New Machines for Creep and Creep-Rupture Tests

Abstract

Abstract This paper describes two new creep-rupture machines. One combines eight conventional lever-arm creep machines into a single unit but with individual furnaces, controls, and recording equipment. The elongation of each test specimen is indicated by a revolution counter and can be read directly. The indicating counters for the eight specimens are brought to a single panel and photographed periodically to obtain a continuous record of the creep. The counters are driven by new extensometers which are attached to the test specimens. Two types of extensometers are used; one which gives readings over a 3-in. gage length in hundred thousandths of an inch for measuring small strains up to 2 per cent total strain, and a second extensometer which records in ten-thousandths inch for strains up to rupture. The second is a screw-driven creep-rupture machine in which the specimen is loaded through a stiff spring. A continuous elongation-time curve up to rupture is automatically recorded without the need of an extensometer on the test specimen. The machine has a capacity of 10 tons and occupies a floor space of only 15 × 15 in. It can also be used to make short-time tensile, constant-strain-rate, and relaxation tests. The latter test requires the use of an extensometer on the gage length of the test specimen. To illustrate the satisfactory operation of these machines, the results of creep-to-rupture tests on a cast 25 Cr 12 Ni alloy are presented. The data from these tests are summarized in “design curves” which serve to describe the behavior of a material at a given temperature.