Changes In Fiber Orientation Research Articles

Buckling analysis of functionally graded carbon nanotube-reinforced curved panels under axial compression and shear

Abstract The need for high-performance lightweight materials for the design of aerospace structures predicts a remarkable future role of carbon nanotubes (CNTs). In particular, thin curved fuselage panels are widely employed. However, the theoretical difficulties in the underlying differential problem induced by the curvature, as well as a still under development technology of CNT-based composites, the number of studies dealing with buckling behavior of this structural typology is limited. The present study aims to provide some insight into the linear buckling analysis of functionally graded carbon-nanotube reinforced (FG-CNTRC) cylindrical curved panels under compressive and shear loading. Effective properties of materials of the panels reinforced by single-walled carbon nanotubes (SWCNTs) are estimated through a micromechanical model based on either the Eshelby-Mori-Tanaka approach or the extended rule of mixtures. A series of numerical simulations have been carried out to inspect the influence of curvature, panel aspect ratio, the distribution profile of reinforcements (uniform and three non-uniform distributions) and CNTs orientation angle on the buckling critical load under compressive and shear loading in uniform thermal environments. Results demonstrate that the change of fiber orientation, CNTs distribution, panel aspect ratio, loading condition and temperature have noticeable effects on the buckling strength and buckling modes of FG-CNTRC curved panels.

Influence of selected process parameters on changes of the fiber orientation in unidirectional reinforced thermoplastics during a hot pressing process

The research described in this paper is part of SFB 639 “Textile‐reinforced composite components for function integrating multi‐material design in complex lightweight applications.” In this study, changes in fiber orientation of unidirectional (UD) aligned glass polypropylene hybrid yarn were investigated. A new model for simulating changes in fiber orientation of unidirectional reinforced thermoplastics during a hot pressing process was developed. The material observed during this study is a hybrid yarn made out of homogenous aligned glass and polypropylene filaments. The mechanistic model, which was used to simulate the fiber behavior, allows the user to define different input data, such as velocity, vorticity, and viscosity of the molten polymer as well as fiber radius, initial fiber positions and fiber stiffness to characterize material properties. To determine fiber orientations, a program was written in MATLAB. Hence, it is possible to calculate the angle of any desired segment at any point of time during the hot pressing process. Thereby, it was feasible to compare the numerical obtained changes in fiber orientation with those measured during the experiments conducted at the end of the research. The post‐processing algorithm was used to determine the effects of selected processing parameters and model parameters on the fiber behavior respectively. POLYM. COMPOS., 39:2241–2249, 2018. © 2016 Society of Plastics Engineers

Influence of intramuscular fiber orientation on the Achilles tendon curvature using three-dimensional finite element modeling of contracting skeletal muscle

Tendon curvature plays a key role in mechanical gain (amplifying the joint excursion relative to fiber length change) during joint motion, but the mechanism remains unresolved. A three-dimensional finite element (FE) model was used to investigate the influence of intramuscular fiber orientation upon the curvature pattern of the Achilles tendon during active muscular contraction. Two simulation models, with fiber pennation angles of θ = 25° and 47° were tested for the gastrocnemius and soleus muscles. A smaller pennation angle (25°) of the soleus muscle fibers was accompanied by a large change in curvature whereas a larger pennation angle (47°) of the soleus muscle was accompanied by small effects. These results suggest that the fiber pennation angle determines the curvature of the tendon, and the magnitude of the curvature varies along the length of the aponeurosis. Such FE modeling has the potential of determining changes in force output consequent to changes in intramuscular fiber orientation arising from resistance training or unloading, and provides mechanism for predicting the risk of Achilles tendon ruptures.

