Research on a Novel Non-contact Metrology Technology of Stress Measurement Based on Deflection Method

With the aerospace and aviation industry development, machining deformation is the most prominent and urgent problem in the production process. Studies have shown that initial residual stress (RS) is the main factor causing the deformation of this type of part. Since residual stresses must be analyzed quantitatively, a series of measurement methods have been developed for this purpose. Remarkably, a series of measurement technologies inevitably need to include the corresponding calibration process, which is the fundamental element to ensure RS measurement accuracy. In this investigation, we developed a non-contact stress calibration method based on deflection value to study the measurement deviation of forging residual stress in the aerospace field. The constant stress beam (CSB) mechanical and finite element models of Ti6Al4V titanium alloy were established. The deflection measurement method was implemented using the visual system based on pattern speckle technology. A high precision loading device was developed to provide an accurate external load for CSB. A novel calibration technology based on the deflection method was proposed to realize RS measurement’s calibration process. We have successfully applied the CSB bending test campaigns and deflection metrology method to calibrate the stress values measured by the Static strain measuring instrument of Sigma and the Stress measuring instrument of Proto-ixrd. The results of theoretical and simulation stress are highly consistent with the calibration experiment. Calibration experiments combining the pattern speckle technology and the deflection method allow the stress measurement process’s calibration according to the correction factor. The research provides a great impetus to the development of precise quantitative measurement of RS.