Selection of Materials and Sensors for Health Monitoring of Composite Structures
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Selection of Materials and Sensors for Health Monitoring of Composite Structures Seth S. Kessler1,2 and S. Mark Spearing2 1
Metis Design Corporation, Cambridge, MA, 02141 Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, MA 02139 2
ABSTRACT Embedded structural health monitoring systems are envisioned to be an important component of future transportation systems. One of the key challenges in designing an SHM system is the choice of sensors, and a sensor layout, which can detect unambiguously relevant structural damage. This paper focuses on the relationship between sensors, the materials of which they are made, and their ability to detect structural damage. Sensor selection maps have been produced which plot the capabilities of the full range of available sensor types vs. the key performance metrics (power consumption, resolution, range, sensor size, coverage). This exercise resulted in the identification of piezoceramic Lamb wave transducers as the sensor of choice. Experimental results are presented for the detailed selection of piezoceramic materials to be used as Lamb wave transducers.
INTRODUCTION Structural health monitoring is the term used to encompass a variety of approaches utilizing permanently mounted sensors to monitor the integrity of structures. Health monitoring methodologies are envisioned as replacements or supplements to existing inspection and maintenance schedules. Amongst the attractions of in situ health monitoring are that it has the potential to be less intrusive than many visual inspections, which require disassembly of built up structure, and that it has the potential to only require disassembly of the structure when there is some indication that damage has occurred. These potential benefits are particularly pronounced for the case of structures made from fiber-reinforced composite materials. In these cases, damage can often not be detected by visual means, and also the fabrication processes for composites are most economic if they avoid use of mechanical fasteners, which limits the ability to disassemble the structure. There is thus considerable interest in developing structural health monitoring systems for composite structures [1,2]. However, as yet, despite considerable progress, no systems have been accepted into service. One of the key issues in defining a structural health monitoring system is to determine the first level system architecture, comprising the sensor type and sensor density (or sensor spacing). This decision must account for the nature of the damage that is expected, and the size of damage that must be detected for the system to fulfill its purpose. Decisions at this level will have a flow-down effect on the higher-level system decisions. This paper documents an effort to select the operating principles and materials for a structural health monitoring system, beginning with overall systems considerations and then focusing on the detailed selection transducer materials via experimentation.
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SELECTION OF OP
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