1、Designation: E2948 161E2948 16aStandard 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
2、 year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1 NOTETable X1.1 was editorially corrected in July 2016.1. Scope1.1 This test method is intended as a procedure for the p
3、erformance of rotating bending fatigue tests of solid round fine wireto obtain the fatigue strength of metallic materials at a specified life in the fatigue regime where the strains (stresses) arepredominately and nominally linear elastic. This test method is limited to the fatigue testing of small
4、diameter solid round wiresubjected to a constant amplitude periodic strain (stress). The methodology can be useful in assessing the effects of internalmaterial structure, such as inclusions, in melt technique and cold work processing studies. However, there is a caveat. The strain,due to the radial
5、strain gradient imposed by the test methodology, is a maximum at the surface and zero at the centerline. Thusthe test method may not seek out the “weakest link,” largest inclusions, that govern uniaxial high cycle fatigue life where the strainis uniform across the cross section and where fatigue dam
6、age initiates at a subsurface location (1-5).2 Also, pre-strain, which caninfluence fatigue life, is not included in this test method.NOTE 1The following documents, although not specifically mentioned, are considered sufficiently important to be listed in this test method:ASTM STP 566 Handbook of Fa
7、tigue TestingASTM STP 588 Manual on Statistical Planning and Analysis for Fatigue ExperimentsASTM STP 731 Tables for Estimating Median Fatigue Limits (6-8)1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematicalconversions to SI units
8、 that are provided for information only and are not considered standard.2. Referenced Documents2.1 ASTM Standards:3E177 Practice for Use of the Terms Precision and Bias in ASTM Test MethodsE468 Practice for Presentation of Constant Amplitude Fatigue Test Results for Metallic MaterialsE691 Practice f
9、or Conducting an Interlaboratory Study to Determine the Precision of a Test MethodF562 Specification for Wrought 35Cobalt-35Nickel-20Chromium-10Molybdenum Alloy for Surgical Implant Applications(UNS R30035)E739 Practice for Statistical Analysis of Linear or Linearized Stress-Life (S-N) and Strain-Li
10、fe (-N) Fatigue DataE1823 Terminology Relating to Fatigue and Fracture Testing2.2 ANSI Standard:4ANSI B4.1 Standard Limits and Fits3. Terminology3.1 Definitions:3.1.1 Terms used in this practice shall be as defined in Terminology E1823.1 This test method is under the jurisdiction of ASTM Committee E
11、08 on Fatigue and Fracture and is the direct responsibility of Subcommittee E08.05 on CyclicDeformation and Fatigue Crack Formation.Current edition approved May 1, 2016Oct. 1, 2016. Published June 2016November 2016. Originally approved in 2014. Last previous edition approved in 20142016 asE294814.16
12、1. DOI: 10.1520/E2948-16E0110.1520/E2948-16A2 The boldface numbers in parentheses refer to a list of references at the end of this standard.3 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume
13、 information, refer to the standards Document Summary page on the ASTM website.4 Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http:/www.ansi.org.This document is not an ASTM standard and is intended only to provide the user of an ASTM st
14、andard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by A
15、STM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14. Summary of Test Method4.1 This test methodology describes a means to characterize the fatigue response of small diameter solid round wire
16、 using arotating bending test. Small diameter wire, to be consistent with Specification F562 definition of “fine wire”, is less than or equalto a diameter of 0.063 in. (1.60 mm). The wire is subjected to a constant-amplitude bending strain (stress) while it rotates at a fixedspeed. This creates a fu
17、lly reversed, R = (minimum strain (stress)/ maximum strain (stress)= 1, bending strain at any point onthe circumference of the wire. The number of revolutions or cycles is counted until a failure (fracture into two or more distinctpieces) is detected. Surface effects due to environmental factors (fo
18、r example corrosion or cavitation) can be extremely importantin assessing fatigue performance. Such effects can be assessed in a myriad of environments (air, phosphate buffered saline (PBS),NaCl, O2, N2, varying humidity, etc.) using the protocol outlined in the standard.5. Significance and Use5.1 A
