Anisotropy unidirectional

Anisotropic material In an anisotropic material the properties vary, depending on the direction in which they are measured. There are various degrees of anisotropy, using different terms such as orthotropic or unidirectional, bidirectional, heterogeneous, and so on (Fig. 3-19). For example, cast plastics or metals tend to be reasonably isotropic. However, plastics that are extruded, injection molded, and rolled plastics and metals tend to develop an orientation in the processing flow direction (machined direction). Thus, they have different properties in the machine and transverse directions, particularly in the case of extruded or rolled materials (plastics, steels, etc.). 

The major directions of changing porosity in DRP are schematically shown in Figure 9.22 [3,61], As a starting point, one can use the porosity of DRP of monospheres s0 = 0.36-0.42. Values of >s0 increase with particles anisotropy, roughness, and internal porosity, and also with the influence of wall effects at K> 0.1, and DIH > 0.05. Values of < (J are characteristic for polydis-perse particles when denser zones with ordered or unidirectional packings are formed, and also under forced densification and deformation of particles, correspondingly. 

There are essential differences between the systems we have presented here, even in the limit of very strong anisotropy. The RKKY spin glasses are Heisenberg systems with random unidirectional anisotropy. Ferrofluids frozen under zero field are Heisenberg systems with random uniaxial anisotropy, while an Ising system is characterized by parallel uniaxial anisotropy. 

Grain - The unidirectional orientation of rubber or filler particles occurring during processing (extrusion, milling, calendering) resulting in anisotropy of a rubber vulcanizate. 

Unidirectionally reinforced materials are more of a problem to test than multidirectional reinforcements because of the anisotropy of the properties. This anisotropy leads to differences in moduli, strain-to-failure, and other properties of the composite which allow failure of the material to occur in a mode other than that which the researcher may wish to investigate. 

Effect of Dopants on Thermoelectric Properties and Anisotropies for Unidirectionally Solidified n-Bi2Te3... 

In this work, HgBr2, Hgl2, SbBr.i and Sbis were used as the dopants. These dopants consist of combination Hg or Sb and Br or I. Each dopant was added in the unidirectionally solidified n-type Bi2Tes to form a n-type compound. The effects of each element were determined by the combination of the observed values of four specimens. Anisotropies in the... 

Anisotropy in the permeability begins to be more significant due to the different orientation of fractures and increasing differential stresses. The maximum anisotropy in permeability has a factor of 2 for the stress ratio 2. The model for this study has near-randomly distributed orientations of fractures. If the model has more unidirectional orientations of fractures, this effect of anisotropic stress will be more significant. 

Xu et al. [63] also address directionahty in a composite plate, which is more difficult to achieve because the inherent anisotropy of the medium. Figure 16.29(c) shows such directional pattern obtained through guided wave simulation in a unidirectional GFRP plate. A further extension of this concept to achieve continuous steering through a double spiral shape is presented in BaraveUi et al. [64]. 

The anisotropy of the mechanical properties, caused by unidirectional orientation, is clearly demonstrated by Fig. 1. It shows a microtome section of the wall of an injection-moulded beaker perpendicular to the direction of flow. Bending causes numerous cracks to be formed in the oriented surface layers but they stop abruptly at the unoriented spherulitic core, because this material does not split so easily. Samples taken parallel to the direction of flow do not show these premature cracks on bending, on the contrary, the samples are less brittle than unoriented material. 

For a material such as a unidirectional lamina that contains all of its fibres aligned in one direction, the conditions of transverse anisotropy apply. The stress/strain relationship can be written as (Eckold 1994, Herakovich 1998) ... 

II. 1.2b. 1.Thermal Expansion Thermal expansion of unidirectional SiC/RBSN composite is mainly a function of constituents volume fractions and measurement direction relative to the fiber, and is not affected by constituents porosity. Measurement of linear thermal expansion with temperature in nitrogen for the 1-D SiC/RBSN composites parallel and perpendicular to the fibers indicates a small amount of anisotropy (Fig. 5). This is attributed to small difference in thermal expansion coefficients of SiC fibers (4.2 x 10 ) and RBSN matrix (3.8 x 10 ) as well as anisotropic thermal expansion of carbon coating on SiC fibers. In the fiber direction, linear thermal expansion is controlled by the SiC fiber, and in the direction perpendicular to the fiber, it is controlled by the RBSN matrix. 

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