Fiber Elastic Modulus Research Articles

Evaluation of fibrinogen self-assembly: role of its αC region.

Exposure of cryptic, functional sites on fibrinogen upon its adsorption to hydrophobic surfaces of biomaterials has been linked to an inflammatory response and fibrosis. Such adsorption also induces ordered fibrinogen aggregation which is poorly understood. To investigate hydrophobic surface-induced fibrinogen aggregation. Contact and lateral force scanning probe microscopy, yielding topography, image dimensions and fiber elastic modulus measurements were used along with transmission and scanning electron microscopy. Fibrinogen aggregation was induced under non-enzymatic conditions by adsorption on a trioctyl-surface monolayer (trioctylmethylamine) grafted onto silica clay plates. A more than one molecule thick coating was generated by adsorption on the plate from 100 to 200 μg mL⁻¹ fibrinogen solutions, and three-dimensional networks formed from 4 mg mL⁻¹ fibrinogen incubated with uncoated or fibrinogen-coated plates. Fibrils appeared laterally assembled into branching and overlapping fibers whose heights from the surface ranged from approximately 3 to 740 nm. The elastic modulus of fibrinogen fibers was 1.55 MPa. No fibrils formed when fibrinogen lacking αC-domains was used as a coating or was incubated with intact fibrinogen-coated plates, or when the latter plates were sequentially incubated with anti-Aα529-539 mAb and intact fibrinogen. When an anti-Aα241-476 mAb was used instead, fine, long fibers formed. Similarly, sequential incubations of fibrinogen-coated plates with recombinant αC-domain (Aα392-610 fragment) or αC-connector (Aα221-372 fragment) and fibrinogen resulted in distinctly fine fiber networks. Adsorption-induced fibrinogen self-assembly is initiated by a more than one molecule-thick surface layer and eventuates in three-dimensional networks whose formation requires fibrinogen with intact αC-domains.

Physical properties of ion beam treated electrospun poly(vinyl alcohol) nanofibers

We show that the mechanical properties of nano-sized electrospun poly(vinyl alcohol) fibers can be modified using broad-energy ion beam implantation. The elastic moduli were determined using atomic force microscopy multi-point mechanical bending tests on individual fibers before and after treatment. With a dose of 8.0 × 10 15 ions/cm 2 of nitrogen ion we observed 30% increases in fiber elastic modulus with a simultaneous fiber diameter reduction. Two additional doses of nitrogen ion as well as a 8.0 × 10 15 ions/cm 2 of helium ion treatment showed that this stiffness improvement effect was dependent on ion dosage and ion species. The surface morphological features of the fiber mat were shown to be unaltered due to the ion beam treatment. Key chemical modifications via nitrogen ion treatment were the introduction of the functional groups amine and amide. These groups are important in promoting cell compatibility on polymer surfaces.

Generalized Stress Intensity Factor at the Corner of Debonded Fiber Ends

This paper deals with intensity of singular stress field at the corner of debonded ends of an elastic cylindrical inclusion in an infinite body under tension. The problem is formulated as a system of singular integral equations, where unknown functions are densities of body forces distributed in infinite bodies having the same elastic constants as those of matrix and inclusion. In the numerical analysis, the unknown function of the body force densities are expressed as a linear combination of two types of fundamental density function and power series, where the fundamental density functions are chosen to express the symmetric stress singularity of the from rλ1-1 and the skew-symmetrics stress singularity of the from rλ2-1. Then, generalized stress intensity factors, which control the singular stress fields at the end of the cylindrical inclusion are discussed with varying the fiber lengths and elastic modulus ratio. The effect of debonding length on the generalized stress intensity factors is also discussed in comparison with the results of a cylindrical cavity. The results are also compared with ones for a rectangular inclusion.

Measurement of wet fiber flexibility by confocal laser scanning microscopy

A new method for fiber flexibility measurement has been developed using confocal laser scanning microscopy (CLSM), based on the fiber conformability method. Freespan length was measured directly from the transverse view of the fiber span, so the accuracy of the measurement was greatly improved. The collapsibility and moment of inertia can also be measured from the fiber cross section obtained from CLSM. Thus, it was possible to measure the elastic modulus of individual fibers. Therefore, all the basic properties of fiber that affect its conformability, including fiber wall thickness, moment of inertia, and elastic modulus, can be measured within a single test. Results show that both fiber collapsibility and the elastic modulus of the fiber wall affect the fiber flexibility. Collapsibility is controlled mainly by fiber wall thickness. A refining or bleaching process can increase fiber flexibility mainly by altering fiber elastic modulus.

