Random Fiber Orientation Research Articles

Investigating histological aspects of scars in children.

Very little is known about histological aspects of paediatric scars and the possible role of the immune system during their formation. In this study, the histology thoracic scars caused by the placement of an implantable central venous access device in children who underwent treatment for cancer was assessed. The amount and type of collagen, the collagen orientation, the type of elastic fibres, the vascularsation, and the count of neutrophils, macrophages, and lymphocytes were analysed. The severity of scarring was assessed using the Vancouver scar scale (VSS). To evaluate the role of the immune system on scar severity and histology, the scars of children suffering from acute lymphoblastic leukaemia (ALL) were compared with the scars of children suffering from other types of childhood cancer. Our results showed an extremely random orientation of the collagen fibres of the paediatric scars with a mean collagen orientation index of 0.22 (standard deviation (SD) 0.10, zero indicating a perfectly random orientation and a perfectly parallel orientation). A lower collagen orientation index was seen in scars with a lower VSS score (VSS score <3: 0.19 versus VSS score ≥3 0.29, p=0.037). A higher total VSS score, resembling a worse scar, was assessed to the scars in the non-ALL group compared with the children with ALL (mean ALL: 0.91 (0-3) versus mean non-ALL: 2.50 (0-6), p=0.037). To our knowledge, this is the first study investigating a wide array of histological aspects in paediatric scars. Compared with adult scars, an extremely random collagen orientation was found (0.22 in children versus 0.41 and 0.46 adult normotrophic and hypertrophic scars, respectively). A lower collagen orientation index was found in scars with a lower VSS score. In addition, less severe scarring was measured in children suffering from ALL compared with children suffering from other types of childhood cancer. This suggests that the immune system could play a role in the development of aberrant scarring and should be a target for future research.

Radiative Characteristics of High-Porosity Media Containing Randomly Oriented Fibers in Space

This paper proposed radiative characteristics' expressions for media containing randomly oriented fibers in space. In deriving these simple radiative characteristics' expressions, the fibrous medium effective extinction coefficient is defined to match with the one of large particle obtained by combining geometric optics and Fraunhofer diffraction theory. Fibrous media radiative characteristics are then derived as an average over all incident radiation angles of single fiber radiative characteristics. Theoretical hemispherical reflectance and normal transmittance predictions using the proposed fibrous media radiative characteristics based on the Mie theory agreed well with literature experiments. Therefore, media containing fiber randomly oriented in space can be scaled to a suitable equivalent media such that scattering mechanisms behave similarly to that occurring in a participating media containing spherical particles. Numerical investigations show that a theoretical model which assumes Henyey–Greenstein (HG) scattering phase function can conveniently be used for the estimation of equivalent fibrous media radiative characteristics using hemispherical reflectance measurements. On the other hand, the estimated equivalent fibrous media radiative characteristics from hemispherical measurements and using a two-flux model with isotropic scaling radiative characteristics may be subjected to serious errors in the case of semitransparent media for which the absorption is significant.

Shear capacity of steel fiber‐reinforced concrete beams

This study proposes a shear strength model for steel fiber‐reinforced concrete (SFRC) beams—the so‐called dual potential capacity model (DPCM). It can suitably consider the dominant shear failure mode, including the shear contributions of the compression side and the cracked tension side, at the section considered. In the proposed approach, the direct tension force transfer model (DTFTM), which can consider the random orientation and bond characteristics of steel fibers at a crack surface, has been introduced to calculate the shear contribution of the steel fibers. Shear test results of SFRC beams have been collected from various references and compared with the analysis results of the proposed DPCM. A simplified version of the DPCM was also developed for practical applications by reducing the iterative computational procedures.

