Investigation On The Interaction Mechanism Of Dislocations Nearby Surface

This thesis investigates the evolution of microscopic defects (dislocation, inhomogeneity and crack) near to the surface, and studies the interaction of different types of defects under different loads, has an important scientific value and practical significance. Using the general complex variable method and some techniques (conformal mapping technique and image method), a series of closed form solutions or series form solutions to the interaction among dislocations, nanoscale inhomogeneities and surface cracks in elastic half-plane materials are obtained. The influence of the orientation of the dislocation, the location and length of the crack, the location and size of the inhomogeneity, the material elastic dissimilarity and the interface effect on the stress fields, image force (slip force and climb force),and shielding effect are investigated.Firstly, the interaction between a screw dislocation and a nanoscale circular inhomogeneity nearby the surface is investigated, the effects of the size and location of inclusions and the surface/interface stresses on image force acting on the screw dislocation are discussed. The results show that more equilibrium positions of the dislocation may be available and only exist at the y-axis due to surface/interface stresses. The negative interface stresses attract the dislocation, and the positive interface stresses repel the dislocation. The interfacial effects have more significant on the dislocation motion as inclusion radius become smaller.Secondly, the interaction between an edge dislocation and the elastic thin layered semi-infinite matrix is investigated when an edge dislocation inside the elastic thin layered semi-infinite matrix, the effects of the material elastic dissimilarity, the thickness of thin layer and the position of the dislocation on image force (slip and climb forces) acting on the edge dislocation are discussed. The results show that The glide and climb force will increase with the decrease the thickness of thin layer when an edge dislocation is in the matrix or in the layer. In addition, they will increase with the decrease the shear modulus ratio of the layer to the matrix, when the matrix is softer than the layer and an edge dislocation is in the matrix or in the layer.Lastly, the interaction between edge crack and edge dislocation as well as concentrated force and point heat source is investigated, the influence of the concentrated force, point heat source and edge dislocation on the shielding and anti-shielding effects to edge crack as well as the glide and climb forces acting on the edge dislocation is examined. The results show that the shielding and anti-shielding effects increase acutely with the increment of concentrated force and point heat source. In addition, the glide and climb forces increase acutely with the decrement of the distance between the dislocation and the crack tip.