Search

In this study, the dispersion of reclaimed carbon fibres following cost-effective surface treatment is explored with a hydrodynamic fibre moving model, and a practical fibre dispersion effect is investigated through various physical dispersion methods. To utilise reclaimed carbon fibres for a desired composite product, our proposed low-cost surface treatment is shown to be beneficial to the physical and chemical properties of the reclaimed carbon fibres and to yield polar-hydrophilic characteristics. Single fibre tensile testing is performed to explore the effect of surface treatment on the reclaimed carbon fibres (a higher tensile strength was observed). A computational hydrodynamic fibre moving model based on a moving particle semi-implicit method is newly designed to perform hydrodynamic simulation to determine aqueous dispersion of discontinuous reclaimed carbon fibres. This simulation helps understanding fibre flocculation phenomena from the perspective of fibre stiffness, which should not be disregarded for the fibre dispersion. Fibre surface analyses including morphology and functional groups are carried out to investigate the effect of surface treatment. The hydrodynamic simulation and proposed fibre dispersion methods with a cost-effective surface treatment approach can be widely applicable to any type of reclaimed carbon fibres to produce recycled fibre reinforced polymer composite materials. [ABSTRACT FROM AUTHOR]

With the development of next-generation cardiovascular prosthesis, the requirement for more advanced simulations for predicting the mechanical response of biological tissue has arisen. Finite-element analysis represents a powerful tool capable of simulating complex behaviours within this framework. The present work proposes the computational implementation of an advanced constitutive model for the fibre-reinforced tissue making up the aortic wall. The formulation available in literature is numerically implemented within the FE software Abaqus© through specific user subroutines, and model predictions are compared with the already available single-dispersion-model results. The influence of each dispersion parameter on the macroscopic behaviour is analysed and discussed. Finally, the model is extended by a damage regime based on strain invariants, which is capable of considering the influence of patient ageing on the mechanical response failure strain. The user subroutines are here provided in the Appendix for applications. [ABSTRACT FROM AUTHOR]

It is widely acknowledged that an imbalanced biomechanical environment can have significant effects on myocardial pathology, leading to adverse remodelling of cardiac function if it persists. Accurate stress prediction essentially depends on the strain energy function which should have competent descriptive and predictive capabilities. Previous studies have focused on myofibre dispersion, but not on fibres along other directions. In this study, we will investigate how fibre dispersion affects myocardial biomechanical behaviours by taking into account both the myofibre dispersion and the sheet fibre dispersion, with a focus on the sheet fibre dispersion. Fibre dispersion is incorporated into a widely-used myocardial strain energy function using the discrete fibre bundle approach. We first study how different dispersion affects the descriptive capability of the strain energy function when fitting to ex vivo experimental data, and then the predictive capability in a human left ventricle during diastole. Our results show that the chosen strain energy function can achieve the best goodness-of-fit to the experimental data by including both fibre dispersion. Furthermore, noticeable differences in stress can be found in the LV model. Our results may suggest that it is necessary to include both dispersion for myofibres and the sheet fibres for the improved descriptive capability to the ex vivo experimental data and potentially more accurate stress prediction in cardiac mechanics.

This work accompanies the first part of our study "effects of dispersed fibres in myocardial mechanics: Part I passive response" with a focus on myocardial active contraction. Existing studies have suggested that myofibre architecture plays an important role in myocardial active contraction. Following the first part of our study, we firstly study how the general fibre architecture affects ventricular pump function by varying the mean myofibre rotation angles, and then the impact of fibre dispersion along the myofibre direction on myocardial contraction in a left ventricle model. Dispersed active stress is described by a generalised structure tensor method for its computational efficiency. Our results show that both the myofibre rotation angle and its dispersion can significantly affect cardiac pump function by redistributing active tension circumferentially and longitudinally. For example, larger myofibre rotation angle and higher active tension along the sheet-normal direction can lead to much reduced end-systolic volume and higher longitudinal shortening, and thus a larger ejection fraction. In summary, these two studies together have demonstrated that it is necessary and essential to include realistic fibre structures (both fibre rotation angle and fibre dispersion) in personalised cardiac modelling for accurate myocardial dynamics prediction.

