Metallic Materials - Tensile Testing - Part 1: Method of Test at Room Temperature

Transcription

1 ICS H NATIONAL STANDARD OF THE PEOPLE S REPUBLIC OF CHINA 中华人民共和国国家标准 GB/T Replace GB/T 8-00 Metallic Materials - Tensile Testing - Part 1: Method of Test at Room Temperature 金属材料拉伸试验第 1 部分 : 室温试验方法 (ISO 689-1:009, MOD) Issued on: December 3, 010 Implemented on: December 01, 011 Jointly Issued by the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China (AQSIQ) and the Standardization Administration (SAC) of the People's Republic of China

2 Contents Foreword... I Introduction... III 1 Scope... 1 Normative References Terms and Definitions Terms and Symbols Test Piece Determination of Original Cross-sectional Area Marking the Original Gauge Length Accuracy of Testing Apparatus Conditions of Testing Determination of the Upper Yield Strength Determination of the Lower Yield Strength Determination of Proof Strength, Plastic Extension Determination of Proof Strength, Total Extension Method of Verification of Permanent Set Strength Determination of the Percentage Yield Point Extension Determination of the Percentage Plastic Extension at Maximum Force Determination of the Percentage Total Extension at Maximum Force Determination of the Percentage Total Extension at Fracture... 0 Determination of Percentage Elongation After Fracture... 1 Determination of Percentage Reduction of Area... 3 Rounding of Numerical Values of Testing Results Test Report Measurement Uncertainty... 4 Appendix A (Informative) Recommendations Concerning the Use of Computer-controlled Tensile Testing Machines Appendix B (Normative) Types of Test Pieces to Be Used for Thin Products: Sheets, Strips and Flats Between 0.1mm and 3mm Thick Appendix C (Normative) Types of Test Pieces to Be Used for Wire, Bars and Sections with a Diameter or Thickness of Less Than 4mm Appendix D (Normative) Types of Test Pieces to Be Used for Sheets and Flats of Thickness Equal to or Greater than 3mm, and Wire, Bars and Sections of Diameter or Thickness Equal to or Greater Than 4mm Appendix E (Normative) Types of Test Pieces to Be Used for Tubes... 4 Appendix F (Informative) Estimation of the Crosshead Separation Rate in Consideration of the Stiffness (or Compliance) of the Testing Machine... 45

3 Appendix G (Informative) Measuring the Percentage Elongation after Fracture If the Specified Value Is Less Than 5% Appendix H (Informative) Measurement of Percentage Elongation after Fracture Based on Displacement Method Appendix I (Informative) Determination of the Percentage Plastic Elongation Without Necking, Awn, for Long Products Such as Bars, Wire and Rods Appendix J (Normative) Determination for Proof Strength of Plastic Extension (Rp) under Successive Approximation Method Appendix K (Informative) Examples for Measurement of Permanent Set Strength (Rr0.) under Force Removing Method... 5 Appendix L (Informative) Assessment for the Uncertainty of Measuring Result of Tension Test Appendix M (Informative) Precision of Tension Test-According to Results of Interlaboratory Tests Bibliography... 69

4 Foreword This standard was drafted according to the rules specified in GB/T GB/T8 consists of the following parts under the general tile Metallic Materials - Tensile Testing - Part 1: Method of Test at Room Temperature - Part : Method of Test at Elevated Temperature - Part 3: Method of Test at Low Temperature - Pat 4: Method of Test in Liquid Helium This Part is the Part 1 of GB/T 8 The modification of this part adopts the international standard ISO 689-1: 009 Metallic Materials - Tensile Testing - Part 1: Method of Test at Room Temperature". The integral structure, hierarchical division, development, formulation and technical content of this part are consistent with ISO basically. This part has made modifications and supplements on the international standard in the following aspects, which are marked with perpendicular single line in the margin of evant clauses in the text. - In the normative references, this part directly refers to our national standard corresponding to the international standard. - The following normative references have been added: Rules of rounding off for numerical values & expression and judgment of limiting values (GB /T 8170), Metallic Material - Mechanical Testing - Vocabulary (GB/T 1063) and Evaluation for Computerized Data Acquisition Systems for Used in Static Uniaxial Testing Machines - The minimum value among three measurements of the original cross-sectional area in Chapter 7 has been changed into average value. - Basic principles of judgment on the positions of upper and lower yield strength have been added in Chapter 1. - Chapter "the Numerical Rounding of Test Results" has been added. The Normative Appendix J " Determinations and Specifications of plastic elongation strength Rp) with Successive Approximation Method" has been added. - The examples of the measurement of permanent set strength (Rro.) with K Removal of Force have been added. - The detailed description of proportional sample and non-proportional sample in Appendix B, Appendix C, Appendix D and Appendix E has been modified correspondingly. - The verification method of uncertainty measurement has been modified and was formed into Appendix L - the uncertainty evaluation of tensile testing measurement result. To be convenient for use, the following editing revisions are made in this Part: a) "This part of the international standard" was changed into "this Part"; b) The decimal ", " has been replaced with the decimal ".". c) The foreword of the international standard was deleted. This Part replaces GB/T 8-00 "Metallic Materials--Tensile Testing at Ambient Temperature", and has made atively great modification and supplement on the former I

