Standard Test Methods for Bend Testing of Material for Ductility - PDF

ASTM E290 Bend Fixture – Universal Grip Data Sheet (PDF)

 

ASTM E290 covers bend testing of metals for ductility. A strip, bar, wire or weld coupon is bent through a set angle around a set radius, and the outside (convex) surface is checked for cracks. It is a pass/fail check of how well the material forms. The mandrel diameter, bend angle and crack limits come from the product or welding specification that calls up E290, not from E290 itself.

The Four E290 Bend Test Arrangements

• Guided bend: a mandrel or plunger pushes the middle of the specimen down between two supports a fixed distance apart; the most common lab setup, run in a universal testing machine

• Semi-guided bend: the specimen bends in contact with a mandrel through a set angle or to a set inside radius, measured while under load (for example, wrapped around a pin)

• Free bend: the specimen ends are pushed toward each other with no force on the inside of the bend, so the bend forms freely

• Bend-and-flatten: the legs are pressed together until they touch along their length, for the most severe ductility check

Bend force is never reversed during the test.

Guided Bend Setup

• Mandrel diameter D: set by the product spec, often expressed as a multiple of the specimen thickness t (for example 2t or 4t)

• Support spacing: commonly D + 3t ± t/2, so the specimen can wrap the mandrel without being pinched (as in ISO 7438); confirm against the governing spec

• Supports and mandrel should be hardened and free to rotate, or lubricated, to limit friction

• Bend angle: usually 180°; some specs call for 90° or 120°

• Round off sharp specimen edges so edge cracks are not mistaken for material failure

Specimens

• Full-section products (bar, wire, rod, tube) can be tested as-is; width and thickness ratios then do not apply

• Flat specimens are cut from plate, sheet or weld coupons; face, root and side bends for weld qualification follow the welding code (ASME IX, AWS D1.1)

• Mark the face that will be on the outside (tension side) of the bend

Evaluating the Result

• A specimen that fractures has failed

• Otherwise, examine the convex (outside) surface for cracks visible without magnification

• Cracks within one specimen thickness of the edge are not counted as failures

• Corner cracks count only if they exceed what the product specification allows

• The number and size of acceptable cracks come from the product or welding spec; for example, many weld bend codes reject an open discontinuity over 3 mm (1/8 in)

Example

A 10 mm thick steel plate specimen is bent 180° over a 40 mm mandrel (4t). Support spacing = 40 + 3 × 10 = 70 mm (±5 mm). After the bend, the outside surface shows no cracks larger than the spec allows, so the plate passes.

Equipment

• Universal testing machine with enough stroke to take the specimen through 180°

• Guided bend test fixture with interchangeable mandrels and adjustable roller supports

• Wrap-around (semi-guided) bend jig for wire and thin strip

• Weld bend jig for AWS and ASME face, root and side bends

Related Standards

• ISO 7438 – metallic materials bend test

• ASME Section IX and AWS D1.1 – weld procedure and welder qualification bend tests

• ASTM A370 – mechanical testing of steel products (bend test requirements)

• ASTM E8/E8M – tension testing of metals

ASTM E290 FAQ

What are the E290 bend test methods?

Guided bend, semi-guided bend, free bend and bend-and-flatten. They differ in how the specimen is constrained while it bends.

What mandrel diameter and bend angle should I use?

Both come from the product or welding specification. Bends are usually 180°, with the mandrel diameter given as a multiple of the specimen thickness, such as 2t or 4t.

How far apart should the supports be?

A common rule is D + 3t ± t/2, where D is the mandrel diameter and t is the specimen thickness, but follow the governing specification.

How is an E290 bend test judged?

By examining the outside of the bend for cracks visible to the unaided eye. Fracture is a failure; crack size limits come from the product spec. Cracks within one thickness of the edge do not count.