Changes in Corneal Subbasal Nerve Morphology and Sensitivity During Orthokeratology: Onset of Change

PurposeTo investigate changes in corneal subbasal nerve fiber density and orientation during a 3-month orthokeratology (OK) lens wear period and their relationship with concurrent changes in corneal sensitivity. MethodsSixteen subjects wore overnight OK lenses for 90 days and were assessed at baseline, Day 30, and Day 90. Nerve images at the corneal apex and temporal mid-periphery were captured from the right eye only using in vivo confocal microscopy and analyzed to calculate nerve fiber density (NFD) and global nerve fiber orientation (GNFO). Corneal sensitivity was measured using the Cochet-Bonnet aesthesiometer at similar corneal locations. Control groups of non-lens (NL) wearing and conventional rigid gas-permeable (GP) lens-wearing subjects were also examined. ResultsSignificant changes in NFD, GNFO and corneal sensitivity were observed during OK lens wear over the study period. In the central cornea, both NFD and corneal sensitivity decreased by Day 30, with further reductions at Day 90. Reduced NFD was associated with reduced corneal sensitivity. In the mid-peripheral cornea only, GNFO was rotated in a clockwise direction at Day 30, with further rotation at Day 90. Corneal sensitivity reduction plateaued by Day 30. In the GP lens-wearing subjects, only corneal sensitivity decreased by Day 30 at both corneal locations. No changes were observed in the NL control subjects. ConclusionsAlterations in corneal nerve morphology occur rapidly with commencement of OK lens wear and appear to underpin functional sensitivity loss. Nerve fiber orientation can provide a useful index for changes in corneal nerve morphology.

Impact on Diffusion Parameters Computation in Gas Diffusion Layers, Considering the Land/Channel Region, Using the Lattice Boltzmann Method

A deep understanding of the behavior of microstructural parameters in proton exchange fuel cells (PEFCs) will help to reduce the material cost and to predict the performance of the device at cell scale. Changes in morphological configuration, i.e., fiber diameter and fiber orientation, of the gas diffusion layers (GDLs) result in variations of fluid behavior throughout the layer, and therefore; the microstructural parameters are affected. The aim of this study is to analyze, for three selected fiber diameters and different percentages presence of inclined fibers, the behavior of the different microstructural parameters of the GDLs. This study is carried out over digitally created two-dimensional GDL models in which the fluid behavior is obtained by means of the Lattice Boltzmann method (LBM). Once the fluid behavior is determined, the microstructural parameters, i.e., the porosity, gas-phase tortuosity, obstruction factor, through-plane permeability, and inertial coefficient, are computed. Several relationships are found to predict the behavior of such parameters as function of the fiber diameter, presence of inclined rods or porosity. The results presented in this work are compared and validated by previous theoretical and experimental studies found in the literature.

Physiological and architectural changes in the ageing muscle and their relation to strength and function in sarcopenia

In the ageing muscle, many changes occur. Some are on an architectural level, like alterations in muscle composition, or modifications in the characteristics of the muscle fiber itself, where muscle fiber length, orientation and type change. Other changes are neuronal, which occur on all levels, from the central activation over the spinal properties down to the level of the motor unit and the neuromuscular junction. There are also hormonal factors that undergo agerelated concentration variations. All these alterations in the muscle have an effect on both strength and function. In this matter, they contribute to the process of sarcopenia. Although many different components are identified, it is still unclear to what degree these components contribute to the loss of muscle mass, strength and function. This review summarizes the occurring physiological and anatomical changes within the ageing muscle and links them to outcomes such as strength and function.

Investigation of the effects of myocardial anisotropy for shear wave elastography using impulsive force and harmonic vibration

The myocardium is known to be an anisotropic medium where the muscle fiber orientation changes through the thickness of the wall. Shear wave elastography methods use propagating waves which are measured by ultrasound or magnetic resonance imaging (MRI) techniques to characterize the mechanical properties of various tissues. Ultrasound- or MR-based methods have been used and the excitation frequency ranges for these various methods cover a large range from 24–500 Hz. Some of the ultrasound-based methods have been shown to be able to estimate the fiber direction. We constructed a model with layers of elastic, transversely isotropic materials that were oriented at different angles to simulate the heart wall in systole and diastole. We investigated the effect of frequency on the wave propagation and the estimation of fiber direction and wave speeds in the different layers of the assembled models. We found that waves propagating at low frequencies such as 30 or 50 Hz showed low sensitivity to the fiber direction but also had substantial bias in estimating the wave speeds in the layers. Using waves with higher frequency content (>200 Hz) allowed for more accurate fiber direction and wave speed estimation. These results have particular relevance for MR- and ultrasound-based elastography applications in the heart.

