| Piezoelectric smart materials are widely used in aerospace, civil engineering, ship, vehicle engineering, etc. With the developing in composite technology, piezoelectric sensors or actuators can be embedded or bonded into the composite structures, making integration of the piezoelectric materials and composites as possible, for the composite structure health monitoring and active control technology to provide a broad development prospects. However, in practice, when the piezoelectric materials combined with composite materials, due to the dismatch of material properties between the piezoelectric material and composite, such as Young’s modulus, tensile strength, ductility and toughness, for the difference or discontinuity, the adhesive interface may be weaken either in the process of manufacture because of the introduction of small flaws or during the service time, this may be in the subsequent service process to generate a macro-cracks, eventually leading to failure of the entire smart structure.This dissertation, based on theoretical, numerical and experimental methods, investigates the interfacial fracture behavior of piezoelectric smart composites/structures, in which, the controlled composites are fiber reinforced resin-based composites, and develops an interface mechanics analysis model and interface toughness fracture experiment, then the finite element method for interface crack onset and debonding growth is developed. According to the analysis of typical piezoelectric composite structures, investigates the effects of physics, geometry and mechanical-electrical coupling on interfacial crack onset and debonding growth from the static views, the viscoelastic interface and impact loading on interfacial dynamic fracture behavior. In addition, the buckling and delamination growth control of stiffened laminated plates by distributed PZT actuators are investigated by numerical method. The research done in this dissertation as follows:1. Based on Timoshenko beam theory, a simple, closed-form and novel interface fracture analysis model is developed for calculating interface peel and shear stresses and mode I and II energy release rates for an interfacial crack in a piezoelectric composite beam. The present novel analytical solutions include the effects of transverse shear forces and adhesive interface layer. The interface stresses and energy release rates are expressed in terms of a generic material and geometry combination as well as an arbitrary combination of axial loads, bending moments and transverse shear forces acting on the two cracked substrates at the cross section of the interface crack tip. Then the effects of the geometry and adhesive on the fracture behavior for piezoelectric composite beam are discussed.2. A digital FRMM fracture experiment system has been set up.High-speed photography have been combined to study the crack onset and growth of piezoelectric composite adhesive interface, and the influence of different adhesive on the interface fracture characteristics is discussed, and the deformation and strain fields are obtained by using digital image correlation technologies. The data reduction schemes based on beam theory is used to calculate interface fracture toughness. Then a piezoelectric composite beam fracture experiment under electro-mechanical coupled loading is set up to verify the fracture toughness obtained by FRMM experiment, furtherly. Based on the fracture toughness of FRMM experiment, according to3D finite element model and VCCT, the effects of different ply angles and different thickness ratios on the delamination growth behavior for piezoelectric composite beam are investigated.3. The dynamic fracture behaviors of piezoelectric composites are studied. Based on interlayer-based interface fracture mechanics method, a three-phase medium model is established for the piezoelectric composite structures with viscoelastic adhesive interface crack. The effects of the viscoelastic on the fracture behavior of the piezoelectric composites have been discussed. Then a nonlinear finite element analysis of impact interfacial fracture for piezoelectric composite is provided. Numerical results are provided to show the effects of the piezoelectricity, the applied voltage, the stack sequence of composite and crack contact on the resulting dynamic energy release rate of piezoelectric composites. In addition, the influence of damping for interfacial crack of piezoelectric composites under the impact loading is also discussed.4. The buckling and delamination growth control of stiffened laminated plates by distributed PZT actuators are investigated by numerical method. The stiffened laminated plates are based on the first order shear deformation theory, and the cohesive elements are used to simulate the interface of the delamination region in the composite skin. According to mechanical-electrical coupling nonlinear finite element method, the buckling and delamination growth control of stiffened laminated plates by distributed PZT actuators under compression loads are investigated By some typical numerical examples, the control effects of buckling and delamination of stiffened laminated plates are discussed.The analytical model, experiment, numerical method and conclusions provided in this dissertation would contribute to better understanding interface failure of piezoelectric composites, and benefit the interface design and interface safety assessment of piezoelectric composite structures. The research is supported by National Natural Science Foundation of China "The mechanism of piezoelectric smart composite structures with interface damage "(10872038), Science Foundation of Dalian University of Technology "The mechanism of piezoelectric smart composite laminated plates and shells with damage"(SFDUT07011) and Fundamental Research Funds for the Central Universities (DUT11ZD(G)O1), in addition, the financial support of National Natural Science Foundation of China " Design optimization theory of mult-functional extra-weighted structures for the near space vehicle"(90816025) is also appreciated. |
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