EURONORM 2-80

U.D.C.: 620.720.669.14 March 1980

Tensile test on steel EURONORM

2 - 8 0

1 SCOPE AND FIELD OF APPLICATION

2 TEST PRINCIPLE

3 DEFINITIONS AND SYMBOLS

3.1 Gauge length

3.2 Extensometer gauge length

3.3 Elongation

3.4 Reduction of area

3.5 Load

3.6 Stress

4 TEST PIECES

4.1 General shape

4.2 Shape and dimensions of the parallel portion

4.3 Parallel length

4.4 Gauge length

4.5 Preparation of test pieces

CONTENTS 5 TEST CONDITIONS

5.1 Rate of stressing

5.2 Accuracy of the test equipment

5.3 Gripping method

6 DETERMINATION OF ELONGATION AFTER FRACTURE

7 DETERMINATION OF PROOF STRESS NON-PROPORTIONAL ELONGATION AND TOTAL ELONGATION

8 METHOD OF VERIFYING THE PERMANENT SET STRESS

ANNEX Nomogram for calculating gauge length of test pieces of rectangular cross-section

COMMENTS

1 SCOPE A N D FIELD OF APPLICATION

This EURONORM specifies requirements for a tensile test on steel products and defines the mechanical properties which can be determined by this test. It applies to steel products of diameter equal to or greater than 4 mm or thickness equal to or greater than 3 mm and to products of

small dimensions such as bars and sections. There are separate standards applicable to tensile tests on certain products such as wires and tubes. Thin sheets are covered by EURONORM 11.

2 TEST PRINCIPLE

The test consists of straining a test piece by tensile stress, generally to fracture, with a view to determining one or more of the properties given below.

The test shall be carried out at ambient temperature (23 C 5 C) unless otherwise specified. If a test temperature outside the range 18 C28 C is used this shall be reported.

3 DEFINITIONS A N D SYMBOLS

3.1 Gauge length

The gauge length, at a given moment in the test, is the length of the cylindrical or prismatic part of the test piece over which elongation is to be measured. In particular, a distinction is to be made between the following:

3.1.1 Original gauge length

The original gauge length (L0) the test piece is strained.

3.1.2 Final gauge length

is the gauge length before

The final gauge length (Lu) is the gauge length after the test piece has been fractured and the fractured parts have been carefully fitted together so that their longitudinal axes are coincident.

Only the last edition of the EURONORMS quoted is valid

Copyright by the Standardization Offices of the European Communities' Member States

3.2 Extensometer gauge length

The extensometer gauge length (Le) is the length of the parallel portion of the test piece used for the measurement of extension by means of an extensometer. (This length may differ from L 0 but shall be greater than b or d (see table 1) and less than the parallel length Lc.)

3.5 Load

3.5.1 Maximum load

The maximum load (Fm) is the highest load which the test piece withstands during the test.

3.3 Elongation

The elongation is, at a given moment in the test, the variation in the gauge length.

3.3.1 Percentage permanent set elongation

The percentage permanent set elongation is the variation in the gauge length of the test piece after application then removal of a specified stress (see 3.6.3); this increase is expressed as a percentage of the original gauge length. If a symbol for this elongation is used it shall be supplemented by an index indicating the specified stress.

3.3.2 Percentage elongation after fracture

The percentage elongation after fracture (A) is the permanent elongation of the gauge length after fracture Lu L0 expressed as a percentage of the original gauge length L0.

Note: In the case of proportional test pieces, only when the gauge length is other than 5 65 l/So, (*) S0 being the original cross-sectional area of the parallel length, is A supplemented by an index indicating the coefficient of proportionality, thus: A 11,3 = percentage elongation after fracture on an original

gauge length of 11-3 |/S0.

In the case of non-proportional test pieces, the symbol A is to be supplemented by an index indicating the original gauge length used, for example: Aso = percentage elongation after fracture on an original

gauge length of 80 mm.

