“Structural Damage Detection via Contact Acoustic Nonlinearity”
Dr. Fabio Semperlotti, University of Michigan
The development of structural health monitoring (SHM) techniques for active monitoring of structural systems has attracted considerable interest during the last decade from the scientific and engineering communities. Many aerospace, civil and mechanical structures operate in an extremely severe environment where the combination of multiple factors such as operating dynamic loads, environmental conditions and ballistic impacts can induce a wide variety of structural damage. This talk will provide an overview of two novel techniques for the detection of fatigue cracks and loose joints, which are relevant damage types encountered in many engineering applications. At a very early stage, these damage types exhibit a characteristic nonlinear response that can be successfully exploited to identify and localize the damage. The nonlinear signature is originated by a physical phenomenon known as contact acoustic nonlinearity (CAN). The nonlinear contact occurring at the damage interface when subjected to an incident periodic elastic wave induces a nonlinear scattering process that redistributes vibration energy over multiple nonlinear harmonics. The CAN phenomenon is combined with the wave propagation and mechanical power flow theory yielding two complementary approaches for structural damage detection. The theoretical foundation of these techniques is presented and their performances are investigated through numerical and experimental analyses. An application to a complex mechanical system represented by a helicopter transmission frame will also be discussed.
Fabio Semperlotti is a mechanical engineering research associate at the University of Michigan. He holds a PhD in aerospace engineering from Pennsylvania State University. He previously worked as a structural engineer for the French aerospace agency and other European space industries. His work was mainly related to the structural design of space propulsion systems. More recently his research has focused on theoretical and experimental techniques for the development of SHM systems with applications to rotorcraft structures. Current research activities include the development of SHM techniques for carbon-nanotube-based polymers as well as novel adaptive structures for extreme stiffness and damping performance.