Fiber slip

One key factor for producing acceptable WPCs is the interaction between the wood and thermoplastic components (wood-polymer interface). It is difficult to achieve wood/plastic interaction because the hydrophobic thermoplastic (nonpolar) and hydrophilic wood (polar) are energetically different [2, 4]. During wood/plastic mixing, the thermoplastic must first coat or spread over the wood fiber surface to interact [4]. It is observed in Figure 26.2 that the polymer-fiber interface and a poor surface adhesion lead to fiber slipping from the matrix. 

The aspect of the flow curves in Fig. 9.6 indicates the predominant condition of the test. For instance. Fig. 9.6a shows uniform serrations (stick-shp) associated with a continuous, step-by-step process of fiber slipping away off the polymeric block. This exclusive pullout mechanism occurred only in the first part of the curve depicted in Fig. 9.5c. In this case, the fiber was intact after the test and, in some cases, covered with a layer of polyester. By contrast. Fig. 9.6d shows a smooth curve up to fracture. In this case, no pullout process occurred, and the fiber had undergone tensile rupture in association with the last horizontal part of the curve. The intermediate condition of both pullout and fiber rupture are shown in Fig. 9.6b, c. 

Inter-fiber slip occurs when the fibers move relative to each other. 

Antioxidants acting synergistically with HAS, UV stabilizers for PP films and fibers Polyethyleneglycolethers as spin finishes for PO fibers Slip and antistatic agent for PP fibers... 

Interna] Insulation The practice of insulating within the vessel (as opposed to applying insulating materials on the equipment exterior) is accomplished by the use of fiber blankets and hghtweight aggregates in ceramic cements. Such construction frequently incorporates a thin, high-alloy shroud (with slip joints to allow for thermal expansion) to protect the ceramic from erosion. In many cases this design is more economical than externally insulated equipment because it allows use of less expensive lower-alloy structural materials. 

Mandrel must remain motionless during pass of carriage and thenxotate a precise amount near 180° while carriage dwells. Fibers must be held close to support shaft during mandrel motion or fibers will slip. 

For successful filament winding, it must be possible to hand-wind with no sideways slipping of fibers on mandels surface. 

Even in a homogeneous solid elastic wheel the distortion is complex and requires sophisticated methods to arrive at a precise relation between force and slip. For tires this is even more difficult because of its complex internal structure. Nevertheless, even the simplest possible model produces answers which are reasonably close to reality in describing the force-slip relation in measurable quantities. This model, called the brush model—or often also the Schallamach model [32] when it is associated with tire wear and abrasion—is based on the assumption that the wheel consists of a large, equally spaced number of identical, deformable elements (the fibers of a brush), following the linear deformation law... 

Analogous results have been found for stress relaxation. In fibers, orientation increases the stress relaxation modulus compared to the unoriented polymer (69,247,248,250). Orientation also appears in some cases to decrease the rate, as well as the absolute value, at which the stress relaxes, especially at long times. However, in other cases, the stress relaxes more rapidly in the direction parallel to the chain orientation despite the increase in modulus (247.248,250). It appears that orientation can in some cases increase the ease with which one chain can slip by another. This could result from elimination of some chain entanglements or from more than normal free volume due to the quench-cooling of oriented polymers. 

The. differences in the properties of polymers go back to the chemical configurations. In simple terms, thermoplastics can be molded because they are iong-chain molecules that slip if pushed or pulled, especially at higher temperatures. Thermosets are cross-linked, so the long chains stay put under stress, strain, or heat. They dont melt, and they cant be molded once they set. The fibers get their flexibility and strength when the polymer molecules align during filament formation. 

In the debonded regions L z - (L - ) and (L - )<,z L), frictional slip occurs between the fiber and matrix and the stress transfer is governed by the Coulomb friction law for a constant coefficient of friction, p... 

Determination of the crack tip debond stress, ae, at a debond length, , is contingent to the condition that the fiber axial strain is equivalent to the matrix axial strain at the boundary between the bonded and debonded regions (i.e. duf z)/dz — diP a,z)/dz at z = (L — )). Within the debonded region, the matrix axial strain at the interface is greater than the fiber axial strain due to the relative slip between fiber and matrix. Therefore, combining Eqs. (4.8), (4.9) and (4.61) at the boundary, is obtained from... 

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