Residual Stress Measurement Technology By X-Ray And The Applied Research

The effect of three-dimensional residual stress on fatigue properties of materials can't be ignored. In failure analysis for the high-power motor shaft 35CrMo steel of the subject, three-dimensional residual stress by x-ray measurement method of the delamination theory and experiment have been studied along the depth of large axisymmetric component.It provides experimental evidence to improve the treatment system ,to reduce deformation in the heat treatment and to prevent the early fracture of steel shaft. X-ray diffraction characteristics of special materials have been calibrated by a wide range of system in this subject. A breakthrough has been got in x-ray measurement key technology. The research results for the engineering applications of residual stress detection technology of austenitic stainless steel and etc have some guiding significance.This subject relates to two key problems in x-ray measurement technology. One is axial stress is taken into account amendment in three-dimensional residual stress by x-ray measurement method of the delamination theory, based on circumferential and radial stress amendments. Integral form of amendment formula and the discrete formula which facilitates the practical application have been deduced. Another is x-ray diffraction characteristics of special materials have been system evaluated. For some materials because many diffraction peaks occurs in x-ray diffraction stress measurement of actual engineering structure and the stresses determined according to different diffraction peaks are different from each other. According to this problem, diffraction characteristics of special materials have been discussed by uniform intensity girder calibration.In the exploration of three-dimensional residual stress test method by x-ray stripping layer method, it is assumed that cylinder is infinitely and is axisymmetric whole-ring stripped. Based on saint-venant principle, axial stress correction formula has been deduced. In accordance with the thin-walled cylinder subjects to internal pressure theory, radial and circumferential stress correction formula are deduced. By making use of this theory, residual stress test and amendments to the diameter of 280mm high-power motor shaft after stripping the surface layer have been done, and residual stress distribution along the depth of layer have been got. The results show: Actual stress for each direction is the sum of measurement value and correction value. The correction values of circumferential and radial are equal to each other. The affected depth for quenching technology of the shaft is 47mm.The maximum circumferential compressive stress is -737.47MPa. The maximum axial compressive stress is-569.90MPa.They occur in the depth of 7mm department, and the difference is 29.4% between each other. The distribution trends of circumferential and axial stress curve after amendment remain unchanged. But the stresses value have increased, the correction value of maximum axial stress is greater than circumferential stress 61.9%.The radial stress is tensile stress and is gradually increased with the increase of stripping layer depth of peeling layers. In the three-dimensional residual stress of quenching layer, circumferential and axial stress are main stresses, and accounts for 55%-40% . The radial stress is secondary stress. To eliminate the effects of machining, the electropolishing depth is at least 0.5mm. Experimental results show that in the delamination application, the amendment is necessary.According to the difficulty in accurate determination of the true stress in x-ray diffraction stress measurement, it is discussed in this paper. It is found this paper presents x-ray diffraction characteristics of five different materials, carbon steel (Q235), austenite stainless steel (1Cr18Ni9Ti), martensitic stainless steel (A335P92), Al alloy (LY12) and Ti alloy (TA15) in x-ray diffraction stress measurement by uniform intensity girder calibration. The results show that austenite stainless steel presents two diffraction peaks when it is diffracted by X-ray.Although 127°for austenite stainless steel is apparent, the stress calculated from this peak does not represent the actual stress according to this peak; however, although Kβdiffraction peak at 149°, in spite of the lower peak- back ratio, 149°diffraction peak can be used to obtain the actual stress. For the Al alloy, two diffraction peaks occur in x-ray measurement. Only the diffraction peak at 158°can represent its stress in the material. The two diffraction peaks for the Ti alloy can both be used to calculate its actual stress.The calibration results of stress constant show: under the premise of considering material grade and heat treatment status, the difference between the stress constants of austenite stainless steel by experimental calibration and conventionalγ-Fe is 22.5%.The error is 7.8% between martensitic stainless steel and conventionalα-Fe. The error for the stress constant values from two diffraction peaks of Ti alloy is 10%-8%.It is proved by experiment results that X-ray diffraction peaks at some angles can't well reflect the real change of stress, which is a common problem.