Frequency Domain Stress Gradient Detection via Phase Delay Conversion
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Solution Overview
Problem
Current ultrasonic stress measurement methods in the aerospace field face challenges in accurately determining stress gradients within materials due to the averaging of stress measurements across different depths, leading to reduced accuracy and inability to reflect internal stress distributions effectively.
Innovation Solution
A stress gradient non-destructive detection system utilizing frequency domain calculation of broadband swept frequency signals, comprising an arbitrary waveform generator, power amplifier, transmitting and receiving transducers, and a high-speed data acquisition system, which calculates phase delays to determine stress values at different depths, enhancing the characterization of stress gradients in the depth direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If time domain acoustic time difference measurement method is used, then the measurement device is simple, but the stress gradient measurement accuracy is low and cannot reflect internal stress distribution at different depths
Solution Approach 1:
The patent segments the broadband ultrasonic signal into multiple frequency components, where each frequency component penetrates to a specific depth range in the material. By analyzing the acoustic time difference of each frequency component separately, the method obtains stress information at different depths, transforming a single average stress measurement into multiple depth-resolved stress measurements. This segmentation approach enables stress gradient detection while maintaining device simplicity.
Solution Approach 2:
The patent introduces the frequency dimension to the traditional time domain measurement method. Instead of measuring only the overall acoustic time difference in the time domain, the method transforms the signal to the frequency domain and measures acoustic time differences at different frequencies. This adds a frequency dimension to the measurement, enabling depth-resolved stress detection without increasing device complexity.
2Adaptability or versatility
If broadband transducer with multiple frequency components is used, then the detection range is improved, but the time domain method cannot accurately reflect the influence of internal stresses at different depths on different frequency components
Solution Approach 1:
The patent applies the local quality principle by assigning different frequency components to different depth ranges within the material. Each frequency component is made sensitive to stresses at its specific penetration depth, creating a depth-dependent measurement capability. This allows the broadband transducer to provide localized stress information at different depths rather than a single averaged value, improving both detection range and measurement precision.
3Reliability
If ultrasonic velocity change due to stress is measured, then the theoretical basis is sound, but the velocity change is very small (about 1% for 100 MPa stress) and difficult to measure accurately
Solution Approach 1:
The patent substitutes direct velocity measurement with acoustic time difference measurement. Instead of measuring the small velocity change directly (which is difficult due to the small magnitude), the method measures the time difference of ultrasonic signal propagation, which can be measured with much higher precision. This substitution transforms a difficult velocity measurement into a more feasible time measurement while maintaining the theoretical foundation of acoustoelasticity.
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 approach allows for high-precision characterization of stress gradients by converting phase delays into time delays, improving the accuracy and spatial resolution of stress measurements, reducing interference from noise, and enabling efficient layer-by-layer scanning of internal stresses.
Implementation Method 1
an ultrasonic method is widely used due to unique advantages such as simple measuring device and wide application range
Implementation Method 2
When the internal stress of the measured object is measured by means of acoustic elasticity, the change of the ultrasonic velocity due to the stress is very small
Data Source
AI summary
The disclosure discloses a stress gradient high-efficiency non-destructive detection system based on frequency domain calculation of broadband swept frequency signals, and a detection method thereof. The detection method includes: step 1: calibrating an LCR wave velocity of an object to be measured; step 2: calculating a starting frequency and a cut-off frequency of broadband swept frequency signals based on the LCR wave velocity of the object to be measured in the step 1 and a stress gradient measuring range in a depth direction of the object to be measured; step 3: converting phase delay to time delay information based on the phase delay of the starting frequency and the cut-off frequency in the step 2; and step 4: determining stresses of depths corresponding to different frequency components based on the time delay information in the step 3 to finally realize layer-by-layer scanning of stresses at different depths of the measured object. The disclosure is used to solve the problem of low stress gradient measuring accuracy, and realize the high-efficiency characterization of the stress gradient in the depth direction.