5 Metallic Materials - Tensile Testing - Part 1: Method of Test at Room Temperature 金属材料拉伸试验第 1 部分 : 室温试验方法 1 Scope This part of GB/T 8 specifies the principle, definition, symbols, explanation, test piece and dimensional measurement, testing equipment, testing requirements, performance determination, the numerical rounding of determination results and testing report of the method for tensile testing of metallic materials. This Part applies the determination of tensile performance of metallic materials at room temperature. Note: Appendix A indicates complementary recommendations for computer controlled testing machines. Normative References The following referenced document is indispensable for the application of this document. For dated references, only the edition cited applies. For the undated references, the latest edition of the referenced document (including all the amendments) applies. GB/T 975 Steel and Steel Products - Location and Preparation of Samples and Test Piece for mechanical testing (GB/T , eqv ISO 377: 1997) GB/T 8170 Rules of rounding off for numerical values & expression and judgment of limiting values GB/T 1063 Metallic material - Mechanical testing - Vocabulary (GB/T , ISO 3718:007, MOD) GB/T 1160 Calibration of Extensometers Used in Uniaxial Testing (GB/T , ISO 9513: 1999, IDT) GB/T 1685 Verification of Static Uniaxial Testing Machines - Part 1: Tension/ Compression Testing Machines -Verification and Calibration of the Force-measuring System (GB/T , ISO : 004 IDT) GB/T Steel-Conversion of Elongation Values - Part 1: Carbon and Low Alloy Steels (GB/T , eqv ISO 566-1: 1984) GB/T 066 Evaluation for Computerized Data Acquisition Systems for Used in Static Uniaxial Testing Machines 3 Terms and Definitions. 1

6 The following terms and definitions as well as those in GB/T 1063 are applicable to this Part. 3.1 Gauge length L The length of the circular column or prism part of the sample in measurement of the elongation Original gauge length L o Length between gauge length marks on the piece measured at room temperature before the exertion of forces 3.1. Final, gauge length after fracture L u Length between gauge length marks on the test piece measured after rupture, at room temperature, the two pieces having been carefully fitted back together so that their axes lie in a straight line. 3. Parallel length L c Length of the parallel reduced section of the test piece. Note: The concept of parallel length is replaced by the concept of distance between grips for unmachined test pieces. 3.3 Elongation Increase in the original gauge length at any moment during the test 3.4 Percentage elongation Elongation expressed as a percentage of the original gauge length [1] Percentage of permanent elongation Increase in the original gauge length L o of a test piece after removal of a specified stress, expressed as a percentage of the original gauge length Percentage elongation after fracture A Permanent elongation of the gauge length after fracture (L u -L o ) expressed as a percentage of the original gauge length (L o ) [1]. Note: For proportional test pieces, if the original gauge length is not equivalent to ) S o where S o is the original cross-sectional area of the parallel length, the symbol A should be supplemented by a subscript indicating the coefficient of proportionality used e.g. A 11.3 indicates a percentage elongation of the gauge length, 11.3 S O. For non-proportional test pieces, the symbol A should be supplemented by a subscript indicating the original gauge length used, expressed in mllimetres, e.g. A 80mm indicates a percentage elongation of gauge lenth of 80mm. 3.5 Extensometer gauge Iength L e Initial extensometer gauge length used for measurement of extension by means of extensometer. Note: For measurement of yield and proof strength performances, L e should span as much of the parallel length of the test piece as possible. Ideally, as a minimum, Le should be great than L o /, but less than approximately 0.9Lc. This should ensure

7 Value of the increase of strain over the parallel length of the test piece per time based on the crosshead separation rate and the parallel length of the test piece Crosshead separation rate v c displacement of the crossheads per time Stress rate Increase of stress per time Note: Stress rate should only be used in the elastic part of the test (Method B) 3.8 Percentage reduction of area Z Maximum change in cross-sectional area which has occurred during the test, (S o -S u ) expressed as a percentage of the original cross-sectional area S o. Z = S O S S o u Maximum force Note: For materials which display discontinuous yielding, but where no workhardening can be established, F m is not defined in this part (see footnote in Figure 8c) Maximum force F m As for materials displaying no obvious yielding (discontinuous yielding) highest force during the test Maximum force F m As for materials displaying discontinuous yielding, highest force that the test piece withstands during the test after the beginning of workhardening. See Figure 8a) and b) Stress R At any moment during the test, force divided by the original cross-sectional area, S o of the test piece. Note 1: All references to stress in this Part of GB /T8 are to engineering stress. Note : In what follows, the designation force and stress or extension, percentage extension and strain respectively, are used on various occasions (as figure axis labels or in explanations for the determination of different properties). However, for a general description of definition of a well-defined point on a curve, the designations force and stress or extension, percentage extension and strain, respectively, are interchangeable Tensile strength R m. Stress corresponding to the maximum force F m [1] Yield strength When the metallic material exhibits a yield phenomenon, stress corresponding to the point reached during the test at which plastic deformation occurs without an increased. The upper and lower yield strengths should be categorized respectively [1]. 5