Comparative Study of Impact Strength Characteristics of Treated and Untreated Sisal Polyester Composites

In the present study both treated and untreated sisal polyester composites are tested to study its impact strength characteristics. ASTM D256 norms are followed to conduct the impact test on the specimens of 2 mm, 3 mm, 4 mm, 5 mm and 6 mm thicknesses for fiber volume of 10%, 15%, 20%, 25% and 30%. Random orientation of fibers was adopted. Length of fibers used in casting the specimen is as 10 mm. Here all the specimens are fabricated by using manually operated hot compression moulding technique. The results obtained from the present study have shown that impact strength increases with increase in the thickness. Untreated sisal polyester composite yielded its peak impact strength of 3.581 N-m at its 30% fiber volume fraction. Treated sisal polyester composite has shown highest impact strength of 1.962 N-m at its 30% fiber volume fraction.

The performance prediction and optimization of the fiber-reinforced composite structure with uncertain parameters

The fiber-reinforced composites display the random fiber orientations and uncertain material parameters because of the manufacturing error and scattering feature. For this problem, the uncertain prediction and optimization based on the transformed perturbation stochastic method, the edged-based smoothing technique and the optimization theory is presented. In this method, the non-Gaussian probability density functions and the cumulative distribution functions of multi-variables for stochastic static responses of fiber-reinforced composite structure are explicitly exhibited as the prediction result compared with the Monte Carlo solution. Unlike the direct MCs, it only needs an iteration as the FEM and has the potential in the complex construction. In order to improve the efficiency and capability to resist the mesh distortion compared with the traditional stochastic FEM, the edged-based smoothing technique is introduced into the present framework. Furthermore, the stable performance feature of the fiber-reinforced composite in the uncertain working condition is presented. Consequently, objectives of the structural stability and insensitivity criteria based on the second-order perturbation expansion are proposed, and overall uncertain conditions coupled by uncertain fiber orientation, external load, material parameters and geometry sizes are analyzed and optimized within this framework, respectively. To verify the effectiveness and accuracy of the uncertain analysis and optimization in this study, three examples including the composite plates, the composite shell and the composite top cover of automobile are provided.

Effect of the Orientation of Hexagonal Fibers on the Effective Elastic Properties of Unidirectional Composites

AbstractExisting studies reveal that the shape corners of hexagonal fiber affect the degree of constraint on the matrix material. However, none of these studies included the effect of orientation of hexagonal fibers. In this study, a computational micromechanics model of oriented hexagonal fibers in periodic unidirectional composite materials is established for the determination of effective orthotropic elastic properties of the composite. In the present numerical modeling, the representative unit composite cell including the matrix material and the single oriented hexagonal fiber or random oriented hexagonal fibers is solved by micro-scale finite element analysis with different stress loads and periodic displacement boundary conditions, which are applied along the cell boundary to meet the requirement of straight-line constraint during deformation of the cell. Subsequently, the effective elastic properties of the composite are evaluated for periodic regular packing and random packing using the homogenization approach for investigating the influence of unified orientation and random orientation of the hexagonal fibers on the overall elastic properties of the fiber-reinforced composites. The numerical results are verified by comparing with other available results.

Analisa Kekuatan Tarik dan Bending pada Komposit Widuri-Polyester

The purpose of this study to analyze the tensile strength and flexural strength of widuri fiber reinforced polyester. Treatment with 5% NaOH for 1 hour. Directions random fiber orientation with a fiber size of 1 cm, 3 cm and 5 cm. The test specimen is printed with a printing press method, the fiber volume fraction of 30%, polyester resin binder. The test specimens were performed according to ASTM testing standard ASTM D638 to for tensile and D790 to flexural test. The calculation result obtained an increase in the tensile strength fiber length of 5 cm is 43.0809 MPa. While the value of the highest tensile modulus of elasticity of the fiber length of 3 cm. While testing the flexural obtained the highest bending strength in the fiber length of 3 cm is 62.8874 MPa and flexural strength values were lower in fiber length of 5 cm. While the value of the highest flexural modulus of elasticity of 3.1325 MPa with a fiber length of 5 cm and the lowest fiber length of 3 cm, for the highest value of 6509.916 Nmm flexural moments on the fiber length of 3 cm and the lowest value of flexural moment of the fiber length of 1 cm. From the results of photo fracturing shape tensile test specimens showed that the fiber length of 1 cm, 3 cm, 5 cm is a fault caused by a failure in the weight-bearing matrix. The images form flexural fracture test specimens showed that the fiber length of 5 cm is a fault caused by a failure in the weight-bearing matrix, whereas the fiber length of 1 cm and 3 cm showed the form fracture caused by the failure of fiber in weight-bearing