3.4 Reduction of area

The reduction of area is the local reduction in cross-sectional area of the test piece which has occurred during the test due to the effect of stress.

3.4.1 Percentage reduction of area

The percentage reduction of area (Z) is the ratio of the maximum change in the cross-sectional area, S0Su , which has occurred during the test to the original cross-sectional area S0. It is expressed as a percentage.

The original cross-sectional area (S0) is the cross-sectional area before the test piece is strained.

The minimum cross-sectional area after fracture (Su) is the minimum cross-sectional area after fracture measured after the test pieces have been fitted together again.

3.6 Stress

The stress is, at any time during the test, the load divided by the original cross-sectional area S0 of the test piece.

3.6.1 Tensile strength

The tensile strength (R maximum load.

3.6.2 Yield stress

is the stress corresponding to the

[1)565]/^ = 5]/0

The yield stress is also known as the apparent yield stress. The following distinctions are made:

3.6.2.1 Upper yield stress

The upper yield stress (ReH) ' s t n e value of the stress at the moment when the first actual fall in stress is observed (see figure 1).

3.6.2.2 Lower yield stress

The lower yield stress (ReL) is the lowest value of the stress during plastic deformation at yield but disregarding any initial transient effects (see figure 1).

3.6.3 Permanent set stress

The permanent set stress (Rr) is also known as the stress at permanent set limit: the stress which corresponds, after removal of load, to a specified permanent elongation, expressed as a percentage of the original gauge length. The specified value is often 02%. The symbol used is followed by an index denoting the specified percentage of the original gauge length, for example R r 02 (see figure 2).

3.6.4 Proof stress (non-proportional elongation)

The proof stress (non-proportional elongation) (Rp), is also known as proof stress, and is the stress corresponding to a non-proportional elongation equal to a specified percentage of the original gauge length. The specified value is often 0-2%. The symbol used is followed by an index denoting the specified percentage of the original gauge length, for example Rp0-2 (see figure 3).

3.6.5 Proof stress (total elongation)

The proof stress (total elongation) (Rt), or proof stress under load, is the stress corresponding to a total elongation (elastic elongation plus plastic elongation) equal to a specified percentage of the original gauge length. The specified value is often 0-5%. The symbol used is followed by an index denoting the specified percentage of the original gauge length, for example R t 0-5 (see figure 4).

Table I

Svmbols and units of measurement

Reference number f1)

Units of measurement Svmbois Designations

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16(2)

17

mm

mm

mm

mm

mm

mm

mm

mm2

mm

mm2

N / m m 2 (3)

N/mm 2

N

N/mm 2

mm

%

%

18

19

20

21

22

N/mm2

%

N/mm2

%

N/mm2

d

a

b

L0

L,

Le

L,

So

Lu

Su

Re

Re

F

Rn

Lu-L0

R,

R

R,

Diameter of test piece with circular cross-section

Thickness of flat test piece

Width of flat test piece

Original gauge length

Parallel length

Extensometer gauge length

Total length of test piece

Gripped ends

Original cross-sectional area of tne parallel length

Final gauge length

Minimum cross-sectional area after fracture

Upper yield stress

Lower yield stress

Maximum load

Tensile strength

Permanent elongation after fracture

Percentage elongation after fracture:

^ - ^ x l O O Lo

Percentage reduction of area:

S - S x 100

s0 Permanent set stress

Permanent set elongation

Proof stress (non-proportional elongation)

Specified non-proportional elongation

Proof stress (total elongation)

Sec figures 1 to 7. In the case of proportional test pieces the symbol A is followed by an index indicating the coefficient of proportionality k in the formula L0 k "J S0 when it is other than 5-65. In the case of non-proportional test pieces, the symbol A is followed by an index indicating the original gauge length used. 1 N / m m 2 = 1 M Pa.

4 TEST PIECES

4.1 General shape

The machined test pieces shall have a transition curve suitably radiused between the parallel length and the gripped ends. The gripped ends may be of any shape suitable for the grips of the testing machines.

