Three-dimensional discrete dislocation dynamics simulations were used to calculate the effects of an anisotropy of the dislocation line tension (increasing Poisson’s ratio, υ) upon the strength of single-ended dislocation sources in micron-sized volumes with free surfaces, and to compare them with the strength of double-ended sources of equal length. The plastic responses were directly modelled within a 1µm3 volume of monocrystalline face-centred cubic metal. In general, double-ended sources were stronger than single-ended sources of equal length, and exhibited no significant effects due to truncating the long-range elastic fields at this scale. The double-ended source-strength increased with υ; exhibiting an increase of about 50% at υ = 0.38 (value for Ni) as compared to the value at υ = 0. Regardless of the dislocation-line direction, for υ greater than 0.20 the strengths of single-ended sources depended upon the sense of the applied stress. The value for α in the expression for strength, τ = α(L)µb/L was shown to vary from 0.4 to 0.84; depending upon the character of the dislocation and the direction of operation of the source at υ = 0.38 and L = 933b. By varying the lengths of the sources, from 933 to 233b, it was shown that the scaling of the strength of single-ended and double-ended sources with length both obeyed a ln(L/b)/(L/b) dependence. Surface image stresses were shown to have little effect upon the critical stress of single-ended sources at a length of about 250b or above. This suggested that, for 3-dimensional discrete dislocation dynamics simulations of the plastic deformation of micron-sized crystals (0.5 to 20µm), image stresses which made the surface traction-free could be neglected. There was a relationship between these results and those of a statistical model for the hardening of small volumes.

Estimating the Strength of Single-Ended Dislocation Sources in Micron-Sized Single Crystals. S.I.Rao, D.M.Dimiduk, M.Tang, T.A.Parthasarathy, M.D.Uchic, C.Woodward: Philosophical Magazine, 2007, 87[30], 4777-94