Twisted Fiber Research Articles

New twist on artificial muscles

Lightweight artificial muscle fibers that can match the large tensile stroke of natural muscles have been elusive. In particular, low stroke, limited cycle life, and inefficient energy conversion have combined with high cost and hysteretic performance to restrict practical use. In recent years, a new class of artificial muscles, based on highly twisted fibers, has emerged that can deliver more than 2,000 J/kg of specific work during muscle contraction, compared with just 40 J/kg for natural muscle. Thermally actuated muscles made from ordinary polymer fibers can deliver long-life, hysteresis-free tensile strokes of more than 30% and torsional actuation capable of spinning a paddle at speeds of more than 100,000 rpm. In this perspective, we explore the mechanisms and potential applications of present twisted fiber muscles and the future opportunities and challenges for developing twisted muscles having improved cycle rates, efficiencies, and functionality. We also demonstrate artificial muscle sewing threads and textiles and coiled structures that exhibit nearly unlimited actuation strokes. In addition to robotics and prosthetics, future applications include smart textiles that change breathability in response to temperature and moisture and window shutters that automatically open and close to conserve energy.

Multilongitudinal mode fiber laser for highly-sensitive magnetic field measurement

In this paper, a magnetic field sensor based on a multilongitudinal mode fiber laser has been proposed by employing a rotary apparatus modulated by an external magnetic field. Due to the remarkable birefringence change caused by the fiber twist, the polarimetric mode beat frequency (PMBF) of the laser is sensitive to the applied magnetic field intensity. Experimental results show that the PMBF linearly shifts with the variation of the magnetic field intensity and the sensitivity reaches up to 10.4 KHz Oe−1 in the range of 0–270 Oe. Moreover, such a device has the advantages of easy fabrication, low cost and high resolution, offering potentials in the weak magnetic field applications.

Mechanical properties of ultra-high-performance fiber-reinforced concrete: A review

A comprehensive investigation into the mechanical properties of ultra-high-performance fiber-reinforced concrete (UHPFRC), considering various influential factors, is imperative in order to obtain fundamental information for its practical utilization. Therefore, this paper reviewed the early-age strength (or setting) development and mechanical properties of hardened UHPFRC. In connection with the latter, the effects of the curing conditions, coarse aggregate, mineral admixtures, fiber properties, specimen size, and strain-rate on the mechanical performance of UHPFRC were specifically investigated. It was obvious that (1) heat treatment accelerates the hydration process, leading to higher strength; (2) a portion of the silica fume can be replaced by fly ash, slag, and rice husk ash in mechanical perspective; (3) the use of deformed (hooked and twisted) or long straight steel fibers improves the mechanical properties at a static rate; and (4) high rate loading provides a noticeable increase in the mechanical properties. Alternatively, there are some disagreements between the results from various ‘size effect’ tests and the effectiveness of using twisted steel fibers at static and high rate loadings. Further research to reduce the production cost of UHPFRC is also addressed in an attempt to make its widespread use more practical.

Performance of deformed steel fibers embedded in ultra-high performance concrete subjected to various pullout rates

Fiber-matrix bond properties are typically evaluated using a single-fiber pullout test. Such tests for ultra-high performance concrete (UHPC) are few in the literature and, in particular, those that focus on high pullout rates are exceedingly rare. In this research program, different types of high-strength steel fibers (twisted, straight and hooked) are embedded in two UHPC matrices with varying amounts of glass powder, which is a key ingredient of UPHC. The specimens are subjected to loading rates ranging from 0.018mm/s (representing quasi-static loading) to 1800mm/s (representing impact loading). Experimental results show that the pullout response of all of the fiber types exhibit progressively increasing rate sensitivity as the pullout speed increases and becomes significant during impact loading. It is most prominent in the smooth and twisted fibers and least in the hooked fibers. Additionally, scanning electron microscope studies are presented and used to explain the mechanism of rate enhancement from a microscopic perspective.

