摘要
为解决传统压电传感器(piezoelectric, PZT)不能植入弹药内部监测高聚物粘结炸药(polymer bonded explosives, PBX)损伤问题,利用可调谐窄带光源搭建了基于光纤布拉格光栅(fiber Bragg grating, FBG)微细传感器的PBX声发射监测系统(FBG‑AE),开展了PBX单轴拉伸、压缩及断铅实验,对比了FBG与PZT两种传感器的信号特征;同时还开展了FBG方法的环境适应性、信号方向敏感性等研究,以验证该监测系统的基本性能。研究结果表明:虽然试验中FBG信号幅值略低于PZT,但也能产生毫伏级以上输出信号,可以应用于PBX损伤在线监测;在环境温度与变形场分别小于±3 ℃或±25 με范围内时,该FBG‑AE系统能够有效监测到PBX上产生的断铅信号;FBG对AE信号方向具有敏感性,在90°和270°方向(即垂直于FBG轴向方向)信号幅值最低,提出并验证了采用弯曲粘贴FBG方法可以减小声发射监测方向敏感性差异,有利于提高PBX损伤定位精度。
图文摘要
The AE monitoring system based on FBG sensor was built to study the feasibility of damage monitoring for PBX. The environmental adaptability of the system was investigated to satisfy the wide temperature range of PBX materials. The damage of PBX under mechanical loading was detected using the FBG‑AE method.
高聚物粘结炸药(PBX)材料或构件在贮存、运输中由于长期外载荷的作用,将萌生裂纹并持续发展为破坏性断裂,裂纹在发展过程中积聚的能量突然释放产生瞬态应力波的现象,即为声发射(AE)。利用AE技术对PBX材料因损伤产生的声信号实施在线监测,不仅能掌握PBX损伤趋势规律、揭示PBX损伤破坏机理,而且对提高武器系统安全性和可靠性具有重要意
目前,FBG‑AE技术主要应用于航空航天和航海业、采矿业、电力工业等领域,针对铝板、碳纤维增强材料、岩石、变压器局部放电等损伤或异常情况实施在线实时监
PBX的声阻抗较高,FBG‑AE监测PBX的损伤破坏具有一定难度。因此,为了研究FBG‑AE监测系统对PBX损伤监测的可行性和适用性,建立了基于FBG的AE监测方法,测试了机械载荷作用下PBX的损伤情况,在此基础上,为了使系统能适应PBX宽温域监测条件,研究了PBX损伤监测系统的环境适应性。进而,提出FBG弯曲粘贴方法,提供了一种提高PBX损伤定位精度的实施方法。
AE源产生的弹性振动会以应力波的形式释放,随即传播到材料表面引起表面位移,用传感器感知材料表面位移的机械振动,并通过高频采集系统以电信号的形式采集到该机械振动,便可对被测材料的AE信号进行分析和处
(1) |
式中,Δλb为FBG中心波长漂移量,pm;neff0为初始纤芯折射率;ΔΛ为几何效应引起的光栅周期弹性变形量,pm;Δneff为弹光效应引起的纤芯折射率变化量;Λ0为初始光栅周期,μm。
作用于FBG的AE应力波,描述为时间的余弦函
(2) |
式中,εm为AE波振幅,V;λs为应力波在介质中的波长,mm;z为FBG轴上的一点;fs为应力波频率,Hz。当FBG在AE应力波的作用下,由几何效应和弹光效应引起的纤芯折射率和光栅周期变化量为(满足条件:超声波波长远大于栅区长度):
(3) |
(4) |
式中,P11、P12为弹光系数,ν为泊松比。
(5) |
本研究中采用HMX基PBX,由质量分数95%的HMX晶体颗粒和质量分数5%的氟橡胶压制而成的毛坯件,参考GJB772A-1997炸药试验方法417.1、418.1机加成哑铃型拉伸试件和圆柱形压缩试件,方向敏感性测试所用的HMX基PBX试件尺寸为Φ220 mm×70 mm。
实验利用可调谐窄带激光光源搭建了FBG‑AE高速解调的监测系统。监测系统的工作原理如

