Upto 100 kNTJ-145
Manually Operated Heavy Duty Wedge Grips
Manually operated heavy duty wedges with interchangeable faces — serrated V-faces for round specimens, flat serrated faces for sheet.
SpecificationsTesting standard
ISO 6892-1
Metallic materials — Tensile testing — Part 1: Method of test at room temperature
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ISO 6892-1 is the room-temperature tension test for metals. A specimen is pulled along its axis until it fractures, and the method reports proof or yield strength, tensile strength, elongation after fracture and reduction of area — the values a structural engineer designs against and a mill certificate must carry before a grade can be released.
At a glance
- Test type
- Tensile — the specimen is pulled apart
- Published by
- ISO
- Edition
- ISO 6892-1:2019
- Material
- Metals, alloys & welds
- Runs on
- Series 7200 and Series 9000
What the test does
A metal specimen — a machined round bar, a flat coupon or a full-section product — is held at both ends and pulled along its axis until it fractures. The crosshead moves under controlled strain rate or stress rate while force is recorded from the load cell and extension from an extensometer clamped over a defined gauge length. The output is a continuous stress–strain curve through elastic response, yielding, necking and fracture.
What it measures, and why it matters
The method reports upper and lower yield strength or 0.2 % proof strength, tensile strength, percentage elongation after fracture and percentage reduction of area. Proof and yield strength are the design allowables a structural engineer sizes sections against, and they are the figures a mill certificate must carry for a steel grade to be released. Tensile strength bounds the section's ultimate capacity. Elongation and reduction of area rank formability and warn of embrittlement — a batch meeting strength but failing elongation is the classic sign of a heat-treatment error.
Specimen and gauge length
The gauge length is the thing to get right. ISO ties it to the cross-section by default, and that is what makes an elongation figure from a thin sheet comparable with one from a heavy forging.
- Proportional gauge length
- L₀ = 5.65 √S₀Five diameters for a round bar. The default, and the reason ISO elongation figures transfer between product forms.
- Non-proportional gauge
- Commonly 50 mm or 80 mmFixed length, used where the material standard calls for it.
- Never mix the two
- In one datasetElongation from a proportional and a non-proportional gauge are different quantities. Averaging them produces a number that describes nothing.
- Full-section testing
- Permitted for wire, tube and thin sheetNo machining, so no risk of cold work altering the property being measured.
- Test temperature
- 10 °C to 35 °C, or 23 ± 5 °CThe tighter band where controlled conditions are specified.
- Discard and replace
- Fracture outside the gauge lengthIt voids the elongation figure entirely — the test is repeated, not adjusted.
- Keep machining cool
- No overheating, minimal cold workDakSurface finish and radius both seed premature fracture. The specimen has to represent the material rather than the workshop.
Rate control — Method A or Method B
This is where ISO 6892-1 is strictest, and where it differs most from its ASTM counterpart. Two methods, and which one was used has to be stated because the same steel returns different yield strengths under each.
- Method A — strain rate
- 0.00007 or 0.00025 s⁻¹ to yieldStrongly recommended. Closed-loop control on the extensometer signal.
- Method A — after yield
- 0.002 or 0.0067 s⁻¹ to fracture
- Method B — stress rate, E ≥ 150 GPa
- 6 to 60 MPa/s
- Method B — stress rate, E < 150 GPa
- 2 to 20 MPa/s
- State the method in the report
- AlwaysDakYield in mild steel is rate-sensitive. A laboratory that switches between A and B without saying so produces two valid, different answers for the same material.
A frame that cannot hold rate through the yield discontinuity reports a number that depends on its own stiffness rather than on the steel. This is the single strongest argument for closed-loop strain-rate control on metals work.
Calculations
Tensile strengthRm
Rm = F_m / S₀
- F_m
- maximum force, N
- S₀
- original cross-sectional area, mm²
Proof strength, plastic extensionRp0,2
Rp0,2 = stress at 0.2 % plastic extension
- 0,2
- the plastic extension percentage; other values are specified as Rp0,1, Rp1 and so on
For materials with no distinct yield. The offset line runs parallel to the elastic slope, so the quality of the modulus region sets the quality of the proof figure.
Upper and lower yield strengthReH / ReL
ReH = F_eH / S₀ · ReL = F_eL / S₀
- F_eH
- force at the first peak of the yield discontinuity, N
- F_eL
- lowest force during yielding, ignoring transient effects, N
Only for materials that show a genuine yield point — most carbon steels do. Reporting Rp0,2 for such a material where the specification asks for ReH is a common substitution error.