In some cases, sections, bars, etc. may be tested without being machined. In these cases, the free lengths between the grips of the machine shall be sufficient to ensure that the gauge marks are at a reasonable distance from the grips.

4.2 Shape and dimensions of the parallel portion

The cross-section pf the test piece may be circular, square, rectangular, or in special cases, of other shapes.

For test pieces of rectangular cross-section, it is recommended that a width/thickness ratio of 8 : 1 should not be exceeded.

As a general rule, the diameter of the parallel portion of cylindrical machined test pieces shall not be less than 4 mm.

Tolerances

The tolerances on the cross-sectional dimensions of the test pieces are specified in table II below. An example of the application of these tolerances is given in comment No 1.

Table II

Tolerances on cross-sectional dimensions of test pieces

Cross-sectional dimensions of test pieces Nominal dimensions in mm Machining tolerances on nominal dimensions (') in mm Tolerances on form in mm

Diameter of machined circular cross-section test pieces

Cross-sectional dimensions of rectangular test pieces machined on the 4 faces

Cross-sectional dimensions of rectangular test pieces machined on two opposite faces only

over not over

over not over

over not over

over not over

3 6

6 10

10 18

18 30

over not over over not over

over not over

over not over

over not over

3 6

6 10

10 18

18 30 j

30 1 50 I

0 0 6

0-075

0 0 9

0 1 0 5

0-03 (2)

0-04 (2)

0-04 (2)

0-05 (2)

Same tolerances as for the diameter of test pieces of circular

cross-section

0-18 (3)

0-22 (3)

0-27 (3)

0-33 (3)

0-39 (3)

f1) The machining tolerances (js 12 to ISO/R 2,Ni> ipplicable when it is desired to use the nominal value of the cross-section in the calculation, without need to measure it.

(2) Tolerance IT 4 \ Maximum deviation between the measurements of a specified cross-sectional dimension along the parallel length of the (3) Tolerance IT l J test piece.

4.3 Parallel length

The parallel length Lc shall be between:

L0 +~2~ and L0 + 2 d in the case of test pieces of circular cross-section;

L0 + 1-5 | /S 0 and L0 + 2-5 prismatic test pieces.

| /S 0 in the case of

According to the type of test piece, the length L0 + 2 d or L0 + 2 | /S0 shall be used in cases of dispute, provided there is sufficient material.

4.4 Gauge length

4.4.1 Proportional test pieces

A proportional test piece is a test piece having a gauge length related to the cross-section in the ratio L0 = k 1 S0 where k is equal to 5-65. For test pieces of circular cross-section this gives L0 = 5 d.

Test pieces of circular cross-section should preferably have the dimensions given in the table below.

Table III

Dimensions for test pieces of circular cross-section

k

5-65

Gauge length I-o = k \| S

in mm

100 1-0

50 0-5

Diameter d

in mm

20 0-150

10 0-075

Cross-section S 0

in mm 2

314

78-5

Parallel length

in mm

110 to 140

55 to 70

Total length

in mm

Depends on the method of gripping the test piece in the machine grips In principle: L t : > L c + 2 d or L,2? L c + 4 d

A nomogram in the annex to this standard facilitates the calculation of the gauge length corresponding to the actual dimensions of test pieces of rectangular cross-section.

4.4.2 Non-proportional test pieces

For economic reasons, it is sometimes necessary in the series testing of flat test pieces to adopt an original gauge length that is independent of the cross-section. The

elongation on the proportional gauge length can then be deduced by means of conversion tables from the elongation obtained. However, in cases of dispute, the elongation measured on the non-proportional test piece can only be accepted if the product standard explicitly specifies this.

4.5 Preparation of test pieces

The test pieces shall be taken and prepared in accordance with EURONORM 18.

