抄録
It is well known that X-ray diffraction breadth varies with stress cycles. Let the variation of breadth be designated by y=b/B-1, where b is breadth after any number of stress cycles, and B is its initial value. In order to analyze the fatigue process, the equation for the breadth variation was introduced by the authors. The equation is constructed with two parts. One expresses a quickly increasing part of breadth in early fatigue cycles, and corresponds with workhardening process. If the variation is denoted y1, the equation is as follows where k1 and m1 are constants, n is the number of stress cycles, σ1 is designated as σ1=σ-0.7σw, σis the stress amplitude and σw is the endurance limit. The other one expresses the slowly increasing part of that over the whole fatigue life, and it corresponds with fatigue damage process. If the value is denoted y2, the equation is as follows where k, A, D and m are constants. S-N curve can be represented with the following equation under constant amplitude loadings.
The constants A, D and m are the same as those mentioned above, and can be determined from the fatiguc tests. The variation of breadth y is represented with sum of y1 and y2.
The tested material was 0.10%C steel which was annealed at 700°C for 2hr. For the X-ray apparatus CoKα line was used. The distance between the specimen and the film was 70mm.
In the present experiment, when the variation of breadth increased until y=0.19, the material fractured in the case not only of constant amplitude test but also of sinusoidally varying amplitude test. The measurement values and calculated curves agreed well with each other.