Understanding the mechanical effects of smooth muscle cell (SMC) contraction on the initiation and the propagation of cardiovascular diseases such as aortic dissection is critical. Framed by elastic lamellar sheets in the lamellar unit, there are SMCs in the media with a distinct radial tilt, which indicates their contribution to the radial strength. However, the mechanical effects of this type of anisotropy have not been fully discussed. Therefore, in this study, we propose a constitutive framework that models the passive and active mechanics of the aorta, taking into account the dispersed nature of the aortic constituents by applying the discrete fibre dispersion method. We suggest an isoparametric approach by evaluating various numerical integration methods and introducing a non-uniform discretization of the unit hemisphere to increase its computational efficiency. Finally, the constitutive parameters are fitted to layer-specific experimental data and initial computational results are briefly presented. The radial tilt of SMCs is also analysed, which has a noticeable influence on the mechanical behaviour of the aorta. In the absence of sufficient experimental data, the results indicate that the active contribution of SMCs has a remarkable impact on the mechanics of the healthy aorta. [ABSTRACT FROM AUTHOR]

Detailed fibre architecture plays a crucial role in myocardial mechanics both passively and actively. Strong interest has been attracted over decades in mathematical modelling of fibrous tissue (arterial wall, myocardium, etc.) by taking into account realistic fibre structures, i.e. from perfectly aligned one family of fibres, to two families of fibres, and to dispersed fibres described by probability distribution functions. It is widely accepted that the fibres, i.e. collage, cannot bear the load when compressed, thus it is necessary to exclude compressed fibres when computing the stress in fibrous tissue. In this study, we have focused on mathematical modelling of fibre dispersion in myocardial mechanics, and studied how different fibre dispersions affect cardiac pump function. The fibre dispersion in myocardium is characterized by a non-rotationally symmetric distribution using a π -periodic Von Mises distribution based on recent experimental studies. In order to exclude compressed fibres for passive response, we adopted the discrete fibre dispersion model for approximating a continuous fibre distribution with finite fibre bundles, and then the general structural tensor was employed for describing dispersed active tension. We first studied the numerical accuracy of the integration of fibre contributions using the discrete fibre dispersion approach, then compared different mechanical responses in a uniaxially stretched myocardial sample with varied fibre dispersions. We finally studied the cardiac pump functions from diastole to systole in two heart models, a rabbit bi-ventricle model and a human left ventricle model. Our results show that the discrete fibre model is preferred for excluding compressed fibres because of its high computational efficiency. Both the diastolic filling and the systolic contraction will be affected by dispersed fibres depending on the in-plane and out-of-plane dispersion degrees, especially in systolic contraction. The in-plane dispersion seems affecting myocardial mechanics more than the out-of-plane dispersion. Despite different effects in the rabbit and human models caused by the fibre dispersion, large differences in pump function exist when fibres are highly dispersed at in-plane and out-of-plane. Our results highlight the necessity of using dispersed fibre models when modelling myocardial mechanics, especially when fibres are largely dispersed under pathological conditions, such as fibrosis. [ABSTRACT FROM AUTHOR]

Myofibre architecture is one of the essential components when constructing personalized cardiac models. In this study, we develop a neonatal porcine bi-ventricle model with three different myofibre architectures for the left ventricle (LV). The most realistic one is derived from ex vivo diffusion tensor magnetic resonance imaging, and other two simplifications are based on rule-based methods (RBM): one is regionally dependent by dividing the LV into 17 segments, each with different myofibre angles, and the other is more simplified by assigning a set of myofibre angles across the whole ventricle. Results from different myofibre architectures are compared in terms of cardiac pump function. We show that the model with the most realistic myofibre architecture can produce larger cardiac output, higher ejection fraction and larger apical twist compared with those of the rule-based models under the same pre/after-loads. Our results also reveal that when the cross-fibre contraction is included, the active stress seems to play a dual role: its sheet-normal component enhances the ventricular contraction while its sheet component does the opposite. We further show that by including non-symmetric fibre dispersion using a general structural tensor, even the most simplified rule-based myofibre model can achieve similar pump function as the most realistic one, and cross-fibre contraction components can be determined from this non-symmetric dispersion approach. Thus, our study highlights the importance of including myofibre dispersion in cardiac modelling if RBM are used, especially in personalized models.

