Sheet texture

The notation hkl)[uvw specifies what is called an ideal orientation. Some metals and alloys have sheet textures so sharp that they can be adequately described by stating the ideal orientation to which the grains of the sheet closely conform. Most sheet textures, however, have so much scatter that they can be approximated symbolically only by the sum of a number of ideal orientations or texture components, and even such a description is inadequate. Thus, the deformation texture of brass sheet (70 Cu-30 Zn) is very near the ideal orientation (110)[Tl2]. But both the deformation and recrystallization textures of low-carbon sheet steel have so much scatter that the grain orientations present can be accurately represented only by a graphical description called a pole figure. 

There is not one, but several, diffractometer methods for measuring sheet texture. They fall into two groups, transmission and reflection, both being normally necessary for complete coverage of the pole figure. 

Preferred orientation in wire does not always take the form of a pure fiber texture. For example, the deformation texture of iron wire is usually considered to be a [110] fiber texture, but Leber [9.39] showed that a cylindrical texture was also present. Such a texture may be regarded as a sheet texture, (100) [011 ] for iron, wrapped around the wire axis. Thus at any point on the wire surface, a (100) plane is tangent to the surface and a [011] direction parallel to the wire axis. The presence of a cylindrical component in a fiber texture is disclosed by anomalies in the / sin curve the areas under the peaks ascribed to the fiber-texture component will not be in the ratio to be expected from the multiplicities [9.40]. 

A pole figure shows the distribution of a selected crystallographic direction relative to certain directions in the specimen. Texture data may also be presented in the form of an inverse pole figure, which shows the distribution of a selected direction in the specimen relative to the crystal axes. The projection plane for an inverse pole figure is therefore a standard projection of the crystal, of which only the unit stereographic triangle need be shown. Both wire and sheet textures may be represented. 

Sheet textures may also be represented by inverse pole figures. Here three separate projections are needed to show the distribution of the sheet normal, rolling direction, and transverse direction. Figure 9-24(b) is such a projection for the normal direction of the steel sheet whose (110) pole figure was given in Fig. 9-20 it was calculated from the crystal orientation distribution mentioned in Sec. 9-8. The distribution of the normal direction is also shown in (c), for the same material. This distribution was measured directly in the following way. A powder pattern is made of the sheet in a diffractometer by the usual method, with the sheet equally... 

The inverse pole figure is the best way to represent a fiber texture, but it offers no advantage over a direct pole figure in the description of a sheet texture. Inverse or direct, a pole figure is a two-dimensional plot that fixes, at a point, only a direction in space, be it crystal space or specimen space. Only the three-dimensional plot afforded by the crystal orientation distribution (Sec. 9-8) can completely describe the orientations present, and this approach, being quite general, is just as applicable to fiber textures as it is to sheet. 

This periodicity of about 500 nm has been reported for banded textures observed in both the thermotropic copolyesters and the aramids [407, 430, 439-445]. The lateral banded textures exhibited by some of the thermotropes and the pleated sheet textures exhibited by some of the aramids are observed only in materials which have a poorer degree of molecular orientation. The more highly oriented thermotropic and lyotropic fibers do not exhibit these textures. For instance, heat treated Vectran fibers do not exhibit any lateral banding. Likewise, Kevlar 149 exhibits a higher tensile modulus than Kevlar 49 [448], nearly 80-90% of theoretical predicted values. This is consistent with increased crystallinity and crystallite size, and without a pleated sheet structure. The relationship of the optical... 

Sheet textures can be defined by specifying the Miller indices of a plane parallel to the rolling plane hkl) and a direction parallel to the rolling direction [uvw (see [Lar74]). 

Patterned glass is made by applying texture to one or both glass surfaces by suitably embossed rollers. Applications include shower doors, furniture tops, room dividers, and windows. There is even an application for roller-applied Fourcault-type sheet texture for use in restorations of nineteenth century homes. 

Collation. Collation is the process by which the individual laminate pHes are assembled prior to curing in the press. The buildup of the laminate determines the final properties of the product. The topmost sheet in the buildup may be a texturing or embossing paper as well as being a release sheet to allow for separation of the laminate from the caul plate used to mold it. 

Plastic Sheet. Poly(methyl methacrylate) plastic sheet is manufactured in a wide variety of types, including cleat and colored transparent, cleat and colored translucent, and colored semiopaque. Various surface textures ate also produced. Additionally, grades with improved weatherabiUty (added uv absorbers), mat resistance, crazing resistance, impact resistance, and flame resistance ate available. Selected physical properties of poly(methyl methacrylate) sheet ate Hsted in Table 12 (102). 

Even when plastics are not a preferred material for the stmctural element of paneling, they are often iacorporated as a surface coatiag or sheet to enhance aesthetics. Some lay-ia ceiling panels for commercial and iastitutional appHcations consist of gypsum board covered with a poly(vinyl chloride) surface sheet to add a textured appearance. Many more are based on gypsum board or mineral wall with a fiber glass or PVC surface. 

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