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Designation: B 557M – 02a
METRIC
Standard Test Methods of
Tension Testing Wrought and Cast Aluminum- and
Magnesium-Alloy Products [Metric] 1
This standard is issued under the fixed designation B 557M; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon (e) indicates an editorial change since the last revision or reapproval. This standard has been approved for use by agencies of the Department of Defense.
**1. Scope ***
1.1 These test methods cover the tension testing of wrought and cast aluminum- and magnesium-alloy products, excepting aluminum foil^2 , and are derived from Test Methods E 8M, which cover the tension testing of all metallic materials.
NOTE 1—These metric test methods are the equivalents of those in Test Methods B 557, and are compatible in technical content except for the requirement of longer gage lengths for round specimens. NOTE 2—Exceptions to the provisions of these test methods may need to be made in individual specifications or test methods for a particular material.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility 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 Documents
2.1 The following documents of the issue in effect at the time of reference form a part of these test methods to the extent referenced herein: 2.2 ASTM Standards: E 4 Practices for Force Verification of Testing Machines^3 E 6 Terminology Relating to Methods of Mechanical Test- ing^3 E 8M Test Methods for Tension Testing of Metallic Mate- rials [Metric]^3 E 29 Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications^4
E 83 Practice for Verification and Classification of Exten- someter^3 E 345 Test Methods of Tension Testing of Metallic Foil^3 E 1012 Practice for Verification of Specimen Alignment Under Tensile Loading^3
3. Terminology 3.1 The definitions of terms relating to tension testing appearing in Terminology E 6 shall be considered as applying to the terms used in these test methods. 4. Significance and Use 4.1 Tension tests provide information on the strength and ductility of materials under uniaxial tensile stresses. This information may be useful in comparisons of materials, alloy development, quality control, and design under certain circum- stances. 4.2 The results of tension tests of specimens machined to standardized dimensions from selected portions of a part or material may not totally represent the strength and ductility properties of the entire end product or its in-service behavior in different environments. 4.3 These test methods are considered satisfactory for ac- ceptance testing of commercial shipments and have been used extensively in the trade for this purpose. 5. Apparatus 5.1 Testing Machines —Machines used for tension testing shall conform to the requirements of Practices E 4. The forces used in determining tensile strength and yield strength shall be within the verified force application range of the testing machine as defined in Practices E 4. 5.2 Gripping Devices : 5.2.1 General —Various types of gripping devices may be used to transmit the measured load applied by the testing machine to the test specimens. To ensure axial tensile stress within the gage length, the axis of the test specimen must coincide with the centerline of the heads of the testing
(^1) These test methods are under the jurisdiction of ASTM Committee B07 on Light Metals and Alloys and are the direct responsibility of Subcommittee B07. on Testing. Current edition approved Oct. 10, 2002. Published January 2003. Originally published as B 557M – 76. Last previous edition B 557M – 02. (^2) For test methods of tension testing of aluminum foil, see Test Methods E 345. (^3) Annual Book of ASTM Standards , Vol 03.01. (^4) Annual Book of ASTM Standards , Vol 14.02.
*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 19428-2959, United States.
machine. Any departure from this requirement may introduce bending stresses that are not included in the usual stress computation (load divided by cross-sectional area).
NOTE 3—The effect of this eccentric loading may be illustrated by calculating the bending moment and stress thus added. For a standard 12.50-mm diameter specimen, the stress increase is 1.5 percentage points for each 0.025 mm of eccentricity. This error increases to about 2. percentage points/0.025 mm for a 9-mm diameter specimen and to 3. percentage points /0.025-mm for a 6-mm diameter specimen. NOTE 4—Alignment methods are given in Practice E 1012. 5.2.2 Wedge Grips —Testing machines usually are equipped with wedge grips. These wedge grips generally furnish a satisfactory means of gripping long bars of ductile metal. If, however, for any reason, one grip of a pair advances farther than the other as the grips tighten, an undesirable bending stress may be introduced. When liners are used behind the wedges, they must be of the same thickness and their faces must be flat and parallel. For best results, the wedges should be supported over their entire length by the heads of the testing machine. This requires that liners of several thicknesses be available to cover the range of specimen thickness. For proper gripping, it is desirable that the entire length of the serrated face of each wedge be in contact with the specimen. Proper alignment of wedge grips and liners is illustrated in Fig. 1. For short specimens it is generally necessary to use machined test specimens and to use a special means of gripping to ensure that the specimens, when under load, shall be as nearly as possible in uniformly distributed pure axial tension (see 5.2.3, 5.2.4, and 5.2.5). 5.2.3 Grips for Threaded and Shouldered Specimens —A schematic diagram of a gripping device for threaded-end specimens is shown in Fig. 2, while Fig. 3 shows a device for gripping specimens with shouldered ends. Both of these gripping devices should be attached to the heads of the testing machine through properly lubricated spherical-seated bearings. The distance between spherical bearings should be as large as feasible. 5.2.4 Grips for Sheet Materials —The self-adjusting grips shown in Fig. 4 have proved satisfactory for testing sheet materials that cannot be tested satisfactorily in the usual type of wedge grips. 5.2.5 Grips for Wire —Grips of either the wedge or snubbing types as shown in Fig. 4 and Fig. 5 or flat wedge grips may be used. 5.3 Dimension-Measuring Devices —Micrometers and other devices used for measuring linear dimensions shall be accurate and precise to at least one half the smallest unit to which the individual dimension is required to be measured.
