Microhardness tests pressure

The Eq. (12.1) assumes that the apphed in microhardness tests pressure under the indentor is higher than the 5deld stress in quasistatic tests owing... 

The relationship (9.24) implies, that the exerted in microhardness tests pressure under indentor is higher than yield stress in quasistatic tests owing to restriction, imposed by undeformed polymer, surroimding indentor. However, in works [12, 16, 22, 27, 28] it has been shown that the value c can differ essentially from 3 and varied in wide enough limits 1.5-30. In the work [28] it has been found out, that for the composites HOPE/CaCO depending on strain rate s and type of quasistatic tests, in which the value Oj, was determined (tensile or compression) c magnitude varies within the limits of 1.80-5.83. To c=3 the ratio HJOy approaches only at minimum value s and at using Oy values, received by compression tests. Therefore, in the work [28] the conclusion has been obtained, that the value c=3 can be received only at comparable strain rates in microhardness and quasistatic tests and at interfacial boundaries polymer-filler failure absence. 

The octahedral pressure cells containing the samples were recovered from the multi-anvil experiment and either broken or cut in half, using a diamond wiresaw. In the latter case, the j -sialon samples were also halved in the axial direction. The specimens were then characterized with optical and scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron probe microanalysis (EPMA), powder X-ray diffractometry (XRD), and microhardness testing using the Vickers method. 

Relationship 9.35 implies that the pressure applied in microhardness tests under an indentor is higher than the yield stress in quasi-static tests because of the restriction... 

The Knoop hardness (HK) of a material is a measure of the residual surface changes after the application of pressure with a test diamond. The standard ISO 9385 describes the measurement procedure for glasses. In accordance with this standard, values for Knoop hardness HK are listed in the data sheets for a test force of 0.9807 N (corresponds to 0.1 kp) and an effective test period of 20 s. The test was performed on polished glass surfaces at room temperature. The data for hardness values are rounded to 10 HK 0.1/20. The microhardness is a function of the magnitude of the test force and decreases with increasing test force. 

The temperature dependence of the yield stress obtained in Si down to 275 °C was compared with microhardness data obtained down to room temperature (Fig. 8) [51]. In contrast to microhardness data, the yield stress values do not level off below 400 °C, which is consistent with the occurrence under the microindenter of the phase transition mentioned in Section 2.1.1 [50,52]. In the compression tests, the pressure was kept below the critical value for the onset of this transition. 

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