Ultrasonic Guided Wave Propagation Research Articles

Effects of high-amplitude low-frequency structural vibrations and machinery sound waves on ultrasonic guided wave propagation for health monitoring of composite aircraft primary structures

A reliable damage diagnostic by ultrasonic guided wave (GW) based structural health monitoring (SHM) can only be achieved if the physical interactions between wave propagation, the SHM system and environmental factors are fully understood. The purpose of this research was to gain knowledge about the effects of high-amplitude low-frequency structural vibrations (HA-LFV) and audible sound waves (SW) on ultrasonic GW propagation. Measurements were performed on a stiffened panel of a full-scale composite torsion box containing barely visible impact damage. Time-domain analysis of the filtered GW signals revealed that the main effect of HA-LFV was the presence of coherent noise. This was interpreted as the consequence of superposition of multiple dispersive wave groups produced by mode conversion at the moment of reflection on the corrugated panel surfaces during propagation. It was also observed that the coherent noise amplitude depends on the amplitude of the HA-LFV, and on the ratio between the HA-LFV frequency and the ultrasonic excitation frequency. These relationships can potentially be explored for the development of a HA-LFV compensation mechanism to enable in-service GW based damage diagnostics. In contrast, GW signals in the cases with audible SW present were almost unaffected. It was concluded that there is strong evidence supporting the hypothesis that ultrasonic GW propagation with HA-LFV effects can be analysed under the assumption of a permanently corrugated structure.

Automatic Guided Waves Data Transmission System Using an Oil Industry Multiwire Cable.

Alternative wireless data communication systems are a necessity in industries that operate in harsh environments such as the oil and gas industry. Ultrasonic guided wave propagation through solid metallic structures, such as metal barriers, rods, and multiwire cables, have been proposed for data transmission purposes. In this context, multiwire cables have been explored as a communication media for the transmission of encoded ultrasonic guided waves. This work presents the proprietary hardware design and implementation of an automatic data transmission system based on the propagation of ultrasonic guided waves using as communication channels a high-temperature and corrosion-resistant oil industry multiwire cable. A dedicated communication protocol has been implemented at physical and data link layers, which involved pulse position modulation (PPM), digital signal processing (DSP), and an integrity validation byte. The data transmission system was composed of an ultrasonic guided waves PPM encoded data transmitter, a 1K22 MP-35N multiwire cable, a hardware preamplifier, a data acquisition module, a real-time (RT) DSP LabVIEW (National Instruments, Austin, TX) based demodulator, and a human-machine interface (HMI) running on a personal computer. To evaluate the communication system, the transmitter generated 60 kHz PPM energy packets containing three different bytes and their corresponding integrity validation bytes. Experimental tests were conducted in the laboratory using 1 and 10 m length cables. Although a dispersive solid elastic media was used as a communication channel, results showed that digital data transmission rates, up to 470 bps, were effectively validated.

Optimization of ultrasonic guided wave inspection in structural health monitoring based on thermal sensitivity evaluation

