Significance and Use
Bend tests for ductility provide a simple way to evaluate the quality of materials by their ability to resist cracking or other surface irregularities during one continuous bend. No reversal of the bend force shall be employed when conducting these tests.
The type of bend test used determines the location of the forces and constraints on the bent portion of the specimen, ranging from no direct contact to continuous contact.
The test can terminate at a given angle of bend over a specified radius or continue until the specimen legs are in contact. The bend angle can be measured while the specimen is under the bending force (usually when the semi-guided bend test is employed), or after removal of the force as when performing a free-bend test. Product requirements for the material being tested determine the method used.
Materials with an as-fabricated cross section of rectangular, round, hexagonal, or similar defined shape can be tested in full section to evaluate their bend properties by using the procedures outlined in these test methods, in which case relative width and thickness requirements do not apply.
1.1 These test methods cover bend testing for ductility of materials. Included in the procedures are four conditions of constraint on the bent portion of the specimen; a guided-bend test using a mandrel or plunger of defined dimensions to force the mid-length of the specimen between two supports separated by a defined space; a semi-guided-bend test in which the specimen is bent, while in contact with a mandrel, through a specified angle or to a specified inside radius (r) of curvature, measured while under the bending force; a free-bend test in which the ends of the specimen are brought toward each other, but in which no transverse force is applied to the bend itself and there is no contact of the concave inside surface of the bend with other material; a bend and flatten test, in which a transverse force is applied to the bend such that the legs make contact with each other over the length of the specimen.
1.2 After bending, the convex surface of the bend is examined for evidence of a crack or surface irregularity. If the specimen fractures, the material has failed the test. When complete fracture does not occur, the criterion for failure is the number and size of cracks or other surface irregularity visible to the unaided eye occurring on the convex surface of the specimen after bending, as specified by the product standard. Any cracks within one thickness of the edge of the specimen are not considered a bend test failure. Cracks occurring in the corners of the bent portion shall not be considered significant unless they exceed the size specified for corner cracks in the product standard.
1.3 The values stated in SI units are to be regarded as standard. Inch-pound values given in parentheses were used in establishing test parameters and are for information only.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.