Applications of the SMART project to structural monitoring in military aeronautics

1. STRUCTURAL HEALTH MONITORING PROCESS MONITORING CURE MONITORING, GLASS TRANSITION TEMPERATURE DETECTION, RELAXATION MONITORING. PHASE TRANSITION IDENTIFICATION FBG MULTIFUNCTION SENSING SYSTEM STATIC STRAIN MAPPING, TEMPERATURE DISTRIBUTION, DYNAMIC STRAIN MEASUREMENTS Piezoelectric Patch Crack detection Damage identification High quality Advanced materials Cost reduction Smart Processing Safety Improvement Maintenance costreduction FBG Accelerometer N°4 FBGs Embedded within Spar, Parallel to Wing’s Axis 29 Excitation Points for Experimental Measures N°4 Uni – Axial Accelerometers Bonded to Wing’s Surface FBG Output Accelerometer Simulation Applications of the SMART project to structural monitoring in military aeronautics SUMMARY • In the last years, Fiber Bragg grating (FBG) based devices have been widely exploited in applications ranging from sensing to telecommunications. Based on this technology, with unrivaled performances compared with other optoelectronic devices, a strong cooperation between different institutions has lead to a number of novel configurations which noticeably increased the performance and miniaturization of systems. This innovation has generated a number of applications in the following fields: structural health monitoring, aerospace, aeronautic, railway, electrical plants, ultrasonic diagnostics, high speed optical communications, GHz e.m. beam forming, microwave photonics. This is evident in light of several industrial research projects in cooperation with Italian Aerospace Research Center (CIRA), Alenia and Circumvesuviana and in the creation of a Spin Off company involved in smart applications. In particular, the SMART project, just arrived at the end of the second year, is finalized to integrate advanced materials, sensing and actuator systems in order to develop smart components able to: • perform auto diagnosis on the health state during the operative life • change their structural features such as stiffness, shape and so on. • The critical points in the development of a true structural health monitoring in practical applications are related to the development of resident sensing systems able to retrieve all the required information in order to recovery the health state of the structure and its dependence on the working conditions. • To this aim, a great effort has been spent to develop innovative interrogation techniques of fiber optic sensors based on grating technology, enabling a full integration of the entire measurement apparatus in such a way that the stuff mounted outside the fiber and capable to simultaneously interrogate many gratings on the same fiber can be made smaller than a few cubic inches. In addition, our system is able to fully exploit the dynamic response of the grating in such a way it is able to measure mechanical vibrations and acoustic fields with frequencies higher than 1 MHz. This capability is instrumental in acoustic emission detection and ultrasonic investigations aimed to localize and identify damages within the structure. This ability can be exploited in many fields especially in the case of military aircrafts where over limit performances pose severe problems in structural health monitoring. • Many prototypes have been exploited in industrial applications in industrial sectors such as civil, aeronautic and aerospace. The same technology will be implemented for in flight tests within the European Project Ahmos 2, with the objective to monitor the structural state of the aircraft. • In addition, the integration with actuating systems would enable the possibility to change the structural properties of the components through the modulation of the mechanical and the geometrical properties. • In passing we note that our sensors systems can be easily mounted on the same optical fiber normally used for data transmission. In aeronautic applications, this last property can results in the use of the same optical fiber circuits for structure monitoring and fly by light simultaneously. Modal Analysis Tests on a Composite Aircraft Model Wing Vibration Control for Aeronautic Structures Co-Collocated Sensor-Actuator Syatem • Vpp Optic Fiber 1 lB1 Coating PZT Sensor-Actuator System for Vibration Control PTZ • Coating Straingages lB2 SMART AND MULTIFUNCTION SENSORS Optic Fiber 2 Aluminium Cushion Adaptive close loop Control Approach Damage Detection Tests Fiber Bragg Gratings • One dimensional grating in a fiber • Reflect light in fiber • Change modes in fiber • n index variation in fiber core • Strength of grating is proportional to refractive index modulation depth Different fields of Application Railway track monitoring Ultrasound Wave Detection in Fluids Bragg = 2n  Packaged FBG for Enhanced Performances patent filed with Alenia WASS Optical Fiber with FBG along the railway Embedded Sensors in Composite Materials Experimental Results Time Excitation Signal (Piezoelectric Element) FBG response Multipoint Monitoring system into the Railway Control Cabin