Hardness indenters correlations between

Figure 1.3 Correlation between the Moh scratch hardness and Vickers indentation hardness scales.

Correlations between differing measures of hardness are discussed by Mott (1957). A correlation diagram for Mohs scratch hardness and indentation hardness in the case of minerals is given in Figure 2.11. 

FIG. 25.8 Correlation between indentation hardness and modulus (see Tables 13.12 and 25.4 for reference numbers). 

Another motivation for measurement of the microhardness of materials is the correlation of microhardness with other mechanical properties. For example, the microhardness value for a pyramid indenter producing plastic flow is approximately three times the yield stress, i.e. // 3T (Tabor, 1951). This is the basic relation between indentation microhardness and bulk properties. It is, however, only applicable to an ideally plastic solid showing no elastic strains. The correlation between H and Y is given in Fig. 1.1 for linear polyethylene (PE) and poly(ethylene terephthalate) (PET) samples with different morphologies. The lower hardness values of 30-45 MPa obtained for melt-crystallized PE materials fall below the /// T cu 3 value, which may be related to a lower stiff-compliant ratio for these lamellar structures (BaM Calleja, 1985b). PE annealed at ca 130 °C... 

It is found that the steady state C 7 is about 2.08x10" ar and 1.81x10" ar for the ion-irradiated Fe-9at%Cr alloy and Fe-12.5at%Cr alloy, respectively. In Heintze et al. (2011) correlation between Vickers-hardness/yield stress of neutron-irradiated materials and indentation hardness of both ion-irradiated Fe-9at%Cr and Fe-12.5at%Cr alloys was found, and the assumption that the SANS results can be transferred to the ion-irradiated materials, if the dpa-values agree, was manifested. According to this statement CD modeling of kinetics of a -phase in ion-irradiated Fe-9at% and Fe-12.5at%Cr alloys has been carried out. The value of that provides the best fit of CD results to SANS data is found to be about 3.4 x 10" J/m vs. 0.17 J/m in Gokhman et al. (2011), where TEM data for the neutron-irradiated Fe-12.5at%Cr alloy are taken. 

Koc Koch, T., Seidler, S. Correlations between indentation hardness and yield stress in thermoplastic polymers. Strain 45 (2009) 26-33. 

The microhardness technique is used when the specimen size is small or when a spatial map of the mechanical properties of the material within the micron range is required. Forces of 0.05-2 N are usually applied, yielding indentation depths in the micron range. While microhardness determined from the residual indentation is associated with the permanent plastic deformation induced in the material (see section on Basic Aspects of Indentation), microindentation testing can also provide information about the elastic properties. Indeed, the hardness to Young s modulus ratio HIE has been shown to be directly proportional to the relative depth recovery of the impression in ceramics and metals (2). Moreover, a correlation between the impression dimensions of a rhombus-based pyramidal indentation and the HIE ratio has been found for a wide variety of isotropic poljuneric materials (3). In oriented polymers, the extent of elastic recovery of the imprint along the fiber axis has been correlated to Young s modulus values (4). 

As pointed out above, the semicrystalline polymer can be considered as a two-phase composite of amorphous regions sandwiched between hard crystalline lamellae (Fig. 4.2(a)). Crystal lamellae ( c) are normally 10-25 nm thick and have transverse dimensions of 0.1-1 pm while the amorphous layer thickness, a, is 5-10 nm. As mentioned in the previous section, melt-crystallized polymers generally exhibit a spherulitic morphology in which ribbon-like lamellae are arranged radially in the polycrystalline aggregate (Bassett, 1981). Since the indentation process involves plastic yielding under the stress field of the indenter, microhardness is correlated to the modes of deformation of the semicrystalline polymers (see Chapter 2). These... 

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