清华大学-材料科学基础21.pptVIP

材料科学基础Fundamental of Materials §5.10 Forces on dislocation Ⅰ.Introduction Definition: is a fictitious force which is supposed to be responsible for the motion of dislocation. ∥ Criterion: The work done on crystal by stress must be equal to that done on dislocation by force F. Principle of derivation of : Macroscopic work＝microscopic work (or deformation work) Ⅱ.Derivation: Example: §5.11 Interaction between dislocation $-$ Two parallel dislocation will attract each other if 0 Examples and Discussions Exercise * * Prof: Tian Min Bo Tel: E-mail: tmb@mail.tsinghua.edu.cn Department of Material Science and Engineering Tsinghua University. Beijing 100084 Lesson twenty-one Force on screw dislocation Criterion: The work done on crystal by stress must be equal to that done on dislocation by force . for screw dislocation microscopic work＝macroscopic work Force on edge dislocation ? Give: stress field caused by applies force or other dislocation determine: the slip force fs, climb force fc, and total force F on edge dislocation. microscopic work＝macroscopic wok ? if fs make the dislocation move along the contrary direction fs: let dislocation slip a distance dS fc: let dislocation climb a distance dS ftot ? Force on mixed dislocation given: D a mixed dislocation of unit length with determine: force on for slip and climb Solution： fs: directs to that part of crystal which contains extra-half plane. directs to that part of crystal which moves along . ; For : , For : , fc: x z y o ? to determine fc, is resolved into and General case － Peach-Kochler formula. given: an mixed dislocation with arbitrary shape determine: force on segment － total stress on plane element solut