This study accessed the performance of the four‐level Manchester coding (4‐MC) and four‐level modified Manchester (4‐MM) technique at the bit rates of 20 and 40 Gb/s for the first‐order and second‐order optical equalisers. The performances were evaluated with respect to bit error rate (BER), power penalty, eye diagrams, and dispersion tolerance. Based on the results by utilising the second‐order optical equaliser, at 20 Gb/s, the transmission distance of 4‐MC and 4‐MM was extended by 25 and 27 km of standard single‐mode fibre (SSMF), respectively, while at the bit rate of 40 Gb/s, the 4‐MC and 4‐MM transmission distance was extended by 6.5 and 7.5 km of SSMF, respectively. Hence, the second‐order optical equaliser can adequately compensate for the fibre dispersion and consequently the overall BER performance. Therefore, the proposed system could serve as an alternative to the next‐generation high‐speed optical transmission links. [ABSTRACT FROM AUTHOR]

Multicore fibre (MCF) has attracted considerable attention in mobile fronthaul networks as a promising solution to face the ever‐increasing mobile traffic demand and to support network capacity scaling in a cost‐effective manner. However, MCF‐based systems suffer from the inter‐core crosstalk (IC‐‐XT) noise, which could incur severe performance degradation. In this study, we investigate for the first time, to our knowledge, the performance of an analogue radio‐over‐fibre mobile fronthaul link employing MCF under the joint impact of fibre dispersion and frequency chirp. Herein, the authors consider the radio frequency (RF) power fading induced by fibre dispersion and frequency chirp. In addition, the frequency‐dependent IC‐XT power fluctuations induced by dispersion and frequency chirp have been discussed. Closed‐form equations for the carrier‐to‐noise ratio penalty due to power fading and IC‐XT are derived. Moreover, new expressions for the average and variance of the crosstalk transfer function are obtained. Also, the analysis accounts for inter‐core skew, laser relative intensity noise, shot noise and thermal noise. It has been shown that both the desired signal and IC‐XT signals show the same behaviour in the presence of fibre dispersion and frequency chirp. Moreover, results show that RF power fading is the key issue. [ABSTRACT FROM AUTHOR]

Collagen fibres within fibrous soft biological tissues such as artery walls, cartilage, myocardiums, corneas and heart valves are responsible for their anisotropic mechanical behaviour. It has recently been recognized that the dispersed orientation of these fibres has a significant effect on the mechanical response of the tissues. Modelling of the dispersed structure is important for the prediction of the stress and deformation characteristics in (patho)physiological tissues under various loading conditions. This paper provides a timely and critical review of the continuum modelling of fibre dispersion, specifically, the angular integration and the generalized structure tensor models. The models are used in representative numerical examples to fit sets of experimental data that have been obtained from mechanical tests and fibre structural information from second-harmonic imaging. In particular, patches of healthy and diseased aortic tissues are investigated, and it is shown that the predictions of the models fit very well with the data. It is straightforward to use the models described herein within a finite-element framework, which will enable more realistic (and clinically relevant) boundary-value problems to be solved. This also provides a basis for further developments of material models and points to the need for additional mechanical and microstructural data that can inform further advances in the material modelling. [ABSTRACT FROM AUTHOR]

Abstract The great potential of computational diffusion MRI (dMRI) relies on indirect inference of tissue microstructure and brain connections, since modelling and tractography frameworks map diffusion measurements to neuroanatomical features. This mapping however can be computationally highly expensive, particularly given the trend of increasing dataset sizes and the complexity in biophysical modelling. Limitations on computing resources can restrict data exploration and methodology development. A step forward is to take advantage of the computational power offered by recent parallel computing architectures, especially Graphics Processing Units (GPUs). GPUs are massive parallel processors that offer trillions of floating point operations per second, and have made possible the solution of computationally-intensive scientific problems that were intractable before. However, they are not inherently suited for all problems. Here, we present two different frameworks for accelerating dMRI computations using GPUs that cover the most typical dMRI applications: a framework for performing biophysical modelling and microstructure estimation, and a second framework for performing tractography and long-range connectivity estimation. The former provides a front-end and automatically generates a GPU executable file from a user-specified biophysical model, allowing accelerated non-linear model fitting in both deterministic and stochastic ways (Bayesian inference). The latter performs probabilistic tractography, can generate whole-brain connectomes and supports new functionality for imposing anatomical constraints, such as inherent consideration of surface meshes (GIFTI files) along with volumetric images. We validate the frameworks against well-established CPU-based implementations and we show that despite the very different challenges for parallelising these problems, a single GPU achieves better performance than 200 CPU cores thanks to our parallel designs. Highlights • The computational power offered by GPUs is used to accelerate the analysis of dMRI. • We present a generic and flexible parallel framework for microstructure modelling on GPUs. • And also a framework for performing probabilistic tractography and generating connectomes on GPUs. • A single GPU achieves better performance than 200 CPU cores with our frameworks. [ABSTRACT FROM AUTHOR]

