Adjustable spanTJ-124
Three Point Bend Fixture
A three-point bend fixture with adjustable span and the roller diameters the method specifies — span-to-depth ratio is set on the fixture, not assumed.
SpecificationsTesting standard
IS 1599
Metallic Materials — Bend Test
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
IS 1599 specifies the bend test for assessing a metallic material's ability to undergo plastic deformation in bending. It covers flat products, bars, rods and wire, and the current edition is dual-numbered with ISO 7438:2020.
At a glance
- Test type
- Flexure & bend — the specimen is bent
- Published by
- IS
- Edition
- 2023
- Material
- Metals, alloys & welds
- Runs on
- Series 7200 and Series 9000
What the test does
A test piece — flat product, bar, rod or wire — has its edges rounded and is laid across two supports set at a clear distance of the former diameter plus three times the thickness. A former of the diameter fixed by the material's product standard is driven into it in one continuous movement to a specified angle, commonly 90° or 180°. The piece is then removed and its outer, stretched surface examined under magnification for cracks, which are judged against the acceptance criterion in the product standard rather than in this one.
What it measures, and why it matters
Whether the material will take a bend without cracking — the question behind every folded bracket, formed section and bent reinforcement bar. What makes this page worth reading alongside the others is the dual numbering. An adopted standard normally drifts from its parent: IS 1969 (Part 1) is identical with ISO 13934-1 as it stood in 1999 while ISO has since issued a 2013 edition, and IS 3400 (Part 1) tracks an ISO 37 edition superseded twice over. Publishing one text under two designations removes that gap entirely, and a result is simultaneously an IS and an ISO result.
Dual numbering, and what it means
An adopted standard usually lags its parent. This one is published as the same document under two numbers.
- Relationship to ISO
- Dual-numbered with ISO 7438:2020Not merely 'based on' or 'identical with' an older edition — published as the same text under both designations, which removes the drift that usually opens up.
- Products
- Flat products, bars, rods and wire
- Former diameter
- Fixed by the relevant product standardNot by this one. The severity comes from the material's own specification.
- Angle
- As specified, commonly 90° or 180°
- Support distance
- l = D + 3aFormer diameter plus three times the thickness — enough clearance that the piece bends rather than shears over the supports.
- Round the edges before bending
- DakA sharp machined corner cracks from the edge, and that crack is a preparation defect rather than a material one.
The result is a pass or a fail on the condition of the outer surface, judged against the acceptance criterion in the product standard. This method supplies no criterion of its own.
Test speed
- Movement
- Continuous to the specified angleStopping and restarting leaves a witness mark on the surface being examined.
- Reported
- Whether the outer surface cracked, and the former diameter used
- Examination
- Of the outer, tensile surface
- Examine under magnification, not by eye
- DakA fine crack a few millimetres long is what the test exists to find and is easy to miss on a deformed surface.
Calculations
Support distancel
l = D + 3a
- D
- former diameter
- a
- thickness or diameter of the test piece
Sets the clearance between supports. Too close and the piece is sheared rather than bent.
Outer fibre strainε
Approximately a / (D + a)
Not reported by the method, but it is why a tighter former on a thicker piece is a far more severe test than the diameter alone suggests.
Acceptance—
From the product standard, not from IS 1599
How the test runs
- 01Take the former diameter and the bend angle from the product standard, not from this one.
- 02Prepare test pieces of the specified dimensions.
- 03Round the edges.
- 04Set the supports to a clear distance of D + 3a.
- 05Fit the former of the required diameter.
- 06Place the piece so the surface to be examined faces away from the former.
- 07Bend in one continuous movement to the specified angle.
- 08Remove the piece and examine the outer surface under magnification.
- 09Measure any crack or open defect.
- 10Judge against the product standard's acceptance criterion.
- 11Report the former diameter, the angle and the surface condition together.
Grips and fixtures for this method
Uniform momentTJ-165
Four Point Bend Fixture
Four-point loading where the specification calls for it, putting a length of the specimen under constant moment rather than concentrating it under one nose.
