IS 1599 Bend Testing of Metallic Materials

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13934-1 as it stood in 1999 while ISO has since issued a 2013 edition, and IS 3400 (Part 1) tracks an ISO 37 edition superseded twice over.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

The method sets no rate of traverse at all. It controls the geometry of the bend instead, and those are the figures a set-up sheet has to carry.

Rate of traverse

None specifiedClause 6.3 asks only for a continuously increasing force applied slowly, so as to permit free plastic flow of the material. No speed, force rate or time to angle appears anywhere in the text.

Former diameter, D

From the product standard, never from this oneIt is the entire severity of the test. A larger former makes the test easier and leaves no trace unless the diameter is recorded.

Clear distance between supports

l = D + 3aClause 4.2.2, where a is the thickness or diameter of the test piece. It must not change during the bend. Supports set closer shear the piece across them instead of bending it.

Temperature

10 °C to 35 °C ambient; 23 ± 5 °C under controlled conditionsClause 6.1.

A workable speed, where one has to be chosen

A few mm/min of crossheadDakSlow enough for free plastic flow on ordinary structural material. It is a laboratory choice, not a requirement — record it as the speed used, never quote it as a specified one.

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.

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.

There is no rate of traverse to set, and that is the method rather than a gap here. The procedure requires only that the force increase continuously and be applied slowly enough to permit free plastic flow of the material; no speed, force rate or time appears anywhere in the text. What it does fix, and what a set-up sheet should carry, is geometry: the former diameter D, from the product standard and never from this one; the clear support distance l = D + 3a, where a is the thickness or diameter of the piece; the bend angle; one uninterrupted movement to it; and a temperature of 10 °C to 35 °C, or 23 ± 5 °C controlled. A slow crosshead of a few millimetres per minute satisfies free plastic flow on ordinary structural material, but that is a laboratory choice: record it as the speed used, never as a specified one.

Grips and fixtures for this method

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.

Specifications

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.

Specifications

How the test runs

1. 01Take the former diameter and the bend angle from the product standard, not from this one.
2. 02Prepare test pieces of the specified dimensions.
3. 03Round the edges.
4. 04Set the supports to a clear distance of D + 3a.
5. 05Fit the former of the required diameter.
6. 06Place the piece so the surface to be examined faces away from the former.
7. 07Bend in one continuous movement to the specified angle.
8. 08Remove the piece and examine the outer surface under magnification.
9. 09Measure any crack or open defect.
10. 10Judge against the product standard's acceptance criterion.
11. 11Report the former diameter, the angle and the surface condition together.

Calculations

What 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 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.