Steven E. Owens

Ultrasonic Lamb wave tomography in structural health monitoring

Variations of Lamb wave propagation reflect some changes in effective thickness and material properties caused by such structural flaws as corrosion, fatigue cracks, disbonds and voids that can then be mapped via a reconstructed tomographic image. Ultrasonic Lamb wave tomography can be used to evaluate structural integrity based on the variations in features extracted from measurements made by a transducer array from a reference point in time. In this paper, several tomographic imaging techniques, such as the filtered backprojection algorithm, the algebraic reconstruction technique and the reconstruction algorithm for probabilistic inspection of damage are compared, and the advantages and drawbacks of these methods, as well as practical considerations such as reconstruction fidelity, quality, efficiency and the minimum number of sensors required for each array geometry, are discussed, and some application examples are given.

A Novel Couplant Free Mediator Ultrasonic Rayleigh Wave Technique for Detecting Surface Cracks in Green Parts

Surface cracks initiated by handling and production issues in green parts affect the final integrity of a sintered part. The subject of crack detection in green parts has been of significant interest for decades with no real solution being available until recently. Despite the abundance of applicable techniques for inspecting sintered parts, green part inspection techniques are restricted. Some promise has been recently demonstrated with visual and resonance techniques; however the success of these methods is limited. Presented here is a novel surface wave approach based on the use of a couplant free mediator. Surface wave techniques are presented as an economical and reliable alternative to current nondestructive inspection methods. Design of a test setup for analyzing the applicability of surface wave techniques to detect cracks in specific orientations in green parts is provided. Surface wave generation techniques in conjunction with design considerations of such a system will be demonstrated. Surface wave response evaluation theories, such as amplitude and Fourier analysis methods for detecting and characterizing flaws are discussed and demonstrated through physical testing of samples. Specific applications relative to the automotive and other industries are presented to demonstrate the ability of the techniques to characterize surface defects in green parts.

A Portable Hybrid Ultrasound-Eddy Current NDI System for Metal Matrix Composite Track Shoes

Abstract : Track shoes made of Metal Matrix Composite (MMC) are light in weight, and can resist high temperature and wear. Defects such as disbond, cracks and porosity can be introduced during the manufacturing process and while in service. Presented in this paper is a portable nondestructive inspection (NDI) system to automatically inspect the tank track shoes for disbond, cracks and porosity defects. The work focuses on the inspection of the track shoe center spline where MMC inserts are attached to the aluminum substrate. A hybrid approach has been developed where an array of broadband high frequency ultrasonic transducers operating in a pulse/echo mode are utilized to detect disbond, and a scanning eddy current probe array is used to detect cracks and porosity. The inspection results agree quite well with immersion ultrasonic C-scan images and destructive tests.

A Portable Ultrasonic Nondestructive Inspection System for Metal Matrix Composite Track Shoes

Cast aluminum track shoes reinforced with metal matrix composite (MMC) inserts at heavy loading areas such as center splines and sprocket windows are light in weight, and can resist high temperature and wear. Various defects such as disbonds at the insert‐substrate interface, cracks and porosity in the MMC layer, etc. can be introduced during the manufacturing process and/or in service. This paper presents a portable ultrasonic system to automatically inspect tank track shoes for disbond. Ultrasonic pulse/echo inspection has shown good reliability for disbond detection. A prototype sensor array fixture has been designed and fabricated to prove the feasibility. Good agreements between the sensor fixture results and ultrasonic C‐scan images were obtained.

Ultrasonic nonlinear guided wave inspection of microscopic damage in a composite structure

Sudden structural failure is a severe safety threat to many types of military and industrial composite structures. Because sudden structural failure may occur in a composite structure shortly after macroscale damage initiates, reliable early diagnosis of microdamage formation in the composite structure is critical to ensure safe operation and to reduce maintenance costs. Ultrasonic guided waves have been widely used for long-range defect detection in various structures. When guided waves are generated under certain excitation conditions, in addition to the traditional linear wave mode (known as the fundamental harmonic wave mode), a number of nonlinear higher-order harmonic wave modes are also be generated. Research shows that the nonlinear parameters of a higher-order harmonic wave mode could have excellent sensitivity to microstructural changes in a material. In this work, we successfully employed a nonlinear guided wave structural health monitoring (SHM) method to detect microscopic impact damage in a ...

Long Range Guided Wave Natural Focusing Pipe Inspection

Long range ultrasonic guided wave nondestructive evaluation can be used to inspect pipelines over fairly long distances. Partial loading of transducers around the circumference leads to a non-axisymmetric energy distribution. At particular axial distances and frequencies, the ultrasonic energy is naturally focused at some spots around the circumference via constructive wave interference. This so called “natural focusing” phenomenon can be used to improve guided wave sensitivity for a defect since more energy is sent to the defect. However, defects located in other places could possibly be missed, unless we can move the natural focusing points throughout the pipe. We have done this by frequency and circumferential angle tuning for specific circumferential loading lengths. In order to utilize the natural focusing phenomenon to enhance detection sensitivity, a frequency and angle tuning (FAT) technique is employed to extend the area that is scanned by focal energy. It is observed that the natural focal points at a fixed axial distance move with frequency variation and circumferential excitation length change. In this paper, the natural focusing phenomenon with FAT is theoretically calculated and experimentally investigated. The results show that the natural focusing inspection technique can sufficiently inspect an entire pipe with FAT. Some sample inspection data is compared by applying axisymmetric excitations, FAT, and phased array focusing.Copyright

Application of a high numerical-aperture lens to visualize disbonding between metallic films and polymer substrates with SAM

Due to increased demand for design flexibility, in recent years engineers have progressively employed polymers in the design of electronics enclosures. As the circuits in these enclosures are miniaturized, dissipate more thermal energy and run at higher clock speeds, electromagnetic interference (EMI) and heat dissipation concerns become more apparent and are more problematic. The high thermal impedance of polymers slows their implementation in these situations. In addition, many electronics devices are subject to industrial and governmental regulations for EMI emission and isolation. To address these concerns it is becoming increasingly popular to apply conformal metallic films to polymer-based enclosures to increase EMI shielding and decrease thermal impedance through heat spreading. As with any coating, quality assurance of adhesion between the film and substrate is of immense importance. Without standardized testing procedures for assuring the quality of these processes, it is difficult to place them into practice. When new and alternative manufacturing processes are brought forth quality assurance is of paramount importance. The majority of existing commercial testing procedures for determination of adhesion quality for metallic films pertain to metallic substrates. This paper presents the application of a practical shear wave lens to overcome these issues. It will be demonstrated that the shear wave lens will provide sufficient resolution in this application to allow visualization of bond quality and determination of to what degree a conformal coating has been achieved.