Research Of Fatigue Prediction Technology For EMU Based On Fiber Grating Sensor

Electric Multiple Unit(EMU)plays an increasingly important role in people's travel,many travelers choose it because of its high-speed and comfort.The fatigue strength of bogie frame directly affects the running safety of the train.When the EMU is operating at high speeds,its structure is subject to complex alternating loads.In order to determine the load condition,stress monitoring is required for the vehicle structure.The electromagnetic environment of EMUs is extremely complicated.Optical Fiber Grating sensors uses light as a sensing signal,and it has many advantages,such as anti-electromagnetic interference and high sensitivity.This paper uses fiber grating technology to predict the fatigue life of the EMU structure to reduce the EMU maintenance costs and electromagnetic interference.This paper develops a dynamic stress data acquisition and cumulative damage prediction system for EMU welding structures.The FBG sensor is placed on the weld of the EMU,and the fiber-optic-grating dynamic demodulator SM130 is used to demodulate the light wave signal.The industrial control computer is used for acquisition control and data storage.Based on LabVIEW software designs data acquisition and processing,rain flow count,S-N curve programming,and damage calculation program.Using the Welding Joint S-N Curve Data in International Welding Society Standards,the fatigue life prediction is based on the Miner cumulative damage principle.In this dissertation,the equipment compartment bracket of CRH380B EMU was taken as research object.This system is used for dynamic stress monitoring and damage prediction of the bracket weld.Firstly,the FBG sensor is used to build a stress monitoring platform for the welding seam of the bracket.Then a series of processing and rain flow counts are performed on the measured dynamic stress data to compile the stress spectrum.Finally,the nominal stress method was used to calculate the fatigue damage of the critical fatigue site based on the measured stress spectrum of the measuring point.The fiber grating stress monitoring and structural fatigue prediction system designed in this paper can perform stress monitoring and fatigue evaluation of the EMU structure.The fatigue damage calculation and fatigue life estimation of the equipment compartment bracket show that the damage prediction result is 3.23×10-6,and the mileage can reach 33 million kilometers to meet the design life of 12 million kilometers.This system can be used to monitor the fatigue damage of welded structures under strong electromagnetic interference environment.