Nonlinear ultrasonics has emerged as a sensitive tool for evaluating subtle material changes and detecting early-stage damages in engineered structures. Building on our earlier work, where the quality of thin adhesive bonds was assessed by correlating bond quality to the third harmonic generation of the fundamental shear horizontal (SH) mode—excited using a custom-designed magnetostrictive transducer—this study is planned to extend the methodology to thick adhesive bonds. A nonlinear, non-collinear wave mixing approach is developed to enable localized inspection of thick blocks. This study explores the sensitivity of nonlinear wave interactions to detect localized defects and assess bond integrity. The research involves the design and fabrication of a specialized experimental rig capable of generating and detecting interacting wave modes in bonded structures. A complementary numerical model is also under development to simulate nonlinear wave interactions. The numerical modelling results of wave mixing on aluminium and mild steel samples for various mix frequencies align well with the experimental observations. The findings from the validated numerical model highlight the potential of wave mixing as an effective and localized method for assessing material nonlinearity.