Strength-conductivity ratio

Example 3.5, In support members for cryogenic storage vessels and other equipment, it is desirable to minimize the heat transfer through the members but maximize the strength of the members at the same time. An important parameter in this situation is the strength-conductivity ratio. Determine the strength-conductivity ratio Sy/k at 22.2 K for (a) 2024-T4 aluminum, (b) 304 stainless steel, (c) K Monel, (d) beryllium copper, and (e) Teflon. 

Example 3.1 determined the strength-weight ratio of five materials of construction. Determine the strength-conductivity ratio of these same five materials. Rank order these materials from the most desirable material to the least desirable by these two criteria. Develop another index of merit for material selection that combines both of these criteria e.g., one that includes Sy, and p. 

Material Yield strength (MPa) Thermal conductivity" (W/mK) Strength- conductivity ratio... 

The current conditions can be varied in the most different ways. By a choice of concentrations, or by additions, the conductivity can bo increased or diminished also by raising or lowering the voltage. The height of the electromotive force developed in the ceil determines the current strength the ratio of the latter to the electrode surfaces gives the current density, and to the volume of the electrolytes, the current concentrations.1... 

It should be noted that in both equations, the conductivity ratio of a porous packing is independent of particle size, column length, or electric field strength. 

There are a variety of methods for supporting the inner shell within the outer shell and the cold transfer line within the outer line. Materials that have a high strength to thermal conductivity ratio are selected for these supports. Design of these supports for the inner shell must allow for shipping loads which may be several orders higher than in-service loads. Compression supports such as legs or pads may be used, but tension supports are more common. These may take the form of cables, welded straps, threaded bars, or a combination of these to provide restraint of the inner shell in several directions. 

Fig. 1. Temperature dependence of critical property ratios for uniaxial composite laminates and annealed stainless steel (a) ratio of thermal conductivity to Young s modulus (b) ratio of thermal conductivity to tensile yield strength (c) ratio of Young s modulus to density (d) ratio of tensile yield strength to density.

A 1000 MWh unit would require 1.6 Gg of material. The superconducting magnet requires low thermal conductance structural supports to transmit the magnetic loads from the 1.8 K conductors to the room temperature bedrock. In particular, it needs support struts with a high strength to thermal conductivity ratio, but low elastic modulus and a low strength to weight ratio are quite acceptable. 

Adhesive bonding consists of interposing a layer of an adhesive composition chemically different from the plastics to be bonded between the adherends. It is one of the most popular and versatile methods to join plastics. Some of its advantages are uniform distribution of stresses over the assembled areas, a high strength/weight ratio, a simplified means of assembling smaU or complex-shaped plastic parts, and in some instances thermal or electrical conductivity. 

Fi2. 9-7 fa-c> Correlation of modulus, tensile strength, conductivity and draw ratio for P(TV) fibers. After Reference [315], reproduced with permission. 

The strength to conductivity ratios for several materials employed in support members are listed in Table 7.11. The austenitic steels are most suitable for larger vessels, while Dacron webbing has been successfully used to support smaller inner vessels. 

Table 7.11. Strength-to-Conductivity Ratios for Typical Materials Used in Support Members...

Radiolytic oxidation alters most of the important properties of graphite, including strength, elastic modulus, work of fracture, thermal conductivity, permeability, and diffusivity but does not affect the thermal expansion coefficient or Poisson s ratio. The effects of radiolytic oxidation on the properties of a wide range of graphites have been studied in the U.K. [7,73,74] where it was found that, to a first approximation, they can be described by similar relationships ... 

This is an important relationship. It states that the modulus of a unidirectional fibre composite is proportional to the volume fractions of the materials in the composite. This is known as the Rule of Mixtures. It may also be used to determine the density of a composite as well as other properties such as the Poisson s Ratio, strength, thermal conductivity and electrical conductivity in the fibre direction. 

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