THE BIAXIAL LOADING RESPONSE OF POWDER ALUMINUM AT ELEVATED-TEMPERATURE

Nuclear fuel can be fabricated using powder-metallurgy processes by co mpacting uranium-oxide powder with aluminum powder to form a cermet an d then extruding the cermet to form fuel tubes. This method of product ion, allows greater control of uranium-oxide particle size and distrib ution in the tube, making the production of fuel with greater concentr ations of uranium oxide possible, and thus decreasing the volume of ra dioactive waste remaining after the fuel is spent. As the concentratio n of uranium oxide increases, however, there is an increase in failure s during extrusion. To address this problem, an experimental procedure was developed to examine the response of powder aluminum, a material with a structure similar to that of the cermet fuel, to biaxial loadin gs such as those experienced during extrusion. Biaxial loadings can be varied from pure shear to simple tension or compression, or to combin ations of these loadings in a numerically controlled 'tension-torsion' testing machine. Data obtained using this system were used to develop a model for the post-yield behavior in extruded powder aluminum which includes information derived both from the macroscopic stress-strain behavior of 1100 aluminum and extruded powder aluminum and from the ob served microscopic structure of the extruded powder aluminum. This pap er describes the development of the experimental system and shows the different biaxial mechanical behavior of the two materials. Test fixtu res were developed and software was written to control constant strain -rate tension, compression, torsion, combined tension-torsion, and com bined compression-torsion tests performed using a computer-controlled MTS biaxial testing machine. Extruded powder aluminum and 1100 aluminu m specimens were tested at 427 degrees C, the powder-aluminum extrusio n temperature, under those loading conditions. Each specimen was subje cted to only one loading cycle. Data were recorded during loading only . Tested specimens were also sectioned and examined microscopically.