Microhardness determination

The studies carried out consist of the megascopic description of the master columns study of thin sections for maceral assessment, determination of maceral composition on polished blocks in reflected light, determination of mean maximum reflectance values on polished pellets, proximate analyses of selected petrographic zones, hot stage studies on vitrinoids to determine the thermal behavior at various temperatures, electron microprobe and spectrochemical studies of selected zones to determine the nature of ash forming elements, analyses of certain zones petrographically important to determine the variation of total carbon, and hydrogen and microhardness determinations on certain macerals. 

Khrushchev M. M., Berkovich E. S., 1943, Mikrotverdost, opredelaemaya metodom vdavlivaniya (Microhardness Determined by Indentation Method). Izd. AN SSSR, Moskva. 

For this reason one has to revise the deformation mechanism during microhardness determination commonly used for complex systems comprising components or phases with glass transition temperatures below room temperature. For this purpose it is convenient to remember again the structural peculiarity of the system under investigation. The fact that the PBT crystallites are floating in a matrix of low viscosity has important consequences on the microhardness behaviour. Because they are floating in a liquid of low viscosity, the crystallites of PBT as well as the PBT amorphous phase cannot respond to the external stress in a way that demonstrates their inherent microhardness, however, one can measure the response of the crystallites embedded in the liquid matrix. 

In principal, microhardness determination is rather simple. The indenter may be a square based pyramid of diamond or sapphire with a face angle of a = 136° for the Vickers test, or a rhombic-based pyramid with angles between the edges at the top of P = 130° and = 172° 30 for the Knoop test. The load P between 2 and 200 pond is... 

The connection of microhardness, determined according to the results of the tests in a very localized microvolume, with such macroscopic characteristics of polymeric materials as elasticity modulus E and 5deld stress is another aspect of the problem. At present a large enough number of derived theoretically and received empirically relationships between E and exists [7, 8],... 

Another aspect of the problem is the interconnection of microhardness, determined by the results of tests in a very localised microvolume, and such macroscopic properties of polymeric materials as the elasticity modulus E and the yield stress Oy. At present a large number of relationships derived theoretically and obtained empirically between H, E and Oy exist [58, 59]. 

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). 

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