1、PDF外文：http:/ 4060 字 出处： Accreditation and quality assurance, 2005, 10(5): 208-213 附录 附录 1 英文原文 Reflections regarding uncertainty of measurement, on the results of a Nordic fatigue test interlaboratory comparison Magnus Holmgren, Thomas Svensson, Erland Johnson, Klas Johansson Abstr
2、act This paper presents the experiences of calculation and reporting uncertainty of measurement in fatigue testing. Six Nordic laboratories performed fatigue tests on steel specimens. The laboratories also reported their results concerning uncertainty of measurement and how they
3、calculated it. The results show large differences in the way the uncertainties of measurement were calculated and reported. No laboratory included the most significant uncertainty source, bending stress (due to misalignment of the testing machine, incorrect specimens and/or incorrectly mounted speci
4、mens), when calculating the uncertainty of measurement. Several laboratories did not calculate the uncertainty of measurement in accordance with the Guide to the Expression of Uncertainty in Measurement (GUM) 1. Keyword ： Uncertainty of measurement, Calculation, Report, Fatigue test, Laborator
5、y intercomparison Definitions ： R Stress ratio Fmin/Fmax F Force (nektons) A and B Fatigue strength parameters s and S Stress (megapascals) N Number of cycles. Introduction The correct or best method of calculating and reporting uncertainty of measurement in testing has been the subject of dis
6、cussion for many years. The issue became even more relevant in connection with the introduction of ISO standards, e.g. ISO17025 2. The discussion, as well as implementation of the uncertainty of measurement concept, has often been concentrated on which equation to use or on administrative handling o
7、f the issue. There has been less interest in the technical problem and how to handle uncertainty of measurement in the actual experimental situation, and how to learn from the uncertainty of measurement calculation when improving the experimental technique. One reason for this may be that the accred
8、itation bodies have concentrated on the very existence of uncertainty of measurement calculations for an accredited test method, instead of on whether the calculations are performed in a sound technical way. The present investigation emphasizes the need for a more technical focus. One
9、testing area where it is difficult to do uncertainty of measurement calculations is fatigue testing. However, there is guidance on how to perform such calculations, e.g. in Refs. 3, 4. To investigate how uncertainty of measurement calculations are performed for fatigue tests in real life, UTMIS (the
10、 Swedish fatigue network) started an interlaboratory comparison where one of the most essential parts was to calculate and report the uncertainty of measurement of a typical fatigue test that could have been ordered by a customer of the participating laboratories. For cost reasons, customers often a
11、sk for a limited number of test specimens but, at the same time, they request a lot of information about a large portion of the possible stress-life area from few cycles (high stresses) to millions of cycles (low stresses) and even run-outs. The way the calculation was made should also be reported.
12、The outcome concerning the uncertainty of measurement from the project is reported in this article. Participants Six Nordic laboratories participated in the interlaboratory comparison: one industrial laboratory, two research institutes, two university laboratories and one laboratory in a consultancy
13、 company. Two of the laboratories are accredited for fatigue testing, and a third laboratory is accredited for other tests. Each participant was randomly assigned a number between 1 and 6, and this notification will be used in the rest of this paper. Experimental procedure The participants received
14、information about the test specimens (without material data), together with instructions on the way to perform the test and how to report the results. The instructions were that tests should be performed as constant load amplitude tests, with R=0.1 at three different stress levels, 460, 430 and 400
15、Map, with four specimens at each stress level, at a test frequency between 10 and 30 Hz, with a run-out limit at 65 10 cycles and in a normal laboratory climate ( 020 3 C and 50 15% relative humidity). This was considered as a typical customer ordered test. The test results were to
16、 be used to calculate estimates of the two fatigue strength parameters, A and B, according to linear regression of the logs and long variables, i.e. lo g lo gA B N . The reported result should include both the estimated parameters A and B and the uncertainties in them due to measurement errors. The
17、report should also include the considerations and calculations behind the results, especially those concerning uncertainty of measurement. Several properties were to be reported for each specimen. The most important one was the number of cycles until fracture or if the specimen was a run-out (i.e. s
18、urvived for 65 10 cycles). The tests were to be performed in accordance with ASTM E-46696 5 and ISO5725-2 6. ASTM E-466-96 does not take uncertainty of measurement into account； However, ASTM E-466-96 mentions that the bending stress introduced owing to misalignment must not exceed 5% of the g
19、reater of the range, maximum or minimum stresses. There are also requirements for the accuracy of the dimensional measurement of the test specimen. All participants used hydraulic testing machines. The test specimens were made of steel (yield stress 375390 Map, and tensile strength 670690 Map, tabul
20、ated values). The test specimens were distributed to the participants by the organizer. Results The primary laboratory results that should be compared are the estimated Whaler curves. In order to present all results in the same way, the organizer transformed some of the results. The Whaler curves re
21、ported by the participants are shown in Fig. 1. It can be seen that there are considerable differences between laboratories. An approximate statistical test shows a significant laboratory effect. Material scatter alone cannot explain the differences in the Whaler curves. In order to investigat
22、e if the laboratory effect was solely caused by the modeling uncertainty, we estimated new parameters from the raw data with a common algorithm. We then chose to use only the failed specimens and to make the minimization in the logarithmic life direction. The results are shown in Fig. 2. A formal st
23、atistical significance test was then made, and the result of such a test shows that the differences between the laboratories shown in Fig. 1 could be attributed only to modeling. Uncertainty of measurement calculations One of the most important objectives with this investigation was to compare the o
24、bserved differences between laboratory test results with their estimated uncertainties of measurement. The intention was to analyze the uncertainty analyses as such, and to compare them to the standard procedure recommended in the ISO guide: Guide to the Expression of Uncertainty in Measurement (GUM
25、) 1. The laboratories identified different sources of uncertainty and treated them in different ways. These sources are the load measurement, the load control, the superimposed bending stresses because of misalignment and the dimensional measurements. Implicitly, laboratory temperature and humidity,
26、 specimen temperature and corrosion effects are also considered. In addition, the results show a modeling effect. The different laboratory treatments of these sources are summarized in Table 1. Specific comments on the different laboratories All laboratories gave their laboratory temperature and hum
27、idity, but did not consider these values as sources of uncertainty, i.e. the influence of temperature and humidity was neglected. This conclusion is reasonable for steel in the temperature range and humidity range in question 7. Laboratory 1. The uncertainty due to the applied stress was determined
28、taking load cell and dimensional uncertainties into account. The mathematical evaluation was made in accordance with the GUM. Specimen temperature was measured, but was implicitly neglected. The modeling problem was mentioned, but not considered as an uncertainty source. Laboratory 2. The report contains no uncertainty evaluation. The uncertainties in the load cell and the micrometer are considered, but neglected with reference to the large material scatter. Specimen temperature was measured. Modeling problems are mentioned by a comment regarding the
