Non-uniform multiple slip near a grain boundary plane in face centered cubic bicrystals was examined analytically. Mathematical models for movement and interaction of dislocations were introduced to have a quantitative constitutive relation describing plastic deformation of face centered cubic crystals. Then, a new computer code for finite element structure analyses based on the relation was developed. By applying the code to deformation analyses of isoaxial bicrystals of the nominal strain incompatible type, the formation process and the structure of shear strain in the multiple slip region were examined. Results are summarized as follows:
(1) Very early in the activation of secondary slip systems, shear strain on the systems is on the order of 10⁻⁷ and it is about 1/100 of that on the primary system.
(2) At the deformation stage when the nominal strain is about 12 times as large as that at the elastic limit, the multiple slip region consists of a rather uniform distribution of shear strain on the primary slip system and non-uniform shear strain on the secondary systems. The latter strain ranges from 10⁻⁷ to a value comparable to that on the primary system.
(3) When the interaction intensities between moving and forest dislocations are doubled, the propagation rate of the multiple slip region and shear strain on the secondary systems are reduced to about 1/1.6 and 1/2, respectively.
(4) The propagation rate of double slip is about 1/30 of the rate of single slip. This ratio does not depend significantly on the interaction intensity of dislocations.