alloy processed by MP-FSP showed a great potential for a further SPF as GBS remains as the global deformation mechanism under biaxial testing conditions.