8 5 Principle The test involves straining a test piece by tensile force, generally go fracture, for the determination of one or more of the mechanical properties defined in Chapter 3. The test is carried out at room temperature between 10 ~35, unless otherwise specified. Tests carried out under controlled conditions shall be made at a temperature 3 ±5. 6 Test Piece 6.1 Shape and dimensions General The shape and dimension of the test pieces may be constrained by the shape and dimensions of the metallic product from which the test pieces are taken. The test piece is usually obtained by machining a sample from the product or a pressed blank or casting. However, products of uniform cross-section (sections, bars, wires, etc.) and as-cast test piece (i.e. for cast iron and non-ferrous alloys) may be tested without being machined. The cross-section of the test pieces many be circular, square, rectangular, annular or, in special cases, some other uniform cross-section. Preferred test piece have a direct ationship between the original gauge length L o and the original cross sectional area, S o, expressed by the equation L o = k The internationally adopted value for k is The original gauge length shall be not less than 15mm. When the cross-sectional area of the test piece is too small for this requirement to be met with, k=5.65, a higher value (preferably 11.3) or a non-proportional test piece may be used. Note: By using an original gauge length smaller than 0mm, the measurement uncertainty is increased. For non-proportional test pieces, the original gauge length, Lo is independent of the original cross-sectional area, So. The dimensional tolerances of the test pieces shall be in accordance with the Appendixes b to E (see 6.) 6.1. Machined Test Pieces Machined test pieces shall incorporate a transition radius between the gripped ends and the parallel length if these have different dimensions. The dimensions of the transition radius are important and it is recommended that they be defined in product specification if they are not given in the appropriate Appendix (see 6.) The gripped ends may be of any shape to suit the grips of the testing machine. The axis of the test piece shall coincide with the axis of application of the force. The parallel length L c or in the case where the test piece has no transition radii, the free length between the grips, shall always be greater than the original gauge length, L o. S o 11

9 Each end of the original gauge length shall be marked by means of fine marks or scribed lines or thin ink lines, but not by notches which could result in premature fracture. For proportional test pieces, the calculated value of the original gauge length may be rounded to the nearest multiple of 5mm according to GB /T 8170, provided that the difference between the calculated and marked gauge length is less than 10% of L o. The original gauge length shall be marked to an accuracy of ±1%. If the parallel length L c is much greater than the original gauge length, as, for instance, with unmachined test pieces, a series of overlapping gauge lengths may be marked. In some cases, it may be helpful to draw, on the surface of the test piece, a line parallel to the longitudinal axis, along which the gauge lengths are marked. 9 Accuracy of Testing Apparatus The force-measuring system of the testing machine shall be calibrated in accordance with GB/T , class 1 or better. The accuracy level of the extensometer s shall meet the requirements of GB /T For the determination of upper yielding strength, lower yielding strength, percentage yield point extension, proof strength of plastic extension, proof strength of total extension, permanent set strength and verification test of permanent set strength, the used extensometer shall be at Class 1 or better; for the determination of other properties with greater percentage extension s such as the tensile strength, percentage total extension at the maximum force, percentage plastic extension force, the percentage total extension at fracture and percentage elongation after fracture, the used extensometer shall be at or better than Class. The computer-controlled tensile testing machine shall be in accordance with GB /T 066 and referred to Appendix A. 10 Conditions of Testing 10.1 Setting the force zero point The force-measuring system shall be set to zero after the testing loading chain has been assembled, but before the test piece is actually gripped at both ends. Once the force zero point has been set, the force-measuring system may not be changed in any way during the test. Notes: The use of this method ensure, that on one hand the weight of the gripping system is compensated for in the force measurement and on the other hand any force resulting from the clamping operation does not affect this measurement. 10. Method of gripping The test pieces shall be gripped by suitable means, such as wedges, screwed grips, parallel jaw faces or shouldered holders. Every endeavor should be made to ensure that the test pieces are held in such a way that the force is applied as axially as possible, in order to minimize bending (more information is given in ASTM E101 [], for example). This is of particular importance when testing brittle materials or when determining proof strength, plastic extension, proof strength (total extension), permanent set strength or yield strength. 13

