Fatigue failure behaviors of open hole structures enhanced by a single-sided surface ultrasonic impact method

7075 aluminum alloy is widely used in aircraft structures but suffers from fatigue failure due to stress concentration around connection holes. In this study, a single-sided ultrasonic impact treatment (UIT) was applied prior to drilling an open hole in 7075 Al alloy specimens. Surface metallography, hardness, tensile behavior and fatigue performance were systematically investigated. Through this study, we discovered that UIT induced surface plastic deformation and grain refinement, forming a hardened layer around 63 μm thick, and significantly increasing surface hardness by 63.9%. Static tensile behavior showed minimal change, while Digital Image Correlation (DIC) results indicated reduced tensile strain concentration in the loading direction. Fatigue life was improved by around 27% under low and medium load levels. However, the strengthening effect was not demonstrated under high load, possibly due to the localized and shallow residual compressive stress layer. The results demonstrate that single-sided UIT can effectively enhance fatigue resistance of open-hole structures under moderate or low loading.