Optimization Of The X-ray Method Parameters Measuring Residual Stress In A7N01 Aluminum Alloy

In practical engineering,the magnitude of residual stress draws large amounts of attention,and there are requirements for residual stress detection in the aerospace industry,nuclear power industry and rail transportation industry.As the most mature residual stress detection method,X-ray method is widely used because of its high accuracy and portability.However,in the actual measurement,the results obtained by X-ray method sometimes greatly exceed the normal range of the stress value,or the dispersion of the data is more serious.Therefore,it is of great significance to study the parameter influence and error analysis of X-ray detection method for experimental research and engineering application.The principle of measuring residual stress by X-ray diffraction method is based on the Bragg equation diffraction theory.By detecting the change of crystal plane spacing,the strain on the crystal plane is calculated,and the corresponding residual stress is calculated by using Hook's law.Because the testing depth of the X-ray stress meter is very shallow and belongs to the micron level,it is easy to be affected by the surface state of the sample.In addition,when the grain size of aluminum alloy is large and the texture material exists,the diffraction peak of X-ray is abnormal,and the setting of parameters has a great influence on the testing.Since the final residual stress is calculated by fitting multiple diffraction data,it is also important to screen the data effectively.In this paper,A7N01S-T5 aluminum alloy is selected as test material,the test data of aluminum alloy welded joints detected by sin~2?method and cos?method are compared.It is found that the value of residual stress with sin~2?method in base metal position is smaller than that of cos??method,the value of residual stress value in heat affected zone and weld seam sin~2?is larger than that of cos??method,and the trend of longitudinal stress distribution with cos?method is obvious.The trend of transversestress with sin~2?method is more obvious.In the analysis of test error,it is found that,the remove of background,the deletion of discrete points on the fitting curve of?-sin~2?and the adjustment of focal length will affect the detection results to a certain extent,in addition,different grinding levels,the selection of the number ofangles and the curvature of the surface of the specimen are also important factors in practical engineering applications.The test of aluminum alloy is optimized by oscillating method in this paper,.The results show that the oscillation can obviously improve the test results,especially the position of weld center.Moreover,the measured stress can be corrected by reducing the calculation range properly,and the corrected range will be enough if there is just no diffraction vacancy,too much exclusion will make the diffraction information insufficient,and the error will also be serious.In this paper,the residual stress of aluminum alloy is measured by X-ray method and ultrasonic method,and the distribution of residual stress along the layer depth is studied by means of delamination method.The results show that the stress measured by X-ray method below 450?m is obviously lower than that by ultrasonic method,when the depth of stripping is more than 750?m,the results of X-ray method are similar to that of ultrasonic method,some points are even larger than those measured by ultrasonic method,and the sizes of the test results tend to be stable.Through the method of database,the test data are summarized,which makes the test results of residual stress more concrete,and it has a more intuitive guiding significance to judge the quality of the product.