Fiber modulus

The air jet textured yam process is based on overfeeding a yam into a turbulent air jet so that the excess length forms into loops that are trapped in the yam stmcture. The air flow is unheated, turbulent, and asymmetrically impinges the yam. The process includes a heat stabilization zone. Key process variables include texturing speed, air pressure, percentage overfeed, filament linear density, air flow, spin finish, and fiber modulus (100). The loops create visual and tactile aesthetics similar to false twist textured and staple spun yams. 

Two observations are useful to rationalize why in Figures 2-11 and 2-12 (1) Gyy exceeds l (2) E45. is less than for composite materials that have a fiber modulus much greater than the matrix modulus ... 

Composite materials typically have a low matrix Young s modulus in comparison to the fiber modulus and even in comparison to the overall laminae moduli. Because the matrix material is the bonding agent between laminae, the shearing effect on the entire laminate is built up by summation of the contributions of each interlaminar zone of matrix material. This summation effect cannot be ignored because laminates can have 100 or more layersi The point is that the composite material shear moduli and G are much lower relative to the direct modulus than for isotropic materials. Thus, the effect of transverse shearing stresses. 

Figure 24 Total modulus E, of PC-TLCP composite sample as function of the fiber modulus / for the four sample groups.

Table 5 compares the tensile properties of Vectra A950 in the form of dispersed fibers and droplets in the matrix by injection molding, microfibril by extrusion and drawing [28], injection molded pure thick sample and pure thin sample, and the pure drawn strand [28]. As exhibited, our calculated fiber modulus with its average of 24 GPa is much higher than that of the thick and thin pure TLCP samples injection molded. It can be explained that in cases of pure TLCP samples the material may only be fibrillated in a very thin skin layer owing to the excellent flow behavior in comparison with that in the blends. However, this modulus value is lower than that of the extruded and drawn pure strand. This can be... 

It is assumed that k and trp depend on the filling ratio (Vf), fiber modulus, method of fabrication. In [151] for example, the k for carbon fiber bundles has been found to be ... 

As the laser beam can be focused to a small diameter, the Raman technique can be used to analyze materials as small as one micron in diameter. This technique has been often used with high performance fibers for composite applications in recent years. This technique is proven to be a powerful tool to probe the deformation behavior of high molecular polymer fibers (e.g. aramid and polyphenylene benzobisthiazole (PBT) fibers) at the molecular level (Robinson et al., 1986 Day et al., 1987). This work stems from the principle established earlier by Tuinstra and Koenig (1970) that the peak frequencies of the Raman-active bands of certain fibers are sensitive to the level of applied stress or strain. The rate of frequency shift is found to be proportional to the fiber modulus, which is a direct reflection of the high degree of stress experienced by the longitudinally oriented polymer chains in the stiff fibers. 

The transverse modulus (Mt) and many other properties of a long fiber resin composite may be estimated from the law of mixtures. The longitudinal modulus (Ml) may be estimated from the Kelly-Tyson equation (8.5), where the longitudinal modulus is proportional to the sum of the fiber modulus (Mp) and the resin matrix modulus (Mm)- Each modulus is based on a fractional volume (c). The constant k is equal to 1 for parallel continuous filaments and decreases for more randomly arranged shorter filaments. 

This, too, is the simple rule of mixtures of Eq. (5.82) applied to modulus. Care must be exercised to use the correct fiber modulus, Ei in the case of anisotropic fibers such as carbon and Kevlar . In Eq. (5.88), it is the axial tensile modulus that must be used. The second term in Eq. (5.88) usually makes only a small contribution, since Except at very low fiber volume fractions, Ei is then given to a good approximation by... 

Note the similarity of this relationship to the equation of mixing given at the beginning of this section by Eq. (5.82). The factor /Si is called the fiber length correction factor, and it corrects the fiber modulus for the shortness of the fibers. It is plotted in Figure 5.95 as a function of the product na. When na becomes very large, fii approaches one, as is expected since this limit is the case of continuous fibers, and Eq. (5.110) reduces to Eq. (5.82). When na falls below about 10, Pi is significantly less than one. 

The fiber modulus and matrix shear modulus are also required for the analysis. The fiber s coordinates are recorded directly from the stage controllers to the computer. The operator begins the test from the keyboard. The x and y stages move the fiber end to a position directly under the debonder tip the z stage then moves the sample surface to within 4 yum of the tip. The z-stage approach is slowed down to 0.04 jan/step at a rate of 6 steps/s. The balance readout is monitored, at a load of 2 g the loading is stopped, and the fiber end returned to the field of view of the camera. The location of the indent is noted and corrections are made, if necessary, to center the point of contact. Loading is then continued from 4 g in approximately 1 g increments. Debond is determined to have occurred when an interfacial crack is visible for 90-120° on the fiber perimeter. The load at which this occurs is used to calculate the interfacial shear stress at debond. 

For conditioned PET, the T ranges from 69 to 73 C and, for wet PET, from 50 to 63 C. The Slder range obtained with the wet fibers probably results from Increased experimental difficulty In obtaining some of the data on wet fibers. In all cases, however, the wet T was 10 to 20 C lower than the conditioned T for PET fibers. Sf these methods, the use of fiber modulus Is preferred because It Is applicable to all fibers, that exhibit distinct... 

VARIATION IN CARBON FIBER MODULUS AS A FUNCTION OF CARBONIZING TEMPERATURE. PRECURSOR WAS A CAT CRACKER BOTTOM PITCH EXTRACTED WITH A SOLVENT HAVING A SOLUBILITY PARAMETER OF 8. -... 

Fiber modulus can be regulated by orientation and crystalhnity, but a third parameter, chain stiffness, is available for modification if additional control is required. 

It is recognized that glass-fiber reinforcement can be replaced by superior fiber materials offering high improvements over the upper limit of properties in GRP. As an example the carbon fibers modulus ranges from 0.17 x 10 to 0.34 MPa (25 x 10 to 50 x 10 psi) and tensile strength at 2,760 MPa (400,000 psi). Densities of RPs made from these fibers would only be less than 75% of the weight of GRP. 

These values are on the order of the resin modulus at cryogenic temperatures. Some increase of the fiber modulus at low temperatures may be expected. 

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