Fatigue Crack Detection Technique Research Articles

Fatigue crack detection in rotating steel shafts using noncontact ultrasonic modulation measurements

In this study, a noncontact fatigue crack detection technique for rotating steel shafts is developed using air-coupled transducers (ACTs). Two ACTs are used for ultrasonic wave generation at two distinctive frequencies, and a third ACT is used for sensing. The proposed technique is based on the premise that nonlinear ultrasonic modulation appears at the sum and difference of two input frequencies in the presence of any crack due to crack opening and closing. First, the spectral correlation (SC) between ultrasonic modulation components at the sum and difference of two input frequencies is computed. Next, an outlier analysis is performed on spectral correlations obtained from different input frequency combinations for automated crack diagnosis. To the best of the authors’ knowledge, this is the first study in which a sub-millimeter fatigue crack is detected in a rotating steel shaft using noncontact transducers. In this study, real fatigue cracks on half-scale and full-scale steel shafts used in automobile assembly lines are produced through cyclic loading tests, and the performance of the proposed technique is experimentally validated using ultrasonic response data obtained from the half-scale and full-scale steel shaft specimens. The formation of fatigue cracks is confirmed using fluorescent magnetic particle inspection (MPI), fluorescent penetrant inspection (FPI), and metallographic analysis.

Reliability improvement of nonlinear ultrasonic modulation based fatigue crack detection using feature-level data fusion

In this study, the reliability of nonlinear ultrasonic modulation based fatigue crack detection is improved using a feature-level data fusion approach. When two ultrasonic inputs at two distinct frequencies are applied to a specimen with a fatigue crack, modulation components at the summation and difference of these two input frequencies appear. First, the spectral amplitudes of the modulation components and their spectral correlations are defined as individual features. Then, a 2D feature space is constructed by combining these two features, and the presence of a fatigue crack is identified in the feature space. The effectiveness of the proposed fatigue crack detection technique is experimentally validated through cyclic loading tests of aluminum plates, full-scale steel girders and a rotating shaft component. Subsequently, the improved reliability of the proposed technique is quantitatively investigated using receiver operating characteristic analysis. The uniqueness of this study lies in (1) improvement of nonlinear ultrasonic modulation based fatigue crack detection reliability using feature-level data fusion, (2) reference-free fatigue crack diagnosis without using the baseline data obtained from the intact condition of the structure, (3) application to full-scale steel girders and shaft component, and (4) quantitative investigation of the improved reliability using receiver operating characteristic analysis.

Research on fatigue crack detection technique by residual stress measurement

Research on fatigue crack detection technique by residual stress measurement

Development and field application of a nonlinear ultrasonic modulation technique for fatigue crack detection without reference data from an intact condition

In this study, a fatigue crack detection technique, which detects a fatigue crack without relying on any reference data obtained from the intact condition of a target structure, is developed using nonlinear ultrasonic modulation and applied to a real bridge structure. Using two wafer-type lead zirconate titanate (PZT) transducers, ultrasonic excitations at two distinctive frequencies are applied to a target inspection spot and the corresponding ultrasonic response is measured by another PZT transducer. Then, the nonlinear modulation components produced by a breathing-crack are extracted from the measured ultrasonic response, and a statistical classifier, which can determine if the nonlinear modulation components are statistically significant in comparison with the background noise level, is proposed. The effectiveness of the proposed fatigue crack detection technique is experimentally validated using the data obtained from aluminum plates and aircraft fitting-lug specimens under varying temperature and loading conditions, and through a field testing of Yeongjong Grand Bridge in South Korea. The uniqueness of this study lies in that (1) detection of a micro fatigue crack with less than 1 μm width and fatigue cracks in the range of 10–20 μm in width using nonlinear ultrasonic modulation, (2) automated detection of fatigue crack formation without using reference data obtained from an intact condition, (3) reliable and robust diagnosis under varying temperature and loading conditions, (4) application of a local fatigue crack detection technique to online monitoring of a real bridge.

