Welding Residual Stress Measurement System Based On Virtual Instrument

Welding residual stress affects the bearing capacity and service life of welded structure. In the welding process, the welding residual stress in welding area is often used as a standard to improve the welding process. The research on welding residual stress is of great significance to the research of welding process. The development of virtual instrument and its application in the field of testing have broken through the concept of the traditional instrument, the function of virtual instrument has been changed, which provides technical support for the further research and improvement of testing methods.At present, compared to the rapid development of numerical simulation of welding technology and welding. Study on testing method of welding residual stress is slightly less, therefore, study on the regularities of distribution of welding residual stress by a certain degree of limitation. Based on the LabVIEW2011 software platform, the PXIe-4330 NI data acquisition card and the BE120-2CA-K type resistance strain gauge are used as the data acquisition hardware, a set of residual stress testing system is built. Small hole testing method of residual stress has been made a deep research and then improve the testing method.Residual stress testing system is divided into hardware part and software part. Hardware system mainly includes data acquisition card, resistance strain gauge and an industrial computer. Software was applied in welding residual stress measurement based on graphical programming language of virtual instrument. The software system mainly includes residual stress testing module, release coefficient calibration module, signal playback module, and data file operation module. The stress testing and analysis system has realized the function of the experiment parameter record, the coefficient calibration experiment, the residual stress data return and so on. Optimization of the testing system module design effectively enhance the control ability of residual stress testing error.Experimental error has been studied, results show that the error of the patch is 20%-24%, the sample reading time error is about 2%, and the error of the elastic modulus of the weld center in the residual stress test is 9.8%. The patch error can be effectively solved by the natural results of the patch operation link and the detection of the pre testing. The determination of value time can be determined by observing the variation of the residual stress release curve, and then the error can be reduced. The welding component elastic modulus were measured, and variation curve of elastic modulus has been draw; while elastic modulus acts as the input variables could effectively reduce the error introduced by elastic modulus in the test of welding residual stress. The system is more specific to welding residual stress testing, and improves the accuracy of testing results, and then provides technical support for further study of welding residual stress distribution and the draft of welding control methods.Welding residual stress of VPPA-MIG welding component of 7A52 aluminum alloy with 11 mm thick was measured, it is found that stress concentration zone is narrow. and longitudinal welding residual stress is 20%-33% of yield strength, horizontal welding residual stress is 30%-39% of yield strength in the variation area of yield strength σs which happened in welding process.