Stroboscopic Elastic Wave Defect Detection
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Solution Overview
Problem
Existing defect detection methods, such as electronic speckle pattern interferometry, have limited accuracy due to measuring only one phase state of the elastic wave, leading to uneven defect detection capabilities across the examination area and difficulties in determining defect depth without prior material-specific relationships.
Innovation Solution
A method involving stroboscopic illumination and control of the elastic wave phase to measure displacement in multiple phases across the examination area, followed by injecting a second elastic wave to determine defect depth, using a common transducer for both operations to enhance accuracy and reduce costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If electronic speckle pattern interferometry is used to measure the entire examination area at one time, then the measurement speed is improved, but the defect detection accuracy becomes uneven depending on the location within the measurement area
Solution Approach 1:
The patent applies periodic action by inducing elastic waves that oscillate in time and measuring the displacement at multiple phase points (0°, 90°, 180°, 270°) during one complete vibration cycle. This periodic measurement approach ensures that all locations within the examination area are measured at the same phase points, eliminating the uneven detection accuracy problem while maintaining the advantage of collective area measurement.
2Device complexity
If only one phase state of the elastic wave is measured, then the measurement process is simplified, but the defect detection accuracy becomes uneven across different locations
Solution Approach 1:
The patent utilizes the periodic nature of elastic wave vibration to take measurements at four equally spaced phase points (0°, 90°, 180°, 270°) during one complete cycle. This approach systematically captures the displacement information at multiple phases without significantly increasing device complexity, as the same interferometric setup is used at each phase point with only the timing controlled differently.
3Measurement precision
If the relationship between displacement magnitude, defect length, and defect depth is determined beforehand for each material and shape, then the defect depth can be determined, but the examination process becomes complex and time-consuming
Solution Approach 1:
The patent employs parameter changes by utilizing the ratio between the amplitudes of elastic waves reflected from the defect and the incident wave. This ratio parameter directly relates to the defect depth through the reflection coefficient, eliminating the need for preliminary experiments or numerical calculations for each material and shape. The method transforms the complex relationship into a direct measurement-based calculation.
4Device complexity
If a point-like laser beam is used for displacement measurement, then the measurement setup is simpler, but the entire examination area requires scanning which takes considerable time
Solution Approach 1:
The patent transitions from one-dimensional point-by-point scanning to two-dimensional collective measurement by using electronic speckle pattern interferometry. This technique illuminates the entire examination area with a laser beam and captures the displacement field across the whole area simultaneously using a CCD camera, thereby eliminating the time-consuming scanning process while maintaining measurement capability.
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 quick and accurate detection of defects across large areas and precise measurement of defect depth, eliminating uneven detection capabilities and the need for prior material-specific relationships.
Implementation Method 1
laser light is cast onto the object and the thereby reflected light is detected with a laser interferometer to measure the displacement of the surface of the object
Implementation Method 2
laser light is cast onto the object and the thereby reflected light is detected
Implementation Method 3
while an elastic wave is induced in an object to be examined... If a defect is present, the displacement due to the elastic wave discontinuously changes at the location of the defect
Implementation Method 4
performing stroboscopic illumination on the entire surface of an object to be examined within an examination area on the object while inducing a first elastic wave across the entire examination area on the object
Implementation Method 5
injecting a second elastic wave into a region inside the surface location... and determining the location and/or size in the depth direction of the defect, based on a response wave of the second elastic wave
Data Source
AI summary
A defect detection method includes the following processes: a) stroboscopically illuminating the entire surface of an object within an examination area of the object while inducing a first elastic wave across the examination area on the object, and controlling the phase of the elastic wave and the timing of the stroboscopic illumination to collectively measure a back-and-forth displacement of each point within the examination area in at least three phases of the elastic wave; b) identifying a surface location which is the location of a defect on the examination area, based on the back-and-forth displacement of each point within the examination area in the at least three different phases; and c) injecting a second elastic wave into a region inside the surface location from a limited area including the surface location, and determining the location and/or size in the depth direction of the defect, based on a response wave.