A probabilistic model of the tensile strength of a UD flax–fabric‐reinforced polymer composite

In order to fully realize the efficiency of bast fibers or their yarns as reinforcement of polymer composites, they should be aligned. Tensile strength of such composites in the direction of reinforcement has been found to exhibit size effect commensurable with that of unidirectionally reinforced (UD) composites with inorganic fibers, necessitating a probabilistic modeling approach. Strength distribution of a polymer matrix composite reinforced with aligned twisted bast fiber yarns is considered allowing for the strength scatter of elementary fibers, the presence of defects in the form of adjacent fiber breaks, and twist of the yarns. The model is applied to predicting the strength of flax/acrylated epoxidized soy oil resin composite specimens of different sizes. The theoretical prediction is found to be in a reasonable agreement with strength test results. POLYM. COMPOS., 39:2101–2109, 2018. © 2016 Society of Plastics Engineers

Surface plasmon resonance effect in helical core fibers

Using a rigorous modeling method based on transformation optics formalism, we have studied, for the first time to our knowledge, the surface plasmon resonance (SPR) effect in helical core fibers with a cladding covered by a gold layer. The obtained results prove that by twisting the fiber one can tune several parameters of the SPR resonance which may be of importance in sensing applications. In particular, we have shown that circularly polarized fundamental modes propagating in the helical core fiber exhibit almost the same SPR loss. Moreover, the SPR loss can be amplified with a twist rate by more than two orders of magnitude due to twist-induced displacement of the core modes towards a metal layer. The fiber twist modifies the coupling conditions between the fundamental modes and plasmons, which results in the redshift and split of the resonance wavelengths for circularly polarized modes of opposite handedness. Analytical formulas were derived for the SPR peak loss, redshift and split, which are valid for small twist rates, in which the fundamental modes couple only with plasmons. For higher twist rates we observed the coupling between fundamental and cladding modes, which results in significant broadening of the SPR resonance peaks and emergence of additional maxima in the SPR loss curves.

Investigation of Aramid Fibers Compared with Steel Fiber on Bending Behavior of Hybrid RC Beams

This paper presents an experimental study on bending behavior of aramid and steel fiber reinforced concrete (AFRC and SFRC) members. The objective is to investigate effects of two types of aramid fiber and one type of steel fiber in hybrid reinforced concrete (RC) beams. The term hybrid beam is defined as the beam with fiber reinforced concrete (FRC) cast in tension zone and normal concrete (without fiber) cast in compression zone of the beam. The diameter of aramid fiber (AF) is 0.5mm and the surface condition is twist fiber consisting of two single fibers. The fiber lengths are 30mm and 40mm for two types of aramid fiber. The diameter of steel fiber (SF) is 0.6mm and the length is 33mm with hooked ends. Four reinforced concrete (RC) beams with a dimension of 150×200×2100 mm3 were designed to undergo flexural failure. All the tested beams are with the same reinforcement ratio (0.93%), having a fiber volume fraction (Vf) of 1% for each type of fiber. One RC beam without fiber was prepared and tested as a controlled specimen. The height of the FRC tension zone at ultimate state was calculated to be 170mm. Load capacity, average and maximum crack widths of hybrid aramid and steel fiber reinforced concrete beams (HAFRCs & HSFRC) under four-point bending tests were discussed.

Injectable Hydrogel: Amplifying the pH Sensitivity of a Triblock Copolypeptide by Conjugating the N-Termini via Dynamic Covalent Bonding.

We explore the self-assembly behavior of aqueous solutions of an amphiphilic, pH-sensitive poly(l-alanine)-b-poly(l-glutamic acid)-b-poly(l-alanine), (A5E11A5) triblock copolypeptide, end-capped by benzaldehyde through Schiff base reaction. At elevated concentrations and under physiological pH (7.4) and ionic strength (0.15M), the bare copolypeptide aqueous solutions underwent a sol-gel transition after heating and slow cooling thermal treatment, forming opaque stiff gels due to a hierarchical self-assembly that led to the formation of β-sheet-based twisted super fibers (Popescu et al. Soft Matter 2015, 11, 331-342). The conjugation of the N-termini with benzaldehyde (Bz) through a Schiff base reaction amplifies the copolypeptide pH-sensitivity within a narrow pH window relevant for in vivo applications. Specifically, the dynamic character of the imine bond allowed coupling/decoupling of the Bz upon switching pH. The presence of Bz conjugates to the N-termini of the copolypeptide resulted in enhanced packing of the elementary superfibers into thick and short piles, which inhibited the ability of the system for gelation. However, partial cleavage of Bz upon lowering pH to 6.5 prompted recovery of the hydrogel. The sol-gel transition triggered by pH was reversible, due to the coupling/decoupling of the benzoic-imine dynamic covalent bonding, endowing thus the gelling system with injectability. Undesirably, the gelation temperature window was significantly reduced, which however can be regulated at physiological temperatures by using a suitable mixture of the bare and the Bz-conjugated coplypeptide. This triblock copolypeptide gelator was investigated as a scaffold for the encapsulation of polymersome nanocarriers, loaded with a hydrophilic model drug, calcein. The polymersome/polypeptide complex system showed prolonged probe release in pH 6.5, which is relevant to extracellular tumor environment, rendering the system potentially useful for sustained delivery of anticancer drugs locally in the tumor.

