抄録
The technique analysing the cause and the mechanism of fracture from the information obtained by X-ray irradiation on the fractured surface is called X-ray fractography. As a basic study of X-ray fractography, the relation between the residual stress along the crack propagation direction on the fatigue fractured surface and the range of stress intensity factor (ΔK) was investigated. The crack closure was also measured and was correlated with the residual stress.
The material used was Boron steel 10 B 35 tempered at 600°C after quenching. The specimens were 12mm thick 1 CT by ASTM standard. The fatigue tests were carried out under the constant range of stress intensity factor. The constant load fatigue test was also carried out as a reference. The main results obtained from the present experiments were as follows.
(1) In the constant ΔK fatigue tests, the crack length was linearly proportional to the number of load cycles, and the crack propagation rate and the crack opening ratio were constant. The crack propagation rate was about the same as that at the equal ΔK value under the constant load.
(2) In the case of crack opening ratio U=1.0, the residual stress on the fractured surface by the constant ΔK test was almost constant and independent of the crack length.
(3) In the case of crack opening ratio U=0.6, however, the residual stress slightly increased with increasing crack length.
