抄録
Twin-counter method different from the ordinary X-ray method of determination of residual stresses characterizes itself by the fact that the residual strains can be directly read out on the counting rate meter whose indication corresponds directly to a small shift in the position of an X-ray reflection line due to lattice strain.
The Twin-counter consists of two semi-cylindrical G. M. counters which are symmetrically situated on both sides of a thin separator which serves as the common cathode. A beam of reflected X-ray from a specimen may be divided into two by this fine common cathode, and each counting rate due to the two inner counters may be adjusted by shifting the Twin-counter so that the out put of the differential rate meter connected to each counter becomes zero. Then, an out put of the counting rate meter corresponds to the position of an X-ray reflected line.
Some experimental methods and examples for determinations of the residual principal stress and its distributions on the specimen surface are demonstrated by making practical application of such a character of the Twin-counter method.
According to the basic principle of the X-ray method of stress measurement, the surface stress component σφ is given by the well known equation
σφ=dp, ψ-d⊥/d⊥E/1+ν1/Sin2ψ.
Now ψ is kept at constant different from the ordinary“Sin2ψ method”, while φ is changed as φ1, φ2, ……, φi, etc. by rotating the specimen around the axis normal to the specimen surface. Then, the following equation is obtained by subtracting σφj from σφi,
σφi-σφj=dφi, ψ-dφj, ψ/d⊥E/1+ν1/Sin2ψ.
If the value of (dφiψ-dφj, ψ) becomes maximum, the direction of principal stresses is the same as directions of φi and φj respectively. The angle in the direction of the principal stress, therefore, are found out from the experimental data with ease. If it can be estimated that one of the principal stresses σ1 is a tension or compression and the other σ2 is negligible small, σ1 is determined using the equation given above.
Since the incident angle ψ is kept at constant during the experiment, the focusing circle in a back-reflection focusing technique does not change, and it does not change the irradiated area nor the depth of the penetration of X-rays in the specimen.
For other applications of this Twin-counter method, the relative surface stress distribution may be continuously recorded by shifting the specimen.
