Depth of penetration

The Stsndard Depth of Penetration is defined as that depth at which the eddy current strength has dropped to 37% of that at the surface. 

Knoop developed an accepted method of measuring abrasive hardness using a diamond indenter of pyramidal shape and forcing it into the material to be evaluated with a fixed, often 100-g, load. The depth of penetration is then determined from the length and width of the indentation produced. Unlike WoodeU s method, Knoop values are static and primarily measure resistance to plastic flow and surface deformation. Variables such as load, temperature, and environment, which affect determination of hardness by the Knoop procedure, have been examined in detail (9). 

A special coil configuration is used to heat thin strips of metal that caimot be heated efficiently with a coil that encircles the load, as the strip thickness is small compared to the depth of penetration. The transverse flux induction coil is positioned on either side of a strip to produce a uniformly heated strip with good efficiency in a much smaller space than conventional radiant or convective strip heating furnaces (6). 

The relationship between depth of penetration and the Rockwed hardness number is... 

Most instmments make use of a probe geometry which gives an increasing area of contact as penetration proceeds. In this way, at some depth of penetration, the resisting force can become sufficient to balance the appHed force on the indentor. Unfortunately, many geometries, eg, diamonds, pyramids, and cones, do not permit the calculation of basic viscoelastic quantities from the results. Penetrometers of this type include the Pfund, Rockwell, Tukon, and Buchholz testers, used to measure indentation hardness which is dependent on modulus. 

Toners and Tinted Sealers. These materials are usually pigments dispersed in nonpenetrating lacquers. In some instances, solvent or spirit dyes can be used to improve clarity. The soHds of the vehicle can be adjusted to control the depth of penetration into the substrate. 

Eor a food container, the amount of sorption could be estimated in the following way. Eor simple diffusion the concentration in the polymer at the food surface could be estimated with equation 3. This would require a knowledge of the partial pressure of the flavor in the food. This is not always available, but methods exist for estimating this when the food matrix is water-dorninated. The concentration in the polymer at the depth of penetration is zero. Hence the average concentration C is as from equation 9. 

Penetration theoiy often is used in analyzing absorption with chemical reaction because it makes no assumption about the depths of penetration of the various reacting species, and it gives a more accurate result when the diffusion coefficients of the reacting species are not equal. When the reaction process is veiy complex, however, penetration theoiy is more difficult to use than film theory, and the latter method normally is preferred. 

Figure 17.12 Corroded area beneath a tubercle on the external surface. The shiny black corrosion product has been partially removed to reveal the depth of penetration.

At a certain depth, the current density reduces to Me = 0.368 of the value at the surface. This depth is termed the depth of penetration, 5p. Of the total heal generated in such conductors, alinosl 80% occurs within this depth (annulus). In other words, around 90% of the total cunenl heal generated 0.9 = 0.8 is concentrated in this area alone. This depth can be represented by... 

Figure 31.11 Skin effect in tubular Isolated conductors in terms of depth of penetration Sp...

Since the Wenner formula [Eq. (24-41)] was deduced for hemispherical electrodes, measuring errors appear for spike electrodes. To avoid errors in excess of 5%, the depth of penetration must be less than a 5. Soil resistivity increases greatly under frost conditions. While electrodes can be driven through thin layers of frost, soil resistivity measurements deeper than 20 cm in frozen ground are virtually impossible. 

Usually in calculating ac interference it is assumed that/= 50 Hz, soil resistivity p = 50 O m and with/= 16% Hz due to the greater depth of penetration, p = 30 m. The following distances from the pipeline on both sides of the center of the right-of-way rail are those in which the extent of the interference should be determined ... 

In this expression, z is the distance from the surface into the sample, a(z) is the absorption coefficient, and S, the depth of penetration, is given by Eq. 2. A depth profile can be obtained for a given functional group by determining a(z), which is the inverse Laplace transform of A(S), for an absorption band characteristic of that functional group. 

It should be noted that the total loss of head of a filter bed is in inverse ratio to the depth of penetration of the matter in suspension. In a normal wastewater treatment plant, the water is brought onto a series of rapid sand filters and the impurities are removed by coagulation-flocculation-filtration. Backwashing is typically performed in the counterfiow mode, using air and water. One type of common filter is illustrated in Figure 6, consisting of closed horizontal pressurized filters. 

It follows from the depth of penetration of the nucrowaves, which is calculated... 

Note A corrosion rate of 300 g m y " corresponds to a uniform depth of penetration between 50 and 60 for the ZA alloys. 

For detecting stress-corrosion cracks and estimating their depth of penetration, the ultrasonic technique and, to a lesser extent, A -radiography, have proved successful. 

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