Study On Process And Accuracy Of Three-Dimensional Residual Stress Determination Using The Deep-hole Drilling Method

The residual stress exists in the processing and manufacturing of aerospace indus-try,nuclear power,marine equipment and advanced rail transit fields.The residual stress has a comprehensive influence on the generation and growth of the fracture cracks with the increase of the plate thickness.Therefore,the accurate assessment of the residual stress distribution along the thickness has important scientific significance and engineering application value for structural integrity evaluation and equipment op-eration monitoring.The current three-dimensional residual stress measurement meth-ods have various deficiencies in the feasibility of measurement process,reliability of measurement results,cost economy and material applicability.In recent years,the deep-hole drilling method as a new three-dimensional residual stress measurement method is attracting more and more attention.In order to improve the engineering practicability of the deep-hole drilling method for measuring the three-dimensional,the circumferential trepanning technology with the machining process of WEDM(wire electric discharge materials)was introduced in the dissertation.The difference of measurement results and stress release between the circumferential and traditional axial trepanning was studied when the applied stress field changes in the range of 0.1?0.9?s(?s is the yield strength of material)with the numerical simulation.The research results show that the measurement error of circum-ferential and axial trepanning is small when the applied stress does not exceed 0.5?s.The measurement error of circumferential trepanning in high stress field is lower and does not exceed 5%even the stress reaches 0.6?s.And the stress distribution along the depth direction is more consistent with the actual situation than that of the axial trepan-ning.When the residual stress exceeds 1/3?s,plastic deformation will occur at the edge of the reference hole for the stress concentration,and thus the measurement results ac-curacy will be affected for the large plastic deformation.Based on the circumferential trepanning technology with the machining process of WEDM,the combination of ex-perimental and numerical simulation was used to study the effect of deep-hole drilling method with multistep trepanning technology on the measurement results when the re-sidual stress is close to the yield strength.The results show that the multistep trepanning technology can release the high stress field to the elastic field gradually and control the stress measurement error within 6%comparing with the direct trepanning technology.There may be some error factors in the actual measurement process of the deep-hole drilling method.Based on the experimental measurement and the finite element model,the effects of the wall quality of the reference hole,the angle deviation of the experimental measurement,and the effect of stress in the thickness direction(?z)on the plane stress measurement results were analyzed in the dissertation respectively.The main conclusions obtained include:1.When the roughness of the reference hole wall is less than 0.4?m,the data sta-bility can be guaranteed and the fluctuation can be controlled within the range of 0.5?m.2.The relationship of the measurement results relative error and the deflection angle between the measurement direction and the actual principal stress direction is conformed to the quadratic function,and the relative error of the measurement result is less than 1%when the measurement deflection angle is less than 60.3.The angular deviation of two independent measurements of the reference hole has little effect on the final result,and the error generated is less than 1%when the angle deviation is no more than 60.4.When the original stress is completely elastic released or the material defor-mation state caused by the ?z is same as the original plane stress state,the calculation error caused by ?z is less influential.Conversely,the influence of ?z can't be despised.The relationship between the measurement error caused by ?z and the numerical value of ?z is a cubic function.