Fiber orientation, effect

The level of modulus increase by chopped high modulus fibers is less than for continuous filaments at the same volume loading. There is both a fiber length effect and a fiber orientation effect both of which reduce the modulus. One may accoimt for the fiber length effect by writing Eq. 2.16b as [78]... 

Figure I represents a two-dimensional damage distribution of an impact in a 0/90° CFRP laminate of 3 mm thickness. Unlike in ultrasonic testing, which is usually the standard method for this problem, there is no shadowing effect on the successive layers by delamination echos. With the method of X-ray refraction the exact concentration of debonded fibers can be calculated for each position averaged over the wall thickness. Additionally the refraction allows the selection of the fiber orientation. The presented X-ray refraction topograph detects selectively debonded fibers of the 90° direction.

Figure 6 Effect of fiber orientation on (a) tensile strength and (b) tensile modulus of PALF-LDPE composites.

DTI has already been demonstrated to be effective in analyzing the internal micro structure of different tissues. For instance, orientation of nerve fiber bundles in the white matter of the brain or hollow fiber orientations in material science can be visualized using DTI [11],... 

Figure 12.9 Effect of spinning speed on fiber orientation and shrinkage [14]. From Brunnschweiler, D. and Hearle, J. (Eds), Polyester - 50 Years of Achievement, 1993, p. 193, and reproduced by permission of The Textile Institute, Manchester, UK...

Fu, S. and Lauke, B Effects of fiber length and fiber orientation distributions on the tensile strength of short-fiber-reinforced polymers, Composites Sci. Technol., 56, 1179 (1996). 

The insight from AFM images may be greatly boosted by sophisticated image analysis. Fritzsche and Henderson [30,31] have extracted cross-sections of nucleosomes at half-maximum height and have fitted them to virtual ellipsoids. These ellipsoids had relatively smooth perimeter and an aspect ratio of 1.2 1.4 moreover, the orientation of the ellipsoids was correlated with the direction of the fiber axis, with more than 50% of nucleosomes aligned with the axis. While this orientation effect may result from surface interactions, as discussed by the authors themselves, it may also represent an actual, and structurally important, feature of fiber structure. Ellipsoid-shaped nucleosomes have been reported in electron EM studies [32,33], and have been predicted in models of chromatin... 

Orientation effects are important in utilizing fibrous composites. The theoretical relationships are shown in Figure 9. The greatest benefit is obtained with unidirectional fibers. The more common case in practice is closer to the random orientation in two dimensions. The theoretical modulus that is obtained in this fiber configuration is one-third of the fully oriented composite. 

The orientation effect is magnified when the compound contains fibrous reinforcement which tends to align itself with the direction of milling. The amount of orientation depends upon the viscosity of the stock as well as the type of rubber and type of fiber. 

Figure 17 illustrates the effect of orientation on the stress-strain properties of the rayon composite shown in Figures 10 and 11. The upper curve represents stress-strain behavior for stress applied parallel to the fiber orientation direction. In the lower curve the force is applied perpendicularly. Even a small degree of orientation has a large effect on the anisotropy of the composite. The differences in tensile strength, modulus and elongation at break in the two directions are considerable. 

The higher thermal conductivity of inorganic fillers increases the thermal conductivity of filled polymers. Nevertheless, a sharp decrease in thermal conductivity around the melting temperature of crystalline polymers can still be seen with filled materials. The effect of filler on thermal conductivity for PE-LD is shown in Fig. 2.5 [22], This figure shows the effect of fiber orientation as well as the effect of quartz powder on the thermal conductivity of low density polyethylene. 

To illustrate the effect of fiber orientation on material properties of the final part, Fig. 8.60 [5] shows how the fiber orientation distributions that correspond to 67 50 and 33% initial mold coverage affect the stiffness of the finished plates. The Folgar-Tucker model has been implemented into various, commercially available compression mold filling simulation programs and successfully tested with several realistic compression molding applications. 

Fig. 11.24 The effects of the fiber aspect ratio, at constant 30% wt loading, on glass-filled polyamide-6. [Reprinted by permission from H. M. Latin, Orientation Effects and Rheology of Short Glass Fiber-reinforced Thermoplastics, Colloid Polym. Sci., 267, 257 (1984).]...

H. M. Laun, Orientation Effects and Rheology of Short Glass Fiber-reinforced Thermoplastics, Colloid Polym. Sci., 262, 257-269 (1984). 

For tests other than E-84, there have been some studies on the effects of fiber loading and fiber layup on composite flammability. This has primarily been work done by the U.S. Navy on the flammability of composites used in naval vessel flammability,19-20 or work by Kandola et al.10-21-22 on the effect of fiber type and content on polymer composites studied by cone calorimeter. More work is being conducted in studying the effects of fiber orientation and lay-up not on overall flammability performance, but flammability performance under structural load. This is the most important for aircraft, vehicles, and buildings where the composites are structural members. The concern here is... 

It has been known for some time that the color of fabrics and the types of dyes used can be important factors in determining the solar reflectance of fabrics (15., l6). However, color of fabrics in apparel has no effect on the loss of body heat since the color of a fabric has a small effect on its surface emittance (16). Other factors such as fiber orientation and length, yarn twist, and fabric structure also influence the infrared and visible reflection properties of various fabrics (17). In a recent study, the various radiant properties of textiles measured at the peak emission wavelength of sunlight (0.6 urn), were found to approach constant values of absorptivity (0.67), absorptance (0.33), transmissivity (0.0), and reflectivity (0.33) at infinite superficial density (3.) ... 

In this expression, Ef and Em are the Young modulus of respectively the fiber and the matrix, and f is the fiber volume fraction. //0 is the fiber orientation factor this factor is equal to 1 for perfectly oriented fibers and 1/6 for a random orientation, tj, is the so-called effective length coefficient (10), which mainly depends on the aspect ratio of the fiber. Indeed ... 

Numerous studies have been made of the mechanical properties of fibrous composites these include recently published papers on impact properties by Izod (1,2, 3,4) and Charpy (5,6) and drop weight (7) tests. We reported the Charpy impact fracture behavior of various glass-polyester composites regarding the effects of temperature (8,9,10), specimen size (8), and fiber orientation (10). This paper describes the effects of the tough-brittle transition in the impact behavior of glass-polyester composites which occurs with a variation of temperature and specimen size. 

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