# Delamination Localization in CFRP Laminates Using One-Way Mixing of Ultrasonic Guided Waves

## TL;DR

This paper introduces a method to detect and locate delamination in carbon fiber composites using ultrasonic waves, which could improve safety in aircraft structures.

## Contribution

The study demonstrates a novel use of one-way mixing of ultrasonic guided waves for precise delamination localization in CFRP laminates.

## Key findings

- One-way mixing of A0 and S0 modes generates difference- and sum-frequency components useful for delamination detection.
- Delamination in CFRP laminates can be localized by adjusting the time delay of the mixing zone.
- The method allows ultrasonic signals to be excited and received on the same side, suitable for buried structures.

## Abstract

What are the main findings?
The one-way mixing of A0 and S0 modes generates both difference-frequency components (A0 modes) and sum-frequency components (A0 and A1 modes), which propagate along both the forward and backward directions.Delamination in CFRP laminates is successfully localized using one-way mixing of ultrasonic guided waves by adjusting the corresponding time delay.

The one-way mixing of A0 and S0 modes generates both difference-frequency components (A0 modes) and sum-frequency components (A0 and A1 modes), which propagate along both the forward and backward directions.

Delamination in CFRP laminates is successfully localized using one-way mixing of ultrasonic guided waves by adjusting the corresponding time delay.

What are the implications of the main findings?
Ultrasonic signals can be excited and received on the same sides, and be applied in buried plate-like or pipe-like structures.We offer an efficient approach for the early damage detection and accurate damage localization of buried plate-like and pipe-like structures.

Ultrasonic signals can be excited and received on the same sides, and be applied in buried plate-like or pipe-like structures.

We offer an efficient approach for the early damage detection and accurate damage localization of buried plate-like and pipe-like structures.

Carbon fiber-reinforced polymer (CFRP) laminates are widely used in aircraft skins due to their advantages of high strength and lightweight properties. However, their laminate structure and energy-absorbing characteristics result in low-energy impact damage, such as delamination, that is often invisible but can lead to catastrophic failure. Consequently, early detection of delamination in CFRP laminates is necessary. Nonlinear ultrasonic guided waves exhibit high sensitivity to delamination, and second harmonics are widely employed. Compared to second harmonics, one-way mixing of ultrasonic guided waves can excite and receive signals simultaneously at the same location, thereby precisely localizing delamination. This capability has the potential for inspecting buried structures. However, existing literature has not yet fully addressed the generation mechanism of one-way mixing in CFRP laminates nor its interaction with delamination. Based on finite element simulation, this study investigates one-way mixing of A0 modes and S0 modes in CFRP laminates. Utilizing pulse-inversion techniques and two-dimensional fast Fourier transforms, the modes and propagation directions of difference-frequency components and sum-frequency components are determined. Furthermore, by utilizing the normalized acoustic nonlinearity parameter χ’ and adjusting the position of the mixing zone through different time delays, delamination in the CFRP laminate is successfully localized.