Shaped Laser Excitation for Non-Contact Shearography
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Solution Overview
Problem
Existing non-destructive testing methods face limitations such as limited detection range, long imaging times, restricted applications to metallic materials, radiation hazards, and the need for physical contact, which constrain their effectiveness in detecting defects within materials and structures.
Innovation Solution
A non-contact laser acoustic shearography method and system that combines high-power patterned laser pulses to induce acoustic waves and a full-field shearography imaging system for non-contact, fast, and large-area defect detection, allowing for spatial and temporal control of laser excitation to generate directional or focused acoustic waves without physical contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If physical contact loading methods are used in shearography testing, then the test object can be loaded effectively, but the field of view is limited and applications are restricted to situations where physical contact can be established
Solution Approach 1:
The patent replaces physical contact loading methods with optical loading using laser-induced acoustic waves. The laser beam interacts with the test object surface to generate acoustic waves that load the object internally without mechanical contact, enabling testing of complex structures and high temperature components that cannot be accessed by physical probes
Solution Approach 2:
The patent introduces acoustic waves as an intermediary between the laser energy and the test object. The laser generates acoustic waves that propagate through the object, providing indirect loading that avoids the need for direct physical contact while still achieving effective defect detection
2Ease of operation
If diffused laser beam is used for thermal loading, then non-contact loading is achieved, but the energy density is low resulting in poor signal strength and low sensitivity
Solution Approach 1:
The patent uses pulsed laser excitation instead of continuous diffused laser illumination. The periodic pulsed action concentrates energy delivery into discrete time intervals, generating strong acoustic waves that improve signal strength while maintaining non-contact operation
Solution Approach 2:
The patent changes the temporal parameters of laser excitation from continuous to pulsed mode, and adjusts the spatial distribution to create focused acoustic waves. This parameter optimization increases energy density and acoustic wave intensity, thereby improving measurement precision without sacrificing non-contact capability
3Measurement precision
If acoustic waves are used to probe internal structural defects, then high penetration depth and good resolution are achieved, but the detection range of a single measurement is limited and imaging time is long
Solution Approach 1:
The patent segments the excitation into multiple focused acoustic wave sources distributed across the test object. By creating multiple independent excitation points simultaneously, the system achieves both deep penetration at each point and broad overall coverage, improving productivity without sacrificing measurement precision
Solution Approach 2:
The patent transitions from single-point to multi-point or line-based acoustic excitation, adding spatial dimensionality to the probing process. This allows parallel detection across multiple locations, expanding the effective detection range and reducing total imaging time while maintaining the high resolution capabilities of acoustic wave probing
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
Enables fast, full-field, and non-contact inspection of defects with improved signal strength and sensitivity, capable of detecting subsurface defects in various materials and structures, including those with complex geometries or at high temperatures, without the limitations of existing methods.
Implementation Method 1
High-power laser pulse is directed on the surface of the test object to induce acoustic waves in the test object
Implementation Method 2
The surface illuminated by the laser beam will be heated up and generate surface deformation anomalies due to thermal expansion
Implementation Method 3
Shearography is an optical measurement technique for NDT, offering full-field large area inspection with fast acquisition rate. Defect detection in shearography is typically performed by comparing the speckle patterns of the test object acquired by a charge coupled device (CCD) sensor under loaded and unloaded states
Implementation Method 4
High-power laser pulse is directed on the surface of the test object to induce acoustic waves in the test object. The acoustic waves induced by the patterned laser pulses interact with surface or subsurface defects to generate surface deformation anomalies in the test object
Data Source
AI summary
A non-contact non-destructive testing method includes spatially and/or temporally controlling a laser excitation light based on a predetermined pattern. The laser excitation light is projected onto a surface of a test object to generate acoustic waves on the test object. The acoustic waves apply stress loading to the test object. The method also includes imaging the test object with and without stress loading using shearography imaging, and analyzing shearography imaging data to determine a presence of a defect in the test object.