Simultaneous precision measurement of high temperature and large strain based on twisted FBG considering nonlinearity and uncertainty

The measurement of temperature and strain during metal machining process has several challenges, such as high temperature, large strain, great gradient, and many interference factors, and so on. This paper uses the fiber Bragg grating (FBG) to achieve the simultaneous precision measurement of high temperature and large strain that occurred in the metal machining process. Considering the FBG nonlinear problem caused by the cross-sensitive item and high-order sensitivity due to the high temperature and large strain, and the uncertainty caused by the measurement error and modeling error, the Bayesian nonlinear model is proposed. The results of the proposed approach not only give the accurate values of temperature and strain, but also provide the corresponding uncertainty in the form of posterior probability density function. Then the indicators of measured accuracy and consistency are defined to evaluate the measurement performance of FBG. Finally, the experimental platform of controlled high temperature and large strain is constructed to verify the proposed method. Next we plan to use the proposed method in the real machining environment.