Amirkabir University of Technology AUT Journal of Mechanical Engineering 2588-2937 10 4 2026 10 01 Experimental and Numerical Modal Analysis of Complete and Partial Bonding States of Single-Lap Adhesive Joints 6066 10.22060/ajme.2026.24561.6212 EN Setareh Garazhian Department of Mechanical Engineering, University of Tabriz, Tabriz, Iran Milad Shabani Yousefabad Department of Mechanical Engineering, University of Tabriz, Tabriz, Iran Morteza Homayoun Sadeghi Department of Mechanical Engineering, University of Tabriz, Tabriz, Iran Mir Mohammad Ettefagh Department of Mechanical Engineering, University of Tabriz, Tabriz, Iran Hasan Biglari Department of Mechanical Engineering, University of Tabriz, Tabriz, Iran Karim Shelesh-Nezhad Department of Mechanical Engineering, University of Tabriz, Tabriz, Iran Journal Article 2025 08 15 This study evaluates the sensitivity of modal parameters to incomplete adhesion in single-lap adhesive joints by comparing the vibrational behavior of fully bonded joints and joints with a macroscopic partial bond (≈50% loss of bonded area in the overlap). Beyond prior studies on crack-like or delamination-type defects, often using intrusive or destructive inspections, the present work targets a practically relevant macroscopic manufacturing flaw within a fully non-destructive modal testing framework. An integrated experimental–numerical approach is employed: aluminum 7075-T6 beams bonded with epoxy 828 are tested using impact-hammer excitation and laser Doppler vibrometer, and responses are processed in MATLAB and MEscope to extract natural frequencies and damping ratios. A three-dimensional finite element model in Abaqus/CAE is refined via limited experimental calibration. Results show 3–15% reductions in the first eight bending natural frequencies of defective joints relative to intact ones, with stronger effects in higher modes due to dominant stiffness loss over minor mass reduction. The damping ratio increases about sevenfold (0.0032 to 0.0236) in the defective specimen, attributed to frictional dissipation at the unbonded interface and contact nonlinearities supported by mode-shape analysis. These quantified shifts in frequency and damping establish modal parameters as reliable, non-destructive indicators of incomplete adhesion in single-lap joints and provide a basis for vibration-based structural health monitoring and defect detection in adhesively bonded components in aerospace, automotive, and multi-material structures. https://ajme.aut.ac.ir/article_6066_2be5f9c2e3620eb73c2972d7552b6cb5.pdf