An Empirical Approach to Determining Rockwell Hardness Measurement Uncertainty (original) (raw)

Proposal for a practical procedure for the expression of uncertainty in hardness measurements

Hardness measurement is widely used in industrial applications for quality control and acceptance testing of products because it is fast, inexpensive and relatively non-destructive. Uncertainty evaluation is complicated because calibration procedures require the use of direct and indirect verification tests, but the effects on the measurand itself due to test parameters variations are difficult to predict, such as the force-time pattern, inelastic performances of Rockwell indenters and the numerical aperture for Brinell and Vickers indentations measurement. This paper starts by accepting as a matter of fact that standard specifications have demonstrated acceptable performance, indicating that their application is correct for most of the materials generally used. Accepting this premise, the next step was to try to translate the practice, confirmed by many years of experience, into the new language of uncertainty, strongly required by quality documents.

Experimental analysis on the influence quantities in the Rockwell C hardness test

Hardness is a conventional quantity defined by means operational rules in procedures described in the relevant standards. As it is well known, this method gives some problems on the side of uncertainty evaluation. The intrinsic limit is the difficulty to evaluate the sensitivity coefficients of all the influence parameters involved in the measurement procedure. This subject was recently faced in the framework of the European cooperation for Accreditation of Laboratories. IMGC has carried out an experimental analysis, limited to Rockwell C scale, within which a quasi-factorial experimental plan has been used to evaluate the influence of time and velocity of all indentation phases. The results of this analysis could be useful as support for the evaluation of uncertainty, made following the recent International and European guides.

TRACEABILITY OF INDUSTRIAL ROCKWELL, BRINELL, VICKERS AND KNOOP HARDNESS MEASUREMENTS

The measurement of hardness is used extensively by many of the world’s manufacturing industries. The conventional hardness tests are the most commonly used methods for acceptance testing and production quality-control of metals and metallic products. For these industries to be successful, it is important that measurements made by suppliers and customers agree within some practical limits. Measurement traceability is a key factor in assuring hardness measurement agreement. This paper discusses the traceability issues related to the measurement of conventional hardness, including calibration, verification and uncertainty.

Determination and Uncertainty Propagation of Sensitivity Coefficients in Rockwell Hardness Measurements

SSRN Electronic Journal

In the field of hardness measurements, a problem arises when trying to understand how different measurement parameters (speed of the indenter, force, thermal drift, etc.) affect the outcome of the measurement itself. Because the mathematical model defining hardness scales do not consider such factors, the simplest way to include additional influence parameters in the mathematical model is to introduce them linearly via sensitivity coefficients, which are obtained experimentally and thus characterized by uncertainties. Uncertainties of the sensitivity coefficients are in general not considered in the evaluation of the combined standard uncertainty of the hardness measurements. In this paper a general procedure is presented and applied to HRA and HRC measurements.

Installation and Uncertainty Evaluation of Reference Hardness Standard of Croatia

Reference hardness standard with HV1 – HV50 measuring range was installed at LIMS (Laboratory for Testing Mechanical Properties) at the end of 2007 with the aim of providing continuous improvement of the metrology infrastructure of Croatia. The evaluation of the measurement uncertainty is one of the most important tasks for establishing this reference standard. Therefore, the influence quantities contributing to the uncertainty were determined and the machine calibrated by direct and indirect method. In this paper the results of the measurements are presented and discussed. A reference hardness machine has been provided to represent the hardness reference standard in Croatia. The machine was made by Indentec, England, type 5030TKV Std. with hardness scale for Vickers. Vickers measurement in the range of force from 9,807 N up to 490,3 N should be realized with uncertainties which assure accurate measurement in the Croatian industry. This reference hardness machine is intended to: -sa...

Metrological Characterization of Hardness Indenter Calibration System

Journal of Physics: Conference Series

There are four main components constituting the conventional hardness scales, in all types of hardness measurements, from testing machines to standardizing ones : Force application, indentation size measurement, indenter and measurement cycle. To assure the quality, reliability and uniformity in hardness measurement in all over the world it is important to constitute traceability of each parameter to the base SI units and confirm the performance of the system as a whole. One of the most interesting subject to be discussed is the calibration of the geometrical properties of the diamond indenters used in Rockwell and Vickers scales, sphero-conical Rockwell and square-based pyramid Vickers diamond indenters. The indenters to be used in testing and calibration/standardizing machines are supposed to be in accordance with some international hardness standards , namely ISO 6507-2 [5] and ISO 6508-2 [2] for testing Vickers and Rockwell mach ines, respectively; ISO 6507-3 [6] and ISO 6508-3 [3] for Vickers and Rockwell calibration/standardizing machines, respectively, and relevant ASTM standards. This paper describes the metrological characterization of UM E Hardness Diamond Indenters Calibration System and the traceability of each measured parameter subject to calibrat ion.

Traceability in hardness measurements: from the definition to industry

Metrologia, 2010

ABSTRACT The measurement of hardness has been and continues to be of significant importance to many of the world's manufacturing industries. Conventional hardness testing is the most commonly used method for acceptance testing and production quality control of metals and metallic products. Instrumented indentation is one of the few techniques available for obtaining various property values for coatings and electronic products in the micrometre and nanometre dimensional scales. For these industries to be successful, it is critical that measurements made by suppliers and customers agree within some practical limits.To help assure this measurement agreement, a traceability chain for hardness measurement traceability from the hardness definition to industry has developed and evolved over the past 100 years, but its development has been complicated. A hardness measurement value not only requires traceability of force, length and time measurements but also requires traceability of the hardness values measured by the hardness machine. These multiple traceability paths are needed because a hardness measurement is affected by other influence parameters that are often difficult to identify, quantify and correct. This paper describes the current situation of hardness measurement traceability that exists for the conventional hardness methods (i.e. Rockwell, Brinell, Vickers and Knoop hardness) and for special-application hardness and indentation methods (i.e. elastomer, dynamic, portables and instrumented indentation).

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 world- wide unification of Rockwell hardness scales using diamond indenters (HRC, HRA, HRD, HR15N, HR30N and HR45N) (1) - (5). 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 (1). 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. Partners for the round robin test

Developing definitions of conventional hardness tests for use by National Metrology Institutes

Measurement: Sensors, 2021

This paper describes the process used by the Consultative Committee for Mass and Related Quantities-Working Group on Hardness (CCM-WGH) of the International Committee of Weights and Measures (CIPM) to develop international definitions of the conventional Rockwell, Brinell, Vickers and Knoop hardness test methods, for use by the National Metrology Institutes (NMI) that standardize hardness measurement.

Application of the software package of engineering analysis for improving the metrological assurance of hardness measurement

Ukrainian Metrological Journal, 2017

Application of the software package of engineering analysis for improving the metrological assurance of hardness measurement The article considers the application of the principle of computational modeling in the construction, improvement and research of the national measurement standards of Ukraine in the field of hardness measurement. The results of modeling research using the finite element method are presented. The methodology of research is proposed in order to improve the characteristics and reduce the uncertainty. The analysis of the further use of computational modeling for the study of components of the national measurement standards is given. The purpose of the article is to improve the research of the measurement standards, particularly, in preparation for international comparisons.