Method for identifying microcrack direction in plate based on nonlinear frequency mixing technology of Lamb waves

A direction identification, nonlinear technology, applied in the processing of the detected response signal, the use of sonic/ultrasonic/infrasonic waves to analyze solids, and the use of sonic/ultrasonic/infrasonic waves for material analysis, etc. It can solve the problem of small amplitude, sum frequency and difference frequency The signal is not easy to extract and identify, the signal is weak, etc.

Active Publication Date: 2020-05-15
NANJING UNIV OF TECH
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  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

[0004] The purpose of the present invention is to address the above-mentioned deficiencies, and propose a method for identifying the direction of micro-cracks in plates based on the nonlinear frequency mixing technology of Lamb waves. The characteristics of the components, the effective frequency components in the structural response signal are effectively extracted by the pulse inversion method, the sum frequency signal and the difference frequency signal are extracted, and the identification of the direction of the microcrack is realized by studying the nonlinear scattering degree of the Lamb wave in different directions of the microcrack. Effectively solve the technical problem that the sum frequency and difference frequency signals with too small amplitude and weak signal are difficult to extract and identify

Method used

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  • Method for identifying microcrack direction in plate based on nonlinear frequency mixing technology of Lamb waves
  • Method for identifying microcrack direction in plate based on nonlinear frequency mixing technology of Lamb waves
  • Method for identifying microcrack direction in plate based on nonlinear frequency mixing technology of Lamb waves

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Embodiment 1

[0062] A method for identifying the direction of micro-cracks in a plate based on the nonlinear frequency mixing technology of Lamb waves. The steps are as follows:

[0063] S1. Two exciters with frequency signals of 450kHz and 600kHz mixing signals are respectively used to excite the incident Lamb wave signal on the upper and lower surfaces of the plate material under two opposite phase conditions, and the excitation method is the same The Lamb wave of a single S0 mode is excited at all times, and two kinds of damage response signals corresponding to two opposite phase conditions are generated respectively. Both damage response signals contain sum frequency signal, difference frequency signal and fundamental frequency component; A sensor (at least 4 sensors) is fixed on the upper surface of the plate-shaped material, and the plurality of sensors form a circular sensor network for collecting signals; the circular sensor network receives the above two kinds of damage response si...

Embodiment 2

[0075] In the present invention, based on the nonlinear frequency mixing technology of Lamb wave, the method for identifying the direction of micro-cracks in the plate detects the micro-cracks of the damaged aluminum plate, and the steps are as follows:

[0076] S1, such as figure 1 As shown, using two piezoelectric chips P t1 and P t2 (P t1 and P t2 is the exciter, the two frequency signals of the exciter are 450kHz and 600kHz respectively) under the condition of two opposite phases (the two opposite phases are 0° phase and 180° phase respectively), and the plate material is located at (-70mm, 0mm) on the upper and lower surfaces respectively excite the incident Lamb wave signal, specifically: the exciter P t1 and P t2 First, under the condition of 0° phase, a single S0 mode Lamb wave signal is excited on the upper and lower surfaces of the plate material along the thickness direction of the plate, and a damage response signal including sum frequency signal, difference f...

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Abstract

The invention discloses a method for identifying a microcrack direction in a plate based on a nonlinear frequency mixing technology of Lamb waves. The method includes, firstly, extracting a sum frequency signal and a difference frequency signal in a damage response signal by adopting a pulse inversion method; obtaining a directional mode pattern of a nonlinear scattering coefficient beta through the extracted sum frequency signal and difference frequency signal; and determining the maximum forward scattering point and the minimum backward scattering point of the Lamb wave, and taking the direction vertical to the connecting line of the maximum forward scattering point and the minimum backward scattering point of the Lamb wave as the direction of the micro-crack, thereby realizing the identification of the direction of the micro-crack. According to the invention, the Lamb wave excited by frequency mixing interacts with the nonlinear medium to generate a new frequency component; the sumfrequency and difference frequency effective frequency components in the damage response signal are effectively extracted through a pulse inversion method, the microcrack direction is recognized by researching the nonlinear scattering degree of Lamb waves in different directions of the microcrack, and the technical problems that the amplitude is too small, and the sum frequency and difference frequency signals with weak signals are not easy to extract and recognize are effectively solved.

Description

technical field [0001] The invention relates to the field of non-destructive testing, and more specifically, relates to a method for identifying the direction of microcracks in a plate based on the nonlinear frequency mixing technology of Lamb waves. The method is suitable for identifying the direction of microcracks in plate structures. Background technique [0002] Plate structures are widely used in various equipment, and fatigue cracks are one of the main forms of damage. Fatigue cracks will lead to stress concentration in the structure. If no treatment measures are taken in time, the cracks will accelerate the expansion under load and eventually lead to structural fracture. Therefore, the detection of cracks at an early stage using non-destructive testing (NDE) is crucial to maintain the integrity and safety of structures. [0003] Lamb wave has the characteristics of long propagation distance and slow energy attenuation, and is considered to be one of the most potenti...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G01N29/44G01N29/04
CPCG01N29/4454G01N29/041
Inventor 李义丰关立强万夕里余辉洋
Owner NANJING UNIV OF TECH
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