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Nonlinear effects are reported of hydrostatic pressure on dislocations in the framework of the square‐law approximation in the derivatives of dislocation displacement. The pressure effect on the interaction of two dislocations, the interaction of a dislocation with a low‐angle boundary, and the crystal boundary is considered. The magnitude of the effect allows to find it for some materials at pressures up to 10 kbar.

The quantitative theory of a double cross‐slip mechanism is proposed, the main equations of which are expressed in terms of the activation parameters of dislocation mobility. This allows to take into account the effect of the thermodynamic conditions (temperature and hydrostatic pressure) on the dislocation multiplication. It is noted that when initiating new dislocation loops by a double cross slip mechanism the motion of a screw dislocation component in the slip plane is not obligatory.

Theoretical and experimental investigations are made of the effect of the initial structure and deformation conditions on the dislocation multiplication in b.c.c. metals. The dependence of the dislocation density on the deformation value is obtained. In this case the dislocation multiplication rate is expressed in terms of the velocities of the motion of different dislocation components and the initial density of dislocation loops. The theoretical conclusions agree well with the experimental results obtained in Mo single crystals.

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