1、ASD-STAN STANDARD NORME ASD-STAN ASD-STAN NORM ASD-STAN prEN 4861 Edition P 1 April 2018 PUBLISHED BY THE AEROSPACE AND DEFENCE INDUSTRIES ASSOCIATION OF EUROPE - STANDARDIZATION Rue Montoyer 10 - 1000 Brussels - Tel. 32 2 775 8126 - Fax. 32 2 775 8131 - www.asd-stan.org ICS: Descriptors: ENGLISH VE
2、RSION Aerospace series Metrological assessment procedure for kinematic fields measured by digital image correlation Luft- und Raumfahrt Metrologisches Messverfahren fr kinematische Felder durch digitale Bildkorrelation Srie arospatiale Procdure dvaluation mtrologique applicable aux mesures de champs
3、 cinmatiques par corrlation dimages numriques This “Aerospace Series“ Prestandard has been drawn up under the responsibility of ASD-STAN (The AeroSpace and Defence Industries Association of Europe - Standardization). It is published for the needs of the European Aerospace Industry. It has been techn
4、ically approved by the experts of the concerned Domain following member comments. Subsequent to the publication of this Prestandard, the technical content shall not be changed to an extent that interchangeability is affected, physically or functionally, without re-identification of the standard. Aft
5、er examination and review by users and formal agreement of ASD-STAN, the ASD-STAN prEN will be submitted as a draft European Standard (prEN) to CEN (European Committee for Standardization) for formal vote and transformation to full European Standard (EN). The CEN national members have then to implem
6、ent the EN at national level by giving the EN the status of a national standard and by withdrawing any national standards conflicting with the EN. ASD-STAN Technical Committee approves that: “This document is published by ASD-STAN for the needs of the European Aerospace Industry. The use of this sta
7、ndard is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefrom, is the sole responsibility of the user.” ASD-STAN reviews each standard and technical report at least every five years at which time it may be revised, reaf
8、firmed, stabilized or cancelled. ASD-STAN invites you to send your written comments or any suggestions that may arise. All rights reserved. No parts of this publication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying,
9、recording, or otherwise, without prior written permission of ASD-STAN. Order details: E-mail: salesasd-stan.org Web address: http:/www.asd-stan.org/ Edition approved for publication 1st April 2018 Comments should be sent within six months after the date of publication to ASD-STAN Material Domain Cop
10、yright 2018 ASD-STAN prEN 4861:2018 (E) 2 Contents Page Foreword 2 1 Scope 3 2 Normative references 3 3 Terms and definitions . 3 4 Symbols and abbreviations . 4 5 Principle . 4 6 System for the assessment of the metrological performance . 5 7 Pre-assessment inspection 5 8 Measurement of physical pi
11、xel size 6 9 Metrological assessment process 6 10 Classification of the extensometer system 10 11 Uncertainty determination 12 12 Metrological performance assessment intervals for extensometer systems . 12 13 Metrological performance assessment certificates 12 Annex A (informative) Uncertainty of me
12、asurement . 14 Annex B (informative) Classification of the system for the assessment of the metrological performance . 20 Annex C (normative) Covariance and covariance matrix 21 Annex D (informative) Template for metrological assessment report 27 Annex E (informative) Alternative approach for optica
13、l model identification in the case of monovision measurements . 34 Bibliography 36 Foreword This standard was reviewed by the Domain Technical Coordinator of ASD-STANs Material Domain. After inquiries and votes carried out in accordance with the rules of ASD-STAN defined in ASD-STANs General Process
14、 Manual, this standard has received approval for Publication. prEN 4861:2018 (E) 3 1 Scope This standard specifies the monitoring of mechanical tests and inspections performed both at the material (coupon) and at the structural scale by the implementation of kinematic field measurements by digital i
15、mage correlation. This document describes an in situ method for evaluating the metrological performance of an extensometer system using image correlation for the delivery of displacement fields, and by extrapolation, of deformation fields. It can be implemented prior to the actual start of the test
16、(or inspection). It will inform of the metrological performance in testing conditions. This document allows the metrological performance of the measuring technology to be quantified. The methodology described herein is not to be considered as a calibration step. This reference document does not exha
17、ustively specify the constitutive elements of a generic system of Digital Image Correlation measurement. This reference does not address the measurement of 3D shapes via stereocorrelation systems. 2 Normative references There are no normative references in this document. 3 Terms and definitions For
