ASTM A938-97(2003) pdf free download.Standard Test Method for Torsion Testing of Wire.
ASTM A938-97(2003) describes the torsion (or twist) testing of metallic wire.
6.Specimen Preparation
6.1 Str’aightening-The test piece, consisting of a length of wire. should be straight before being tested. If straightening is necessary, it shall, unless otherwise specified, be done by hand Other straightening techniques are permitted provided surface damage is avoided. Since the shear stress is maximum at the surface of the wire during testing. even slight surface damage such as pits or scratches can cause early fracture, and the results may not be indicative of the full capability of the wire.
NOTE 1-During straightening. it is important that the properties and cross section remain unchanged as far as possible. In particular. the specimen shall not be subjected to any twisting.
6.2 Test Length
6.2.1 Recommended test length is 8 in.(203 mm)(distance between the clamping heads ).Suficient material must also be provided to allow for gripping.
6.2.2 Other test lengths may be used as agreed upon between the .producer and purchaser or as specified in the appropriate product specification.
7. Procedure
7.1 Tensile Force-Clamp the specimen in the clamps of the test apparatus with its longitudinal axis coaxial with the clamping heads and in such a manner that the specimen remains as straight as possible during testing (see 5.1.1).Unless specified otherwise, this can be accomplished by applying a small tensile force to the specimen. This force should be just sufficient to prevent the specimen from deflect ing away from the axis of rotation during twisting. Recom- mended tensile forces are shown in Table 1.
7.2 Speed of Tivisting-The speed of testing should be such that the wire is not heated appreciably during the test since excessive speed results in a lowering of torsion values Recommended maximum speeds are shown in Table 2.
7.3 Nmber of Turns:
7.3. 1 After placing the test specimen in the machine, rotate one clamp at a reasonably constant speed until the test specimen fractures, defined as a complete separation of the broken ends.
10. Kevword
10.1 coaxial clamping; fracture revolution counter; test length; torsion; torsion testing; twisting rates; wire: wire axis; wire ductility.