Procedure and Instruments for the Material Damage Assessment by the LM-Hardness Method on the In-Service Scratching of S
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PROCEDURE AND INSTRUMENTS FOR THE MATERIAL DAMAGE ASSESSMENT BY THE LM-HARDNESS METHOD ON THE IN-SERVICE SCRATCHING OF STRUCTURE ELEMENT SURFACES N. R. Muzyka,a V. P. Shvets,a,1 and A. V. Boiko
UDC 620.178.14
b
The procedure for the material damage assessment by the LM-hardness method, consisting of the in-service scratching of structure element surfaces and employing portable instruments for its implementation, is described. These instruments can provide the rapid analysis of damage of a structural element to be diagnosed, continuous measurement of axial displacements of the embedded scratching tip, moving over the surface of this element, systematization, and statistical processing of experimental data for Weibull homogeneity coefficient computations. The latter results derived via the LM-hardness method are used to assess the damage rate of the material. The advantage of these instruments is their high accuracy and performance in measuring a large number of axial displacements of the tip necessary for statistical processing as well as actual testing on vertical, ceiling, and inclined surfaces of structural elements. Keywords: material damage, portable instruments, scratching tip, scattering of axial tip displacements, Weibull homogeneity coefficient. Introduction. Studies on the material damage are currently central for critical structure elements operating at in-service thermomechanical loads. Standards [1] regulating the check for damage of products are based on the procedures for evaluating the material damages by the change in its mechanical characteristics before and after the service life: hardness-determined yield limit and ultimate strength [2, 3], that gain wider acceptance due to their availability, ease of implementation, and minimization of costs for testing. Among the procedures for evaluating the mechanical characteristics of materials based on hardness assessment, let us note an ingenious procedure of instrumented indentation, involving the plotting of hardness diagrams [4]. The hardness method cannot always provide the evaluation of damage for the material of structural elements, e.g., for the elements with a small surface area through a large number of hardness measurements according to standard requirements [5, 6]. The most promising technique offering a large number of data for statistical processing of mechanical test results is the sclerometric method. It consists of scratching the surface of a product with an indentor tip at a constant load and measuring the scratch parameters, which are compared with hardness [7–9]. The theoretical grounds of the scratching method are described in [7, 8]. This method is not standardized in Ukraine; the data are cited in [10, 11]. A possibility of getting multiple values of scratch parameters on its small length permits replacing the experimental hardness measurements necessary for its statistical processing [12, 13]. However, the relation between a
Pisarenko Institute of Problems of Strength, National Academy of Sciences of Ukraine, Kiev, Ukraine ( shv
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