Mechanical Twist Research Articles

A new twist on torsion: A connection between vector calculus and mechanics of materials

In engineering education, the topic of torsion is taught in both calculus and mechanics of materials, but using different definitions. Apparently, a clear connection between these two concepts is not currently found in the literature. In this paper, for the case of a homogeneous linear-elastic cylindrical shaft subjected to external torques, mathematical expressions are derived for relating torsional stress, strain and angle of twist to the torsion of a curve as taught in calculus. A physical connection is also presented, in that the curve torsion resulting from the deformation of a longitudinal line close to the shaft axis is shown to be approximately equal to the mechanical twist per length in the shaft. Although some researchers have hinted at this connection, to our knowledge the full precise connection has not been previously established.

Strain Engineering of Twisted Bilayer Graphene: The Rise of Strain-Twistronics.

The layer-by-layer stacked van der Waals structures (termed vdW hetero/homostructures) offer a new paradigm for materials design-their physical properties can be tuned by the vertical stacking sequence as well as by adding a mechanical twist, stretch, and hydrostatic pressure to the atomic structure. In particular, simple twisting and stacking of two layers of graphene can form a uniform and ordered Moiré superlattice, which can effectively modulate the electrons of graphene layers and lead to the discovery of unconventional superconductivity and strong correlations. However, the twist angle of twisted bilayer graphene (tBLG) is almost unchangeable once the interlayer stacking is determined, while applying mechanical elastic strain provides an alternative way to deeply regulate the electronic structure by controlling the lattice spacing and symmetry. In this review, diverse experimental advances are introduced in straining tBLG by in-plane and out-of-plane modes, followed by the characterizations and calculations toward quantitatively tuning the strain-engineered electronic structures. It is further discussed that the structural relaxation in strained Moiré superlattice and its influence on electronic structures. Finally, the conclusion entails prospects for opportunities of strained twisted 2D materials, discussions on existing challenges, and an outlook on the intriguing emerging field, namely "strain-twistronics".

Capsizing due to friction-induced twist in the failure of stopper knots

We investigate the failure mechanism of stopper knots, with a particular focus on the figure-8 knot as a representative example. Stopper knots are widely used in climbing, sailing, racket stringing, and sewing to maintain tension in ropes, strings, or threads while preventing them from passing through an orifice. Combining high-precision model experiments and Finite Element Analyses, we systematically explore the influence of frictional interactions and their role in the build-up of mechanical twist. Our findings reveal that the failure of stopper knots via capsizing, which involves configurational alterations of the filament, is primarily due to friction-induced twisting when loading the knot against a restraining plate containing a clearance hole. Our study offers a comprehensive understanding of the mechanical behavior of stopper knots under diverse loading conditions, thereby providing crucial insights for their reliable application across various domains.

Low-Frequency Raman Study of Large-Area Twisted Bilayers of WS2 Stacked by an Etchant-Free Transfer Method.

Monolayer transition metal dichalcogenides have strong intracovalent bonding. When stacked in multilayers, however, weak van der Waals interactions dominate interlayer mechanical coupling and, thus, influence their lattice vibrations. This study presents the frequency evolution of interlayer phonons in twisted WS2 bilayers, highly subject to the twist angle. The twist angle between the layers is controlled to modulate the spacing between the layers, which, in turn, affects the interlayer coupling that is probed by Raman spectroscopy. The shifts of high-frequency E2g1 (Γ) and A1g (Γ) phonon modes and their frequency separations are dependent on the twist angle, reflecting the correlation between the interlayer mechanical coupling and twist angle. In this work, we fabricated large-area, twisted bilayer WS2 with a clean interface with controlled twist angles. Polarized Raman spectroscopy identified new interlayer modes, which were not previously reported, depending on the twist angle. The appearance of breathing modes in Raman phonon spectra provides evidence of strong interlayer coupling in bilayer structures. We confirm that the twist angle can alter the exciton and trion dynamics of bilayers as indicated by the photoluminescence peak shift. These large-area controlled twist angle samples have practical applications in optoelectronic device fabrication and twistronics.

Heat transport with a twist.

