Determination of Cyclic Nonlinear Energy Toughness for 7075-T6 Aluminum Sheets.

In this report, the nonlinear energy method for fracture toughness determination has been applied to cyclic loading conditions. The nonlinear energy toughness for cyclic loading, G(fc), was obtained from an envelope of the cyclic load-displacement record for thin center-cracked sheet specimens of 7075-T6 aluminum alloy. A cyclic loading program, in which each succeeding load peak approached the static load in an exponential manner, was applied to these specimens. With constant specimen dimensions, different load increments were used for different specimens, which resulted in varying cyclic lives. The specimens used in these tests exhibited a significant reduction in G(fc) with increasing cyclic life in a manner analogous to the classical S-N diagram. This reduction in life for 7075-T6 was significantly less than for 2024-T3, which had been evaluated previously although 2024-T3 has considerably higher toughness. (Author)