High Sensitivity Chiral Long-Period Grating Sensors Written in the Twisted Fiber

A chiral long-period grating (CLPG) was fabricated successfully by scanning CO2 laser in a twisted conventional single-mode fiber. The strong mode coupling can be achieved in a short grating length. The sensing characteristics of the CLPGs were investigated experimentally. Compared with the conventional long-period fiber gratings, the CLPGs were found to have the similar temperature and refractive index sensitivities and much higher torsion, bending, and strain sensitivities. The high sensitivity of the CLPG can be attributed to the screw-type waveguide structure induced by the scanning laser in the twisted fiber. The proposed CLPGs could have great potential applications as filters and optical sensors.

Twisted hollow fiber membranes for enhanced mass transfer

Computational fluid dynamic simulations are used to examine incompressible flow through twisted elliptical and helically-coiled cylindrical fibers for typical flow Reynolds numbers employed in membrane filtration processes (Re<200). The resulting flow fields are compared in terms of the distributions of vorticity and wall shear rate, the pressure drop, and the azimuthally-averaged normal velocity in the vicinity of the wall. The secondary flow in twisted elliptical fibers generates significant recirculation flow leading to near-wall velocities directed normal to the surface of the membrane. The azimuthally-averaged normal velocity near the wall of a twisted elliptical fiber is found to be two to four orders of magnitude larger than typical ultrafiltration velocities. For Re<75, the average wall shear rate and normal velocity near the wall are found to be significantly higher in twisted elliptical fibers compared to their helical counterparts. These findings highlight the potential for mass transfer and flux enhancement using twisted elliptical hollow fiber membrane systems.

Effect of Twisted Fiber Anisotropy in Cardiac Tissue on Ablation with Pulsed Electric Fields.

BackgroundAblation of cardiac tissue with pulsed electric fields is a promising alternative to current thermal ablation methods, and it critically depends on the electric field distribution in the heart.MethodsWe developed a model that incorporates the twisted anisotropy of cardiac tissue and computed the electric field distribution in the tissue. We also performed experiments in rabbit ventricles to validate our model. We find that the model agrees well with the experimentally determined ablation volume if we assume that all tissue that is exposed to a field greater than 3 kV/cm is ablated. In our numerical analysis, we considered how tissue thickness, degree of anisotropy, and electrode configuration affect the geometry of the ablated volume. We considered two electrode configurations: two parallel needles inserted into the myocardium (“penetrating needles” configuration) and one circular electrode each on epi- and endocardium, opposing each other (“epi-endo” configuration).ResultsFor thick tissues (10 mm) and moderate anisotropy ratio (a = 2), we find that the geometry of the ablated volume is almost unaffected by twisted anisotropy, i.e. it is approximately translationally symmetric from epi- to endocardium, for both electrode configurations. Higher anisotropy ratio (a = 10) leads to substantial variation in ablation width across the wall; these variations were more pronounced for the penetrating needle configuration than for the epi-endo configuration.For thinner tissues (4 mm, typical for human atria) and higher anisotropy ratio (a = 10), the epi-endo configuration yielded approximately translationally symmetric ablation volumes, while the penetrating electrodes configuration was much more sensitive to fiber twist.ConclusionsThese results suggest that the epi-endo configuration will be reliable for ablation of atrial fibrillation, independently of fiber orientation, while the penetrating electrode configuration may experience problems when the fiber orientation is not consistent across the atrial wall.

