Many composite materials are used in the aerospace industry because of their excellent mechanical properties. However, the nature of aviation exposes these materials to high temperature and high moisture conditions depending on climate, location, and altitude. Therefore, the molecular arrangement ch...
Many composite materials are used in the aerospace industry because of their excellent mechanical properties. However, the nature of aviation exposes these materials to high temperature and high moisture conditions depending on climate, location, and altitude. Therefore, the molecular arrangement chemical properties, and mechanical properties of composite materials can be changed under these conditions. As a result, surface disruptions and cracks can be created. Consequently, moisture-impregnating defects can be induced due to the crack and delamination of composite materials as they are repeatedly exposed to moisture absorption moisture release, fatigue environment, temperature changes, and fluid pressure changes. This study evaluates the possibility of detecting the moisture-impregnating defects of CFRP and GFRP honeycomb structure sandwich composite materials, which are the composite materials in the aircraft structure, by using an active infrared thermography technology among non-destructive testing methods. In all experiments, it was possible to distinguish the area and a number of CFRP composite materials more clearly than those of GFRP composite material. The highest detection rate was observed in the heating duration of 50 mHz and the low detection rate was at the heating duration of over 500 mHz. The reflection method showed a higher detection rate than the transmission method.
Many composite materials are used in the aerospace industry because of their excellent mechanical properties. However, the nature of aviation exposes these materials to high temperature and high moisture conditions depending on climate, location, and altitude. Therefore, the molecular arrangement chemical properties, and mechanical properties of composite materials can be changed under these conditions. As a result, surface disruptions and cracks can be created. Consequently, moisture-impregnating defects can be induced due to the crack and delamination of composite materials as they are repeatedly exposed to moisture absorption moisture release, fatigue environment, temperature changes, and fluid pressure changes. This study evaluates the possibility of detecting the moisture-impregnating defects of CFRP and GFRP honeycomb structure sandwich composite materials, which are the composite materials in the aircraft structure, by using an active infrared thermography technology among non-destructive testing methods. In all experiments, it was possible to distinguish the area and a number of CFRP composite materials more clearly than those of GFRP composite material. The highest detection rate was observed in the heating duration of 50 mHz and the low detection rate was at the heating duration of over 500 mHz. The reflection method showed a higher detection rate than the transmission method.
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가설 설정
1) In all experiments, it was possible to distinguish the area and a number of CFRP composite material more clearly than those of GFRP composite material. For CFRP composite material, it was possible to identify the area and number of moisture-impregnating defects at 75 and 100% depths under all heating durations.
4) The reflection method showed a high detection rate than transmission method did.
제안 방법
Therefore, it is an important technology, which can detect the defects of the aircraft, a large structure, quickly without contacting it. Consequently, the objectives of the study were to develop an active IRT technology system by using a light source as a heat source to detect the moisture-impregnating defects of composite materials and detect the moistureimpregnating defects occurring in CFRP and GFRP honeycomb sandwich composites [2].
Passive methods detect defects by processing response signals of a target object by transmitting a specific stimulus source of the target object as a harmonic function, unlike active methods. In order to detect defects in honeycomb sandwich composite, this study used the lock in phase technology, which can convert thermography into a signal in a conventional IRT system to effectively detect the defects of flat plate specimens. The IRT testing device is composed of a light source heating device and an IRT camera.
The surface of specimens was painted with black matte paint in order to satisfy the near black condition with a complete emissivity value of 1, which was required to increase the IRT detection sensitivity. Moreover, the experiment was conducted by dividing the testing surface into CFRP and GFRP in order to understand the characteristics of the defect detection rate according to the CFRP and GFRP composite materials [4,5].
Honeycomb cores were fabricated with containing different amounts of moisture in order to evaluate if they can be distinctively detected by IRT under different conditions. The moisture defects were fabricated in the number shapes and a square shape and each cell were fabricated by inserting moisture at 25, 50, 75, and 100 % depths.
