A three-dimensional dislocation dynamics study of the effects of grain size and shape on strengthening behavior of fcc Cu

•We study the effect of grain size and shape on yield strength in Cu using 3D-DD.•The grain boundary strengthening effect is greater in the columnar grains.•The yield strength increases with the increase in initial dislocation density.•Hall–Petch relationship holds well at small grain sizes (0.5–2μm).•The initial dislocation density significantly affects the Hall–Petch relationship.