| Due to its unique properties,fine-grained piezoelectric materials have been widely used in many high-tech intelligent composite structures in recent years,and achieved significant social value and economic benefits.In order to protect or monitor devices,a layer of coating is often applied on the surface of devices to meet the needs of practical engineering.However,due to the level of manufacturing technology and other uncertain factors,there are often dislocations,cracks and other defects in the coating or interface joint.If the defects expand or lose stability,they will cause device failure and produce a series of losses.Therefore,it is very important to study the mechanical behavior of interface defects.Based on this situation,this paper systematically studies the mechanical behavior of the interface between piezoelectric coating and substrate with defects under the multi field coupling effect.The main work of this paper is as follows:Firstly,the mechanical problems of fine-grained piezoelectric coating/substrate with multiple Griffith type interface cracks under the coupling action of anti-plane mechanical load and in-plane electric field are analyzed by using Fourier integral transform and continuous dislocation density function method.By transforming the problem into the first kind of double singular integral equations with Cauchy kernel,the semi analytical expressions of the intensity factor and energy release rate of the problem are obtained,and the numerical solution is carried out with the help of Chebyshev point method and MATLAB software.Finally,numerical examples are given to discuss the variation of energy release rate with elastic modulus,potential shift,stress,crack size,coating thickness,and other factors in three cases of single interface crack,double interface crack and three interface crack,and the conditions under which stress and potential can inhibit crack propagation.Secondly,the interaction between the edge crack and screw dislocation of the fine-grained piezoelectric coating/substrate interface under the force and electric multi field load is studied.By using the method of complex variable function and two mapping functions constructed,the problem is simplified to a right half infinite plane piezoelectric bimaterial structure with screw dislocation.The expressions of electric field,displacement field,image force and intensity factor of the problem are obtained.At the same time,the special case when the fine-grained piezoelectric coating/substrate structure degenerates into the same piezoelectric material is discussed,and the same conclusion as the previous research is obtained,which verifies the correctness of the theoretical derivation in this paper.With the help of numerical examples,the influence of material parameters,crack size and coating thickness on the interface crack and the structure of fine-grained piezoelectric coating/substrate with screw dislocation is discussed.The results show that the dislocation can inhibit and promote the growth of interface crack according to the different position,and the coating material with higher elastic modulus or smaller coating thickness can better resist the structure fracture under appropriate conditions.Thirdly,The interaction between the fine-grained piezoelectric coating/substrate structure with screw dislocation and the interface edge crack under the coupled thermal,mechanical and electrical fields is analyzed.By constructing two mapping functions,the problem is transformed into a piezoelectric bi-material structure problem with screw dislocation in the right half infinite plane.With the help of complex variable function,Riemann Schwarz analytic continuation theorem and the theory of linear equations,the expression of temperature field under steady thermal load and the general solution of control equations containing temperature function are constructed The image force,the heat flux intensity factor and the theoretical expression of the intensity factor are given.Finally,the effects of material parameters,temperature gradient,coating thickness and crack size on the image force are discussed by numerical examples.The results show that the temperature factor can promote the fracture of material structure.Fourthly,the interface fracture of isotropic fine grained piezoelectric coating/ substrate with interface crack is studied theoretically under the coupling effect of thermal,mechanical and electrical fields.Under steady thermal load,the expression of temperature field is constructed by Fourier integral transform,and the expression of thermal intensity factor is given.With the help of the theory of linear equations,the general solution of the governing equation with temperature function is constructed,and the expressions of temperature field,thermal intensity factor,thermal stress intensity factor and electric displacement intensity factor are derived.Numerical examples show the relationship among temperature,coating/substrate thickness,material parameters and thermal intensity factor,stress intensity factor,and electric displacement intensity factor. |
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