Measurement of the dynamics of residual stresses in copper during heating
- Mr. Ilya BALASH
- Mr. Ilya BALASH (Budker INP, NSU)
In a fusion reactor plasma impacts the divertor as periodic heat pulses. These heat pulses cause residual plastic deformations and mechanical stresses in the divertor which leads to the divertor’s material being destroyed. Residual deformations and stresses can be relieved due to high temperature of the divertor which is caused by the constant flow of plasma. The relaxation of deformations and stresses may bring the material back to its initial state during the time interval between two subsequent heat pulses, so that after the second plasma pulse stresses would not exceed ultimate tensile strength and the material would not be destroyed. The temporal dependence of residual stresses is needed to be examined in order to test the possibility. The relaxation of stresses in copper samples were measured using X-ray diffractometry in development of the technique. In order to create residual stresses one sample was irradiated by an electron beam on the BETA facility while another one was left in its initial state for the comparison. Experimental station "Anomalous scattering" on the beam line 2 of VEPP-3 was used to obtain diffractograms that were used to obtain scattering angle – tilt angle dependencies. By expressing the variation of crystal lattice interplanar distance and using it in Bragg’s law, a formula of scattering angle – tilt angle dependency was derived. The dependencies were substituted in the formula and used for calculation of deformation tensor components, which in their turn were used for calculation of stress tensor components. The difference between the diffraction maximum angles of the irradiated and the non-irradiated samples was a significant ~0.1°. For the dynamic measurement of the residual stresses samples were examined at constant tilt angle and changing temperature at scattering station “Diffraction movie”. The samples were heated for the relaxation of stresses. Time dependencies of temperature and diffraction maximums were measured. By combining those time dependencies the diffraction maximum angle – temperature dependencies were acquired. The relaxation of the samples in the condition of changing temperature was studied by comparing of the irradiated sample’s graph to the non-irradiated sample’s graph with the latter having no relaxation effect.