图1 FBG‑AE监测系统示意图
Fig.1 Schematic diagram of FBG‑AE monitoring system

a. initial FBG reflection spectrum position

b. drifting FBG reflection spectrum position
图2 基于窄带激光的AE解调原理图
Fig.2 Schematic diagram of AE demodulation based on narrowband laser source
FBG‑AE监测系统的环境适应性将决定PBX损伤监测的环境要求,根据窄带激光的AE解调原理,在温度场和应变场变化的环境下,FBG反射谱发生左右漂移,可能会导致初始设定的窄带光源波长照射到FBG透射光谱区,使得FBG反射的光强变化量极小,FBG‑AE监测系统就监测不到AE信号引起的光强变化现
研究PBX的力学性能,能优化PBX配方设计、提高武器性

a. a tensile specimen

b. a compression specimen
图3 PBX试件拉伸、压缩实验示意图
Fig.3 Schematic diagram of tensile and compression experiments of PBX specimens
解决FBG方向敏感性问题是开展高精度的PBX损伤定位AE监测工作的重要目标之一。FBG方向敏感性取决于声波传播方向和FBG轴向的相对取向,当超声波的传播方向平行于FBG轴向时,FBG受到最大应变影响,具有最好的方向敏感

图4 FBG方向敏感性测试图
Fig.4 Test diagram of FBG direction sensitivity

图5 FBG反射谱的传感波长范围图
Fig.5 Sensing wavelength range of FBG reflection spectrum

a. PZT sensor⁃tensile test

b. FBG sensor⁃tensile test

c. PZT sensor⁃compression test

d. FBG sensor⁃compression test
图6 加入力学曲线的PBX试件AE信号幅值对时间结果图
Fig.6 Result diagram of the AE signal amplitude versus time in PBX specimen and embedded into mechanical loading curve

a. AE signal monitored by PZT sensor

b. AE signal monitored by FBG sensor
图7 PBX试件幅值最大的AE信号波形
Fig.7 The waveform of the AE signal with the maximum amplitude in PBX specimen

图8 不同测试距离下PBX试件AE信号幅值与FBG方向的变化关系
Fig.8 Relationship between amplitude of AE signal and direction of FBG in PBX specimen under different test distances
通过以上实验分析发现FBG的方向敏感性与AE波作用的角度和距离相关。引入

图9 FBG‑AE的传感模型图
Fig.9 The sensing model of FBG ‑AE
(6) |
式中,Cx、Cy为AE波作用于FBG的方向系数(0<-Cx<Cy),θ为AE波传播方向与FBG轴向的夹角,ε为AE波作用于FBG中心产生的变形。
由上述模型可知,当θ=0°时,Δλb达到最大值,则FBG轴向是AE信号最为敏感的方向,当θ=90°时,Δλb达到最小值,则FBG径向是AE信号最不敏感的方向,因此,使用常规粘贴FBG方法进行PBX损伤定位,存在以下问题: (1) PBX为高声阻抗材料,使得AE波在传播过程中衰减较大,FBG监测的声信号幅值较小。(2) 损伤定位一般采用多个传感器,当AE波传播方向作用于FBG轴向的夹角不同,会导致FBG对AE信号响应的方向敏感性差异较大。当某一FBG距AE源较远且夹角为90°或270°时,可能会监测不到AE信号,影响损伤定位精度。(3) 夹角差异会增加AE源到达FBG的时间,消除夹角引起的时间差异,将提高损伤定位精

