Some Dynamic Problems In Micro Air Vehicles

MAVs (Micro Air Vehicles) is one kind of integrated intelligent micro system involving MEMS (Micro-Electro-Mechanical Systems) and many other technologies. MAVs is not a simplified miniature of conventional air vehicle. It is necessary to develop a large number of new conceptions for the design of MAVs. Micro system mechanics is one of the basic scientific principles to develop the new generation of MAVs. Therefore, some dynamic problems in MAVs are studies in this dissertation.At first, the dissertation reviews the backgrounds, development and state-of-the-art of MAVs, and presents the basic characteristics, application prospects and key technologies of MAVs. At the same time, the dissertation summarizes the scientific principles involved in MAVs and elucidates the importance of micro system mechanics for the development of MAVs.Then, for the difficulties when flying under lower Reynolds number, the dissertation carries out some researches on the flight mechanism of animals and insects, and demonstrates that it is possible and necessary to adopt flapping wing configuration after the nature flying creatures. Also, the dissertation presents some valuable principles for the flapping wing configuration, and has induced the scaling laws for the MAVs with flapping wings.Usually, MAVs is working under dynamic environment. Considering the scale effects with the decrease of dimension in MAVs, the dissertation studies the scale effects of plastic strain rate in some mechanical problems and presents a detail discussion on two dynamic constitutive equations considering strain rate effects.There have been many theoretical and experimental studies on the dynamic plastic behavior of structures. For the first time, the author reformulates many results and physical parameters about the structure dynamic response into new dimensionless concise forms with response number, which could be used to study the corresponding structures in MAVs.As an important basic problem on the dynamic failures and reliabilities of micro systems under impact loadings, the propagation of stress wave in gradient elastic medium has been studied. The dissertation has derived the relationships between phase speed and wave length, which relate to the transverse waves and longitudinal waves in infinite medium, the longitudinal waves and torsional waves in a thin rod.At last, a kind of inertial MEMS devices for MAVs, micromachined accelerometer, has been studied experimentally and numerically and their dynamic reliability has beenalso investigated. In this dissertation, drop tests and some structural failure analyses have been implemented for two typical newly designed microaccelerometers fabricated by the standard bulk-machining process. Researches in this dissertation have presented the main characteristics and modes for the failures on the structures of micro accelerometer, and elucidated the application of stress waves in the failure analysis of micro structures. Also, the dissertation has demonstrated the problem on structural design, fabrication and tests of micro accelerometers. The most important is that some new kinds of failure modes on adhesion have been found in micromachined accelerometers under impact loadings, and it is valuable for the study on the adhesion failure of micro systems subjected to impact loadings.