An Investigation of Strain Concentration in High-Strength Al-Zn-Mg-Cu Alloy 7085 Subjected to Tensile Deformation

The strain concentration factors were determined for aluminum alloy 7085 in the T7651 temper using multi-hole structural coupon specimens. Samples of the alloy were evaluated for both the 6.25 mm (0.25 in.) thick and 10 mm (0.4 in.) thick specimens having widths of 50 mm (2 in.) and 100 mm (4 in.), respectively. For the case of the specimens that were 50 mm in width, the mechanical tests were conducted for both the open-hole and filled-hole conditions and the corresponding strain concentration value was determined. For the filled-hole test specimens, threaded fasteners having collars were used. In order to provide for some interference, the fasteners had a shank diameter that was slightly larger than the nominal hole size. The strain concentration values were evaluated at both the failure strain (ε f ) and the strain at maximum load (ε max ). The average strain concentration value was then used to predict the results for the stack-up tests.