Abstract Generalised Structure Tensors (GSTs) are used to formulate constitutive models for anisotropic fibre-reinforced materials in which fibres are dispersed. The GST approach has been applied so far to models based on invariants I 4 and I 5 (I 6 and I 7). These anisotropic invariants capture the effect of deformation on each fibre family in isolation, unlike the invariant I 8 , which couples two fibre families. We extend the GST approach to models based on the invariant I 8. We consider two different formulations and for each model derive expressions for stress and elasticity tensors in both the general case and for axisymmetric distributions. We apply the proposed formulation to the hyperelastic Holzapfel–Ogden model for myocardium and obtain a modified model, in which fibre dispersion is consistently accounted for in every term of the strain-energy function. We demonstrate that when accounting for fibre dispersion in the coupling term, the effect on the predicted material response can be significant and may also reduce material symmetry. Highlights • Generalised structure tensor (GST) expressions derived for the coupling invariant I 8. • The GST approach is thereby extended to a complete set of anisotropic invariants. • Orientation dispersion of fibres can be consistently included into a general model. • The proposed approach is applied to the Holzapfel–Ogden (HO) model for myocardium. • Fibre splay in I 8 may soften the response and reduce material symmetry. [ABSTRACT FROM AUTHOR]

The effective transverse relaxation rate (R 2 *) is sensitive to the microstructure of the human brain like the g-ratio which characterises the relative myelination of axons. However, the fibre-orientation dependence of R 2 * degrades its reproducibility and any microstructural derivative measure. To estimate its orientation-independent part (R 2,iso *) from single multi-echo gradient-recalled-echo (meGRE) measurements at arbitrary orientations, a second-order polynomial in time model (hereafter M2) can be used. Its linear time-dependent parameter, β 1 * when neglecting the myelin water (MW) signal in the hollow cylinder fibre model (HCFM). Here, we examined the performance of M2 using experimental and simulated data with variable g-ratio and fibre dispersion. We found that the fitted 2,iso * when neglecting the myelin water (MW) signal in the hollow cylinder fibre model (HCFM). Here, we examined the performance of M2 using experimental and simulated data with variable g-ratio and fibre dispersion. We found that the fitted β 1 can estimate R 2,iso * using meGRE with long maximum-echo time (TE max  ≈ 54 ms), but not accurately captures its microscopic dependence on the g-ratio (error 84%). We proposed a new heuristic expression for β 1 that reduced the error to 12% for ex vivo compartmental R 2 values. Using the new expression, we could estimate an MW fraction of 0.14 for fibres with negligible dispersion in a fixed human optic chiasm for the ex vivo compartmental R 2 values but not for the in vivo values. M2 and the HCFM-based simulations failed to explain the measured R 2 *-orientation-dependence around the magic angle for a typical in vivo meGRE protocol (with TE max  ≈ 18 ms). In conclusion, further validation and the development of movement-robust in vivo meGRE protocols with TE max  ≈ 54 ms are required before M2 can be used to estimate R 2,iso * in subjects., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Fritz, Mordhorst, Ashtarayeh, Periquito, Pohlmann, Morawski, Jaeger, Niendorf, Pine, Callaghan, Weiskopf and Mohammadi.)

This study presents the external modulation and direct detection of duobinary signal in optical access networks at 25 and 50 Gb/s with the use of first‐order optical equaliser at the transmitter output (pre‐equalisation) to compensate the waveform distortion induced by fibre dispersion. The first‐order optical equaliser is then replaced by second‐order optical equaliser to further improve the bit error rate (BER) performance and extend the maximum transmission distance by compensating the residual dispersion for the first time. The authors explain the enhancement in the BER by analysing the eye diagrams and optical spectra. The authors also investigate non‐return‐to‐zero signal with similar setup parameters for reference. [ABSTRACT FROM AUTHOR]