Silver 420m model (NETD: 25 mK, Cedip, France) was used as an IRT camera. The surface of specimens was painted with black matte paint in order to satisfy the near black condition with a complete emissivity value of 1, which was required to increase the IRT detection sensitivity. Moreover, the experiment was conducted by dividing the testing surface into CFRP and GFRP in order to understand the characteristics of the defect detection rate according to the CFRP and GFRP composite materials [4,5].
Consequently, it becomes a major factor deforming or destroying the materials. This study used infrared thermography nondestructive testing (IRT-NDT) in order to detect the moisture-impregnating defects of composite materials [1]. IRT-NDT is a defect detecting method, which detects infrared radiated from a specimen, converts the changes in the energy intensity of infrared light into electric signals, and displays the temperature distribution of the specimen.
This study was conducted to analyze the defect detection characteristics of CFRP and GFRP composite materials at different light source heating durations and heating directions for detecting the moisture-impregnating defects of honeycomb sandwich composite material by using the IRT technology.
대상 데이터
0 mm in thickness. SKYFLEX WSN3KY (SK Chemicals) and Mitsubushi Rayon TR-30 (carbon fiber) were used. GFRP composite specimen was GEP7628 and E-glass was applied.
With reference to the previous experiments, the heating durations were classified. Silver 420m model (NETD: 25 mK, Cedip, France) was used as an IRT camera. The surface of specimens was painted with black matte paint in order to satisfy the near black condition with a complete emissivity value of 1, which was required to increase the IRT detection sensitivity.
In order to detect defects in honeycomb sandwich composite, this study used the lock in phase technology, which can convert thermography into a signal in a conventional IRT system to effectively detect the defects of flat plate specimens. The IRT testing device is composed of a light source heating device and an IRT camera. Moreover, the testing device was installed in a thermally insulation chamber to minimize the heat exchange between the test specimens and the outside.
The used CFRP specimen was 300.0 × 300.0 mm in size and 2.0 mm in thickness.
GFRP composite specimen was GEP7628 and E-glass was applied. The used honeycomb material was made by ACT Aero Grade Aramid Honeycomb (ACT). Heat resistant phenolic resin was coated on Nomax T412 aramid paper.
성능/효과
2) The highest detection rate was observed in the heating duration of 50 mHz and the low detection rate was at the heating duration of over 500 mHz. It was possible to determine the area and the number of defects regardless of the composite material.
3) The analysis of defect detection characteristics of moisture-impregnating depth showed that the detection rate was the highest at the 100% depth moisture-impregnating defects. Contrarily, it was the lowest at the 25% depth.
The characteristics of defect detection were compared based on the moisture-impregnating defects at the 75% depth because the moisture-impregnating defects at the 100% depth showed a high defect detection rate regardless of heating duration and composite material type.
The image of defects in the GFRP composite material is shown in Fig 5. The results of the experiment showed that the images of the most distinct defects could be acquired at the heating during of 50 mHz and only the moisture-impregnating defects at 100% depth was clearly observed. The defect detection rate was similar in other depths.
참고문헌 (5)
X. P. V. Maldague, "Theory and Practice of Infrared Technology for Nondestructive Testing," John Wiley & Sons, New York (2001)
G. Gaussorgurs, "Infrared Thermography," Translated by S. Chomet, Champman & Hall, London, pp. 415-452 (1994)
M. Y. Choi, H. S. Park, J. H. Park, W. T. Kim and W. J. Choi. "Study on the qualitative defects detection in composites by optical infrared thermography," Journal of the Korean Society for Nondestructive Testing, Vol. 31, No. 2, pp. 150-156 (2011)
G. Busse, D. Wu and W. Karpen, "Thermal wave imaging with phase sensitive modulated thermography," J. Appl. Phys., Vol. 71, No. 8, pp. 3962-3965 (1992)
V. P, Vavilov, "Infrared and thermal testing: heat transfer," Nondestructive Testing Handbook Series III (3rd Ed.), X. P. V. Maldague Maldague, P. O. Moore Ed., ASNT, Columbus, USA, pp. 54-86 (2001)
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