Fiber Elastic Modulus Research Articles

The Effective Dilatational Response of Fiber-Reinforced Composites With Nonlinear Interface

This paper presents a model of the dilatational response of fiber-reinforced composites for situations where the fibers interact with the matrix through a nonlinear interfacial separation mechanism. The solution to a planar solitary fiber-interface-matrix problem is employed together with the geometrically consistent composite cylinders model to obtain an exact solution for the bulk response of an elastic matrix reinforced with unidirectional elastic fibers. In the solitary fiber problem interface characterization assumes the form of a nonlinear force-separation law which couples the normal component of displacement jump to the normal component of interface traction and which requires a characteristic length for its prescription. Under decreasing values of characteristic length to inclusion radius ratio ductile or brittle decohesion or closure can occur provided the applied load, interface strength and elastic moduli of fiber and matrix are within the required bounds. Interaction effects due to finite fiber volume concentration, along with the phenomenon of brittle decohesion arising in the solitary fiber problem from the bifurcation of equilibrium separation at the fiber matrix interface, are shown to precipitate instability in the composite. An inequality relating the elastic moduli and interface properties is provided which governs the smooth or abrupt transition in composite response from rigid interface behavior to void behavior. The results are shown to apply equally well for composite geometry based on the three-phase model.

Effects of fiber and interphase on matrix-initiated transverse failure in polymer composites

Failure initiation in polymer-matrix composites loaded transverse to the fibers is investigated by a numerical parametric study where the effects of constituent properties, interphase properties and thickness are examined. Failure initiation in the matrix only is studied, interfacial debonding not being considered. Two modes of failure—yielding and cavitation-induced brittle failure—are examined. A criterion for the cavitation-induced brittle failure has been proposed previously and failure prediction based on this criterion was found to agree with experimental data for a glass-fiber-reinforced epoxy. The present study shows that the elastic modulus of fibers has a large effect on the stress and strain to failure initiation. A rubbery interphase material is found in most cases to have a beneficial effect. The site at which failure initiates and the governing mode of failure initiation are also affected by the fiber modulus and the interphase properties.

On the fracture of reinforced thermoplastics

In the designing of engineering fiber-reinforced thermoplastics and of the processing technology to make such, their behaviour at failure should be taken into consideration. The processes of deformation and failure from compression were investigated for polycarbonate and polyarylate reinforced with polyaramide fiber, particularly, poly- m-phenyleneisophthalamide and poly- p-amidobenzimidazole, the results obtained being described in this paper. The acoustic emission (AE) technique was used to reveal the essential dependences of the deformation and the fracture on the fiber length and elastic modulus of the composites. Chemical, plasma or biochemical pre-treatment of the fiber surface appeared to considerably influence the kinetics of damage accumulation in the material. The relationship between the interphase interaction of the components and the characteristics of the fracture surface is considered for fiber-reinforced thermoplastics. Morphological differences were established by the secondary electron emission technique using the scanning electron microscope and a computer system. The statistical characteristics of the fracture surfaces of composites differing in the fiber origin and in the degree of interaction between the components are described. The strength properties of the fiber-reinforced thermoplastics are described for quasistatic (deformation rate 10 −4 s −1) and dynamic (deformation rate 10 2 s −1) loading conditions.

Effect of hindlimb unloading on rat soleus fiber force, stiffness, and calcium sensitivity.

The purpose of this study was to examine the time course of change in soleus muscle fiber peak force (N), tension (Po, kN/m2), elastic modulus (Eo), and force-pCa and stiffness-pCa relationships. After 1, 2, or 3 wk of hindlimb unloading (HU), single fibers were isolated and placed between a motor arm and a transducer, and fiber diameter, peak absolute force, Po, Eo, and force-pCa and stiffness-pCa relationships were characterized. One week of HU resulted in a significant reduction in fiber diameter (68 +/- 2 vs 57 +/- 1 microns), force (3.59 +/- 0.15 vs. 2.19 +/- 0.12 x 10(-4) N), Po (102 +/- 4 vs. 85 +/- 2 kN/m2), and Eo (1.96 +/- 0.12 vs. 1.37 +/- 0.13 x 10(7) N/m2), and 2 wk of HU caused a further decline in fiber diameter (45 +/- 1 microns), force (1.31 +/- 0.06 x 10(-4) N), and Eo (0.96 +/- 0.09 x 10(7) N/m2). Although the mean fiber diameter and absolute force continued to decline through 3 wk of HU, Po recovered to values not significantly different from control. The Po/Eo ratio was significantly increased after 1 (5.5 +/- 0.3 to 7.1 +/- 0.6), 2, and 3 wk of HU, and the 2-wk (9.5 +/- 0.4) and 3-wk (9.4 +/- 0.8) values were significantly greater than the 1-wk values. The force-pCa and stiffness-pCa curves were shifted rightward after 1, 2, and 3 wk of HU. At 1 wk of HU, the Ca2+ sensitivity of isometric force, assessed by Ca2+ concentration required for half-maximal force, was increased from the control value of 1.83 +/- 0.12 to 2.30 +/- 0.10 microM. In conclusion, after HU, the decrease in soleus fiber Po can be explained by a reduction in the number of myofibrillar cross bridges per cross-sectional area. Our working hypothesis is that the loss of contractile protein reduces the number of cross bridges per cross-sectional area and increases the filament lattice spacing. The increased spacing reduces cross-bridge force and stiffness, but Po/Eo increases because of a quantitatively greater effect on stiffness.

