A new testing technique has been devised for studying thermal ratchetting behavior. It employs low-cycle fatigue-type specimens (hourglass shape) in conjunction with two closed-loop, servo-controlled testing machines operating in unison to provide an exact simulation of the familiar three-bar assembly.

Diametral extensometers are employed in conjunction with an analog strain computer to provide instantaneous values for the total axial strain and to isolate the mechanical and thermal strain components. Stress-strain measurements are recorded continuously throughout each cycle to provide an extensive evaluation of the response to initial load level, maximum and minimum cycle temperatures, hold-time effects, different specimen diameters, and rate of temperature cycling. Demonstration tests are described which employ 304 and 316 stainless steel specimens subjected to an initial stress level of 10 000 psi and a temperature cycle from 1100 to 800 F.