Torsion sensing characteristics of long period fiber gratings fabricated by femtosecond laser in optical fiber

With the alignment of the fiber core systems containing dual-CCDs and high-precision electric displacement platform, twisted long period fiber gratings (T-LPFGs) were fabricated in two different twisted SMF-28 fibers by femtosecond laser. The torsion characteristics of the T-LPFGs were experimentally and theoretical investigated and demonstrated in this study. The achieved torsion sensitivity is 117.4pm/(rad/m) in the torsion range −105–0rad/m with a linearity of 0.9995. Experimental results show that compared with the ordinary long period fiber gratings, the resonance wavelength of the gratings presents an opposite symmetrical shift depending on the twisting direction after the applied torsion is removed. In addition, high sensitivity could be obtained, which is very suitable for the applications in the torsion sensor. These results are important for the design of new torsion sensors based on T-LPFGs fabricated by femtosecond laser.

Excitation and separation of vortex modes in twisted air-core fiber.

An air-core fiber imposed by torsion is investigated in this paper. We refer to this kind of fiber as twisted air-core fiber (TAF). It has been demonstrated that the eigenstates of the TAF consist of guided optical vortex waves with different propagation constants of a different effective index. With the increase of the twist rate, TAF could separate the OAM modes which are near degenerate or degenerate in the air-core fiber. The separation of OAM modes in TAF is conductive to ultralong distance propagation with low crosstalk. TAF could be considered as an ideal candidate fiber for OAM based optical communication. Moreover, we investigated the twisted air-core photonic crystal fiber (TAPCF) which can improve the relative energy distribution of the OAM modes. Compared with TAF, more energy is located in the ring shaped core, which is conductive to ultralong distance propagation. TAF and TAPCF are of potential interest for increasing channel capacity in optical telecommunications, and the result is also of interest to the photonic crystal community.

Anisotropic Compressive Properties and Energy Absorption Efficiency of Porous Twisted Short Fiber Materials

Novel stainless steel porous twisted short fiber materials (PTSFMs) with spatial composite intertexture structure are produced by compaction following with sintering of twisted short fibers. The stainless steel twisted short fibers are fabricated using a cutting stainless steel fiber ropes method with a self-developed rotary multi-cutter tool. The porous structure of the stainless steel PTSFMs exhibits a large difference in the through-thickness and in-plane direction, which results in differences in compressive behavior. During the compressive process, it is determined that the stainless steel PTSFMs exhibit typical elastic–plastic behaviors (three deformation stages) in the in-plane direction, but in the through-thickness direction, entered the compact densification zone after short-term nonlinear elastic deformation without a plastic platform stage. The compression deformation resistance in the through-thickness direction is obviously stronger than that in the in-plane direction at a given porosity. The compression strength and the anisotropy both decreased with increased porosity. The compression properties are anisotropic, which also result in different energy absorption efficiencies of the two directions. The relationship between the porosity and the energy absorption efficiency is not monotonically increasing or decreasing, but with the change of porosities, there is an optimal porosity, which has relatively high-energy absorption efficiency.

Numerical Modeling of Pump Absorption in Coiled and Twisted Double-Clad Fibers

We report the analysis of multimode pump absorption in double-clad rare-earth-doped fibers under realistic bending conditions. The finite-element beam-propagation method is used for the analysis. The fiber bending is approximated by the transformation of the refractive index profile of the fiber. Double-clad fibers of hexagonal, circular and stadium-like cross-sections are studied as examples. In addition, the double-clad waveguide structure of a two-fiber bundle is investigated. Simulations show that the bending effects cannot be neglected in double-clad fiber multimode pump propagation analysis and optimization. The reported rigorous numerical model opens new way to design double-clad fibers and to optimize the pump absorption efficiency. We show that high pump-absorption efficiency better than the ideal (ergodic) limit, can be achieved by simultaneous coiling and twisting of the double-clad fiber.

Determining the twist in an optical fiber

We determine the twist in a birefringent optical fiber from measurements, at one end of the fiber, of the fiber response to an impulsive source at the same end. This is the inverse problem of determining a non-constant coefficient, of a first order hyperbolic system in one space dimension with two speeds of propagation, from measurements at one end of an interval, of the solution of this system corresponding to an impulsive source at the same end. We prove a stability result for this inverse problem and give a provable reconstruction algorithm for this inverse problem.