Predicting the flexural behavior of ultra-high-performance fiber-reinforced concrete

To predict the flexural behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) beams including straight steel fibers with various lengths, micromechanics-based sectional analysis was performed. A linear compressive modeling was adopted on the basis of experiments. The tensile behavior was modeled by considering both pre- and post-cracking tensile behaviors. Pre-cracking behavior was modeled by the rule of mixture. Post-cracking behavior was modeled by a bilinear matrix softening curve and fiber bridging curves, considering three different probability density functions (PDFs) for fiber orientation, i.e., the actual PDF from image analysis and PDFs assuming either random two-dimensional (2-D) or three-dimensional (3-D) fiber orientation. Analytical predictions using the fiber bridging curves with the actual PDF or the PDF assuming 2-D random fiber orientation showed fairly good agreement with the experimental results, whereas analysis using the PDF assuming 3-D random fiber orientation greatly underestimated the experimental results.

Applications for carbon fibre recovered from composites

Commercial operations to recover carbon fibre from waste composites are now developing and as more recovered fibre becomes available new applications for recovered fibre are required. Opportunities to use recovered carbon fibre as a structural reinforcement are considered involving the use of wet lay processes to produce nonwoven mats. Mats with random in-plane fibre orientation can readily be produced using existing commercial processes. However, the fibre volume fraction, and hence the mechanical properties that can be achieved, result in composites with limited mechanical properties. Fibre volume fractions of 40% can be achieved with high moulding pressures of over 100 bar, however, moulding at these pressures results in substantial fibre breakage which reduces the mean fibre length and the properties of the composite manufactured. Nonwoven mats made from aligned, short carbon fibres can achieve higher fibre volume fractions with lower fibre breakage even at high moulding pressure. A process for aligning short fibres is described and a composite of over 60% fibre volume fraction has been manufactured at a pressures up to 100 bar with low fibre breakage. Further developments of the alignment process have been undertaken and a composite of 46% fibre volume fraction has been produced moulded at a pressure of 7 bar in an autoclave, exhibiting good mechanical properties that compete with higher grade materials. This demonstrates the potential for high value applications for recovered carbon fibre by fibre alignment.

Modeling Magnetomyograms of Uterine Contractions during Pregnancy Using a Multiscale Forward Electromagnetic Approach.

Understanding the mechanisms of uterine contractions during pregnancy is especially important in predicting the onset of labor and thus in forecasting preterm deliveries. Preterm birth can cause serious health problems in newborns, as well as large financial burdens to society. Various techniques such as electromyography (EMG) and magnetomyography (MMG) have been developed to quantify uterine contractions. However, no widely accepted method to predict labor based on electromagnetic measurement is available. Therefore, developing a biophysical model of EMG and MMG could help better understand uterine contractions, interpret real measurements, and detect labor. In this work, we propose a multiscale realistic model of uterine contractions during pregnancy. At the cellular level, building on bifurcation theory, we apply generalized FitzHugh-Nagumo (FHN) equations that produces both plateau-type and bursting-type action potentials. At the tissue level, we introduce a random fiber orientation model applicable to an arbitrary uterine shape. We also develop an analytical expression for the propagation speed of transmembrane potential. At the organ level, a realistic volume conductor geometry model is provided based on magnetic resonance images of a pregnant woman. To simulate the measurements from the SQUID Array for Reproductive Assessment (SARA) device, we propose a sensor array model. Our model is able to reproduce the characteristics of action potentials. Additionally, we investigate the sensitivity of MMG to model configuration aspects such as volume geometry, fiber orientation, and pacemaker location. Our numerical results show that fiber orientation and pacemaker location are the key aspects that greatly affect the MMG as measured by the SARA device. We conclude that sphere is appropriate as an approximation of the volume geometry. The initial step towards validating the model against real MMG measurement is also presented. Our results show that the model is flexible to mimic the limited-propagation magnetic signature during the emergence and decay of a uterine contraction.

