抄録
The stress measurement by X-rays is based on the variation of lattice spacings of metallic crystals due to stress. Therefore complicated problems concerning the theory and equipment are present in the practical application of this measurement. Recently, however, the experimental procedures of X-ray stress measurement are applied to many fields of engineering studies in consequence of the development of equipments as well as of the improvement in measuring method and theoretical background. We have investigated the X-ray stress measurement from the standpoint of engineering application.
However, there are two sorts of problems regarding the X-ray stress measurement. One is that the X-ray stress measurement depends on the measurement of the local lattice strains due to heterogeneous deformation of the metallic crystals. Consequently it seems that the generation of these lattice strains is closely related to the deformation mechanism of the crystal grains. The other is that in the two phase alloys containing the α- and the β-phases, the plastic deformation is expected to appear preferentially in the α-phase due to the difference in yield stress or crystal lattice structure. Therefore, in regard to the X-ray stress measurement, it is necessary to discuss the problems of “Gefügespannungen”in relation to the mechanism of plastic deformation and the interrelation of elastic constants of the α- and the β-phases. In this connection, the authors carried out some experiments on Cu-Zn alloys containing the α- and the β-phases. One is the measurement of elastic constants of the α- and the β-grains, and the other is the measurement of residual stresses in these phases. In connection with the above experiments, the authors performed the observation of microstructure of the extended 6-4 brass plate specimen.
Round bar specimens of 6-4 and 7-3 brasses were used in the experiments. After being finished, all the specimens were annealed at 400°C for 1hr in the air, and then the specimens were electopolished before being subjected to X-ray photography. The specimens were stressed stepwise by a tensile testing machine, and at several stages of applied stress, the CoKα1 beams were radiated to the center of the specimen surface in vertical and oblique incidences with several angles Ψ. Using the film technique, the changes in atomic distances of the α- and β-phases were measured by the conventional sin2Ψ method. The value of cosec θψ was calculated from the measurement of radius of diffraction ring, using a microphotometer of automatic recording type.
At several stages of the applied stress, the relation between εψ and sin2ψ was obtained, and then the curve representing δε/δsin2ψ-σ (stress) relation was drawn by using the method of least square. Based on these diagrams, another curve of εψ=0 versus stress was drawn similarly. From the slopes of these lines, the elastic constants Were calculated for each phase. For the observation of microstructure of extended 6-4 brass, an optical microscope of 600 magnifications and an electron microscope of 10Å resolving power were used.
The conclusions of the present study are as followes;
(1) The elastic constants of the α-phase were measured by the X-ray technique using annealed 7-3 and 6-4 brasses. The values obtained were in fairly good agreement with those measured mechanically within the experimental errors. In the case of the specimens deformed plastically, the same results were obtained also.
(2) On the contrary, for the β-phase of deformed 6-4 brass, the elastic constants obtained by X-rays showed a little divergence from those measured mechanically.