图10 FBG弯曲粘贴示意图
Fig.10 Diagram of the bending FBG
弯曲粘贴FBG的实验验证结果如

a. 30 mm

b. 70 mm
图11 FBG和弯曲粘贴FBG在距AE源不同距离下的方向敏感性测试结果图
Fig.11 Directional sensitivity test results of FBG and bending FBG at different distances from AE source
(1)通过FBG‑AE监测系统对PZT激励信号、断铅信号和PBX机械载荷损伤信号的响应分析,结果证明该系统灵敏度虽然低于商用技术,但可以监测、判定PBX的损伤与断裂。
(2)基于可调谐窄带光源解调方法搭建的FBG‑AE监测系统还不够完善,仅具有±3 ℃或±25 με的动态监测范围能力。因此,为了适用于PBX使用环境的AE损伤监测,还需要开展研究以拓宽其温度与应变变化的适用范围。
(3)通过FBG的弯曲粘贴方法改善了常规粘贴FBG对AE信号方向敏感性不同的问题,分析了采用该方法有利于提高PBX损伤定位精度。
(责编:高 毅)
参考文献
温茂萍, 田勇, 游开兴. 炸药部件无损检测综述[J]. 含能材料, 1994(1): 31-38. [百度学术]
WEN Mao‑ping, TIAN Yong, YOU Kai‑xing. A review for non‑destructive testing of explosive parts[J]. Chinese Journal of Energetic Materials (Hanneng Cailiao), 1994, 2(1): 31-38. [百度学术]
高登攀, 郑家贵, 田勇, 等. 浅谈声发射技术在含能材料研究中的应用[J]. 含能材料, 2004, 12(4): 252-255. [百度学术]
GAO Deng‑pan, ZHENG Jia‑gui, TIAN Yong, et al. Application of acoustic emission technique in energetic materials[J]. Chinese Journal of Energetic Materials(Hanneng Cailiao), 2004, 12(4): 252-255. [百度学术]
沈功田, 戴光, 刘时风. 中国声发射检测技术进展——学会成立25周年纪念[J]. 无损检测, 2003, 25(6): 302-307. [百度学术]
SHEN Gong‑tian, DAI Guang, LIU Shi‑feng. Acoustic emission testing progress in china: celebration for the 25(th) anniversary of chinese society for NDT[J]. NDT, 2003, 25(6): 302-307. [百度学术]
付涛. PBX热强度评估相关技术研究[C]// 中国工程物理研究院科技年报.2018. [百度学术]
FU Tao. Research on related technology of PBX thermal strength assessment[C]//China Academy of Engineering Physics Annual Report. 2018. [百度学术]
赵方芳, 罗景润, 田常津, 等. 利用声发射技术监测颗粒填充聚合物材料的裂纹扩展过程[J]. 高压物理学报, 2000, 14(3): 235-240. [百度学术]
ZHAO Fang‑fang, LUO Jing‑run, TIAN Chang‑jin, et al. The crack growth process of particulate filled polymer monitored by acoustic emission[J]. Chinese Journal of High Pressure Physics, 2000, 14(3): 235-240. [百度学术]
高登攀, 田勇, 王丽玲, 等. 高聚物粘结炸药热冲击过程中的声发射现象研究[J]. 无损检测, 2006, 28(4): 173-176. [百度学术]
GAO Deng‑pan, TIAN Yong, WANG Li‑ling, et al. Study on acoustic emission phenomena of plastic bonded explosive during thermal shock[J]. NDT, 2006, 28(4): 173-176. [百度学术]
Wang X, Ma S P, Zhao Y T, et al. Observation of damage evolution in polymer bonded explosives using acoustic emission and digital image correlation[J]. Polymer Testing, 2011, 30(8): 861-866. [百度学术]
Fu T, Wei P, Han X L, et al. Application of fiber Bragg grating acoustic emission sensors in thin polymer‑bonded explosives[J]. Sensors, 2018, 18(11): 377-392. [百度学术]
刘娟, 丁克勤. 光纤声发射传感器的研究现状与展望[J]. 传感器与微系统, 2010, 29(9): 5-7. [百度学术]
LIU Juan, DING Ke‑qin. Survey on development and prospect of fiber‑optic acoustic emission sensor[J]. Transducer and Microsystem Technologies, 2010, 29(9): 5-7. [百度学术]
Vidakovic M, Mccague C, Armakolas I, et al. Fiber Bragg grating‑based cascaded acoustic sensors for potential marine structural condition monitoring[J]. Journal of Lightwave Technology, 2016, 34(19): 1-2. [百度学术]
Wu Q, Yu F M, Okabe Y, et al. Application of a novel optical fiber sensor to detection of acoustic emissions by various damages in CFRP laminates[J]. Smart Materials and Structures, 2014, 24(1): 11-15. [百度学术]
