Research On Hole-edge Crack Quantification Method For Aluminum Alloy Based On FBG Sensor

The aluminum alloy with holes is prone to crack damage at the hole edge under the action of cyclic loading.Fiber Bragg grating(FBG)sensors are widely used in structural crack damage monitoring due to their sensitivity to small changes in the structure.Compared with the traditional method,which only uses the FBG sensor to obtain the structural strain response for damage monitoring,the FBG reflection spectrum contains more structural damage information,but the mechanism of the FBG reflection spectrum and the change of the strain field at the crack tip is complex.Quantitative relationships between injuries remain challenging.In this paper,taking the hole edge crack of aluminum alloy as the research object,focusing on the problem of quantitative crack monitoring,based on the extended finite element and transmission matrix methods,the mechanism of the hole edge crack and the FBG reflection spectrum is systematically studied.Deterministic has an in-depth study of the impact of crack monitoring.Based on the extended finite element method,the crack propagation process of the aluminum alloy porous structure under cyclic loading was simulated,and the variation law of the strain field at the crack tip was analyzed.Based on the transmission matrix method,the FBG reflection spectrum under different crack lengths during the crack propagation process was reconstructed,and the mechanism of the strain change at the crack tip and the FBG reflection spectrum during crack growth was studied.The seven damage characteristic values are wavelength shift,broadening,reflection spectrum area,coincidence area,correlation coefficient,number of peaks and fractal dimension.Based on the support vector regression method,a quantitative monitoring model between the damage eigenvalues of the FBG reflection spectrum and the crack length is established.FBG sensors parallel to and perpendicular to the crack direction were set up respectively,and the effects of sensor layout and number of sensors on the accuracy of the crack monitoring model were comparatively studied,and the optimal crack quantitative monitoring scheme was formed.A quantitative monitoring test system for aluminum alloy hole edge cracks was established,and fatigue crack propagation tests were carried out to verify the effectiveness of the method.Based on the Bayesian statistical inference method,a quantitative crack monitoring method for uncertain factors and few samples is proposed,and the parameter update of the simulation quantitative model is studied in the case of a small amount of measured sample data.The quantitative crack model established in the simulation is studied.After the parameters are updated,an aluminum alloy with hole structure that can be applied to the actual working state is obtained,and the quantitative monitoring of cracks under uncertain factors and less samples is realized.Finally,the effectiveness of the above method is verified by the combination of experiments.