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Updated: Nov 3, 2025

Subsurface Defect Localization by Structured Heating Using Laser Projected Photothermal Thermography
Published on: May 15, 2017
Tianfang Gao1, Yishou Wang1, Xinlin Qing1
1School of Aerospace Engineering, Xiamen University, Xiamen 361005, China.
This study introduces a new laser-based method to detect multiple delamination defects in carbon fiber composites. Traditional methods struggle with detecting multiple defects at once. The researchers used a noncontact system with laser excitation and a scanning sensor. They applied aluminum foil to the composite surface to improve signal quality. Different foil sizes and shapes were tested, and a 3 mm by 5 mm rectangle worked best. The wavefield was analyzed using simulated defects made of Teflon. Time-windowed algorithms helped identify each defect. The method successfully detected both single and multiple defects. This approach could improve inspection accuracy for composite materials.
Area of Science:
Background:
Delamination in carbon fiber reinforced plastic (CFRP) composites is a widespread issue. Current inspection methods struggle with detecting multiple defects simultaneously. Prior research has mainly focused on single delamination cases. Traditional ultrasonic testing relies on contact transducers, which can be impractical for certain composite structures. Laser-based techniques offer noncontact advantages but face challenges due to low thermal conductivity. This limitation affects ultrasonic wave excitation in CFRP. The need for a reliable method to detect multiple delaminations remains unmet. This gap motivated the development of a new laser ultrasonic inspection approach.
Purpose Of The Study:
This study aimed to develop a noncontact laser ultrasonic method for detecting multiple delamination defects in CFRP composites. The challenge lies in overcoming the low thermal conductivity of composites during ultrasonic wave excitation. The goal was to find a reliable way to detect multiple defects using laser techniques. The study focused on optimizing the setup for wavefield analysis. Aluminum foil was introduced to improve signal acquisition. The shape and size of the foil were tested to determine optimal conditions. The purpose also included evaluating the effectiveness of time-windowed algorithms for defect detection. This approach could enhance inspection accuracy in composite materials.
Main Methods:
The study used a fully noncontact system with laser excitation and a scanning laser sensor. Aluminum foil was applied to the composite surface to improve signal acquisition. Different foil sizes and shapes were tested to assess their impact on wavefield characteristics. A 3 mm by 5 mm rectangular foil was selected for further experiments. The wavefield was analyzed using single- and multi-layered Teflon inserts as defect simulators. Time windows were chosen based on standard ultrasonic testing references. Algorithms were developed to localize wave energy within these windows. The method was tested on composites with one or multiple Teflon inserts to evaluate performance.
Main Results:
The study found that a 3 mm by 5 mm rectangular aluminum foil provided optimal signal acquisition. The wavefield characteristics varied with foil size and shape. Time-windowed algorithms successfully localized wave energy for defect detection. The method detected both single and multiple Teflon inserts in composite plates. The appropriate time window was crucial for identifying each delamination. The algorithm performed well in distinguishing multiple defects. Signal clarity improved with the use of aluminum foil on the composite surface. These findings suggest the method is effective for noncontact inspection of CFRP composites.
Conclusions:
The study demonstrated that a laser ultrasonic method with aluminum foil can detect multiple delamination defects in CFRP composites. The use of a 3 mm by 5 mm rectangular foil improved signal acquisition. Time-windowed algorithms effectively localized wave energy for defect identification. This approach offers a noncontact solution for inspecting composites with multiple defects. The results align with the goal of developing a reliable inspection method. The method successfully detected both single and multiple Teflon inserts. The findings support the potential of this technique for practical applications. The authors suggest that this approach could enhance inspection accuracy in composite materials.
The method uses laser excitation with aluminum foil to improve signal acquisition, enabling detection of multiple delamination defects in CFRP composites.
A 3 mm by 5 mm rectangular foil provided optimal signal acquisition, as determined through experiments on wavefield characteristics.
The algorithm localizes wave energy within specific time windows, allowing accurate identification of single and multiple delamination defects.
Teflon inserts simulate delamination defects in composite plates, allowing the method to be tested on both single and multiple defect scenarios.
A noncontact system avoids physical contact with the composite surface, making the inspection process safer and more versatile for different materials.
The authors suggest that the method could enhance inspection accuracy in composite materials, particularly in detecting multiple delamination defects.