| Ultrasonic guided wave-based structural health monitoring(GWSHM)is an important means to improve the safety of aircraft structures and reduce maintenance costs.However,the change of service environment can easily cause the change of diagnostic signal of ultrasonic guided waves,which will lead to the false alarm or negative damage and reduce the reliability of the diagnostic results,limits its engineering application.Therefore,it is needed to compensate the effect of environmental factors on ultrasonic guided waves.This paper adopted a research method combining numerical simulation with experiment verification.Firstly,the propagation process of ultrasonic guided wave respectively under the effect of temperature and load separately is described in a way of theoretical analysis and numerical simulation to obtain the change rules of ultrasonic guided wave propagation characteristics.Then several piezoelectric sensors are layout on some typical aviation aluminum plates to generate and receive ultrasonic guided wave.These test specimens are put into the temperature box,tensile testing machine and high temperature tensile machine to perform tests of guided waves under a single environment factor and two coupling environmental factors.The signal features such as amplitude,phase,and time of arrival are extracted to characterize the effect of environment factors on the ultrasonic guided wave.Then,based on the idea of Matching Pursuit algorithm,a reference signal matching-based environmental compensation methods for ultrasonic guided waves is put forward.The damage diagnostic algorithm based on probability weighted distribution imaging is used to verify the effectiveness of the proposed environment compensation method.The main research contents are summarized as follows:(1)The propagation mechanism of ultrasonic guided wave on the plate structure under a single changing environment(temperature and load).Based on COMSOL multi-physics,the propagation process of ultrasonic guided wave under different changing environment is simulated.The law of temperature and load effect on amplitude and time of arrival of ultrasonic guided waves is summed up to provide the guidance for experiments.(2)From the view of experiment,the experiment schemes of ultrasonic guided wave propagation under a single changing environmental factor(temperature and load)are design to illustrate the changing laws of three signal characteristics(i.e.the amplitude,the phase and the time of arrival).It has been found that the influence of temperature on the ultrasonic guided wave is greater than that of load on ultrasonic guided wave,while the influence of the load on the guided wave is dependent on direction,and the change of three features of guided waves is approximate linear to the change of a single environment.A reference signal matching-based environment compensation method is proposed.The effects of different frequencies and different paths on compensated results are analyzed and discussed.The characteristic of the proposed method is that the compensation performance can be improved through multiple iterations of residual signals obtained by matching pursuit,when the first iteration did not meet the given requirements.(3)From the perspective of multiple environmental factors coupling,a test scheme of jointing load and temperature is designed.Three signal features of two modes of Lamb waves(A0 and S0)are extracted to illustrate the relationship between signals and two environments.It has been found that the coupled changes of two factors cause to a highly non-linear effect on signal characteristics change.By improving the selection of the reference signal set,the ultrasonic guided wave environment compensation method based on the reference signal matching is used to realize the compensation under the influence of the temperature-load coupling effect.In short,environmental factors alone effect and the coupling effect of the experimental results verify the effectiveness of the proposed compensation method. |
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