Preferred Fiber Orientation Research Articles

Effects of Scanning Strategy and Printing Temperature on the Compressive Behaviors of 3D Printed Polyamide-Based Composites.

In this work, the effects of scanning strategies and printing temperature on mechanical properties and crush behaviors of columns manufactured using the fused deposition modeling (FDM) technique were studied. The results showed that scanning strategy and printing temperature had significant influences on mechanical response and deformation mode of the columns. The columns printed in different scanning strategies showed significant anisotropy due to the preferred orientation of short fibers during the printing process. The columns printed in a circular direction presented the highest compressive force response. The columns printed with carbon fiber-reinforced polyamide in a circular direction showed the final oblique fracture failure mode, in which there were fiber pull-out and matrix pull-apart on fracture surfaces. Different indicators were also used to evaluate the mechanical properties and crushing characteristics of the columns. The carbon fiber reinforcement columns presented the highest energy absorption, and the glass fiber reinforcement columns showed the highest elastic modulus and yield strength. The results indicated that the scanning strategy and printing temperature not only influenced the elastic modulus and yield strength, but also affected the energy absorption performances of the columns.

Injection molding of short fiber thermoplastic bio-composites: Prediction of the fiber orientation

Injection molding of short fiber reinforced thermoplastic polymer results in a preferential fiber orientation in the part, which leads to an anisotropy in the material mechanical properties. To anticipate the molded part performances, it is necessary to predict the fiber orientation pattern. Our goal is to have a practical tool that accurately predicts fiber orientation patterns, and to use that information to estimate the final product properties. Consequently, an efficient way to determine the flow induced fiber orientation for different flow cases under real injection molding conditions is presented. The proposed approach allows the average orientation angle prediction in a section by considering the close interaction between the fibers and the flow rheology, the fibers aspect ratio and the mold geometry. Finally, to validate the model, experimental data were taken with different matrices, fibers and mold geometries, where good agreements (R2 ≥ 0.8) were obtained for the fiber orientations measurements.

Elastic fibers: The missing key to improve engineering concepts for reconstruction of the Nucleus Pulposus in the intervertebral disc

The increasing prevalence of low back pain has imposed a heavy economic burden on global healthcare systems. Intense research activities have been performed for the regeneration of the Nucleus Pulposus (NP) of the IVD; however, tissue-engineered scaffolds have failed to capture the multi-scale structural hierarchy of the native tissue. The current study revealed for the first time, that elastic fibers form a network across the NP consisting of straight and thick parallel fibers that were interconnected by wavy fine fibers and strands. Both straight fibers and twisted strands were regularly merged or branched to form a fine elastic network across the NP. As a key structural feature, ultrathin (53 ± 7 nm), thin (215 ± 20 nm), and thick (890 ± 12 nm) elastic fibers were observed in the NP. While our quantitative analysis for measurement of the thickness of elastic fibers revealed no significant differences (p < 0.633), the preferential orientation of fibers was found to be significantly different (p < 0.001) across the NP. The distribution of orientation for the elastic fibers in the NP represented one major organized angle of orientation except for the central NP. We found that the distribution of elastic fibers in the central NP was different from those located in the peripheral regions representing two symmetrically organized major peaks (±45⁰). No significant differences in the maximum fiber count at the major angles of orientation (±45⁰) were observed for both peripheral (p = 0.427) and central NP (p = 0.788). Based on these new findings a structural model for the elastic fibers in the NP was proposed. The geometrical presentation, along with the distribution of elastic fibers orientation, resulting from the present study identifies the ultrastructural organization of elastic fibers in the NP important towards understanding their mechanical role which is still under investigation. Given the results of this new geometrical analysis, more-accurate multiscale finite element models can now be developed, which will provide new insights into the mechanobiology of the IVD. In addition, the results of this study can potentially be used for the fabrication of bio-inspired tissue-engineered scaffolds and IVD models to truly capture the multi-scale structural hierarchy of IVDs. Statement of SignificanceVisualization of elastic fibers in the nucleus of the intervertebral disk under high magnification was not reported before. The present research utilized extracellular matrix partial digestion to address significant gaps in understanding of nucleus microstructure that can potentially be used for the fabrication of bio-inspired tissue-engineered scaffolds and disk models to truly capture the multi-scale structural hierarchy of discs.

