On the representative strain in Vickers hardness testing of 7010 aluminum alloy

A review of the concept of representative strain in Vickers hardness testing is provided and different values reported in the literature are summarized. A new criterion for the proper selection of the representative strain is introduced. By using this criterion, the stress-strain curves of 63 specimens excised from a 7010 aluminum alloy rectilinear forging, cooled differently from the solution treatment temperature have been analyzed. Regression analyses have been conducted between the Vickers hardness numbers and the true stress values corresponding to twenty eight true plastic strain levels. These results indicate that the representative strain associated with diamond indentation is between 0.0185 and 0.0301 with the most likely number of 0.0240. The value of the constraint factor changes with the assumed representative strain and is essentially equal to 3.00 when 0.0240 is chosen as the representative strain.