# Simulation of detecting contact nonlinearity in carbon fibre polymer using ultrasonic nonlinear delayed time reversal

## TL;DR

This paper uses finite element simulations and ultrasonic nonlinear delayed time reversal techniques to detect contact nonlinearity caused by delamination in carbon fibre reinforced polymers, demonstrating effective damage detection without baseline data.

## Contribution

It introduces a novel application of delayed time reversal combined with pulse inversion for detecting contact nonlinearity in composite materials.

## Key findings

- Nonlinear signatures are detectable with pulse inversion.
- Delayed time reversal enhances nonlinear signal detection.
- No baseline data from undamaged medium is needed.

## Abstract

A finite element method simulation of a carbon fibre reinforced polymer block is used to analyse the nonlinearities arising from a contacting delamination gap inside the material. The ultrasonic signal is amplified and nonlinearities are analysed by delayed Time Reversal -- Nonlinear Elastic Wave Spectroscopy signal processing method. This signal processing method allows to focus the wave energy onto the receiving transducer and to modify the focused wave shape, allowing to use several different methods, including pulse inversion, for detecting the nonlinear signature of the damage. It is found that the small crack with contacting acoustic nonlinearity produces a noticeable nonlinear signature when using pulse inversion signal processing, and even higher signature with delayed time reversal, without requiring any baseline information from an undamaged medium.