CRITERIA FOR LABORATORY ACCREDITATION IN THE FIELD OF FORCE METROLOGY:- CALIBRATION OF UNIAXIAL TESTING MACHINES

Transcription

1 CRITERIA FOR LABORATORY ACCREDITATION IN THE FIELD OF FORCE METROLOGY:- CALIBRATION OF UNIAXIAL TESTING MACHINES Approved By: Chief Executive Officer: Ron Josias Executive - Accreditation: Mpho Phaloane Revised By: Calibration STC Members Date of Approval: Date of Implementation: SANAS Page 1 of 8

2 CONTENTS: 1. Purpose and Scope Definitions and References General Requirements Measurements Calibration Certificates Authorship... 6 ADDENDUM 1: Schedule of Accreditation... 7 ADDENDUM 2: Amendment Record... 8 SANAS Page 2 of 8

3 1. Purpose and Scope The purpose of this document is to define the minimum technical requirements to be met by accredited laboratories in the field of Force metrology for the calibration of uniaxial testing machines in either tension and/or compression. This document is applicable to South African National Accreditation System (SANAS) Accredited Laboratories performing calibration of uniaxial testing machines. 2. Definitions and References 2.1 Definitions Loading Mode: The direction of an applied compression or tension force, about the principal axis of rotation Displacement: Amount of displacement (in millimetres) in particular direction Auxiliary measurement devices: Instrument for measuring changes in linear dimensions. For example extensometers, LVDTs, strain gauges, etc Elongation: Increase in the original gauge length at any moment during the test Percentage elongation (also referred to as strain): Elongation expressed as a percentage of the original gauge length Straining Rate: Time of elongation normally measured in seconds Testing machine: Device (or assembly of devices) for testing material specimens Reference force measuring instrument: Force measuring instrument that has been calibrated and tested with force standards traceable to national standards Accuracy class: Class of measuring instrument that meets certain metrological requirements that are intended to keep errors within specified limits Maximum permissible error: Maximum value of the error permitted by laws, regulations, or specifications for a given measuring instrument. 2.2 References ISO 376 ISO ISO ISO 9513: ISO 5893 OIML R 65 ISO 6892 ISO Calibration of force-proving instruments used for the verification of uniaxial testing machines. Metallic materials - Verification of static uniaxial testing machines. Part 1: Tension/compression testing machines - Verification and calibration of the force measuring system. Metallic materials - Verification of static uniaxial testing machines. Part 2: Tension creep testing machines - Verification of the force applied. Metallic materials - Calibration of extensometers in uniaxial testing Rubber and plastics test equipment Force measuring system of uniaxial material testing machines Metallic materials tensile testing at ambient temperature General requirements for the competence of testing and calibration laboratories SANAS Page 3 of 8

4 JCGM International vocabulary of metrology Basic and general concepts and associated terms (VIM) Note: List of reference is not exhaustive. SANAS PM01 SANAS A01 SANAS R 79 SANAS Policy Manual References, Acronyms and Definitions Requirements for the Issue of SANAS Calibration Certificates 3. General Requirements The Laboratory must ensure that the magnitude of vibration, shock or other disturbing conditions is not so great as to affect the results of the measurements. Acoustic noise should be at a low level. Lighting must be adequate for the purpose, but care should be taken that it does not cause local heating of the device. 3.1 Temperature requirements Calibration of the testing machine shall be carried out at an ambient temperature of between 10ºC and 35ºC. The temperature at which the calibration is carried out shall be noted on the calibration certificate. Sufficient time shall be allowed for the instruments to reach a stable temperature. The temperature of the Unit Under Test (UUT) shall remain stable to within ± 2ºC during each calibration run. Note 1: When it is known that either the reference or UUT or both, are not temperature compensated, care should be taken to ensure that temperature variations do not affect the calibration. (i.e. force proving rings). Note 2: If a laboratory cannot operate within the specified requirement, it must produce documented evidence that it has made measurements under extreme conditions outside the prescribed requirements to determine that the measurement results are not invalidated. Should the results be adversely affected, the evidence must be produced to indicate that these influences are considered in the uncertainty budgets. 4. Measurements 4.1 Procedure for force measuring system Inspection of the testing machine The testing machine shall be inspected to ensure that it operates in accordance with its intended use, and is safe to operate. Manufacturer s instructions or operating manual should be used Warm-up and conditioning The reference and UUT shall be energised and a sufficient period of time allowed for them to reach a stable temperature Pre-loading Before the calibration forces are applied, in a given mode, (tension or compression), the maximum calibration force shall be applied to the UUT three times Application of discrete forces SANAS Page 4 of 8

