1、Designation: E2948 14Standard Test Method forConducting Rotating Bending Fatigue Tests of Solid RoundFine Wire1This standard is issued under the fixed designation E2948; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of l
2、ast revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method is intended as a procedure for theperformance of rotating bending fatigue tests of solid roundfine wir
3、e to obtain the fatigue strength of metallic materials ata specified life in the fatigue regime where the strains (stresses)are predominately and nominally linear elastic. This testmethod is limited to the fatigue testing of small diameter solidround wire subjected to a constant amplitude periodic s
4、train(stress). The methodology can be useful in assessing the effectsof internal material structure, such as inclusions, in melttechnique and cold work processing studies. However, there isa caveat. The strain, due to the radial strain gradient imposedby the test methodology, is a maximum at the sur
5、face and zeroat the centerline. Thus the test method may not seek out the“weakest link,” largest inclusions, that govern uniaxial highcycle fatigue life where the strain is uniform across the crosssection and where fatigue damage initiates at a subsurfacelocation (1-5).2Also, pre-strain, which can i
6、nfluence fatiguelife, is not included in this test method.NOTE 1The following documents, although not specificallymentioned, are considered sufficiently important to be listed in this testmethod:ASTM STP 566 Handbook of Fatigue TestingASTM STP 588 Manual on Statistical Planning and Analysis for Fati
7、gueExperimentsASTM STP 731 Tables for Estimating Median Fatigue Limits (6-8)1.2 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. The values stated ineach system may not be exact equivalents; therefore, eachsystem shall be used independently of the ot
8、her. Combiningvalues from the two systems may result in non-conformancewith the standard.2. Referenced Documents2.1 ASTM Standards:3E468 Practice for Presentation of Constant Amplitude Fa-tigue Test Results for Metallic MaterialsF562 Specification for Wrought 35Cobalt-35Nickel-20Chromium-10Molybdenu
9、m Alloy for Surgical ImplantApplications (UNS R30035)E739 Practice for StatisticalAnalysis of Linear or LinearizedStress-Life (S-N) and Strain-Life (-N) Fatigue DataE1823 Terminology Relating to Fatigue and Fracture Testing2.2 ANSI Standard:4ANSI B4.1 Standard Limits and Fits3. Terminology3.1 Defini
10、tions:3.1.1 Terms used in this practice shall be as defined inTerminology E1823.4. Summary of Test Method4.1 This test methodology describes a means to characterizethe fatigue response of small diameter solid round wire usinga rotating bending test. Small diameter wire, to be consistentwith Specific
11、ation F562 definition of “fine wire”, is less than orequal to a diameter of 0.063 in. (1.60 mm). The wire issubjected to a constant-amplitude bending strain (stress) whileit rotates at a fixed speed. This creates a fully reversed,R= minium strain stress! / maximum strain stress!=-1, bending strainat
12、 any point on the circumference of the wire. The number ofrevolutions or cycles is counted until a failure (fracture intotwo or more distinct pieces) is detected. Surface effects due toenvironmental factors (for example corrosion or cavitation) canbe extremely important in assessing fatigue performa
13、nce. Sucheffects can be assessed in a myriad of environments (air,1This test method is under the jurisdiction of ASTM Committee E08 on Fatigueand Fracture and is the direct responsibility of Subcommittee E08.05 on CyclicDeformation and Fatigue Crack Formation.Current edition approved May 1, 2014. Pu
14、blished July 2014. DOI: 10.1520/E2948-142The boldface numbers in parentheses refer to a list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume info
15、rmation, refer to the standards Document Summary page onthe ASTM website.4Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.
