Study On Interface Mechanics And Local Effects Of Multi-field Coupling Materials

Due to their coupling among various fields, multi-field materials such as piezoelectric materials, functionally graded piezoelectric materials (FGPM) and piezoelectric fibre composites have been widely used as sensors and actuator in applications such as sonar projectors, under-water use, medical ultrasonic imaging applications and health monitoring systems, etc. Thus, study on these materials be of great importance scientifically and potential in engineering applications.In this thesis, a comprehensive review on the research background and development of the multi-field materials is presented, and some problems related to interface mechanics and local effects of multi-filed coupled materils such as singularity and Sanit-Venant's decay effect are pointed out have been systematically studied. In the following, the thesis puts emphasis on the solution process of these problems.Based on some assumptions, a modified shear-lag model for piezoelectric fibre composites has been developed. Using the model, stress transfer and electric fields for a piezoelectric fibre composite with a fully bonded interface or frictional interface has been investigated. For a composite with partially debonded interface, a debonding criterion for the piezoelectric effect is presented utilizing a fracture mechanics approach to investigate the debonding process of piezoelectric fibre in the push-out test under combined electrical and mechanical loading within the framework of shear-lag theory. In addition, the problem of a penny-shaped crack in a piezoelectric fibre with an elastic coating embedded is investigated. By using the potential theory and Hankel transform, this problem is formulated as the solution of a system of dual integral equations which are reduced to a Fredholm integral equation of the second kind. Numerical studies are conducted to show the effect of the thickness and the elastic material properties of the coating on the fracture of piezoelectric fibre.Finally, the singularity behaviour of electroelastic fields in a wedge with homogeneous piezoelectric materials (PM) and/or angularly graded piezoelectric material (AGPM) under anti-plane deformation is investigated based on the Hamiltonian system and/or the mixed–variable state space formulation developed in this thesis. Numerical examples demonstrate that the materials properties, wedge angle and the angular variation of the materials properties have an important influence on the singularities of the PM wedge and AGPM wedge and the material inhomogeneity degreeηcan be used to control the singularities of AGPM wedge systems. Using a similar procedure to the singularity analysis, the Saint-Venant decay effects for the PM and FGPM strip and laminate under plane deformation and anti-plane deformation have been investigate. These studies indicate that the decay rate of stress and electric fields can be determined by way of the real part of the eigenvalue with the smallest positive real part of the matrix operator. There exist two type of decay mode depended on the materials properties and the characteristic decay lengths for the piezoelectric materials under plane deformation are larger that that for elastic materials. In addition, the material inhomogeneity plays an important role in Saint-Venant end effects for FGPM laminates.