5 TEST CONDITIONS

5.1 Rate of stressing

5.1.1 Yield stresses

5.1.1.1 Upper yield stress

In the elastic range, the rate of stressing of the test piece shall not exceed 30 N/mm2 s.

In cases of dispute, the minimum rate shall not be less than 3 N/mm2 s.

5.1.1.2 Lower yield stress

The rate of straining of the parallel length of the test piece shall not exceed 0-0025/s. The rate of straining of the parallel length shall be kept constant. If this rate cannot be regulated directly, it must be fixed by regulating the rate of

stressing just before the onset of yielding after which the machine control shall not be changed again until yield stress has been determined.

Under no circumstances may the rate of stressing in the elastic range exceed 30 N/mm2 s.

5.1.1.3 Proof stresses

For determination of the proof stress (non-proportional elongation) (RP) or proof stress (total elongation) (Rt), the rate of stressing shall not exceed 30 N/mm2 s.

5.1.2 Tensile strength

To determine the tensile strength, the rate of separation of the crossheads of the testing machine, expressed as a percentage of the parallel length per minute shall not at any

time exceed in the plastic range twice the specified minimum elongation plus 10. In cases of dispute, the minimum rate of separation shall not be less than 1/10 of the limit defined above.

When testing steels of a nominal tensile strength below 1 100 N/mm2 and if it is not intended to determine their yield stress, the rate in the elastic range is permitted to attain the limit specified above for the plastic range.

In all cases, the testing rate shall be kept as constant as possible and the change in rate from the elastic to the plastic range shall be made gradually and without shock.

5.2 Accuracy of the test equipment The testing machine shall be calibrated in accordance with the requirements of EURONORM 157 (at present in preparation) and shall be maintained to grade 1 0 unless otherwise specified.

5.3 Gripping method

5.3.1 Test pieces shall be held by suitable means, e.g. wedges, screwed holders, shouldered holders, etc.

5.3.2

Every endeavour shall be made to ensure that the test pieces are gripped so that the load is applied as axial as possible. This is particularly important for the testing of brittle materials or for the determination of proof or apparent yield stresses.

6 DETERMINATION OF ELONGATION AFTER FRACTURE

6.1 As a general rule, the elongation is measured on the gauge length k | /S0 which is marked before the test to within 1%. For this purpose, the two broken parts of the test piece are carefully fitted together axially in such a way that their axes lie in a straight line. The variation in the gauge length is measured to within 0-25 mm f1) and the calculated value of the elongation after fracture is rounded off to the nearest 1%.

This method of determination is applied only if the distance from the fracture to the nearest gauge mark is not less than one-third of the gauge length after fracture for proportional test pieces (L0 = 5-65 J/S0). However, the measurement remains valid, whatever the position of the fracture, if the elongation reaches the specified value.

Note: In tests using automatic machines and when the elongation indicated by the machine is the total elongation, the elastic elongation shall be deducted to obtain the percentage elongation after fracture.

6.2 Special case

To avoid having to reject test pieces which fracture outside the limits specified in 6.1, the following method may be used: (2)

Before the test, subdivide the gauge length L0 into N equal parts.

After the test, let A be the end mark on the short fragment and the graduation mark on the long fragment, the distance of which from the fracture is most nearly equal to the distance from the fracture to the end mark A.

If is the number of intervals between A and B, the elongation after fracture is determined as follows:

The two pieces are fitted together as specified in 6.1.

(a) If is an even number (see figure 9):

Measure the distance between A and and the distance from to the division C located at:

j - " - spaces beyond B;

Calculate the percentage elongation after fracture by the formula:

. AB + 2 BC - L . . . A 100.

f-o

(b) If is an odd number (see figure 10): Measure the distance between A and and the distance from to the division C' and C" located at:

N - n - 1 n j N - n + 1 and spaces beyond respectively;

i1) See Comments Nos 2a and 2b. (2) This method obviously is laborious and adds considerably to the length

of the operation. It should only be used in exceptional circumstances; it would be justified, for instance, for a very large item from which it would be impossible to take a sample for additional tests or re-testing.

