Standard Test Methods for Tension Testing of …

1 Designation: E 8/E 8M 08 American Association StateHighway and Transportation Officials StandardAASHTO No.: T68An American National StandardStandard Test Methods forTension Testing of Metallic Materials1 This Standard is issued under the fixed designation E 8/E 8M; 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 (e) indicates an editorial change since the last revision or Standard has been approved for use by agencies of the Department of Scope* These test Methods cover the Tension Testing of metallicmaterials in any form at room temperature, specifically, themethods of determination of yield strength, yield point elon-gation, tensile strength, elongation, and reduction of The gage lengths for most round specimens are requiredto be 4D for E 8 and 5D for E 8M.

2 The gage length is the mostsignificant difference between E 8 and E 8M Test SpecimensTest specimens made from powder metallurgy (P/M) materialsare exempt from this requirement by industry-wide agreementto keep the pressing of the material to a specific projected areaand Exceptions to the provisions of these test Methods mayneed to be made in individual specifications or test Methods fora particular material. For examples, see Test Methods andDefinitionsA 370and Test MethodsB 557,B Room temperature shall be considered to be 10 to 38 C[50 to 100 F] unless otherwise The values stated in SI units are to be regarded asseparate from inch/pound units. The values stated in eachsystem are not exact equivalents; therefore each system mustbe used independently of the other.

3 Combining values from thetwo systems may result in non-conformance with the 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 Referenced standards :2A 356/A 356 MSpecification for Steel Castings, Carbon,Low Alloy, and Stainless Steel, Heavy-Walled for SteamTurbinesA 370 Test Methods and Definitions for Mechanical Testingof Steel ProductsB 557 Test Methods for Tension Testing Wrought and CastAluminum- and Magnesium-Alloy ProductsB 557 MTest Methods for Tension Testing Wrought andCast Aluminum- and Magnesium-Alloy Products [Metric]

4 E4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical Test-ingE29 Practice for Using Significant Digits in Test Data toDetermine Conformance with SpecificationsE83 Practice for Verification and Classification of Exten-someter SystemsE 345 Test Methods of Tension Testing of Metallic FoilE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE 1012 Practice for Verification of Test Frame and Speci-men Alignment Under Tensile and Compressive AxialForce ApplicationE 1856 Guide for Evaluating Computerized Data Acquisi-tion Systems Used to Acquire Data from Universal TestingMachines3. The definitions of terms relating to tensiontesting appearing in TerminologyE6shall be considered asapplying to the terms used in these test Methods of tensiontesting.

5 Additional terms being defined are as yielding in a uniaxial test, a hesitationor fluctuation of force observed at the onset of plastic defor-mation, due to localized yielding. (The stress-strain curve neednot appear to be discontinuous.) at fracture the elongation measured justprior to the sudden decrease in force associated with many materials not exhibiting a sudden decrease in force,the elongation at fracture can be taken as the strain measuredjust prior to when the force falls below 10 % of the maximumforce encountered during the test Methods are under the jurisdiction of ASTM Committee E28 onMechanical Testing and are the direct responsibility of Subcommittee onUniaxial edition approved Feb.

6 1, 2008. Published March 2008. Originallyapproved in 1924. Last previous edition approved 2004 asE8 referenced ASTM standards , visit the ASTM website, , orcontact ASTM Customer Service at ForAnnual Book of ASTMS tandardsvolume information, refer to the Standard s Document Summary page onthe ASTM *A Summary of Changes section appears at the end of this ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United yield strength, LYS [FL-2] in a uniaxial test,the minimum stress recorded during discontinuous yielding,ignoring transient elongation, Elu, [%] the elongation deter-mined at the maximum force sustained by the test piece justprior to necking or fracture, or Uniform elongation includes both elas-tic and plastic yield strength, UYS [FL-2] in a uniaxial test,the first stress maximum (stress at first zero slope) associatedwith discontinuous yielding at or near the onset of point elongation, YPE in a uniaxial test, thestrain (expressed in percent) separating the stress-strain curve sfirst point of zero slope from the point of transition fromdiscontinuous yielding to uniform strain hardening.

7 If thetransition occurs over a range of strain, the YPE end point isthe intersection between(a)a horizontal line drawn tangent tothe curve at the last zero slope and(b)a line drawn tangent tothe strain hardening portion of the stress-strain curve at thepoint of inflection. If there is no point at or near the onset ofyielding at which the slope reaches zero, the material has 0 % Significance and Tension tests provide information on the strength andductility of materials under uniaxial tensile stresses. Thisinformation may be useful in comparisons of materials, alloydevelopment, quality control, and design under certain The results of Tension tests of specimens machined tostandardized dimensions from selected portions of a part ormaterial may not totally represent the strength and ductilityproperties of the entire end product or its in-service behavior indifferent These test Methods are considered satisfactory for ac-ceptance Testing of commercial shipments.

8 The test methodshave been used extensively in the trade for this Machines Machines used for Tension testingshall conform to the requirements of PracticesE4. The forcesused in determining tensile strength and yield strength shall bewithin the verified force application range of the testingmachine as defined in Practices E Various types of gripping devices may beused to transmit the measured force applied by the testingmachine to the test specimens. To ensure axial tensile stresswithin the gage length, the axis of the test specimen shouldcoincide with the center line of the heads of the testingmachine. Any departure from this requirement may introducebending stresses that are not included in the usual stresscomputation (force divided by cross-sectional area).

9 NOTE1 The effect of this eccentric force application may be illus-trated by calculating the bending moment and stress thus added. For astandard [ ] diameter specimen, the stress increase is points for each mm [ in.] of eccentricity. This errorincreases to percentage points/ mm [ in.] fora9mm[ ] diameter specimen and to percentage points/ mm[ in.] for a 6-mm [ ] diameter Alignment Methods are given in PracticeE Grips Testing machines usually are equippedwith wedge grips. These wedge grips generally furnish asatisfactory means of gripping long specimens of ductile metaland flat plate test specimens such as those shown inFig. 1. If,however, for any reason, one grip of a pair advances fartherthan the other as the grips tighten, an undesirable bendingstress may be introduced.

10 When liners are used behind thewedges, they must be of the same thickness and their facesmust be flat and parallel. For best results, the wedges should besupported over their entire lengths by the heads of the testingmachine. This requires that liners of several thicknesses beavailable to cover the range of specimen thickness. For propergripping, it is desirable that the entire length of the serratedface of each wedge be in contact with the specimen. Properalignment of wedge grips and liners is illustrated inFig. 2. Forshort specimens and for specimens of many materials it isgenerally necessary to use machined test specimens and to usea special means of gripping to ensure that the specimens, whenunder load, shall be as nearly as possible in uniformlydistributed pure axial Tension ( , , ).