5.4 Extensometers —Extensometers used in tensile testing shall conform to the requirements of Practice E 83 for the classifications specified by the procedure section of these test methods. Extensometers shall be used and verified to include the strains corresponding to the yield strength and elongation at fracture (if determined). 5.4.1 Extensometers with gage lengths equal to or shorter than the nominal gage length of the specimen (dimension shown as “G-Gage Length” in the accompanying figures) may be used to determine the yield behavior. For measuring elongation at fracture with an appropriate extensometer, the gage length of the extensometer shall be equal to the nominal gage length required for the specimen being tested.
6. Test Specimen 6.1 General : 6.1.1 Test specimens shall be of the full section of the material whenever practical. Otherwise, machined specimens of rectangular or round cross section shall be used. 6.1.2 Improperly prepared test specimens often are the reason for unsatisfactory and incorrect test results. It is important, therefore, that care be exercised in the preparation of specimens, particularly in the machining, to ensure the desired precision and bias in test results. 6.1.3 The cross-sectional area of the specimen should be FIG. 1 Wedge Grips with Liners for Flat Specimens smallest at the center of the reduced section to ensure fracture
FIG. 2 Gripping Device for Threaded-End Specimens
6.2 Type, Direction, and Location in Wrought Products — This paragraph and subparagraphs provide the standard re- quirements for the testing of wrought products for the purpose of quality control and lot release testing. Additions or excep- tions to these requirements may need to be made in individual specifications for a particular material or product.
NOTE 5—These requirements also do not preclude the use of these test methods for purposes other than quality control as desired for research, material evaluation, or other purpose utilizing other test locations, test directions, and test specimen sizes. In these cases, the general require- ments in 6.1 should be followed for specimen type and the requirements in Sections 5 and 7 shall be followed for test apparatus, testing, and analysis.
6.2.1 Sheet and Plate : 6.2.1.1 Rectangular specimens shall be used for thicknesses of 12.50 mm and less, and round specimens for all others. 6.2.1.2 For thicknesses over 12.50 mm through 40 mm, in-plane specimens shall be taken from the center of the thickness; for larger thicknesses, they shall be taken midway from the center to the surface. Short transverse specimens shall be taken so that the midpoint of their axis lies on the plate mid-thickness. 6.2.1.3 For non-heat-treatable aluminum alloys, specimens shall be taken parallel to the direction of rolling.
6.2.1.4 For heat-treatable aluminum alloys, specimens shall be taken perpendicular to the direction of rolling (long- transverse) unless otherwise specified in the material specifi- cation. For widths too narrow for long-transverse standard rectangular or 12.50-mm diameter specimens, specimens shall be taken parallel to the direction of rolling. 6.2.1.5 For magnesium alloys, specimens shall be taken parallel to the direction of rolling. 6.2.2 Wire, Rod, and Bar : 6.2.2.1 Full-section specimens shall be used when practical. It is permissible to reduce the section slightly throughout the test section in order to ensure fracture within the gage length. Otherwise, round specimens shall be used, except that for rectangles of 12.50 mm and less in thickness, rectangular specimens of the full thickness may be used. 6.2.2.2 Specimens shall be taken in the longitudinal direc- tion from the locations specified in Table 2. 6.2.3 Extrusion Profiles : 6.2.3.1 Round specimens shall be used whenever it is not practical to use full-section specimens, except that for extru- sion profiles 12.50 mm and less in thickness, rectangular specimens may be used.
