A new method of stress measurement by X-ray is proposed. The apparatus of the method consists of two parts; a camera and the supporter of the X-ray tube, combined with the camera.
The camera is cylindrical and has cylindrical film around the axis which is strictly coincident with the incidental X-ray beam. The back reflected the X-ray patterns generally form corns around the axis of the incidental X-ray beam, and the intersections of these cones with the plat film make rings which are known as Debye Scherrer rings rings.
When the materials are void of stress these rings become perfect circles on the film and appear as straight lines on the developed film, in the case of the cylindrical film.
But if there is stress operating or some residual stress locked in the material, these cones are not perfect, but are deformed and the center is shifted. Then the diffracted and recorded patterns on the cylindrical film would appear as complicated biquadratic curves as the result of the intersection of the two quadratic curved surfaces.
Then the existence of stress can be judged from a glance at the developed film. This is the most convenient point. Another point is that there is no need to measure the exact distance between the film and the specimen surface, as is seen in the following equation.
σx=1/2RE/(1+ν)·1/tanθ·sin2θ·ΔDD
ΔDD=ΔD+-ΔD-=(D+-Ds)-(D--Ds) (From figure)
E: elastic modulus
ν: poissons' ratio
R: camera constant
This equation does not include the term of the distance between the film and the specimen-surface. These two characteristics resemble the Schoal method (flat plate method), but in the present method the required exposure time is only one half of the Schaals' method. The latter must have two times, exposures that on the first half of film and next on the covered half of it.