Hydrochemical factors influencing the crystallinity and composition of kaolins and other silicates, revisited

Increasing pH of aluminum-bearing aqueous solutions causes most of the aluminum to pass from octahedral to tetrahedral coordination over a narrow pH interval: 5.5 to 6.5 at 25°C and 4 to 5 at 100°C. Thus silicates that grow from Al-bearing solutions having pH>6.5 at 25°C (or >5 at 100°C) should incorporate significant Al(tet) substituting for Si (especially if the solution provides monovalent cations to compensate for the charge defect), but should not do so if pH<5.5. This applies to a number of phyllosilicates, quartz, opal-CT, and opal-A in scales formed in tubes of geothermal power plants.In turn the predicted Al(tet)-for-Si substitution can explain the aggregate deformation of certain crystal structures induced by the larger size of the AlO4 tetrahedra, including the curling of the 1:1 layers of halloysite and the observed twisting of the tiny fibers of chalcedonic quartz making up agate layers.

Knotted synthetic polymer or carbon nanotube microfibres with enhanced toughness, up to 1400 J/g

In the past 50 years, a number of synthetic polymer microfibres, such as para-aramid or ultra-high-molecular-weight polyethylene, have been developed, exhibiting remarkable strength. However, their toughness is considerably smaller than that of some natural fibres such as spider silk, thus limiting their performance in applications ranging from surgical devices to vehicle parts. Here, we implement a recently proposed strategy, using micro-knots as frictional energy dissipators, to achieve record toughness values of up to 1400 J/g in synthetic microfibres, while maintaining their strength virtually unchanged. The same strategy is also applied to carbon nanotube microfibres, exploiting their superior ideal mechanical strength compared to any other existing fibre at the nanoscale, and toughness improvements of more than an order of magnitude are observed. We also show how knotted nanotube fibre configurations can be optimized for maximum toughness by modifying fibre diameter and twist angle, and how frictional and wear levels can be tuned by varying tightening and number of coils in the micro-knots. The results demonstrate the potential to design and produce fibres and textiles with unprecedented simultaneous strength and toughness for a variety of technological applications.

Using experimental and computational energy equilibration to understand hierarchical self-assembly of Fmoc-dipeptide amphiphiles.

Despite progress, a fundamental understanding of the relationships between the molecular structure and self-assembly configuration of Fmoc-dipeptides is still in its infancy. In this work, we provide a combined experimental and computational approach that makes use of free energy equilibration of a number of related Fmoc-dipeptides to arrive at an atomistic model of Fmoc-threonine-phenylalanine-amide (Fmoc-TF-NH2) which forms twisted fibres. By using dynamic peptide libraries where closely related dipeptide sequences are dynamically exchanged to eventually favour the formation of the thermodynamically most stable configuration, the relative importance of C-terminus modifications (amide versus methyl ester) and contributions of aliphatic versus aromatic amino acids (phenylalanine F vs. leucine L) is determined (F > L and NH2 > OMe). The approach enables a comparative interpretation of spectroscopic data, which can then be used to aid the construction of the atomistic model of the most stable structure (Fmoc-TF-NH2). The comparison of the relative stabilities of the models using molecular dynamic simulations and the correlation with experimental data using dynamic peptide libraries and a range of spectroscopy methods (FTIR, CD, fluorescence) allow for the determination of the nanostructure with atomistic resolution. The final model obtained through this process is able to reproduce the experimentally observed formation of intertwining fibres for Fmoc-TF-NH2, providing information of the interactions involved in the hierarchical supramolecular self-assembly. The developed methodology and approach should be of general use for the characterization of supramolecular structures.

Investigation on mechanical behaviour of twisted natural fiber hybrid composite fabricated by vacuum assisted compression molding technique

Nowadays, automotive, packaging and sport equipment industries are using natural fibre based composite materials as they are cheap, abundantly available and having a lot of ecological advantages. The main objective of this paper is to introduce a new concept of fibre twisting and to investigate the effect of twisting and the fibre orientation on the mechanical properties of bio degradable green composites. Here, the composites are fabricated by vacuum assisted compression molding technique in which the problems of hand lay process are eliminated. Here, two fibers namely twisted neem and twisted kenaf are sandwiched between layers of glass fibres to enhance the stiffness and strength of the laminates. Initially, the fibers are alkalized to increase the mechanical properties. The result shows that there is a significant improvement in mechanical properties of composites due to the presence of twisted fibers. It also shows the influence of fiber orientation on mechanical properties.