PH up-regulation as a potential mechanism for the cold-water coral <i>Lophelia pertusa</i> to sustain growth in aragonite undersaturated conditions

Abstract. Cold-water corals are important habitat formers in deep-water ecosystems and at high latitudes. Ocean acidification and the resulting change in aragonite saturation are expected to affect these habitats and impact coral growth. Counter to expectations, the deep water coral Lophelia pertusa has been found to be able to sustain growth even in undersaturated conditions. However, it is important to know whether such undersaturation modifies the skeleton and thus its ecosystem functioning. Here we used Synchrotron X-Ray Tomography and Raman spectroscopy to examine changes in skeleton morphology and fibre orientation. We combined the morphological assessment with boron isotope analysis to determine if changes in growth are related to changes in control of calcification pH. We compared the isotopic composition and structure formed in their natural environment to material grown in culture at lower pH conditions. Skeletal morphology is highly variable but shows no distinctive differences between natural and low pH conditions. Raman investigations found no difference in macromorphological skeletal arrangement of early mineralization zones and secondary thickening between the treatments. The δ11B analyses show that L. pertusa up-regulates the internal calcifying fluid pH (pHcf) during calcification compared to ambient seawater pH and maintains a similar elevated pHcf at increased pCO2 conditions. We suggest that as long as the energy is available to sustain the up-regulation, i.e. individuals are well fed, there is no detrimental effect to the skeletal morphology.

Optimization-based fiber orientation modeling for computational mitral valve evaluation

Biomechanical response of the mitral valve (MV) leaflet tissue is closely related to the characteristics, density, and orientation of the collagen fibers. Alterations of collagen fiber arrangement have a direct influence on the biomechanical characteristics of the MV leaflets leading to physiologic deterioration. In this study, we describe a nonlinear optimization technique to define fiber orientations across the MV posterior leaflet. A symmetric MV model consisting of the saddle-shaped annulus, the anterior leaflet, and the triscalloped posterior leaflet was modeled. The posteromedial half portion of the posterior leaflet was segmented and meshed. An unconstrained nonlinear multi-objective optimization protocol with lower and upper boundaries was developed to determine realistic collagen fiber distribution across the posterior leaflet. In the cleft region, the optimization-based fiber orientation modeling method demonstrated a sharp change of fiber orientation near the annular region followed by a slow adjustment of fiber orientation near the free leaflet margin, which corresponds well to the native MV leaflet tissue. Fiber distribution in the cleft region revealed a large difference between the optimization and the linear interpolation methods. This optimization strategy has the potential to effectively model the natural fiber orientation across the MV leaflets for improved computational evaluation of MV function.

Possible role of collagen reorientation during airway remodeling on mucosal folding

Airway remodeling in patients with chronic asthma is characterized by thickening and structural change of airway walls. It has been demonstrated in previous theoretical models that changes in airway thickness can have an important mechanical effect, in particular, on the mucosal folding induced by smooth muscle contraction. In this paper, we examine the effect of collagen fiber orientation change on the mucosal folding. The airway is modeled as a two-layer cylindrical tube, with the submucosa (outer layer) represented as isotropic tissue and subepithelial collagen layer (inner layer) as fiber-reinforced anisotropic tissue. In order to follow the most recent advancement for modeling anisotropic material, we carry out computation under a reduced form of strain energy, as well as a form of strain energy compatible with linear theory in infinitesimal strains. We explore the effects of varying collagen density, strain-stiffening behavior of collagen fibers as well as the layer thickness change on the folding behavior. We demonstrate that collagen orientation change can have a significant impact on mucosal folding, including the critical pressure required to induce folding and the buckling mode. We demonstrate that proper collagen density combined with proper collagen orientation might be a strategy used by organisms to prevent low-mode buckling thus to prevent airway narrowing. Deviation from these balances caused by disease status will favor low-mode buckling. We also find that the two forms of strain energy give very similar results, and therefore, most important features of buckling behavior can still be captured by the reduced form. We conclude that anisotropic property of the subepithelial collagen layer may be an important component in airway remodeling.