Dimensions, mm Standard Specimen Sheet-Type 12.5 mm Wide Subsize Specimen 6 mm Wide G—Gage length 50.00 6 0.10 25.00 6 0. W—Width (Note 1 and Note 2) 12.50 6 0.05 6.01 6 0. T—Thickness (Note 3) thickness of material thickness of material R—Radius of fillet, min 12.5 6 L—Overall length, min (Note 4) 200 100 A—Length of reduced section, min 57 32 B—Length of grip section, min (Note 5) 50 30 C—Width of grip section, approximate (Note 2 and Note 6) 20 10
NOTE 1—The ends of the reduced section shall not differ in width by more than 0.06 mm for the 50.00-mm gage length specimen or 0.025 mm for the 25.00-mm gage length specimen. There may be a gradual taper in width from the ends of the reduced section to the center, but the width at each end shall not be more than 1 % greater than the width at the center. NOTE 2—For each of the specimens, narrower widths ( W and C ) may be used when necessary. In such cases the width of the reduced section should be as large as the width of the material being tested permits: however, unless stated specifically, the requirements for elongation in a product specification shall not apply when these narrower specimens are used. If the width of the material is less than W, the sides may be parallel throughout the length of the specimen. NOTE 3—The dimension T is the thickness of the test specimen as stated in the applicable material specifications. Maximum nominal thicknesses of 12.5-mm and 6-mm wide specimens shall be 12.5 mm and 6 mm, respectively. NOTE 4—To aid in obtaining axial loading during testing of 6-mm wide specimens, the overall length should be as large as the material will permit, up to 200 mm. NOTE 5—It is desirable, if possible, to make the length of the grip section large enough to allow the specimen to extend into the grips a distance equal to two thirds or more of the length of the grips. If the thickness of 12.5-mm wide specimens is over 9 mm longer, grips and correspondingly longer grip sections of the specimens may be necessary to prevent failure in the grip section. NOTE 6—The grip-end centerline of the 12.5-mm wide and 6-mm wide specimens shall coincide with the centerline of the reduced section within 0. mm and 0.1 mm, respectively. FIG. 6 Rectangular Tension Test Specimens
6.2.3.2 Specimens shall be taken in the longitudinal direc- tion from the predominant section of the extrusion profile. The specimens shall be taken from a location that most nearly satisfies the intent of Table 2.
6.2.4 Tube and Pipe —Specimens shall be taken in the longitudinal direction. 6.2.4.1 For all tube (Note 6), particularly sizes 25 mm and under in nominal outside diameter, and frequently for larger
Dimensions, mm G—Gage length 50.00 6 0. W—Width (Note 1) 12.50 6 0. T—Measured thickness of specimen Note 2 R—Radius of fillet, min 12. A—Length of reduced section, min 57 B—Length of grip section, min (Note 3) 75 C—Width of grip section, approximate (Note 4) 20
NOTE 1—The ends of the reduced section shall not differ in width by more than 0.06 mm. There may be a gradual taper in width from the ends of the reduced section to the center, but the width at each end shall not be more than 1 % greater than the width at the center. NOTE 2—The dimension T is the thickness of the tubular section as provided for in the applicable material specifications. N OTE 3—It is desirable, if possible, to make the length of the grip section great enough to allow the specimen to extend into the grips a distance equal to two thirds or more of the length of the grips. NOTE 4—The grip-end centerline of the specimen shall coincide with the centerline of the reduced section within 1.00 mm. NOTE 5—For circular segments, the cross-sectional area shall be calculated using the formula shown in 7.2.3. NOTE 6—The radii of all fillets shall be equal to each other within a tolerance of 1.00 mm, and the centers of curvature of the two fillets at a particular end shall be located across from each other (on a line perpendicular to the centerline) within a tolerance of 2.00 mm. FIG. 7 Longitudinal Tension Specimens for Large-Diameter Tubular Products
Dimensions, mm G—Gage length 50.00 6 0. W—Width (Note 1) 12.50 6 0. T—Thickness, max (Note 2) 12. R—Radius of fillet, min (Note 3) 13 L—Overall length, min 200 A—Length of reduced section, min 57 B—Length of grip section, min 50 C—Width of grip section, approximate 50 D—Diameter of hole for pin, min (Note 4) 13 E—Edge distance from pin, approximate 40 F—Distance from hole to fillet, min 15
NOTE 1—The ends of the reduced section shall not differ in width by more than 0.06 mm. There may be a gradual taper in width from the ends of the reduced section to the center, but the width at each end shall not be more than 1 % greater than the width at the center. NOTE 2—The dimension T is the thickness of the test specimen as stated in the applicable product specifications. N OTE 3—For some materials, a fillet radius R larger than 13 mm may be needed. N OTE 4—Holes must be on centerline of reduced section, within 6 0.05 mm. NOTE 5—Variations of dimensions C, D, E, F, and L may be used that will permit failure within the gage length. FIG. 8 Pin-Loaded Tension Test Specimen with 50-mm Gage Length
the midpoint of its axis lies on the longitudinal centerline of the forging. Each specimen shall be so chosen that the distance from the midpoint of its axis to the end of the forging is at least half the thickness of the forging. 6.3 Type of Specimen from Sand and Permanent Mold Castings : 6.3.1 Test specimens shall be separately cast or, if called for by product specification or customer requirements, machined from the casting itself. 6.3.2 Cast Test Specimens —Cast test specimens shall be prepared in accordance with the appropriate product specifica- tion. 6.3.3 Specimens Machined from Castings : 6.3.3.1 Round specimens in accordance with Fig. 9 shall be used for section thicknesses over 12.50 mm. 6.3.3.2 Either small-size round specimens proportional to the standard specimen in Fig. 9 or rectangular specimens in accordance with Fig. 6 may be used for section thicknesses from 8.0 to 12.50 mm, except as limited by 6.1.3.
