It is shown that by using alternate layers of materials with high and low elastic constants resolved shearing stresses of the order of $\frac{{\mu }_{\mathrm{low}}}{100}$ will be required in order to drive dislocations through the combination. The layers should be so thin that a Frank Read source cannot operate inside one layer. The low-elastic-constant material should be such that perfect dislocations rather than partials occur in bulk specimens of the material. Several possible combinations are suggested.

• Received 16 February 1970

DOI:https://doi.org/10.1103/PhysRevB.2.547