Percentage elongation after fractureA
A = ((L_u − L₀) / L₀) × 100
- L_u
- final gauge length after fitting the pieces together, mm
Quoted with the gauge convention — A for proportional, A₈₀ₘₘ for an 80 mm non-proportional gauge. The subscript is not optional.
How the test runs
- 01Prepare the specimen, machining gently or testing full-section where the product allows.
- 02Measure the cross-section and compute S₀ from the actual dimensions.
- 03Determine L₀ from 5.65 √S₀, or take the fixed gauge the material standard specifies, and mark it.
- 04Select grips that load axially — serrated wedges, threaded holders or pin grips — and check alignment.
- 05Fit an extensometer to ISO 9513 Class 1 over the marked gauge.
- 06Choose Method A or Method B and set the rate, recording which was used.
- 07Load through the elastic region and the yield or proof determination at the first-stage rate.
- 08Change to the second-stage rate and continue to fracture.
- 09Remove a clip-on extensometer before fracture unless it is rated to survive it.
- 10Fit the fractured halves together, measure L_u and the minimum area, and compute A and Z.
- 11Discard and repeat any test that fractured outside the gauge length.
Watch the test
Grips and fixtures for this method
Self-tighteningTJ-135
Heavy Duty Circular Hydraulic Wedge Grips
Hydraulic closure, tightening further as load rises. What high-strength alloys need to reach proof strength without creeping in the jaws first.
SpecificationsWhat the report has to contain
- Reference to ISO 6892-1 and the method used, A or B
- Material identification, product form, cast or lot, and orientation
- Specimen type, dimensions and whether proportional or non-proportional
- Gauge length, and the subscript convention used for elongation
- Test temperature
- Rate, and the control mode it was applied in
- ReH and ReL, or Rp with its plastic extension percentage
- Rm, the tensile strength
- Percentage elongation after fracture, A, with its gauge convention
- Percentage reduction of area, Z
- Fracture location, and any test repeated
What the machine must be capable of
Force demand spans a wide band. Machined coupons mostly run on 100–300 kN frames; thin sheet needs only hundreds of newtons, while full-section plate and bar products can push demand towards 600 kN. Force indication must be verified to ISO 7500-1 Class 1.
Rate control is where this method is strict. Method A, strain-rate control, is strongly recommended and runs 0.00007 or 0.00025 s⁻¹ up to yield or proof strength, then 0.002 or 0.0067 s⁻¹ to fracture; Method B, stress-rate control, allows 6–60 MPa/s for materials with E ≥ 150 GPa and 2–20 MPa/s below that. Yield strength in mild steels is rate-sensitive, so a machine that cannot hold rate through the yield discontinuity reports a number that depends on its own stiffness rather than the material.
Strain measurement needs ISO 9513 Class 1 for proof and yield determination over the first 0.5 % of strain; Class 2 is permitted for properties measured at larger extension, typically out to 50 % total elongation, which means either a clip-on gauge removed before fracture or a long-travel or automatic device that follows to break.
Gripping may be wedge grips with serrated faces, threaded or shouldered holders, or pin grips — any means that loads axially. Alignment is the requirement behind all of them: off-axis gripping superimposes bending, which depresses measured proof strength. Ambient 10–35 °C applies, or 23 ± 5 °C where controlled conditions are specified.
What goes wrong in practice
Grip slippage is the common one — a smooth or under-clamped specimen creeps in the jaws, adding false extension and flattening the modulus region. Fracture outside the gauge length voids the elongation figure entirely and the test must be repeated. Off-axis loading from worn wedges or a misaligned load train bends the specimen and biases proof strength low. Rate sensitivity catches laboratories that switch between Method A and Method B without saying so: the same steel returns different yield strengths, and both are valid.
ISO 6892-1 or ASTM E8/E8M
The two documents the world's mill certificates are written against. They measure the same properties and do not produce interchangeable numbers.
| ISO 6892-1 | ASTM E8/E8M | |
|---|---|---|
| Gauge length | Proportional, 5.65 √S₀ | Fixed by specimen type |
| Rate control | Method A strain-rate, or Method B stress-rate | Stress-rate window, then crosshead rate |
| Yield reported as | ReH / ReL, or Rp0,2 | Yield strength by offset or EUL |
| Strength symbol | Rm | Tensile strength |
| Elongation symbol | A, or A₈₀ₘₘ | Elongation, with gauge length stated |
| Extensometer class | ISO 9513 Class 1 | ASTM E83 Class B-2 |
A purchaser specifying one and a supplier testing to the other will disagree on a compliant material. The certificate must name the method, and a contract that says only "tensile test" has not specified anything.
