Experimental detection of micro-destructions viscosity in central and boundary areas of brittle samples while loading on the substrate by vickers pyramid

DOI: 10.34759/vst-2019-4-230-239

Аuthors

Ushakov I. V.^*, Simonov Y. V.^**

National University of Science and Technology "MISIS", 4, Leninsky Prospect, Moscow, 119991, Russia

*e-mail: ushakoviv@mail.ru
**e-mail: MAK.101@yandex.ru

Abstract

The main purpose of the work consists in developing the earlier proposed technique for viscosity detection of micro-fracture of thin brittle amorphous nano-crystalline samples.

The regularities of deformation and fracture under local loading of solid thin samples of nano-crystalline material by Vickers pyramid are determined experimentally. The main studies were performed on amorphous metallic alloy Co_71,66Si_17,09B_4,73Fe_3,38Cr_3,14, converted into the nano-crystalline state by controlled isothermal annealing.

The dependency of the symmetry of micro-patterns of destruction from the load value and a distance to the sample boundary was established. It is established that with the load growth occurrence of symmetry elements starts to be observed in the initially asymmetric fracture patterns. Statistical analysis of symmetric cracks, as well as the distances between them, allows find the micro-destruction viscosity of the material. At a certain optimal load, the probability of symmetrical micro-patterns formation is maximal. A further load increase leads to the symmetry reduction, and, accordingly, to the decrease of micro-destruction viscosity calculation accuracy.

For the first time, a technique for determining the minimum allowable distance to the boundary of a thin sample, on which the micro-destruction viscosity determining was possible, was proposed. It was established that the optimal load value while determining the micro-fracture viscosity near the sample boundary coincides with the value of such for the central areas.

For the first time, mechanical testing modes, which allow obtain symmetrical and analyzable micro­patterns of destruction were determined. These conditions include the following: using the optimal load on the indenter; accounting for the allowable distance between the adjacent loading areas and a distance from the loaded area to the sample boundaries. Based on the experimental results analysis, algorithms for to determining the optimal load on the indenter and the allowable distance to the sample boundary have been developed. The obtained results allowed improve the earlier proposed technique for micro-fracture viscosity detection by local loading of thin, hard and brittle samples.

Keywords:

micro-indentation, composites, viscosity of micro-fracture, mechanical testing, micro-cracks, coatings

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