6.3.3.3 Rectangular specimens in accordance with Fig. 6 shall be used for section thickness less than 8.0 mm. 6.3.3.4 All test specimens must have a machined finish of 1.6 μm RMS (1.4 μm AA) or smoother. 6.4 Specimen for Die Castings —For testing die castings the test specimen shown in Fig. 13 shall be used unless otherwise provided in the product specifications.
Dimensions, mm Specimen 1 Specimen 2 Specimen 3 Specimen 4 Specimen 5 G—Gage length 62.50 6 0.10 62.50 6 0.10 62.50 6 0.10 62.50 6 0.10 62.50 6 0. D—Diameter (Note 1) 12.50 6 0.25 12.50 6 0.25 12.50 6 0.25 12.50 6 0.25 12.50 6 0. R—Radius of fillet, min 9 9 9 9 9 A—Length of reduced section 75, min 75, min 100, approximately 75, min 75, min L—Overall length, approximate 145 155 140 140 255 B—Length of end section (Note 2) 35, approximately 25, approximately 20, approximately 15, approximately 75, min C—Diameter of end section 20 20 20 22 20 E—Length of shoulder and fillet section, approximate 15 20 15 F—Diameter of shoulder 15 15 15
NOTE 1—The reduced section may have a gradual taper from the ends toward the center with the ends not more than 1 % larger in diameter than the center. NOTE 2—On Specimen 5 it is desirable, if possible, to make the length of the grip section great enough to allow the specimen to extend into the grips a distance equal to two thirds or more of the length of the grips. FIG. 10 Various Types of Ends for Standard Round Tension Test Specimen
TABLE 2 Location of Axis of Specimen in Rod, Bar, and Extrusion Profiles
Section Diameter, Thickness or Width, mm
Location of Axis of Specimen with Respect to Thickness(T) and Width(W) of Bar and Shapes or Diameter (D) of Rod Thickness Width Diameter Up through 40.0, incl T/2 W/2 D/ Over 40.0 T/4 W/4 D/
N OTE 1—The diameter of the plug shall have a slight taper from the line limiting the testing machine jaws to the curved section. FIG. 11 Metal Plugs for Testing Tubular Specimens, Proper Location of Plugs in Specimen and of Specimen in Heads of Testing Machine
6.5 Specimens for Powdered Metals —For testing powdered metals the test specimens shown in Fig. 14 and Fig. 15 shall be used, unless otherwise provided in the product specifications.
7. Procedure
7.1 Preparation of the Test Machine —Upon startup, or following a prolonged period of machine inactivity, exercise or warm up the test machine to normal operating temperatures to minimize errors that may result from transient conditions. 7.2 Measurement of Dimensions of Test Specimens : 7.2.1 To determine the cross-sectional area of a tension test specimen, measure the dimensions of the cross section at the center of the reduced section. However, for referee testing of specimens under 5.0 mm in their least dimension, measure the dimensions where the least cross-sectional area is found. Measure and record the cross-sectional dimensions of tension test specimens 5.0 mm and over to the nearest 0.025 mm; the cross-sectional dimensions less than 5.0 mm and not less than 2.5 mm to the nearest 0.01 mm; the cross-sectional dimensions less than 2.5 mm and not less than 0.5 mm, to the nearest 0. mm and when practical, the cross-sectional dimensions less than 0.5 mm, to at least the nearest 1 % but in all cases to at least the nearest 0.002 mm.
NOTE 7—Measurements of dimensions presume smooth surface fin- ishes for the specimens. Rough surfaces due to the manufacturing process such as hot rolling, metallic coating, and so forth, may lead to inaccuracy of the computed areas greater than the measured dimensions would indicate. Therefore, cross-sectional dimensions of tension test specimens with rough surfaces due to processing may be measured and recorded to the nearest 0.025 mm.
