PHOTO-ACOUSTIC BASED NON-CONTACT AND NON-DESTRUCTIVE EVALUATION FOR DETECTION OF DAMAGE PRECURSORS IN COMPOSITES

Damage precursor in composites can lead to large structural damages, such as delamination, in carbon fiber reinforced plastic (CFRP) composites due to complex load conditions and environmental effects. In addition, multiple types of damage precursors including micro-scale matrix cracks, fiber pull-out from matrix, and fiber breakages, are extremely difficult to detect due to the limitation of resolution of current non-destructive evaluation (NDE) technologies. This paper presents a photo-acoustic based non contact NDE system for the detection of damage precursors with extremely high resolution up to one hundred micrometers. This system consists of three major components: picoseconds pulsed laser based ultrasonic actuator, ultrasound receiver, and data processing and computing subsystem. Picoseconds pulsed laser is used to generate ultrasonic propagations in composites during the NDE process, and the ultrasound signals are recorded by the ultrasound receiver. Three-dimensional microstructure of the individual composites grid within the composite is able to be reconstructed for further analysis. The size and position of the damage precursors are evaluated with high accuracy up to 100 pm. The experimental results demonstrate that this imaging system is able to provide a novel non-contact approach with extremely high resolution for damage detection of CFRP composites. In addition, the developed NDE system has a wide industrial application in aerospace, automobile, civil, mechanical, and other key industries.