SpecificationsWhat the report has to contain
- Reference to IS 1599 and the edition
- Material, grade and product form
- Test piece dimensions and orientation
- Former diameter and where it came from
- Support distance used
- Bend angle achieved
- Condition of the outer surface after bending
- Length and location of any crack
- The acceptance criterion applied and its source
- Whether the edges were rounded
What the machine must be capable of
Enough force to complete the bend — a thick plate or a large bar can need hundreds of kilonewtons — and the stroke to reach the specified angle in one continuous movement. Force accuracy matters less here than in most methods, since nothing is calculated from the load; what the frame needs is stability and travel. The formers themselves are the consequential hardware, because the diameter is the entire severity of the test and it comes from the product standard.
What goes wrong in practice
Using a former larger than the product standard specifies, which makes the test easier while leaving no trace in the report unless the diameter is recorded — which is why it is recorded. Sharp edges producing preparation cracks. Stopping mid-bend, which leaves a witness mark on the very surface being examined. Examining by eye rather than under magnification, when the defect sought is a fine crack on a work-hardened surface. And stating a pass without naming the document the acceptance criterion came from, since IS 1599 supplies none of its own. A quieter failure is recording the bend angle but not the former, when the former is the parameter that decided whether the piece could pass at all.
IS 1599 or ISO 7438
| IS 1599 : 2023 | ISO 7438:2020 | |
|---|---|---|
| Relationship | Dual-numbered — the same text | Dual-numbered — the same text |
| Former diameter | From the product standard | From the product standard |
| Acceptance criteria | Not given | Not given |
| Drift risk | None while dual numbering holds | None while dual numbering holds |
This is the counter-example to the adopted-standard drift that IS 1969 and IS 3400 illustrate. Dual numbering publishes one text under two designations, so the Indian and ISO versions cannot diverge.
Questions we are asked about this test
What is IS 1599?
It is the Indian Standard bend test for metallic materials, assessing a material's ability to undergo plastic deformation in bending. It covers flat products, bars, rods and wire. The current edition, IS 1599 : 2023, is the fifth revision and is dual-numbered with ISO 7438:2020.
What does dual numbering mean in practice?
That the Indian and ISO documents are the same text published under two designations, rather than the Indian one being an adoption of a particular ISO edition. It matters because adopted standards normally drift: IS 1969 (Part 1) is identical with ISO 13934-1:**1999** while ISO has moved to 2013, and IS 3400 (Part 1) is aligned with an ISO 37 edition that has since been superseded twice. Dual numbering closes that gap.
Where does the former diameter come from?
From the product standard for the material, not from this one. IS 1599 supplies the method — how to set the supports, how to bend, what to examine — while the severity is set by whatever specification the material is supplied to. That is why a bend test report is incomplete without both the former diameter and the document it was taken from.
Why is the support distance D + 3a?
To give the piece room to bend rather than shear. If the supports sit too close to the former, the material is forced over a short span and fails by shearing across the supports instead of by stretching its outer surface, which is a different failure and not what the test is looking for. The formula scales the clearance with both the former size and the material thickness.
Does IS 1599 say whether a result passes?
No. It gives no acceptance criterion. What counts as an acceptable outer surface after bending comes from the product standard or the contract, and a report that states a pass without naming where that criterion came from is claiming an authority the method does not have.
Why round the edges first?
Because a sharp machined corner is a stress raiser at the very edge of the surface being stretched, and a crack that starts there is a preparation defect rather than a material one. Once it has run, the two are indistinguishable, and the test piece is lost. Rounding the edges beforehand removes a whole class of false failures.
Why examine under magnification?
Because a fine crack a few millimetres long on a deformed, work-hardened surface is genuinely easy to overlook, and it is exactly the defect the test exists to reveal. Examining by eye at arm's length passes material that should have failed, and nothing downstream will catch it.
Running IS 1599 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 | Moderate to high — a thick plate or a large bar can need hundreds of kilonewtons to bend | Load cells from 1 kg to 60 ton on the Series 7200, and 0.5 to 100 kN on the Series 9000 |
| Force accuracy | Class 1 over the working range | ISO 7500-1 Class 0.5, verified to ASTM E4, DIN 51221 and BS 1610 |
| Gripping | A bend former of the diameter the product standard fixes, with supports set to a clear distance | Our bend fixtures, built to the specimen |
| Environment | 23 ± 2 °C standard laboratory atmosphere | 3009 series chambers, −150 °C to +400 °C — temperature only |
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.