Mechanical Investigations of Reactor Graphite AS-II-500 (Order No. 191/220158)

Automatic translation: Graphite is brittle at temperatures below 0.5 T_m, i.e. around 1900°C brittle. Due to the anisotropy of the thermal expansion and elasticity coefficients coefficients of elasticity, residual stresses arise during the cooling process and due to external stresses, which, unlike with metals, cannot be reduced by homogeneous plastic deformation as is the case with metals. Residual stresses can also be be generated by dislocation mechanisms. The large number of possible residual stresses result in a wide range of values, which is essentially determined by the crystallite, grain and pore size distribution, i.e. also by the anisotropy factor. is also influenced by the anisotropy factor. The degree of purity and the corrosion and oxidation mechanisms oxidation mechanisms determine the intergranular fracture energies or those in the area of the grains and binder phase. bonding phase. In contrast to many other technical materials, these cracking fracture energies are extremely low compared to many other technical materials. Internal or external stress therefore results in during the pre-critical crack widening and lengthening due to the dissipative processes caused by residual stresses at critical K_Ii < K_Ic values predominantly in the area of a stress concentration Microcracks (secondary cracks), which can be detected both optically and both optically and by bottom emission analysis in numerous graphite qualities are observed (1 -3).