In X-ray residual stress measurements for uni-directionally deformed surfaces such as ground, planed or rolled, a non-linearity of d-sin2ψ diagram, so called ψ-splitting (ψ-Aufspaltung), has been observed recently. It has been known that this is caused by the residual shear stress induced in the deformed layer by external forces. To gain a further understanding of the ψ-splitting, d-sin2ψ relations were measured under various combinations of the method of working, the material worked and the diffraction plane. The strain distributions were measured not only for a matrix phase but also for a carbide phase.
The results obtained are summarized as follows:
(1) The ψ-splitting was observed when the measurements were taken in the working direction but not in the perpendicular direction. The extent of ψ-splitting became larger as the degree of working increased.
(2) The ψ-splitting was observed in pure iron as well as in steels containing carbide phase. The extent of ψ-splitting increased as the volume fraction of carbide phase increased.
(3) Although the appearance of ψ-splitting did not depend on the selection of diffraction plane, the behavior of the ψ-splitting, upon changing the sign of ψ, for the matrix phase and that for the carbide phase were mutually reversed. This means that the sign of the residual shear stress in the carbide phase is opposite to that in the matrix phase.
On the basis of these experimental facts, a model of dislocation arrangement in the unidirectionally deformed layer is proposed by which the appearance of ψ-splitting can be easily understood. It is concluded that the ψ-splitting is caused by a dislocation structure within the X-ray penetrating layer which is composed by cell structure and by dislocation loops around carbide particles.
