Mr. Walter A. Kruse Profile

Walter A. Kruse

at New Mexico Institue of Mining and Technology

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Proceedings Article | 9 April 2010 Paper

Active sensing of fatigue damage using embedded ultrasonics

Walter Kruse, Andrei Zagrai, Vlasi Gigineishvili

Proceedings Volume 7650, 76501J (2010) https://doi.org/10.1117/12.847672

KEYWORDS: Sensors, Aluminum, Structural dynamics, Electromagnetic coupling, Damage detection, Resistors, Bone, Ultrasonics, Signal processing, Active remote sensing

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Dynamic measurements are widely used for structural condition assessment and damage detection. A wide range of studies are available on vibration-based detection and identification of fatigue cracks in simple and complex structures. This research explores the application of the electromechanical impedance method and nonlinear resonance measurements to high frequency detection of incipient fatigue damage in aluminum alloy specimens. The electromechanical impedance method relies on the coupling between the mechanical properties of a structure and the electrical properties of attached piezoelectric wafer active sensors (PWAS). This coupling allows structural properties to be inferred from the electrical impedance signature of the sensor. In this study, the electromechanical impedance method is utilized for assessment of material deterioration under cyclic fatigue loads. Aluminum specimens were subjected to increasing fatigue cycles at stress amplitudes below the yield point, and electromechanical impedance signatures were taken at discrete levels of fatigue damage. Linear and nonlinear features of the impedance signatures were compared for different damage conditions. The results show a downward frequency shift of impedance peaks with increasing fatigue load. This frequency shift is observed before visible crack development and fracture. Nonlinear resonance tests were applied to fatigued aluminum samples. PWAS were utilized for transmission and reception of elastic waves at increasing amplitude levels. Variations in structural dynamic characteristics were considered for different excitation conditions and increasing damage severity. This paper discusses damage detection capabilities of each method and provides perspectives for utilizing information on incipient damage for predicting structural performance under known operational loads.

Proceedings Article | 9 April 2010 Paper

Acousto-elastic measurements and baseline-free assessment of bolted joints using guided waves in space structures

Andrei Zagrai, Vlasi Gigineishvili, Walter Kruse, Andrew Murray, Derek Doyle, Whitney Reynolds, Brandon Arritt, Hugh Gardenier

Proceedings Volume 7650, 765017 (2010) https://doi.org/10.1117/12.847883

KEYWORDS: Sensors, Ultrasonics, Wave propagation, Satellites, Waveguides, Aluminum, Phase shifts, Wave plates, Signal detection, Analytical research

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Integrity of bolted joints is critical for successful deployment and operation of space structures. Conventional structural qualification tests span weeks if not months and inhibit rapid launch of space systems. Recent developments in the embedded ultrasonic acousto-elastic method offer fast diagnosis of bolted joints and opportunities for locating the fault. However, in current acousto-elastic measurement procedures, a baseline representing the healthy condition of the joint is necessary. To mitigate a requirement of the baseline, a new methodology based on relative amplitude and phase measurements is developed. The approach has been validated on laboratory specimens, and modifications were suggested for applications in realistic structures. The paper discusses principles of the baseline-free acoustoelastic method, its practical realization, and respective advantages and disadvantages. Comparison of baseline and baseline-free approaches is presented showing the utility of the recently proposed methodology. Fundamentals of the acousto-elastic response were studied in experiments involving guided wave propagation in a thin plate under tension. The results indicate a difference between acousto-elastic responses collected using sensors oriented parallel and perpendicular to the applied stress. It is suggested that this effect may be used to infer stress orientation in the sample. Practical issues related to acousto-elastic measurements in realistic complex structures are discussed, damage diagnosis algorithms are presented, and potential extensions of the acousto-elastic technique are proposed.

Proceedings Article | 8 April 2009 Paper

Active sensing of fatigue damage using embedded ultrasonics

Andrei Zagrai, Walter Kruse, Vlasi Gigineishvili

Proceedings Volume 7295, 72950F (2009) https://doi.org/10.1117/12.815650

KEYWORDS: Ultrasonics, Sensors, Active remote sensing, Acoustics, Amplifiers, Structural health monitoring, Active sensors, Aluminum, Wave propagation, Semiconducting wafers

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Embedded ultrasonics has demonstrated considerable utility in structural health monitoring of aeronautical vehicle. This active sensing approach has been widely used to detect and monitor cracks, delaminations, and disbonds in a broad spectrum of metallic and composite structures. However, application of the embedded ultrasonics for active sensing of incipient damage before fracture has received limited attention. The aim of this study was to investigate the suitability of embedded ultrasonics and nonlinear acoustic signatures for monitoring pre-crack fatigue damage in aerospace structural material. A harmonic load was applied to structural specimens in order to induce fatigue damage accumulation and growth. Specimens of simple geometry were considered and piezoelectric active sensors were employed for generation and reception of elastic waves. The elastic wave signatures were analyzed in the frequency domain using nonlinear impedance and nonlinear resonance methods. A relationship between fatigue severity and linear as well as nonlinear acoustic signatures was investigated and considered in the damage classification procedure. Practical aspects of the active sensing of the fatigue damage before fracture were discussed and prospective avenues for future research were suggested.

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