This paper presents a continuum-based transverse isotropic model incorporating rate-dependency and fibre dispersion, applied to the planar biaxial deformation of aortic valve (AV) specimens under various stretch rates. The rate dependency of the mechanical behaviour of the AV tissue under biaxial deformation, the (pseudo-) invariants of the right Cauchy-Green deformation-rate tensor C ̇ associated with fibre dispersion, and a new fibre orientation density function motivated by fibre kinematics are presented for the first time. It is shown that the model captures the experimentally observed deformation of the specimens, and characterises a shear-thinning behaviour associated with the dissipative (viscous) kinematics of the matrix and the fibres. The application of the model for predicting the deformation behaviour of the AV under physiological rates is illustrated and an example of the predicted σ − λ curves is presented. While the development of the model was principally motivated by the AV biomechanics requisites, the comprehensive theoretical approach employed in the study renders the model suitable for application to other fibrous soft tissues that possess similar rate-dependent and structural attributes. [ABSTRACT FROM AUTHOR]

Detailed information on the three-dimensional dispersion of collagen fibres within layers of healthy and diseased soft biological tissues has been reported recently. Previously we have proposed a constitutive model for soft fibrous solids based on the angular integration approach which allows the exclusion of any compressed collagen fibre within the dispersion. In addition, a computational implementation of that model in a general purpose finite element program has been investigated and verified with the standard fibre-reinforcing model for fibre contributions. In this study, we develop the proposed fibre dispersion model further using an exponential form of the strain-energy function for the fibre contributions. The finite element implementation of this model with a rotationally symmetrical dispersion of fibres is also presented. This includes explicit expressions for the stress and elasticity tensors. The performance and implementation of the new model are demonstrated by means of a uniaxial extension test, a simple shear test, and an extension–inflation simulation of a residually stressed carotid artery segment. In each example we have obtained good agreement between the finite element solution and the analytical or experimental results. [ABSTRACT FROM AUTHOR]

In this work, we constructed a novel collagen fibre remodelling algorithm that incorporates the complex nature of random evolution acting on single fibres causing macroscopic fibre dispersion. The proposed framework is different from the existing remodelling algorithms, in that the microscopic random force on cellular scales causing a rotational-type Brownian motion alone is considered as an aspect of vascular tissue remodelling. A continuum mechanical framework for the evolution of local dispersion and how it could be used for modeling the evolution of internal radius of biaxially strained artery structures under constant internal blood pressure are presented. Alinear evolution form for the statistical fibre dispersion is employed in the model. The random force component of the evolution, which depends on the mechanical stress stimuli, is described by a single parameter. Although the mathematical form of the proposed model is simple, there is a strong link between the microscopic evolution of collagen dispersion on the cellular level and its effects on the macroscopic visible world through mechanical variables. We believe that the proposed algorithm utilizes a better understanding of the relationship between the evolution rates of mean fibre direction and fibre dispersion. The predictive capability of the algorithm is presented using experimental data. The model has been simulated by solving a single-layered axisymmetric artery (adventitia) deformation problem. The algorithm performed well for estimating the quantitative features of experimental anisotropy, the mean fibre direction vector and the dispersion (κ) measurements under strain-dependent evolution assumptions. [ABSTRACT FROM AUTHOR]

We study dispersion mismatches and compensation in high-resolution frequency scanning interference measurements. Compared to semiconductor lasers, external cavity lasers can, in theory, provide wideband frequency modulation and high-resolution measurements. However, experiments indicate that the dispersion mismatch cannot be ignored in measurement systems containing wideband tuning lasers. Fibre auxiliary interferometer external clock sampling results indicate that the beat frequency of measurement signals exhibits linear chirp. In turn, the frequency spectrum of the measurement signal broadens, thus lowering the measurement resolution and limiting the measurement distance. We present a dispersion mismatch model and analyse the associated measurement effects. We also propose a dispersion compensation method based on a focused definition evaluation function. By studying the relationship between the compensation coefficient and evaluation function, the optimal compensation coefficient can be determined quickly and accurately. Our experiments demonstrate that within a tuning bandwidth of 40 nm, the peak full width at half maximum (FWHM) after dispersion compensation is 32.2 µm at a distance of 3.8931671 m, which is close to the theoretical resolution. Our method provides a technical approach to realizing large, high-resolution distance measurements for broadband laser frequency scanning interferometers. [ABSTRACT FROM AUTHOR]

