Apparent hardness

It is observed that indentations made with low loads on an indenter are smaller than expected from the sizes made with high loads. Thus the apparent hardness of a specimen increases as the indentation size decreases. This is known as the indentation size effect (ISE). It has been given a variety of interpretations, but the most simple is that it is associated with friction at the interface between the indenter and the specimen (Li et al., 1993). 

ISO 7267-1 1997 Rubber-covered rollers - Determination of apparent hardness - Part 1 IRHD method... 

It has been stated previously that hardness readings are influenced by test piece thickness. Consequently, the term standard hardness refers to measurements made on standard test pieces, and measurements on non-standard test pieces are called apparent hardness. 

Generally, the apparent hardness will increase as the test piece thickness is reduced because of the effect of compression against the rigid test piece support. 

There is, apparently, hardly any orientation of the molecules when they are adsorbed on charcoal. This is due to the rather unspecific nature... 

If test pieces are too thin, the base material has an effect, and different results may also be obtained on curved surfaces. Measurements made on nonstandard test pieces arc sometimes referred to as apparent hardness measurements. 

Fig. 3.13 Change in apparent hardness AH in a-AI2O3 as a function of 100 keV He-ion fluence at irradiation temperatures 300, 470, 670 and 870 K [11], With kind permission of Elsevier...

The apparent hardness of these carbides naturally depends on the composition and purity if cast materials are measured, and on the annealing temperature if the pieces were sintered from powders. Because these variables cannot be easily related to the fundamental property of the material, only microhardness values of reasonably well-characterized material have been listed. 

Figure 1.2. Grain size effects in microhardness testing, (a) Results from tungsten carbide cutting-tool compositions, (b) Apparent hardness changing as grain size to indent size decreases.

Scenario two We define as the diameter of a bare SWCNT and D2 as the new effective diameter of the SWCNT. The PEDOT PSS layer is now included in the hard-core diameter. This scenario describes the case in which the PEDOT PSS layer is taken to be an impenetrable layer, which simply increases the apparent hard-core diameter of the SWCNT. This would be a reasonable approximation if the mobility of the layer is low in the melt state [minimal flow]. The change in the percolation threshold is still viewed in terms on the SWCNTs themselves, and not in terms of the additional PEDOT PSS. For this reason, the original connectedness criterion remains unchanged. This situation is schematically illustrated in Figure 6.7, along with the Equation 6.1 rewritten for scenario two. 

The increase in density and apparent hardness produced by steam treating is illustrated in the micrograph of a sintered steel (Fig. 4). By filling... 

Before leaving the topic of normal hardness it is appropriate to mention further the role of lubrication. The effect of lubrication is to produce a reduction in the apparent hardness see Figure 7. Lubrication influences the stress fields and facilitates both elastic relaxation and plastic flow. First order theoretical treatments are available. ... 

Figure 12 shows as a function of 6 for PTFE and PMMA. The trend is similar to that seen in the normal hardness (see Figure 6) for PTFE but this is not the case for PMMA. Also shown in Figure 12 is the influence of lubrication on for PMMA. Unlike the normal hardness behaviour, lubrication increases the apparent hardness, although for the PMMA system there are several... 

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