Mechanical behaviors of concrete combined with steel and synthetic macro-fibers

In this paper, hybrid fibers including high elastic modulus steel fiber and low elastic modulus synthetic macro-fiber (HPP) as two elements were used as reinforcement materials in concrete. The flexural toughness, flexural impact and fracture performance of the composites were investigated systematically. Flexural impact strength was analyzed with statistic analyses method; based on ASTM and JSCE method, an improved flexural toughness evaluating method suitable for concrete with synthetic macro-fiber was proposed herein. The experimental results showed that when the total fiber volume fractions (<TEX>$V_f^a$</TEX>) were kept as a constant (<TEX>$V_f^a=1.5%$</TEX>), compared with single type of steel or HPP fibers, hybrid fibers can significantly improve the toughness, flexural impact life and fracture properties of concrete. Relative residual strength RSI', impact ductile index <TEX>${\lambda}$</TEX> and fracture energy <TEX>$G_F$</TEX> of concrete combined with hybrid fibers were respectively 66-80%, 5-12 and 121-137 N/m, which indicated that the synergistic effects (or combined effects) between steel fiber and synthetic macro-fiber were good.

Strain hardening in regenerated cellulose fibres

Viscose and lyocell are two types of regenerated cellulose fibre which show different structure and mechanical properties due to their different production process. In order to study changes in the elastic modulus of fibres after plastic deformation, viscose and lyocell fibres were repeatedly strained and unloaded in cyclic tensile tests. The elastic modulus of both types of regenerated cellulose fibre increased with increasing plastic strain. With an increase in the elastic modulus of 47%, the strain hardening effect was more pronounced in lyocell, which shows higher crystallinity and higher orientation of cellulose chains than viscose, where an increase by 24% was observed.

Mechanical analysis of hollow fiber membrane integrity in water reuse applications

In order to gain insight into membrane fiber failure (i.e., loss of integrity), properties of five hollow fiber membranes and four hollow fiber modules were evaluated. Specifically, membrane material, membrane symmetry, fiber modulus of elasticity, fiber diameter and thickness, module potting technique, module flow pattern (inside-out or outside-in), and coliform breakthrough were investigated. The approach combined evaluation of the above properties with mathematical modeling of structure-fluid interactions to comprehensively evaluate the properties most important for maintaining hollow fiber membrane integrity. Tensile strength testing revealed that the strongest fiber was an asymmetric polyacrylonitrile membrane fiber. The weakest fiber was a symmetric polyethylene membrane fiber. Pilot plant testing on the four membrane modules revealed that membrane symmetry may be a more important factor than potting technique for hollow fiber integrity. Results from the SEM and tensile testing were used as input to a finite element analysis model used to evaluate time-dependent structure-fluid interactions. It was found that additional stresses at the juncture of the potting material and the hollow fiber membranes exist. These stresses likely lead to the formation of fractures.

Material Properties of the Human Lumbar Facet Joint Capsule

The human facet joint capsule is one of the structures in the lumbar spine that constrains motions of vertebrae during global spine loading (e.g., physiological flexion). Computational models of the spine have not been able to include accurate nonlinear and viscoelastic material properties, as they have not previously been measured. Capsules were tested using a uniaxial ramp-hold protocol or a haversine displacement protocol using a commercially available materials testing device. Plane strain was measured optically. Capsules were tested both parallel and perpendicular to the dominant orientation of the collagen fibers in the capsules. Viscoelastic material properties were determined. Parallel to the dominant orientation of the collagen fibers, the complex modulus of elasticity was E*=1.63MPa, with a storage modulus of E'=1.25MPa and a loss modulus of: E" =0.39MPa. The mean stress relaxation rates for static and dynamic loading were best fit with first-order polynomials: B(epsilon) = 0.1110epsilon-0.0733 and B(epsilon)= -0.1249epsilon + 0.0190, respectively. Perpendicular to the collagen fiber orientation, the viscous and elastic secant moduli were 1.81 and 1.00 MPa, respectively. The mean stress relaxation rate for static loading was best fit with a first-order polynomial: B (epsilon) = -0.04epsilon - 0.06. Capsule strength parallel and perpendicular to collagen fiber orientation was 1.90 and 0.95 MPa, respectively, and extensibility was 0.65 and 0.60, respectively. Poisson's ratio parallel and perpendicular to fiber orientation was 0.299 and 0.488, respectively. The elasticity moduli were nonlinear and anisotropic, and capsule strength was larger aligned parallel to the collagen fibers. The phase lag between stress and strain increased with haversine frequency, but the storage modulus remained large relative to the complex modulus. The stress relaxation rate was strain dependent parallel to the collagen fibers, but was strain independent perpendicularly.

