1、Designation: A 1038 08Standard Practice forPortable Hardness Testing by the Ultrasonic ContactImpedance Method1This standard is issued under the fixed designation A 1038; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of
2、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. Scope*1.1 This practice covers the determination of comparativehardness values by applying the Ultrasonic Contact ImpedanceMeth
3、od (UCI Method).1.2 The measured values are stated in SI units, which areregarded as standard. Equivalent inch-pound values, whengiven, are in parentheses and may be approximate.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is therespons
4、ibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A 370 Test Methods and Definitions for Mechanical Testingof Steel ProductsE10 Test Method for
5、Brinell Hardness of Metallic Materi-alsE18 Test Methods for Rockwell Hardness of MetallicMaterialsE92 Test Method for Vickers Hardness of Metallic Mate-rialsE 140 Hardness Conversion Tables for Metals RelationshipAmong Brinell Hardness, Vickers Hardness, RockwellHardness, Superficial Hardness, Knoop
6、 Hardness, andScleroscope HardnessE 384 Test Method for Microindentation Hardness of Ma-terials3. Terminology3.1 Definitions:3.1.1 UCI methodUltrasonic Contact Impedance, a hard-ness testing method developed by Dr. Claus Kleesattel in 1961based on the measurement of the frequency shift of a resonat-
7、ing rod caused by the essentially elastic nature of the finite areaof contact between the indenter and the test piece during thepenetration.3.1.2 UCI hardness testa hardness testing practice using acalibrated instrument by pressing a resonating rod with adefined indenter, for example, a Vickers diam
8、ond, with a fixedforce against the surface of the part to be tested.3.1.3 calibrationdetermination of the specific values ofthe significant operating parameters of the UCI instrument bycomparison with values indicated by a standardized workbenchhardness tester or by a set of certified reference test
9、 pieces.3.1.4 verificationchecking or testing the UCI instrumentto ensure conformance with this practice.3.1.5 surface finishall references to surface finish in thispractice are defined as surface roughness (that is, Ra = averageroughness value).4. Significance and Use4.1 The hardness of a material
10、is a defined quantity havingmany scales and being dependent on the way the test isperformed. In order to avoid the creation of a new practiceinvolving a new hardness scale, the UCI method converts intocommon hardness values, for example, HV, HRC, etc.4.2 The UCI hardness test is a superficial determ
11、ination,only measuring the hardness condition of the surface con-tacted. The results generated at a specific location do notrepresent the part at any other surface location and yield noinformation about the material at subsurface locations.4.3 The UCI hardness test may be used on large or smallcompo
12、nents at various locations. It can be used to makehardness measurements on positions difficult to access, such astooth flanks or roots of gears.A. GENERAL DESCRIPTION OF INSTRUMENTSAND TEST PROCEDURE FOR UCI HARDNESSTESTING5. Apparatus5.1 Instruments used for UCI hardness testing generallyconsist of
13、 (1) a probe containing a rod with a defined indenter,for example, a Vickers diamond, attached to the contacting endper Test Method E92and Test Method E 384, (2) vibration1This practice is under the jurisdiction of ASTM Committee A01 on Steel,Stainless Steel and Related Alloys and is the direct resp
14、onsibility of SubcommitteeA01.06 on Steel Forgings and Billets.Current edition approved Nov. 1, 2008. Published November 2008. Originallyapproved in 2005. Last previous edition approved in 2005 as A 1038 05.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer
15、 Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA
16、 19428-2959, United States.generating means, (3) vibration detecting means, (4) electronicmeans for the numerical evaluation, and (5) a digital display,indicating the measured hardness number.5.2 UCI ProbesThere are different probes available forUCI hardness testing. They typically cover static load
17、s rangingfrom1Nto98N.Seealso Appendix X1. They come also indifferent sizes with longer and shorter sensor rods for specialsapplications. And they are developed in two versions, that is,manually operated or equipped with a servo-motor for auto-matic testing.5.3 Summary of PracticeIn conventional work
18、benchhardness testing like Brinell or Vickers testing according toTest Methods E10, E92, and E 384, the hardness value isdetermined optically by the size of the indentation in thematerial generated by a certain test load, after the indenter hasbeen removed. In the mobile hardness test under applied
