DEFORMATION FROM TWIN-BOUNDARY STRESSES AND THE ROLE OF TEXTURE - APPLICATION TO FATIGUE

Calculations of the elastic stresses in the region adjacent to a twin boundary (TB) subjected to uniaxial tension are carried out for different orientations of the tensile axis. It is found that the principal stresses reach a maximum when the tensile axis is a [111] direction and that their value strongly depends on orientation. In general, the presence of the twin tends to favour the early development of secondary and multiple slip on at least one side of the TB. For cyclic deformation at intermediate amplitudes, this result is supported by experimental findings on the role of annealing TBs in favouring persistent slip band nucleation and promoting higher local hardening rates adjacent to them. The fact that the TB stress concentration' is found to vary significantly as a function of orientation suggests that, in twinned polycrystalline materials, texture is an important factor in determining the role of TBs under loading, and thus their consideration as actual grain boundaries.