Abstract
Abstract— Non‐isothermal fatigue crack growth tests were performed on Hastelloy‐X single edge notch specimens in which strain and temperature were varied simultaneously. Conditions were selected to include nominally elastic and nominally plastic conditions and temperatures up to 925°C. The crack growth rates were first reported as a function of the strain intensity factor (δKε) derived from a crack compliance analysis. Out‐of‐phase (εmax at Tmax) cycling showed faster crack growth rates than isothermal or in‐phase (εmax at Tmax) cycling under elastic straining. Under fully plastic cycling, the opposite results was observed, i.e. crack growth rates under isothermal cycling are faster than under TMF cycling. On a δKε‐basis, a strain range effect was observed. All the results were rationalized using a corrected stress‐intensity factor (δKeff) computed from the actual load, the closing bending moment caused by the increase compliance with crack length, and with the effective opening stress. Each mode of fracture was found to be characterized by a unique crack growth rate vs δKeff curve. On a δKeff‐basis, the isothermal crack growth rates at Tmin and Tmax provide an upper and a lower bound for the TMFCG rates. The effectiveness of δKeff to correlate crack growth rates under fully plastic cycling is discussed in detail.
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