Collagen fibre architecture in articular cartilage is commonly described in terms of the predominant direction of fibre alignment. X-ray scattering has been used to study the distribution of fibre orientations in cartilage. In this paper, a new methodology for the analysis of small-angle X-ray scattering (SAXS) patterns of articular cartilage in order to quantitatively determine the distribution of collagen fibre orientations in the tissue is presented. A simple three-component model was used to fit intensity data from SAXS patterns to separate diffraction maxima from general diffuse scatter. Deconvolution of angular distributions of intensities of diffraction maxima obtained from SAXS patterns of articular cartilage and ligament samples yielded fibre orientation distributions in the cartilage samples. The methodology developed in this study worked reliably on a large set of SAXS patterns collected from native, dehydrated and trypsin-treated articular cartilage samples. The methods can be extended to quantitative analysis of small or wide angle X-ray scattering patterns obtained from other collagenous materials. [ABSTRACT FROM AUTHOR]

Propose: In vitro biomechanical properties of the skin are of important to cosmetic product development, plastic surgery, surgical practice, skin disease pathology, mechanical trauma and artificial skin design. However, complex biomechanical properties of the skin have not been fully understood so far. The literature of histology, in vitro biomechanical properties and modelling methods of the skin is reviewed to identify important problems that need to be tackled. Methods: A PubMed literature search was conducted using the terms 'skin,' 'biomechanical property,' 'damage,' 'collagen fibre,' 'viscoelastic' and 'dermis.' Relevant papers were read and analysed. Results: The histology of the skin has been studied considerably by means of optical and electron microscopies. The collagen fibre structure in the dermis has been observed with image analysis approach, and a few formulas for fibre orientation dispersion are proposed. The uniaxial, biaxial and bulge test methods were commonly applied to determine in vitro biomechanical properties of the skin. In vitro biomechanical properties exhibit nonlinear anisotropic behaviour, and at a higher strain rate, there is damage effect. Simple elongation model, isotropic model, collagen fibre recruitment model and micro-structure based model are applicable for the skin. The biomechanical property constants can be determined from the stress-stretch curves obtained in uniaxial or biaxial or multi-axial or bulge tests. Conclusions: The collagen fibre network 3D structure remain unclear and the fibre orientation dispersion characteristics are not totally understood. The damage effect in the skin has not been tackled by using constitutive laws so far. The tensile damage and fracture process, multi-layer biomechanical models developing, viscoelastic property testing and modelling in the skin should be paid significant attention in future. [ABSTRACT FROM AUTHOR]

• Hooked-end shape memory alloy fibres (PSMAFs) were developed for fibrous concrete. • PSMA-FRC were compared with steel fibre reinforced concrete. • Fresh properties and compressive/flexural behaviour of PSMA-FRCs were investigated. • DIC technique was used to capture cracking sequences in specimens. • PSMA-FRCs outperformed SF-FRC in terms of flexural behaviour with mush higher performance factor. The results of experimental analyses for the full-range compressive and flexural response of concrete reinforced with pseudoelastic shape memory alloy fibres (PSMAFs) are discussed in this paper. PSMAFs were manufactured with two types of end hooks and were used in four different fibre contents ranging between 0.5% and 1.25%, with an interval of 0.25% by volume. Cracking patterns and full-depth crack width profiles of PSMAFs reinforced concrete (PMSA-FRC) were also generated by the 2D digital image correlation (DIC) technique. The results obtained for PMSA-FRC are compared with those of steel fibre reinforced concrete (SFRC). The flexural responses of PSMA-FRC and SFRC were significantly different at fifferent stages of flexural behaviour. Compared to SFRC, PSMA-FRC showed lower flexural strength but considerably higher flexural toughness and deflection capacity. PSMA-FRC also exhibited slightly lower compressive strength (5-8%) and modulus of elasticity (4–10%) than SFRC. However, no significant difference was noticed between PSMA-FRC and SFRC regarding the overall shape of the compressive stress–strain curve, compressive toughness and failure mode. It is also shown that PSMAFs type 2, the fibre with 45° end hook, is more efficient in distributing stress over a larger cementitious matrix area. DIC analyses displayed better control over cracking, improved multiple-cracking performance, and tighter crack profiles for PSMAFs type 2 at all four fibre contents tested in this study. [ABSTRACT FROM AUTHOR]

