Crack propagation tests in creep were carried out on 0.16 percent carbon steel at 400 and 500°C in air and at 400°C in vacuum, on Type 316 stainless steel at 600 and 650°C in air, and on Type 304 stainless steel at 650°C in air and vacuum. As a nonlinear fracture mechanics approach, the applicability of the creep J-integral for a controlling parameter of the crack propagation rate was investigated using a few types of specimens subjected to constant tensile loads. A good correlation was obtained between crack propagation rate and creep J-integral. Crack propagation rate was nearly proportional to the creep J-integral, and the relationship was almost independent on the width of plate specimens, the test temperatures, the testing environments, and the fracture mode. The creep crack propagation rate in round notched bar specimens was a little smaller than that in the center notched plate specimens at the same magnitude of the creep J-integral.
Push–pull fatigue tests were conducted under a sinusoidal stress waveform with a frequency of 1 Hz and a trapezoidal one with a hold time in both tension and compression at 300 MPa‐amplitude. Tests were conducted at a temperature of 1273 K using smooth bar specimens of the nickel‐base single‐crystal superalloy CMSX‐10. Small cracks were observed on the surface of the interrupted specimens by means of optical and scanning electron microscopes and their number and length were measured. The fatigue behaviour was characterized as follows: (1) A number of small cracks were initiated at a relatively early stage on the grain boundaries of the surface oxide which were perpendicularly to the tensile stress axis direction. (2) Some of these cracks grew inside and reached the base metal. Their growth brought about final fracture of the specimen. (3) The creep strain during the stress hold period accelerated the growth rate of the small cracks and shortened the fatigue life.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.