10 ė Lc - the estimated strain rate over the parallel length; L c - the parallel length In the range following R p or R t or end of yielding (see 3.7.), ė Lc or ė L e can be used. The use of ė Lc is recommended to avoid any control problems which may arise if necking occurs outside the extensometer gauge length. The strain rates specified in to shall be maintained during the determination of the evant material property (See Figure9). During switching to another strain rate to another control mode, no discontinuities in the stress-strain curve should be introduced which distort the values of Rm, Ag, Agt (See Figure 10). The effect can be reduced by a suitable gradual switch between the rates. The shape of the stress-strain curve in the workhardening range can also be influenced by the strain rate. The testing rate used should be documented. (See 10.6) Determination of the upper yield strength or the set extension strength R p, R t R r. The strain rate, ė L e, shall be kept as constant as possible up to and including the determination of R eh, or R p,or R t or R r..during the determination of these material properties the strain rate ė L e shall be in one of the two following specified ranges (see also Figure 9). Range 1: ė L = s-1 e, with ative tolerance± 0%; Range : ė = L s-1 e, with a ative tolerance of ± 0%; (recommended unless otherwise specified) If the testing machine is not able to control the strain rate directly, the estimated strain rate over the parallel length, ė L e, i.e. constant crosshead separation rate, shall be used. This rate shall be calculated using Equation (1). If the flexibility of the testing machine is considered, Appendix F shall be referred to The determination of the lower yield strength, R e, and percentage yield point extension, A e. Following the detection of the upper yield strength, the estimated strain rate over the parallel length ė L e, shall be maintained in one of the following two specified ranges (see Figure 9) until discontinuous yielding has ended. -Range : ė L =0.0005s-1 e, with ative tolerance of 0% (recommended, when R el is determined) - Range 3: ė L =0.00s-1 e, with a ative tolerance of 0% Strain rate for the determination of the tensile strength, R m, percentage after fracture, 15

11 directly, it shall be fixed by regulating the stress rate just before yield begins, the controls of the machine not being further adjusted until completion of yield. In no case shall the stress rate in the elastic range exceed the maximum rates given in Table Upper and lower yield strengths, R eh and R el If both upper and lower yield strengths are determined during the same test, the conditions for determining the lower yield strength shall be complied with (see ) Proof strength (plastic extension),r p, proof strength (total extension), R t, and permanent set strength R r The rate of separation of the crossheads of the machine shall be kept as constant as possible and within limits corresponding to the stress rates in Table 3 within the elastic range. Within the plastic range and up the proof strength (plastic extension, total extension, and permanent set strength), the strain rate shall not exceed 0.005s Rate of crossheads separation If the testing machine is not capable measuring or controlling the strain rate, a crosshead separation rate equivalent to the stress rate given in Table 3 shall be used until completion of yield Tensile strength, Rm, percentage elongation after fracture, A, percentage total extension at the maximum force, Agt, percentage plastic extension at maximum force, Ag, and percentage reduction area Z. After determination of the required yield/plastic extension strength, the test rate may be increased to a strain rate (or equivalent crosshead separation rate) no greater than 0.008s-1. If only the tensile strength of the material is to be measured, a single strain rate can be used throughout the test which shall not exceed 0.008s Choice of the testing method and rates Unless otherwise specified, the choice of Method (A or B) and test rates are at the discretion of the producer or the test laboratory assigned by the producer, provided that these meet the requirements of this part of GB /T Expression of the chosen testing conditions In order to report the test control mode and testing rates in an abridged for,, the following system of abbreviation can be used. GB /T 8Annn or GB /T 8Bn Where A defines the use of method A (strain rate control), and B the use of method B (stress rate based). The symbols nnn are a series of up to 3 characters that refer to the rates used during each phase of the test, as defined in Figure 9, and n may be added to indicate the stress rate selected during elastic loading. Example 1: GB/T8A defines a test based on strain rate control, using range, and 4. Example : GB/T8B30 defines a test based on stress rate, performed at a nominal stress rate of 30MPa s -1. Example 3: GB/T8B defines a test based on stress rate, performed at a nominal stress rate according to Table Determination of the Upper Yield Strength The upper yield strength R eh may be determined from the force-extension curve or peak 17

12 14 Determination of Proof Strength, Total Extension 14.1 On the force-extension curve, draw a line parallel to the ordinate axis (force axis) and at a distance from this equivalent to the prescribed total percentage extension. The point at which this line intersects the curve gives the force corresponding to the desired total extension strength. The latter R t is obtained by dividing this force by the original cross-sectional area of the test piece S o (see Figure 4). 14. The set total extension strength may be obtained without plotting the force-extension curve using automatic devices (see Appendix A). 15 Method of Verification of Permanent Set Strength The test piece is subject to a force corresponding to the specified set permanent extension strength for 10s to 1s. After removing the force, it is then confirmed that the permanent set extension or elongation is not more than the percentage specified (See Figure 5). Note: This is a pass/fail test, which is not normally performed as a part of the standard tensile test. The stress applied to the test piece and the permissible permanent set extension or elongation is specified by the product specification or requesters of the test. Example: Reporting R r0.5 =750MPa stress indicates that a stress of 750MPa was applied to the test piece and the resulting permanent set was less than or equal to 0.5%. To obtain the specific numerical values of permanent set elongation strength, determination shall be carried out and Appendix K provides the examples to determine the permanent set extension strength. 16 Determination of the Percentage Yield Point Extension For materials that exhibit discontinuous yielding, A c is determined from the force-extension curve by subtracting the extension at R o from the extension of the start of uniform workhardening. The extension at the start of uniform worharding is defined by the intersection of a horizontal line through the last local minimum point, or a regression line through the range of yielding, prior to uniform wokhardening and a line corresponding to the higherst slope of the curve occurring at the start of uniform workhardenign. The yield point extension percentage is obtained from the yield point extension divided by extensometer gauge length (see Figure 7). The test report shall be marked with the method of determination of uniform processing workdhardening starting point. (See Figure 7a or 7b) 0

