Study On Vibration And Sound Of Composite Laminated Plate With Delamination

In the 21st century the composite laminated structures, with their distinctive superiority, will find wide use in various fields of engineering. The advances in science and technology will require higher and higher standards for the design and assessment of engineering structures, and will naturally involve wide-ranging and indepth theoretical studies. The research on the performance of composite laminated structures has drawn much interest among researchers in the related domains.The composite laminated materials have the properties of high specific strength and specific stiffness, fatigue-resistance, vibration-resistance, etc. The composite structures may be designed to fulfil various functions. Owing to their structural characteristics, the laminated plates often suffer delamination damage during manufacturing and service. Delamination not only diminishes the strength and stiffness of laminated plate structures, but may also result in deterioration in mechanical properties or even overall failure of the whole structure when the delamination area propagates to a certain degree under external loading. In order to effectively guarantee the safety of load-carrying capacity of the laminated plate structures, it is of great value to investigate mechanical and acoustic characteristics of laminated structures considering the weakening of strength and the variation in acoustic spectrum of some special structures.Aiming at the sonar dome in submarines, this thesis mainly addresses the vibration and acoustic characteristics of intact and delamination-damaged structures of composite materials. This study deals with many branches of modem mechanics, such as structural dynamics, damage mechanics as well as coupling of multi-media and multi-fields. Therefore, the research on structural dynamic properties and underwater acoustic properties of intact and delaminated composite plate structures is not only of great theoretical importance but also of practical value.The delamination damage in fibre-reinforced composite plates may be investigated in three ways: microscopic damage mechanics, continuum damage mechanics and statistical mechanics. In this paper, the methodology for structural damage analysis was studied within the scope of continuum, and the coupling of structural finite elements and fluid boundary elements was employed in numerical analysis. To sum up the thesis work encompasses these aspects: in the model test on structural vibration and acoustics, the measurement of natural frequencies and modal damping was conducted for T300/QY8911 laminated plate beams with various sizes of delamination; in the analysis of delaminated structures, fictitious interface elements were utilised for modelling thedelaminated zones, and based on the material properties of lamina and the structural energy dissipation theory, the effects of delamination extent on such structural vibration parameters as natural frequencies, modal damping and transfer function were analysed and discussed; in order to examine the effects of delamination damage in structures on their acoustic characteristics, the eigenvalues of structures in contact with water were analysed, and the vibration responses of structures damaged by plane waves were examined by taking into account the extent and position in thickness direction of delamination and their effects on the variation of characteristics of vibration transfer function. A program system has been developed and utilised for the analyses of vibration and acoustics. This has laid the foundation for further studies on the behaviour and identification of damaged structures.Based on the study on vibration and acoustic characteristics of composite laminated structures with delamination damage, preliminary methods have been established. Some typical structures have been numerically analysed and the influence of structural damage on the vibration and acoustic characteristics has been conceptually described. Therefore, the work presented in this paper has both theoretical significance and prospective engineering...