Yu F M, Wu Q, Okabe Y, et al. The identification of damage types in carbon fiber–reinforced plastic cross‑ply laminates using a novel fiber‑optic acoustic emission sensor[J]. Structural Health Monitoring, 2016, 15(1): 93-103. [百度学术]
Rajan G, Karekal S. High frequency fiber Bragg grating interrogator for monitoring rock cracking events for mining applications[C]// Fiber‑optic & Photonic Sensors for Industrial & Safety Applications. IEEE, 2017. [百度学术]
马宾, 徐健. 一种用于变压器局部放电在线监测的光纤声发射传感器试验研究[J]. 光谱学与光谱分析, 2017, 37(7): 2273-2277. [百度学术]
MA Bin, XU Jian. Study of fiber‑optic acoustic emission sensor for partial discharges detection in power transformer[J]. spectroscopy and spectral analysis, 2017, 37(7): 2273-2277. [百度学术]
阳能军, 姚春江, 袁晓静, 等. 基于声发射的材料损伤检测技术[M]. 北京: 北京航空航天大学出版社, 2016: 5-13. [百度学术]
YANG Neng‑jun, YAO Chun‑jiang, YUAN Xiao‑jing, et al. Material damage detection technology based on acoustic emission [M]. Beijing: Beihang University Press, 2016: 5-13. [百度学术]
Kersey A D, Davis M, Patrick H J, et al. Fiber grating sensors[J]. Journal of Lightwave Technology, 1997, 15(8): 1442-1463. [百度学术]
Minardo A, Cusano A, Bernini R, et al. Response of fiber Bragg gratings to longitudinal ultrasonic waves[J]. IEEE Transactions on Ultrasonics Ferro‑electrics & Frequency Control, 2005, 52(2): 12-20. [百度学术]
张法业, 姜明顺, 隋青美, 等. 基于光纤光栅的冲击激励声发射响应机理与定位方法研究[J]. 物理学报, 2017, 66(7): 202-210. [百度学术]
ZHANG Fa‑ye, JIANG Ming‑shun, SUI Qing‑mei, et al. Acoustic emission localization technique based on fiber Bragg grating sensing network and signal feature reconstruction[J]. Acta Physica Sinica, 2017, 66(7): 202-210. [百度学术]
Kanakambaran S, Sarathi R, Srinivasan B. Robust classification of partial discharges in transformer insulation based on acoustic emissions detected using fiber Bragg gratings[J]. IEEE Sensors Journal, 2018, 18(24): 18-27. [百度学术]
Lee J R, Tsuda H. A novel fiber Bragg grating acoustic emission sensor head for mechanical tests [J]. Scripta Materialia, 2005, 53(10): 1181-1186. [百度学术]
温茂萍, 唐维, 董平, 等. 粘结剂含量对热压TATB基PBX残余应力的影响[J]. 含能材料, 2017, 25(8): 661-666. [百度学术]
WEN Mao‑ping, TANG Wei, DONG Ping, et al. Effect of binder content on residual stress of thermally compacted TATB based PBX[J]. Chinese Journal of Energetic Materials (Hanneng Cailiao), 2017, 25(8): 661-666. [百度学术]
Betz D C, Thursby G, Culshaw B, et al. Structural damage location with fiber Bragg grating rosettes and Lamb waves[J]. Structural health monitoring, 2007, 6(4): 299-308. [百度学术]
廖延彪, 黎敏, 张敏, 等. 光纤传感技术与应用[M]. 北京:清华大学出版社,2010: 20-25. [百度学术]
LIAO Yan‑biao, LI Min, ZHANG Min, et al. Optical fiber sensing techniques and applications[M]. Beijing: Tsinghua University Press, 2010: 20-25. [百度学术]
温茂萍, 庞海燕, 唐明峰, 等. 基于应力应变曲线的断裂能参数表征炸药韧性[J]. 含能材料, 2015, 23(4): 351-355. [百度学术]
WEN Mao‑ping, PANG Hai‑yan, TANG Ming‑feng, et al. Toughness measurement of explosive based on fracture energy of the stress‑strain curve[J]. Chinese Journal of Energetic Materials (Hanneng Cailiao), 2015, 23 (4): 351-355. [百度学术]
Ono K. Review on structural health evaluation with acoustic emission[J]. Applied Sciences, 2018, 8(6): 958-980. [百度学术]