Material selection density

Why are barium- and iodine-based materials selected for contrast media The production of X-ray images depends on the differences between the X-ray absorbing power of various tissues. This difference in absorbing power is called contrast and is directly dependent on tissue density. To artificially enhance the ability of a soft tissue to absorb X-rays, the density of that tissue must be increased. The absorption by targeted soft tissue of aqueous solutions of barium sulfate and iodized organic compounds provides this added density through the heavy metal barium and the heavy nonmetal iodine. 

FIGURE 1 Materials selection chart for a material s strength as a function of density. 

Figure 8.5 Example of a materials selection design chart for modulus vs. density. Reprinted, by permission, from M. F. Ashby, Materials Selection in Mechanical Design, 2nd ed., p. 34. Copyright 1999 by Michael F. Ashby.

That is, ttcr is directly proportional to K c/cry) since oh is a fraction of Oy. Thus, the larger the value of acr, the more attractive is the material, since cracks can be easily detected without the use of sophisticated equipment. The Ashby plot of fracture toughness versus density (Figure 8.10) indicates that of the three classes of materials selected with Criterion 1, only the engineering composites and engineering alloys provide suitable possibilities for Criterion 2. Again, of the alloys, titanium, steel, nickel, and copper alloys are the best here. 

A component is presently made of brass. Use a modulus-density materials selection diagram, or look up the appropriate data, to suggest two metals which, in the same shape, would be stiffer. 

Gravimetric separation occurs due to a difference in mass between particles. Densiometric separation is more selective as it classifies materials by density, a property specific to each type of component. Size has no effect on densiometric separation. A number of methods exist to separate materials in these ways. 

Advantages Disadvantages Comparison of properties of selected materials [8] Density Unidirectional tensile (g cm4) strength (GPa) ... 

Single-crystal OFETs provide a unique tool for the express analysis of transport characteristics of new molecular materials with defect densities much smaller than those in TFTs. Therefore, even though large-scale applications will ultimately rely on thin films, research on single-crystal OFETs can play an important role in the material selection for applied devices. The case of rubrene perfectly illustrates this point. The unprecedented quality of OFETs based on vapor-grown rubrene crystals has stimulated work on the deposition of rubrene thin-films from solution Stingelin-Stutzmann et al. have recently demonstrated solution-processed rubrene TFTs with high mobility (up to 0.7 cmWs at room temperature) [111]. 

Studies on the mechanical behavior of the mitral leaflet tissue have been conducted to determine the key connective tissue components which influence the valve function. Histological studies have shown that the tissue is composed of three layers which can be identified by differences in ceUularity and collagen density. Analysis of the leaflets under tension indicated that the anterior leaflet would be more capable of supporting larger tensile loads than the posterior leaflet. The differences between the mechanical properties between the two leaflets may require different material selection for repair or replacement of the individual leaflets [Kunzehnan et al., 1993a,b]. 

Ashby [16] has created material selection charts displaying property clusters for different material t5rpes by plotting one property against another (for example, modulus versus relative cost). These charts are overlaid with the contours for applications-based property indices (such as modulus over density times cost), as schematically displayed in Figure 5.5. This permits selection of materials according to application specifications. These charts have been developed for several important mechanical and thermal properties and for the easiest environmental effect to measure, namely energy. It would be feasible to expand these charts to include further environmental parameters, if quantitative measures of environmental impact were to be developed. 

Material selection for structural members depends on a number of factors, including the density of the material, its strength, its toughness, its reaction to the surroundii environment, and its appearance. In this example, we will only consider the strength of the material as the 5 mm design factor. The average normal stress in the member is given by... 

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