Damage detection in a mechanical structure using ultrasonic guided waves becomes even more problematic when the effect of variation in environmental and operating conditions, such as mechanical noise, temperature, flow rate, inner pressure, etc. is taken into account. The variation in these environmental and operating conditions can degrade the accuracy of the damage inspection process. The basic purpose of current research work is to propose a finite element model–based simulation model to identify and estimate the influence of environmental temperature on the measured signal and meanwhile perceive the temperature invariant points to provide an optimal baseline for thermal attenuation in real-time ultrasonic guided wave inspections. This model signifies the variation in material elastic properties, thermal sensitivities, and the abrupt changes in group and phase velocities of S0 wave mode with temperature. A low bandpass filter is used to keep the excitation frequency in a certain range and remove the noise from it. The numerical investigation is achieved in [Formula: see text] on the basis of six parameters, including variation in strain rate and stress, the amplitude of displacement, symmetric and anti-symmetric dispersion curves, time of flight, group velocity, and natural frequency of the beam. A wave velocity function has been generated in the Matlab® environment to calculate the group velocity of guided waves considering the effect of both temperature and excitation frequency. A linear fit curve (first-degree polynomial) is utilized in this function to analyze the effect of temperature on group velocity. An analytical estimation has also been applied to evaluate the impact of temperature on the material properties and damage detection. The simulation model is validated against the analytical group velocity results and experimental wave amplitude results. The comparison with minute percentage error is achieved in a convincing manner. The proposed thermal sensitivity simulation model is more efficient and reliable as compared to optimal baseline selection and baseline signal stretch. It detects not only the occurrence of damage but also examines the influence of environmental temperature on ultrasonic guided wave propagation and perceives the temperature invariant points to provide an optimal baseline for thermal attenuation in real-time ultrasonic guided wave inspections. This model can also be implemented practically in transportation and industrial applications to ensure structural reliability.

An Improved Matching Pursuit-Based Temperature and Load Compensation Method for Ultrasonic Guided Wave Signals

Temperature and load variations significantly affect ultrasonic guided wave propagation and therefore lead to the increasing of diagnostic uncertainty of the guided wave-based structural health monitoring system, which may cause false reports and false positives and limit the practical application of the method. Most of the existing researches focus on guided wave compensation for a single factor. Therefore it's an important challenge that how to compensate for guided waves under the influence of multiple environmental factors. This study firstly analyzes the coupled effect of temperature and load variations on the propagation characteristics of guided waves. It has been found that the two factors variations cause a highly non-linear effect on the change of guided wave signal characteristics. Based on the previous work of temperature compensation methods based on matching pursuit, this paper develops an improved matching pursuit-based temperature and load compensation method for ultrasonic guided wave signals. The developed method is featured with that the compensation performance can be improved by multiple iteration compensation of the residual signal. By improving the selection of the reference signal set, the developed environmental compensation method based on the reference signal matching is used to realize the compensation under the influence of the temperature-load coupling effect, and the experimental results verify the effectiveness of the proposed compensation method and the proposed compensation method proves to be effective under the influence of temperature and load variations.

Ultrasonic guided wave propagation in a dental implant

Ultrasound techniques can be used to characterize and stimulate dental implant osseointegration. The acoustical energy transmitted to the bone-implant interface is an important parameter that must be controlled for both applications, since it should be sufficiently low to avoid damaging the surrounding tissues, but sufficiently high for stimulation purposes to enhance bone growth. However, the interaction between an ultrasonic wave and a dental implant remains unclear. The objective of this study combining experimental, analytical and numerical approaches is to investigate the propagation of an ultrasonic wave in a dental implant by assessing the amplitude of the displacements along the implant axis. An ultrasonic transducer was excited in transient regime at 10 MHz. Laser interferometric techniques were employed to measure the amplitude of the displacements, which varied between 5 and 12 nm according to the position. The results show the propagation of a guided wave mode along the implant axis with a velocity of first arriving signal equal to 2110 m s−1 and frequency components lower than 1 MHz, which was confirmed by the analytical and numerical results. This work paves the way to improve techniques for the characterization and stimulation of the bone-implant interface.

A wave packet enriched finite element for electroelastic wave propagation problems

A two dimensional finite element (FE) is developed by enriching the conventional Lagrange interpolation functions with local element domain wave functions, for accurate solution of general wave propagation problems in piezoelastic media. The enrichment functions, applied to both displacement and electric potential fields, satisfy the partition of unity condition, and vanish at the nodes. The formulation is developed using the extended Hamilton’s principle for piezoelastic solids, considering two-way electromechanical coupling. The enriched FE is shown to perform equally well in terms of computational efficiency and accuracy for broadband impact induced electroelastic wave to narrowband ultrasonic guided wave propagation problems, unlike the other available elements. The solution for impact in a piezoelectric plate is shown to alleviate the spurious undulations in both velocity and electric potential fields, which are encountered in the conventional FE solutions. For the problem of high frequency Lamb wave actuation and sensing in a thin plate bonded with piezoelectric actuator/sensor patches, the element shows significant improvement in the computational efficiency over the conventional FE. Further, the free edge effect of steep gradients in the shear stress distribution at the actuator-plate interface is accurately captured by the proposed element using much fewer degrees of freedom than the conventional FE.

