Scanning laser thermographic system for non-destructive evaluation of incipient thermal damages in aircraft composite panel
Composite materials applied in aerospace structure are getting popular due to advantages such as high specific strength and stiffness with favorable strength to weight ratio. However, incipient thermal damage (ITD) that can cause reduction of 60% of composite mechanical strength are still unab...
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| Main Author: | |
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| Format: | Thesis |
| Language: | English |
| Published: |
2018
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/75698/1/FK%202018%20141%20-%20IR.pdf |
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| Summary: | Composite materials applied in aerospace structure are getting popular due to
advantages such as high specific strength and stiffness with favorable strength to
weight ratio. However, incipient thermal damage (ITD) that can cause reduction of
60% of composite mechanical strength are still unable to be detected using
conventional NDT&E method.
This project aims to develop an effective NDT&E tool that can detect or evaluate ITD
through these three objectives. First, to synchronize laser system, laser scanner system
and thermal imager as an active infrared imaging system. Second, to develop
corresponding data acquisition and noise removal algorithm for extraction of local
temperature-time profiles. Third, to validate the effectiveness of the system and
algorithm for non-destructive evaluation of ITD in glass fiber reinforced composite
plate (GFRP). In correspondence to research objective, laser pulse was implemented
as a powerful thermal energy source in thermography method for evaluating ITD.
GFRP plate was insulted with high temperature at range of material glass transition
temperature, 0.8T g,1.0 T g,1.1 T g,1.2 T g and 1.3 T g (T = 97°C,121°C,133°C,145°C and
157°C) at time t = 120, 60, 30, 15, 10 and 5 minutes to prepare ITD as well as thermal
damage (TD) for reference. Focus was done on ITD which are insulted at borderline
temperature of T g with relatively longer insult time; 0.8T g and 1.0 T g at t = 120,60,30
minute. ITD evaluation in this study are realized in the form of percentage difference
between damage and reference derived from thermal contrast base principle.
Following this, result gained represents outliers with respective to reference area and
thus indicate detection of damage. Result gained for ITD at 0.8 T g are 1.93851%,
0.30561% and 0.20913% meanwhile 2.02966%, 1.73518% and 0.53167% at 1.0T g for t = 120,60,30 minute. A gradual decrement trend can be seen from longer
insult time to lower insult time to indicate level of severity on damage detected.
According to system resolution and capability, these values are within the range and
thus proves the detection of ITD. Further verification done using ultrasonic method
also proves the inability of conventional NDT&E method to detect ITD as expected.
Hence, with proposed Scanning Laser Thermographic system, all ITD that were
insulted with temperature at borderline of T g at relatively longer insult time had been
successfully detected at minimum of 0.20913% at insult temperature; 0.8 T g with insult
time t = 30 minute and at maximum of 2.02966% at insult temperature; 1.0 T g with
insult time t = 120 minute. |
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