7.2.2 Determine cross-sectional areas of full-size tension test specimens of nonsymmetrical cross sections by weighing a length not less than 20 times the largest cross-sectional dimension and using the value of density of the material. Determine the weight to the nearest 0.5 % or less. 7.2.3 When using specimens of the type shown in Fig. 7 taken from tubes, the cross-sectional area shall be determined as follows: If D/W # 6: A (^5) @~ W /4! 3 ~ D^2 2 W^2 !1/2# 1 @~ D^2 /4! (1) 3 arcsin ~ W / D !# 2 @~ W /4! 3 ~~ D 2 2 T! 2 2 W^2 !1/2# 2 @~~ D 2 2 T !/2! 2 3 arcsin ~ W /~ D 2 2 T !!#
where: A = exact cross-sectional area, mm^2 , W = width of the specimen in the reduced section, mm, D = measured outside diameter of the tube, mm, and T = measured wall thickness of the specimen, mm. Arcsin values to be in radians If D/W > 6, the exact equation or the following equation may be used: A 5 W 3 T (2)
where: A = approximate cross-sectional area, mm^2 , W = width of the specimen in the reduced section, mm, and T = measured wall thickness of the specimen, mm. 7.3 Gage Length Marking of Test Specimens : 7.3.1 The gage length for the determination of elongation after fracture shall be in accordance with the product specifi- cations for the material being tested. Gage marks shall be stamped lightly with a punch, scribed lightly with dividers, or drawn with an ink as preferred. For material that is sensitive to the effect of slight notches and for small specimens, the use of layout ink will aid in locating the original gage marks after fracture. 7.3.2 In the absence of a product specification, the following gage lengths shall be used: 7.3.2.1 For 12.5 mm-wide rectangular specimens and full section specimens from tube and pipe, the gage length shall be 50 mm (Figs. 6-8, and Fig. 11). 7.3.2.2 For round specimens taken from products 4 mm or larger, the gage length shall be 5D, except for wire for electric conductors (Fig. 9). 7.3.2.3 For wire for electric conductors the gage length shall be 250 mm. 7.3.2.4 For die cast specimens, the gage length shall be 50 mm (Fig. 13). 7.3.2.5 For powdered metal specimens, the gage length shall be 25.4 mm (Figs. 14 and 15). 7.3.2.6 Elongation measurements are not required for extru- sion profiles less than 1.6 mm in thickness and of wire, other than electric conductors, 3.20 mm and less in diameter. 7.3.3 When required by the material specification, or when making retests or referee tests of products other than wire when the specified elongation is less than 3 % or the elongation measured in the usual manner is less than 4 %, mark the original gage length of the specimen and measure to an accuracy of 6 0.05 mm. 7.4 Zeroing of the Test Machine —The testing machine shall be set up in such a manner that zero force indication signifies a state of zero force on the specimen. Any force (or preload) imparted by the gripping of the specimen (see Note 8) must be indicated by the force measuring system unless the preload is physically removed prior to testing. Artificial methods of removing the preload on the specimen, such as taring it out by a zero adjust pot or removing it mathematically by software, are prohibited because these would affect the accuracy of the test results. N OTE 8—Preloads generated by gripping of specimens may be either
NOTE 1—The edges of the specimen shall be cut parallel to each other. FIG. 12 Location from Which Longitudinal Tension Test Specimens Are to Be Cut from Large-Diameter Tube
In such instances, depending upon the material and the use for which it is intended, one or more of the methods described in the following paragraphs is recommended for specifying speed of testing.
7.5.2 Free-Running Crosshead Speed —The allowable lim- its for the rate of movement of the crosshead of the testing machine, with no force applied by the testing machine, shall be specified in millimetres per millimetre (mm/mm) of length of reduced section (or distance between grips for specimens not having reduced sections) per minute. The limits for the crosshead speed may be further qualified by specifying differ- ent limits for various types and sizes of specimens. The average crosshead speed can be experimentally determined by using a suitable measuring device and a timing device.
7.5.3 Rate of Separation of Heads During Tests —The al- lowable limits for rate of separation of the heads of the testing machine during a test shall be specified in millimetre per millimetre of length of reduced section for distance between grips for specimens not having reduced sections per second. The limits for the rate of separation may be further qualified by specifying different limits for various types and sizes of specimen. Many testing machines are equipped with pacing or indicating devices for the measurement and control of the rate of separation of the heads of the machine during a test, but in the absence of such a device the average rate of separation of the heads can be experimentally determined by using a suitable length measuring device and a timing device.
7.5.4 Elapsed Time —The allowable limits for the elapsed time from the beginning of force application (or from some specified stress) to the instant of fracture, to the maximum force, or to some other stated stress, shall be specified in seconds. The elapsed time can be determined with a timing device.
7.5.5 Rate of Stressing —The allowable limits for rate of stressing shall be specified in megapascals per second. Many testing machines are equipped with pacing devices for the measurement and control of the rate of stressing, but in the absence of such a device the average rate of stressing can be determined with a stopwatch by observing the time required to apply a known increment of stress.
7.5.6 Rate of Straining —The allowable limits for rate of straining shall be specified in millimetres per millimetre per second. Some testing machines are equipped with pacing or indicating devices for the measurement and control of rate of straining, but in the absence of such a device the average rate of straining can be determined with a timing device by observing the time required to effect a known increment of strain.
