Normalized Defect Characterization in Pulse Thermography
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Solution Overview
Problem
Thermographic nondestructive evaluation techniques face challenges in accurately detecting and quantifying subsurface defects due to noise from thermal cameras, non-uniform heating, and difficulties in generating numerical simulations without known thermo-mechanical properties, leading to inconsistencies between experimental and simulated results.
Innovation Solution
A normalization scheme is implemented to reduce noise and non-uniform heating effects by normalizing temperature data with respect to a characteristic time and steady-state temperature, allowing for direct estimation of defect depth and enabling comparison with validated numerical simulations for defect evaluation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional thermographic nondestructive evaluation techniques are used to detect subsurface defects, then defect detection capability is provided, but measurement precision deteriorates due to noise from thermal cameras and non-uniform heating effects
Solution Approach 1:
The patent introduces normalized temperature data as an intermediary representation that mediates between the raw thermal camera measurements (affected by noise and non-uniform heating) and the defect characterization. The normalized temperature data serves as a filtered, standardized intermediate state that eliminates harmful variations while preserving defect-related thermal signatures, thereby improving measurement precision without requiring changes to the thermal camera hardware itself.
2Reliability
If quantitative defect characterization is performed using traditional methods, then defect depth estimation is attempted, but reliability deteriorates due to difficulty in generating numerical simulations without known thermo-mechanical properties
Solution Approach 1:
The patent transforms the problem by changing the parameters used for defect characterization. Instead of relying on absolute temperature values and known thermo-mechanical properties for numerical simulations, the method uses normalized temperature data that is independent of material properties. This parameter transformation eliminates the need for complex simulations with uncertain material properties, thereby improving reliability while reducing the complexity of the evaluation process.
3Temperature
If flash heating is applied to heat the surface uniformly, then temperature rise is achieved, but harmful factors worsen due to non-uniform heating and difficulty in detecting defect-free locations for comparison
Solution Approach 1:
The patent applies preliminary normalization to the temperature data before defect analysis. By normalizing the temperature data with respect to reference locations and characteristic times, the harmful non-uniform heating effects are compensated for in advance. This preliminary action creates a corrected dataset where defect-free locations are properly accounted for, eliminating the need to manually identify and compare defect-free regions while reducing the harmful effects of non-uniform heating.
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 enables accurate detection and quantification of defect depth and geometry, improving signal-to-noise ratio and facilitating defect evaluation in different materials with the same geometry, thus enhancing the reliability of thermographic nondestructive evaluation methods.
Implementation Method 1
Pulse thermography, an active thermographic technique, includes a pulse of heat energy that may be applied to the surface of the test object, usually by a flash lamp. The heat energy may cause a rise in the temperature of the surface of the test object.
Implementation Method 2
In a defect free sample, the heat may diffuse through a thickness of the object, resulting in an asymptotic drop in temperature across the surface.
Implementation Method 3
Following this temperature rise, the rate of change of temperature across the surface as a function of time may be monitored using an infrared camera.
Data Source
AI summary
A method of thermographic nondestructive evaluation may include heating a portion of a surface of an object from a first surface temperature to a second surface temperature that is greater than the first surface temperature, collecting a plurality of thermal images of the portion of the surface of the object, detecting the sound zone of the portion of the surface of the object, determining a characteristic time corresponding to a time after the heating of the portion of the surface of the object wherein the sound zone of the surface of the object approaches a steady state temperature, normalizing temperature data of the plurality of thermal images with respect to the characteristic time and the steady state temperature, and detecting the defect zone based on differences between normalized temperature data of pixels of the defect zone and normalized temperature data of pixels of the sound.