18、the purposes of this document, the following terms and definitions apply. ISO and IEC maintain terminological databases for use in standardization at the following addresses: IEC Electropedia: available at http:/www.electropedia.org/ ISO Online browsing platform: available at http:/www.iso.org/obp 3
19、.1 extensometer system equipment used to measure displacement or strain fields on the surface of a tested piece Note 1 to entry: The equipment consists of an image acquisition device and a computer system for calculating the displacement and / or strain fields from the recorded images. Note 2 to ent
20、ry: For the purposes of this document, the term “Extensometer system“ applies in particular to kinematic field measurements by digital image correlation. 3.2 user person in charge of the extensometer system implementation 3.3 2D measurement - monovision extensometer system consisting of a single ima
21、ger is a monovision system Note 1 to entry: This system can provide full-field measurements in two (2) dimensions. The relevant plane is perpendicular to the optical axis of the imaging system. prEN 4861:2018 (E) 4 3.4 3D surface measurement - stereocorrelation extensometer system consisting of (at
22、least) two (2) imagers is a stereovision system Note 1 to entry: Through prior calibration following the suppliers instructions, the system provides measured displacement fields in three (3) dimensions of the monitored surface. This practice applied to image correlation is defined by the term stereo
23、correlation. 4 Symbols and abbreviations Symbols used throughout this document are given in Table 1 together with their designation. Table 1 Symbols and designations Symbol Designation Unit lmax Maximum limit of measured displacement mm lmin Minimum limit of measured displacement mm li Displacement
24、indicated by extensometer system m lt Displacement given by apparatus for assessment of metrological performance m qrb Relative bias error of extensometer system % qb Absolute bias error of extensometer system m r Resolution of extensometer system m 5 Principle The assessment of the metrological per
25、formance of an extensometer system involves a comparison of the readings given by the extensometer system with known variations in length provided and prescribed by a system for the assessment of the metrological performance. NOTE The user can define the displacement range(s) over which the metrolog
26、ical performance assessment is to be performed. In this way, the performance of the extensometer system can be optimized. The user should take special care to distinguish real displacements induced in the structure of interest motions from the experimental displacement commonly called “rigid body mo
27、tions.“ Hence, it would be appropriate in this case to concentrate the performance assessment to the centre of the operating range. The assessment process compares the known displacement from the calibration device with the output of the extensometer system. This output is provided in the form of da
28、ta from computer files generated by the software performing the kinematic field analysis based on the acquired images. These files should contain the displacement fields that will be evaluated and the coordinate at which they are evaluated. NOTE For certain types of extensometer systems, the calibra
29、tion and classification will also be dependent upon the ability of the system for the assessment of the metrological performance. prEN 4861:2018 (E) 5 6 System for the assessment of the metrological performance 6.1 Principle The system for the assessment of the metrological performance, which allows
30、 a known displacement lt to be applied with respect to the object of interest, may consist of a rigid frame to which the image acquisition device is attached. The system for the assessment of the metrological performance shall comprise a mechanism for moving along the three (3) axes in space by tran
31、slation, optionally from one (1) to three (3) rotations and a measuring device allowing to allow these displacements to be known accurately. These variations in length can be measured by, for example, by an interferometer, a linear incremental encoder or gauge blocks and a comparator, or a micrometr
32、e. The calibration apparatus should be calibrated and should meet the performance requirements given in Table B.1 in Annex B. 6.2 Traceability of metrological performance assessment The calibration apparatus and the supporting equipment (such as micrometres, callipers, and optical projection microsc
33、opes) shall be calibrated using standards that are traceable to the International System of Units (SI). The uncertainty associated with any measurement made by the supporting equipment shall not exceed one third of the allowable error of the extensometer system being calibrated, see Table 2. The tem