7.5.7 Unless otherwise specified, any convenient speed of testing may be used up to one half the specified yield strength, or up to one quarter the specified tensile strength, whichever is smaller. The speed above this point shall be within the limits specified. If different speed limitations are required for use in determining yield strength, tensile strength, and elongation, they should be stated in the product specifications. In the absence of any more specified limitations on speed of testing the following general rule shall apply:
7.5.7.1 The speed of testing shall be such that the forces and strains used in obtaining the test results are accurately indi- cated. 7.5.7.2 During the conduct of a test to determine yield strength the rate of stress application shall not exceed 12 MPa/s. The speed may be increased after removal of the extensometer, but it shall not exceed 0.01 mm/mm of gage length (or distance between grips for specimens not having reduced sections) per second. 7.6 Yield Strength —Determine yield strength by the offset method at an offset of 0.2 %. Acceptance or rejection of material may be decided on the basis of Extension-Under-Load Method. For referee testing, the offset method shall be used. 7.6.1 Offset Method —To determine the yield strength by the “offset method,” it is necessary to secure data (autographic or numerical) from which a stress-strain diagram may be drawn. Then on the stress-strain diagram (Fig. 16) lay off Om equal to the specified value of the offset, draw mn parallel to OA , and thus locate r, the intersection of mn with the stress-strain diagram (Note 10). In reporting values of yield strength obtained by this method, the specified value of “offset” used should be stated in parentheses after the term yield strength. Thus: Yield strength ~ offset 5 0.2 %! 5 360 MPa (3) A Class B2 extensometer (see Practice E 83) would be sufficiently sensitive for most materials when using this method. N OTE 10—Automatic devices are available that determine offset yield strength without plotting a stress-strain curve. Such devices may be used if their accuracy has been demonstrated to be satisfactory. NOTE 11—If the force drops before the specified offset is reached, technically the material does not have a yield strength (for that offset), but
FIG. 16 Stress-Strain Diagram for Determination of Yield Strength by the Offset Method
the stress at the maximum force attained before the specified offset is reached may be reported instead of the yield strength.
7.6.2 Extension-Under-Load Method —For tests to deter- mine the acceptance or rejection of material whose stress-strain characteristics are well-known from previous tests of similar material in which stress-strain diagrams were plotted, the total strain corresponding to the stress at which the specified offset occurs will be known within satisfactory limits; therefore, in such tests a specified total strain may be used, and the stress on the specimen, when this total strain is reached, is taken to be the value of the yield strength (Fig. 17). The total strain can be obtained satisfactorily by use of a Class B2 extensometer. It is recommended that this approximate method be used only after agreement between the manufacturer and the purchaser, with the understanding that check tests be made for obtaining stress-strain diagrams for use with the offset method to settle any misunderstandings.
NOTE 12—There are two general types of extensometers, averaging and non-averaging, the use of which is dependent on the product tested. For most machined or reduced section specimens, there are minimal differ- ences. However, for some materials such as some forgings and tube sections, significant differences in measured yield strength can occur. For these cases it is recommended that the averaging type be used.
7.7 Tensile Strength —Calculate the tensile strength by di- viding the maximum force carried by the specimen during a tension test by the original cross-sectional area of the speci- men. 7.8 Elongation : 7.8.1 To determine elongation after fracture, carefully fit the ends of the fractured specimen together and measure the distance between the gage marks to the nearest 0.25 mm. A percentage scale reading to 0.5 % of the gage length may be used. The elongation after fracture is the increase in length of the gage length, expressed as a percentage of the original gage length. Report the elongation after fracture using both the percentage increase and the original gage length. 7.8.2 If any part of the fracture takes place outside of the middle half of the gage length or in a punched or scribed mark
within the reduced section, the elongation value obtained may not be representative of the material. If the elongation so measured meets the minimum requirements specified, no further testing is required, but the location of fracture shall be noted. If the elongation is less than the minimum requirements, discard the test and test a replacement specimen as allowed in 8.1. 7.8.3 Elongation at fracture is defied as the elongation measured just prior to the sudden decrease in force associated with fracture. For many ductile materials not exhibiting a sudden decrease in force, the elongation at fracture can be taken as the strain measured just prior to when the force falls below 10 % of the maximum force encountered during the test. 7.8.3.1 Elongation at fracture shall include elastic and plastic elongation and may be determined with autographic or automated methods using extensometers verified over the strain range of interest (see 5.4). Use a Class B2 or better extensometer for materials having less than 5 % elongation, a Class C or better extensometer for materials having elongation greater than or equal to 5 % but less than 50 %, and a Class D or better extensometer for materials having 50 % or greater elongation. In all cases, the extensometer gage length shall be the nominal gage length required for the specimen being tested. Due to the lack of precision in fitting fractured ends together, the elongation after fracture using the manual methods of the preceding paragraphs may differ from the elongation at fracture determined with extensometers. 