Three-dimensional crystallizing pi-bondings and uniaxial tensile deformation in polycrystalline metals

It is visualized that dislocations move in a straight-line manner in polycrystalline structures and that trans-grain dislocation movement occurs from the yield point to the ultimate tensile stress. Some fracture modes in the uniaxial tensile test are illustrated in order to explain that after the ultimate point the grains deform by twins and the rotations of grains make cracks at the grain-boundaries due to incompatibility. Luders banks, which propagate along the axis of the specimen, are twin bands which are formed by rearrangement of the atoms within the structure of three-dimensional crystallizing pi-bondings. The fatigue limit can be found through the rolling-back motion of the atoms during elastic deformation in the uniaxial tensile test, brought about by the change of the gradient. (C) 1997 Elsevier Science S.A.