Non-linear Lamb Wave Mixing for Stress Detection in Metal Plates
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Solution Overview
Problem
Current stress detection methods for metal plate structures, such as drilling and non-destructive testing techniques like X-ray diffraction and ultrasonic methods, face limitations in depth, radiation safety, measurement stability, and the ability to detect early microscopic damage, particularly in ferromagnetic materials and thin metal plates.
Innovation Solution
A non-linear Lamb wave mixing method using piezoelectric ultrasonic probes to generate and detect sum-frequency signals, which allows for the detection of stress distribution and localization of stress concentration areas in metal plates by analyzing the amplitude of sum-frequency signals and adjusting probe excitation delays to scan the test piece effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional linear ultrasonic testing is used, then larger stresses and developed defects can be measured, but early microscopic damage cannot be effectively detected
Solution Approach 1:
The patent changes the fundamental parameter of ultrasonic testing from linear to non-linear regime. By applying high-amplitude ultrasonic waves and analyzing non-linear parameters (such as harmonic ratios, intermodulation frequencies), the system achieves sensitivity to early microscopic damage while maintaining the capability to measure larger stresses, thus resolving the contradiction between detection sensitivity and applicability range
Solution Approach 2:
The patent utilizes mechanical vibration at ultrasonic frequencies to induce non-linear responses in the material. By exciting the material with ultrasonic waves and analyzing the non-linear vibrational characteristics (harmonic generation, frequency mixing), early microscopic damage becomes detectable through changes in vibration behavior that are not visible in linear testing
2Measurement precision
If X-ray diffraction method is used, then stress detection depth is extremely shallow (10-35 μm), but radiation damage to human body occurs
Solution Approach 1:
The patent replaces the X-ray electromagnetic radiation-based detection system with a mechanical ultrasonic wave-based system. Ultrasonic waves mechanically interact with the material structure to detect stress, eliminating ionizing radiation and its associated health hazards while maintaining the capability for precise stress detection in thin metal plates
3Adaptability or versatility
If magnetic measurement methods are used, then ferromagnetic materials can be detected, but measurement stability is poor and data is scattered
Solution Approach 1:
The patent replaces magnetic field-based measurement methods with mechanical ultrasonic wave propagation methods. Ultrasonic waves interact with material density and elastic properties rather than magnetic domains, providing stable and consistent measurements that are not affected by magnetic domain orientation or magnetization conditions, thus improving measurement reliability while maintaining applicability to various materials including ferromagnetic ones
4Measurement precision
If drilling method is used, then stress can be converted to strain for measurement, but strict requirements on drilling process and tools are needed
Solution Approach 1:
The patent replaces the mechanical drilling and strain gauge installation process with a non-contact (or minimal contact) ultrasonic wave propagation method. Stress is measured through changes in ultrasonic wave velocity and characteristics as waves travel through the material, eliminating the need for drilling operations, strain gauge installation, and associated strict process control requirements
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method effectively suppresses system nonlinearity interference and provides sensitive detection of stress distribution and concentration areas in metal plates, enhancing the ability to detect early material damage and improving measurement accuracy compared to traditional methods.
Implementation Method 1
piezoelectric ultrasonic probe as excitation sensor
Implementation Method 2
Non-linear Lamb wave mixing method for measuring stress distribution in thin metal plates
Implementation Method 3
non-linear response generated by interaction between sound wave and microstructure of material to characterize the material performance
Implementation Method 4
piezoelectric sensor with center frequency near the sum frequency signal is arranged between two excitation probes to receive the signal
Data Source
AI summary
The invention discloses a non-linear Lamb wave mixing method for measuring stress distribution in thin metal plates. The method is suitable for stress distribution detection and stress concentration area positioning in a plate structure and belongs to the field of nondestructive detection. The steps of the present invention is: first determines the excitation frequencies of two fundamental waves according to the measured object and the nonlinear Lamb wave mixing resonance conditions; the left and right ends of the test piece are oppositely excited two rows of A0 mode waves, and the excitation signal receive the sum-frequency S0 signal at a certain position to detect non-linear mixing stress of the plate structure; by changing the excitation time delay of the excitation signal, perform mixing scan on different positions of the test piece to extract the mixing wave amplitude; finally, according to the variation of amplitude of sum frequency difference signal with mixing position to realize the detection of stress distribution of metal plate and the positioning of the stress concentration area.