Load-dependent extracellular matrix organization in atrioventricular heart valves: differences and similarities

The extracellular matrix of the atrioventricular (AV) valves' leaflets has a key role in the ability of these valves to properly remodel in response to constantly varying physiological loads. While the loading on mitral and tricuspid valves is significantly different, no information is available on how collagen fibers change their orientation in response to these loads. This study delineates the effect of physiological loading on AV valves' leaflets microstructures using Second Harmonic Generation (SHG) microscopy. Fresh natural porcine tricuspid and mitral valves' leaflets (n = 12/valve type) were cut and prepared for the experiments. Histology and immunohistochemistry were performed to compare the microstructural differences between the valves. The specimens were imaged live during the relaxed, loading, and unloading phases using SHG microscopy. The images were analyzed with Fourier decomposition to mathematically seek changes in collagen fiber orientation. Despite the similarities in both AV valves as seen in the histology and immunohistochemistry data, the microstructural arrangement, especially the collagen fiber distribution and orientation in the stress-free condition, were found to be different. Uniaxial loading was dependent on the arrangement of the fibers in their relaxed mode, which led the fibers to reorient in-line with the load throughout the depth of the mitral leaflet but only to reorient in-line with the load in deeper layers of the tricuspid leaflet. Biaxial loading arranged the fibers in between the two principal axes of the stresses independently from their relaxed states. Unlike previous findings, this study concludes that the AV valves' three-dimensional extracellular fiber arrangement is significantly different in their stress-free and uniaxially loaded states; however, fiber rearrangement in response to the biaxial loading remains similar.

0305 : Heterogeneous conduction properties in the pig right ventricle

The right ventricular outflow tract (RVOT) has a distinct embryological origin and is a common anatomical source of arrhythmias in the healthy and diseased myocardium. We hypothesised that specific RVOT activation and conduction properties may underlie the preferential RVOT origin of arrhythmias. Pig right ventricular (RV) wedge preparations were perfused via the left anterior descending and right coronary arteries. Electrical activation and conduction properties were obtained by optical mapping of the epicardial surface (di-4- ANEPPS 10μM) upon electrical stimulation of the preparation. Transmural needles were inserted in the RV free wall and RVOT and unipolar electrograms (EGMs) were recorded. Fiber orientation was obtained by diffusion tensor MRI. Regional mRNA expression was determined by RT-PCR and fibrosis was assessed histologically. Longitudinal and transverse conduction velocities were significantly reduced in RVOT compared to RV free wall (P<0.01). A different direction of propagation was observed in the RVOT compared to the RV free wall and a line of slowed propagation was found at the interface between the 2 regions. This was consistent with a 135±2° change in fiber orientation observed between the 2 regions within a restricted distance (<6cm). The RVOT showed more sites with fractionated EGMs (P<0.01) and more deflections per electrode (P<0.001) than the RV free wall. In line with these findings, a decreased expression of Scna5 and Gja1 was found in the RVOT compared to the RV free wall (P<0.001). Moreover, the RVOT was characterized by an upregulation of type I collagen mRNA, a higher collagen content (P<0.05) and the presence of fat infiltrations which were absent in the free wall. Conduction is slower in the pig RVOT and is associated with fractionated unipolar electrograms. Conduction slowing was related to (i) reduced connexin and sodium channel expression and (ii) region-specific structural properties which may generate a substrate for RVOT arrhythmias.

Investigating the relationship between changes in collagen fiber orientation during skin aging and collagen/water interactions by polarized-FTIR microimaging.

Upon chronological aging, human skin undergoes structural and molecular modifications, especially at the level of type I collagen. This macromolecule is one of the main dermal structural proteins and presents several age-related alterations. It exhibits a triple helical structure and assembles itself to form fibrils and fibers. In addition, water plays an important role in stabilizing the collagen triple helix by forming hydrogen-bonds between collagen residues. However, the influence of water on changes of dermal collagen fiber orientation with age has not been yet understood. Polarized-Fourier Transform Infrared (P-FTIR) imaging is an interesting biophotonic approach to determine in situ the orientation of type I collagen fibers, as we have recently shown by comparing skin samples of different ages. In this work, P-FTIR spectral imaging was performed on skin samples from two age groups (35- and 38-year-old on the one hand, 60- and 66-year-old on the other hand), and our analyses were focused on the effect of H2O/D2O substitution. Spectral data were processed with fuzzy C-means (FCM) clustering in order to distinguish different orientations of collagen fibers. We demonstrated that the orientation was altered with aging, and that D2O treatment, affecting primarily highly bound water molecules, is more marked for the youngest skin samples. Collagen-bound water-related spectral markers were also highlighted. Our results suggest a weakening of water/collagen interactions with age. This non-destructive and label-free methodology allows us to understand better the importance of bound water in collagen fiber orientation alterations occurring with skin aging. Obtaining such structural information could find benefits in dermatology as well as in cosmetics.

