Composite Joint Inspection Using Inductive Thermography
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Solution Overview
Problem
Existing non-destructive testing methods struggle to reliably assess the quality of composite component joints, particularly those involving mixed-material connections, as they fail to account for the transition between different materials and potential defects like air gaps and cracks.
Innovation Solution
A method using thermal imaging and inductive excitation to evaluate the heat conduction through the connection point, capturing reference and test images at specific times to calculate temperature changes, allowing differentiation between 'OK' and 'Not OK' joints based on predefined temperature intervals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional non-destructive testing methods are used for composite component joints, then the testing process is simplified, but the reliability of quality assessment deteriorates due to inability to detect defects like air gaps and cracks in mixed-material connections
Solution Approach 1:
The evaluation area on the head surface is divided into multiple sub-areas (pixels), and temperature changes are evaluated independently for each sub-area. This segmentation allows detection of localized defects such as air gaps and cracks that would be invisible in a uniform evaluation, thereby improving reliability without requiring complex additional hardware.
Solution Approach 2:
A reference image is captured before inductive excitation to establish a baseline temperature distribution. This preliminary action enables comparison with the test image taken after excitation, allowing detection of temperature changes that indicate defects. The reference measurement is performed in advance under identical conditions to ensure reliable defect detection.
2Measurement precision
If thermal imaging with inductive excitation is used to detect defects like air gaps and cracks, then measurement precision improves, but the testing time increases due to sequential image capture and evaluation
Solution Approach 1:
The method uses periodic inductive excitation followed by sequential image capture at specific time points (reference image before excitation, test image after excitation). This periodic action allows precise defect detection through temperature change analysis while maintaining efficient testing节奏. The timing is optimized to capture thermal responses that indicate defects without excessive waiting time.
3Reliability
If the evaluation considers transition zones between different materials, then comprehensive quality assessment improves, but the complexity of evaluating multiple heat conduction paths increases
Solution Approach 1:
Different sub-areas of the head surface are evaluated with different criteria based on their local characteristics. Sub-areas corresponding to transition zones between different materials are analyzed for temperature changes that indicate defects specific to those regions. This local quality approach allows comprehensive evaluation of multiple heat conduction paths while managing complexity through localized evaluation rules.
Solution Approach 2:
The head of the connecting element serves as an intermediary that translates internal connection quality (including transition zone integrity) into observable temperature changes on its surface. By evaluating temperature changes on the head surface, the method indirectly assesses the quality of transitions between different materials without requiring direct measurement of internal interfaces.
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 reliable, non-destructive evaluation of composite joints by identifying defects such as cracks and air gaps, ensuring both internal and external quality assessment with high accuracy and efficiency.
Implementation Method 1
the component assembly to be tested comprises a base layer, at least one cover layer and a connecting element with a head and a shank. The inductor inductively excites the base layer at a specific excitation time via an excitation pulse over an effective surface.
Implementation Method 2
evaluating heat conduction from the base layer via the connection point of the connecting element with the base layer and the cover layer and the connection of the head to the cover layer
Implementation Method 3
The temperature behavior is preferably recorded by a thermal imaging camera.
Implementation Method 4
The absolute temperature is measured at the precise moment when the heat radiation from the weld reaches the surface of the top layer.
Data Source
Figure 1a~2b
Figure 2c
Figure 3
AI summary
The invention relates to a method for non-destructively testing a connection point (10) in a component assembly, comprising a base layer (14), at least one cover layer (16), and a connection element (12a, 12b) with a head (18a, 18b) and a shaft (22a, 22b). The connection point (10) is formed between the shaft (22a, 22b) of the connection element (12a, 12b) and the base layer (14), and the cover layer (16) has a thermal conductivity which is greater than that of the base layer (14) and the connection element (12a, 12b). The test is carried out by means of a thermal imaging camera (34) and an inductor (36) which is arranged on the component assembly side opposite the thermal imaging camera (34). The inductor (36) is inductively excited by means of a pulse via an active surface of the base layer (14) at an excitation time. Furthermore: • at a first detection time, a reference image of the connection point (10) is captured by the thermal imaging camera (34), the head (18a, 18) being imaged in said reference image as a head surface area (20a, 20b); • at a second detection time (44), a test image which is analogous to the reference image is captured, said second detection time (44) occurring after the first detection time and a specified duration after the excitation time; • an analysis region (42) is defined in the test image and/or in the reference image, wherein the analysis region (42) at least partly comprises the head surface (20a, 20b), and the analysis region (42) is divided into sub-regions, in particular pixels, said sub-regions being assigned a temperature value; • a temperature change value is formed using a rule on the basis of the temperature values of the corresponding sub-regions of the reference and test image; • on the basis of the temperature change value, an "OK" value is formed if the temperature change lies in a pre-defined temperature interval with at least one lower boundary; and • the connection point (10) is classified in that the sum of the sub-regions with an "OK" value is compared with a reference interval with at least one specified lower interval boundary. The connection point (10) is classified as an "OK" connection if the sum lies in the reference interval, otherwise the connection point (10) is classified as a "not OK" connection.