7.8.3.2 Percent elongation at fracture may be calculated directly from elongation at fracture data and reported instead of percent elongation after fracture as calculated in 7.8.1 and 7.8.2. However, the two parameters are not interchangeable. Use of the elongation at fracture method generally provides more repeatable results. N OTE 13—When disagreements arise over the percent elongation re- sults, agreement must be reached on which method to use. 7.8.4 When required by the material specification, or when making retests, or for referee tests of products other than wire, and the specified elongation is less than 3 % or the elongation measured in the usual manner is less than 4 %, determine the elongation of a round specimen as follows: 7.8.4.1 Prior to testing, the original gage length of the specimen shall be marked and measured to an accuracy of 6 0.05 mm as required in 7.3.3. 7.8.4.2 After testing, remove any partly torn fragments that might influence the final measurement from the broken ends of the specimen. 7.8.4.3 Fit the fractured ends together with matched sur- faces and apply an end load along the axis of the specimen sufficient to close the fractured ends together. If desired, this load may then be removed carefully, provided the specimen remains intact. N OTE 14—The use of an end load of approximately 15 MPa has been found to give satisfactory results on test specimens of aluminum alloy. 7.8.4.4 Measure the final gage length to the nearest 0.05 mm and report the elongation to the nearest 0.1 % in 62.5 mm or 0.2 % in shorter lengths.
FIG. 17 Stress-Strain Diagram for Determination of Yield Strength by the Extension-Under-Load Method
APPENDIX
(Nonmandatory Information)
X1. FACTORS AFFECTING TENSION TEST RESULTS
X1.1 The precision and bias of tension test strength and ductility measurements depend on strict adherence to the stated test procedure and are influenced by instrumental and material factors, specimen preparation, and measurement/testing errors.
X1.2 The consistency of agreement for repeated tests of the same material is dependent on the homogeneity of the material, and the repeatability of specimen preparation, test conditions, and measurements of the tension test parameters.
X1.3 Instrumental factors that can affect test results in- clude: the stiffness, damping capacity, natural frequency, and mass of the tensile test machine, the accuracy of force indication and the use of forces within the verified range for the machine, rate of force application, alignment of the test specimen with the applied force, parallelism of the grips, grip pressure, nature of the force control used, appropriateness and calibration of extensometers used, and so forth.
X1.4 Material factors that can affect test results include: homogeneity of the test material, sampling scheme, and specimen preparation (surface finish, dimensional accuracy, fillets at the ends of the gage length, taper in the gage length, bent specimens, thread quality, and so forth).
X1.4.1 Test results for specimens with as-cast, as-rolled, as-forged, or other non-machined surface conditions can be affected by the nature of the surface (see Note 7). X1.4.2 Test specimens taken from appendages to the part or component, such as prolongs or risers, or from separately produced castings (for example, keel blocks) may produce test results that are not representative of the part or component. X1.4.3 Test specimen dimensions can influence test results. For cylindrical or rectangular specimens, changing the test specimen size generally has negligible effect on the yield and tensile strength but may influence elongation. Comparison of elongation values determined using different specimens require that the following ratio be controlled:
Lo /~ A (^) o !1/2^ (X1.1)
where: Lo = original gage length of specimen, and Ao = original cross-sectional area of specimen. X1.4.3.1 Specimens with smaller Lo /(Ao ) 1/2^ ratios generally give greater elongation values. This is the case for example, when the width or thickness of a rectangular tensile test specimen is increased. X1.4.3.2 Holding the L (^) o /(Ao ) 1/2^ ratio constant minimizes, but does not necessarily eliminate differences. Depending on material and test conditions, increasing the size of the propor- tional specimen of Fig. 9 may be found to increase or decrease elongation values somewhat. X1.4.4 Use of a taper in the gage length, up to the allowed 1 % limit, can result in lower elongation values. Reductions of as much as 15 % have been reported for a 1 % taper.
X1.4.5 Changes in the strain rate can effect the yield strength, tensile strength, and elongation values, especially for materials which are highly strain-rate sensitive. In general, yield strength and tensile strength will increase with increasing strain rate, although the effect on tensile strength is generally less pronounced. Elongation values generally decrease as the strain rate increases. Aluminum alloys at room temperature are not highly strain-rate sensitive; some exhibit a slightly higher yield strength with increasing strain rate while others show the opposite effect X1.4.6 Brittle materials require careful specimen prepara- tion, high-quality surface finishes, large fillets at the ends of the gage length, oversize threaded grip sections, and cannot tolerate punch or scribe marks as gage length indicators. X1.4.7 Flattening of tubular products to permit testing does alter the material properties, generally nonuniformly, in the flattened region which may affect test results.
