Numerical Simulation of Ultrasonic Nondestructive Testing for Adhesively Bonded Lap Joints
Nondestructive inspection (NDI) of damages (e.g., imperfect or degraded bonding lines) or the remaining strength of adhesively bonded lap joints is critical for the operational safety of aircrafts and vehicles. It remains a challenge to use the conventional NDI to quantitatively infer the poor adhesion between the adherend and the adhesive. Essentially, the direct NDI measurements were related to the latent parameters indicating bond integrity in many studies. Our work is to build a physics-based simulation model of NDI for adhesively bonded lap joints in COMSOL Multiphysics by incorporating latent spring interfaces between the adherend and the adhesive. The physics interfaces used in the NDI simulation include Solid Mechanics (Wave), Electrostatics (Piezoelectricity) and Electrical Circuit. The Multiphysics coupling enables modeling both single transducer probes and phased array probes. In this study, we are modeling transducers with wedges. An absorbing layer is defined on the top of the transducer. The NDI model can be either global (e.g., full-size) or local. For computational efficiency, we build a local NDI model assuming periodic boundaries to mimic the pulse-echo-like wave propagation across transducer, wedge, adherend and adhesive. The imperfect bonding interfaces between the adherend and adhesive are modeled as thin elastic layers that can be represented as spring material in COMSOL, i.e., spring interfaces. Then the interfacial stiffness matrix (or the damping constants) of the spring-like thin elastic layers is employed to characterize the bonding status, e.g., the infinite interfacial stiffness indicates a perfectly bonding. The simulation model allows investigation of the relationship between interfacial properties (e.g., the stiffness equals 0.5~5Mpa/nm) and NDI measurements, such as ultrasound reflection coefficients, enabling real-time evaluation of bond integrity. The ultimate goal of this research is to establish a comprehensive understanding of bond assessment through NDI, enhancing safety and reliability in aerospace and automotive applications.
