Fiber Curvature Research Articles

On the incorporation of curvature effects into the isogeometric analysis of fibre‐reinforced solids

AbstractIn the context of engineering on the micro‐ and nanoscale, size‐dependency is an important characteristic of material behaviour. In order to avoid complex experiments and predict size effects in simulations instead, classic continuum approaches are extended by the introduction of a length scale, e.g. through the consideration of gradient contributions. For the particular case of fibre‐reinforced materials, such a gradient‐enhanced approach can be achieved by introducing the fibre curvature as an additional kinematic quantity. This implies that basis functions with a global continuity higher than C0 are required for a finite element‐based approach which accounts for these fibre curvature effects. The present contribution shows that the isogeometric finite element method can provide a framework for the simulation of the respective higher‐gradient continua.

Modeling of fiber‐bending stiffness in fiber‐reinforced composites with a dynamic mixed finite element method based on the principle of virtual power

AbstractInvestigating the bending stiffness of fibers in fiber‐reinforced composites for rotor‐dynamical systems which are subjected to dynamical loads are essential in the development of system design. The proposed numerical modeling approach of fiber‐reinforced composites uses a multi‐field mixed finite element formulation based on a dynamic variational approach to perform long‐term dynamic simulations with CPU‐time efficient and increased accurate numerical solutions. To model the bending stiffness of fibers accurately, we extend a Cauchy continuum with higher‐order gradients of the deformation mapping as an independent field in the functional formulation. This extended continuum also takes into account the higher‐order energy contributions including the fiber curvature along with popular proven approaches that efficiently avoid the numerical locking effect of the fibers. The effect of the proposed approach is demonstrated through transient dynamic analysis on a cantilever beam with a hyperelastic, transversely isotropic, polyconvex material behavior. The beam is subjected to bending load with a strong dependence of the overall stiffness on the fiber orientation. The material and conservation properties are analyzed.

Hollow core negative curvature fiber based refractive index sensor design and investigation for tuberculosis monitoring

A myriad of pensile but pertinent issues found in the optical fiber sensors can be sought resolution based on the antiresonant reflecting optical waveguide (ARROW) working principle. Due to its compact structure, the anti-resonance based sensor has several advantages such as high sensitivity response, low confinement loss, and high stability that make the sensor more effective for health monitoring. In this manuscript, an anti-resonance fiber sensor has been proposed for the detection of tuberculosis cells. An analytical structure has been explored to simulate the characteristics of the ARROW. For the suggested structure, the Finite Element Method (FEM) is used to conduct its numerical investigations. The proposed optical sensor working on the ARROW principle was implemented on the Comsol Multiphysics software. From the numerical analysis, it is noted that the designed sensor has reached around 99% sensitivity with negligible confinement loss and single modality due to the excellent light-guiding properties of the anti-resonance fiber. Besides, lots of optical parameters such as effective area, V-Parameter, spot-size along beam divergence have been calculated over the wide wavelength region. The achieved result indicates the various application’s suitability of Antiresonant Hollow-Core Fiber (ARHCF) as a tuberculosis sensor.

A micropolar approach to microbuckling problems in unidirectionally reinforced polymer composites

The present contribution considers the application of micropolar continuum theory to predict the microbuckling strength of microbuckling problems in long fiber reinforced composites and to extend simulations into the collapse regime. The approach considers a homogenized description at a coarse length scale where fiber and matrix phases are not individually resolved, but are represented indirectly via an effectively equivalent homogenized solid. The salient characteristic of this approach is its superior numerical efficiency over a fine-scale micromechanical representation where fibers and matrix would need to be discretized separately. A disadvantage of conventionally homogenized models, however, is the circumstance that fiber curvature is not accounted for. Hence, the local fiber bending stiffness cannot be preserved in the homogenization process and the strain localization stage of microbuckling problems is rendered ill-posed. Micropolar homogenization rectifies this deficiency by introducing additional rotational degrees of freedom to account for curvature strain. The present contribution distinguishes itself from earlier micropolar homogenization approaches by adapting a Total-Lagrangian finite strain plasticity theory for micropolar continua to the microbuckling problem under consideration here. From this theoretical basis, a constitutive model and a finite element formulation are derived, and the extra parameters introduced by the micropolar solid are identified.