Nondestructive Analysis of Debonds in a Composite Structure under Variable Temperature Conditions.

This paper presents a nondestructive analysis of debonds in an adhesively-bonded carbon-fibre reinforced composite structure under variable temperature conditions. Towards this, ultrasonic guided wave propagation based experimental analysis and numerical simulations are carried out for a sample composite structure to investigate the wave propagation characteristics and detect debonds under variable operating temperature conditions. The analysis revealed that the presence of debonds in the structure significantly reduces the wave mode amplitudes, and this effect further increases with the increase in ambient temperature and debond size. Based on the debond induced differential amplitude phenomenon, an online monitoring strategy is proposed that directly uses the guided wave signals from the distributed piezoelectric sensor network to localize the hidden debonds in the structure. Debond index maps generated from the proposed monitoring strategy show the debond identification potential in the adhesively-bonded composite structure. The accuracy of the monitoring strategy is successfully verified with non-contact active infrared-thermography analysis results. The effectiveness of the proposed monitoring strategy is further investigated for the variable debond size and ambient temperature conditions. The study establishes the potential for using the proposed damage index constructed from the differential guided wave signal features as a basis for localization and characterization of debond damages in operational composite structures.

Ultrasonic de-icing of wind turbine blades: Performance comparison of perspective transducers

Icing brings a significant harm for renewable energy installations and in aviation. Wind turbine blades, high voltage transmission lines, photovoltaic panels, airplane wing and helicopter blades often suffer from icing, which causes considerable losses of energy due to performance deterioration. Energy efficiency is a pivotal issue for wind turbines. Active ice mitigation system for wind turbines has not yet been commercialized due to the difficulty in overcoming the higher costs associated with a decrease in turbine power output. Ultrasonic de-icing as a new and potential energy-efficient de-icing technique has raised the increasing interest with its energy-saving effect, low running costs, good applicability and environmental conservation. Basic parameters of semi-hard lead zirconate titanate (PZT-4), lead magnesium niobate-lead titanate (PMN-PT) and lithium niobate (LiNbO3) materials are compared in this paper in terms of ultrasonic de-icing feasibility and efficiency. The theoretical models with applied ultrasonic guided wave propagation theory are established and the following simulations are carried out. The experiments with aluminum and composite plates are conducted to demonstrate the feasibility of ultrasonic de-icing and correspondence with simulations. Comparing with the lead zirconate titanate transducer, lithium niobate actuator shows the advantages both in performance and in environmental concern.

Modeling concept and numerical simulation of ultrasonic wave propagation in a moving fluid-structure domain based on a monolithic approach

• New multiphysics model for structural health monitoring (SHM) systems for alternative material specifications. • The problem of ultrasonic guided waves (UGWs) propagation in fluidstructure interface features the NDT principle. • Modeling the UGWs propagation with/without the fluid-structure interaction (FSI) problem in the ALE framework. • The double-loop linear solving technique applied for the time-dependent coupled models using monolithic approach. • Numerical simulations of multiphysics problems, contrasted against the approximate experimental data. In the present study, we propose a novel multiphysics model that merges two time-dependent problems – the Fluid-Structure Interaction (FSI) and the ultrasonic wave propagation in a fluid-structure domain with a one directional coupling from the FSI problem to the ultrasonic wave propagation problem. This model is referred to as the “eXtended fluid-structure interaction (eXFSI)” problem. This model comprises isothermal , incompressible Navier–Stokes equations with nonlinear elastodynamics using the Saint-Venant Kirchhoff solid model. The ultrasonic wave propagation problem comprises monolithically coupled acoustic and elastic wave equations. To ensure that the fluid and structure domains are conforming, we use the ALE technique. The solution principle for the coupled problem is to first solve the FSI problem and then to solve the wave propagation problem. Accordingly, the boundary conditions for the wave propagation problem are automatically adopted from the FSI problem at each time step. The overall problem is highly nonlinear, which is tackled via a Newton-like method. The model is verified using several alternative domain configurations . To ensure the credibility of the modeling approach, the numerical solution is contrasted against experimental data.