Spectral stochastic finite element vibration analysis of fiber-reinforced composites with random fiber orientation

Fiber-reinforced composites exhibit random fiber orientations due to the manufacturing tolerances. The present study concerns with a numerical investigation of the vibrational behavior of the long fiber-reinforced composites under uncertainty in fiber orientations. The basic constitutive equations of laminate theory based on the first-order shear deformation are developed in stochastic form. It is assumed that each ply-orientation exhibits individual spatial and random variations from the nominal mean value. These lead to local variations in mechanical properties such as structural stiffness and mass matrices and, accordingly, in structural responses. The finite element formulation utilizes the spectral stochastic discretization in the sense that the random fiber orientations are approximated by a truncated Karhunen–Loève expansion. The expansion provides a framework to capture the spatial and random variations. The generalized polynomial chaos with unknown deterministic coefficients is employed to represent the structural responses. The coefficients are estimated using probabilistic collocation points where any deterministic in-house code or commercial FEM package can be treated as a black-box for the modeling and analysis of structure. A numerical case study is used to illustrate the features of the method, where impact of the uncertainty in fiber orientations on the natural frequencies and mode shapes of a 12 plies rectangular composite plate with nominal orientation of [0/90]s is investigated.

Effect of Sterilization Methods on Electrospun Poly(lactic acid) (PLA) Fiber Alignment for Biomedical Applications.

Medically approved sterility methods should be a major concern when developing a polymeric scaffold, mainly when commercialization is envisaged. In the present work, poly(lactic acid) (PLA) fiber membranes were processed by electrospinning with random and aligned fiber alignment and sterilized under UV, ethylene oxide (EO), and γ-radiation, the most common ones for clinical applications. It was observed that UV light and γ-radiation do not influence fiber morphology or alignment, while electrospun samples treated with EO lead to fiber orientation loss and morphology changing from cylindrical fibers to ribbon-like structures, accompanied to an increase of polymer crystallinity up to 28%. UV light and γ-radiation sterilization methods showed to be less harmful to polymer morphology, without significant changes in polymer thermal and mechanical properties, but a slight increase of polymer wettability was detected, especially for the samples treated with UV radiation. In vitro results indicate that both UV and γ-radiation treatments of PLA membranes allow the adhesion and proliferation of MG 63 osteoblastic cells in a close interaction with the fiber meshes and with a growth pattern highly sensitive to the underlying random or aligned fiber orientation. These results are suggestive of the potential of both γ-radiation sterilized PLA membranes for clinical applications in regenerative medicine, especially those where customized membrane morphology and fiber alignment is an important issue.

Comprehensive Characterization of Lignocellulosic Fruit Fibers Reinforced Hybrid Polyester Composites

This work is focused to fabricate and characterize hybrid polyester composites containing equal weight percentages of lignocellulosic fruit fibers namely Cocos nucifera and Luffa cylindrica . Samples with four different compositions (10%, 20%, 30%, and 40%) containing random fiber orientation are fabricated using handlayup technique and their effect on the flexural strength and impact strength is studied and compared with their individual counterparts. Enhanced mechanical properties are obtained when the combined weight percentage of both fibers is 30% by weight. This hybrid composite sample is characterized by Fourier Transform Infrared spectroscopy, X-ray diffraction and Thermogravimetric analysis. Surface morphology of the fractured sample with elemental analysis is studied using scanning electron microscope and Energy Dispersive Analysis of X-rays. FTIR peaks confirm the presence of biopolymers cellulose, hemicellulose and lignin. The thermogram confirms the presence of lignin, an amorphous hydrophobic biopolymer with strong intermolecular, intramolecular hydrogen bond and cross linking of the molecules requiring more energy to breakdown resulting in good thermal stability of the hybrid composites around 200°C. Elemental analysis gives O/C ratio of 0.45 corroborating the lignin presence at the surface.

