Three-dimensional reinforcements

The characteristic features of a cord—mbber composite have produced the netting theory (67—70), the cord—iaextensible theory (71—80), the classical lamination theory, and the three-dimensional theory (67,81—83). From stmctural considerations, the fundamental element of cord—mbber composite is unidirectionaHy reinforced cord—mbber lamina as shown in Figure 5. From the principles of micromechanics and orthotropic elasticity laws, engineering constants of tire T cord composites in terms of constitutive material properties have been expressed (72—79,84). The most commonly used Halpin-Tsai equations (75,76) for cord—mbber single-ply lamina L, are expressed in equation 5 ... 

Directed Oxidation of a Molten Metal. Directed oxidation of a molten metal or the Lanxide process (45,68,91) involves the reaction of a molten metal with a gaseous oxidant, eg, A1 with O2 in air, to form a porous three-dimensional oxide that grows outward from the metal/ceramic surface. The process proceeds via capillary action as the molten metal wicks into open pore channels in the oxide scale growth. Reinforced ceramic matrix composites can be formed by positioning inert filler materials, eg, fibers, whiskers, and/or particulates, in the path of the oxide scale growth. The resultant composite is comprised of both interconnected metal and ceramic. Typically 5—30 vol % metal remains after processing. The composite product maintains many of the desirable properties of a ceramic however, the presence of the metal serves to increase the fracture toughness of the composite. 

Fibrous Composites. These composites consist of fibers in a matrix. The fibers may be short or discontinuous and randomly arranged continuous filaments arranged parallel to each other in the form of woven rovings (coUections of bundles of continuous filaments) or braided (8). In the case of chopped strand mat the random arrangement is planar. In whisker (needle-shaped crystals or filaments of carbon and ceramics) reinforced materials the arrangement is usually three-dimensional and the resulting composites are macroscopically homogeneous. 

It should be noted that when there is no jet reinforcement of the flow, i.e., the exhaust hood is used in its conventional mode, then in the two-dimensional form of the Aaberg principle the fluid flow velocity due to the exhaust decays approximately inversely proportionally to the distance from the exhaust opening. However, for three-dimensional exhaust hoods the fluid velocity outside the hood decays approximately inversely as the square of the distance from the exhaust hood. Thus in the three-dimensional conventional hood operating conditions the hood has to be placed much closer to the contaminant in order to exhaust the contaminant than is the situation for the two-dimensional hood (see section on Basic Exhaust Openings). Thus for ease of operation it is even more vital to develop hoods with a larger range of operation in the three-dimensional situation in comparison with two-dimensional hoods. 

The toughest challenge and the greatest opportunity in chemical engineering for high-performance materials lie in the development of wholly new designs for composite solids. Such materials are typified by composites reinforced by three-dimensional networks and trass-works—microstractures that are multiply cormected and that interpenetrate the multiply cormected matrix in which they are embedded. In such materials, both reinforcement and matrix are continuous in three dimensions the composite is bicontinuous. Geometric prototypes of... 

Marloff, R.H. and Daniel, I.M. (1969). Three dimensional pholoelastic analysis of a fiber reinforced composite model. Exp. Mech. 9, 156-162,... 

This section examines the advantages and disadvantages of using three-dimensional textile preforms, especially through-the-thickness stitches, as the reinforcements for composites. Their major mechanical properties are compared with those of conventional two-dimensional composites, such as strength, stiffness, interlaminar properties, impact resistance and tolerance, etc. Dransfield et al. (1994) have recently given a useful review on the improvement of interlaminar fracture toughness of stitched composites. 

The zeolites are generally thought of as having three-dimensional rather than sheet or chain structures. The existence of tetrahedral ring linkages that produce chainlike substructures characteristic of the natural zeolitic species found as needles or fibers reinforces the earlier statement fibers can be constructed from any number of basic units that grow in a preferential direction. 

Figure 1.76 Types of fiber reinforcement orientation (a) one-dimensional, (b) two-dimensional, and (c) three-dimensional.

Much of what we need to know abont the thermodynamics of composites has been described in the previous sections. For example, if the composite matrix is composed of a metal, ceramic, or polymer, its phase stability behavior will be dictated by the free energy considerations of the preceding sections. Unary, binary, ternary, and even higher-order phase diagrams can be employed as appropriate to describe the phase behavior of both the reinforcement or matrix component of the composite system. At this level of discussion on composites, there is really only one topic that needs some further elaboration a thermodynamic description of the interphase. As we did back in Chapter 1, we will reserve the term interphase for a phase consisting of three-dimensional structure (e.g., with a characteristic thickness) and will use the term interface for a two-dimensional surface. Once this topic has been addressed, we will briefly describe how composite phase diagrams differ from those of the metal, ceramic, and polymer constituents that we have studied so far. 

Let us consider two hypothetical phases in our composite, A and B, without specifying their physical state. They conld be a polymer melt and a glass fiber reinforcement during melt infiltration processing, a metal powder and ceramic powder that are being snbjected to consolidation at elevated temperatnre and pressure, or two immiscible polymer melts that will be co-extruded and solidified into a two-phase, three-dimensional object. In any case, the surface that forms between the two phases is designated AB, and their individual surfaces that are exposed to their own vapor, air, or inert gas (we make no distinction here) are labeled either A or B. The following three processes are defined as these surfaces interact and form ... 

Using Equations 5.53-5.56 a three-dimensional non-isothermal simulation of a typical IP process has been performed using a finite element control volume technique [31,34-36], The density specific heat and thermal conductivity of the resin and reinforcement used in the simulations are given in Table 5.1. 

Discussion - The morphological properties of active fillers are important aspects of rubber reinforcement. The structure of the reinforcing filler is characterized by aggregates of primary particles, which form cavities for attachment and penetration of polymer molecules. The SEM pictures show that the three-dimensional morphology is basically maintained. 

Source discrimination was accomplished by examining a series of two- and three-dimensional plots of the obsidian source data. Discovery of graphical representations which show the clearest picture of inter-source versus intra-source variation, makes possible source discrimination with a high degree of confidence. The greater the number of elements that one can use to reinforce the observed discrimination the smaller becomes the chances for misassignment of artifacts when compared to the obsidian source database. 

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