Ultrasonic inspection of thin composite laminates

Abstract

Non-destructive evaluation (NDE) methods, like ultrasonic inspection, face numerous challenges detecting defects within thin laminates. Short backwall distances paired with wave scattering and high attenuation caused by innate properties of stacked laminates result in difficulties with distinguishing sub-surface defects, such as delamination from geometric features. To improve the effectiveness of ultrasonic inspections for thin composite laminates the authors have implemented a multi-step approach to predict wave propagation behavior. This plan focuses on the use of finite element methods to simulate wave propagation behavior utilizing a single element transducer: (i) in water; (ii) in isotropic materials; (iii) in thin composite laminates. Analytical verification based on the Fresnel approximation was performed for ultrasonic wave propagation in water prior to modeling scenarios with isotropic materials and thin composites. In addition, experimental validation was performed in parallel to gauge the accuracy of all simulations. Initial computational results using a single element transducer for on-axis pressure measurements showed that acoustic elements were well suited for modelling water paths due to their computational efficiency and accuracy when paired with continuum stress elements. Preliminary experimental results showed it was possible to physically detect defects in both isotropic and composite material cases. The authors believe that computational models can be used for evaluating complex ultrasonic signals, aiding in the development of new ultrasonic inspection techniques for thin composite structures.