Despite the desirability of polymers for use in many products due to their flexibility, light weight, and durability, their status as thermal insulators has precluded their use in applications where thermal conductors are required. However, recent results suggest that the thermal conductance of polymers can be enhanced and that their heat transport behaviors may be highly sensitive to nanoscale control. Here we use non-equilibrium molecular dynamics simulations to study the effect of mechanical twist on the steady-state thermal conductance across multi-stranded polyethylene wires. We find that a highly twisted double-helical polyethylene wire can display a thermal conductance up to three times that of its untwisted form, an effect which can be attributed to a structural transition in the strands of the double helix. We also find that in thicker wires composed of many parallel strands, adding just one twist can increase its thermal conductance by over 30%. However, we find that unlike stretching a polymer wire, which causes a monotonic increase in thermal conductance, the effect of twist is highly non-monotonic, and certain amounts of twist can actually decrease the thermal conductance. Finally, we apply the Continuous Chirality Measure (CCM) in an attempt to explore the correlation between heat conductance and chirality. The CCM is found to correlate with twist as expected, but we attribute the observed heat transport behaviors to structural factors other than chirality.

Optimization of air pressure and speed of air jet loom; impact on fabric tensile and tear strength properties using Response Surface Methodology

ABSTRACT Weaving industries that use air jet loom are always emphasized to increase production and keep up the quality of woven fabric. But due to faulty mill practices or negligence, fabric mechanical properties of the fabric made on air jet loom are impaired. Improving the fabric quality can be achieved by improving work practices and optimization. The aim of this research is to optimize the air pressure and loom speed to produce a fabric with optimum mechanical properties and twist loss of weft yarn after weaving. To perform the experiment, three independent variables (loom speed, left-side relay nozzle pressure, and right-side relay nozzle pressure) was taken. With the combination of the three independent variables at five levels each, nineteen fabric samples were produced and each tensile and tear strength of the fabric in the weft direction were tested. Central composite design (CCD) was used to design the experiment, analyze the results of the experiment, and optimize the process. The results of the experiment show that variation in loom speed and air pressure affects twist of the weft yarn and mechanical properties of the fabric significantly and loom speed had a most significant effect on yarn twist loss, fabric tensile, and tear strength.

Twist and strain tuning of third harmonic generation in glass nanostrand with two sub-wavelength hollow channels.

A major challenge in third harmonic generation and its converse, parametric down-conversion, is how to arrange phase matching between signals at ω and 3ω while maintaining a high nonlinear overlap. In this Letter, we present a design consisting of a nanostrand of glass with two hollow channels. The fundamental and third harmonic modal fields, enhanced in the region between the channels, have high nonlinear overlap, while the phase-matching wavelength can be coarse-tuned by gas pressure and fine-tuned by axial strain and mechanical twist, which, remarkably, have opposite effects. The ability to adjust the phase-matching condition may facilitate efficient generation of entangled photon triplets.

Twist-induced control of near-field thermal radiation in multilayered black phosphorus/vacuum system

Modulating the photonic transmission coefficient (PTC) is a critical factor in regulating the near-field radiative heat transfer (NFRHT) between two objects. Extending previous studies, we find that multiple body-vacuum interfaces can support various resonance modes and flexibly amplify the PTC. We show that black phosphorus (BP)/vacuum multilayers support coupled multiple anisotropic surface plasmon polaritons (MASPPs) and propose a theoretical model of a pattern-free noncontact thermal modulator based on the mechanical twist between two BP/vacuum multilayer structures. The various symmetric and antisymmetric branches of MASPPs strengthens the PTC, and with it the NFRHT. We also analyze the combined effects of the number of layers and twisted angle. Changing the integral twisted angle and inter-layer twisted angle modulates the positions and intensities of MASPPs. In addition to the twist between the emitter and receiver, the inter-layer twist gives the BP/vacuum multilayer heat transfer system another pathway to modulate the NFRHT. These results pave the way for using two-dimensional anisotropic materials to actively manipulate heat currents.