5 A minimum of three series of measurements shall be taken with either increasing or decreasing forces Recording of results One of the following methods should be used:- i) A given force, as indicated by the UUT, is applied. The true applied force, as measured by the reference, is then noted; or ii) If this is not possible, a true force, (reference), is applied. The force indicated by the UUT is noted. 4.2 Measurement procedure for displacement This calibration should be performed under 'no-load' conditions. A minimum of three series of measurements over the calibration range of the UUT should be taken with either increasing or decreasing displacement. 4.3 Measurement procedure for speed calibration (crosshead) Where possible, this calibration should be performed under 'no-load' conditions. The speed should be calibrated by measuring the crosshead displacement over a suitable period. A minimum of three series of measurements over the range of the UUT should be taken. 4.4 Measurement procedure for strain calibration (auxiliary measurement devices) A minimum of three series of measurements over the calibration range of the auxiliary measurement device should be taken with either increasing or decreasing displacement. Where applicable, auxiliary measurement devices shall be detached from the calibration apparatus between each run. The auxiliary measurement device shall be attached to the calibrating device in a similar way as during uniaxial testing. 4.5 Calibration to other standards (specifications). If the laboratory performs a calibration according to a recognised national or international standard, the standard shall become the mandatory document and all tests and measurements as required by the standard must be performed and reported on. The relevant standard must be referred to in the calibration certificate. 4.6 Limitation imposed. If compliance to selected clauses of a specification is made the relevant clauses complied with shall be clearly indicated on the calibration certificate. 5. Calibration Certificates In addition to the requirements of SANAS and ISO/IEC for calibration certificates the following shall also be reported on certificates: 5.1 The resolution and range that is applicable to the UUT. 5.2 Calibration units as displayed and must be recorded together with the values of the measurement unit. 5.3 The mounting orientation of the auxiliary measurement device if applicable. 5.4 The gauge length(s) of the auxiliary measurement device if applicable. 5.5 Actual temperature during calibration. SANAS Page 5 of 8

6 5.6 Refer to R 79 Requirements for the issue of SANAS Calibration Certificates. 6. Authorship This Technical Requirement document was prepared by the following members of an approved subcommittee of the SANAS Force, Torque and Hardness STC:- E Tarnow NMISA C Gouws NMISA S Moela NMISA B Burke NMISA J Jacobs SABS I Ramsey Advanced Laboratory Solutions (Pty) Ltd V Diniz Victor Diniz Testing Machine Services D Keet Archimedes Laboratory Solutions cc Y Volschenk Technology Solutions SANAS Page 6 of 8

7 ADDENDUM 1: Schedule of Accreditation S C H E D U L E O F A C C R E D I T A T I O N FORCE METROLOGY Laboratory Accreditation Number 4321 Permanent Address of Laboratory: Name of Company Address Street Address Suburb Address Town Address Code Postal Address Address 1 Address 2 Address Code Technical Signatories Nominated Representative : Signatory 1 : Signatory 2 : Signatory 3 : Representative 1 : Representative 2 : Representative 3 Tel : (012) Fax : (012) Issue Number Date of Issue Expiry Date : 01 : Month / Year : Month / Year ITEM MEASURED QUANTITY OR TYPE OF GAUGE OR INSTRUMENT RANGE OF MEASURED QUANTITY CALIBRATION MEASUREMENT CAPABILITIES EXPRESSES AS AN UNCERTAINTITY (±) 4 FORCE 4.1 Tension Tension: Uniaxial Testing Machines Compression Compression: Uniaxial Testing Machines 10 to 100 kn or 10 to 100 kn 0, F or 2 kn 4.3 Tension and compression or or Tension and compression: Uniaxial Testing Machines 0 to 10 kn ( F+0,1 kn) On site calibrations for items 4.3 Note: Number according to the BIPM Classification of Services in Mass and related quantities Original date of accreditation: August 2003 Page 1 of 1 The CMC, expressed as an expanded uncertainty of measurement, is stated as the standard uncertainty of measurement multiplied by a coverage factor k = 2, corresponding to a confidence level of approximately 95% SANAS Page 7 of 8

8 ADDENDUM 2: Amendment Record Proposed by Section Change STC 2.2 Added reference to R79 STC rd sentence: allowed for replaced provided to allow STC st sentence: shall replaced must 2 nd sentence should replaced may STC allowed for them replaced provided to STC 4.4 shall be detached from the calibration apparatus between each run replaced should be removed and then replaced back on the calibration apparatus between each series STC WG 5.6 Replaced The calibration results measured shall be reported in SI units. If reporting of results in non SI units is required, the conversion factor used, and its source (reference) must be specified on the calibration certificate. STC Addendum 1 Addendum added SANAS Page 8 of 8