Abstract
The direct current potential drop (DCPD) method is widely used in laboratory environments to monitor the crack initiation and propagation of specimens. In this study, an anti-interference signal processing approach, combining wavelet threshold denoising and a variable current amplitude DCPD signal synthesis technique, was proposed. Adaptive wavelet threshold denoising using Stein’s unbiased risk estimate was applied to the main potential drop signal and the reference potential signal under two different current amplitudes to reduce the interference caused by noise. Thereafter, noise-reduced signals were synthesized to eliminate the time-varying thermal electromotive force. The multiplicative interference signal was eliminated by normalizing the main potential drop signal and the reference potential drop signal. This signal processing approach was applied to the crack growth monitoring data of 316 L stainless steel compact tension specimens in a laboratory environment, and the signal processing results of static cracks and propagation cracks under different load conditions were analyzed. The results showed that the proposed approach can significantly improve the signal-to-noise ratio as well as the accuracy and resolution of the crack growth measurement.
Highlights
Two C(T) specimens were used for the fatigue tensile and direct current potential drop (DCPD) monitoring experiments in an ambient laboratory air environment. e ambient temperature range was 24–30°C
Static crack), and four sets of signals were randomly selected to illustrate the effect of the signal processing approach. e signals shown in Figure 7 are the main DCPD signals, and the signals shown in Figure 8 are the reference DCPD signals
It can be observed that after wavelet threshold denoising, the noise on signals VI1 and VI2 is significantly reduced while retaining the change characteristics of the lower frequency signals. e signal VSYN is the signal obtained by the signal synthesis algorithm in equation (12)
Summary
Two C(T) specimens were used for the fatigue tensile and DCPD monitoring experiments in an ambient laboratory air environment. e ambient temperature range was 24–30°C. Two C(T) specimens were used for the fatigue tensile and DCPD monitoring experiments in an ambient laboratory air environment. In the DCPD crack growth monitoring test, the specimen was injected with a constant current, and the DCPD signals between specific positions were monitored. E tensile testing machine can apply static or dynamic tensile loads to the specimen and can conduct fatigue precracking and crack growth experiments on specimens. The DCPD of the specimen was monitored using a DCPD crack growth monitoring system
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