Nano Piezo Sensors for Structural Health Monitoring, Damage Detection and Failure Prevention

Background: Structural health monitoring (SHM) addresses an urgent need of our aging infrastructure. The United States spends more than $200 billion each year on the maintenance of plant equipment and facilities. Maintenance and repairs represent about a quarter of commercial aircraft operating costs. Out of approximately 576,600 bridges in our national inventory, 32% are either “structurally deficient” and in need of repairs, or “functionally obsolete” and in need of replacement. Much of the civilian and military aircraft fleets have exceeded their design life. Some of NASA’s space shuttles are more than 20 years old. The mounting costs of maintaining our aging infrastructure can be addressed through SHM systems that will reduce unscheduled repairs while increasing safety and reliability. The Aloha Airlines Boeing 737 experienced catastrophic “un-zipping” of large portions of the fuselage in 1988 due to multi-site cracks in the skin joints (Figure 1). More recently, Flight 587 accident in Queens, NY on Nov. 12, 2001, experienced the loss of its entire tail resulting in the second deadliest aviation accident in US history (Figure 2). It is conceivable that, if SHM systems were installed in these aircraft, then such accidents could have been prevented or at least alleviated. Boeing’s new 7E7 aircraft will have a full-time built-in SHM system comprising sensors embedded in the structure to assess the state of structural health. SHM systems consist of networks of embedded sensors that are permanently inserted into the structure and monitored over time. Piezoelectric wafer active sensors (PWAS) are used in SHM applications are able to detect structural damage using Lamb waves. PWAS are small, lightweight, unobtrusive, and low cost (Figure 3a). PWAS achieve direct transduction between electric and elastic wave energies. PWAS are essential elements in the Lamb-wave SHM