Design of Low Cost Carbon Fiber Composites via Examining the Micromechanical Stress Distributions in A42 Bean-Shaped versus T650 Circular Fibers

Recent advancements have led to new polyacrylonitrile carbon fiber precursors which reduce production costs, yet lead to bean-shaped cross-sections. While these bean-shaped fibers have comparable stiffness and ultimate strength values to typical carbon fibers, their unique morphology results in varying in-plane orientations and different microstructural stress distributions under loading, which are not well understood and can limit failure strength under complex loading scenarios. Therefore, this work used finite element simulations to compare longitudinal stress distributions in A42 (bean-shaped) and T650 (circular) carbon fiber composite microstructures. Specifically, a microscopy image of an A42/P6300 microstructure was processed to instantiate a 3D model, while a Monte Carlo approach (which accounts for size and in-plane orientation distributions) was used to create statistically equivalent A42/P6300 and T650/P6300 microstructures. First, the results showed that the measured in-plane orientations of the A42 carbon fibers for the analyzed specimen had an orderly distribution with peaks at |ϕ|=0∘,180∘. Additionally, the results showed that under 1.5% elongation, the A42/P6300 microstructure reached simulated failure at approximately 2108 MPa, while the T650/P6300 microstructure did not reach failure. A single fiber model showed that this was due to the curvature of A42 fibers which was 3.18 μm−1 higher at the inner corner, yielding a matrix stress that was 7 MPa higher compared to the T650/P6300 microstructure. Overall, this analysis is valuable to engineers designing new components using lower cost carbon fiber composites, based on the micromechanical stress distributions and unique packing abilities resulting from the A42 fiber morphologies.

Temperature-insensitive bending measurement method using optical fiber sensors

This paper presents a new and simple method for indirect bending measurements. The main advantage of the proposed method is its immunity from temperature as well as electromagnetic interference. It uses small and simple-to-fabricate transducer-based fiber Bragg gratings tilted in the fiber core at a small angle. In this work, analysis of the characteristic changes in the transmission of tilted Bragg gratings with different bending treatments are presented. It is shown that selected areas of the spectrum are more or less sensitive to different fiber curvatures. Additionally, the sensitivity of the method to changes in the polarization angle is presented for selected examples. The division of the complete transmission spectrum into more or less sensitive areas provides a development of output parameter dynamics by improving the usable range. This paper shows the difference between the curvature-dependent transmission spectrum changes for 2-degree and 4-degree tilted gratings. The contour length changes in selected divided ranges of the spectrum have a quasi-linear character, which is promising for applications. The influence of changes in the input light polarization direction on changes in the calculated contour length is also investigated. In three boundary polarization cases, the greatest difference in the normalized contour length for a constant curvature radius is 0.01028, which is 1,028% of the maximum. The results for bending radius measurements based on contour changes are presented for the range from 30 to 12 mm, but the proposed system allows for bending radius measurements over a wider range.

Exploration of hybrid cladding elements in chalcogenide hollow-core fibers for low-loss mid-infrared transmission

Optical losses of chalcogenide negative curvature hollow-core fibers with hybrid cladding elements were numerically investigated in this study. Microstructured cladding formed by the combination of tubular and elliptical elements was designed for low-loss operation in the mid-infrared spectrum. A confinement loss value of 0.287 dB/km was calculated for the proposed ellipse-nested tubular negative curvature fiber with optimized design parameters at 10.6 µm. Achieved confinement losses with the proposed design are several orders of magnitude lower than the tubular/elliptical negative curvature fibers in the targeted spectrum. The effect of the material absorption to the total fiber losses was also investigated along with the confinement losses. Suppression on the higher-order modes by the proposed fiber was numerically observed. The negative curvature fibers are promising for the low-loss guidance of CO2 lasers that are widely used for various applications spanning from material processing to surgery.

Oxidative stress and its impact on skin, scalp and hair.

Oxidative stress is an unbalanced condition in which the tissues of the body are not sufficiently able to counteract either exogenous or endogenous sources of reactive oxygen species. Oxidative stress is strongly associated with ageing, both local and systemic, as well as a wide range of local health conditions. This review focuses on the oxidative stress data known for skin, scalp and hair. This oxidative stress may be the 'currency' by which an unhealthy scalp leads to deleterious consequences to the hair. The ramifications of this scalp oxidative stress to normal hair elongation, retention and replacement are discussed.

High sensitivity curvature sensor based on the long period fiber grating inscribed in the two-mode fiber.