Modeling of the influence of fibers on creep of fiber reinforced cementitious composite

An analytical model has been developed to study the influence of fibers on creep of fiber reinforced cementitious composites. The model is based on the assumption that shear stress is produced between fiber and surrounding matrix as the matrix deforms. This shear stress in turn influences the matrix creep behavior resulting in macroscopic creep strain lower than that of pure cement-based matrix. In the present paper, a creep strain expression in the form of matrix creep strain multiplying by a fiber influence factor, which reflects the influences of matrix and fiber properties as well as fiber orientation characteristics, is presented. A parametric study, including the influence of elastic moduli of fiber and matrix, fiber dimension and fiber content is carried out. The modeling results indicate that creep strain of fiber reinforced cement-based composite is significantly influenced by the elastic moduli of fiber and matrix as well as fiber length and thickness (i.e. diameter for fiber with circular cross-section). Model predictions compare favorably with experimental measurements of creep strain of fiber reinforced mortar and concrete under compressive load.

Effect of inclination angle on fiber rupture load in fiber reinforced cementitious composites

A model has been formulated for analyzing the influence of fiber inclination angle on its rupture load in fiber reinforced cementitious composite. As a stiff fiber is pulled with an angle to the direction of pulling, the fiber rupture load decreases compared to the case with zero inclination angles. This phenomenon is called fiber apparent strength (defined as rupture load divided by fiber cross-section area) degradation. A parametric study, including the influence of elastic moduli of fiber and matrix, fiber/matrix interfacial bond strength as well as fiber orientation in matrix on the fiber apparent strength is carried out. The model results indicate that with the increase of fiber inclination angle, fiber apparent strength decreases. In addition, fiber apparent strength degradation degree is influenced by the elastic moduli of fiber and matrix and fiber/matrix interfacial bond strength. A fiber rupture test of carbon fiber in cementitious matrix was used for model verification. Model predictions based on independent parametric input compare favorably with experimental measurements of fiber apparent strength.

Modification of polyacrylonitrile (PAN) carbon fiber precursor via post-spinning plasticization and stretching in dimethyl formamide (DMF)

This study investigates the possibility of using a post-spinning plasticization and stretching process to eliminate suspected property-limiting factors in polyacrylonitrile-based carbon fibers. This process was performed with the intention of removing surface defects (to improve tensile strength), attenuating fiber diameter (to promote more uniform heat treatment), and reducing molecular dipole interactions (to facilitate further molecular orientation). Among the various organic and inorganic solutions tested, treatment using aqueous dimethyl formamide (DMF) offered far and away the best properties and was therefore selected for further testing. Tested individually (as single filaments), fibers exposed to 80% DMF for 10 s gave the highest precursor values of elastic modulus (9.07 GPa) and tensile strength (675 MPa). While fibers treated in 80% DMF gave a 73% improvement in elastic modulus and a 53% improvement in tensile strength over as-received PAN, limitations in sample preparation and carbonization necessitated a reduction in DMF concentration (to 30%) to allow extraction of individual carbon fibers for tensile testing. Despite this compromise, results for fibers carbonized at 1000°C ultimately showed a 32% improvement in carbon fiber elastic modulus and a 14% improvement in carbon fiber tensile strength over regularly prepared carbon fibers. These results show that, to a certain extent, improvements in PAN precursor properties can translate to corresponding improvements in subsequently produced carbon fibers. Additional characterization using wide angle X-ray scattering (WAXS) and scanning electron microscopy (SEM) suggests that these improvements are due in part to improved lateral order as well as the successful elimination of surface defects and prevention of skin-core formation.

