Research On The Piezoelectric Sensor Array Based Lightweight Impact Monitoring Of Composite Structures

With the advantages of light weight,excellent strength-to-weight ratio and high specific stiffness and so on,composites have been gradually used in the aerospace field.However,impact may occur during manufacture,service and maintance in the whole lifetime of aerospace composite structures,which causes barely visible impact damages because of the the poor impact resistance of composites.These damages,such as matrix cracking,fiber breakage and inter-ply delamination,may cause serious threat to the service safety of aircraft structures.The piezoelectric sensor(referred as PZT)array based impact monitoring method is able to monitor impact events of composite structures in real time,ensure the structural safety and reduce the maintenance cost.This method has been proved to be one of the most promsing impact monitoring methods and has been widely stuided wordwide.But,impact is a kind of instant event and needs to be monitored on-line continuously.And aerospace engineering application has strict limitations on the weight and size of the monitoring system.Hence,it is urgent to conduct the lightweight research of impact monitoring of aerospace composite structures.Considering the lightweight impact monitoring requirements of aerospace composite structures,this thesis studies the key technical issues in the current research of PZT array based lightweight impact monitoring,by taking advantage of the lightweight PZT array and transmission method of monitoring signals.The main works and innovations are as follows.(1)The wireless sensor network(WSN)based lightweight impact monotirng method is studied.In order to realize the online impact networking monitoring of large size and multiple parts of aircraft composite structures,an energy weighted factor based impact sub-region localization method is proposed.This method is able to globally characterize the impact energy distribution on every sub-region within the whole monitoring scope,solve the localization confliction issue when adopting several digital impact monitoring nodes to perform networking monitoring and locate the mid-regions.Based on this method,a large scale wireless impact monitoring network is further built by adopting the digital wireless impact monitoring nodes and the multi-radio sink node,which is capable of achieving accurate and lightweight online impact networking monitoring of large size and multiple of composite structures.(2)The dense PZT array based lightweight impact monitoring method is studied.Aiming at the issue that there may exist multiple impacts or impact induced damages on the structure at the same time,the linear PZT array based spatial sampling theory of multiple sources is researched.Then the design method of spatial wavenumber scanning-synthesis filter of multiple sources is proposed to conduct wavenumber filtering of multi-source spatial sampling signals without depending on the actual signal wavenumber.The multi-source wavenumber-time imaging is realized,which is able to represent the wavenumber projections and arrival times on the linear PZT array of different sources and is verified on a carbon fiber laminate plate.(3)Based on the study of the spatial wavenumber scanning-synthesis filter of multiple sources,the characteristic of wavenumber-time images of multi-source spatial sampling signals is studied,by combining with a PZT 2D cross-shaped array.The feature extraction method of multi-source is proposed.Then,a cross-shaped array based adaptive backtracking mapping mechanism from multi-source wavenumber-time image to angle-distane image is developed.The reliable imaging and localization of multiple impacts and impact induced damges of composite structures can be achieved and are verified on a carbon fiber laminate plate and an epoxy laminate plate,respectively.(4)Experiments are performed on real and complex aircraft composite structures to verify the research of lightweight impact monitoring of composite structures conducted in this thesis.A composite unmanned aerial vehicle(UAV)wing and an aircraft composite wing box are adopted to build a lightweight large-scale wireless impact monitoring network,by which the energy weighted factor based impact sub-region localization method and the online impact networking monitoring of large size and multiple parts of composite structures are successfully virified.Besides,a real aircraft fuel tank structure with variable thickness and stiffener is used to verify the multi-source signals spatial wavenumber scanning-synthesis imaging method.The validation results show the accurate imaging and localization of multiple impacts and damages.