| Smart skin technology for aircraft is an innovative technology that will change the design of future advanced aircraft and realize autonomous flight.It has the ability of selfdiagnosis,self-adaptation,self-learning and self-repair.Aircraft requires real-time monitoring of aerodynamic parameters(such as pressure,temperature,speed)and structural state parameters(such as strain,vibration,impact)during flight.However,the studies of flexible smart skin and its core sensors are still in the early stage of small area,single function and low speed test,which cannot match the measurement requirements of aircraft surface such as large-area,non-plane,multi-parameter and refinement.The lead zirconate titanate(PZT)sensor is sensitive to both pressure stimuli and vibration stimuli,making it ideal for multi-parameter sensing of smart skin.Based on flexible piezoelectric sensors,intensive research is carried out from the aspects of theoretical modeling,multi-functional integrated design,fabrication process development,algorithm integration and impact monitoring,wind tunnel test and so on.The main research contents and innovations include:(1)The relationship between the theoretical voltage output of flexible PZT sensor,the material thickness and the attached curvature was established under the constraint of conformal attaching with curved surface,which provided theoretical guidance for the parameter design of flexible PZT sensor.The influence of adhesion curvature on the performance of PZT sensor was analyzed quantitatively,which provided theoretical support for the measurements of sensor in curved airfoil.(2)According to the multi-parameter measurement requirements of aircraft,the structure design,fabrication process and acquisition scheme of a flexible piezoelectric sensor with multiple in-suit functions are further proposed.The in-situ integration of temperature,humidity,strain,pressure,impact,and hot-film sensing functions on the same sensor with μm-thickness is completed via only three layers.The device can measure both environmental parameters and structural parameters,and is of great significance to sensor signal compensation and sensor data fusion.(3)The low-temperature fabrication process of ultra-thin flexible PZT devices based on laser lift-off was developed.The process windows of device stripping success rate depending on laser energy,sacrificial layer thickness,and flexible substrate thickness were obtained through experiments and finite element analysis.Two stable stripping modes of high energy stripping and low energy stripping were found,and their stripping mechanisms(thermal ablation and thermal expansion)were revealed,which improved the success rate of preparation and process compatibility of ultra-thin PZT devices.(4)The impact monitoring and locating technology combined the flexible PZT array with an artificial intelligence algorithm was proposed to measure large-area structure via small-area sensors.Through the fusion of multiple signal classification algorithm and artifitial neural network algorithm,the spatial phase difference was adopted as the main characteristic value,which greatly reduced the training data and improved the recognition rate of impact location,which provided the possibility of flexible integration of aerodynamic load sensing and structural health monitoring.(5)For the synchronous monitoring requirements of environmental and structural parameters of advanced aircraft,a large-area,full-coverage flexible smart skin sensing method based on flexible piezoelectric sensors was proposed.The maximum area of the skin is larger than 300 mm × 500 mm.The flexible smart skin has been verified and analyzed in low-speed,subsonic and hypersonic wind tunnel tests respectively.The results show that the flexible PZT sensor can measure the stall and flutter of the airfoil successfully.Meanwhile,it has also been applied to the structural impact monitoring,realizing the integrated monitoring of multiple structural and environmental parameters of the aircraft. |
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