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ASTM A1038 - 13.pdf

Designation A1038 − 13Standard Test Method forPortable Hardness Testing by the Ultrasonic ContactImpedance Method1This standard is issued under the fixed designation A1038; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the 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. Scope*1.1 This test method covers the determination of compara-tive hardness values by applying the Ultrasonic ContactImpedance Method UCI Method.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility 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 Standards2A370 Test Methods and Definitions for Mechanical Testingof Steel ProductsE10 Test Method for Brinell Hardness of Metallic MaterialsE18 Test Methods for Rockwell Hardness of Metallic Ma-terialsE140 Hardness Conversion Tables for Metals RelationshipAmong Brinell Hardness, Vickers Hardness, RockwellHardness, Superficial Hardness, Knoop Hardness, Sclero-scope Hardness, and Leeb HardnessE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE384 Test Method for Knoop and Vickers Hardness ofMaterialsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 Definitions3.1.1 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 pieces.3.1.2 surface finishall references to surface finish in thistest method are defined as surface roughness that is, Ra average roughness value.3.1.3 UCI hardness testa hardness testing method using acalibrated instrument by pressing a resonating rod with adefined indenter, for example, a Vickers diamond, with a fixedforce against the surface of the part to be tested.3.1.4 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-ing rod caused by the essentially elastic nature of the finite areaof contact between the indenter and the test piece during thepenetration.3.1.5 verificationchecking or testing the UCI instrumentto ensure conformance with this test method.4. Significance and Use4.1 The hardness of a material is a defined quantity havingmany scales and being dependent on the way the test isperformed. In order to avoid the creation of a new methodinvolving 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 determination,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 smallcomponents at various locations. It can be used to make1This test method is under the jurisdiction of ASTM Committee A01 on Steel,Stainless Steel and Related Alloys and is the direct responsibility of SubcommitteeA01.06 on Steel Forgings and Billets.Current edition approved Nov. 1, 2013. Published March 2014. Originallyapproved in 2005. Last previous edition approved in 2010 as A1038 – 10a. DOI10.1520/A1038-13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1hardness 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 1 a probe containing a rod with a defined indenter,for example, a Vickers diamond, attached to the contacting endper Test Method E384 see Fig. 1, 2 vibration generatingmeans, 3 vibration detecting means, 4 electronic means forthe numerical evaluation, and 5 a digital display, indicatingthe measured hardness number.5.2 UCI ProbesThere are different probes available forUCI hardness testing. They typically cover static loads 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 Test MethodIn conventional workbenchhardness testing like Brinell or Vickers testing according toTest Methods E10 and E384, the hardness value is determinedoptically by the size of the indentation in the material generatedby a certain test load, after the indenter has been removed. Inthe mobile hardness test under applied load according to theUCI method, however, the size of the produced indents are notdetermined optically. Instead the contact area is derived fromthe electronically measured shift of an ultrasonic resonancefrequency. To carry out the UCI test, a probe containing the rodwith the indenter is excited into a longitudinal ultrasonicoscillation of about 70 kHz by piezoelectric ceramicstheso-called zero frequency, which occurs when the indenter isvibrating in air.5.3.1 A spring inside the probe applies the specified testload, the vibrating tip penetrates into the material creating anelastic contact, which results in a positive frequency shift of theresonating rod. This shift is related to the size of the indent areacontact 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, HVUCI according to Eq1.5.3.2 Therefore, the frequency shift is relatively small forhard materials, because the indenter penetrates not very deepinto the test material leaving only a small indent.5.3.3 The frequency shift becomes larger if the indenterpenetrates deeper into the material, indicating mediumhardness, in accordance with the larger test indentations.Analogously, the frequency shift becomes largest when softmaterials are tested see Fig. 2.5.3.4 The instrument constantly monitors the resonancefrequency, calculates the frequency shift when the