Theoretical And Experimental Research Ondynamic Mechanics Of Laminated Composite Beam With Delamination

With the development of modern material manufacturing technology, new composite materials have been presented and applied widely in engineering fields such as aerospace, ocean engineering , energy transportation and sports equipments. Resin-based fiber-reinforced composite laminates have been used in many important structures due to their excellent properties such as high ratio strength and stiffness to weight, against corrosion and property designable. On the other hand, scholars have been focusing on problems like anisotropic material mechanics, discontinuity between fiber and matrix, lower properties between plies, lager deformation and physical nonlinear, so far-ranging investigations have been carried out on static strength, buckling, dynamic response and buckling, failure characteristic, etc.The beam which is the basic structure form in engineering applications is taken into account in this paper. Modern composite material mechanics and structure mechanics are employed to investigate the transverse vibration, dynamic buckling and failure under axial impulse based on theoretical discussion, experimental analysis and numerical simulation respectively. Based on Timoshenko beam theory, the energy finite element method (EFEM) is applied in beam vibration analysis. Considered transverse shear deformation and rotate inertia, an energy density equilibrium equation is deduced and solved by finite element method, in order to investigate the transmission and distribution of vibration energy. The interaction of interface in delamination is considered by contact pressure, and power flow transmission and the effect of delamination to energy distribution is discussed. Dynamic buckling of laminated beam subjected to axial impact is investigated experimentally. The effect of delamination, ply-up configuration and initial imperfections is considered. Finally, a numerical simulation model is applied to predict the initial and development of delamination in laminated beam under axial impact.Main research works which have been achieved in this paper are as follows:The status of investigation on vibration, dynamic buckling and failure under axial impulse of fiber-reinforced composite structures are reviewed comprehensively at first. The advantages of different theories, analysis methods are discussed. Therefore, the primary study objects based on previous works are determinedBased on Timoshenko's beam theory, equilibrium equation of composite laminated beam under transverse excitation by a harmonic force at a specified point is established and rotation inertia, shear deformation is considered. According to power flow theory, the differential relationship among flexural, extensional energy density and power flow is deduced and a second differential equation which is similar to the Fourier thermal conduction equation is obtain due to a power balance at the steady state. The equation can be transformed to"weak"integral equation by Galerkin method, and be solved by normal finite element approach in element level. Numerical analysis is developed by a simple support span beam model and compare with results from the commercial finite element software ABAQUS, the results present that energy density average in space and time is agreed well with FEA average value in high frequency. The effect of different ply-up configuration to energy density distribution is discussed.Based on works of chapter 2, energy finite element method (EFEM) is employed to investigate energy distribution of a continual connected beams structure with arbitrary connection angles. The expression of transmission and reflection coefficient is deduced according to internal force equilibrium and continual displacement condition. And the nodal coupling matrix is obtained based on power flow's vector transmission and physical relation to energy density, then global matrix equations can be assembled and solved. A transmission loss coefficient is introduced to consider the energy loss at connection node, the effect of ply-up configuration and connection angle is discussed, and the results show that energy transmission loss is lower in beams with same ply-up configuration and increases with connection angle. Finally, a beam frame model under transverse excitation is analyzed and the result is compared with FEA model.The vibration of composite laminated beam with delamination is investigated by a sub-division model. The equilibrium equation is deduced including transverse rotation inertia, shear deformation effect, and an interface pressure p ( x ,t ) is used to avoid penetration of sub-beam's surface in delamination zone. The expression of transmission and reflection coefficient of flexural waves and extensional wave is deduced in the end cross section of delamination due to internal force equilibrium and continual displacement condition. The relation curves of transmission, reflection coefficient and frequency show that the cut-off frequency is an important division point in transmitting of energy flow. The effect of delamination and its position along beam's thickness to energy flow is studied is this chapter.An experimental study on dynamic response and buckling of fiber reinforced composite laminated beam with delamination subjected to axial impact by moving mass is presented. The specimens are manufactured by unidirectional E-glass fiber fabric and epoxy resin with [0°],[45°],[90°] ply-up configuration and different initial imperfections. The delamination is simulated by copper foils between designed plies. Data of bullet velocities and time history curves of strain is recorded respectively by laser setup, high dynamic strain indicator and oscilloscope. Based on B-R buckling criterion, the critical impact velocity of bullet is determined by relation curves of impact velocity and maximal strain in beam. Experimental results show that ply-up sequences play a significant role in laminated composite material properties and delamination has a significant effect on dynamic response and buckling of laminated beams.The initiation and growth of delamination in E-glass/epoxy reinforced laminated beam subjected to axial impact has been investigated numerically and experimentally. Introducing a mixed failure mode which was made up of quadratic nominal stress criterion and B-K (Benzeggagt-Kenane) fracture criterion, a finite element model with cohesive element which is employed to simulate the intra-laminar failure area is established by the commercial software ABAQUS/Explicit. The results show that the initiation and growth of delamination depended beam's ply-up configuration and impact velocity. A good agreement is obtained between numerical simulation and experimental results.