X1.5 Measurement errors that can affect test results in- clude: verification of the test force, extensometers, microme- ters, dividers, and other measurement devices, alignment and zeroing of chart recording devices, and so forth. X1.5.1 Measurement of the dimensions of as-cast, as-rolled, as-forged, and other test specimens with non-machined sur- faces may be imprecise due to the irregularity of the surface flatness. X1.5.2 If any portion of the fracture occurs outside of the middle of the gage length, or in a punch or scribe mark within the gage length, the elongation may not be representative of the material. Wire specimens that break at or within the grips may not produce test results representative of the material.
X1.6 Because standard reference materials with certified tensile property values are not available, it is not possible to rigorously define the bias of tension tests. However, by the use of carefully designed and controlled interlaboratory studies, a reasonable definition of the precision of tension test results can be obtained. X1.6.1 An interlaboratory test program^5 was conducted where six specimens each, of six different materials were prepared and tested by each of six different laboratories. Tables X1.1-X1.3 present the precision statistics, as defined in Prac- tice E 691, for: tensile strength, 0.2 % yield strength, and % elongation in 5D. In each table, the first column lists the six materials tested, the second column lists the average of the average results obtained by the laboratories ( X ), the third and fifth columns list the repeatability standard deviation (sr ) and reproducibility standard deviation (sR ), the fourth and sixth columns list the coefficients of variation for these standard deviations (sr / X and sR / X as a percent), and the seventh and eighth columns list the 95 % repeatability limit (r) and repro- ducibility limit (R).
X1.6.2 The averages (below columns four and six in each table) of the coefficients of variation permit a relative compari- son of the repeatability (within-laboratory precision) and reproducibility (between-laboratory precision) of the tension test parameters. This shows that the ductility measurement exhibits less repeatability and reproducibility than the strength measurements. The overall ranking from the least to the most repeatable and reproducible is: % elongation in 5D, 0.2 % offset yield strength, and tensile strength. Note that the rankings are in the same order for the repeatability and reproducibility average coefficients of variation and that the
reproducibility (between-laboratory precision) is poorer than the repeatability (within-laboratory precision), as would be expected. X1.6.3 No comments about bias can be made for the interlaboratory study due to the lack of certified test results for these specimens. However, examination of the test results showed that one laboratory consistently exhibited higher than average strength values and lower than average ductility values for most of the specimens. One other laboratory had consis- tently lower than average tensile strength results for all specimens.
SUMMARY OF CHANGES
This section identifies the principal changes to this standard that have been incorporated since the last issue.
( 1 ) References to several casting specifications were removed from paragraph 6.3.2 and Referenced Documents.
TABLE X1.1 Precision Statistics—Tensile Strength, MPa Material X sr s (^) r/X, % sR s (^) R/X, % r R EC-H19 176.9 4.3 2.45 4.3 2.45 12.1 12. 2024-T351 491.3 6.1 1.24 6.6 1.34 17.0 18. ASTM A105 596.9 4.1 0.69 8.7 1.47 11.6 24. AISI 316 694.6 2.7 0.39 8.4 1.21 7.5 23. Inconel 600 685.9 2.9 0.43 5.0 0.72 8.2 13. SAE 51410 1253.0 3.2 0.25 7.9 0.63 8.9 22. Averages: 0.91 1.
TABLE X1.2 Precision Statistics—0.2 % Yield Strength, MPa Material X sr s (^) r/X, % sR s (^) R/X, % r R EC-H19 158.4 3.3 2.06 3.3 2.07 9.2 9. 2024-T351 362.9 5.1 1.41 5.4 1.49 14.3 15. ASTM A105 402.4 5.7 1.42 9.9 2.47 15.9 27. AISI 316 481.1 6.6 1.36 19.5 4.06 18.1 54. Inconel 600 268.3 2.5 0.93 5.8 2.17 7.0 16. SAE 51410 967.5 8.9 0.92 15.9 1.64 24.8 44. Averages: 1.35 2.
TABLE X1.3 Precision Statistics—% Elongation in 5D Material X sr s (^) r/X, % sR s (^) R/X, % r R EC-H19 14.60 0.59 4.07 0.66 4.54 1.65 1. 2024-T351 17.99 0.63 3.48 1.71 9.51 1.81 4. ASTM A105 25.63 0.77 2.99 1.30 5.06 2.15 3. AISI 316 35.93 0.71 1.98 2.68 7.45 2.00 7. Inconel 600 41.58 0.67 1.61 1.60 3.86 1.88 4. SAE 51410 12.39 0.45 3.61 0.96 7.75 1.25 2. Averages: 2.96 6.