Количественная характеристика полей локальных деформаций в образце картона топлайнер при одноосном растяжении

The paper presents the method for quantifying the distribution of local tensile (longitudinal), compressive (transverse) and shear strains in a sample of pulp and paper material. The results of its use for the sample of top-liner board when uniaxial tensile testing are provided. Applying this method, we have determined the values, the degree of heterogeneity and change patterns of local strains in inhomogeneous and anisotropic structure of the sample, depending on the total strain and the direction of fiber orientation. The method is based on constant-speed tensile testing of samples with a pre-applied dot matrix to their surface. The test is accompanied with photo fixing and recording a load-elongation curve. The coordinates and displacements of dots are determined by means of the specially designed software. The analysis of data and calculation of local deformations are performed by finite elements method (FEM) algorithms. The outcomes have shown that the local longitudinal deformations increased, transverse – decreased, and shear – had their maximum at 45° to machine direction (MD) when increasing the angle of preferential fiber orientation to MD in the board samples. The rise of the average absolute values of all components of local strains when increasing total deformation in the sample was confirmed. As it has been found, the heterogeneity of local strains, estimated through the standard deviation, rose when increasing their absolute value; the trends of changing depend on the fiber orientation direction in the sample structure. For citation: Romanova A.N., Kazakov Ya.V., Malkov A.V. Quantitative Characteristics of Local Strain Fields in a Top-Liner Board Sample under Uniaxial Tension. Lesnoy Zhurnal[Russian Forestry Journal], 2020, no. 1, pp. 180–189. DOI: 10.37482/0536-1036-2020-1-180-189

Analysis on Property Discrepancy between Core and Sheath Fibers in Braided Harness Cords

Harness cord is widely used in the industries of trademark, carpet, home textile and towel, which is the most important lifting part in the jacquard loom. In this article, the tensile properties and crystallization performance of core and sheath fibers in harness cords were measured separately. The influence of heat setting during the finishing process on the fibers’ properties was studied. The results showed that the tensile strength, elongation at break and specific work of core fibers were higher than that of sheath fibers. This was because the crystallinity and preferred orientation of fibers were changed by the heat and applied tension during the heat setting process. The core fibers showed better crystallinity, preferred orientation and crystallite size than that of sheath fibers. Besides, the tensile properties and crystallization performance of fibers before and after heat setting was compared. It revealed that the heat setting enhanced the tensile properties and crystallization performance of core fibers, while the opposite phenomenon was observed in sheath fibers.

Effects of pressure, boundary conditions, and cutting reliefs on thermo-hydroforming of fiber-reinforced thermoplastic composite helmet based on numerical optimization

Compared with layup techniques, thermo-hydroforming is shown to be a viable process for mass production of thermoplastic composite structures due to its relatively rapid cycle time and low impact on the microstructure of the material. However, unlike layup technique, thermo-hydroforming can produce wrinkles in the formed part. A research was conducted wherein ABAQUS/CAE (6.14-1) was employed to numerically study the impact of thermo-hydroforming process parameters on the formation of wrinkles in a thermoplastic helmet. The optimized properties of the fiber-reinforced polymer composite was previously determined by the authors using the preferred fiber orientation model implemented as a user material subroutine (VUMAT). To account for the interaction between different layers of the laminated composite, the cohesive zone model was employed. The objective of the study was to use the simulation tool to minimize the overall wrinkle density and wrinkle height in the formed helmet as a function of the fluid pressure, boundary conditions, and especially the blank shape and the relief cuts made in the blank.

Anodic stimulation misunderstood: preferential activation of fiber orientations with anodic waveforms in deep brain stimulation

Objective. During deep brain stimulation (DBS), it is well understood that extracellular cathodic stimulation can cause activation of passing axons. Activation can be predicted from the second derivative of the electric potential along an axon, which depends on axonal orientation with respect to the stimulation source. We hypothesize that fiber orientation influences activation thresholds and that fiber orientations can be selectively targeted with DBS waveforms. Approach. We used bioelectric field and multicompartment NEURON models to explore preferential activation based on fiber orientation during monopolar or bipolar stimulation. Preferential fiber orientation was extracted from the principal eigenvectors and eigenvalues of the Hessian matrix of the electric potential. We tested cathodic, anodic, and charge-balanced pulses to target neurons based on fiber orientation in general and clinical scenarios. Main results. Axons passing the DBS lead have positive second derivatives around a cathode, whereas orthogonal axons have positive second derivatives around an anode, as indicated by the Hessian. Multicompartment NEURON models confirm that passing fibers are activated by cathodic stimulation, and orthogonal fibers are activated by anodic stimulation. Additionally, orthogonal axons have lower thresholds compared to passing axons. In a clinical scenario, fiber pathways associated with therapeutic benefit can be targeted with anodic stimulation at 50% lower stimulation amplitudes. Significance. Fiber orientations can be selectively targeted with simple changes to the stimulus waveform. Anodic stimulation preferentially activates orthogonal fibers, approaching or leaving the electrode, at lower thresholds for similar therapeutic benefit in DBS with decreased power consumption.

