Study of residual stresses in welded joints using the blind hole drilling method

In today's production of cranes' welded structures objective information about the state of residual stresses after welding is needed. The greatest residual stresses (RS) in combination with a high propensity to ruin have heat-affected zones (HAZ) of welded joints. The calculated as well as experimental determination of RS in these areas is difficult. Purpose. The purpose of this article is selection, adaptation and further improvement of the methodology for RS determining in the HAZ of crane welded joints. Methodology. To analyze the HAZ of welded joints the experimental method of drilling blind holes was chosen. A high-speed multiple-step drilling with inverted-cone drills is used. The resulting response of surface deformation is captured by three-element strain gauge rosette. To improve the calculation stage of the experimental method for determining RS a finite element simulation in three-dimensional formulation was performed along with experiments. The technique of the experiment was simulated by finite element method; the influence of a number of boundary conditions on the calculations' deviations was examined. Findings. The influence of the proximity of the weld bead on the error of the experiment has been analyzed. For different ratios of hole diameter to the diameter of the strain gauge rosette the errors from averaging deformation results on the basis of gauge were investigated. For low-carbon structural steel the abnormalities of the experimental results depending on the level of RS were presented. Originality. Methodology of RS experimental determination by the blind hole drilling method was improved. In particular, recommendations for the quantitative measurement of high RS (close to the yield point) by this method were introduced. Correctional coefficients for accounting the averaging deformation on the basis of the gauge in hole's contour strain measurements were presented. Practical value. The obtained results extend the possibilities of the blind hole drilling methodology in the context of HAZ RS research on welded joints made from low-carbon structural steels. Based on the obtained results the 5...20 % increase of accuracy of the RS definition in the immediate vicinity of the fillet weld was achieved. Performing the RS measurements in the most problematic areas of welded metal structures will allow one to find ways to optimize the cranes' steel structures production technology.