Dynamic Mechanical Behavior of 7075Al Laminated Bolted Joints under Cold Expansion-Interference Driven by Electromagnetic Impact Loading

Damage frequently occurs in aircraft interference-fit bolted joints under long-term fatigue and impact loading, directly impacting structural integrity and service life. To address critical repair requirements for fuselage and wing joints, a hybrid strengthening repair method for damaged bolted joints based on electromagnetic-driven mandrel cold expansion and interference installation is proposed for the first time. Localized mechanical behaviors and synergistic strengthening mechanisms were investigated through integrated experimental and numerical approaches. First, a finite element model encompassing the entire repair process was developed and validated for accuracy and reliability. Furthermore, based on the analysis of residual stress distribution, plastic strain evolution, and springback characteristics under varying expansion levels, a quantitative characterization method for the springback effect induced by mandrel cold expansion was proposed and verified. Utilizing the principles of stress superposition and deformation compatibility, the synergistic strengthening mechanism between cold expansion and interference-fit installation was elucidated. Finite element results at the continuum mechanics level indicate that a "secondary yielding" phenomenon occurs during the composite reinforcement process. The axial residual stress field around the hole exhibits significant non-uniformity, with the strengthening effectiveness being highly sensitive to process parameter matching. Specifically, the design parameter combination of "low expansion + high interference" ( E 2 + I 1 ) configuration demonstrated optimal performance, achieving a 22.6% reduction in peak residual stress while improving stress uniformity by 2.2%. Additionally, it was identified that interference-fit installation exerts a dual regulatory effect—expansion and relaxation—on the pre-existing stress field; the balance of this relationship governs the final quality of strengthening. This research provides a theoretical foundation and technical guidance for the life extension and restorative reinforcement of critical aircraft bolted structures. • Quantitative characterization of springback in cold expansion, validated by finite element analysis and experiments. • Optimal residual stress with improved thickness uniformity at the designed 4.3% expansion prevents premature local failure. • Synergistic and competitive interactions revealed: modest expansion with large interference maximizes strengthening. • Dual-index criterion distinguishes strengthening and degradation regimes, enabling optimized repair and joint design.