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E. Aslanyan, A. Doinikov
ON EXPRESSION OF HARDNESS MEASUREMENTS RESULTS UNCERTAINTY

Approach to hardness measurements data processing has been examined. The basis of this approach is that the scales of hardness are, in accordance with the general measurements theory, scales of order. The advantage of the method consists in the fact that it is more adequate and simple which is characteristic of hardness measurements as such.

P. Grau, H.S. Leipner, D. Lorenz, A. Zeckzer
TRENDS IN THE DEVELOPMENT AND APPLICATION OF THE NANOINDENTATION METHOD

One of the most important trends now is the application of nanoindentation for fundamental investigations of elementary mechanisms of mechanical deformation under very high pressure in the local contacted region. Representative examples are given. We have studied in detail the homogeneous generation of dislocations at room-temperature by nanoindentation in locally dislocations-free monocrystals. The discontinuity of load-penetration depth-curve referred to as Pop-in-effect is the result of the nucleation of the first dislocation loops and subsequent drastic plasticity response of the material by indentation due to multiplication processes. The mechanical stresses responsible for this process were calculated in the framework of elastic contact theory (Hertz, Sneddon). The measured critical stresses for loop nucleation are in good agreement with theory of dislocations within the isotropic approach. Corresponding dislocation loops were proved by means of microscopy imaging techniques (transmission electron microscopy (TEM), cathodoluminescence imaging (CL), and imaging of dislocation-etched surfaces.

E. Reimann
MARTENS HARDNESS - MORE THAN JUST HARDNESS TESTING

Exemplary results of the instrumented indentation test within the macro region are presented to provide an insight into the potential of the Martens hardness test method and to deliver new knowledge. Measurements on reference test blocks are carried out using a Zwick hardness testing machine, which is equipped with digital measurement and control technology. Representative results show, for instance, the influences of test force, as is well-known from Vickers hardness, and of test parameters on the result gained. An overview describes the manifold uses of the hardness measurement head of Zwick, in R & D and in industrial applications.

M. Fujitsuka, T. Ishibashi, S. Sukigara, H. Amano, M. Ohki
STUDY ON EVALUATION METHOD OF DETERMINING YOUNG'S MODULUS USING ULTRAMICRO HARDNESS TESTER WITH A SMALL BALL INDENTER

The aim of this study is to determine Young’s modulus by means of measured indentation load, depth and elastic recovery displacement of an indenter during loading and unloading processes using a developed horizontal ultramicro hardness tester. In order to determine correctly Young’s modulus of materials in narrower and shallower area of nanometer or micrometer level, authors use very small ball indenters that are made by bearing ball of a diameter in 0.3 mm and 0.5 mm. Several metal specimens [carbon steel, stainless steel, high tension brass and aluminum alloy] are used in test. Young’s moduli of metal specimens calculated on the ball indentation theory show good agreements with that of uniaxial compression test. As a result, effectiveness of evaluation method of determining Young’s modulus with a small ball indenter is confirmed.

M. Tietze, M. Kompatscher
PREDICATIVE HARDNESS TESTING FOR PRODUCTION CONTROL AND MATERIALS DESIGN

In-situ high-temperature rebound hardness testing according to the EQUOTIP® principle is useful to study effects of secondary hardening on strength and thermal stability, e.g., of highly alloyed tool steels. In-line material characterization and in-production testing are now feasible and offer new possibilities for production control and materials design.

Th. Polzin, D. Schwenk
WORLD-WIDE UNIFIED SCALES FOR THE ROCKWELL HARDNESS TEST WITH CONICAL INDENTERS

The aim of this round robin test was to discover what needs to be done to achieve the worldwide unification of Rockwell hardness scales using diamond indenters (HRC, HRA, HRD, HR15N, HR30N and HR45N). These scales are the most commonly used and their unification is of high industrial importance. The current degree of unification at an international level was assessed by conducting a round robin test. Seventy four specially developed hardness test blocks were all calibrated by twelve laboratories in eleven countries and the results were compared. Test parameters were specified that were more precise than those required by the standards. The indenters used to make hardness measurements have a significant effect on the measured result. To separate these indenter effects, measurements were made using common indenters as well as the indenters normally used by the laboratories.