19、method for obtaining fatigue strain (stress) at a specific life is of interest to the wire manufacturer, designer and consumer.The method is useful in production control, material acceptance and determination of the fatigue strain (stress) of the wire at aspecific fatigue life, that is, fatigue stre
20、ngth. Rotating bending fatigue testing of small diameter solid round wire is possible bylooping a specimen of predetermined length through an arc of 90 to 180. The bending strain (stress) is determined from thegeometry of the loop thusly formed. The methodology is capable of high frequency testing p
21、rovided the temperature of the testarticle is constant and there is no adiabatic heating of the wire. A constant temperature can be maintained by immersing thespecimen in a constant temperature fluid bath or test media. This makes it practical to quickly test a sufficient number of specimensto provi
22、de a statistical frequency distribution or survival probability distribution of fatigue life at a given strain (stress). Fatiguelife information is useful to ascertain wire in-service durability and to assess, for example, the effects of melt practice and coldwork processing.6. Methods6.1 Non-guided
23、 or guided rotating bending tests, or both are included in this test method. Typical test frequency ranges from1 to 37 000 cycles per minute. Test frequency should be selected carefully since it can influence the rate at which fatigue damageaccumulates. In the guided rotating bending test, the guidi
24、ng mandrel maintains the test specimen geometry and is recommendedfor test specimens under high bending strain (stress); test specimens that exhibit strain (stress)-induced phase transformations; testspecimens with asymmetrical tension and compression behavior; test specimens with a non-central neut
25、ral axis and test specimensexhibiting excessive vibration during high speed tests (9, 10).6.1.1 Non-guided rotating bending fatigue testThe ends of the precut wire are attached to two driven, parallel,counter-rotating, shafts such as illustrated in Fig. 1. Or, in an alternate method, one end of the
26、wire (precut to a precise length)is attached to a driven shaft and the other end is inserted into a restraining bushing, Fig. 2. The wire end is free to rotate withinthe bushing. A cumulative cycle counter records each revolution of the wire as a fatigue cycle. Cumulative cycles can also bedetermine
27、d from the time to fracture at a constant rotation rate. The specimen is rotated in the arc geometry until a failure occurs(herein defined as complete separation or fracture of the wire) tripping the failure sensor, see Fig. 1 and Fig. 2, and terminatingthe test. Spacing between the rotating shafts
28、and the specimen length determine the bending strain (stress) through the radius ofcurvature thereby making the bending strain (stress) readily adjustable. It is necessary to maintain the shaft spacing and specimenlength relations of X1.1 for a valid test. These relations ensure a zero bending momen
29、t at the collets (or collet and bushing) andan axial stress that is negligible compared to the maximum bending stress at the midpoint of the specimen.6.1.2 Guided rotating bending fatigue testOne end of the precut test wire is attached to a driven shaft, Fig. 3. The wire passesthrough a bushing to h
30、elp reduce vibration and ensure more consistent results. The test wire is then bent around a mandrel (or ina machined groove) of a low friction material with a fixed radius of curvature. The mandrel radius determines the outer-fiber strain(stress). The other end of the wire is supported by an idler
31、mandrel in which the wire freely spins. A cumulative cycle counterrecords each revolution of the wire as a fatigue cycle. The specimen rotates while bent around the mandrel until a failure occurs(herein defined as complete separation or fracture of the wire) tripping the failure sensor and terminati
32、ng the test.6.2 Fracture detectionMultiple forms of fracture detection devices are available. In one method a corrosion resistant metalwire is connected electrically such that when contact is made with the fractured metal test specimen the test is terminated and theinstrument motor and timer/cycle c
33、ounter stop. Fracture detection by sensing electrical continuity between the collets should belimited to less than 1 mA mm-2. Other possible fracture detection devices are fiber optic or laser sensors that are triggered by thefracture of the test specimen.7. Test Procedure7.1 Non-guided rotating ben