Anatomic and histologic features and ultrasonographic appearance of the collateral ligaments of the metacarpophalangeal and metatarsophalangeal joints in cadaveric limbs from horses without lameness.

To describe the anatomic and histologic features of the collateral ligaments (CLs) of the metacarpophalangeal (MCP) and metatarsophalangeal (MTP) joints in cadaveric limbs obtained from nonlame horses and to compare the histologic findings with the ultrasonographic appearance of the CLs. Medial and lateral CLs of the MCP and MTP joints of 28 limbs (16 forelimbs and 12 hind limbs) from 9 adult nonlame horses euthanized for reasons unrelated to the study. 26 limbs of 8 horses were examined by ultrasonography immediately after euthanasia. Postmortem gross and histologic examinations were performed for all 28 limbs. Histologic and ultrasonographic images were graded and compared. Ultrasonographically, the mean ± SD depth and width of the superficial CL were 5.1 ± 0.7 mm and 20.5 ± 1.7 mm, respectively. On histologic examination, only 125 of 319 (39%) specimens obtained from 56 medial and lateral CLs appeared normal. Histopathologic findings varied from mild changes in cellular density and collagen fiber orientation to severe fibrocartilaginous metaplasia. The degree of CL lesion severity increased distally, and the lateral CL was affected more frequently than was the medial CL. Ultrasonographically detectable abnormalities were not correlated with the histologic findings. In horses, histologic abnormalities within the CLs of the MCP and MTP joints may be an adaptive response to joint hyperextension and compression and might predispose horses to desmopathy and ligament failure in the event of trauma. Ultrasonography did not detect morphologic changes of the CL matrix. For an accurate diagnosis of subclinical lesions, more sensitive imaging techniques (eg, MRI) should be considered.

Highly oriented carbon fiber–polymer composites via additive manufacturing

Additive manufacturing, diverging from traditional manufacturing techniques, such as casting and machining materials, can handle complex shapes with great design flexibility without the typical waste. Although this technique has been mainly used for rapid prototyping, interest is growing in using this method to directly manufacture actual parts of complex shape. To use 3D-printing additive manufacturing in wide spread applications, the technique and the feedstock materials require improvements to meet the mechanical requirements of load-bearing components. Thus, we investigated the short fiber (0.2 mm to 0.4 mm) reinforced acrylonitrile-butadiene-styrene composites as a feedstock for 3D-printing in terms of their processibility, microstructure and mechanical performance; and also provided comparison with traditional compression molded composites. The tensile strength and modulus of 3D-printed samples increased ~115% and ~700%, respectively. 3D-printer yielded samples with very high fiber orientation in printing direction (up to 91.5 %), whereas, compression molding process yielded samples with significantly less fiber orientation. Microstructure-mechanical property relationships revealed that although the relatively high porosity is observed in the 3D-printed composites as compared to those produced by the conventional compression molding technique, they both exhibited comparable tensile strength and modulus. Furthermore, this phenomena is explained based on the changes in fiber orientation, dispersion andmore » void formation.« less

Effect of Fiber Orientation on Vibration Characteristic of Composite Laminated Plates

To describe vibration characteristic of composite laminated plates with various fiber orientations, a composite laminated finite element, which follows classical lamination theory, was constructed. In each ply of rectangular composite laminated plates, the fiber orientation changes with respect to the horizontal coordinate. Natural frequencies and mode shapes of composite laminated plates were studied. The first six natural frequencies and mode shapes of composite laminated plates with various fiber orientations are obtained. The accuracy of this composite laminated element is verified by comparing numerical and theoretical results. The results show that the changes of fiber orientation bring a greater degree of flexibility for structure design of composite laminated plates, which can be used to adjust frequencies and mode shapes of composite laminated plates according to practical engineering need.