Micromechanical modelling of deformation and failure in Ti–6Al–4V/SiC composites

The tensile behaviour and the associated fracture micromechanisms were determined in a Ti–6Al–4V alloy uniaxially reinforced with 35 vol. % Sigma 1140+SiC monofilaments. Damage in the form of fiber fracture was localized in a given section of the composite, and the critical micromechanical parameters which control the composite behavior (namely the matrix elasto-plastic response, the fiber elastic modulus and strength, the interfacial sliding resistance, and the residual stresses originated by the thermal expansion mismatch between matrix and fibers) were determined using various experimental and analytical techniques. They were used as input data to simulate the composite deformation and fracture. The composite stress–strain curve was determined by the self-consistent method. The failure locus was determined by computing the probability of nucleating clusters containing one, two, three or more broken fibers. The analysis was based on the stress concentration introduced by one fiber failure in its neighbours, which was determined from the finite element analyses of a representative volume of the composite containing one fiber break, and included the effects of matrix plasticity, residual stresses, and interfacial sliding. This result was extended to analyze the stress concentration around a cluster of broken fibers by a superposition technique. The average composite strength and the extent of damage were accurately predicted by the model when failure was dictated by the nucleation of a cluster containing two neighbour broken fibers. These results demonstrate the potential of the new model to assess the strength and ductility of fiber-reinforced composites which fail under local load sharing conditions by the unstable propagation of a cluster of broken fibers.

Monte Carlo simulation of the effect of fiber characteristics on creep life of a fiber tow

Fatigue of reinforced ceramics at elevated temperatures was numerically evaluated with a fiber dominated, power-law creep model. A Monte Carlo simulation of fiber creep in a uniaxially loaded tow was used to examine the influence of fiber radius, elastic modulus, and strength on creep respose. The simulation permitted variation of both the average magnitude and dispersion of fiber characteristics while maintaining constant power-law creep parameters. A linear increase in creep life was predicted for an increase in mean fiber radius, and a linear decrease in creep life was predicted for an increase in the standard deviation of fiber radii. A linear increase in creep life was predicted for both an increase in mean fiber elastic modulus and standard deviation of elastic moduli. Characteristic fiber strength and Weibull modulus were predicted to have a significant effect on creep life of a SiC fiber low. An increase in either the characteristic strength or Weibull modulus was predicted to result in an increase in creep life.

Flexural properties of a hybrid polymer matrix composite containing carbon and silicon carbide fibres

The flexural properties of hybrid unidirectional fibre reinforced polymer (FRP) composites containing a mixture of carbon (C) and silicon carbide (SiC) fibres were evaluated at span-to-depth (S/d) ratios of 16, 32, and 64. The flexural strength generally increased with increasing S/d ratio with a maximum value of 2316 MPa being achieved for the specimen with nominally equal volume fractions of C and SiC fibre. However, even replacing 12.5 vol% of the C fibres by SiC fibres increased the flexural strength by 22%. The mechanical property most strongly influenced by the incorporation of SiC fibres was the work of fracture with a maximum value of 206.5 kJ m-2 (compared to 78.8 kJ m-2 for the specimen containing only C fibres). First estimate values for the SiC fibre compressive strength, elastic modulus, and strain to failure were 3.46 GPa, 157 GPa, and 0.018, respectively.

Micromechanics of three-dimensional fibrewebs: constitutive equations

This paper extends the fibre–network theory of Cox to three–dimensional anisotropic fibrewebs. It presents a micromechanical model employing fibre axial deformation as the elemental deformation mechanism giving rise to assembly stress as a result of applied normal and shearing strain field. This model predicts the elastic constants of an assembly in terms of fibre linear density, fibre elastic modulus, fabric bulk density and the first 15 spherical harmonic coefficients of direction distribution function. A computer simulation has been performed to study the effect of structure on the initial elastic moduli of fibrewebs. This simulation shows that: (a) Young9s modulus evaluated for each fabric axis is directly dependent on the fibre orientation distribution density (FODD) along the same axis; (b) shear modulus in any reference plane is maximized when orientation distribution function is isotropic in that plane and it decreases with increasing FODD along the direction normal to that plane; and (c) Poisson9s ratio, ν ij , increases as the FODD along the i –axis decreases and the FODD along the j –axis increases, but the effect of FODD along the k –axis is minimal.

