Development And Design Of Polyurethane Encapsulation FBG Sensor

Marine resources are an important field for human survival and development,and the development of marine resources is inseparable from various equipment,such as offshore platforms,benders,oil pipelines,etc.These equipments have long been in a harsh environment and must be healthy monitor.At present,fiber Bragg grating?FBG?is the best choice for long-term structural monitoring due to its small size,high accuracy,low cost,high sensitivity,reliable durability,anti-electromagnetic interference and other advantages,so it is widely applied to the field of Engineering monitoring.However,the bare fiber grating is easy to break,and it needs to be packaged and protected to be applied in practical engineering.According to research,FBG has a variety of packaging methods,most of which are mainly made of metal,carbon fiber,adhesives,etc.However,such packaged FBG sensors have long been used in marine environments,and there are varying degrees of damage from packaging material corrosion,adhesives,and structural failure.Therefore,it is necessary to select a packaging material suitable for long-term application in extreme environments,so that its packaged FBG sensor can provide monitoring data stably in a harsh environment for a long time.Because polyurethane has excellent comprehensive properties?such as wear resistance,corrosion resistance,light weight,hydrolysis resistance,low cost,etc.?,polyurethane elastomer is used as packaging material,and the following research is carried out on the FBG sensor with its package:Firstly,a mold and a packaging method in which the cavity is an I-shaped type are designed.A cast polyurethane elastomer?CPU?is prepared by a pre-polymer method,and a FBG in the mold is packaged by a manual casting method to prepare a strain sensor.The performance of the FBG strain sensor prepared by CPU package was experimentally studied by calibrating the FBG sensor,measuring the effective measurement range and field application test.The experimental results show that the prepared FBG strain sensor is sensitive,linear,the effective measurement range reaches 14000??.In addition,the interface between the CPU and the fiber grating was observed by an optical microscope,and it was found that the interface between the two had no obvious pores and no relative slip.Secondly,after the package test,it was found that the sensitivity parameter of the above-mentioned packaged FBG sensor was 0.835 pm/??,which was lower than the 1.2pm/??of the bare FBG.In order to improve its sensitivity parameters,the mold cavity was redesigned and improved from the I-shaped to the dumbbell-shaped thickened at both ends.The FBG strain sensor was prepared by a new encapsulation method.Through the strain calibration experiment,the sensitivity parameter of the dumbbell-shaped FBG sensor was0.926 pm/??,which was 1.1 times that of the I-shaped FBG sensor.Finally,in order to explore the influence of packaging materials on the performance of FBG sensors,this paper uses different elastic modulus CPU package FBG to prepare strain sensors.The CPUs with modulus of 10,500,and 1000 MPa were prepared by pre-polymer method,and FBG₁,FBG₂,and FBG₃ sensors were packaged respectively.Through the calibration test,aging test,effective measurement range test and polyurethane curing of FBG sensor,the FBG₂ sensor's sensitivity,stability,effective measurement range and center wavelength drift are the highest among the three,and FBG₂ is effective.The measurement range reaches 20086.433??,and the sensitivity is 1.12 times that of bare FBG.Therefore,it is recommended to select a CPU package FBG sensor with an elastic modulus of 10⁵00 MPa according to the actual situation in practical engineering applications.