Yield points during cyclic strain of a Cu–7.5% al alloy

Abstract

Constant strain amplitude cycling (Δϵp = 0.00275) of Cu–7.5% Al specimens causes development of a yield plateau after five cycles and an increasing yield drop thereafter. Several features are consistent with the known re‐loading yield point behavior of f.c.c. metals, such as a linear relation between yield drop and flow stress. The magnitude of the drop is time‐independent for times below 1000 s. It is suggested that the dislocation rearrangements responsible for the yield point might include dipole formation during unloading, a behavior consistent with the fatigue literature and other considerations.

Investigation of the Unloading Yield Effect in Aluminum and Magnesium Sheet Metal Alloys at Room Temperature

“…The definition of unloading yield includes tests with fully unloading and reloading (FUR) and repeated stress relaxation tests (RSR), which means no limitation regarding the magnitude of unloading. In addition, different synonyms are used for the unloading yield effect like "strain aging" [2], "yield effect" [3] and "yield point effect" [4]. Besides of magnesium alloys, the effect was observed for titanium alloys [5] and copper [3].…”

“…Supplementary, Birnbaum [6] observed an additional dependency of the yield drop on the crystal orientation for copper single crystals. Thompson [2] investigated a time and strain-rate dependency of the subsequent yield drop for Cu-7.5%Al alloy, which increases for aging times higher than 1000s with ongoing load cycles. Haasenet al [4] tested pure aluminum and nickel and found out that the yield drop depends on the aging time, while no significant dependency of yield drop was observed for times higher than one minute.…”