Automated nondestructive testing of composites using air-coupled guided ultrasound

Abstract

In order to support the continued trend of increased use of composite materials in many industries, efficient testing systems need to be developed. That is, existing visual inspection techniques may be inadequate as they do not allow for the detection of internal flaws such as delaminations. The contributions of this paper to the nondestructive testing (NDT) community are threefold: it provides 1) an overview of an opportunity for undergraduate engineering education in form of a class project, 2) a description and demonstration of a newly developed multi-axis positioning system for air-coupled transducers and 3) the application to the characterization of composites. A competition-based course project was designed for an undergraduate machine design class. The objective of the project was to design a low-cost, multi-axis positioning system for NDT experiments. The winning design was built and features an innovative robotic arm with many custom-made components, including a 2-D goniometric stage for orienting air-coupled ultrasound transducers. The system allows for automated and accurate positioning to acquire detailed wave propagation and scattering data from NDT experiments on composite specimens. The NDT positioning system’s capabilities are demonstrated via dispersion characterization problems on metal and composite specimens. Specifically, a pitch-catch methodology is employed where one stationary transducer is complemented by a roving transducer positioned with the robotic arm. Several datasets are collected and different signal processing techniques are employed in an effort to characterize the studied specimens. The results are compared to the existing literature and simulation data, showing good agreement.