13 18 Determination of the Percentage Total Extension at Maximum Force The method consists of determining the extension at maximum force on the force-extension curve obtained with an extensometer, A gt, from the equation (3): Calculate the percentage total extension at maximum force Where L e - the extensometer gauge length; L m - the extension at maximum force. ΔLm A gt = 100 (3) L e Note: For materials which exhibit a plateau at maximum force, the percentage total extension at maximum force is the extension at the mid-point of the plateau, see Figure Determination of the Percentage Total Extension at Fracture The method consist of determining the extension at fracture on the force-extension curve obtained with an extensometer. Calculate the percentage total elongation at fracture A t form Equation (4): Where L e - is the extensometer gauge length; L f - is the extension at fracture. ΔLf A t = 100 (4) L e 0 Determination of Percentage Elongation After Fracture 0.1 Percentage elongation after fracture shall be determined in accordance with the definition given in For this purpose, the two broken pieces of the test piece shall be carefully fitted back together so that their exes lie in a straight line. Special precautions shall be taken to ensure proper contact between the broken parts of the test piece when measuring the final gauge length. This is particularly important for test pieces of small cross-section and test pieces having low elongation values. Calculate the percentage elongation after fracture, A from Equation (5)

14 Where S o - the original cross-sectional area of the parallel length; S u - the minimum cross-sectional area after fracture. S o S u Z = 100 (6) S o Note: It is very hard for the measurement accuracy of the cross-sectional area after fracture to arrive at ± % for the testing pieces of small diameter round test pieces or other cross-sectional geometries. Rounding of Numerical Values of Testing Results Results should be rounded to the following precisions or better, if not otherwise specified in product standards: - strength values, to 1MPa, to the nearest whole number; - percentage yield point extension values, to the nearest 0.1%, and all other percentage extension and elongation values to the nearest 0.5%; - percentage reduction of area, to the nearest 1%. 3 Test Report The test report shall contain at least the following information unless otherwise agreed by the partied concerned. a) number of this Part of national standard; b) reference to this part of the national standard extended with the test condition information specified in c) identification of the test piece; d) Specified material name and designation, (if known); e) type of test piece f) location and direction of sampling of test pieces, if known; g) testing control model(s) and testing rate(s) or testing rate range(s) (see 10.6) if different from the recommended methods and values given in 10.3 and h) test results. 4 Measurement Uncertainty 4.1 General Measurement uncertainty analysis is useful for identifying major sources of inconsistencies of measured results. Measurement uncertainty analysis is useful Product standards and material property databases based on this part of GB/T8 and earlier edition of GB/T8 have been an inherent contribution from measurement uncertainty. 4

15 Appendix A (Informative) Recommendations Concerning the Use of Computer-controlled Tensile Testing Machines A.1 General This Appendix contains additional recommendations for the determination of mechanical properties by using a computer-controlled tensile testing machine. In particular it provides the recommendations that should be taken into account in the software and testing conditions. These recommendations are ated to the design, the software of the machine and its validation, and to the operating conditions of the tensile test. A. Terms and definitions For the purposes of this Appendix, the following definition applies. A..1 Computer-controlled tensile testing machine Machine for which the control and monitoring of the test, the measurements, and the data processing are undertaken by computer. A.3 Tensile testing machine A.3.1 Design The machine should be designed in order to provide outputs giving analogue signals untreated by the software. If such outputs are not provided, the machine manufacturer should give raw digital data with information on how these raw digital data have been obtained and treated by the software. They should be given in basic Sl units ating to the force, the extension, the crosshead separation, the time and the test piece dimensions. An example of the format of suitable data files is given in Figure A.1. A.3. Data sampling frequency The frequency bandwidth of each of the measurement channels and the data sampling frequency should be sufficiently high to record the material characteristics to be measured. For example to capture R eh, Equation (A.1) may be used to determine the minimum sampling frequency, f min : e E f min = 100 R q eh (A.1) Where, f min is the minimum sampling frequency, in reciprocal seconds; e is the strain rate, in reciprocal seconds; E is the modulus of elasticity, in MPa; R eh is upper yield strength, in MPa; q is the ative force measurement accuracy grade of the testing machine. The choice of R eh in Equation (A.1) is due to the fact that it corresponds to a transient 31