104 温度ギャップ法による疲労き裂検出技術の実用化(FM2 実務に使えそうな最新の計測技術(2),研究討論セッション)

104 温度ギャップ法による疲労き裂検出技術の実用化(FM2 実務に使えそうな最新の計測技術(2),研究討論セッション)

Fatigue crack detection using structural nonlinearity reflected on linear ultrasonic features

This paper theoretically and experimentally demonstrates that (1) a localized nonlinear mechanism such as a fatigue crack not only generates nonlinear modulations or harmonics, but also reduces the amplitudes of the linear responses at the excitation frequencies, (2) the energy in the linear responses is partially transmitted to the nonlinear components in the presence of structural nonlinearity, and (3) the amplitude reduction of the linear responses is larger than the amplitude increase of the nonlinear components. In addition, a baseline-free fatigue crack detection technique is proposed considering the additional amplitude reduction of the linear components due to nonlinear ultrasonic modulation.

Reference-free fatigue crack detection using nonlinear ultrasonic modulation under various temperature and loading conditions

This study presents a reference-free fatigue crack detection technique using nonlinear ultrasonic modulation. When low frequency (LF) and high frequency (HF) inputs generated by two surface-mounted lead zirconate titanate (PZT) transducers are applied to a structure, the presence of a fatigue crack can provide a mechanism for nonlinear ultrasonic modulation and create spectral sidebands around the frequency of the HF signal. The crack-induced spectral sidebands are isolated using a combination of linear response subtraction (LRS), synchronous demodulation (SD) and continuous wavelet transform (CWT) filtering. Then, a sequential outlier analysis is performed on the extracted sidebands to identify the crack presence without referring any baseline data obtained from the intact condition of the structure. Finally, the robustness of the proposed technique is demonstrated using actual test data obtained from simple aluminum plate and complex aircraft fitting-lug specimens under varying temperature and loading variations.

Nonlinear ultrasonic wave modulation for online fatigue crack detection

Abstract This study presents a fatigue crack detection technique using nonlinear ultrasonic wave modulation. Ultrasonic waves at two distinctive driving frequencies are generated and corresponding ultrasonic responses are measured using permanently installed lead zirconate titanate (PZT) transducers with a potential for continuous monitoring. Here, the input signal at the lower driving frequency is often referred to as a ‘pumping’ signal, and the higher frequency input is referred to as a ‘probing’ signal. The presence of a system nonlinearity, such as a crack formation, can provide a mechanism for nonlinear wave modulation, and create spectral sidebands around the frequency of the probing signal. A signal processing technique combining linear response subtraction (LRS) and synchronous demodulation (SD) is developed specifically to extract the crack-induced spectral sidebands. The proposed crack detection method is successfully applied to identify actual fatigue cracks grown in metallic plate and complex fitting-lug specimens. Finally, the effect of pumping and probing frequencies on the amplitude of the first spectral sideband is investigated using the first sideband spectrogram (FSS) obtained by sweeping both pumping and probing signals over specified frequency ranges.

In Situ Fatigue Crack Detection using Piezoelectric Paint Sensor

This article reports the recent development of a surface fatigue crack detection technique based on the use of surface-mount piezoelectric paint sensor. Polymer-based piezoelectric paints that can be directly deposited onto the surface of host structures are being utilized to make the sensor for surface crack detection. Because of its electromechanical coupling properties, voltage signals can be generated by the piezoelectric paint sensor when subjected to mechanical strain in its film plane. Results from recent development of the piezoelectric paint-based surface crack detection technique indicate that piezoelectric paint sensors with a special electrode design can potentially provide an effective method to detect fatigue cracks occurring in structural surfaces. A simple damage index is defined to determine the occurrence of surface cracks in a pre-specified region. However, complex sensor electrode patterns may be necessary in some cases to improve the spatial resolution of surface crack detection. Experiments conducted to validate this surface crack detection technique are also described in this study.

An on-line combined linear–nonlinear fatigue crack detection technique

To monitor the structural health during fatigue tests, classical nondestructive tests (ultrasonic inspection, liquid penetration, eddy current, etc.) are usually performed at regular time instances. Unfortunately, the fatigue tests should be interrupted to use these techniques. In addition, a large amount of user interaction is required. In this article, vibration features are used to detect cracks on-line with the execution of a fatigue test. To perform this task, an experimental strategy is developed to simultaneously estimate static and dynamic as well as linear and nonlinear vibration features. By means of these features the sensitivity of static versus dynamic and linear versus nonlinear damage detection techniques will be qualified. Finally, it will be shown that by using nonlinear identification techniques, additional information on the damage scenario can be extracted. The validation will be done on a steel beam with a propagating fatigue crack.