Finite strain analysis of nonlinear vibrations of symmetric laminated composite Timoshenko beams using generalized differential quadrature method

In this study, free vibrations of laminated composite Timoshenko beams undergoing finite strain have been studied. The Green-Lagrange strain tensor according to finite strain assumption has been used to obtain governing equations and boundary conditions of the beam. The generalized differential quadrature method has been employed for solving the governing equations and boundary conditions. Frequencies of the beam have been calculated for carbon/epoxy material subjected to different boundary conditions. The dimensionless frequencies of the beam for different lay-ups based on finite strain and von Karman assumptions have been obtained and compared to each other. Also, the effects of fiber orientation change and lay-ups sequence of angle-ply composite beams have been investigated on the lateral frequency of the beam.

Artery buckling analysis using a four-fiber wall model

Artery bent buckling has been suggested as a possible mechanism that leads to artery tortuosity, which is associated with aging, hypertension, atherosclerosis, and other pathological conditions. It is necessary to understand the relationship between microscopic wall structural changes and macroscopic artery buckling behavior. To this end, the objectives of this study were to develop arterial buckling equations using a microstructure-based 4-fiber reinforced wall model, and to simulate the effects of vessel wall microstructural changes on artery buckling. Our results showed that the critical pressure increased nonlinearly with the axial stretch ratio, and the 4-fiber model predicted higher critical buckling pressures than what the Fung model predicted. The buckling equation using the 4-fiber model captured the experimentally observed reduction of critical pressure induced by elastin degradation and collagen fiber orientation changes in the arterial wall. These results improve our understanding of arterial stability and its relationship to microscopic wall remodeling, and the model provides a useful tool for further studies.

Effect of relative ply orientation on the through-thickness permeability of unidirectional fabrics

Abstract When unidirectional stitched fabrics are used as reinforcement in composites, plies are typically stacked on top of each other to build up the desired thickness. Strength and stiffness requirements dictate the orientation of individual layers and the accuracy of angular alignment is limited. A pressure differential across the thickness is used to distribute the resin, either from a pre-impregnated fabric or injected from a resin source, to occupy all of the empty spaces between the fibers. This process is commonly modeled using Darcy’s law, which describes flow of resin through porous media in which the flow rate is directly proportional to the applied pressure differential by the through-thickness permeability of the fabric. A different orientation between layers or even a slight misalignment during the stacking can change the through-thickness permeability dramatically due the change of resin pathways. In this work, we characterize the through-thickness permeability of a series of unidirectional fabrics stacked in various orientations to address both the effect of stacking sequence and those of misalignment of the individual layers. We conduct numerical simulations to predict the effect of change in fiber orientation on the through-thickness permeability. The results from the numerical model are compared with experimental measurements. Our results show that averaging approach is not suitable to calculate the through-thickness permeability component when using unidirectional fabrics and that the stacking sequence of the unidirectional fabrics may significantly influence the through-thickness permeability. We also show that the effects of small misalignments between individual layers do not significantly modify the transverse flow.

Geared up to stretch: pennate muscle behavior during active lengthening

Many locomotor activities require muscles to actively lengthen, dissipate energy and decelerate the body. These eccentric contractions can disrupt cytoskeletal structures within myofibrils and reduce force output. We examined how architectural features of pennate muscles can provide a protective mechanism against eccentric muscle damage by limiting fascicle lengthening. It has been previously shown that the angled fibers of pennate muscles change orientation when shortening. This change in fiber orientation can amplify fascicle shortening, resulting in a velocity advantage at the level of the muscle-tendon unit (MTU) that is characterized by a gear ratio (MTU velocity/fascicle velocity). A muscle's architectural gear ratio (AGR) has been shown to vary as a function of force during shortening, while AGR during lengthening remains largely unknown. We independently measured fascicle length and MTU length in vitro in the bullfrog plantaris. We characterized the muscle's force-velocity curve and AGR during both shortening and lengthening across a broad range of forces (10-190% peak isometric force). AGR was measured during the isotonic portion of each contraction, to eliminate possible contributions of series elasticity to MTU length changes. We found that gear ratio varies with force during both shortening and lengthening contractions. The highest AGR was observed during lengthening contractions, indicating that lengthening of the MTU can occur with relatively little stretch of the fascicle. As fascicle strain is considered an important determinant of muscle damage, a high gear ratio may afford pennate muscles protection against the damaging effects of active lengthening.