抄録
Fatigue tests were conducted using solid cylindrical specimens of pure copper with circumferential blunt notches subjected to combined axial-torsional loadings. The behavior of crack growth was observed by a plastic replication technique, and the property of fatigue life was investigated. The cracking at notch root was identified as an intergranular type. The dominant morphology of crack growth was found to be the coalescence of distributed small-cracks, while some difference was observed depending on the stress multiaxiality. The fatigue life was correlated with the equivalent stress of the Mises type and the maximum shear stress. The fatigue life for the same value of each stress parameter became longer as increasing shear component in the stress state at notch root.
An analytical procedure for the crack growth at notch root was established by using a model based on the competition between the coalescence growth and the propagation of a dominant crack. Characteristics of intergranular cracking at the notch root and its dependence on the stress state were very well simulated by the present analytical model. Fatigue lives in several test conditions were statistically estimated by a simulation of the Monte Carlo type. The prediction with the simulated scatter-bands almost coincided with the experimental results.
