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Page 916 of 939 Results 9151 - 9160 of 9382

Laurence Brice
THE INFLUENCE OF INDENTER CHARACTERISTICS ON HARDNESS MEASUREMENTS

This paper details work carried out to determine the influence of indenter geometry on measured hardness values for both Vickers and Rockwell hardness methods. For Vickers Hardness, the effect of indenter angle is quantified, and for Rockwell Hardness, the effect of varying both cone angle and tip radius is investigated.

Samuel Low, James Fink
EFFECTS OF BENDING IN BRASS ROCKWELL B SCALE TEST BLOCKS

As part of a project to produce primary hardness reference blocks for the Rockwell B hardness scale at the National Institute of Standards and Technology (NIST), studies were conducted to observe the stability of the hardness value of the blocks over a period of time and with use. A study of brass test blocks at the 42 HRBW level revealed some interesting instability results when tested using the NIST standardizing machine with it’s large diameter sample support.
After a relatively small number of indentations, each block exhibited an abrupt change in the apparent hardness of the test block. Examination of this phenomena revealed that the abrupt change in hardness was the result of a combination of the bending of the block and the use of the NIST machine’s large diameter flat anvil. This paper discusses the reasons that block bending affects the hardness measurement.

E. Aslanyan, A. Doynikov, V. Pivovarov
METROLOGICAL CHARACTERISTICS OF THE NATIONAL SHORE D SCALE HARDNESS STANDARD

Design specifics and study results are provided for the new National Shore D scale hardness standard. At the metrological study of the standard the calculations of uncertainty in measurements with two methods are considered: in accordance with the international guide on expression of uncertainty in measurement and in accordance with the principles based on the scales of order properties.
According to the metrological study, the standard ensures the reproduction and dissemination of the scale in the actually used range of HSD numbers of 20 to 102 with an HSD uncertainty of no more than 0.5.

Anton Štibler, Konrad Herrmann
UNCERTAINTY EVALUATION OF THE REFERENCE HARDNESS STANDARD OF SLOVENIA

A commercial hardness testing machine has been provided to represent a reference hardness standard in Slovenia. Various hardness scales which are important for calibration purposes are realized on this machine. The evaluation of measurement uncertainty is one of the most important tasks for establishing this reference standard. Therefore the influence quantities contributing to the uncertainty are determined and the calibration of the machine by direct and indirect method is carried out. Calculations of measurement uncertainties for Brinell, Vickers and Rockwell hardness scales are presented. The hardness scales for Brinell HBW 2,5/187,5; HBW 2,5/62,5; HBW 2,5/31,25, Vickers HV 30 and Rockwell are subject of uncertainty determination in this paper.

V. Augutis, R. Ramanauskas, V.Vasauskas
MEASUREMENT OF THE MECHANICAL STATE OF SUBSURFACE LAYERS BY EDDY-CURRENT METHOD

Methods of structural strength and lifetime control for short and safe components are traditionally based on the most structural and functional materials. Mechanical tests do not give a reliable data because of inconsistency of wear and fracture mechanism of specimens and real structural members. For the structural members the essential charges of anisotropy (texture) of the initial material occur after various technological operations. Because of this it is necessary to develop nondestructive methods of structure control of structural members under loading directly in technological process, that subjects components to a 100% test (i.e. testing of all items) and which can guarantee their safety. The determination of Young’s modulus (E), hardness (H), and strain hardening exponent (n) by means of indentation experiments can be successfully achieved by establishing the relation between the bulk tensile response of a material and the local indentation test. The uses of indentation tests are also relevant of the structural integrity assessments of components, where tensile specimens may not be readily available. Alternative methods are required; therefore we turn to nondestructive methods directly applied to the structure number, such as eddy-current technique. The objective of the study was to determinate and quantify the changes in the magnetic and mechanical properties in the layers of microstructure after quenching, the hardening depth and surface hardness using CS-pulsed eddy current technique, and to correlate them with technological parameters.

