Microhardness studies

The Knoop test is a microhardness test. In microhardness testing the indentation dimensions are comparable to microstructural ones. Thus, this testing method becomes useful for assessing the relative hardnesses of various phases or microconstituents in two phase or multiphase alloys. It can also be used to monitor hardness gradients that may exist in a solid, e.g., in a surface hardened part. The Knoop test employs a skewed diamond indentor shaped so that the long and short diagonals of the indentation are approximately in the ratio 7 1. The Knoop hardness number (KHN) is calculated as the force divided by the projected indentation area. The test uses low loads to provide small indentations required for microhardness studies. Since the indentations are very small their dimensions have to be measured under an optical microscope. This implies that the surface of the material is prepared approximately. For those reasons, microhardness assessments are not as often used industrially as are other hardness tests. However, the use of microhardness testing is undisputed in research and development situations. 

A. Flores, F. J. Balta Calleja, G. E. Attenburrow, and D. C. Bassett, Microhardness Studies of Chain-extended PE III. Correlation with Yield Stress and Elastic Modulus, Polymer, 41, 5431 (2000). 

On the other hand, microhardness studies of short paraffin crystals reveal the influence of the molecular packing and hence of the chain ends on b (Ania et al, 1986). 

Mina, M. R, Ania, R, Balta Calleja R and Asano, T. 2004. Microhardness studies of PMMA/natural rubber blends. Journal of Applied Polymer Science 91(1) 205-210. 

Mina, M. R, Hague, M. E., Balta CaUeja, P. J., Asano, T., and Alam, M. M. 2004. Microhardness studies of the interphase boundary in rubber-softened glassy polymer blends prepared with/without compatibilizer. Journal of Macromolecular Science B Physics 43(5) 1005-1014. 

M. Krumova, C. Klingshirn, F. Haupert, K. Friedrich, Microhardness studies on functionally graded polymer composites, Composites Science and Technology 2001, 61, 557. 

F.J. (2009) From the glassy state to ordered polymer structures a microhardness study. Polymer, 50, 729-746. 

Boyanova M and Fakirov S (2004) Effect of an obstacle during processing on the weld line of injection-molded glassy polystyrene Microhardness study. Polymer 45 2093-2098. 

Garcia Gutierrez M C, Rueda D R, Balta Calleja, F J, Kuehnert I and Mennig G, (1999) Microhardness study across the weld line in doubly injection-molded glassy polymers, J Mater Sd Lett 18 1237-1238. 

Balth Galleja F J (1994) Microhardness studies of polymers and their transitions. 

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. 

Dmitrev S. D., 1949, Izuchenie mikrotverdosti kristallicheskikh poverkhnostei (Studies on Microhardness of Crystalline Surfaces), Dissertation, Leningrad. ... 

Teeth fulfill very specific functions and it can be safely assumed that the tooth structure is finely tuned for this purpose. The dentin structure is clearly anisotropic, with all the mineralized fibrils being located on one plane, and all the tubules oriented perpendicular to this plane. It is therefore most surprising that in terms of microhardness, dentin is isotropic. This has recently been confirmed in a careful study in which root dentin microhardness was measured at the same precise location in three orthogonal directions [33],... 

Deformation induced by indentation. The deformation induced in single crystals of San Carlos (Arizona, USA) olivine around the in-denter in a Vickers microhardness test has been studied by Gaboriaud... 

Microsegregation was studied by electron microprobe analysis of samples cooled at 0,5°C/s and quenched from just below the solidus temperature. Line scans were performed in selected areas of the specimens. Before analysis the samples were etched and the lines to be traversed were marked with microhardness indentations. Strongly etched specimens were repolished before measuring. Two lines were selected from different areas in each specimen, on the same principle as that for selecting lines for dendrite arm measurement. Consequently, in most cases secondary dendrite arms were crossed at right angles but some primary dendrites were intersected also. A typical example of a traverse for analysis is shown in figure 1.9. 

The measurement of local mechanical properties is an important step in understanding of the macroscopic behavior of multiphase materials. The indentation hardness test is probably the simplest method of measuring the mechanical properties of materials. Figure 12.2b shows the evolution of the microhardness as a function of the thermal treatment temperature of a Nasicon sample. The use of load-controlled depth-sensing hardness testers which operate in the (sub)micron range enables the study of each component of the composite more precisely. 

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