Processing fiber pulling

In the fiber pull-out test, a fiber(s) is partially embedded in a matrix block or thin disc of various shapes and sizes as shown in Fig 3.6. When the fiber is loaded under tension while the matrix block is gripped, the external force applied to the fiber is recorded as a function of time or fiber end displacement during the whole debond and pull-out process. There are characteristic fiber stresses that can be obtained from the typical force (or fiber stress). The displacement curve of the fiber pull-out... 

The radial (compressive) stress, qo, is caused by the matrix shrinkage and differential thermal contraction of the constituents upon cooling from the processing temperature. It should be noted that q a, z) is compressive (i.e. negative) when the fiber has a lower Poisson ratio than the matrix (vf < Vm) as is the normal case for most fiber composites. It follows that q (a,z) acts in synergy with the compressive radial stress, 0, as opposed to the case of the fiber pull-out test where the two radial stresses counterbalance, to be demonstrated in Section 4.3. Combining Eqs. (4.11), (4.12), (4,18) and (4.29), and for the boundary conditions at the debonded region... 

To evaluate the stability of the debond process, the instability parameter, z,nax, is compared, z ax values calculated based on Eqs. (4.104) and (4.139) respectively for fiber pull-out and fiber push-out give z ax = 6-5, 6.2 mm for coated steel wire-epoxy matrix and z ax = 0.5, 0.49 mm for the untreated SiC-fiber-glass matrix composite... 

The analytical solutions derived in Sections 4.3 and 4.4 for the stress distributions in the monotonic fiber pull-out and fiber push-out loadings are further extended to cyclic loading (Zhou et al., 1993) and the progressive damage processes of the interface are characterized. It is assumed that the cyclic fatigue of uniform stress amplitude causes the frictional properties at the debonded interface to degrade... 

Fig. 4.41. Schematic drawings of loading and unloading processes measuring the relative displacements 5 and 6, in (a) fiber pull-out and (b) fiber push-out models under cyclic loading. After Zhou et al. (1993).

Roll coating is widely used for uniform, whether flat or cylindrical, surfaces including fiber bundles. In a roll coating process, fibers are coated between two rollers, an applicator roller and a backup roller coating is fed continuously to the applicator roller by a feed roller which runs partially immersed in a coating bath and the backup roller pulls the fibers by rotating in opposite directions. Slow... 

Continuous filament process multiple pulling of wires througli ever narrower dies with intermediate annealing. The process is used for the manuraclure of steel fibers for tire cord (ca. 1.50 pm)... 

New types of ceramic composites with high thermal shock resistance have recently been developed that show some promise for gas turbine applications. These composites consist of a ceramic matrix reinforced by ceramic fibers or platelets inside the matrix. The fibers pull out of the matrix during fracture to resist crack propagation. Such composites can be readily fabricated using a new process developed by Lanxide Corporation [18]. The process uses directed oxidation reactions of molten metals to grow a ceramic matrix around a reinforcing material. 

Fig4. shows the microstructures of the fracture surfaces. Some holes can be observed in both composites as a result of the fibers-pull-out, however, the lengths of the pulled-out fibers are very short. Compared to the nitridation temperature of 1800°C, the carbonization temperature of carbon fibers in the preparation process is relatively low, therefore, in the nitridation process, some damages may be done to the fibers and lead to the degradation in the strengths of fiber reinforcements and result in the low strength of composites. Some phases with layered structures can also be observed in the miciostructures of composite with boron, which corresponds to h-BN in situ formed in the nitridation process. When the cracks propagate to h-BN, they will deflect. 

The interface between HM carbon fiber and a Pyrex borosilicate glass matrix was Analyzed by Bleay and Scott [111,112] and found to be some 100 nm thick and believed to comprise Na enriched silicon oxycarbide, showing that some reaction had taken place during fabrication. Measurement of the interlaminar shear strength of the composite indicated that this layer was not a source of weakness. Substantial fiber pull-out had occurred, however, exposing clean fiber surfaces and smooth sockets. It was concluded that the interfacial shear process was confined to the outer layer of the fiber. Heat treatment of the composite in air caused preferential oxidation of the fiber, the rate being higher parallel to the fiber axis than perpendicular to it. 

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