Cyclic stress-strain responses and dislocation structure of copper single crystals with varioustensile axes were systematically studied and compared with each other.Experimental resultsreveal that the evolution of microscopic dislocation configurations in a crystal and,accordingly,its macroscopic cyclic behaviours are closely related with its orientation.Re-markable secondary slip has been observed in some crystals with orientations well inside thecrystallographic triangle, which are usually considered as single-slip ones.Their cycliobehaviours and dislocation structures at saturation are similar to those of their neighbouringmulti-slip crystals.These results have constructed the experimental basis for the newly pro-posed dislocation interaction model Jor cyclic deformation of fee crystals,which will be des-cribed in the second part of this article.
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