Then calculate the percentage elongation after fracture by the formula:

. AB + BC' + BC" - L0 A -= 2- 100

7 DETERMINATION OF PROOF STRESS NON-PROPORTIONAL ELONGATION A N D TOTAL ELONGATION

These properties are determined by a graphic method using the load-extension curve.

Note: When tests are carried out on automatic machines, these properties can be obtained directly without plotting this curve.

7.1 Method of determining proof (non-proportional elongation) (Rp)

stress

The stress (ordinate) versus percentage extension (abscissa) curve is plotted with suitable accuracy. On this diagram, a line is drawn parallel to the straight-line portion of the curve, the offset between the two, measured on the extension axis, being equal to the specified percentage of the original gauge length. The proof stress corresponds to the intersection of this line with the curve.

When the straight-line portion of the load-extension diagram is not defined sufficiently clearly for the parallel line to be drawn with sufficient certainty, the following procedure is recommended (see Figure 11).

After the assumed proof stress has been exceeded, the load is reduced to approximately 10% of the load which had been reached. The load is then increased again until it exceeds the load originally reached. To determine the desired proof stress, a straight line is drawn through the hysteresis loop. A line is then drawn parallel to this straight line, its distance from the origin of the curve, measured along the abscissae, being equal to the specified non-proportional elongation. The load corresponding to the intersection of this parallel line and the load-extension curve is the desired proof stress.

7.2 Method of determining proof stress (total elongation) (Rt)

The stress (ordinate) versus percentage extension (abscissa) curve is plotted with suitable accuracy. On this diagram, a line is drawn parallel to the ordinate axis at a distance from this axis equal to the specified percentage total extension. The proof stress (total elongation) corresponds to the intersection of this straight line with the curve.

8 METHOD OF VERIFYING THE PERMANENT SET STRESS (Rr)

The test piece is subjected to the load corresponding to the specified permanent set stress for ten to twelve seconds and, after the load has been removed, it is verified that the

permanent elongation is not greater than the specified percentage of the original gauge length.

ANNEX

Nomogram for the calculation of the gauge length of test pieces of rectangular cross-section

This nomogram is constructed by the alignment method (see A2).

Al INSTRUCTIONS FOR USE

Find on the outer scales the points a and b corresponding to the width and thickness of the rectangular test piece.

Join these two points by a straight line (a stretched thread or the edge of a ruler).

Read off the corresponding gauge length from the left-hand side of the central scale where it is intersected by the straight line.

Example:

a = 21 mm

Notes

b = 15-5 mm L 0 = 102 mm

(1) With a reading error on L0 of less than 1%, the nomogram can be used in all cases without further calculation.

(2) The reading error may be greater than 1% for the area (S0), so that the desired accuracy may not be reached in some cases. It is then preferable to calculate the product of a and b directly.

A2 CONSTRUCTION OF THE NOMOGRAM

Draw 3 equidistant parallel straight lines to form the bases of the logarithmic scales. These shall be graduated with a unit such that log 10 is represented by 250 mm; the 3 scales increase towards the top of the page. Place the points (20) and (10) approximately in the middle of the page on each of the lateral scales. Join up the two points (10) on the lateral scales.

This line intersects the central scale at the point 56-5 on the left-hand side Lo of the central scale.

The area scale S0 is the right-hand side of the central scale. The point 56-5 is the point 100 on the area scale. Complete the gradu-ation with a unit half the size of the previous one (log 10 = 125 mm).

60 250 2000

30

1500

50 200

40

30

1000

150

SOO

400

20

100- 300

20 80 200 10

15 "= 60 Lys

50

100 90

c -s

II LO

70

60

c

-s

10 AO 50

9

COMMENTS

1 Examples of the application of tolerances (see Clause 4.2)

(a) Machining tolerance

The value given in table II, clause 4.2, i.e. 0075 mm for a nominal diameter of 10 mm, means that no test piece may have a diameter outside the two values given below when the nominal value of the cross-section is to be used in the calcu-lation without need to measure it:

10 + 0-075 = 10075 mm 10 - 0075 = 9-925 mm.