19、loadaccording to the UCI method, however, the size of theproduced indents are not determined optically. Instead thecontact area is derived from the electronically measured shiftof an ultrasonic resonance frequency. To carry out the UCI test,a probe containing the rod with the indenter is excited int
20、o alongitudinal ultrasonic oscillation of about 70 kHz by piezo-electric ceramicsthe so-called zero frequency, which occurswhen the indenter is vibrating in air.A spring inside the probe applies the specified test load, thevibrating tip penetrates into the material creating an elasticcontact, which
21、results in a positive frequency shift of theresonating rod. This shift is related to the size of the indent area(contact area of the indenter with the material). The size, inturn, is a measure for the hardness of the test material at a givenmodulus of elasticity, for example, HV(UCI) according to Eq
22、1.Therefore, the frequency shift is relatively small for hardmaterials, because the indenter penetrates not very deep intothe test material leaving only a small indent.The frequency shift becomes larger if the indenter penetratesdeeper into the material, indicating medium hardness, inaccordance with
23、 the larger test indentations. Analogously, thefrequency shift becomes largest when soft materials are tested(see Fig. 2).The instrument constantly monitors the resonance frequency,calculates the frequency shift when the specified test load hasbeen reached either after the internal switch has trigge
24、red thecorresponding measurement frequency in the case of handheldprobes or after a specific dwell time has been elapsed in thecase of motor driven probes. The instrument carries out theevaluation and calculations, and displays instantaneously thehardness value, for example, HV(UCI).UCI Vickers (1)D
25、f 5 fEeff A! and HV 5FA_The frequency shift is a function of the indentation size of adefined indenter, for example, a Vickers diamond, at a givenmodulus of elasticity of the measurement system.Eq 1 describes the basic relation in comparison to thedefinition of the Vickers hardness value: Df = Frequ
26、ency shift,A = indentation area, Eeff= effective elastic modulus (containsthe elastic constants of both the indenter and the test piece), HV= Vickers hardness value, F = Force applied in the hardnesstest.5.4 The Influence of the Elastic ConstantsAs can be seenin Eq 1, the frequency shift not only de
27、pends on the size of thecontact area but also on the elastic moduli of the materials incontact. To allow for differences in Youngs modulus, theinstrument has to be calibrated for different groups of materi-als. After calibration, the UCI method can be applied to allmaterials, which have the correspo
28、nding Youngs modulus.As manufactured, the UCI instrument usually has beencalibrated on non-alloyed and low-alloyed steel, that is, certi-fied hardness reference blocks according to Test Method E92.Legend:T = Piezo TransducerR = ReceiverO = Oscillating rodV = indenter, for example, Vickers diamondm =
29、 test materialFIG. 1 Schematic Description of the UCI ProbeFIG. 2 Hardness Value versus Frequency Shift of the OscillatingRodA1038082Besides this, some instruments may be calibrated quickly, alsoat the test site, for metals such as high-alloyed steels, aluminumor titanium.6. Calibration to Other Mat
30、erials6.1 A test piece of the particular material is needed. Thehardness value should than be determined with a standardizedworkbench hardness tester like one for Vickers, Brinell orRockwell according to Test Methods and Definitions A 370.Itis recommended to take at least 5 readings and calculate th
31、eaverage hardness value. Now carry out a set of at least 5 singleUCI measurements on your test material according to instruc-tions in 10.6, adjust the displayed average value to the beforemeasured hardness of the material and thus find the calibrationvalue which is necessary for further measurements
32、 on thisparticular material in the desired hardness scale and range.Some instruments allow storing all calibration data andadjustment parameters for hardness testing of different mate-rials. They can be recalled to the instrument as needed.7. Comparison with Other Hardness Testing Methods7.1 As oppo
33、sed to conventional low load hardness testers,the UCI instruments do not evaluate the indentation sizemicroscopically but electronically according to the UCImethod. The UCI method yields comparative hardness mea-surements when considering the dependency on the elasticmodulus of the test piece.After
34、removing the test force, an indentation generated bythe UCI probe using a Vickers diamond as indenter andmounted in a test stand is practically identical to a Vickersindentation produced by a workbench tester of the same load.The indentation can be measured optically according to thestandard Vickers