Hiroshi Yamamoto, Takashi Yamamoto, Hiroyuki Kawashima, Mikie Shibata
ISO HARDNESS STANDARDS INDENTATION HARDNESS TESTS AND HARDNESS STANDARD BLOCKS

ISO standards for hardness are established from metrological standards for force, length, etc. and daily control requirements via hardness standard blocks. The authors have already stated that the unification of loading speed via ISO standards is important both industrially and economically. In consideration of the international importance of ISO standards for hardness testing, the authors review the current ISO specifications in this report, particularly their definition of loading speed, tolerances for Rockwell reference loads, and other test-block requirements, based on our own experiments. Although it may be necessary to have continuous experimental findings using various hardness testers and test blocks, the following conclusions can be said at present.
(1) As a result of reviewing the basis of defining test force application, it can be generally concluded that LRT would be more appropriate than the indentation velocity as a basis of defining the test force application for indentation hardness tests.
(2) Considering the experiment results and the present situation concerning testing machine and method, the tolerances for the first and second reference loads for Rockwell hardness should be specified independently, and it may be necessary to loosen the tolerance for the second reference load.
(3) In the future, it is hoped that the test load tolerances for overall indentation hardness tests will be reviewed by studying the method of testing the dynamic load being applied during hardness testing, rather than the checking mass of weight or static load.
(4) As regards the ISO requirement for hardness block thickness, it is desirable that that for micro Vickers blocks should be 5 mm or more, and that for non-ferrous HR blocks should be 7 mm or more, based on a through consideration of the characteristics of individual testing methods, test forces, and block materials, as is the case with JIS standards.
(5) It has been confirmed that high-precision hardness blocks play an important role in the experimental verification of various aspects of hardness testing.

Vytautas Vasauskas, Vytautas Capas
PARTICULAR ASPECTS IN THE CALIBRATION AND APPLICATION DYNAMIC AND STATIC HARDNESS

The paper summarizes some results obtained at investigation of the main quantities influencing the uncertainty of measuring dynamic hardness. Some parameters concerning the force and time behaviour for full test cycle (loading and unloading) is discussed in terms of a systematic characterization of the dynamic set up used. The technique parallels the method for static indentation hardness determination and allows direct comparisons between dynamic and static hardness measurements.

L. Ma, S. Low, J. Song, J. Zhou
DETERMINING MECHANICAL PROPERTIES OF O1 TOOL STEEL FROM REVERSE COMPUTATION OF INDENTATION MEASUREMENT

Besides obtaining the hardness of materials, the indentation test has also been developed as a popular method for investigating mechanical properties. There exist some empirical or semi-analytical methods for determining the hardness, Young’s modulus and work hardening exponent from indentation experiments. In this paper, a reverse computation method is introduced to determine the elastic modulus and stress-strain curve of O1 tool steel from the Rockwell C hardness (HRC) indentation test combined with finite element analysis (FEA) simulation. The forcedepth data from the HRC spheroconical indentation measurement is used to start an iterative FEA simulation procedure to extract the elastic-plastic stress-strain relationship which is consistent with the experimentally measured data. The reverse computation results agree well with HRC test results.

Sheau-shi Pan, Chiu-Hsien Chen, Chi-Sheng Chang
EVALUATION OF THE UNCERTAINTY DUE TO ABBE’S ERROR FOR PRIMARY ROCKWELL HARDNESS STANDARD SYSTEM

The Primary Rockwell Hardness Standard System was established in the Center for Measurement Standards since July 1996 till June 1997. During the time, a laser interferometer, HP10737R 3-axis compact interferometer system, was substituted for the optical linear scale and combined with the mechanical structure of the original system to measure the Rockwell Hardness nominated values from 20 HRC to 70 HRC. Subsequently the laser interferometer was performed the measurement of the pitch and yaw of the indenter when the hardness was measured; then we evaluated the uncertainty caused by the Abbe’s error, pitch and yaw. The results showed that the expanded uncertainty of the primary Rockwell hardness standard system due to the Abbe’s error of the indenter was 0,046 HRC at the confidence level of 95%. The expanded uncertainty caused by the angle difference between the indenter moving axis and the measuring optical path was 0,0028 HRC at the confidence level of 95%.

Renato R. Machado, Tácito B. Pinto, Itamar Ferreira
COMPARISON BETWEEN CONVENTIONAL ROCKWELL HARDNESS TESTING AND INSTRUMENTED INDENTATION TESTING

With base in the precepts and technical procedures of ISO 6508-1 standard and ISO/FDIS 14577-1 standard draft, Rockwell hardness testing and instrumented indentation testing (IIT) were carried out using a universal testing machine, through adaptation of a system developed for these ends. The results pointed out a good relation between the two hardness tests, taking into account that IIT can provide other materials parameters besides being the simplest method, not requiring any preliminary force or operator influence. Nevertheless, it was observed the necessity of the improvement of the used system, regarding the monitoring of zero-point.

Page 916 of 939 Results 9151 - 9160 of 9382