ASTM B820-23

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Designation: B820 − 18 B820 − 23
Standard Test Method for
Bend Test for Determining the Formability of Copper and
Copper Alloy Strip
This standard is issued under the fixed designation B820; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope*
1.1 This test method describescovers the technique of bend testing copper and copper alloy strip samples to determine product
formability or the ability to resist cracking when forming a bend around a specific radius. The criterion for failure is the occurrence
of cracks on the outer (convex) radius of curvature.convex surface of the bend.
1.2 This bend test is limited to strip from 0.0030.003 in. to and including 0.031 in. (0.076(0.076 mm to and including 0.79 mm)
thick.
1.3 The forming or punch radius for the bend test is to shall be determined by agreement between the producer and the
customer.manufacturer or supplier and purchaser. This punch radius is typically equal to or greater than the minimum bend radius
without failure for the alloy, temper and thickness combination of the strip being tested.
1.4 Units—Values The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are
mathematical conversions to SI units which are provided for information only and are not considered standard.
1.5 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, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
B846 Terminology for Copper and Copper Alloys
E6 Terminology Relating to Methods of Mechanical Testing
E290 Test Methods for Bend Testing of Material for Ductility
3. Terminology
3.1 For definitions of terms related to copper and copper alloys, refer to Terminology B846.
This test method is under the jurisdiction of ASTM Committee B05 on Copper and Copper Alloys and is the direct responsibility of Subcommittee B05.06 on Methods
of Test.
Current edition approved March 1, 2018Nov. 1, 2023. Published March 2018November 2023. Originally approved in 1992. Last previous edition approved in 20142018
as B820 – 14a.B820 – 18. DOI: 10.1520/B0820-18.10.1520/B0820-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
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B820 − 23
3.2 For definitions of terms related to mechanical testing, refer to Terminology E6.
3.3 Definitions of Terms Specific to This Standard:
3.3.1 bend, longitudinal (or good way bend)—a bend with an axis perpendicular to the direction of rolling, drawing, or extrusion
(see Fig. 1).
3.3.2 bend, transverse (or bad way bend)—a bend with an axis on a plane parallel to the direction of rolling, drawing, or extrusion
(see Fig. 1).
NOTE 1—The usage of these two terms is consistent with Test Methods E290.
4. Summary of Test Method
4.1 The bend test is made by applying a force transversely to the length of the specimen in the portion being bent, usually at
mid-length. The 90° bending forces are applied through an arrangement illustrated in Fig. 2, while 180° bending forces are applied
through an arrangement illustrated in Fig. 3. When complete fracture does not occur, the convex surface of the specimen is
examined for cracks. In general, the test using a 180° bend angle is a more severe test than the test using a 90° bend angle.
5. Significance and Use
5.1 This bend test provides information as to the formability or the ability of copper and copper alloy strip to resist cracking when
being formed.
5.2 This test method can be used as a quality control tool to determine if material will form to a given radius.
5.3 This test method is also useful in research and development to provide data for use in selecting a spring material that will safely
form to the geometry of a given part.
5.3.1 The forming characteristic of interest is the smallest bend radius that can be formed without cracks or otherwise unacceptable
surface conditions (8.4). This radius, R, is the radius of curvature of the nose of the punch used in the test.
5.3.2 In addition, the difference between the angle of the bend after testing and 90° provides a measure of post-forming
springback.
5.4 The results are suitable for direct application in design and manufacturing, only when all factors such as the geometry of the
part, punch and die design, lubrication, stamping speed, and other material properties are known.
6. Apparatus
6.1 Various devices are suitable for 90° or 180° bend testing. The apparatus shall provide these features:
6.1.1 90° Bend Test Fixture—An illustration of this test fixture is shown in Fig. 2. A specimen rests on a pair of pins, rollers, or
radiused flat supports; a pin, mandrel, or 90° V-block 90° V-block die. A punch of a given bend radius for applying applies the
bending force directly at the specimen mid-length.
FIG. 1 Direction of Bending
B820 − 23
FIG. 2 V-Block and Punch for 90° Bend Test
FIG. 3 Fixture for 180° Bend Test
6.1.2 180° Bend Test Fixture—An illustration of this test fixture is shown in Fig. 3. A specimen rests on a pair of pins, rollers, or
radiused flat supports; asupports. A pin, mandrel, or 180° punch of a given bend radius for applying applies the bending force
directly at the specimen mid-length. Dial indicators with a precision of 0.0005 in. (0.013 mm) or better are necessary to accurately
position the two supports.
6.1.2.1 To prevent breaking the punch, it is recommended not to use a radius smaller than ⁄2 the thickness of the material being
tested.
6.2 The radius of the single pin, mandrel, or punch applying the bend force at the mid-length shall differ not more than 65 % from
the nominal value of the radius.
6.3 The length of all pins, rolls, mandrels, and radius flats must exceed the width of the specimen; they must be strong enough
and sufficiently rigid to resist significant deformation.
7. Test Specimens
7.1 Test Specimen Requirement: Four test specimens shall be required, two in the longitudinal and two in the transverse directions
for the 90° and 180° tests.
1 1
7.1.1 When the purchaser does not define a bending width requirement, the default width shall be ⁄2 6 ⁄16 in. (12.7 6 1.57 mm).
7.1.1.1 Four test specimens shall be required, two in the longitudinal and two in the transverse directions for the 90° and 180° test
angles.
7.1.2 When the purchaser defines a bending test at or below ⁄4 in. (6.35 mm), then the producer can optionally apply the narrow
width specimen as defined in 7.1.2.1 (see Fig. 4).
7.1.2.1 The narrow width specimen consists of four beams: 0.024 6 0.002 in. (0.6 6 0.05 mm), 0.047 6 0.003 in. (1.2 6 0.08
mm), 0.095 6 0.004 in. (2.4 6 0.1 mm), and 0.189 6 0.005 in. (4.8 6 0.13 mm). Four test specimens shall be required, two in
the longitudinal and two in the transverse directions, for the 90° and 180° angles.
B820 − 23
FIG. 4 Narrow Width Specimen – Produced by Stamping
7.1.2.2 When the purchaser does not identify a specific width in the narrow width specimen, the default width shall be 0.095 6
0.004 in. (2.4 6 0.1 mm).
7.2 The test specimens specimen may be prepared by cutting, shearing, or stamping.
7.3 The test specimens shall have any convenient length greater thanspecimen thickness shall be measured using a micrometer
with ⁄2 in. (12.7 mm) unless specified otherwise by the purchaser.a precision of 0.0001 in. (0.00254 mm) or higher.
7.4 Direction of Specimen:The specimen length be any convenient length greater than ⁄2 in. (12.7 mm) unless specified otherwise
by the purchaser.
7.4.1 The bending characteristics of a metal vary with the orientation of the bends to the direction of rolling. A longitudinal bend
will typically take a sharper bend radius than a transverse bend. This characteristic becomes more pronounced as the metal
thickness increases.
7.4.1 In a longitudinal specimen, its length shall be parallel to the direction of rolling as indicated in Fig. 1.
7.4.2 In a transverse bend specimen, its length shall be perpendicular to the direction of rolling as indicated in Fig. 1.
NOTE 2—The bending characteristics of a metal vary with the orientation of the bends to the direction of rolling. A longitudinal bend will typically take
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