Professor Mick Brown, University of Cambridge
Abstract: By modelling slip bands as ellipsoidal inclusions in which dislocations move collectively, one can understand how secondary slip blocks them and gives rise to a fixed average number of dislocations in each band. Like sand in a sand pile, the packing of ellipsoidal bands in a deforming crystal acts as an attractor in stage ii, and gives rise to an equation of state for logarithmic creep. At very high strain rates, the collective motion cannot occur, and work-hardening increases substantially. Finally, the question arises: can we now rationalise the design of alloys to improve ductility, ultimate tensile strength, and fatigue resistance?