Neoteric Conjugative Electrospinning towards Alloplastic Nanofiber Yarns Affording Enhanced Upconversion Luminescence and Tailored Magnetism

AbstractUpconversion luminescent‐magnetic [Y2O3:Yb3+, Er3+/polyacrylonitrile (PAN)]//[CoFe2O4/PAN] alloplastic nanofiber yarns (ANYs) are successfully prepared by a novel conjugative electrospinning. The ANYs consist of two different kinds of nanofibers, respectively called as [CoFe2O4/PAN] magnetic nanofibers and [Y2O3:Yb3+, Er3+/PAN] upconversion luminescent nanofibers, and the two kinds of nanofibers are combined together and twisted to form ANYs. Pumped by 980‐nm laser, the ANYs exhibit excellent upconversion luminescence (UCL) and orange‐red fluorescence. ANYs demonstrate tailored saturation magnetization by modulating CoFe2O4 nanoparticles (NPs) content. The influence mechanism of magnetic CoFe2O4 NPs on the UCL of ANYs is detailedly explored. The relationship between mechanical properties and twist for ANYs is explored through the tensile test. Compared with the counterpart coessential nanofiber yarns (CNYs), ANYs exhibit about 10 times stronger UCL intensity owing to the complete separation of the upconversion luminescent substance from the magnetic substance and thereby great reduction of impact of the magnetic substance on the upconversion luminescent substance. Thus, concurrent enhancive upconversion luminescence (UCL) and tunable magnetism of the ANYs are successfully achieved. The detailed formation mechanism of ANYs is advanced and a novel fabrication technique of yarns is established and can be popularized to prepare other bi‐ and multi‐functional nanofibrous yarns.

Mechanical rotation and bending sensing by chiral long-period grating based on an axis-offset rotating optical fiber

A chiral long-period fiber grating (CLPFG) was fabricated by rotating the standard single mode fiber that was fixed on two fiber holders with an axis-offset. We investigated the performance of CLPFGs by sensing the mechanical twist, bending, and liquid refractive index experimentally. A wide twist sensing range of ±720° and 26.7 nm wavelength tuning range were achieved. Compared with tapered long-period fiber grating, the bending sensitivity of CLPFG is 5 times higher. Considering the simple and flexible fabrication process and low cost, this CLPFG may offer a simple and alternative choice for sensing mechanical deformation in industrial applications.

Stacking, strain, and twist in 2D materials quantified by 3D electron diffraction

The field of two-dimensional (2D) materials has expanded to multilayered systems where electronic, optical, and mechanical properties change-often dramatically-with stacking order, thickness, twist, and interlayer spacing [1-5]. For transition metal dichalcogenides (TMDs), bond coordination within a single van der Waals layer changes the out-of-plane symmetry that can cause metal-insulator transitions [1, 6] or emergent quantum behavior [7]. Discerning these structural order parameters is often difficult using real-space measurements, however, we show 2D materials have distinct, conspicuous three-dimensional (3D) structure in reciprocal space described by near infinite oscillating Bragg rods. Combining electron diffraction and specimen tilt we probe Bragg rods in all three dimensions to identify multilayer structure with sub-Angstrom precision across several 2D materials-including TMDs (MoS2, TaSe2, TaS2) and multilayer graphene. We demonstrate quantitative determination of key structural parameters such as surface roughness, inter- & intra-layer spacings, stacking order, and interlayer twist using a rudimentary transmission electron microscope (TEM). We accurately characterize the full interlayer stacking order of multilayer graphene (1-, 2-, 6-, 12-layers) as well the intralayer structure of MoS2 and extract a chalcogen-chalcogen layer spacing of 3.07 +/- 0.11 Angstrom. Furthermore, we demonstrate quick identification of multilayer rhombohedral graphene.

Effects of different ultrasound power application on left ventricular rotation and twist in vivo open-chest beagle canines

Objective To evaluate left ventricular (LV) myocardial mechanical rotation and twist with contrast agent and different power irradiation in open-chest beagle canines by ultrasound velocity vector images (VVI). Methods The anesthetized open-chest Beagle canines were assigned into two groups randomly: group A (n=6) for baseline, diagnostic ultrasound power irradiation (300 mW) 5 min, combined with contrast agent irradiation 5 min and contrast agent 20 min conditions; group B (n=6) for baseline and intensity ultrasound irradiation (1 W, 2 W and 3 W, 5 min respectively) conditions. The standard short-axis gray-scale views at basal level (BL), and apical level(AL) during three complete cardiac cycles in open-chest beagle canine models were acquired. The peak subendomyocardium rotation (subendo-rot), subepimyocardium rotation (subepi-rot) of BL and AL were analyzed using a dedicated Syngo velocity vector imaging (VVI) method and LV subendomyocardium twist (subendo-twi) and subepimyocardium twist (subepi-twi) were defined as apical subendo-rot/subepi-rot-basal subendo-rot/subepi-rot. Results In group A, the LV subendo-twi, subepi-twi, subendo-rot and subepi-rot of BL and AL in the most of segments were significant different on diagnostic power irradiation, contrast agent irradiation 5 min and contrast agent 20 min (P 0.05); subendo-rot and subepi-rot of LV AL were different compared with those on baseline condition (P<0.05); LV subendo-twi and subepi-twi in group B under the same condition were significant difference (P<0.05). Conclusions LV rotation and twist increase on diagnostic ultrasound power irradiation 5 min, combined with contrast agent irradiation 5 min, contrast agent 20 min conditions, 1 W and 2 W; LV twist and AL rotation decrease on ultrasound power 3 W, but BL rotation is not affected on ultrasound power 3 W. Key words: Sonication; Ventricular function, left; Rotation; Twist