Material Usage of Oil-Palm Empty Fruit Bunch (EFB) in Polymer Composite Systems

This paper describes the material use of EFB biomass in the form of composite systems. It describes the tensile characteristics, hardness and wear resistance of polymeric disordered composites epoxy/EFB prepared by vacuum infusion. Electron microscopy was used to describe cellulose EFB fibers and their microstructures. The paper deals with a very simple material when the fibers were not separated from the EFB biomass - EFB biomass was used as it is produced by the processing line. The experiment describes composites with untreated EFB biomass and EFB biomass treated chemically with alkali - 6% aqueous NaOH. Due to the residue of the seed shells and clumps/fiber additions, the cracks initiate and the tensile characteristics decrease up to 46%. Although there have been no significant increases in observed characteristics, this material has some potential in terms of design or in the form of insulating material. The resulting properties could be enhanced by chemical treatment of the fibers, separation of fibers from the residues of the fruit and preferred fiber orientation.

Mechanical analysis of thermo-hydroforming of a fiber-reinforced thermoplastic composite helmet using preferred fiber orientation model

The composite thermo-hydroforming process, utilizing heated and pressurized fluid, was used to form an advanced helmet with the Spectra Shield. Experimental results obtained from the forming process show that thermo-hydroforming is a feasible process for manufacturing thermoplastic composite materials. Concurrent to the forming experiments, the forming process was numerically modeled using ABAQUS/CAE. The behavior of the fiber reinforced polymer composite was modeled using the Preferred Fiber Orientation model, which was implemented into the explicit finite element code ABAQUS by writing a User Material Subroutine. The preferred fiber orientation model was further adapted to work with a composite laminate consisting of multiple layers. Numerical results were compared with experimental data to validate the method in terms of predicting the deformed geometry of the multilayer composite, wrinkling, as well as the punch force–displacement curve. Overall, the deformed shape of the fiber-reinforced thermoplastic composite helmet, including the distribution of wrinkles were predicted accurately.

Fibre distribution and tensile response anisotropy in sprayed fibre reinforced concrete

Sprayed steel fibre reinforced concrete (SSFRC) is a material that tends to present anisotropy, due to the action of the spraying process inducing preferential fibre orientation. Despite numerous applications worldwide since the 1980s, no study has been found of the assessment of fibre distribution and its influence on the residual tensile strength of SSFRC. This work addresess this issue from a quantitative standpoint through an experimental programme with specimens extracted in various orientations within a SSFRC panel. The fibre content and 3D orientation were quantified using the inductive method and correlated with an indirect tensile behaviour for the same specimen with the Barcelona test. The results confirm the high level of anisotropy of SSFRC. The fibre orientation number parallel to the spraying direction is three times bigger than that found in the perpendicular direction. Similar differences were observed between the residual tensile response measured in those directions. Comparison of test results suggest that the preferential fibre orientation creates weaker planes that favours the increase of crack opening at lower load levels.

Quantitative Analysis of the Preferential Orientation of Collagen and Elastin Fibers in Blood Vessel with an Imaging Methodology Combined with Birefringence Measurement

Quantitative Analysis of the Preferential Orientation of Collagen and Elastin Fibers in Blood Vessel with an Imaging Methodology Combined with Birefringence Measurement

INFLUENCE OF LEAFLET’S MATRIX STIFFNESS AND FIBER ORIENTATION ON THE OPENING DYNAMICS OF A PROSTHETIC TRILEAFLET HEART VALVE

Biological valves are employed for aortic valve substitution since a long time but there is a growing effort toward the development of new engineered tissues, in which the complex mechanical response of native leaflets is replicated using composite materials consisting of a soft matrix with embedded reinforcing fibers. The main goal of the present study is to investigate the influence that variations on fiber orientation and matrix stiffness may have on valve dynamics. To this aim, a fluid–structure interaction (FSI) model of a trileaflet valve was implemented in which the opening phase was simulated and leaflet matrix stiffness and fiber orientation were varied in the framework of an anisotropic hyperelastic strain energy function. Results show that both parameters may affect significantly transvalvular pressure gradient and effective orifice area (EOA). For the opening phase of the valve examined, less favorable flow conditions were found when preferred fiber orientation is circumferential, due to lower maximum EOA achievable. Such configuration in combination with stiffer matrix may result in significant degradation of valve performances. Overall fiber orientation can potentially be taylored to optimize valve dynamics, provided also structural aspects that may be prominent in the closure phase, are considered.

