| It is necessary to carry out long-term monitoring to ensure the safety and reliability of polymer bonded explosive(PBX).Acoustic emission(AE)as a real-time monitoring technology has been applied to PBX damage monitoring,but this technology cannot meet the requirements of AE monitoring for PBX engineering applications.Firstly,there is insufficient understanding of the stress wave propagation law in the PBX wide temperature range,making it difficult to accurately monitor.Secondly,commercial piezoelectric sensors have shortcomings such as large size and hidden safety hazards.It is urgent to develop safe and small AE sensors for PBX narrow spaces.Fiber Bragg Grating Sensor(FBG)is widely used in temperature and strain measurement in aerospace,bridges and other fields due to its small size,flexibility and resistance to electromagnetic interference.At the same time,because of its excellent engineering application performance,it is also concerned by relevant scholars in AE monitoring.At present,FBGs is still in the laboratory research stage as the AE sensors,and it has not been studied in the PBX damage AE monitoring.(1)It is necessary to study the photoelectric signal processing AE system that can demodulate FBG.(2)The feasibility of PBX damage monitoring and location needs to be verified(3)The wide temperature range of PBX service puts forward higher requirements on the environmental adaptability of FBG-AE system.Therefore,on the basis of the research status and development trend of AE monitoring technology,this article has carried out a series of research on PBX damage AE monitoring and localization.Firstly,an AE automatic sensor test system for characterizing the propagation law of stress waves in a wide temperature range was built.The velocity and amplitude attenuation coefficients of longitudinal wave for TATB-PBX and HMX-PBX in the-20??80? are obtained,which provides the data support of wave velocity and arrival time test methods for AE source localization.Meanwhile,according to the viscoelasticity of the PBX binder,the relationship between the velocity and amplitude attenuation laws of longitudinal wave and the physical state of the binder and the plate thickness were analyzed.Based on the wavelet transform and the Lamb-Rayleigh wave dispersion curve,the Rayleigh wave and the high-order Lamb wave are identified.The wave velocity and attenuation law of the Rayleigh wave at room temperature and high temperature are obtained,which provides the data support of different modes of wave for AE source localization.Secondly,tunable narrowband light sources,photodetectors,circulators and other optical passive devices are used to build a photoelectric signal processing system for demodulating FBG-AE sensor,and system sensing mechanism and existing problems were analyzed.In order to solve the problem of FBG directional sensitivity,a combination of theoretical calculations and experiments verified that bending FBG can weaken directional sensitivity.In order to solve the problem of narrow environmental adaptability of the system,a temperature adaptive FBG-AE system for PBX wide temperature range was developed.The FBG demodulation module was introduced in the FBG-AE monitoring system to track the wavelength change caused by temperature.And the wavelength information is fed back to the narrowband light source in real time.Through the research,improvement and testing of the AE monitoring system,it was verified that the FBG-AE monitoring system can monitor the damage of the PBX.Finally,the PBX mechanical damage AE experiment was implemented using the FBG-AE system.It is proved that the signal monitored by FBG is slightly lower than the piezoelectric sensor in number and amplitude,but it can also reflect the AE information of PBX damage,which reveals that the system can be used for actual damage monitoring of PBX.Meanwhile,the four-channel FBG-AE localization system and the time difference of arrival method were used to carry out the PBX plane and body localization experiments,which provides an experimental basis for rapid localization of engineering applications.The analysis showed that the localization error is related to the FBG directional sensitivity and stress wave attenuation.Therefore,it is necessary to introduce research experience of bending FBG and stress wave attenuation law in the subsequent localization work to further improve the localization accuracy.The FBG-AE system built in this article provides a new method for PBX damage AE monitoring.Through the research of stress wave propagation law and FBG-AE system,we had a deep understanding of PBX in ultrasonic field and enriched the theory and practical experience for PBX damage AE monitoring,which is of great significance to promote the study of the law of PBX damage evolution in wide temperature range. |
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