A stretchable fiber nanogenerator for versatile mechanical energy harvesting and self-powered full-range personal healthcare monitoring

Wearable electronics have gained dramatic development in recent years, owing to the advancement in flexible/stretchable electronics, and achieved considerable progress in various applications. Nanogenerators capable of harvesting energy from human activities is considered as a promising alternative for powering the wearable electronic devices, considering the sustainability and rich biomechanical energy from human body. Currently, most of the nanogenerators are aimed at converting limited forms of mechanical energy, mostly pressing or bending, which hampers adaptive exploitation of bodily energy source. Also, the incapability to respond to multiple forms of mechanical stimuli deters the nanogenerators from functioning as full-range human activities sensors. Here, we devise a stretchable integrated nanogenerator-sensory coaxial core-sheath fiber with improved functionality and sustainability. The combination of materials engineering and structure design enables the fiber to scavenge versatile mechanical energy, including stretch, bend, twist and press, through a gap size variation induced electrostatic effect. Besides, the fiber realizes the detection of joint-bending and joint-twisting related motions, such as walking and elbow rotation, and also succeeds in capturing subtle physiological signals, such as breath, pulse and speech recognition, which paves the way for full-range personal healthcare monitoring and documenting in a self-powered, wearable and noninvasive manner.

S65 Neurophysiological data favoring a central mechanism of trigeminal neuralgia

Current opinion is that TN is caused by a proximal compression of the trigeminal nerve root by a ectasic blood vessel leading to mechanical twist of nerve fibers and secondary demyelination. These changes lower the excitability threshold of affected fibers and promote inappropriate ephaptic propagation towards adjacent fibers. Not all patients have a nerve vessel conflict and 25% of people without any clinical signs of TN did show a nerve vessel contact. Possible involvement of central factors, suggesting a central facilitation and resulting hyperexcitability of the trigeminal system sustained by peripheral as well as central mechanisms were discussed. Sensitisation of second order wide dynamic range (WDR) neurons was discussed as additional pathophysiological mechanism. Since these WDR neurons receive convergent information from tactile (A-beta) and nociceptive (A-delta and C) fibers, their sensitisation could facilitate nociceptive input while promoting the perception of pain in response to tactile stimuli (i.e., allodynia). Central facilitation was demonstrated in TN patients with additional constant dull background pain besides their typical TN attacks using pain-related evoked potentials (PREP) and nociceptive blink reflex (nBR) [4]. Borsook et al. (2007) reported increased fMRI activation of a single TN patient in the primary somatosensory cortex, insula, anterior cingulate, and thalamus to further support cortical involvement [28]. Structural changes of the cortical grey matter was also reported to further support a central origin of the disease.

Chiral long-period gratings: fabrication, highly sensitive torsion sensing, and tunable single-band filtering.

A promising technology for fabricating chiral long-period gratings (CLPGs) is demonstrated using a commercial fusion splicer. The key aspect of this technology is the incorporation of a fully automatic program we designed for the fusion splicer. High-quality CLPGs are successfully fabricated from single-mode fibers, which have very flat surfaces and low insertion loss. We also investigate the tuning characteristics of the transmission spectrum with the mechanical twist rate in CLPGs for torsion sensing application. The torsion sensitivity is improved and the shift in resonance wavelength versus the mechanical twist rate shows an almost perfect linear relationship. In addition, by choosing appropriate fabrication parameters, the fabricated CLPGs can be used as tunable single-band-rejection filters in a broad wavelength range.