specifiedtest load has been reached either after the internal switch hastriggered the corresponding measurement frequency in the caseof handheld probes or after a specific dwell time has beenelapsed in the case of motor driven probes. The instrumentcarries out the evaluation and calculations, and displays instan-taneously the hardness value, for example, HVUCI.UCI Vickers 1∆f 5 fEeffA and HV 5FA↑_________________↑5.3.5 The frequency shift is a function of the indentationsize of a defined indenter, for example, a Vickers diamond, ata given modulus of elasticity of the measurement system.5.3.6 Eq 1 describes the basic relation in comparison to thedefinition of the Vickers hardness value ∆f Frequency 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 depends on the size of thecontact area but also on the elastic moduli of the materials incontact. To allow for differences in Young’s modulus, theLegendT Piezo TransducerR ReceiverO Oscillating rodV indenter, for example, Vickers diamondm test materialFIG. 1 Schematic Description of the UCI ProbeFIG. 2 Hardness Value versus Frequency Shift of the OscillatingRodA1038 − 132instrument has to be calibrated for different groups of materi-als. After calibration, the UCI method can be applied to allmaterials, which have the corresponding Young’s modulus.5.4.1 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 E384.Besides this, some instruments may be calibrated quickly, alsoat the test site, for metals such as high-alloyed steels, aluminumor titanium.6. Calibration to Other Materials6.1 A test piece of the particular material is needed. Thehardness value should then be determined with a standardizedworkbench hardness tester like one for Vickers, Brinell orRockwell according to Test Methods and Definitions A370.Itis recommended to take at least five readings and calculate theaverage hardness value. Now carry out a set of at least fivesingle UCI measurements on your test material according toinstructions in 10.6, adjust the displayed average value to thebefore measured hardness of the material and thus find thecalibration value which is necessary for further measurementson this particular material in the desired hardness scale andrange.6.1.1 Some instruments allow storing all calibration dataand adjustment parameters for hardness testing of differentmaterials. They can be recalled to the instrument as needed.7. Comparison with Other Hardness Testing Methods7.1 As opposed 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.7.2 After removing the test force, an indentation generatedby the 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 test if care is taken to apply the forceaccording to Test Method E384 and if a Vickers indenter isused in the UCI probe. In this case special arrangements orprobe attachments have to be used to provide verification of theactual test force of the UCI probe.8. Test Piece8.1 Surface PreparationThe applied 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 surface must always be free ofany impurities oil, dust, etc. and rust.8.1.1 The surface roughness should not exceed ≈30 of thepenetration depth Ra ≤ 0.3 h withhmm 5 0.062 3ŒForce NHardness HV28.1.2 Penetration depth of the Vickers diamond pyramid fora certain hardness in HV and test load in N id is shown inEq 2.8.1.3 Table 1 provides the recommended minimal surfaceroughness 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 completelyremoved. 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 used see Fig. 3for a Vickers indenter corresponding to the Bueckle’s ruleSmin10h.8.3 Minimum Wall ThicknessDistinct reading variationsmay especially occur with a specimen thickness of less thanabout 15 mm if the test material is excited to resonance orsympathetic oscillations for example, thin blocks, tubes, pipes,etc.. Most disturbing are flexural vibrations excited by thevibrating tip. These should be suppressed by suitable means.Sometimes attaching the test piece to a heavy metal block bymeans of a viscous paste, grease or oil film suffices to quenchthe flexural waves. Nevertheless, a minimum wall thickness of2 to 3 mm 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 minimum 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 hardness 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 TemperatureThe 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 instrument.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.TABLE 1 Surface Finish for Different Test LoadsTest Load 98 N 50 N 10 N 3 NRa 15 m 10 m 5m 2.5 mA1038 − 13310. Procedure10.1 Test 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 bestpossible result. Carefully exert steady pressure against the testpiece during the loading phase. Make sure that the verticalprobe position is maintained as long as the load is effective.Some 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. Avoi

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