On the Elastic Buckling of Rod-Shaped Particles in Sheared Suspensions

A correction of the original work by Forgacs and Mason describing the elastic buckling of rod-shaped particles in sheared suspensions is presented. Although the qualitative relationship among critical buckling conditions and the fiber aspect ratio and elastic modulus is unaltered, the new result for the predicted critical buckling condition shows that the resistance of suspended rods to buckling is more than five times greater than had been believed. Reexamination of experimental results using the corrected solution yielded mixed conclusions concerning the validity of the model. The agreement with results of the original experiments by Forgacs and Mason using Dacron fibers suspended in corn syrup and the new result was found to be excellent and quantitative. The results of experiments with glass fibers suspended in glucose solutions were found to be in poor agreement with predictions. The ability of the proposed result to account for an unusual degradation due to shearing in polystyrene melts of Kevlar 29 fibers was also found to be quantitative and excellent. The Kevlar fibers exhibited permanent bends spaced with a uniform spacing which was predicted by application of the new buckling relationship.

Development of Silicon Carbide Composites for Fusion

The use of silicon carbide composites for structural materials is of growing interest in the fusion community. However, radiation effects in these materials are virtually unexplored, and the general state of ceramic matrix composites for nonnuclear applications is still in its infancy. Research into the radiation response of the most popular silicon carbide composite, namely, the chemically vapor-deposited (CVD) SiC-carbon-Nicalon fiber system is discussed. Three areas of interest are the stability of the fiber and matrix materials, the stability of the fiber-matrix interface, and the true activation of these [open quotes]reduced activity[close quotes] materials. Two methods are presented that quantitatively measure the effect of radiation on fiber and matrix elastic modulus as well as the fiber-matrix interfacial strength. The results of these studies show that the factor limiting the radiation performance of the CVD SiC-carbon-Nicalon system is degradation of the Nicalon fiber, which leads to a weakened carbon interface. The activity of these composites is significantly higher than expected and is dominated by impurity isotopes. 52 refs., 12 figs., 3 tabs.

Fiber pull-out and strain localization in ceramic matrix composites

The mechanical properties of ceramic matrices uniaxially reinforced with strong continuous fibers depend on a wide variety of material parameters: the fiber and matrix elastic moduli, the matrix toughness, the statistical fiber strength, the fiber radius and fill fraction, and the sliding resistance τ between the fibers and the matrix. A major contribution to the work of fracture is the work to pull-out broken fibers from the matrix against the sliding resistance. Recent analytic theories of the pull-out predict finite pull-out for very narrow fiber strength distributions, in contrast to prior theories and ideas suggesting zero pull-out. The theories also assume that fiber cracking is distributed throughout the composite and not localized to some narrow region ; such strain localization could modify composite properties tremendously. Here, both analytical arguments and numerical simulations are used to show that finite pull-out does exist for narrow fiber strength distributions. The numerical simulations also demonstrate that strain localization does occur, but that it (i) does not affect the ultimate tensile strength, and (ii) reduces pull-out only slightly but with the detailed trends in pull-out properties predicted by the analytic theory retained. Some basic tenets and results of the analytic models are thus robust and so the analytic models should serve as powerful tools for composite optimization.

Fracture behavior of short-fiber reinforced materials

A discrete model of springs with bond-bending forces is proposed to simulate the fracture process in a composite of short stiff fibers in a softer matrix. Both components are assumed to be linear elastic up to failure. We find that the critical fiber length of a single fiber composite increases roughly linearly with the ratio of the fiber elastic modulus to matrix modulus. The finite size of the lattice in the direction perpendicular to the fiber orientation considerably alters the behavior of the critical length for large values of the modulus ratio. The simulations of the fracture process reveal different fracture behavior as a function of the fiber content and length. We calculate the Young's modulus, fracture stress, and the strain at maximum stress as a function of the fiber volume fraction and aspect ratio. The results are compared with the predictions of other theoretical studies and experiments.

