A new gripping technique for small metal specimens

A new technique has been developed to grip small tension specimens. The spe cimens are 30.5 mm long with a test cross section that is 3.2 by 3.2 mm, an d they have wedge-shaped ends that fit into matching slots in the grips. Al ignment is accomplished by screws that position the specimen into the middl e 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. Th e stress-strain curves of the small specimens agree well with those from st andard-size specimens. The objective was to develop a specimen to study the local behavior of inho mogeneous materials such as steel weldments. The specimen had to be small e nough for the test section to contain material from one weld bead, yet larg e enough to be tested in a servohydraulic test machine using a standard loa d cell, grips, and strain gages. There are two sub-size or small-size specimens described in ASTM E 8 and E 8M [I]. The sub-size rectangular specimen is 6.4 mm(1/4 in.) wide with a ga ge 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 1 1.3 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 diffi cult. The size of the available weld specimen prevented the use of the sub- size rectangular specimen as it required too much extra material for grippi ng.