Fatigue crack detection under the vibration condition based on ultrasonic guided waves

Ultrasonic guided wave is an encouraging tool in structural health monitoring for civil, mechanical, ship, and aerospace devices. Most of heavy devices required a long-time running during the service, and the structure of these devices is under the vibration condition due to their inherent properties and working condition. This article mainly researches fatigue crack detection in vibration condition caused by operation using ultrasonic guided waves, aiming to study the application of ultrasonic guided waves in the field of structure dynamics. The detection method based on the difference index and the sequence curve of difference index between different states of crack is proposed to detect fatigue crack in vibration condition. The experiments are carried out on the fatigue testing platform and the vibration test-bed to investigate the relationship between opening states of fatigue crack and the difference index value of ultrasonic guided waves. In order to reduce the influence of loads applied by the fatigue testing platform on ultrasonic guided waves propagation, the initial experiment is first carried out to select the range of applied loads which have minimal influence on wave propagation. The results show that loads from 0 to 24 MPa have minimal effect on ultrasonic guided waves, and the difference index values of intact beam and cracked beam are in different orders of magnitude. Therefore, the method based on difference index value and sequence of difference index is credible to detect fatigue crack for structure in vibration condition.

Modeling and simulation of Ultrasonic Guided Waves propagation in the fluid-structure domain by a monolithic approach

The present study introduces the coupled multiphysics model as part of the structural health monitoring (SHM) system. In particular, the Ultrasonic Guided Waves (UGWs) propagation is tracked in order to identify the damage to the structure. For this purpose, a multiphysics mathematical model is proposed. The model constitutes a monolithically coupled system of acoustic and elastic wave equations (WpFSI problem) where the wave signal displacement measurements are analyzed as the UGWs propagates in the solid, fluid and their interface. The ultimate goal of this paper is to explore and develop the efficient numerical solution of the WpFSI problem using the finite element method. A detailed description of the modeling framework and conditions that facilitate the coupling is provided. To couple the displacement-based acoustic wave equations for the isothermal fluid with elastic wave equations for the Saint Venant-Kirchhoff material model, the present study uses a monolithic solution algorithm. In particular, at each time step, wave equations are transformed to a fixed reference configuration via the arbitrary Lagrangian-Eulerian (ALE) mapping and automatically adopt the boundary conditions from the previous time step. The implementation is accomplished via the finite element library deal.II (Goll et al., 2017) based software toolbox DOpElib (Bangerth et al., 2007) which provides modularized higher level algorithms. Beyond SHM systems, the model is relevant for problems from biomechanics and biomedicine, vibromechanics, poroelasticity as well as subsurface and porous media flow. The model developed here serves as a first step towards the on-line SHM system modeling, where structural dynamics are accounted for.