Nonlinear flutter of two-dimensional simply supported symmetric composite laminated plates

The nonlinear flutter behavior of a two-dimensional simply supported symmetric composite laminated plate at high supersonic Mach number has been investigated. Yon Karman's large deflection plate theory and quasisteady aerodynamic theory have been employed. Galerkin's method has been used to reduce the governing equations to a system of nonlinear ordinary differential equations in time, which are then solved by a direct numerical integration method. Nonlinear flutter results are presented with the effects of aerodynamic damping, in-plane force, static pressure differential, and anisotropic properties. Results show that the anisotropic properties such as fiber orientation and elastic modulus ratio have significant effects on the behavior of both limit cycle oscillation and chaotic motion.

Nonlinear flutter of composite laminated plates

The nonlinear flutter behavior of a two-dimensional simply supported composite laminated plate at high supersonic Mach number has been investigated. Von Karman's large deflection plate theory and qusai-steady aerodynamic theory have been employed. Galerkin's method has been used to reduce the governing equations to a system of nonlinear ordinary differential equations in time which are then solved by a direct numerical integration method. Nonlinear flutter results are presented with the effects of aerodynamic damping, in-plane force, static pressure differential, and anisotropic preperties. Results show that the anisotropic properties such as fiber orientation and elastic modulus ratio have significant effects on the behavior of both limit cycle oscillation and chaotic motion.

Friction and wear of graphite-fiber-reinforced glass matrix composites

The friction and wear behavior of the graphite-fiber-reinforced glass matrix composite system is described. By reinforcing borosilicate glass with graphite fibers it has been possible to develop a composite whose friction coefficient and mechanical properties can be compared favorably with those of resin matrix composites and whose wear resistance and environmental stability can be comparable with those of glasses and ceramics. Both friction and wear results are described as a function of fiber elastic modulus, fiber orientation and test configuration for unlubricated sliding.

Direct Nondestructive Prediction of Engineering Properties

Abstract Quantitative nondestructive evaluation provides the means for directly predicting engineering properties of materials on individual components. Through proper problem definitions, the working concept of material ↔ energy interaction, and multifunctional/multivariable relationships, a complex material system can now be characterized in terms of both bulk and constituent properties as they actually exist in the finished product. In fiber-reinforced composite materials, properties such as in-plane tension/compression elastic modulus, at any polar angle, or in the thickness direction; shear modulus; poisson's ratio; density; volume fractions of fiber, matrix and porosity; and fiber elastic modulus may be pinpointed. In adhesively bonded joints, where failure mode is brittle fracture at or near the interface, bond adhesive strength may be predicted from nondestructive measurements of substrate surface free energy, contact angle, and bondline thickness, when the reference liquid surface free energy, effective strain, and stress-strain integral are known.

Response of Cottons to Chemical Treatments

Single fibers from six widely different cottons were subjected to a single-fiber resin- finishing treatment during which each fiber was maintained under a controlled tension of 100 mg. Dimethylol-ethylene-urea (DMEU) was used as the resin finishing agent. Fibers receiving suitable control treatments were also examined. The mechanical properties of the treated single fibers were evaluated by a cyclic loading procedure on an Instron tensile tester. It was found that water and blank catalyst treatments did not affect the fiber rupture properties, but that the DMEU treatments caused a signifi cant reduction. Fiber elastic modulus and fiber resilience were increased slightly by the blank treatments but a major increase in these properties resulted from the DMEU resin-finishing treatment.

Response of Cottons to Chemical Treatments

Eleven experimental cottons were subjected to identical yarn mercerization in an attempt to determine whether differences in response to the treatment could be observed. The response was measured in terms of changes in yarn resilience, elastic modulus, and toughness. Changes in yarn elastic modulus and resilience were found to be dependent upon X-ray angle, although the dependence on X-ray angle was found to be the reverse of that for fiber elastic modulus [6].

Response of Cottons to Chemical Treatments Part I: Fiber Mercerization and Urea Treatments 1

In order to determine whether different cottons respond differently to identical chemi cal treatments, single fibers from six carefully selected cottons were subjected to four treatments under a tensile force of 0.1 g. The treatments which were investigated were water, 10 M urea, mercerization, and a combination of 10 M urea and mercerization. The initial, nondestructive portion of the fiber stress-strain curve was evaluated for each fiber prior to the treatment and the entire stress-strain curve was evaluated after the chemical treatments. Thus it was possible to determine the changes in fiber properties on a fiber-to-fiber basis at least as far as the non-rupture fiber characteristics are con cerned. Fiber length, elastic modulus, breaking extension, and breaking tenacity were considered in this research. Many changes in fiber properties due to the chemical treat ments could be interpreted in terms of fibrillar orientation of the six cottons as estimated by the X-ray angle. Under mercerizing conditions, it was observed that cottons with high X-ray angles underwent greater increases in fiber length and elastic modulus and greater decreases in fiber breaking extension than did cottons with low X-ray angles. Changes in fiber breaking tenacity could not be related to known structural features of the cotton fiber.

