Tensile testing of metallic materials is specified according to European EN 10002 standard. In this article the terms, definitions and designation for tensile test made at ambient temperature is described. The test involves straining a test piece in tension, generally to fracture, for the purpose of determining mechanical properties.
The shape and dimensions of the test pieces depend on the shape and dimensions of the metallic product from which the test pieces are taken (Figure1). Their cross-section may be circular, square, rectangular, annular or, in special cases, of some other shape. The test piece is usually obtained by machining a sample from the product or a pressed blank or casting. However, products of constant cross-section and as cast test pieces may be tested without being machined.
Table 1. Symbols and designations of the test piece.
Reference (Figure1) | Symbol | Unit | Designation |
1. | a | mm | Thickness of a flat test piece or wall thickness of a tube |
2. | b | mm | Width of the parallel length of a flat test piece or average width of the longitudinal strip taken from a tube or width of flat wire |
3. | d | mm | Diameter of the parallel length of a circular test piece, or diameter of round wire or internal diameter of a tube |
4. | D | mm | External diameter of a tube |
5. | Lo | mm | Original gauge length |
- | L`o | mm | Initial gauge length for determination of Ag |
6. | Lc | mm | Parallel length |
- | Le | mm | Extensometer gauge length |
7. | Lt | mm | Total length of test piece |
8. | Lu | mm | Final gauge length after fracture |
- | L`u | mm | Final gauge length after fracture for determination of Ag |
9. | So | mm2 | Original cross-sectional area of the parallel length |
10. | Su | mm2 | Minimum cross-sectional area after fracture |
- | k | - | Coefficient of proportionality |
11. | Z | % | Percentage reduction of area: (So - Su) / So x 100 |
12. | - | - | Gripped ends |
The test piece shall be held by suitable means such as wedges, screwed grips, parallel jaw faces, shouldered holders, etc. Every endeavour should be made to ensure that pieces are held in such a way that the tension is applied as axially as possible in order to minimize bending. This is very important for testing brittle materials or when determining proof or yield strength.
For determination of percentage elongation, the two broken test pieces are carefully fitted back together so that their axis lie in a straight line. Elongation after fracture shall be determined to the nearest 0.25 mm with a measuring device with a sufficient resolution and the value of percentage elongation after fracture shall be rounded to the nearest 0.5% (Table 2). On the Figure 2 schematic definitions of elongation are given.
Table 2. Different types of elongation
Reference (Figure 2) | Symbol | Unit | Elongation |
13. | - | mm | Elongation after fracture: Lu - Lo |
14. | A | % | Percentage elongation after fracture: (Lu - Lo) / Lo x 100 |
15. | Ae | % | Percentage yield point extension |
- | Lm | mm | Extension at maximum force |
16. | Ag | % | Percentage non-proportional elongation at maximum force (Fm) |
17. | Agt | % | Percentage total elongation at maximum force (Fm) |
18. | At | % | Percentage total elongation at fracture |
19. | - | % | Specified percentage non-proportional extension |
20. | - | % | Percentage total extension |
21. | - | % | Specified percentage permanent set extension or elongation |
The designations and related curves for yield, proof and tensile strength are given in the Table 3 and on the Figure 3.
Table 3. Symbols and designations for different types of strength
Reference (Figure 3) | Symbol | Unit | Force and strength |
22. | Fm | N | Maximum force |
- | - | - | Yield strength -Proof strength -Tensile strength |
23. | ReH | MPa | Upper yield strength |
24. | ReL | MPa | Lower yield strength |
25. | Rm | MPa | Tensile strength |
26. | Rp | MPa | Proof strength, non-proportional extension |
27. | Rr | MPa | Permanent set strength |
28. | Rt | MPa | Proof strength, total extension |
- | E | MPa | Modulus of elasticity |
The test report shall contain reference to the standard, identification of the test piece, specified material, type of the test piece, location and direction of sampling test pieces and test results. In the absence of sufficient data on all types of metallic materials it is not possible, at present, to fix values of uncertainty for the different properties measured by tensile test.
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