The optical fiber curvature sensor is an important device that is widely used in the field of medical instruments. In this paper, we proposed a high sensitivity curvature sensor based on a long period fiber grating (LPFG), which is inscribed in the two-mode fiber (TMF) by CO2 laser pulses. Unlike the traditional LPFG in the single-mode fiber, TMF-LPFG couples the high-order mode LP11 in the core with the modes in the cladding. From the experiment results, the wavelength shifts to the short-wave direction as the sensor bends. This sensor offers a high curvature sensitivity of -23.67nm/m-1 in the range of 1.137-4.684m-1 and -18.95nm/m-1 in the range of 4.766-6.132m-1, respectively. Moreover, this sensor has the advantage of low transmission loss, which is less than -4dB.

Regional variations in discrete collagen fibre mechanics within intact intervertebral disc resolved using synchrotron computed tomography and digital volume correlation

Many soft tissues, such as the intervertebral disc (IVD), have a hierarchical fibrous composite structure which suffers from regional damage. We hypothesise that these tissue regions have distinct, inherent fibre structure and structural response upon loading. Here we used synchrotron computed tomography (sCT) to resolve collagen fibre bundles (∼5μm width) in 3D throughout an intact native rat lumbar IVD under increasing compressive load. Using intact samples meant that tissue boundaries (such as endplate-disc or nucleus-annulus) and residual strain were preserved; this is vital for characterising both the inherent structure and structural changes upon loading in tissue regions functioning in a near-native environment. Nano-scale displacement measurements along >10,000 individual fibres were tracked, and fibre orientation, curvature and strain changes were compared between the posterior-lateral region and the anterior region. These methods can be widely applied to other soft tissues, to identify fibre structures which cause tissue regions to be more susceptible to injury and degeneration. Our results demonstrate for the first time that highly-localised changes in fibre orientation, curvature and strain indicate differences in regional strain transfer and mechanical function (e.g. tissue compliance). This included decreased fibre reorientation at higher loads, specific tissue morphology which reduced capacity for flexibility and high strain at the disc-endplate boundary. Statement of significanceThe analyses presented here are applicable to many collagenous soft tissues which suffer from regional damage. We aimed to investigate regional intervertebral disc (IVD) structural and functional differences by characterising collagen fibre architecture and linking specific fibre- and tissue-level deformation behaviours. Synchrotron CT provided the first demonstration of tracking discrete fibres in 3D within an intact IVD. Detailed analysis of regions was performed using over 200k points, spaced every 8 μm along 10k individual fibres. Such comprehensive structural characterisation is significant in informing future computational models. Morphological indicators of tissue compliance (change in fibre curvature and orientation) and fibre strain measurements revealed localised and regional differences in tissue behaviour.

An Exterior Optical Fibre Sensing Technology Used for Interface Pressure Measurement Between Cable and Accessory

Interface pressure between cable and accessory is the key to ensure the long-term reliable operation of cable accessories. The traditional measurement method of interface pressure is off-line measurement through a built-in piezoelectric sensor. However, this method is difficult to operate and damages the interface structure. In addition, the offline measurement cannot reflect the real-time dynamic change of interface pressure during the operation of cable accessories. Therefore, this paper proposes a new method for the on-line measurement of interface pressure between cable and accessory by means of an exterior optical fibre curvature sensor, whose design mechanism is based on the pure bending theory of optical fibre. Then the relationship model involving the exterior curvature of the cable accessory, the radial displacement and the inner interface pressure is established. Finally, interface pressures of the 8.7/10 kV cable accessory under different expansion ratios are measured by the calibrated optical fibre curvature sensor. The measurement results show that the optical fibre curvature sensor measures the exterior curvature of the accessory accurately; the average sensitivity reaches 7.679 nm/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> , and the measurable curvature ranges from 0.03 to 0.05 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> . The conversion results of interface pressure are basically consistent with the results measured directly by a traditional piezoelectric sensor or simulated mechanically by finite element software. Therefore, the exterior optical fibre sensing technology proposed in this paper is expected to be used for the on-line measurement of the interface pressure between cable and accessory.

