The application of fracture for low carbon steel under extra-low cycle rotating bending fatigue is studied in this paper. The experiments have been made in special rotating bending fatigue fracture equipment designed by us. Several problems, the relations of the cycle times of fracture, the strain amplitude near notch tip and fatigue fracture toughness to the presetting deflection, the effects of depth and tip radius of notch to the cycle times of fracture, are discussed through the experiments. The suitable parameters of fracture in rotating bending fatigue for low carbon steel under extra-low cycle times have been proposed.
Safety designs and fracture designs are the two important fields of crack theory. The fracture problems of middle carbon steel under extra-low cycle rotating bending fatigue loading are studied in this paper. The experiments have been made in special rotating bending fatigue fracture machine designed by us. Several problems, the relations of the cycle times of fracture and the strain amplitude near notch tip to the deflection, the effects of depth and tip radius of notch to the cycle times of fracture, are discussed through the experiments. The mathematical expression of fracture
toughness to the cycle times of fracture is obtained. The suitable parameters of rotating bending fatigue fracture model for middle-carbon steel in extra-low cycle times has been proposed.
The special clamp for fatigue of shaft under bending, torsion, and bending-torsion that used on the fatigue machine is designed and manufactured. The low-cycle fatigue experiments of shaft with annular notch under cantilever bending have been made. Through experiments and analysis, the effects of tip radius, depth and open angle of notch on low cycle fatigue life of shaft with annular notch under cantilever bending are obtained. The method and results will play an important role on the fatigue life prediction and anti-fatigue design.
A series multi-axial tension and torsion low cycle fatigue life experiments of Ti-6Al-4V alloy were conducted on the MTS tension and torsion joint testing machine, in which the torsional strain control and non proportional cyclic loading method under the loading paths of circular, rectangular, square, oval and diamond were successively used. The experimental results are compared and analyzed with the results that calculated by the equivalent strain model, the energy method model and the critical plane method model. The results show that the critical plane method is the accurate prediction model to predict the multi-axial low cycle fatigue life of Ti-6Al-4V alloy.
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