Nucleation and propagation of dislocations near a precipitate using 3D discrete dislocation dynamics simulations

A 3D dislocation dynamics code linked to the finite element procedures is u sed to simulate the case of a matrix containing a cubical precipitate. Sinc e the matrix and the precipitate do not have the same elastic moduli and th ermal expansion coefficients, a heterogeneous stress field is generated in the whole volume when the sample is submitted to a temperature change. In m any cases this may nucleate dislocations in the matrix as experimentally ob served. Here, the phenomenon of dislocations nucleation in the matrix is si mulated using dislocation dynamics and the first results are presented. In a first time, a glissile loop has been put surrounding a precipitate. The e quilibrium position of the glissile loop is investigated in terms of the im age stress field and the line tension of the loop. In a second time, the di slocations are introduced as a prismatic loop admitting a Burgers vector pe rpendicular to the plane containing the loop. The prismatic loops are movin g in the sample according to the heterogeneous stress field resulting from the summation of the internal stress field generated by the dislocations an d the stress field enforcing the boundary conditions, which is computed by the finite element method. The latter takes into account the presence of th e precipitate as well as the interactions between the precipitate and the d islocations. The equilibrium configuration of the rows of prismatic loops i s analysed and the spacing of loops is compared to the analytic solution.