LOCAL VARIATIONS OF LATTICE-PARAMETER AND LONG-RANGE INTERNAL-STRESSES DURING CYCLIC DEFORMATION OF POLYCRYSTALLINE COPPER

X-ray line profiles and line positions were measured on single grains of cyclically deformed polycrystalline copper specimens unloaded from characteristic points of the stress-strain hysteresis loop. A high-res olution double crystal diffractometer was used to obtain local lattice parameter changes, from which long-range internal stresses and mean s tresses were evaluated. In the case of samples unloaded from the load- reversal points the asymmetry of the characteristically broadened X-ra y line profiles indicated forward and backward internal stresses preva iling in the dislocation cell walls and cell interiors of the dislocat ion cell structure, respectively. The changes of the long-range intern al stresses after unloading from different points of the stress-strain hysteresis loop can be explained in terms of the composite model. In addition, mean strains and stresses, varying from grain to grain, coul d be determined from the shifts of the Bragg reflections. A detailed m icrostructure-based discussion of the elastic stored energy, evaluated from the analysis of the stress-strain hysteresis loop, is given.