Apparatus for strain and load cycling at elevated temperature with high-accuracy control during hold periods

Abstract

A description is given of apparatus which has been developed to determine accurately the cyclic stress-strain behaviour of materials subjected to combined high-strain fatigue and creep at temperatures up to 700°C. The servo-hydraulic testing machine has a load capacity of ±20 000 lbf in push-pull and can operate in either a strain-cycling or a load-cycling mode. The specimen has a diameter of 0.5 in and a parallel gauge length of 1.5 in terminating in conic-section ridges on which extensometers are mounted for the measurement and control of axial strain. Strain is held constant to better than ±1 × 10−5 during hold times of up to 12 h and temperature control is better than ±0.5 degC.