Silica bonded mullite fiber composite with isotropic geometry and properties for thermal insulating

Widespread approaches to fabricate fibrous porous composite with robust micro-structured topographies have been stimulated by opportunities to enhance thermal insulation performance. This article firstly presents a facile method to enhance the geometry and properties of fibrous porous composite through incorporating starch as pore forming agent into mullite fibers matrix by pore forming method. Due to the constraint effect of starch on the preferred orientation of fibers, mullite fibers oriented randomly, leading to isotropic structure with high porosity (76.4–91.3%) and low density (0.28–0.67 g/cm3), and thus low thermal conductivity (0.035–0.043 W/m·K). The mechanical tests shows that the compressive strength of the composite increase following the increase of binder concentration and decrease as the increase of starch concentration. With the 20 wt% binder and 30 vol% starch, the compressive strength of composite is enhanced to 1.22 MPa.

Fiber suspension investigation in a backward-facing step by PIV

A dilute suspension (volume fraction 0.05%) of rod-like particles in a turbulent backward-facing step flow at Reynolds number ReH=14900, is investigated by means of Particle Image Velocimetry. Two-way interactions between fluid and dispersed phase are analyzed by exploiting the high spatial resolution of the acquisitions. Mutual interactions between phases can be investigated by considering flow turbulence modulations and phenomena related to preferential concentration and orientation of fibers. Slight turbulence enhancement is reported in the laden flow and concentration data show a moderate tendency of fibers to accumulate at the channel centreline. Orientation data display a strong preferential orientation of fibers. Local fiber orientation is correlated to the direction of maximum shear showing a high level of correlation also in the flow regions featuring strong gradients.

Effect of extrusion dies angle on the microstructure and properties of (TiB+TiC)/Ti6Al4V in situ titanium matrix composite

Forged 5vol% (TiB+TiC)/Ti6Al4V titanium matrix composite billets with a heterogeneous reinforced structure was successfully hot indirect extruded with different dies angle (θ=45°, 60° and 75°) at 1303K. The dies angle was found to work as one key factor to change the microstructures and mechanical properties. Detail investigation on the microstructural evolution revealed that the significant grain refinement was obtained after extrusion due to dynamic recrystallization, the fully dynamic recrystallization takes place during indirect extrusion at dies angle 75°. In situ TiB and TiC reinforcements were also significantly refined by the indirect extrusion process, while highly developed preferred orientation of TiB short fibers along extrusion direction. Meanwhile, the mechanical properties showed that the ultimate tensile strength, yield strength and elongation exhibited a simultaneous increase after the indirect extrusion, especially on the ductility of the materials. The strength was slightly improved but not too much by hot extrusion. However, both tensile strength and elongation to fracture were reduced as the extrusion dies angle enlarged from 45° to 75°. Higher strength and elongation were obtained with optimal dies angle 45°, confirmed by matrix refinement, dynamical recrystallization and the optimal aspect ratio of TiB short fibers. Therefore, the optimal hot extrusion with the extrusion dies angle should be controlled less than 60°.

Quantitative analysis of three-dimensional fibrillar collagen microstructure within the normal, aged and glaucomatous human optic nerve head.

The aim of this study was to quantify connective tissue fibre orientation and alignment in young, old and glaucomatous human optic nerve heads (ONH) to understand ONH microstructure and predisposition to glaucomatous optic neuropathy. Transverse (seven healthy, three glaucomatous) and longitudinal (14 healthy) human ONH cryosections were imaged by both second harmonic generation microscopy and small angle light scattering (SALS) in order to quantify preferred fibre orientation (PFO) and degree of fibre alignment (DOFA). DOFA was highest within the peripapillary sclera (ppsclera), with relatively low values in the lamina cribrosa (LC). Elderly ppsclera DOFA was higher than that in young ppsclera (p < 0.00007), and generally higher than in glaucoma ppsclera. In all LCs, a majority of fibres had preferential orientation horizontally across the nasal–temporal axis. In all glaucomatous LCs, PFO was significantly different from controls in a minimum of seven out of 12 LC regions (p < 0.05). Additionally, higher fibre alignment was observed in the glaucomatous inferior–temporal LC (p < 0.017). The differences between young and elderly ONH fibre alignment within regions suggest that age-related microstructural changes occur within the structure. The additional differences in fibre alignment observed within the glaucomatous LC may reflect an inherent susceptibility to glaucomatous optic neuropathy, or may be a consequence of ONH remodelling and/or collapse.