35、 test if care is taken to apply the forceaccording to Test Method E92and if a Vickers indenter is usedin the UCI probe. In this case special arrangements or probeattachments have to be used to provide verification of theactual test force of the UCI probe.8. Test Piece8.1 Surface PreparationThe appli
36、ed test force (that is, theselected UCI probe) must not only match the application butalso the surface quality and roughness of the material. Whilesmooth, homogeneous surfaces can be tested with low testloads, rougher and coarse-grained surfaces require test loads ashigh as possible. However, the su
37、rface must always be free ofany impurities (oil, dust, etc.) and rust.The surface roughness should not exceed 30 % of thepenetration depth (Ra# 0.3 3 h) with:hmm 5 0.062 3Force NHardness HV(2)Penetration depth of the Vickers diamond pyramid for acertain hardness (in HV) and test load (in N) id is sh
38、own in Eq2.Table 1 provides the recommended minimal surface rough-ness for certain UCI probes that use a Vickers indenter. Ifsurface preparation is necessary, care must be taken not to alterthe surface hardness by overheating or cold working. Anypaint, scale or other surface coatings shall be comple
39、telyremoved. Failure to provide adequate surface finish willproduce unsteady readings. Coarse finishes will tend to lowerthe measured value.8.2 Minimum ThicknessThin coatings or surface layers onbulk material must have a minimum thickness of at least tentimes of the indentation depth of the indenter
40、 used (see Fig. 3for a Vickers indenter) corresponding to the Bueckles rule:Smin=103 h.8.3 Minimum Wall ThicknessDistinct reading variationsmay especially occur with a specimen thickness of less thanabout 15 mm (58 in.) if the test material is excited to resonanceor sympathetic oscillations (for exa
41、mple, thin blocks, tubes,pipes, etc.). Most disturbing are flexural vibrations excited bythe vibrating tip. These should be suppressed by suitablemeans. Sometimes attaching the test piece to a heavy metalblock by means of a viscous paste, grease or oil film suffices toquench the flexural waves. Neve
42、rtheless, a minimum wallthickness of 2 to 3 mm (332 to18 in.) is recommended.8.4 Influence of the OscillationThe UCI method is basedon measuring a frequency shift. Parts less than about 300 g cango into self-oscillating causing erroneous or erratic readings.Test pieces of weights less than the minim
43、um or pieces of anyweight with sections less than the minimum thickness requirerigid support and coupling to a thick, heavier non-yieldingsurface to resist the oscillation of the UCI probe. Failure toprovide adequate support and coupling will produce test resultslower or higher than the true hardnes
44、s value.8.5 Surface CurvatureTest pieces with curved surfacesmay be tested on either the convex or concave surfacesproviding that the radius of curvature of the specimens ismatched to the appropriate probe and probe attachment in orderto ensure a perpendicular positioning of the probe.8.6 Temperatur
45、eThe temperature of the test piece mayaffect the results of the UCI hardness test. However, if theprobe is exposed to elevated temperature for only the time ofmeasurement, measurements are possible at temperatureshigher than room temperature, without influencing the perfor-mance of the UCI instrumen
46、t.9. Verification of the Apparatus9.1 Verification MethodPrior to each shift or work periodthe instrument shall be verified as specified in Part B. Any UCIhardness testing instrument not meeting the requirements ofPart B shall not be used for the acceptance testing of products.10. Procedure10.1 Test
47、 ProcedureTo perform a hardness test, the probeis connected to the indicating unit and the instrument is turnedon. The probe is held firmly (using a probe grip if needed) withits axis in a perpendicular position relative to the test piecesurface. Hold the probe with both hands to achieve the bestpos
48、sible result. Carefully exert steady pressure against the testpiece during the loading phase. Make sure that the verticalTABLE 1 Surface Finish for Different Test LoadsTest Load 98 N 50 N 10 N 3 NRa # 15 m # 10 m # 5m # 2.5 mA1038083probe position is maintained as long as the load is effective.Some
49、instruments indicate the end of the measurement by anacoustic signal and display the hardness value instantaneously.10.2 AlignmentTo prevent errors from misalignmentmove the UCI probe with slow and steady speed. The probeshould be perpendicular with respect to the surface. Themaximum angular deviation from the perpendicular positionshould be less than 5 degrees. Avoid twisting of the probehousing. There should be no lateral forces on the indenter.Therefore, avoid slip.10.3 Test DirectionHardness testing according to the UCImet
