A New Gripping Technique for Small Metal Specimens

Document Type

Article

Publication Date

1-1-1999

Abstract

A new technique has been developed to grip small tension specimens. The specimens are 30.5 mm long with a test cross section that is 3.2 by 3.2 mm, and they have wedge-shaped ends that fit into matching slots in the grips. Alignment is accomplished by screws that position the specimen into the middle of the slots. Strain is measured with foil gages mounted front and back, and the specimen is tested in a medium-size servohydraulic test machine. The stress-strain curves of the small specimens agree well with those from standard-size specimens. The objective was to develop a specimen to study the local behavior of inhomogeneous materials such as steel weldments. The specimen had to be small enough for the test section to contain material from one weld bead, yet large enough to be tested in a servohydraulic test machine using a standard load cell, grips, and strain gages. There are two sub-size or small-size specimens described in ASTM E 8 and E 8M [1]. The sub-size rectangular specimen is 6.4 mm (1/4 in.) wide with a gage length of 25.4 mm (1 in.) and an overall length of 101.6 mm (4 in.). The smallest round specimen described has a diameter of 2.87 mm (0.113 in.), a gage length of 11.4 mm (0.450 in.), and an overall length of 32 mm (1.25 in.). While the test section of the round specimen is small enough, cutting and testing these from weld metal using standard techniques would be difficult. The size of the available weld specimen prevented the use of the sub-size rectangular specimen as it required too much extra material for gripping.

Publication Title

Journal of Testing and Evaluation

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