研究目的
To develop a photoacoustic non-destructive evaluation (pNDE) system for the detection of multi-scale damage in carbon fiber-reinforced plastic (CFRP) composites with ultrahigh resolution.
研究成果
The developed pNDE system shows great potential for damage detection and quality assessment in a broad range of engineering applications, including aerospace, automobile, and civil industries. Micro-scale damage precursors in composite laminate samples were identified and represented using 2D and 3D images with a high spatial resolution of 60 μm. Macro-scale impact damage, including delamination and transverse ply cracks, was quickly detected and represented using the ultrasonic C-scan mode.
研究不足
The current pNDE detection speed was limited by the single ultrasonic probe for signal collection during the scanning. Implementing a pair of galvanometer mirrors with optical scanning can dramatically improve the imaging speed. Further increase in laser PRR has been limited mostly by the time required to store raw data and the ultrasound propagation time inside the CFRP composites.
1：Experimental Design and Method Selection:
The pNDE system consists of a picosecond pulsed laser-based ultrasonic actuator, an ultrasound receiver, and a data acquisition/computing subsystem. High-frequency ultrasound is generated by pulsed laser and recorded by an ultrasound receiver. A two-dimensional back projection algorithm is implemented to reconstruct pNDE images from the recorded ultrasound signals.
2：Sample Selection and Data Sources:
CFRP composite samples were fabricated using commercial prepreg carbon fiber fabrics. Micro-scale damage precursors were generated by cutting shallow X-shaped notches on the composite sample's surface. Macro-scale damage was generated under low-velocity impact load.
3：List of Experimental Equipment and Materials:
Picosecond laser (COMPILER 532/266, Passat, Ltd.), PZT ultrasound transducers (V2062 and U8517149, Olympus NDT), low-noise preamplifier (ZFL-1000LN+, Mini-Circuits), second-stage amplifier (ZFL-500+, Mini-Circuits), data acquisition card (NI PCI-5153EX, National Instruments).
4：Experimental Procedures and Operational Workflow:
The composite sample was shifted on a 2D translation stage at an average translation speed of 0.05 mm/s. The position-synchronized output of the translator triggered the pulsed laser. Ultrasonic signals were recorded and analyzed in A-scan, B-scan, and C-scan modes.
5：05 mm/s. The position-synchronized output of the translator triggered the pulsed laser. Ultrasonic signals were recorded and analyzed in A-scan, B-scan, and C-scan modes.
Data Analysis Methods:
5. Data Analysis Methods: Back projection-based photoacoustic reconstruction was performed in MATLAB. Time gain correction (TGC) function was applied to all recorded photoacoustic signals for acoustic attenuation compensation.
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