(b) Shape tolerance

The value given in table II, clause 4.2, means that for a given test piece with a nominal diameter of 10 mm satisfying the machining condition given above, the difference between the smallest and largest measured diameter shall not exceed 004 mm.

Consequently, if the minimum diameter of this test piece is 9-99 mm, its maximum diameter shall not exceed:

9-99 + 004 = 1003 mm.

2 Elongation (see clause 6)

2.a

Application of the conventional rule set out in clause 6.1 is some-times complicated by difficulties in fitting together the two parts of the test piece (when the fracture is skewed). In this case the deter-mination of the elongation after fracture is somewhat inaccurate.

2.b

Where the distance between the fractured cross-section and the nearest gauge mark is less than one-third of the gauge length, after fracture for proportional test pieces the measurement errs on the negative side. However, if there is more than one necking section, which is much less frequent, the error would be on the positive side.

3 Various test conditions

The ends of test pieces with a circular cross-section may either be clamped around their full circumference or be held by wedges or grips along a length at least equal to twice the diameter of the cross-section or be threaded over a length at least equal to their own diameter, i1)

The ends of prismatic test pieces may be fixed either with pins or with wedge grips. The pins shall have a cross-section at least equal to twice the original cross-sectional area S0 of the parallel length; they are inserted into holes bored in each end. The wedge grips shall bear on the ends over a length at least equal to twice the lar-ger side of the cross-section of the test piece. If pins are used, the useful cross-section of the end of the test piece shall be at least twice the original cross-section of the parallel length.

Portions of sections, bars, etc. not provided with enlarged ends shall be held in wedge grips over a length equal to at least three times the diameter d of the smallest circle that can be circum-scribed around the cross-section.

(') The use of ISO metric threads is recommended.

Stress

% elongation

Figure 1

Upper and lower yield stress

Stress Stress

Stress

elongation elongation

Figure 2

Permanent set stress

Figure 3

Proof stress (non-proportional elongation)

% elongation

Figure 4

Proof stress (total elongation)

"-h-

I U-i

/

L

Q

'

Figure 5

j _

" +-Li

- t -

Figure 6

The shape of the test piece ends is given only as a guide

a d to 2 d <

Load

Elongation

Figure 7

Load-elongation

v~ L p = k]/So~

L c = L 0 + to Lo + 2d a d to 2d ^ * L ^ > L c + 2 d o r L c + 4 d depending on method of gripping

Figure 8

The shape of the test piece ends is given only as a guide

Page 13

Jj r N

r

-'S1 ' ^-11

- 4 2

Figure 9

N

- - I S\ I I H-

B N - n - 1 C C "

Figure 10

Stress Figure 11

Proof stress if the straight line portion of the stress-percentage elongation diagram is not clearly defined

- % elongation

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1 SCOPE AND FIELD OF APPLICATION2 TEST PRINCIPLE3 DEFINITIONS AND SYMBOLS3.1 Gauge length3.2 Extensometer gauge length3.3 Elongation3.4 Reduction of area3.5 Load3.6 Stress

4 TEST PIECES4.1 General shape4.2 Shape and dimensions of the parallel portion4.3 Parallel length4.4 Gauge length4.5 Preparation of test pieces

5 TEST CONDITIONS5.1 Rate of stressing5.2 Accuracy of the test equipment5.3 Gripping method

6 DETERMINATION OF ELONGATION AFTER FRACTURE7 DETERMINATION OF PROOF STRESS NON-PROPORTIONAL ELONGATION AND TOTAL ELONGATION8 METHOD OF VERIFYING THE PERMANENT SET STRESS

Documents

EURONORM 2-80