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Principle
Standard test pieces, either 'dog-bone' dumbbells or rings, are stretched in a tensile testing machine at a constant rate of traverse of the driven grip or pulley. Readings of force and elongation are taken as required during the uninterrupted stretching of the test piece and when it breaks.
Dumbbells are preferable for determination of tensile strength. Rings give lower, sometimes much lower, values than dumbbells for Elongation at Break
Rings give approximately the same values as dumbbells, provided that:
- the elongation of rings is calculated as a percentage of the initial internal circumference, and
- dumbbells are cut at right angles to the grain if this is present to a significant degree.
Test pieces
Seven types of test piece are provided, i.e. dumbbell-shaped types 1, 2, 3, 4 and 1A and ring-shaped types A (normal) and B (miniature). The results obtained for a given material are likely to vary according to the type of test piece used. Therefore, the results obtained for different materials should not be regarded as comparable unless the same type of test piece has been used.
Dumbbells
Dumbbell dimensions and test length
| Test piece type | Type 1 | Type 1A | Type 2 | Type 3 | Type 4 |
|---|---|---|---|---|---|
| Overall length (A) | 115 | 100 | 75 | 50 | 35 |
| Width of end tab (B) | 25 | 25 | 12.5 | 8.5 | 6 |
| Length of narrow section (C) | 33 | 21 | 25 | 16 | 12 |
| Width of narrow section (D) | 6.2 | 5 | 4 | 4 | 2 |
| Transition outside radius (E) | 14 | 11 | 8 | 7.5 | 3 |
| Transition inside radius (F) | 25 | 25 | 12.5 | 10 | 3 |
| Test 'gauge' length (G) | 25 | 20 | 20 | 10 | 10 |
- Standard thickness for type 1, 1A, 2, 3 shall be 2.0 mm; for type 4: 1.0 mm.
- Non-standard pieces up to 3 mm thick type 1/1A, 2.5 mm type 2, 3; for type 4: 2 mm.
- Type 3 and 4 dumbbell test pieces shall only be used where insufficient material is available for the larger test pieces.
Specimen cutters
- Die cutters are available from many sources but must be in accordance with ISO 23529, which states geometry and precision of the cutting head.
- Sample presses are also available either manual or pneumatic, the testing machine may also be used to apply the force to cut the sample if it has sufficient capacity.
Apparatus
Tensile tester
The tensile testing machine shall comply with the requirements of ISO 5893, having an accuracy of force measurement complying with Class 1.
ISO 7500-1 Classification 0.5, 1, 2 & 3 – Mecmesin OmniTest machines are Class 0.5.
Speed control capable of speeds between 1 mm/min (+/- 0.2 mm/min) up to 500 mm/min (+/- 50 mm/min).
Test speeds:
- Type 1, 1A and 2 = 500 mm/min
- Type 3 and 4 = 200 mm/min
Any of the OmniTest and MultiTest-dV range are suitable, as they support extensometers.
Extensometer
An extensometer, where used, shall have an accuracy complying with class D for type 1, 1A & 2 dumb-bell test pieces and class E for type 3 and 4 dumbbell test pieces.
| Class | Maximum elongation (deflection) ΔL on given gauge length L | Max permissible error (%) | Accuracy of versification device (%) |
|---|---|---|---|
| A | 5% on 25 mm | +/-2 | +/-0.5 |
| B | 10% on 25 mm | +/-2 | +/-0.5 |
| C | 50% on 25 mm | +/-2 | +/-0.5 |
| D | 1200% on 20 mm | +/-2 | +/-0.5 |
| E | 1200% on 10 mm | +/-2 | +/-0.5 |
The Mecmesin MLTE extensometer range is suitable for extension measurements.
Results
Some of the most common results and calculations include:
- Tensile Strength (TS) Mpa
- Tensile Strength @ Break (TSb) Mpa
- Elongation @Break (Eb) %
- Elongation @ a given Stress (Es) %
- Stress @ a given Elongation (Se) Mpa
- Tensile Stress @ Yield (Sy) Mpa
- Elongation @ Yield (Ey) %
This test standard is similar to ASTM D412-16.