16、United States1phosphate buffered saline (PBS), NaCl, O2,N2, varyinghumidity, etc.) using the protocol outlined in the standard.5. Significance and Use5.1 A method for obtaining fatigue strain (stress) at aspecific life is of interest to the wire manufacturer, designer andconsumer. The method is usef
17、ul in production control, materialacceptance and determination of the fatigue strain (stress) ofthe wire at a specific fatigue life, that is, fatigue strength.Rotating bending fatigue testing of small diameter solid roundwire is possible by looping a specimen of predetermined lengththrough an arc of
18、 90 to 180. The bending strain (stress) isdetermined from the geometry of the loop thusly formed. Themethodology is capable of high frequency testing provided thetemperature of the test article is constant and there is noadiabatic heating of the wire. A constant temperature can bemaintained by immer
19、sing the specimen in a constant tempera-ture fluid bath or test media. This makes it practical to quicklytest a sufficient number of specimens to provide a statisticalfrequency distribution or survival probability distribution offatigue life at a given strain (stress). Fatigue life information isuse
20、ful to ascertain wire in-service durability and to assess, forexample, the effects of melt practice and cold work processing.6. Methods6.1 Non-guided or guided rotating bending tests, or both areincluded in this test method.Typical test frequency ranges from1 to 37 000 cycles per minute. Test freque
21、ncy should beselected carefully since it can influence the rate at whichfatigue damage accumulates. In the guided rotating bendingtest, the guiding mandrel maintains the test specimen geometryand is recommended for test specimens under high bendingstrain (stress); test specimens that exhibit strain
22、(stress)-induced phase transformations; test specimens with asymmetri-cal tension and compression behavior; test specimens with anon-central neutral axis and test specimens exhibiting exces-sive vibration during high speed tests (9, 10).6.1.1 Non-guided rotating bending fatigue testThe ends ofthe pr
23、ecut wire are attached to two driven, parallel, counter-rotating, shafts such as illustrated in Fig. 1. Or, in an alternatemethod, one end of the wire (precut to a precise length) isattached to a driven shaft and the other end is inserted into arestraining bushing, Fig. 2. The wire end is free to ro
24、tate withinthe bushing. A cumulative cycle counter records each revolu-tion of the wire as a fatigue cycle. Cumulative cycles can alsobe determined from the time to fracture at a constant rotationrate. The specimen is rotated in the arc geometry until a failureoccurs (herein defined as complete sepa
25、ration or fracture of thewire) tripping the failure sensor, see Fig. 1 and Fig. 2, andterminating the test. Spacing between the rotating shafts andthe specimen length determine the bending strain (stress)through the radius of curvature thereby making the bendingstrain (stress) readily adjustable. It
26、 is necessary to maintain theshaft spacing and specimen length relations of X1.1 for a validtest. These relations ensure a zero bending moment at thecollets (or collet and bushing) and an axial stress that isnegligible compared to the maximum bending stress at themidpoint of the specimen.6.1.2 Guide
27、d rotating bending fatigue testOne end of theprecut test wire is attached to a driven shaft, Fig. 3. The wireA) Dual driven collets: Both wire ends are held in driven collets. An environmental chamber may be placed on the platform and tests can be performed in a temperaturecontrolled liquid medium.
28、Loss of electrical continuity from one collet through the wire to the other collet indicates wire fracture and test termination. B) Wire supports: Thewire passes through slits in the supports to maintain in-plane motion of the wire during the test. The supports should be placed such that they do not
29、 impose any additionalforce or torque on the wire. Preferred placement for the supports is just off the apex of the wire loop perpendicular to a tangent to the loop. The support material shouldbe a low friction material and support placement should be chosen to minimize friction.FIG. 1 Non-Guided Ro
30、tating Bending Apparatus with Counter-Rotating ShaftsE2948 142passes through a bushing to help reduce vibration and ensuremore consistent results. The test wire is then bent around amandrel (or in a machined groove) of a low friction materialwith a fixed radius of curvature.The mandrel radius determ
31、inesthe outer-fiber strain (stress). The other end of the wire issupported by an idler mandrel in which the wire freely spins.Acumulative cycle counter records each revolution of the wire asa fatigue cycle. The specimen rotates while bent around themandrel until a failure occurs (herein defined as c
32、ompleteseparation or fracture of the wire) tripping the failure sensorand terminating the test.6.2 Fracture detectionMultiple forms of fracture detec-tion devices are available. In one method a corrosion resistantmetal wire is connected electrically such that when contact ismade with the fractured m