Th. Polzin, D. Schwenk
EXPERIENCES WITH THE DETERMINATION OF UNCERTAINTY BRINELL HARDNESS, PC PROGRAM

After the next revision of the Standards for hardness testing, a determination of uncertainty has to be. part of the Standards. In the following text two methods for the determination, proposed for the ISO Standards of hardness, are described and the implementation of both methods in an Excel-based file is explained.

K. Herrmann, A. Germak, F. Menelao, G. Barbato, G. Brondino
INDENTATION VELOCITY EFFECT ON MARTENS HARDNESS MEASUREMENT

The Martens Hardness (HM) is an important parameter characterising the elasticplastic properties of the to be investigated sample material which is derived from the instrumented indentation test. At present the standardisation of the instrumented indentation test in the framework of ISO/DIS 14577-1, -2, -3 is underway. This standard addresses the macro-, micro- and nanorange of the indentation test. The peculiarities of the nanoindentation test when measuring samples with thin coatings (coating thickness d < 2 µm) will be considered in ISO/CD 14577-4 for which inputs came from CEN TC 184/WG 5 and from the EU-project „INDICOAT“. Martens Hardness presents a number of advantages, but, as any newly defined method, requires a general analysis of influence quantities to determine the sensitivity coefficients necessary for the uncertainty evaluation. Indentation velocity was found to be one of the main influence quantities for Rockwell and Vickers scales, therefore its effect was evaluated in a previous work that indicated an effect much higher than expected. In that work some warning was given, because the analysis was based on the results obtained on a single Hardness Standard Machine, moreover based on a simple experimental plan that did not guarantee any separation of the effects of time and velocities. In the present work these drawbacks are overcome. The analysis is based on an experimental plan that takes into account the load increasing time, the velocity of the initial part of indentation and the velocity of the last part of indentation, that is for the Rockwell and the Vickers method the most important influence factor. Moreover, following the resolution adopted within the recent ISO TC 164/SC3 meeting during which Martens Hardness was extended to cover from nano to macro ranges, experiments are performed on each of these ranges and with different machines, delivering in that way more significant results.

R. Barbato, R. Boi, R. Ragazzini
DETERMINATION OF MICRO-INDENTATION HARDNESS OF ORGANIC COATINGS

Many industrial products have to be coated by organic materials not only for aesthetical reasons, but specially to prevent the integrity of the metallic substrate from corrosion attacks during their service life; then, the corrosion resistance of metallic component is often assigned to the physical properties of the coating material. A lot of specific tests are available in the field of surface treatment characterization, in order to assess mechanical, physical and durability properties of paints and varnishes. Among them, indentation hardness allows to investigate on the local properties of a painted layer, not only on the external surface but also into the coating thickness, making it possible to verify hardness at every depth of the layer; non-uniformity in hardness values can be referred to the painting process (curing conditions, coating material, etc.). Hardness measurement technique on the transversal section required particular attention in the specimen preparation; hardness tests were performed by using a Knoop indenter, according to the standard ISO 6441-1. In the present paper are reported the results of several hardness tests performed on the surface and on the transversal section of various aluminium painted samples, some of them partially polymerized to different degrees. The same results have been compared with the results of commonly used tests for coating characterization, as: Taber abrasion test, hardness pencils test, Buchholz indentation test and also impact test.

L. Ma, S. Low, J. Song
COMPARISON OF ROCKWELL B HARDNESS (HRB) TESTS USING STEEL AND TUNGSTEN CARBIDE BALL INDENTERS

Significant measurement differences occur in Rockwell B hardness (HRB) tests when using 1.588 mm diameter ball indenters made of steel and tungsten carbide (WC). In this paper, finite element analysis (FEA) is used to simulate the HRB indentation process using steel, tungsten carbide and rigid ball indenters on the same tested materials under the same testing conditions. The influence of the deformable indenters (made of steel and WC) on the HRB indentation is assessed by comparing their FEA results with those of a non-deformable rigid indenter. The deformations of both the indenters and tested materials during the loading and unloading period are analyzed. The effect of deformable ball indenters on HRB hardness measurement values is discussed and further verified by experiments.

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