Flexural modelling of steel-fibre-reinforced concrete member with conventional tensile rebars

This paper presents an analytical model for the determination of the ultimate flexural capacity of steel-fibre-reinforced concrete (SFRC) rectangular sections using the principles of strain compatibility and the force equilibrium. The proposed model considers an elastic–perfectly plastic model for the compression, and an elastic constant post-peak response of the SFRC in tension. Unlike other flexural models in the literature, the proposed model considers the random distribution and orientation of steel fibres at the cracked section in the analysis, and it is simple enough to find applications in routine practice. The model was verified using existing experimental results, and it predicts the flexural capacity of SFRC beams reasonably well. A parametric study using the proposed model was conducted to assess the effect of fibre parameters, conventional reinforcing bars and the strength of the concrete on the ultimate flexural capacity of a SFRC beam section. Normalised design charts are presented to simplify the analysis procedure, and these can be used for selection of the fibre and the quantity of conventional reinforcing steel during the flexural design of SFRC members.

Numerical simulation on structural behavior of UHPFRC beams with steel and GFRP bars

This study simulates the flexural behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) beams reinforced with steel and glass fiber-reinforced polymer (GFRP) rebars. For this, micromechanics-based modeling was first carried out on the basis of single fiber pullout models considering inclination angle. Two different tension-softening curves (TSCs) with the assumptions of 2-dimensional (2-D) and 3-dimensional (3-D) random fiber orientations were obtained from the micromechanics-based modeling, and linear elastic compressive and tensile models before the occurrence of cracks were obtained from the mechanical tests and rule of mixture. Finite element analysis incorporating smeared crack model was used due to the multiple cracking behaviors of structural UHPFRC beams, and the characteristic length of two times the element width (or two times the average crack spacing at the peak load) was suggested as a result of parametric study. Analytical results showed that the assumption of 2-D random fiber orientation is appropriate to a non-reinforced UHPFRC beam, whereas the assumption of 3-D random fiber orientation is suitable for UHPFRC beams reinforced with steel and GFRP rebars due to disorder of fiber alignment from the internal reinforcements. The micromechanics-based finite element analysis also well predicted the serviceability deflections of UHPFRC beams with GFRP rebars and hybrid reinforcements.

Nonlinear finite element analysis of ultra-high-performance fiber-reinforced concrete beams

A nonlinear finite element analysis was performed to simulate the flexural behaviors of ultra-high-performance fiber-reinforced concrete beams. For this, two different tension-softening curves obtained from micromechanics-based analysis and inverse analysis were incorporated. For micromechanics-based analysis, two-dimensional and three-dimensional random fiber orientations were assumed to obtain the fiber-bridging curve, and a softening curve of matrix in ultra-high-performance fiber-reinforced concrete was used. The use of tension-softening curves obtained from inverse analysis and micromechanics-based analysis using two-dimensional random fiber orientation exhibited fairly good agreement with the experimental results, whereas the use of tension-softening curve from micromechanics-based analysis using three-dimensional random fiber orientation underestimated the experimental results.