33、etal test specimen the test isterminated and the instrument motor and timer/cycle counterstop. Fracture detection by sensing electrical continuity be-tween the collets should be limited to less than 1 mA mm-2.Other possible fracture detection devices are fiber optic or lasersensors that are triggere
34、d by the fracture of the test specimen.7. Test Procedure7.1 Non-guided rotating bending fatigue testThe speci-men free length and the collet-to-collet or collet-to-bushingshaft spacing are determined from the desired fatigue strain orsubsequent nominal elastic stress amplitude, the wire diameterand
35、the modulus of elasticity of the material under test. SeeX1.1 for strain and nominal elastic stress calculations. A cast,or curvature of the wire, is commonly associated with cold-drawn wire. The wire should be straightened only by handwithout the use of any mechanical straightening operation toprev
36、ent any possible changes in material properties. However,if the desired service state includes mechanical or thermal-mechanical straightening then mechanical or thermal-mechanical straightening is acceptable. The wire is assumed tobe in a zero residual stress state. If this is not the case, anassess
37、ment of the residual stress state and its influence on theresults should be made and reported with the test results. Itshould then be cut-to-length and the collet-to-collet or collet-to-bushing shaft center distance adjusted and set according tothe calculations in X1.1. Clamp the wire in the collet,
38、 insertingA) L-bracket: Contains support bushing and allows for adjustment of driven collet to bushing spacing. B) Bushing: In this apparatus, there is a single driven collet. Thewire is free to rotate in the bushing. Clearance between the wire and inside diameter of the bushing is important in orde
39、r to minimize the tendency of the wire to “fly out”of the bushing. Too great a clearance and the wire may not remain in place and too small a clearance may prevent rotation. C) Collet: The spacing of a single driven colletto bushing fixes the strain amplitude. D) Wire supports: The wire passes throu
40、gh small slits in the supports so that it can be held in-plane during the test. Preferredplacement for the supports is just off the apex of the wire loop perpendicular to a tangent to the loop. A test setup with a collet to bushing spacing (that is, center distanceas defined in X1.1) greater than 4-
41、5 inches (10.2-12.7 cm) would benefit from an extra set of supports (not shown) to help minimize possible wire out-of-plane oscillation.E) Break detector: When the wire fractures, contact will be made with one of the strategically placed break detectors. The break detector is a corrosion resistant m
42、etal wire,electrically connected such that when contact is made with the metal test specimen the test is terminated and the instrument motor and timer/cycle counter stop. It isrecommended to place one break detector near the apex of the wire loop and a second detector between the support and the col
43、let. Detectors should be placed within5 10 mm of the rotating wire. Adequate detector to wire clearance is necessary to prevent premature shut down.FIG. 2 Non-Guided Rotary Bending Apparatus with Bushing and Rotating ShaftE2948 143the other end in the proper collet or bushing location, andlocate the
44、 supports and fractured wire sensors. Be cautious atthis point in the test set-up so as not to kink or unduly bend thewire. It is critical that the supports cause the wire to remain ina single vertical or horizontal plane throughout the test.Out-of-plane displacement or oscillation of the specimensh
45、ould be less than 5 mm. Low friction materials, such aspolyoxymethylene or polytetrafluoroethylene, are recom-mended for the support material. Metallic supports such asbronze, with or without lubrication, are not recommendedbecause of higher friction coefficients and possible corrosioninteraction. P
46、lacement of wire supports just off the apex of thewire loop will minimize oscillation. Multiple supports may beused for large collet-to-collet or collet-to-bushing spacing.Friction between the specimen and support may cause fractureunder the support. In this case the test result is consideredinvalid
47、. If the wire is held by a pin-vise collet, cautiously clampthe wire so as not to impart distortion or wire breakage at thecollet. Carefully set the wire to wire-support clearance and thewire to bushing clearance. Clearances should be set to conformto an ANSI Standard RC8 Loose Running Fit (ANSI B4.
48、1). Inthe case of the wire supports, too little clearance will hinderrotation resulting in a frictional torque on the wire and invalidtest result. In the case of the bushing, too great a clearance maylead to the wire jumping out of the bushing during the test ortoo little a clearance may lead to a f
49、rictional torque on the wireand invalid test result. Rotate the collet by hand to ensure thespecimen is properly aligned in the collet(s) and supports toprevent excessive vibration or out-of-plane skew or oscillation.When using an environmental bath, the test specimen shouldbe positioned with bath-in-place and allowed to equilibrate tothe bath temperature. The amount of time required for equili-bration will depend on the mass of the specimen as well as thevolume, temperature, and medium of the bath. Start the test andwait for the specimen to fracture or to reach a prede