Measuring mechanical strain and twist using helical photonic crystal fiber

Solid-core photonic crystal fiber (PCF) with a permanent helical twist exhibits dips in its transmission spectrum at certain wavelengths. These are associated with the formation of orbital angular momentum states in the cladding. Here we investigate the tuning of these states with mechanical torque and axial tension. The dip wavelengths are found to scale linearly with both axial strain and mechanical twist rate. Analysis shows that the tension-induced shift in resonance wavelength is determined both by the photoelastic effect and by the change in twist rate, while the torsion-induced wavelength shift depends only on the change in twist rate. Twisted PCF can act as an effective optically monitored torque-tension transducer, twist sensor, or strain gauge.

Life's ratchet: how molecular machines extract order from chaos

Life is an enduring mystery. Yet, science tells us that living beings are merely sophisticated structures of lifeless molecules. If this view is correct, where do the seemingly purposeful motions of cells and organisms originate? In Life's Ratchet, physicist Peter M. Hoffmann locates the answer to this age-old question at the nanoscale. Below the calm, ordered exterior of a living organism lies microscopic chaos, or what Hoffmann calls the molecular storm--specialized molecules immersed in a whirlwind of colliding water molecules. Our cells are filled with molecular machines, which, like tiny ratchets, transform random motion into ordered activity, and create the purpose that is the hallmark of life. Tiny electrical motors turn electrical voltage into motion, nanoscale factories custom-build other molecular machines, and mechanical machines twist, untwist, separate and package strands of DNA. The cell is like a city--an unfathomable, complex collection of molecular workers working together to create something greater than themselves. Life, Hoffman argues, emerges from the random motions of atoms filtered through these sophisticated structures of our evolved machinery. We are agglomerations of interacting nanoscale machines more amazing than anything in science fiction. Rather than relying on some mysterious force to drive them--as people believed for centuries--life's ratchets harness instead the second law of thermodynamics and the disorder of the molecular storm. Grounded in Hoffmann's own cutting-edge research, Life's Ratchet reveals the incredible findings of modern nanotechnology to tell the story of how the noisy world of atoms gives rise to life itself.

Pockels’ coefficients of alumina in aluminosilicate optical fiber

The photoelastic constants of the alumina component in aluminosilicate optical fibers are evaluated and determined to be p11=−0.237±0.020 and p12=−0.027±0.012, thus confirming that the low and negative pij characteristics of bulk alumina are conserved as part of a binary aluminosilicate glass system in optical fiber form. In order to enumerate these values, the strain- and stress-optic coefficients of two fibers (one with an aluminosilicate core and one with a pure silica core) were measured by applying mechanical tension or twist, respectively, to the fibers and measuring changes to an optical system as a function of the mechanical deformation. In the former, the strain-optic coefficient (eOC) is measured directly by recording changes to the free spectral range of a ring fiber laser. In the latter, the stress-optic coefficient (σOC) is found by measuring the change in polarization angle after linearly polarized light propagates through a segment of twisted test fiber. To the best of our knowledge, this is the first such measurement of its type, i.e., the retrieval of the component photoelastic constants, with their signs, of a multicomponent glass. Binary glass compositions wherein the constituents have opposite signs of the photoelastic constant (such as the aluminosilicates) have the potential to give rise to extremely low values of the Brillouin gain coefficient.

Carbon nanotube-induced macroscopic helical twist in an achiral nematic liquid crystal

An achiral nematic liquid crystal was doped with a small quantity of carbon nanotubes having a net chirality, and the mixture was found to exhibit an average mechanical twist over macroscopic dimensions. The nanotube-induced chiral pitch length P was determined as a function of the average nanotube concentration by measuring the radii of curvature of reverse twist disclination lines in 90° nematic twist cells. The results suggest that the nanotubes’ spatial concentration can vary significantly across the cell and that at high average concentration, the nanotubes undergo aggregation, resulting in an apparent saturation of P−1 at high concentrations. The macroscopic helical twisting power of the nanotubes has been estimated from the results.

Physiology in Phylogeny: Modeling of Mechanical Driving Forces in Cardiac Development

This article explores the heart phylogeny, the development of the heart from embryonic to adult shape. For the shape change from tubular to four-chamber to be initiated, a mechanical twist needs to be present in the embryonic heart tube. The helical shape of the muscle fibers in the embryonic heart is a necessary but not a sufficient condition for the transformation to occur. It is also necessary for the excitation pattern to be in the form of a spatiotemporal wave. Such a combination, while producing twist, does not negatively impact the heart's ability to work as a pump.