Questions we are asked about this test
What is ISO 6892-1?
It is the international standard for tensile testing of metallic materials at room temperature. A specimen is pulled until it fractures, and the method reports proof or yield strength, tensile strength, percentage elongation after fracture and percentage reduction of area.
What is the gauge length in ISO 6892-1?
By default it is proportional: L₀ = 5.65 √S₀, which is five diameters for a round bar. That tie to the cross-section is what allows an elongation figure from thin sheet to be compared with one from a heavy forging. Non-proportional gauges of 50 or 80 mm are used where a material standard calls for them, and the two conventions must never be mixed in one dataset.
What is the difference between Method A and Method B?
Method A controls strain rate and is strongly recommended; Method B controls stress rate. Yield in mild steel is rate-sensitive, so the same material returns different yield strengths under each — both correct. That is why the method used has to appear on the report, and why a frame that cannot hold rate through the yield discontinuity reports its own stiffness rather than the steel's behaviour.
What is the difference between ISO 6892-1 and ASTM E8?
They test the same properties on the same materials but are not interchangeable. ISO uses proportional gauge lengths and reports Rm and Rp0,2; ASTM fixes the gauge by specimen type and reports tensile strength and yield strength. Rate control is defined differently again. A mill certificate should always name which method produced the numbers.
What is Rp0,2 and when is it used instead of ReH?
Rp0,2 is the stress at which 0.2 % plastic extension has occurred, found by offsetting a line parallel to the elastic slope. It is used for materials with no distinct yield point — most non-ferrous alloys and many stainless grades. Carbon steels usually do show a yield discontinuity and are reported as ReH and ReL instead. Substituting one for the other is a common and consequential reporting error.
What extensometer class does ISO 6892-1 need?
ISO 9513 Class 1 for the proof and yield determination over the first 0.5 % of strain, where the accuracy of the result depends entirely on the accuracy of the strain measurement. Class 2 is permitted for properties measured at larger extension. Since total elongation commonly reaches 50 %, either a long-travel device is used or a clip-on is fitted for the yield determination and removed before fracture.
What capacity machine does ISO 6892-1 need?
Machined coupons mostly run on 100 to 300 kN frames. Thin sheet needs only hundreds of newtons, while full-section plate and bar can push demand towards 600 kN, so the frame is chosen for the heaviest product in the programme rather than the average. Force indication must be verified to ISO 7500-1 Class 1.
Why did my specimen fracture outside the gauge length?
Usually a stress concentration the preparation left behind — a machining mark, too sharp a radius at the transition, or cold work from aggressive cutting. Grip misalignment does it too, by adding bending to one side. Whatever the cause, the elongation figure is void: the standard requires the test to be repeated rather than the result adjusted.
Running ISO 6892-1 on the Series 7200 and Series 9000
Dak verifies against whichever standard the method names, and where a class applies our frames sit a class tighter than it asks.
| The method asks for | Dak supplies | |
|---|---|---|
| Capacity | Machined coupons mostly run on 100-300 kN frames; thin sheet needs only hundreds of newtons, while full-section plate and bar products can push demand towards 600 kN. | Load cells from 1 kg to 60 ton on the Series 7200, and 0.5 to 100 kN on the Series 9000 |
| Force accuracy | ISO 7500-1 Class 1 | ISO 7500-1 Class 0.5 — a class tighter than the method asks |
| Strain measurement | An extensometer to ISO 9513 Class 1 (proof and yield strength determination); Class 2 permitted for other properties measured at higher extension, gauge length proportional: Lo = 5.65 √So (5D for rounds); non-proportional commonly 50 or 80 | Certified to ISO 9513 Class 1 and ASTM E83 — non-contact video, clip-on and high-elongation |
| Gripping | wedge grips or threaded/shouldered specimen holders | Our self-tightening serrated wedge grips, with V-jaws for round specimens, built to the specimen |
| Environment | ambient 10-35 °C (23 ± 5 °C where controlled conditions are specified); no conditioning atmosphere | 3009 series chambers, −150 °C to +400 °C — temperature only |
Selecting equipment for this method? Explore DAK metal testing systems.
This page describes the method as practised. The governing text is the current edition from the issuing body. Tell us what you are testing and we will answer with the machine, the fixture and a quotation.