Trigger-Based Dexterous Operation with Multimodal Sensors for Soft Robotic Hand

This paper focuses on how to improve the operation ability of a soft robotic hand (SRH). A trigger-based dexterous operation (TDO) strategy with multimodal sensors is proposed to perform autonomous choice operations. The multimodal sensors include optical-based fiber curvature sensor (OFCS), gas pressure sensor (GPS), capacitive pressure contact sensor (CPCS), and resistance pressure contact sensor (RPCS). The OFCS embedded in the soft finger and the GPS series connected in the gas channel are used to detect the curvature of the finger. The CPCS attached on the fingertip and the RPCS attached on the palm are employed to detect the touch force. The framework of TDO is divided into sensor detection and action operation. Hardware layer, information acquisition layer, and decision layer form the sensor detection module; action selection layer, actuator drive layer, and hardware layer constitute the action operation module. An autonomous choice decision unit is used to connect the sensor detecting module and action operation module. The experiment results reveal that the TDO algorithm is effective and feasible, and the actions of grasping plastic framework, pinching roller ball pen and screwdriver, and handshake are executed exactly.

Design of negative curvature fiber carrying multiorbital angular momentum modes for terahertz wave transmission

We design a novel negative curvature fiber (NCF) to support terahertz orbital angular momentum (OAM) modes. Numerical models are constructed to evaluate the transmission performances of vector modes in the frequency range of 0.40–0.80 THz. The designed fiber made from only one kind of heat-resistance resin (HTL) material can support 50–52 OAM modes with large effective index differences above 10−4 and low confinement loss (in the level of 10−15 dB/cm). Some other significant characteristics of the designed NCF including waveguide dispersion, OAM purity, and effective mode field area (Aeff), are also calculated and analyzed with their effects and applications on terahertz OAM guidance. The optimized absolute value of dispersion is between 0.33 and 0.8 ps/(THz × cm) in the range of 0.45–0.75 THz. The high mode purity (85%−95%) in the range of 0.60–0.80 THz further promotes the mode division multiplexing in OAM fiber. The proposed NCF can offer great potential in high-capacity terahertz communication based on OAM multiplexing.

Geodesic fiber tracking in white matter using activation function

Background and objective:The geodesic ray-tracing method has shown its effectiveness for the reconstruction of fibers in white matter structure. Based on reasonable metrics on the spaces of the diffusion tensors, it can provide multiple solutions and get robust to noise and curvatures of fibers. The choice of the metric on the spaces of diffusion tensors has a significant impact on the outcome of this method. Our objective is to suggest metrics and modifications of the algorithms leading to more satisfactory results in the construction of white matter tracts as geodesics.Methods:Starting with the DTI modality, we propose to rescale the initially chosen metric on the space of diffusion tensors to increase the geodetic cost in the isotropic regions. This change should be conformal in order to preserve the angles between crossing fibers. We also suggest to enhance the methods to be more robust to noise and to employ the fourth order tensor data in order to handle the fiber crossings properly.Results: We propose a way to choose the appropriate conformal class of metrics where the metric gets scaled according to tensor anisotropy. We use the logistic functions, which are commonly used in statistics as cumulative distribution functions. To prevent deviation of geodesics from the actual paths, we propose a hybrid ray-tracing approach. Furthermore, we suggest how to employ diagonal projections of 4th order tensors to perform fiber tracking in crossing regions.Conclusions: The algorithms based on the newly suggested methods were succesfuly implemented, their performance was tested on both synthetic and real data, and compared to some of the previously known approaches.

Low-loss single-mode modified conjoined tube hollow-core fiber.

We explain the effects of cladding geometries on conjoined tube hollow-core negative curvature fibers and offer a modified conjoined tube negative curvature fiber with appropriate positioning of an additional negative curvature D-shaped layer joining the flat bar to reveal attractive performances over existing recent related fibers. The proposed fiber ensures the least loss of 0.003 dB/km at 1.43 µm, a ∼0.04dB/km loss covering the wide bandwidth of approximately 300 nm, the lowest surface scattering loss of ∼0.02dB/km, and the lowest microbending loss of ∼0.04dB/km, thus providing a propagation loss of 0.10 dB/km at the 1.55 µm wavelength and also offering excellent bend loss performance (∼0.015dB/km loss at a 7 cm bend radius). The fiber, with a core diameter of 30.50 µm, also shows a higher-order mode extinction ratio of ∼1600 and maintains greater than 100 over most of the telecom bands; hence, it effectively provides single-mode operation. We show the potential of conjoined tube hollow-core negative curvature fibers in optical communications systems.

