Investigation On The Interaction Mechanism Of Dislocations With Cracks Penetrating The Interface

In this dissertation, considering composite materials with various defects(dislocation, inhomogeneity and crack or rigid line partially penetrating the interfaceof inhomogeneity et al), the interaction among all these different kinds of defectswithin a unified framework has been studied. By use of the general complex variablemethod and some techniques (conformal mapping technique and image method), aseries of closed form solutions or series form solutions to the interaction amongdislocations, inhomogeneities (nanoscale inhomogeneity) and cracks (or rigid lines)in pure elastic materials, piezoelastic materials and magnetoelectroelastic materialsare obtained. The influence of the orientation of the dislocation, the morphology ofthe crack, the size of the inhomogeneity, the material elastic dissimilarity and theinterface effect on the stress fields, image force, shielding effect and the emissioncriterion are elucidated.Firstly, the interaction between a screw dislocation and a semi-infinite wedge crackpenetrating a circular inhomogeneity and a nanoscale circular inhomogeneity areinvestigated. The results show that the positive screw dislocation generates a negativeshear stress which partially offset the stress generated by the applied loads thatenhances the fracture toughness of the material and shields the growth of the crack.The most probable direction for dislocation emission is the front of the straight-linecrack and the negative interface stress decreases the shielding effect and makes thedislocation emission more difficult while the positive interface stress is quite thecontrary.Secondly, the electro-elastic interaction between a piezoelectric screw dislocationand a semi-infinite wedge crack partially penetrating a circular nanoscalepiezoelectric inhomogeneity is investigated. The results show that the shielding effectof the general screw dislocation inside piezoelectric material is stronger than thedislocation inside the corresponding elastic material. The negative interface stressdecreases the shielding effect while the coupling of electric displacement and positivestress at the interface and the increase of the elastic stiffness ratio of nano-fiber tomatrix and the piezoelectric constant ratio of nano-fiber to matrix enhance theshielding effect. The dislocation emission becomes difficult with the increase of theopen angle of the wedge crack and the elastic stiffness ratio and the piezoelectric constant ratio of nano-fiber to matrix. The existence of interface effect makesdislocation emission more difficult and the smaller of the radius of the inhomogeneity,the stronger of the interface effect and the more difficult for dislocation emission.Lastly, closed-form solutions to the mixed boundary value problem of a partiallydebonded rigid line penetrating a circular inhomogeneity in magnetoelectroelasticmaterial are derived. Under the function of the electromagnetic coupling effect, theinfluence of the longitudinal shear stress and the in-plane electric and magnetic loadson coupled fields and the material parameters on the general stress intensity factor ofthe rigid line tip and the general screw dislocation near the rigid line in detail. Theresults show that there exist singular points of stress, electric displacement andmagnetic induction intensity at the rigid line tip and dislocation point. The debondedrigid line and the piezoelectric inhomogeneity attract the screw dislocation and thepotential dislocation while repel the magnetic potential dislocation and the force ofattract to the potential dislocation is stronger. In addition, the effect of the rigid lineand the inhomogeneity in magnetoelectroelastic material is stronger than them in thecorresponding elastic material.