Separation force, fiber

Desorption. Once equilibrium is achieved the fiber is withdrawn into the protective sheath. Immediately after, the sheath is inserted into the sepmm of a GC injector, the plunger is pushed down, and the fiber is forced into the injection insert where the analytes are thermally desorbed and separated in the GC column. 

ASTM D 2612-93a provides a method for measuring the fiber cohesion force required to cause initial separation of fibers in a bundle of fibers. This observed cohesive force is converted to cohesive tenacity based on the linear density of the fiber specimen. The method is not advi,sed for trade purposes but as an in-house quality check, since the coefficient of variation of the test using man-made fibers is in the region of 21%. or 15% with a single operator. The ASTM method advises the conditioning of the test sample to equilibrium with the standard atmosphere from the dry side of the hysteresis curve by-first preconditioning the test sample. Clearly, if the test siimple were to be conditioned from the wet side, the results would be totally uncomparable with tests conducted on preconditioned specimens,... 

The specimen consists of sliver or top mounted (initially on a paper carrier to prevent stretching or fiber separation during mounting) between the jaws of a CRE ten.sile testing machine, and a force extension curve is developed. From this is determined the cohesive force to the nearest 0.1 gf from the maximum point of the curve. The drafting tenacity is calculated by... 

In general, the fiber separation is more significant as the fiber content and fiber length are increased. Moreover, the fibers that are oriented parallel to the flow direction are more susceptible to fiber separation than the fibers that are oriented normal to the flow direction. Even in the case of SMC-CR or XMC, this phenomenon often is observed if continuous fibers are aligned in the parallel direction to the principal flow direction (see Fig. 3.21). If continuous fibers are aligned in the perpendicular direction to the principal flow, the fibers tend to buckle or bend due to the flow-induced drag force. Hence, the precharge placement usually covers nearly 90% of the mold surface in the case of SMC-CR and XMC. 

The interaction among the fibers is the principal reason for the fiber separation (a.k.a. fiber segregation) which results a non-uniform fiber volume fraction in the final part as stated previously (Hojo et al., 1988). The interactions among the fibers can be considered as a frictional force. Consider a single fiber in the fiber network as a sample fiber (see Fig. 3.35). The fibers that are in contact with the sample fiber can be classified into two categories the upstream fibers and the downstream fibers. In the squeezing flow, the resin velocity in the downstream is greater than that in the upstream. Hence, the downstream fibers move faster than the sample... 

If there is a difference between the fiber and resin velocities, the fiber is submitted to a drag force (see Fig. 3.36).The fiber separation velocity, which is the velocity difference between the fiber and the resin, can be obtained from the equilibrium condition between the fiber network force and the drag force. 

Figure 9. shows the dimensionless number X4 for different average fiber separations. At low fiber concentrations, the hydrodynamic forces dominate the lubrication forces. As the fiber concentration increases, the lubrication forces start playing the dominant role, to the point that hydrodynamic forces can be neglected. These results are in accordance with the observations made in experimental results [6,7] and raises the possibility of simplifying mechanistic simulations of fiber suspensions.. 

Other routes to reachieving filament separation have been described and rely on mechanical or aerodynamic forces to affect separation. Figure 4 illustrates one method which utilizes a rotating deflector plane to force the filaments apart while depositing the opened filaments ia overlapping loops (25). After the splayed filaments fall to the deposition surface or forming screen, a suction from below the disposition surface holds the fiber mass in place. 

The fundamental analysis of a laminate can be explained, in principle, by use of a simple two-layered cross-ply laminate (a layer with fibers at 0° to the x-direction on top of an equal-thickness layer with fibers at 90° to the x-direction). We will analyze this laminate approximately by considering what conditions the two unbonded layers in Figure 4-3 must satisfy in order for the two layers to be bonded to form a laminate. Imagine that the layers are separate but are subjected to a load in the x-direction. The force is divided between the two layers such that the x-direction deformation of each layer is identical. That is, the laminae in a laminate must deform alike along the interface between the layers or else fracture must existl Accordingly, deformation compatibility of layers is a requirement for a laminate. Because of the equal x-direction deformation of each layer, the top (0°) layer has the most x-direction ress because it is stiffer than the bottom (90°) layer in the x-direction./ Trie x-direction stresses in the top and bottom layers can be shown to have the relation... 

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