EN ISO 7438 Metallic Materials - Bending Test

The standard "EN ISO 7438 Metallic materials - Bend testing", which has its origins in a European standard and was subsequently published by the International Organization for Standardization (ISO), describes a method for determining the ability of metallic materials to undergo plastic deformation during bending. This standard is valid for test pieces taken from metallic products as specified in the relevant product standard. It does not apply to specific materials or products, such as full-section pipes or welded joints, for which other standards exist.

The bending test consists of bending a test piece of round, square, rectangular or polygonal cross-section to plastic deformation until a specified bending angle is reached, without changing the direction of loading. The axes of the two legs of the test piece remain in a plane perpendicular to the bending axis. In the case of 180 degree bending, the two side surfaces may lie flat or be parallel to each other at a specified distance, depending on the requirements of the product standard, an insert is used to control this distance.

In general, bending testing should be performed on testing machines or presses equipped with the following devices:

Bending device with two supports and one die as shown in the figure given in the standard
A V block and a die bending device as shown in the figure given in the standard
A clamp bending device as shown in the figure given in the standard

The following equipment is also used in the tests:

Bending device with support and die: The length of the supports and the width of the die should be larger than the width or diameter of the test piece. The die diameter is determined by the product standard. The test piece supports and the die should be of sufficient rigidity. Unless otherwise specified, the distance between the supports should be in accordance with the formula given in the standard and should not change during the bending test. When the distance between the supports is specified as less than or equal to a certain length, this may cause compression during the test and tension deformation of the test piece.
V-block bending device: The conical surfaces of the V-block should form a certain angle. The edges of the V-block should have a radius of 1 to 10 times the thickness of the test piece and should have sufficient rigidity.
Clamp bending device: The device consists of a clamp and a die of sufficient rigidity. It may be equipped with a lever to apply force to the test piece. Since the position of the left face of the clamp may affect the test results, the left face of the clamp should not extend up to or beyond the vertical line passing through the centre of the circular die shape as shown in the figure given in the standard.

In general, round, square, rectangular or polygonal cross-section test pieces should be used in testing. Any areas of material affected by cutting or flame cutting or similar operations should be removed during sampling of test pieces. However, testing a test piece with the affected parts not removed is acceptable if the result is satisfactory.

The edges of rectangular test pieces shall be rounded to a radius not exceeding:

50 mm when the thickness of the test pieces is 3 mm or more.
50 mm when the thickness of the test pieces is less than 10 mm and equal to or greater than 1,5 mm (inclusive).
10mm when the thickness is less than 1mm.

Rounding should be done in such a way that no transverse burrs, scratches or marks are formed which could adversely affect the test results. However, testing a test piece without rounded edges is acceptable provided the result is satisfactory.

Unless otherwise specified in the relevant standard, the width of the test piece shall be:

If the product width is 20mm or less, it should be the same as the product width.
When the product width is more than 20mm:
- For products with a thickness of less than 3 mm (should be 20 mm plus/minus 5 mm.
- For products with a thickness of 3 mm or more, it should be between 20 mm and 50 mm.

The thickness of the test pieces made of sheet, strip and sections should be equal to the thickness of the product to be tested. If the thickness of the product is more than 25 mm, it can be reduced by machining a surface to reach a minimum thickness of 25 mm. During bending, the unmachined side should be on the tension side surface of the test piece.

The cross-section of round or polygonal cross-section test pieces shall be equal to the cross-section of the product if the diameter (for round cross-section) or inscribed circle diameter (for polygonal cross-section) does not exceed 30 mm. When the diameter or inscribed circle diameter of the test piece exceeds 30 mm and reaches 50 mm, it may be reduced by not less than 25 mm. When the diameter or inscribed circle diameter exceeds 50 mm, it may be reduced by not less than 25 mm. The unprocessed side during bending shall be on the surface of the test piece on the tensile side.

In the case of forgings, castings and semi-finished products, the dimensions of the test piece and sampling shall be as defined in the general terms of delivery or determined by agreement.

By agreement, test pieces with width and thickness greater than those specified above may be subjected to bending testing.

The length of the test piece depends on the thickness of the test piece and the test equipment used.

In general, tests are performed at ambient temperatures between 10 degrees and 35 degrees. If necessary, tests performed under controlled conditions should be performed at a temperature of 23 degrees plus/minus 5 degrees.

Our organization, which has been trying to support businesses from every sector with its testing, measurement, analysis and evaluation studies carried out in a wide range for years, has a strong staff that closely follows the developments in the world in the field of science and technology and constantly improves itself. In this context, testing services in accordance with the "EN ISO 7438 Metallic materials - Bending test" standard are also provided to businesses.