Experimental determination of material's constitutive laws and of design criteria of reactor structures in extreme dynamic loading conditions

FBR structures which work at temperatures ranging from 4000C to 5500C, may be subjected to explosive accidents and impact of missiles giving rise to stress waves which deform the structures at high strain rate in the plastic domain. Due to the fact that inelastic structural analysis and life predictions are not completely developed, the plant safety protection against catastrophic failure must be achieved by applying conservative stress and/or strain criteria on the mechanical design of structures which must be able to bear extreme dynamic loading conditions. The sound foundation of these stress and/or strain limiting design criteria passes through the experimental determination of dynamic mechanical properties of materials in end-of-life conditions with respect to the damaging processes to which the structures are submitted, under loading conditions representative for the accidental one. The results of a screening programme of dynamic tensile tests performed on some austenitic stainless steels using small specimens (7 mm2 cross section), are reported here. From the discussion of these results it will appear which elements must be checked using 'real size' specimens and which must be considered in developing constitutive equations, stress and/or strain limiting design criteria. (orig./HP)