16 characteristic during the test. If the material tested has no yield phenomena, the proof strength R p0. should be used and the required minimum sampling frequency can be halved. If method B (stress rate based) is used, the minimum sampling frequency should be calculated using Equation (A.): f R min = ReH q 100 (A.) Where, R is the stress rate, in MPa per second. A.4 Determination of the mechanical properties A.4.1 General The following requirements should be taken into account by the software of the machine. A.4. Upper yield strength and lower yield strength A.4..1 Upper yield strength R eh ( ) should be considered as the stress corresponding to the highest value of the force prior to a reduction of at least 0.5% of the force, and followed by a region in which the force should not exceed the previous maximum over a strain range not less than 0.05%. A.4.. Lower yield strength The R el defined in shall meet the basic principles of location judgment of lower yield strength in Chapter 1. A.4.3 Proof strength at plastic extension and proof strength at total extension R p (3.10.3) and R t (3.10.4) can be determined by interpolation between adjacent points on the curve. A.4.4 Percentage total extension at maximum force A gt (see and Figure 1) should be considered as the total extension corresponding to the maximum of the stress-strain curve after the yield point. For some materials it is necessary to smooth the stress-strain curve in which case a polynomial regression is recommended. The smoothing range may have an influence on the result. The smoothed curve should be a reasonable representation of the evant part of the original stress-strain curve. A.4.5 Percentage plastic extension at maximum force A g (see and Figure 1) should be considered as the plastic extension corresponding to the maximum of the stress-strain curve after the yield point. For some materials it is necessary to smooth the stress-strain curve in which case a polynomial regression is recommended. The smoothing range may have an influence on the result. The smoothed curve should be a reasonable representation of the evant part of the original stress-strain curve. A.4.6 Percentage elongation at fracture A Determine A t with reference to the definition of fracture in Figure A.. The fracture is considered to be effective when the force between two consecutive points decreases: a) By more than five times the difference between the value of the previous two points, followed by a decrease to lower than % of the maximum tensile force; b) Lower than % of the maximum tensile force (soft materials). 3

17 range. References to these and other acceptable methods are given in References [4], [5], [6], [7]. A recommended method to determine the slope of the elastic line for evaluation of R p0. (Reference [0]): - linear regression of the linear range; - lower limit: 10% of R P0. ; - upper limit: 50% of R P0. ; - to get more exact data for R p0., the elastic line must be checked and if necessary recalculated with other limits. A.5 Validation of the test machine software The efficiency of the methods used by the testing system to determine the various material characteristics may be checked by comparison with results determined in the traditional manner by examination/calculation from plots of analogue or digital data. Data which are derived directly from the machine transducers or amplifiers should be collected and processed using equipment with frequency bandwidth, sampling frequency and uncertainty, of at least equal to those used to provide the machine computer-calculated results. Confidence may be placed in the accuracy of the machine computer processing if differences in arithmetic means between computer-determined values and those determined manually on the same test piece are small. For the purposes of assessing the acceptability of such differences, five similar test pieces should be tested and the average difference for each evant property should lie within the limits shown in Table A.1. Note: This procedure confirms only that the machine finds the material characteristics for the particular test piece shape, material tested and conditions used. It gives no confidence that the properties of the material tested are either correct or fit for purpose. If other methods are used, e.g. injection of a pre-determined set of data from a known material with a recognized level of quality assurance, these should meet the requirements mentioned above and those in Table A.1. Table A.1 Maximum Permitted Differences between Computer-derived and Manually Derived Results Parameter D a s b Relative c Absolute c Relative c Absolute c R p0. 0.5% MPa 0.35% MPa R p1 0.5% MPa 0.35% MPa R eh 1% 4MPa 0.35% MPa R el 0.5% MPa 0.35% MPa R m 0.5% MPa 0.35% MPa A - % - % D = a 1 n n i = 1 D i b 1 s = n - 1 n i = 1 ( D i D ) Where, D i is the difference between the result of manual evaluation, H i, and the result of computer evaluation, R i, for a test piece (D i =H i -R i ); n is the number of identical test pieces from one sample ( 5). c The highest of the ative and absolute values should be taken into account. 35

18 Table B. Non-proportional Test Pieces of Rectangular Cross Sections b o /mm r/mm L o /mm With ends L c /mm Without ends Test piece No P P a 100 a 10 a P7 a For test pieces with 5mm width, their L c /b o and L o /b o values are very low as compared with test pieces of 1.5mm and 0mm widths. The performances obtained by such kind of test pieces, especially the post-fracture percentage elongation (absolute value and scatter range), are different from other two kinds of test pieces. Table B.3 Tolerances on the Width of the Test Piece in millimeters Nominal width of the test piece Dimensional tolerance Tolerance on shape b 1.5 ± ± ± a If the width tolerance of test pieces meets that specified in Table B.3, the nominal value may be used for the original sectional area instead of calculating through actual measurement. b Maximum deviation between the measurements of the width along the entire parallel length, L c, of the test piece. B.3 Preparation of test pieces The test pieces shall be prepared so as not to affect the properties of the sample. Any areas which have been hardened by shearing or pressing shall be removed by machining. These test pieces are predominantly prepared from sheet or strip. If possible, the as-rolled surfaces should not be removed. Note: The preparation of these test pieces by punching can result in significant changes to the material properties, especially the yield/proof strength (due to work hardening). Materials which exhibit high work hardening should, generally, be prepared by milling, grinding etc. For very thin materials, it is recommended that strips of identical widths should be cut and assembled into a bundle with intermediate layers of a paper which is resistant to the cutting oil. Each small bundle of strips should then be assembled with a thicker strip on each side, before machining to the final dimensions of the test piece. The dimensional tolerance and tolerance on shape of test pieces for machining shall meet the requirements given in Table B.3, e.g. ±0.05mm for a nominal width of 1.5mm, means that no test piece shall have a width outside the two values given below: 1.5mm +0.05mm =1.55mm 1.5mm-0.05mm=1.45mm B.4 Determination of the original cross-sectional area S o shall be calculated from measurements of the dimensions of the test piece. The error in determining the original cross-sectional area shall not exceed ±%. As the greatest part of this error normally results from the measurement of the thickness of the test piece, the error in measurement of the width shall not exceed ±0.%. In order to achieve test results with a reduced measurement uncertainty, it is recommended that the original cross-sectional area be determined with an accuracy of 1% or better. For thin materials, special measurement techniques may be required. 37