Preparation and Properties of Cellulose/Waste Leather Buff Biocomposites

The aim of the present work was to utilize waste leather buff (WLB) as filler in cellulose and make biocomposites for packaging applications such as wrappers. Cellulose was dissolved in the environmentally friendly ionic liquid 1-allyl-3-methylimidazolium chloride (AmimCl). To this solution, WLB was added in amounts of 5 to 25 wt.% of cellulose. The cellulose and cellulose/WLB composite films were prepared by regenerating the corresponding cast solutions in a water coagulation bath followed by washing and drying. These films were tested for their tensile properties, thermal stability, and morphology. The tensile modulus and strength of the composite films were lower than those of the matrix. The lowering of the tensile modulus and strength with increasing WLB loading was attributed to the random orientation of the leather fibers of WLB in the composites. However, the % elongation at break of the composite films was found to be higher than that of the matrix and increased with increasing WLB content. The possible interaction between the matrix and WLB filler was probed using FT-IR analysis. The thermal stability of the composite films was higher than that of the matrix. The increase in thermal stability of the composite films was attributed to cross-linked collagen protein leather fibers in WLB. The fractographs of the composite films indicated good interfacial bonding between cellulose and leather fibers of WLB. These composite films may be considered for packaging and wrapping applications.

Fracture Mechanism of Polypropylene-Kenaf Composite under Cyclic Loading

Mechanism of fracture of polypropylene composite reinforced by kenaf fiber under cyclic loading was investigated. Weight fraction of the composite used is 50% polypropylene and 50% kenaf fiber with random fiber orientation. Skins of composite that contains polypropylene dominant fraction are formed on both surfaces. The experiments were performed with flat specimen under cyclic flexural loading with constant displacement. Cyclic softening was detected by hysteresis loop of a local area. Deformation of the specimen was measured from the observed cycles. Fracture features were investigated using optical microscope and scanning electron microscope. The result shows that polypropylene-kenaf composite with 50%-50% fraction with random fiber orientation has complicated fracture features. The damage of the composite started from internal part. The surface crack proceeded after the internal damage. Moreover, it is discussed that some of fibers were covered by only thin matrix. The strength of specimen was determined the fracture behavior of fibers.

Numerical evaluation of effective elastic properties of composites reinforced by spatially randomly distributed short fibers with certain aspect ratio

The effective elastic properties of composites reinforced by spatially randomly distributed short cylindrical fibers with certain aspect ratio are investigated using the numerical homogenization method. A modified RSA algorithm is proposed to generate the periodic RVEs. The periodic boundary conditions are introduced and the periodic RVEs thus created are analyzed to obtain the mechanical properties of composites by using the FE package ABAQUS. The ABAQUS Python Interface is used to introduce the periodic boundary conditions and to obtain the average stresses and strains of RVEs. The simulation results show that the periodic boundary conditions guarantee the continuity of strain and stress fields on the boundaries of RVEs. In the case of the fiber aspect ratio of 15 and fiber volume fraction of 10%, it is sufficient to consider the size of RVE as L/l=2.5, in which an approximately random fiber orientation exists. The effective elastic properties of composites obtained by the numerical homogenization agreeing well with those obtained from the traditional equations for composites based on the Halpin–Tsai estimation and with those measured from the uniaxial tensile experiments shows the validation of the numerical homogenization for effective elastic properties of composites reinforced by spatially randomly distributed short fibers.

Dynamic simulation of discrete fiber motion in fiber-reinforced composite materials processing

The prediction of fiber orientation is critical in short-fiber-reinforced composite systems. Fiber orientation during the manufacturing process largely determines the mechanical, electrical, and thermal properties of the final product. For example, a product with aligned fibers, i.e. fibers mostly oriented in the same direction, has much better mechanical properties than that with random fiber orientation. In this paper, a three-dimensional finite element simulation tool is developed to study fiber suspensions in various viscous flows, including homogeneous flows and inhomogeneous flows (such as Poiseuille flows). Instead of using commercial finite element solver, we propose a finite element-based simulation package coupled with the analytical Jacobian matrix in the Newton–Raphson iteration in solving fiber’s velocities. The proposed method is extended to investigate the hydrodynamic interaction between fibers, and the change of fiber motion and fluid rheological properties.