Abstract: The variation of fatigue dislocation structure of annealed 40Mn steel with loading cycles was investigated by sinusoidal cyclic tensile testing of sheet specimen, at a frequency of 120 Hz.The transmission electron-microscopic observation was carried out on thin foils prepared by spark-cutting and subseqent electropolishing, Using H700 and 7EM 200CX T.E.M. In the free ferrite and the pearlitic ferrite, the feature of fatigue dislocation structure introduced by cyclic stresses somewhat below or above fatigue limit is dislocation dipole and dislocation loop. However, On the cyclic stresses above fatigue limit, the dislocation arrangement in the steel become nonuniform and dislocation tangles appeare. Dislocation substructure also appears in the cementite of pearlite after certain cycles of ftigue plastic deformation. The variation of feature of dislocation structures during cyclic plastic deformation of ferrite- pearlite steels with numberes of cycles of pulsating tensile stresses slightly above the endurance limit may be roughly divided into three stages. The first stage- inrregular dislocation neetwork, the second stage-dislocation dipole and dislocation loop, and the third stage Dislocation tangles and embryonic dislocation cell.

Key words: active reflector, adaptive connecting mechanism, cable-net structure, finite element, FAST