19 Appendix C (Normative) Types of Test Pieces to Be Used for Wire, Bars and Sections with a Diameter or Thickness of Less Than 4mm C.1 Shape of the test piece The test piece generally consists of an unmachined portion of the product (see Figure 1). C. Dimensions of the test piece The original gauge length, L o, shall be taken as 00mm±mm, or 100mm±1mm. The distance between the grips of the machine shall be equal to at least L o + 3b o or L o +3d o but a minimum of L o +0mm. See Table C.1. Table C.1 Non-proportional test piece d o or a o /mm L o /mm L c /mm Test specimen No R R10 If the percentage elongation after fracture is not to be determined, a distance between the grips of at least 50mm may be used. C.3 Preparation of test pieces If the product is delivered coiled, care shall be taken in straightening it. C.4 Determination of the original cross-sectional area Determine S o to an accuracy of 1% or better. For products of circular cross-section, the original cross-sectional area may be calculated from the arithmetic mean of two measurements carried out in two perpendicular directions. The original cross-sectional area, S o, may be determined from the mass of a known length and its density using Equation (C.1): S o 1000 m = ρ L Where, m is the mass, in grams, of the test piece; L t is the total length, in millimeters, of the test piece; ρ is the density, in grams per cubic centimeter, of the test piece material, (g cm -3 ). t (C.1) 38

20 D.3. Machining tolerances The value given in Table D.4, e.g. ±0.03mm for a nominal diameter of 10mm, means that no test piece shall have a diameter outside the two values given below. 10mm+0.03mm=10.03mm 10mm-0.03mm=9.97mm D.3.3 Tolerances on shape The value given in Table D.4 means that, for a test piece with a nominal diameter of 10 mm which satisfies the machining conditions given above, the deviation between the smallest and largest diameters measured shall not exceed 0.04mm. Consequently, if the minimum diameter of this test piece is 9.99mm, its maximum diameter shall not exceed 9.99 mm+0.04mm=10.03mm. Table D.4 Tolerances Relating to the Transverse Dimensions of Test Pieces Dimensions and tolerances in millimetres Designation Nominal transverse dimension Machining tolerance on the nominal dimension a b Tolerance on shape Diameter of machined test pieces of circular cross-section and transverse dimensions of test pieces of rectangular cross-section machined on all four sides Transverse dimensions of test pieces of rectangular cross-section machined on only two opposite sides 3 6 >6 10 >10 18 > >6 10 >10 18 >18 30 >30 50 ± ± ± ± ± ± ± ± ± a If the tolerances of test pieces meet the requirements specified in Table D.4, then the nominal value of the original cross-sectional area is to be included in the calculation without having to measure it. If these machining tolerances are not complied with, it is essential to measure every individual test piece. b Maximum deviation between the measurements of a specified transverse dimension along the entire parallel length, L c, of the test c piece. D.4 Determination of the cross-sectional area The nominal dimensions can be used to calculate S o for test pieces of circular cross-section and rectangular cross-section machined on all four sides that satisfy the tolerances given in Table D.4. For all other shapes of test pieces, the original cross-sectional area shall be calculated from measurements of the appropriate dimensions, with an error not exceeding ±0.5% on each dimension. 41

21 deformation within the gauge length. It is allowed to flatten the two gripping heads of the pipe section test piece, and carry out tests after adding or not adding slab choke plug. In arbitration test, the gripping heads shall not be flattened, but adding choke plugs. Table E. Test Piece of Pipe Section L o /mm L c /mm Test piece type No L o +1.5 S o Arbitration test: L o + S o S S8 E..3 Machined transverse test piece When the wall thickness of machined transverse test piece of rectangular cross-section is less than 3mm, the test pieces of Table B.1 or Table B. shall be adopted; when the wall thickness is larger than or equal to 3mm, test pieces of Table D. or Table D.3 shall be adopted. For test pieces without heads, there should be sufficient free length between two gripping heads in order to make the distance between original gauge length mark of test piece and proximal gripping head no less than 1.5b o. Special measures shall be adopted to align the transverse test pieces. E..4 Circular cross-section test piece machined in tube wall The test pieces with machined longitudinal circular cross-section shall adopt test pieces of Table D.1. Relevant product standard shall specify circular cross-section dimensions according to the wall thickness; if not required, select according to those specified in Table E.3. Table E.3 Test Pieces with Wall Thickness Machined Longitudinal Circular Cross-sections a o /mm Test pieces adopted 8~13 R7 >13~16 R5 >16 R4 E.3 Determination of the original cross-sectional area S o for the test piece shall be determined to the accuracy of ±1%. The original cross-sectional area, S o, of the pipe section test piece, or longitudinal or transverse test piece without heads may be determined from the mass of the test piece, the length of which has been measured, and from its density using Equation (E.1): S o 1000 m = ρ L t Where, M is the mass, in grams, of the test piece; L t is the total length, in millimetres, of the test piece; ρ is the density, in grams per cubic centimetre, of the test piece material. The original cross-sectional area, S o, of a test piece consisting of a longitudinal sample shall be calculated according to Equation (E.): (E.1) 43

