1、AECMA STANDARD NORME AECMA AECMA NORM prEN 3988 Edition P 1 April 1998 PUBLISHED BY THE EUROPEAN ASSOCIATION OF AEROSPACE INDUSTRIES (AECMA) Gulledelle 94 - 8-1200 BRUXELLES - Tel. (+32) 2 775 81 10 - Fax. (+32) 2 775 81 11 ICs: ENGLISH VERSION Aerospace series Test methods for metallic materials Co
2、nstant amplitude strain-controlled low cycle fatigue testing Srie arospatiale Mthodes dessais applicables aux matriaux mtalliques Essais de fatigue oligocyclique en dformation impose Luft- und Raumfahrt Prfverfahren fr metallische Werkstoffe Niedriglastwechselermdung im dehnungsgesteuerten Versuch T
3、his “Aerospace Series“ Prestandard has been drawn up under the responsibility of AECMA (The European Association of Aerospace Industries). It is published on green paper for the needs of AECMA-Members. It has been technically approved by the experts of the concerned Technical Committee following com
4、ment by the Member countries. 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. After examination and signature of the AECMA Standard C
5、hecking Centre (NPS) and formal agreement of the Official Services of the Member countries it will be submitted as a draft European Standard to CEN (European Committee for Standardization) for formal vote. Nata - Extra copies can be supplied by B.N.A.E. - Technopolis 54 - 199, rue Jean-Jacques Rouss
6、eau - 921 38 ICSY-LES-MOULINEAUX CEDEX I Comments should be sent within six months after the date of publication to I Edition approved for publication 1998-04-30 AECMA Gulledelle 94 B-1200 BRUXELLES C5 Chairman Mr Evetts aecma 1998 Contents list Page O Introduction 1 Scope . 2 Normative references 3
7、 Principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Definitions and symbols . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8、 . . . . . . , . . . . 5 Test equipment 6 Test piece 7 . L O V c O U aJ v) u al c c L v) v) this has to be avoided. B.2.2 Grinding A suitable lubricant shall be used and its flow shall be sufficient to prevent heating of the surface. The abrasive particles shall be continuously removed from the lubr
9、icant. The diameter of the test piece shall be reduced at a rate of no more than 0,5 pm per turn (plunge grinding) or 0,005 mm per pass (traverse grinding) for the last 0,025 mm. The grinding wheel shall be frequently dressed. The characteristics of the wheel and maximum grinding speed shall be sele
10、cted as a function of the alloy to be machined: a silicon carbide abrasive is suitable for titanium and aluminium alloys whereas and aluminium oxide abrasive is suitable for steels, nickel or cobalt base alloys. Page 24 prEN 3988: 1998 Annex B (concluded) B.3 Polishing of the test section The final
11、0,025 mm in diameter shall be removed by longitudinally polishing the test piece. The polishing paper shall be renewed periodically. The force applied to the polishing paper shall be constant and low (2 N to 5 N). An automatic polishing device is recommended. Recommended metal removals and paper gri
12、t are as follows: - 0,012 mm with P800 paper (particle size: 20 pm to 30 pm); - 0,008 mm with PI O00 paper (particle size: 15 pm to 25 pm); - 0,005 mm with PI 200 paper (particle size: 10 pm to 2 pm). All grinding or turning marks shall be removed with the P800 paper before using a finer grit. Polis
13、h with each finer grit paper until all marks left by the previous paper are removed, and to impart a maximum surface roughness Ra of 0,2 pm in the test piece axis direction. NOTE: Extreme caution has to be exercised in polishing to ensure that material is being properly removed rather than merely sm
14、eared to produce a smooth surface. Page 25 prEN 3988: 1998 Annex C (informative) Guidelines on test piece handling and degreasing Unless otherwise specified by the customer or where special surface treatments have been applied, the following guidelines shall be adhered to: C.l Steels Degrease by ful
15、l submersion in an acetone bath immediately prior to testing. The use of an ultrasonic bath is recommended. Test pieces that are degreased and then not tested for some reason shall be retreated with an anti-corrosion fluid. No special handling requirements are necessary subsequently. Thread lubrican
16、ts are not necessary at the test temperatures encountered. C.2 Nickel and cobalt base alloys Degrease the test section with acetone and wipe dry with a clean soft cloth. No special handling requirements are necessary subsequently. For tests at temperatures greater than 650 OC, a thread lubricant sha
17、ll be used sparingly. Any excess evident once the test piece has been inserted shall be removed. C.3 Titanium base alloys Degrease the test section with acetone and wipe dry with a clean soft cloth. Once degreased, the test section shall not be touched other than with clean cotton gloves. In additio
18、n, everything which touches the test section (extensometer probes, string used to tie on thermocouples, etc.) shall be clean and shall be handled with gloves (to prevent any transfer of salt from the skin to the test piece). Thread lubricants shall not be used. C.4 Aluminium and magnesium base alloy
19、s Degrease the test section with acetone and wipe dry with a clean soft cloth. No special handling requirements are necessary subsequently. Thread lubricants are not necessary at the test temperatures encountered. _ STD-AECMA PREN -39-ENGL 1998 = LCi123LL CiOlt11523 9TLi 9 Page 26 prEN 3988: 1998 An
20、nex D (informative) Failure criteria There are various ways of determining a failure criterion, more often associated with an end-of-test criterion than with the total failure of the test piece. It may depend on the interpretation of the fatigue test result and on the nature of the material being te
21、sted. In fact, any development in the material behaviour shall be taken into account during the test (hardening or softening) and consequently the appropriate end-of-test criterion selected. The failure criteria under consideration are generally based on the appearance, presence or intensification o
22、f a phenomenon which has been observed or recorded and which indicates severe damage or imminent failure of the test piece. Several criteria may be considered. The conventional number of cycles to failure is defined as the number of cycles corresponding to: 1) Total failure of the test piece: separa
23、tion into two distinct parts. 2) A certain percentage decrease in the maximum tensile stress in relation to the level determined during the test. 3) A certain percentage decrease in the modulus of elasticity ratios in the tensile and compressive part of the hysteresis loops. 4) A certain percentage
24、decrease in the maximum tensile stress in relation to the maximum com pressive stress. The use of criterion 2 based on a certain percentage decrease in the maximum tensile stress is recommended. This criterion allows a reduction in the scatter observed in the number of cycles-to- complete-failure of
25、 the test piece and may be applied to different stress-strain behaviours (hardening, softening, stable behaviour, see fig. 3). In this case, the usual number of cycles to failure Nf is defined as the number of cycles corresponding to a decrease of x % in the stress value extrapolated over the tensil
26、e stress-versus number of cycles curve when the stress falls sharply. The recommended value of x is 10. This criterion relates to the presence of one (or more) macroscopic crack(s) in the test piece. In general, the fraction of cracked surface in the cross-section of the test piece is of the same magnitude as the fraction of stress decrease.