Relation between the X-Ray Angle of Cottons and Their Fiber Mechanical Properties

Correlations are presented between the spiral angle, as measured by the X-ray angle (40% absorption angle of 002 diffraction are), and the mechanical properties of 16 cot tons. A significant correlation is found for Pressley strength at zero gauge length : however, virtually no correlations exist when cotton strength is measured at 5.0-mm. gauge length. Highly significant correlations are found between the spiral angle and the extensibility properties of cotton fibers, as measured by single fiber elastic modulus and elongation to break.

The Reaction of Formaldehyde with Cellulosic Fibers

The effects of an acid-catalyzed formaldehyde treatment on such mechanical proper ties as breaking strength and crease recovery have been determined for three cellulosic fabrics: cotton, Fortisan, and viscose rayon. Samples of these materials, treated under a selected set of conditions, were compared with three "controls": untreated fabric, fabric treated with distilled water under the conditions of the formaldehyde treatment, and fabric treated with the acid solution used in the formaldehyde treatment under the same conditions. The two-dimensional load-elongation behavior of the fabrics was investi gated, and comparisons were made with the results of corresponding one-dimensional tests. The mechanical properties of single fibers and yarns taken from the variously treated fabrics were also measured. In general, cotton fabrics showed a deterioration in mechanical properties due to formaldehyde cross-linking with respect to the acid-treated control, while correspond ingly, Fortisan and viscose rayon were improved by such treatment. In the case of cotton fibers and fabrics, it was found that the formaldehyde treatment had reduced the fiber and fabric elastic moduli with respect to the acid-treated control, although the formaldehyde treatment had also reduced correspondingly the fiber and fabric breaking strains. The deterioration in mechanical properties caused by hydrochloric acid was most marked in the case of Fortisan. It was found that generally the properties of single fibers, yarns, and fabrics are closely related. The improvement in crease recovery caused by the formaldehyde treatment was great est for cotton, less for Fortisan, and least for viscose rayon. These different responses to the cross-linking reaction appear to be related to the different states of internal order of the three cellulosic fibers. Crease-recovery tests carried out on all the variously treated fabrics showed that marked improvements in crease recovery were usually ob tained only with those treated at an initial pad-bath pH of 2.0, which indicates that a high degree of cross-linking of the hydroxyl groups in the amorphous regions of the fibers is necessary to achieve high degrees of crease recovery.

Cotton Quality and Fiber Properties

The purpose of this research was to evaluate the use of single-fiber testing methods for the determination of cotton fiber properties and for the prediction of yarn quality. Samples of unprocessed cotton, finisher drawing sliver, and 36's carded yarn were ob tained for 21 domestic cotton varieties representing extremes in length, fineness, and strength. Single fibers from all three processing stations were tested for their fineness and mechanical properties: crimp, Hookean slope, breaking load, elongation, elastic modulus, breaking stress, and energy to rupture. Ranges for each of these properties were established. The results were compared with the mechanical properties of the fiber bundles, slivers, and yarns. Correlation studies of the results show that all of the mechanical properties measured on fibers are related to fiber fineness and, among the varieties, to fiber length. Bundle strengths and elongations at clamp spacings greater than 1.5 mm. relate well to fiber breaking strengths and elongations. Sliver force-extension slope is dependent on fiber fineness and fiber elastic modulus. Yarn strength depends strongly on fiber length, fine ness, and elastic modulus, and only weakly on fiber strength; yarn elongation depends greatly on fiber elongation and elastic modulus. These observations suggest that yarn strength and elongation are related to the single fiber properties and can be predicted from them fully as well as from bulk measurements of fineness and bundle strength data. They also indicate that elastic modulus is an im portant parameter for predicting fiber assembly behavior.

Properties of Apparel Wools

A description is given of the measurement of the tensile force-extension curves of fiber as semblies with no net twist—i.e., top and roving produced on the French worsted system. Typical force-extension curves are presented, and the effects of testing conditions on various parameters of these curves have been determined. These force-extension curves are a measure of the forces required to cause the fibers to slip over one another; they depend on such factors as fiber length, fiber diameter, fiber modulus of elasticity, interfiber coefficient of friction, and fiber crimp, and on density of fiber packing in the assembly, fiber parallelism, and weight per unit length of the assembly. The relationships between the above factors and parameters of the force-extension curve are discussed in the light of the use of these measurements to investigate processes which affect any of these factors or to characterize different fiber types. The variability of parameters of the force-extension curve is discussed. Part of the variability may be ascribed to slight differences in the performance of the machine units producing the assemblies.