Interactions between fluid and fibers in a turbulent backward-facing step flow

In this work, a turbulent backward-facing step flow at Reynolds number ReH = 17 520, laden with rod-like particles, is investigated by means of particle image velocimetry. Particle loadings tested are within 0.02% and 0.05% volume fractions; thus, the suspensions may be considered as dilute. The high spatial resolution allows the identification of fiber orientation within the flow, so that mutual interactions between phases can be investigated by considering flow modifications and phenomena related to preferential concentration and orientation of fibers. Fibers’ concentration data show a moderate trend to accumulate at the channel centreline, whereas orientation data display a strong preferential orientation of fibers. Specifically, the local fibers’ orientation is correlated to the flow field in terms of mean flow direction and plane of maximum shear. The occurrence of a symmetrical orientation profile with respect to the channel centre-line is reported as well as the tendency to recover such profile downstream of the step.

Polarized light spatial frequency domain imaging for non-destructive quantification of soft tissue fibrous structures.

The measurement of soft tissue fiber orientation is fundamental to pathophysiology and biomechanical function in a multitude of biomedical applications. However, many existing techniques for quantifying fiber structure rely on transmitted light, limiting general applicability and often requiring tissue processing. Herein, we present a novel wide-field reflectance-based imaging modality, which combines polarized light imaging (PLI) and spatial frequency domain imaging (SFDI) to rapidly quantify preferred fiber orientation on soft collagenous tissues. PLI utilizes the polarization dependent scattering property of fibers to determine preferred fiber orientation; SFDI imaging at high spatial frequency is introduced to reject the highly diffuse photons and to control imaging depth. As a result, photons scattered from the superficial layer of a multi-layered sample are highlighted. Thus, fiber orientation quantification can be achieved for the superficial layer with optical sectioning. We demonstrated on aortic heart valve leaflet that, at spatial frequency of f = 1mm(-1) , the diffuse background can be effectively rejected and the imaging depth can be limited, thus improving quantification accuracy.

Determination of the Combined Effect of Chemical Modification and Compression of Agatis Wood on the Dimensional Stability, Termite Resistance, and Morphological Structure

Agatis wood (Agathis lorantifolia Salisb.) was impregnated with a combination of styrene and methyl methacrylate and compressed to a strain of 50% to improve dimensional stability and termite resistance. The changes in cell structure were analyzed to determine the effects of the combination treatment. The results showed that densification of agatis wood with compression, impregnation, and a combination of treatments resulted in an increase in physical properties (density and dimensional stability) by changing the cellular structure and chemical components (i.e., cellulose crystallinity, microfibril angle, and preferred orientation of fibers) as well as degradation of cellulose. The chemical modification and combination treatment (chemical and compression) of wood generally led to a high resistance to dry wood termites.

Spatial Mapping of Translational Diffusion Coefficients Using Diffusion Tensor Imaging: A Mathematical Description.

In this article, we discuss the theoretical background for diffusion weighted imaging and diffusion tensor imaging. Molecular diffusion is a random process involving thermal Brownian motion. In biological tissues, the underlying microstructures restrict the diffusion of water molecules, making diffusion directionally dependent. Water diffusion in tissue is mathematically characterized by the diffusion tensor, the elements of which contain information about the magnitude and direction of diffusion and is a function of the coordinate system. Thus, it is possible to generate contrast in tissue based primarily on diffusion effects. Expressing diffusion in terms of the measured diffusion coefficient (eigenvalue) in any one direction can lead to errors. Nowhere is this more evident than in white matter, due to the preferential orientation of myelin fibers. The directional dependency is removed by diagonalization of the diffusion tensor, which then yields a set of three eigenvalues and eigenvectors, representing the magnitude and direction of the three orthogonal axes of the diffusion ellipsoid, respectively. For example, the eigenvalue corresponding to the eigenvector along the long axis of the fiber corresponds qualitatively to diffusion with least restriction. Determination of the principal values of the diffusion tensor and various anisotropic indices provides structural information. We review the use of diffusion measurements using the modified Stejskal-Tanner diffusion equation. The anisotropy is analyzed by decomposing the diffusion tensor based on symmetrical properties describing the geometry of diffusion tensor. We further describe diffusion tensor properties in visualizing fiber tract organization of the human brain.