ch2.1位错-位错理论的产生.ppt

Ch2 Dislocation 2.1 位错理论的产生 2.2 位错的几何性质 2.3 位错的弹性性质 2.4 位错与晶体缺陷的相互作用 2.5 位错的动力学性质 2.6 实际晶体中的位错 Dislocation A lattice imperfection in a crystal structure which exerts a profound effect on a structure sensitive properties such as strength, hardness, ductility and toughness. There are two types, edge and screw, both of which are characterized by a Burgers vector which represents the amount and direction of slip when the dislocation moves. 2.1 位错理论的产生 一、晶体的塑性变形方式 二、单晶体与多晶体的塑性变形 三、晶体的理论切变强度 四、位错理论的产生 五、位错的基本知识 Plastic Deformation Permanent change in the shape of a material as a result of the application of an applied stress. The work done in deforming the sample is not recoverable. When a material is stressed beyond its elastic limit, plastic or permanent deformation takes place, and it will not return to its original shape by the application of force alone. Elastic deformation Change in shape of a material subject to an applied stress in which the initial shape is completely recoverable with negligible time delay when the stress is removed. The work done in elastically deforming a material is completely recoverable. When a material is stressed below its elastic limit, the resulting deformation or strain is temporary. Removal of stress results in a gradual return of the object to its original dimensions.(i.e. The work done in elastically deforming a material is completely recoverable.) Plastic Deformation The ability of a metal to undergo plastic deformation is probably its most outstanding characteristic in comparison with other materials. All shaping operations such as stamping冲压, pressing挤压, spinning纺纱, rolling轧制, forging, drawing, and extruding involve plastic deformation of metals. Various machining operations such as milling碾磨, turning, sawing, and punching冲压 also involve plastic deformation. Plastic deformation may take place by : ?Slip ?Twinning ?Combination of slip and twinning 一、晶体的塑性变形方式 位错理论是在研究晶体的塑性和强度等理论中提出和发展起来的；位错的行为也始终与晶体的塑性变形方式联系在一起。 （一）