34、ding fatigue testThe specimen free length and the collet-to-collet or collet-to-bushing shaftspacing are determined from the desired fatigue strain or subsequent nominal elastic stress amplitude, the wire diameter and themodulus of elasticity of the material under test. See X1.1 for strain and nomin
35、al elastic stress calculations. A cast, or curvature ofthe wire, is commonly associated with cold-drawn wire. The wire should be straightened only by hand without the use of anymechanical straightening operation to prevent any possible changes in material properties. However, if the desired service
36、stateincludes mechanical or thermal-mechanical straightening then mechanical or thermal-mechanical straightening is acceptable. TheE2948 16a2wire is assumed to be in a zero residual stress state. If this is not the case, an assessment of the residual stress state and its influenceon the results shou
37、ld be made and reported with the test results. It should then be cut-to-length and the collet-to-collet orcollet-to-bushing shaft center distance adjusted and set according to the calculations in X1.1. Clamp the wire in the collet, insertingthe other end in the proper collet or bushing location, and
38、 locate the supports and fractured wire sensors. Be cautious at this pointin the test set-up so as not to kink or unduly bend the wire. It is critical that the supports cause the wire to remain in a single verticalor horizontal plane throughout the test. Out-of-plane displacement or oscillation of t
39、he specimen should be less than 5 mm. Lowfriction materials, such as polyoxymethylene or polytetrafluoroethylene, are recommended for the support material. Metallicsupports such as bronze, with or without lubrication, are not recommended because of higher friction coefficients and possiblecorrosion
40、interaction. Placement of wire supports just off the apex of the wire loop will minimize oscillation. Multiple supportsmay be used 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 c
41、onsidered invalid. If the wire is held by a pin-vise collet, cautiously clamp thewire so as not to impart distortion or wire breakage at the collet. Carefully set the wire to wire-support clearance and the wire tobushing clearance. Clearances should be set to conform to an ANSI Standard RC8 Loose Ru
42、nning Fit (ANSI B4.1). In the caseof the wire supports, too little clearance will hinder rotation resulting in a frictional torque on the wire and invalid test result. Inthe case of the bushing, too great a clearance may lead to the wire jumping out of the bushing during the test or too little a cle
43、arancemay lead to a frictional torque on the wire and invalid test result. Rotate the collet by hand to ensure the specimen is properlyaligned in the collet(s) and supports to prevent excessive vibration or out-of-plane skew or oscillation. When using anenvironmental bath, the test specimen should b
44、e positioned with bath-in-place and allowed to equilibrate to the bath temperature.The amount of time required for equilibration will depend on the mass of the specimen as well as the volume, temperature, andmedium of the bath. Start the test and wait for the specimen to fracture or to reach a prede
45、termined number of cycles. If the pointof fracture does not occur at the center of the loop (the point of maximum strain (stress), that is, minimum radius of curvature),see X1.2 for a fracture strain (stress) correction factor that may be used based on the location of the fracture.7.1.1 An alternate
46、 geometric method to determine the nominal elastic strain is to take an image of the curved specimen whilein the machines collets and curve fit the minimum radius of curvature using one of three methods; (1) an enlargement andcomputer software; (2) templates with known radii of curvature matched by
47、overlay on the image or; (3) an osculating circle fitto the image. Calibration of length in the enlarged image is necessary. These methodologies provide the strain from the radius ofcurvature. It is important to report the method used and to be consistent in this methodology to reduce within laborat
48、ory andbetween laboratory errors.7.2 Guided rotating bending fatigue testThe fatigue strain amplitude is related directly to the diameter of the tested wire andthe radius of curvature of the mandrel, shown in Fig. 3, around which the wire is bent. See X1.3 for the strain amplitude calculation.A) Dua
49、l 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. 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 impose any additionalforce or torque on the wire. Preferred placement for the support