&lt;i&gt;In situ&lt;/i&gt; Tracking of Individual Collagen Fibre Bundles in Intact Loaded Intervertebral Discs Exposes Damage-Susceptible Collagen Organisations

Many soft tissues, such as the intervertebral disc (IVD), have a hierarchical fibrous composite structure which suffers from regional damage. We hypothesise that clinical injury patterns in these tissues occur in localised regions where there is an integrated requirement for both marked compliance and significant load transfer. Here we used synchrotron computed tomography (sCT) to resolve collagen fibre bundles (~5μm width) in 3D throughout an intact native rat lumbar IVD under increasing compressive load. Using intact samples meant that tissue boundaries (such as endplate-disc or nucleus-annulus) and residual strain were preserved; this is vital for characterising both the inherent structure and structural changes upon loading in tissue regions functioning in a near-native environment. Nano-scale displacement measurements along >10,000 individual fibres were tracked, and fibre orientation, curvature and strain changes were compared between the failure-prone posterior-lateral region and the more robust anterior region. These methods can be widely applied to other soft tissues, to identify fibre structures which cause tissue regions to be more susceptible to injury and degeneration. Our results demonstrate for the first time that highly-localised changes in fibre orientation, curvature and strain indicate differences in regional strain transfer and mechanical function (e.g. tissue compliance), correlating directly with locations clinically at risk of damage. This included decreased fibre reorientation at higher loads, specific tissue morphology which reduced capacity for flexibility and high strain at the disc-endplate boundary.

Understanding bending-induced loss and bending-enhanced higher-order mode suppression in negative curvature fibers

We present a numerical analysis on bending-induced loss and bending-enhanced higher-order mode suppression in negative curvature fibers. We provide underlying mechanisms on how geometrical parameters affect the bending properties. We find that fiber parameters influence the bending performance by altering the resonant coupling conditions, as well as light leakage through inter-tube gaps. We identify regions in the parameter space that exhibit excellent bending properties and offer general guidelines for designing negative curvature fibers that are less sensitive to bending. Moreover, we explore the possibility of enhancing higher-order core mode suppression through mechanical bending. We find that up to nine-fold increase in the higher-order mode extinction ratio can be achieved by bending the fiber.

Compact Fiber Curvature and Temperature Sensor Inscribed by Femtosecond Laser Through the Coating

An integrated structure in the original single mode fiber (SMF) which can measure curvature and temperature simultaneously, is proposed and demonstrated. The key components of the device include an in-fiber Mach–Zehnder interferometer (MZI) and a fiber Bragg grating (FBG), which are integrally fabricated in a coating-unstripped SMF by femtosecond laser direct writing. The curvature sensing of the device is based on the wavelength shift of the MZI interference fringe dips. It is found that the bending response is closely related to the bending orientation. The measured curvature sensitivities are 2.324 and 2.491 nm/m−1 for the 0° and 180° orientation in the range of 0–10 m−1, respectively. Under different bending states, the temperature response of the FBG resonant wavelength is almost the same and the mean temperature sensitivity is 9.72 pm/°. The advantages of compact, simple fabrication, low insertion loss, no assembly, wide operating range of curvature measurement and real-time temperature sensing make our device very attractive in practical engineering monitoring and somatosensory posture recognition.

Effect of Shape of Armoring Fibers on Strength of Composite Materials

In this work, experimental studies of the effect of fiber curvature on the strength and ultimate deformations of epoxy carbon plastic samples under loading are carried out. On the basis of the experimental studies carried out, the static characteristics of the composite layered material, which are promising for use in the structures under consideration, have been determined. Based on the test results, it was demonstrated that in the design calculations for the products under consideration, it is possible to use static characteristics, since an increase in the deformation rate of the material leads to an increase in strength and, therefore, the calculation results will provide an additional margin of safety.

Effect of High Velocity Deformation on Strength of ArmoredComposite Materials

This paper considers the problem of determining the strength of carbon fiber reinforced plastic with straight and curved fibers under high-speed loading. High-speed tests of unidirectional CFRP specimens with rectilinear and wavy structure have been carried out. The influence of the structure and high-speed loading on the ultimate strength and ultimate deformation of the material is investigated. For the first time, a detailed study of the effect of fiber curvature on the properties of CFRP under high-speed deformation has been carried out. As a result of dynamic tests, it was shown that the ultimate strength in unidirectional laying is higher than in wavy laying. The effect of increasing the ultimate deformations of specimens with bent fibers was established, which was noted earlier for the case of tensile tests.