One-way Lamb and SH mixing method in thin plates with quadratic nonlinearity: Numerical and experimental studies

Eliminating undesired high order harmonics in guided ultrasonic waves using local anti-resonance

A method utilizing the previously unexplored local anti-resonance phenomenon in a Flat Bottom Hole (FBH) is developed to eliminate the interference nonlinearity from undesired sources and enable the precise measurement of ultrasonic nonlinearity from material defects. The local anti-resonance phenomenon in an FBH is investigated using finite element method, on which basis the method to suppress the high order harmonics in incident waves is developed. The effectiveness of the method is validated through the experimental detection of a nonlinear scatterer and comparison with results from traditional configurations. The proposed method demonstrates the capability to precisely and reliably measure defect-specific ultrasonic nonlinearity, thereby advancing the application of the material characterization methods utilizing ultrasonic nonlinearity.

A review in guided-ultrasonic-wave-based structural health monitoring: From fundamental theory to machine learning techniques

The development of structural health monitoring (SHM) techniques is of great importance to improve the structural efficiency and safety. With advantages of long propagation distances, high damage sensitivity, and economic feasibility, guided-ultrasonic-wave-based SHM is recognized as one of the most promising technologies for large-scale engineering structures. However, the propagation characteristics of guided ultrasonic waves in in-service engineering structures are highly complex, which results in difficulties in developing precise and efficient signal feature mining methods. The damage identification efficiency and reliability of existing guided ultrasonic wave methods cannot meet engineering requirements. With the development of machine learning (ML), numerous researchers have proposed improved ML methods that can be incorporated into guided ultrasonic wave diagnostic techniques for SHM of actual engineering structures. To highlight their contributions, this paper provides a state-of-the-art overview of the guided-wave-based SHM techniques enabled by ML methods. Accordingly, multiple stages required for ML-based guided ultrasonic wave techniques are discussed, including guided ultrasonic wave propagation modeling, guided ultrasonic wave data acquisition, wave signal pre-processing, guided wave data-based ML modeling, and physics-based ML modeling. By placing ML methods in the context of the guided-wave-based SHM for actual engineering structures, this paper also provides insights into future prospects and research strategies.