The strength of large structures such as vessels, slips or bridges depends mostly not only on the residual stress caused by welding but also on constrained stress, and therefore a non destructive stress measurement on a real object is demanded. Based on the experience that one of the authors previously made X-ray stress measurement of ship construction, authors newly developed a compact type of X-ray diffraction stress analyzer which adopts a modified side inclination method and enables the stress measurement at the corner of structures. This analyzer has also such features as an incident X-ray oscillation mechanism for the stress measurement of coarse grained materials, a direct charge system for making counting circuits small and 5×5mm2 large focal spot X-ray tube which is useful in side inclination method.
The relation between the measured stress σx' and the true stressσx is theoretically calculated as follow.
σx'=0.96σx+0.006σy-0.08Sin2φ(σ1-σ2)
The error of σx' is negligibly small, and is found to be comparable to that of the data by using a conventional type of apparatus, based on the experimental results on S15C and S40C heat-treated specimens under uniaxial stress. Goniometer setting error under ±2mm also does not increase the error in X-ray stress measurement.