22 Appendix F (Informative) Estimation of the Crosshead Separation Rate in Consideration of the Stiffness (or Compliance) of the Testing Machine Equation (1) in does not consider any elastic deformation of the testing equipment (frame, load cell, grips, etc.). This means that the deformation can be separated into the elastic deformation of the testing equipment and the deformation of the test piece. Only a part of the crosshead separation rate is transferred to the test piece. The resulting strain rate at the test piece, e m, is given by Equation (F.1): m So e m = v c /( + Lc ) (F.1) C M Where, C M is the stiffness, in newtons per millimetre, of the testing equipment (around the point of interest such as R p0., if stiffness is not linear, e.g. when using wedge grips); e m is the strain rate generated on the test piece, in per second, (s -1 ); L c is the parallel length, in millimetres, of the test piece; m is the slope, in megapascals, of the stress-percentage extension curve at a given moment of the test (e.g. around the point of interest such as R p0. ); S o is the original cross-section area, in square millimetres; v c is the crosshead separation rate, in millimetres per second. Note: The values of m and C M derived from the linear portion of the stress/strain curve cannot be used. Equation (1) in does not compensate for the effects of compliance. A better approximation of the crosshead separation rate, v c, in millimetres per second, necessary to produce a resulting strain rate at the test piece, e m, around the point of interest, can be made from Equation (F.): m So v c = em( + Lc ) (F.) C M 45

23 Appendix I (Informative) Determination of the Percentage Plastic Elongation Without Necking, Awn, for Long Products Such as Bars, Wire and Rods This method is to be performed on the longer part of a broken tensile test piece. Before the test, equidistant marks are made on the gauge length, the distance between two successive marks. The marking of the initial gauge length, L o, should be being equal to a fraction of the initial gauge length, L o accurate to within ±0.5mm. The measurement of the final gauge length after fracture, L u, is made on the longest broken part of the test piece and should be accurate to within ±0.5mm. In order for the measurement to be valid, the following two conditions should be met: a) the limits of the measuring zone should be located at least 5d o from the fracture and at least.5d o from the grip; b) the measuring gauge length should be at least equal to the value specified in the product standard. The percentage plastic elongation without necking is calculated by Equation (I.1): A wn = L ' u L ' L o ' o 100 (I.1) Note: For many metallic materials, the maximum force occurs in the range where necking starts. This means that the A g and A wn for these materials will be nearly equal. Large differences will be found in highly cold deformed material such as double reduced tin plate or irradiated structural steel or tests performed at elevated temperatures. 49

24 Appendix J (Normative) Determination for Proof Strength of Plastic Extension (Rp) under Successive Approximation Method J.1 Scope The successive approximation method is applicable to the determination for the strength of plastic extension of metallic materials with straight section without obvious elasticity. As for the metallic materials with a height of elasticity straight section no less than 0.5F m in its force-extension curve diagram, the determination for its plastic extension strength also applies. The successive approximation method may be applied to the test for the automation of tension test over this property. J. Method Determine the plastic extension strength according to force-extension curve diagram. In the test, record the force-extension curve diagram at least until the value exceeding the expected plastic extension strength. Estimate a point of A 0 as the force F 0 p0. with a percentage plastic extension equal to 0.% on the force-extension curve, determine two points B 1 and D 1 which respectively stand for the force of 0.1F 0 p0. and 0.5F 0 p0., and draw a straight line B 1 D 1. Intercept segment OC (OC=0.% n L e n n, where n refers to the extension magnification) from the origin O (carry out the origin point correction if necessary) and draw the line CA 1 parallel to the line B 1 D 1 through point C, make CA 1 intersect the curve at point A 1. If A 1 and A 0 are coincident, F 0 p0. shall be regarded as the force under the percentage plastic extension is 0.%. If point A 1 and point A 0 are not coincident, a further approximation shall be carried out according to above-mentioned procedures. In this case, take point A1 as force of F 0 p0., determine two points B and D which respectively stand for the force of 0.1F 0 p0. and 0.5F 0 p0., and draw a straight line B D. Draw the line CA parallel to the line B D through point C, make CA intersect the curve at point A. Carry out the successive approximation in this way until the last intersection point A n and the former intersection point A n-1 are coincident (see Figure J.1). A n shall be regarded as the force under the percentage plastic extension is 0.%. The measured plastic extension strength R p0. shall be obtained by dividing the original cross-sectional area of the test specimen with this force. The slope of the finally obtained straight line B n D n generally may be regarded as the standard slope for determining other plastic extension strength. Note: Under successive approximation method, it shows unsuitable when determining the plastic extension strength (R p ) of materials with a very low strength such as soft aluminium. 50