BIAXIAL HIGH STRAIN FATIGUE TESTING OF 1Cr-Mo-V STEEL

Abstract

— A test facility has been developed in which a thin walled tube can be subjected to fully reversed fatigue cycles for all biaxial stress or strain ratios. Twin loop servo-control allied to high resolution gauge length extensometry, load and pressure transducers permits stress or strain controlled testing. The rig is unique in that cyclic stress-strain hysteresis loops can be obtained for both axial and circumferential directions during a test. Results from a strain controlled series of low cycle fatigue tests on a ferritic 1Cr-Mo-V steel obeyed the Manson-Coffin relationship with the exponent being sensibly constant for all strain ratios. For a given maximum principal biaxial strain, the damaging effect increased as the strain ratio φ increased from –1 to +1. By comparing results from solid and hollow cylindrical specimens, geometry effects on fatigue life were revealed. Data on shakedown and cyclic softening under biaxial strain conditions were also obtained.