ディープホールドリリング法による溶接部残留応力の高精度測定

Abstract

This paper presents a method to improve accuracy of measuring through-thickness residual stress for welds through deep hole drilling (DHD) technique. The focus of this study is the effect of dimensions of the hollow cylinder, which is manufactured by drilling and trepanning processes, on residual stress measurement at the welds. First, stress concentration-induced plastic region around a reference (drilled) hole was theoretically quantified according to value of existing stress. The plastic region around the hole is not negligible for the welds at where high tensile residual stress exists. In order to reduce the influence of the plastic region, it is considered effective to set a large ratio of trepanning diameter to drilling diameter. Another noteworthy thing is that weld residual stress is present in a relatively narrow region along a weld line. Then, DHD technique was applied to measure through-thickness residual stress at the welds of melt-run welded-plate specimens under conditions of various drilling and trepanning diameters. These DHD residual stress measurement results were compared with those measured by X-ray diffraction and contour methods and calculated by weld thermal elastic-plastic analysis. As the results, it was shown that through-thickness residual stresses measured by DHD technique were obviously influenced by dimensions of the hollow cylinder. Measurement accuracy becomes higher with increasing the ratio of trepanning diameter to drilling diameter. Meanwhile, trepanning diameter should not be larger than width of generation area of high tensile residual stress to be measured at the welds. It was concluded that a method for determining appropriate dimensions of the hollow cylinder to be drilled and trepanned was successfully proposed to accurately assess through-thickness residual stress at the welds through DHD technique.