High-resolution ultrasonic detection of subsurface transverse cracks in CFRP laminates - Simulation and experiments

Abstract

Scanning acoustic microscopy (SAM) has proven to be an effective non-destructive evaluation method for damage detection in composite laminates. A new high-number-of-aperture (HA) 30MHz pulse lens (100-degree aperture angle) can detect microcracks such as transverse cracks which cannot be detected by a conventional 30MHz pulse lens (30-degree aperture angle), in addition to delaminations in CFRP laminates. A picture of SAM images results from elastic characteristics of CFRP. Therefore, an ultrasonic wave propagation analysis in anisotropic media is necessary to understand SAM images. Two types of simulations are conducted in this paper to analyze the effect of waves propagating in CFRP on SAM images. One is a ray tracing simulation to demonstrate the energy flow in the media, and the other is an image construction using the method of angular spectrum. They show that SAM images of transverse cracks are constructed by quasi-longitudinal waves and faster quasitransverse waves.