Abstract: The fibre dispersing ability represents a key distinctive feature of the fresh state performance of a Steel Fibre Reinforced Self Compacting Concrete (SFR-SCC) which has to be carefully assessed, also in the sight of its outcomes on the mechanical performance in the hardened state. In this paper, with reference to a typical SFR-SCC mix-composition (containing 50kg/m3 hooked steel fibres 35mm long with an aspect ratio equal to 65), different methods to evaluate the resistance to static and dynamic segregation of fibres have been discussed and the results cross analysed also in order to address a comprehensive testing methodology and to assess its reliability. Among them, cylinder segregation test (for static segregation), channel flow test (for dynamic segregation) as well as the slump flow test: as a matter of fact, through the latter, by measuring the content of fibres in different concentric circular areas of the patty, information on dynamic segregation could be assessed. This test method represents the extension to FR-SCC of a methodology already developed for plain SCC. Results obtained from fresh state performance tests have been finally correlated to the fracture toughness properties in the hardened state, measured on specimens cast according to the same procedure employed for fresh state tests. This set of data allows a thorough evaluation of the correlation among fresh state performance, fibre dispersion and mechanical properties in the hardened state, furthermore enriching the meaningfulness, in a design oriented perspective, of material acceptance tests for quality control in the fresh state. The influence has been finally assessed of expected tolerances in the dosage of the mix constituents (water, cement, and superplasticizers) on the performance in both the fresh and hardened state, as correlated through fibre dispersion related issues. [Copyright &y& Elsevier]

Abstract: In this study, mixture design, workability, fibre dispersion/orientation, mechanical properties and fracture behaviour of hybrid steel fibre reinforced self-compacting concretes (HSFRSCCs) were investigated. Three different types of steel fibres with and/or without hooked-ends were added to the mixtures in two different volume fractions (0.75 and 1.5% of the total volume of concrete). The results of slump flow, U-box, V-funnel and J-ring tests have shown that increasing the fibre content of the concretes slightly reduced the workability of HSFRSCC, and the main influencing factor on flowability is the geometry of fibres. The addition of fibres, although did not change the final flowability, decreased the rate of flowability. The results from the experimental tests showed that the flexural strengths increased slightly with increasing strength of long fibres, whereas the splitting tensile strength remained unchanged. The concretes with high strength, long steel fibres show behaviour of enhanced toughness and ductility compared to that with normal strength steel fibres. The orientation and distribution of fibres in concrete have been investigated by image analysis and it was observed that fibres dispersed homogeneously in all concrete series without any clumping. With increasing the amount of fibres, the fibres were more vertically orientated relative to the bending loading direction, resulting in enhancement in the mechanical properties of concrete. [Copyright &y& Elsevier]

Abstract: Although the mechanical behaviour of the human annulus fibrosus has been extensively studied, the interaction between the collagen fibres and the ground matrix has not been well understood and is therefore ignored by most constitutive models. The objective of this study is to identify the significance of the fibre–matrix interaction in the human annulus fibrosus by careful investigation of the experimental data, the theoretical constitutive models, and the numerical simulation results in the literature. Based on the experimental results from biaxial and uniaxial tests, it is shown that the mechanical behaviour of the matrix can be well simulated by an incompressible neo-Hookean type model, but the effective stiffness of the matrix depends on fibre stretch ratio, which can only be explained by fibre–matrix interaction. Furthermore, we find that this interaction takes place anisotropically between the matrix and the fibres distributed in different proportions in different directions. The dependence of the tangent stiffness of the matrix on the first invariant of the deformation tensor can also be explained by this fibre orientation dispersion. [Copyright &y& Elsevier]

Abstract: This paper presents a three-dimensional phenomenological model for the description of smooth muscle activation. A strain energy function is proposed as sum of the strain energy stored in the passive tissue, consisting of elastin and collagen, and an active calcium-driven energy related to the chemical contraction of the smooth muscle cells. Further, the proposed model includes the dispersions of the orientations of smooth muscle cells and collagen. These dispersions, measured in experiments, can be directly inserted into the model. The approach is implemented into the framework of the finite element method. Consequently, beside a validation with experiments the modelling concept is used for a three-dimensional numerical study. [Copyright &y& Elsevier]

Optical pulse generation based on polarisation modulation and fibre dispersion is proposed that has the ability of generating multiform optical pulse trains by applying a single electro‐optic modulator and a low frequency driving signal. In the experiment, using a 10 GHz RF source, the generation of a 20 GHz time and polarisation interleaved optical pulse train, a 10 GHz single‐polarisation pulse train and a 20 GHz single‐polarisation pulse train is demonstrated. By using differential group delay in a polarisation maintaining fibre to realise time‐division‐multiplexing, the repetition rate of the pulse train can be further increased. Based on this principle, the generation of a 40 GHz time and polarisation interleaved optical pulse train, and a 40 GHz single‐polarisation pulse train is successfully implemented. [ABSTRACT FROM AUTHOR]

