Numerical and Experimental Investigation of Focused Ultrasonic Wave Interaction with Out-of-Plane Fiber Waviness in CFRP Laminates
Pulkit Kumar, Junzhen Wang*, Daniel J. Barnard
Center for Nondestructive Evaluation, Iowa State University, Ames, IA, USA
* Corresponding Author: Junzhen Wang. Email: 
Structural Durability & Health Monitoring https://doi.org/10.32604/sdhm.2026.083081
Received 28 March 2026; Accepted 09 June 2026; Published online 13 July 2026
Abstract
Quantitative characterization of non-uniform out-of-plane fiber waviness in carbon fiber reinforced polymer (CFRP) laminates remains a significant challenge in ultrasonic testing-based nondestructive evaluation (NDE). To elucidate the distinctive interaction mechanisms between a focused normal-incidence ultrasonic wave and embedded wrinkle defects, this study presents a systematic numerical and experimental investigation. Two-dimensional multi-physics finite element models are initially developed to reveal the wave scattering features induced by both convex and concave waviness. The models explicitly account for both the geometric variation of fiber waviness and the accompanying resin-rich and resin-poor zones. In addition, immersion ultrasonic pulse-echo C-scan and pitch-catch A-scan experiments are conducted to validate the numerical predictions. The C-scan approach, employing a focused ultrasonic beam incident on the top surface of the composite plate, enables the successful imaging of spatially varying, successive convex and concave waviness regions. Analysis of the pulse-echo A-scan responses reveals that the temporal signals obtained from convex waviness exhibit greater similarity to those from pristine laminates than those generated by concave waviness. Furthermore, shifts in the resonance frequencies effectively capture local changes in the effective ply thickness caused by waviness-induced geometric variations. The experimentally obtained scattering patterns show remarkable agreement with the simulation results, highlighting the additional lateral scattering phenomena associated with convex waviness. These results demonstrate that the wave scattering features induced by non-uniform out-of-plane fiber waviness can serve as reliable indicators for wrinkle detection. Furthermore, the findings of this work provide valuable insights for the development of more effective ultrasonic inspection strategies for characterizing out-of-plane fiber waviness in CFRP laminates.
Keywords
Ultrasonic testing; fiber waviness; carbon fiber reinforced polymer; wave scattering; nondestructive evaluation; numerical simulation
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