This paper presents a photoacoustic non-destructive evaluation (pNDE) system with an ultrahigh resolution for the detection of multi-scale damage in carbon fiber-reinforced plastic (CFRP) composites. The pNDE system consists of three main components: a picosecond pulsed laser-based ultrasonic actuator, an ultrasound receiver, and a data acquisition/computing subsystem. During the operation, high-frequency ultrasound is generated by pulsed laser and recorded by an ultrasound receiver. By implementing a two-dimensional back projection algorithm, pNDE images can be reconstructed from the recorded ultrasound signals to represent the embedded damage. Both potential macroscopic and microscopic damages, such as surface notches and delamination in CFRP, can be identified by examining the reconstructed pNDE images. Three ultrasonic presentation modes including A-scan, B-scan, and C-scan are employed to analyze the recorded signals for the representation of the detected micro-scale damage in two-dimensional and three-dimensional images with a high spatial resolution of up to 60 µm. Macro-scale delamination and transverse ply cracks are clearly visualized, identifying the edges of the damaged area. The results of the study demonstrate that the developed pNDE system provides a non-destructive and robust approach for multi-scale damage detection in composite materials.
X-ray-induced acoustic computed tomography (XACT) has emerged as a promising imaging modality with broad applications in both biomedicine and nondestructive testing. The previous XACT imaging systems require thousands of averages to achieve reasonable images. Here, we report the experimental demonstration of single-shot XACT imaging of a metal object using a single-shot 50 ns x-ray pulse. A two-stage dedicated amplification and a 128-channel parallel data acquisition configuration were introduced for XACT imaging to enable sufficient acoustic signal amplification and maintain an overall low noise level for single-shot XACT imaging. Details of the system design are presented; the improved signal-to-noise ratio (>23 dB) and image reconstruction have been demonstrated with a ring ultrasound transducer array imaging system. The study paves the way for realizing real-time XACT imaging and its potential applications in image-guided intervention.
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