Crack-bridging Processes and Fracture Resistance of a Discontinuous Fiber-reinforced Brittle Matrix Composite

A simple bridging model is proposed for the toughening of a discontinuous fiber-reinforced brittle matrix composite, in which the frictional bridging of fibers during, as well as after, the interfacial debonding is considered. The R-curve behavior and the work-of-fracture of the composite can be theoretically predicted by the computation of the bridging model applying material parameters, such as fiber volume fraction, size and shape of fibers, fiber tensile strength, elastic moduli of fibers and matrix, fracture toughness and work-of-fracture of matrix, and frictional shear stress at interface. The experimental result obtained from a SiC-whisker-reinforced Al2O3 composite confirms the theoretical predictions of the present bridging model. Through the model calculation, the R-curve, crack profile, and bridging stresses of the composite can be estimated correspondingly to the bridging processes.

Mechanical properties of a self-assembling oligopeptide matrix

We have begun studies of a novel type of biomaterial derived from a recently-discovered class of ionic self-complementary oligopeptides. These short peptides (typically 8, 16, 24, or 32 amino acid residues with internally-repeating sequences) self-assemble in aqueous salt solution into three-dimensional matrices capable of favorable interactions with cells, and offer promise for useful bioengineering design based on rational changes in sequence. In this paper we present preliminary results on mechanical properties, combining experimental and theoretical approaches, of one particular example of these peptide materials, EFK8. The static elastic modulus was measured using an apparatus designed to allow sample fabrication and mechanical testing in the same system with the sample in aqueous solution. The material microstructure was examined by SEM and the measurements interpreted with the aid of a model for cellular solids. Values for the elastic modulus increased from 1.59 ± 0.06 to 14.7 ± 1.0 kPa for peptide concentrations increasing from 2.7 to 10 mg ml-1. SEM photographs showed the microstructure to consist of a relatively homogeneous lattice with fiber thickness of 10 - 30 nm independent of peptide concentration, but with fiber density increasing with peptide concentration. This behavior is consistent with scaling predictions from the cellular solids model and yields an estimate for the individual fiber elastic modulus in the range of 1-20 MPa. We therefore have provided some initial physical principles for guiding improvement of the mechanical properties of these new materials.

Microstructural Based Modelling of the Elastic Modulus of Fiber Reinforced Cement Composites

Microstructural Based Modelling of the Elastic Modulus of Fiber Reinforced Cement Composites

The Optimized Quasi-Planar Approximation for Predicting Fiber Orientation in Injection-Molded Composites1

Abstract Fiber filled injection-molded plastic parts contain complex fiber orientation patterns. This fiber orientation state affects material properties, including both elastic modulus and strength, and the calculation of shrinkage and warpage. Several models are available for predicting fiber orientation, which are based on the theory of Folgar and Tucker [1]. A particular simplification of these models, here called the quasi-planar (QP) approximation, was introduced by Gupta and Wang [2]. Here we develop a substantially improved version of that model, which we call the optimized quasi-planar (OQP) approximation. The OQP approximation is formed by optimizing the QP approximation against a more general fiber orientation model. Details of the current and improved models are discussed, and the typical behavior of the old and new models is explored. In addition, simulations are performed using C-MOLD, a commercial software package that implements the QP approximation, to determine the final fiber orientation state in an end-gated strip. The resulting fiber orientation data is then used to predict the elastic modulus as a function of position, and both predictions are compared to available experimental data for fiber orientation and elastic modulus. The results show that the OQP approximation improves the fiber orientation prediction and the subsequent elastic modulus prediction compared to the QP model, though the OQP approximation is still less accurate than the full three-dimensional model.

ISOTHERMAL FATIGUE BEHAVIOR OF SIGMA/TIMETAL 21S LAMINATES, PART II: MODELING AND NUMERICAL ANALYSIS

Micromechanical modeling is employed to evaluate the stresses and strains in Sigma/ Timetal 2IS liminates under the isothermal fatigue conditions described in Part I [1], The effects of temperature and time variations on the constitutive response of the matrix and fiber are considered. Loading is limited to uniform in-plane stresses and to uniform changes in temperature. The local fields and macroscopic response of the plies are estimated with the finite-element method in conjunction with the transformation field analysis method, which utilizes overall elastic properties and transformation influence coefficients derived from the Mori-Tanaka model. Fiber debonding and sliding are modeled by modifying certain fiber elastic moduli. The results show that the inelastic deformation of the titanium matrix, assisted by extensive fiber debonding in the off-axis plies, promotes stress transfer to the fibers in the 0° plies. Under repeated loads, the fiber strain increase gradually at a certain rate, which depends on the applied load frequency. Regardless of lay up and hading frequency, the laminates fait when the overall axial strain reaches the critical value of (1 ± 0.1)%.