X-ray Diffraction Curve Segmentation for Residual Stress Analysis
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Solution Overview
Problem
Current X-ray diffraction analysis methods are inadequate for accurately determining residual stresses in crystalline materials with complex diffraction patterns, such as those with central peaks and shoulders, leading to random measurement errors and significant errors in stress determination.
Innovation Solution
A processing device that separates global diffraction curves into main and secondary curves, using weighted combinations of Gaussian and Lorentzian distribution curves or pseudo Voigt and Pearson VII curves to accurately determine the end point and deformation parameters, thereby improving the precision of residual stress measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional processing methods (chord, barycenter, maximum methods, or simple simulation methods) are used to determine the end point of diffraction curves, then the process is simple and fast, but the measurement precision deteriorates significantly when the diffraction pattern has a central peak with shoulders (dispersion reaches 300%)
Solution Approach 1:
The patent applies segmentation by dividing the diffraction curve into multiple segments: a main curve representing the central peak and secondary curves representing the shoulders. This segmentation allows each component to be processed independently with appropriate methods, improving the determination of the end point position and reducing measurement dispersion from 300% to less than 10%.
Solution Approach 2:
The patent introduces an intermediary processing step where the diffraction curve is decomposed into main and secondary curves through convolution relationships. This intermediary representation enables more accurate extraction of the end point by separating the overlapping peak and shoulder contributions before final stress calculation.
2Measurement precision
If the diffraction curve is processed as a single overall curve, then the processing is straightforward, but the dispersion of residual stress values increases significantly (up to 300%) when shoulders are present
Solution Approach 1:
The patent segments the overall diffraction curve into a main curve and secondary curves based on their convolution relationship. The main curve corresponds to the central peak while secondary curves correspond to shoulders. This segmentation enables independent processing of each component, significantly reducing the dispersion of residual stress values from 300% to less than 10%.
Solution Approach 2:
The patent applies local quality by using different processing approaches for different parts of the diffraction pattern. The main curve (central peak) and secondary curves (shoulders) are processed with appropriate methods tailored to their characteristics, rather than applying a uniform processing method to the entire curve, thereby improving measurement consistency.
3Measurement precision
If simple curve fitting methods are used, then the computational process is fast and simple, but the accuracy of determining the global angular position of diffraction deteriorates when the pattern includes shoulders from quadratic martensite
Solution Approach 1:
The patent segments the diffraction pattern into a main curve and secondary curves that represent different crystallographic contributions. The main curve is fitted using appropriate functions (Gaussian, Lorentzian, pseudo-Voigt, or Pearson VII) to accurately determine the global angular position, while secondary curves account for shoulder contributions, thereby improving accuracy without excessive computational complexity.
Solution Approach 2:
The patent employs parameter changes by selecting from multiple curve fitting functions (Gaussian, Lorentzian, pseudo-Voigt, Pearson VII) with different parameters to best represent the main curve and secondary curves. This flexibility in parameter selection allows accurate representation of the diffraction pattern features, improving angular position determination accuracy.
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 significantly reduces the dispersion of residual stress values across different analysis directions, providing more accurate and realistic stress measurements with less than 10% dispersion compared to prior methods, which can reach 300% dispersion.
Implementation Method 1
analysis means arranged to analyze each part by diffraction of X-rays in order to obtain sets of points which are representative of intensity measurements of diffraction as a function of different diffraction angles
Implementation Method 2
intensity measurements of diffraction as a function of different diffraction angles
Data Source
Figure 1~2
AI summary
The invention relates to a device (D) for processing sets of points which are representative of measurements of diffraction intensity as a function of diffraction angles obtained on a part (PI) made from a crystalline material and having residual stresses, and which equate to overall curves comprising a main peak and a shoulder. The device (D) comprises: a) first processing means (MT1) for determining, for each overall curve associated with the part (PI) and with a direction of analysis, i) main and secondary curves representative respectively of the main peak thereof and the shoulder thereof, the convolution of which reproduces the overall curve, ii) an extremum defined by an overall angular position of diffraction to which there corresponds a maximum diffraction intensity value resulting from a weighted combination of the maximum diffraction intensity values of the associated main and secondary curves, and iii) a parameter of deformation of the part (PI) in the direction of analysis from the overall angular position of diffraction; and b) second processing means (MT2) for determining a residual stress of the part (PI) from the deformation parameters determined in each of the directions of analysis of the sets of points.