X線による応力測定法に関する研究

炭素鋼の弾性係数のX線的測定について

抄録

It has been reported in the previous paper of the authors that owing to the recent trend in the remarkable development of the X-ray apparatus and improved method of measurement, the stress in metallic materials can be measured with sufficient accuracy. A good correlation is found between the mechanically induced stress and that measured by X-rays where the conventional elastic constant is used in the calculation.
There are some problems left, however, that need further investigation, for example, the problem of elastic anisotropy. This problem was discussed by some investigators, for instance, Möller, Greenough and Macherauch, and it was shown that the lattice strains are dependent on the diffracting planes of metallic crystals even in the elastic state, that is, there exists elastic anisotropy. For this reason, it is proposed that the elastic constant measured by the X-ray method should be used instead of that obtained mechanically for the stress measurement by X-rays.
The metallic materials in practical use are polycrystalline, and the average strain of a number of crystals favorably oriented with respect to the characteristic X-rays is measured in the X-ray procedure. The lattice strain is likely to differ according to the lattice plane in each crystal.
In order to clarify this problem, the authors measured the elastic constant by the X-ray method and compared it with that obtained by the mechanical means using carbon steels with various carbon contents. In this paper, the accuracy of the measurement of the elastic constant by X-rays is reported, and the stress calculated by using the elastic constant of X-rays is compard with that applied mechanically.
Round bar specimens 6mm in dia. and 110mm in length were used in this experiment. All the specimens were annealed before being subjected to X-ray photography. The specimens were stressed stepwise by the tensile testing machine, and at several stages of applied stress, CoKα₁ beams were radiated to the center of the specimen surface in vertical and oblique incidence with several angles ψ. The Stress was measured by the conventional Sin²ψ method using the film technique. The value of cosecθψ was calculated from the measurement of the radius of the diffraction ring using an automatic recording type microphotometer. In this experiment, it was required that because of the round bar type of the specimen, the effect of curvature of the radiated surface on the measured stress was taken into account. Accordingly, as a preliminary experiment, this effect was examined on the annealed specimen of 0.1% carbon steel.
From the slope of the lattic strain (εψ)-sin²ψdiagram for several applied stress, ∂ε/∂ sin²ψ-stress curve was drawn by using the method of least square. Based on this diagram, another curve of εψ=0 versus stress was drawn as above. From these slopes the elastic constant was calculated for each material.
The conclusions of the present study are as follows.
The result shows that the error is within the range of ±600kg/mm² as compared with the value measured mechanically for all the specimens of different carbon steels. Therefore, it may be said that for CoKα₁ radiation the error of the calculated stress between the case where the elastic constant obtained by the X-rays is employed and the case where the mechanical method is used is within the range of ±3%, in other words, within the range of experimental errors. The present results are in accordance with those of the previous studies. However, in general, it may be considered that elastic anisotropy is present in the industrial metallic materials. Consequently, the effect of elastic anisotropy on the stress measurement needs further investigation by examining the cases of different characteristic X-rays