The authors developed the measuring theory of three dimensional residual stresses, in which inherent strains, the source of residual stresses, are used as parameters, and demonstrated L_{z} method and nL_{y}, method. In these methods, inherent strains are estimated using relaxed strains measured at many points. Necessarily, cutting is required many times. In the cutting process, additional inherent strains may be produced by the effect of cutting heat. Therefore, it is desirable to decrease as much as possible the number of cutting, which is also very important to improve the accuracy of measurement and to shorten the time required for experiments.

In this paper, in order to accurately estimate three dimensional residual stresses produced in a region where residual stresses are uniform along the welded line, a measuring theory and its method using a thin plate cut out perpendicular to the welded line are presented.

The main results are as follows:

(1) Using relaxed strains measured before and after the cutting of T-specimen, effective inherent strain, the source of residual stresses, can be estimated being divided into cross-sectional inherent strain components, {ε^{*}_{y}, ε^{*}_{z}, γ^{*}_{yz}}^{T}, and one along the welded line, {ε^{*}_{x}}.

(2) Giving the estimated effective inherent strains to the original three dimensional object, residual stresses are calculated. By this method, three dimensional welding residual stresses at an arbitrary position including the inside of the object can be estimated.

(3) The reliability of this theory was confirmed by numerical experiments.

(4) The number of cutting has greatly been decreased. Accordingly, the time required for experiments can be greatly shortened and experimental expenses cut down.

(5) This method is applicable to measurement of three dimensional residual stresses produced by any causes as well as welding, if the residual stresses are considered to be uniform in one direction.