This study investigated a number of invariant based orthotropic and transversely isotropic constitutive equations for their suitability to fit three-dimensional simple shear mechanics data of passive myocardial tissue. A number of orthotropic laws based on Green strain components and one microstructurally based law have previously been investigated to fit experimental measurements of stress-strain behaviour. Here we extend this investigation to include several recently proposed functional forms, i.e. invariant based orthotropic and transversely isotropic constitutive relations. These laws were compared on the basis of (i) 'goodness of fit': how well they fit a set of six shear deformation tests, (ii) 'variability': how well determined the material parameters are over the range of experiments. These criteria were utilised to discuss the advantages and disadvantages of the constitutive laws. It was found that a specific form of the polyconvex type as well as the exponential Fung-type law from the previous study were most suitable for modelling the orthotropic behaviour of myocardium under simple shear. [ABSTRACT FROM AUTHOR]

This work accompanies the first part of our study "effects of dispersed fibres in myocardial mechanics: Part I passive response" with a focus on myocardial active contraction. Existing studies have suggested that myofibre architecture plays an important role in myocardial active contraction. Following the first part of our study, we firstly study how the general fibre architecture affects ventricular pump function by varying the mean myofibre rotation angles, and then the impact of fibre dispersion along the myofibre direction on myocardial contraction in a left ventricle model. Dispersed active stress is described by a generalised structure tensor method for its computational efficiency. Our results show that both the myofibre rotation angle and its dispersion can significantly affect cardiac pump function by redistributing active tension circumferentially and longitudinally. For example, larger myofibre rotation angle and higher active tension along the sheet-normal direction can lead to much reduced end-systolic volume and higher longitudinal shortening, and thus a larger ejection fraction. In summary, these two studies together have demonstrated that it is necessary and essential to include realistic fibre structures (both fibre rotation angle and fibre dispersion) in personalised cardiac modelling for accurate myocardial dynamics prediction.

It is widely acknowledged that an imbalanced biomechanical environment can have significant effects on myocardial pathology, leading to adverse remodelling of cardiac function if it persists. Accurate stress prediction essentially depends on the strain energy function which should have competent descriptive and predictive capabilities. Previous studies have focused on myofibre dispersion, but not on fibres along other directions. In this study, we will investigate how fibre dispersion affects myocardial biomechanical behaviours by taking into account both the myofibre dispersion and the sheet fibre dispersion, with a focus on the sheet fibre dispersion. Fibre dispersion is incorporated into a widely-used myocardial strain energy function using the discrete fibre bundle approach. We first study how different dispersion affects the descriptive capability of the strain energy function when fitting to ex vivo experimental data, and then the predictive capability in a human left ventricle during diastole. Our results show that the chosen strain energy function can achieve the best goodness-of-fit to the experimental data by including both fibre dispersion. Furthermore, noticeable differences in stress can be found in the LV model. Our results may suggest that it is necessary to include both dispersion for myofibres and the sheet fibres for the improved descriptive capability to the ex vivo experimental data and potentially more accurate stress prediction in cardiac mechanics.

• Hooked-end SMA fibres were manufactured and used in cementitious composites. • Crack-closing and re-centring behaviour of the composites were studied. • DIC technique was used to capture full-depth crack width profiles. • Fibre distribution was examined by μ-CT images and statistical point processes. • The re-centring and crack-closing ratios were as large as 75% and 51%. Newly developed hooked-end pseudoelastic shape memory alloy fibres (PSMAF) provide re-centring and crack-closing behaviour in cementitious composites. Relatively large PSMAF-reinforced specimens are tested under cyclic flexural loading at small and large deflection amplitudes to examine these capabilities realistically. Crack propagation, maximum crack width at each cycle, crack-closing ratio, and full-depth crack width are quantified through 2D digital image correlation (DIC) technique for composites with 0.5% to 1.25% PSMAF. The re-centring ratios are established for the developed composites, and their flexural performances are evaluated based on various parameters, including cyclic modulus, toughness, and ductility. Furthermore, X-ray micro-computed tomography and statistical analysis of spatial point patterns are employed to examine fibre dispersion in the cracked sections. Results indicate that PSMAF-reinforced composites with 0.75% and 1% fibre content exhibit considerable re-centring and crack-closing capabilities with minimal fibre clumping. [ABSTRACT FROM AUTHOR]