34、perature measurement instrument shall have a resolution of 0,1 C. 7 Pre-assessment inspection 7.1 Aim Prior to the assessment, the extensometer system shall be inspected. The quality of mechanical, optical, electronic components and devices have been validated in terms of equipment such as the free
35、motion of tables, lenses, wiring and connections, hard drive space. The extensometer system shall be assessed in the as-found condition if at all possible. The results shall be analyzed and, if necessary, the system shall be adjusted and re-assessed. In this case, both data sets shall be reported. 7
36、.2 Records of the inspection Records of the pre-assessment inspection shall be kept, identifying the “as-found” condition of the extensometer system, when the inspection was performed and who performed it. These pre-assessment inspection records can take the form of either a written report or a comp
37、leted “pro-forma” checklist. 7.3 Identification of extensometer system elements The extensometer system shall be uniquely identified. Parts that may be changed by the user during normal use of the extensometer system that affects the metrological assessment of the extensometer system shall also be u
38、niquely identified whenever possible (e.g. camera, lens, lighting). These unique identifiers are part of the records for the extensometer system. It will enable each component of the system and the adjustment parameters to be referenced (e.g. lens settings, calculation parameters of digital image co
39、rrelation). prEN 4861:2018 (E) 6 8 Measurement of physical pixel size 8.1 Case of monovision measurements software procedure The measurement of the physical size of the pixel is performed according to the measuring system manufacturer specifications. 8.2 Case of monovision measurements manual proced
40、ure The measurement of the physical size of the pixel is performed according to the internal procedure of the user. The procedure and the result of this measurement shall be documented. 8.3 Case of monovision measurements identification during the performance assessment procedure An alternative is t
41、o consider an identification procedure proposed in Annex E. This procedure requires the user to be able to export the displacement field measurements in pixels with the extensometer system and metric measurements for the evaluation of the metrological performance. 8.4 Case of stereovision measuremen
42、ts This measurement is not applicable because it is treated during the calibration step of stereocorrelation codes. 9 Metrological assessment process 9.1 Environmental considerations The ambient temperature during the metrological performance assessment of the extensometer system shall be recorded.
43、In general, the calibration of the extensometer system should be carried out at a temperature stable to within 2 C, the target temperature being within the range of 18 C to 28 C. Temperature changes during the metrological performance assessment process may add to the uncertainty of the calibration
44、and in some cases may affect the ability to properly assess the metrological performance of the extensometer system. For extensometer systems used at temperatures outside the recommended range of 10 C to 35 C, the metrological assessment should be carried out at or near the test temperature, if faci
45、lities exist. The extensometer system shall be placed near the system for the assessment of the metrological performance, or be mounted on it, for a sufficient duration prior to its assessment so that the parts of the extensometer system and of the system for the assessment of the metrological perfo
46、rmance that are in contact stabilize at the metrological assessment temperature. 9.1.4 Lighting conditions Lighting conditions for the metrological performance assessment process should be identical and consistent with those of the operational use of the Extensometer system. NOTE A histogram of gray
47、 level distribution could prove the quality of the lighting conditions between the two (2) uses. prEN 4861:2018 (E) 7 9.1.5 Case of artificial random speckle pattern For experimental coupons or components requiring an artificial application of a random speckle pattern (e.g. paint), it should be stab
48、le and unchanged during the metrological performance evaluation process and during operational use of the extensometer system. NOTE The measurement is performed with the same artificial random speckle pattern as for the metrological performance assessment. 9.2 Calibration increments 9.2.1 The user s
49、hall establish the range of displacements over which the extensometer system shall be assessed. 9.2.2 The number of calibration points, and the number of ranges over which the assessment is performed, shall be based upon the relationship between the minimum displacement at which a property is determined, lmin, and the maximum displacement at which a property is determined, lmax This approach shall be performed for each measurement axis, two (2) for monovision, and t
