Ultrasonic Spot Welding Embedding Of Fiber Bragg Grating Sensor And Its Sensing Characteristics Of Thermal And Strain

The Fiber Bragg Grating(FBG)sensor is a typical representative of the fiber optic sensor.It has the advantages of light weight,small size,anti-electromagnetic interference,etc.,and it is widely used for the smart structures.Ultrasonic spot welding(USW)has the advantages of solid forming,low temperature,low pressure,low energy consumption,etc.,and it is easy to embed fragile sensors such as FBG fibers within metal matrices to obtained smart structures that have the capability to sense their own temperature and strain.In this paper,the ultrasonic welding embeding FBG sensor was studied,The main contents of this study are as follows.(1)Optimization of ultrasonic spot welding process for host metal.The formation mechanism of ultrasonic welding joint was studied by welding process optimization and interfacial interface analysis of tinned aluminum alloy with magnesium alloy.The result shows that tin coating inhibits the inter-diffusion between Mg and Al alloys,and eliminates the formation of the brittle Mg-Al intermetallic compounds(IMCs)to improve the strength of the joints.It is believed that the main reasons for the formation of ultrasonic welding joints are the mechanical mating and the physical metallurgy process of the interface which was accelerated due to the high vacancy concentration,caused by the shaping deformation.(2)Metallization protection of FBG.The methods of electroless nickel plating and electroplating nickel were used to protect the FBG.The electroless nickel plating layer was closely connected with the optical fiber,while the electroplated nickel layer is in close contact with the electroless nickel plating layer and has similar composition.The sensing characteristics of the encapsulated FBG were studied.The result shows that the temperature sensitivity of FBG after metallization is 20.14 pm/?,about two times as much as the bare grating,and bending strain sensitivity is 23052 pm/??.(3)Optimization of ultrasonic spot welding embedding of FBG.Metallization FBG was embedded well within 0.3mm thick 6061 aluminum alloy by the method of ultrasonic spot welding under the welding parameters of welding time 45 ms,welding pressure 5.4MPa,and the metal coating is 45?m.The strength of embedded fiber is 1.89 N,and the embedding process were discussed.(4)The temperature sensing characteristics and strain sensing characteristics of embedded FBG by ultrasonic spot welding.FBGs were found to get good protection after embedding and maintain a good waveform.The central wavelength of FBG has blue shifted after embedding with ultrasonic spot welding due to the result of the mechanical compression induced by plastic deformation of aluminum alloy.The FBGS keep good temperature and strain sensing characteristics after embedding,respectively,and the average temperature sensitivity coefficient was 29.07pm/?,which was about 2.8 times of that of bare grating.The strain sensitivity of the encapsulated FBGs was 0.0973 pm /??.