Research Of Influence On Damping Of Homogeneous Materials And Composites With Damages

Damping is focused in a mass of engineering applications at present. The study of influence on damping caused by damages in engineering materials, has an important sense for prediction of damping change of engineering materials during service. The main contents in this master thesis are summarized as follows:Firstly, frictional energy dissipation and frictional damping caused by micro crack(FSDC) in homogeneous material was investigated in this thesis. Unit cell with individual micro crack was modeled and it was further employed in macro-scale cantilever beams. Frictional damping of the beams with different micro crack angles and densities are predicted. The accuracy of the models was proven by comparing with FE numerical simulation for both regular and random micro cracks.Based on the higher-order zig-zag theory for laminated composites, the laminate elements were presented. The differences of stress and strain distribution in the laminated composites models established by the laminate elements and normal shell elements were analyzed. The results showed that the models established by laminate elements could simulate the stress state accurately, and the computing cost would not rise with the number of laminates increasing.Lastly, viscoelasticity damping and frictional damping models in delaminated composites were established. The damping changes between delaminated and un-delaminated laminated composites with different ply stacking sequences, boundary conditions and load conditions were investigated via the laminate elements. Then the effects of area, location and number of delamination on damping were also researched. The results revealed that viscoelasticity damping and frictional damping would rise as delamination area increase. In addition, the distance between delamination and constrained end of laminates become larger, a higher viscoelasticity damping and a lower frictional damping were observed. In addition, though delamination area is small, viscoelasticity damping and frictional damping are in the same order of magnitude. Frictional damping is needed to be considered in the research of damping of delaminated composites.Among all the numerical simulation, the part relates to the laminate elements was based on ABAQUS together with user defined element(UEL).