Numerical and Experimental Investigation of Guided Wave Propagation in a Multi-Wire Cable

Ultrasonic guided waves (UGWs) have attracted attention in the nondestructive testing and structural health monitoring (SHM) of multi-wire cables. They offer such advantages as a single measurement, wide coverage of the acoustic field, and long-range propagation ability. However, the mechanical coupling of multi-wire structures complicates the propagation behaviors of guided waves and signal interpretation. In this paper, UGW propagation in these waveguides is investigated theoretically, numerically, and experimentally from the perspective of dispersion and wave structure, contact acoustic nonlinearity (CAN), and wave energy transfer. Although the performance of all possible propagating wave modes in a multi-wire cable at different frequencies could be obtained by dispersion analysis, it is ineffective to analyze the frequency behaviors of the wave signals of a certain mode, which could be analyzed using the CAN effect. The CAN phenomenon of two mechanically coupled wires in contact was observed, which was demonstrated by numerical guided wave simulation and experiments. Additionally, the measured guided wave energy of wires located in different layers of an aluminum conductor steel-reinforced cable accords with the theoretical prediction. The model of wave energy distribution in different layers of a cable also could be used to optimize the excitation power of transducers and determine the effective monitoring range of SHM.

Numerical study and comparison of alternative time discretization schemes for an ultrasonic guided wave propagation problem coupled with fluid–structure interaction

Discretization is a crucial step in the numerical treatment of coupled multiphysics problems. In the present paper, we focus on the numerical solution of ultrasonic guided waves (UGWs) propagation problem coupled with fluid–structure interaction. We track UGWs propagation through fluid, solid and their interface, where the structure is in motion. Discretization is done via a Finite Element method. For this, we follow the Rothe method, in which discretization in time is followed by space discretization, solving the resulting problem according to the monolithic approach. Further, we provide a systematic analysis of alternative discretization schemes, time-steps, and mesh refinements. Specifically, we contrast one first-order time discretization scheme (cf. backward Euler) and three second-order schemes (cf. Crank–Nicolson, shifted Crank–Nicolson, and fractional-step-θ). First, we establish the robustness of the convergence result. Second, we estimate the experimental order of convergence for alternative schemes and space–time discretization combinations.

Rail defect inspection based on coupled structural–acoustic analysis

The inspection of rail defects is of importance in high-speed railway operation and maintenance. As a highly efficient method for both nondestructive testing and structural health monitoring of the rail, ultrasonic guided waves (UGWs) inspection provide increased sensitivity to smaller defects. These advantages can be fully exploited only if the complexities of UGWs propagation between the medium of air and rail are unveiled and managed for the given inspection method. The development and validation of modeling procedure for the rail based on coupled structural–acoustic model is presented in this paper. Acoustic–structure interaction between air and rail is simulated based on COMSOL Multiphysics software. The transient response and natural characteristics of UGWs in the rail was computed and predicted. Moreover, the displacement distribution of UGWs in the defective rail and nondefective rail are analyzed both in time and frequency domain. A feasible method for detecting small defects in the rail is proposed in the paper. The results indicated that a defect of 8 mm in rail head can be inspected effectively using UGWs with frequencies of 40 kHz and above. And for small defects in rail web, the X-crystallographic direction ultrasonic transducer should be chosen for inspection.

PZT-Based Ultrasonic Guided Wave Frequency Dispersion Characteristics of Tubular Structures for Different Interfacial Boundaries.

For tubular structures, ultrasonic guided waves (UGWs) which are closely related to interfacial boundary conditions such as gas, liquid and solid materials, are usually used in damage detection. Due to the different phase materials inside tubes, the interfacial boundary (connection) conditions are variable, which has a great influence on the dispersion-related UGW propagation characteristics. However, most UGW-based damage detection methods only consider the pipeline structures as hollow tubes, ignoring the interfacial boundary condition influences on the UGW propagation. Based on the UGW theory, this paper aims to propose a novel method for describing the UGW propagation characteristics for different interfaces, and lay a foundation for the UGW-based tubular structure damage detection. Based on the Navier’s equation of motion and combined with interfacial boundary conditions and coordinate conditions, the dispersion equations for a hollow steel tube, a tube filled with liquid, and a concrete filled steel tube (CFST) were established, respectively. Under the given conditions of both materials and geometric parameters, the transcendental dispersion equations were established and solved by using a numerical method. The UGW propagation characteristics in different interfaces were classified and discussed, and the dispersion curves of both group and phase velocities are drawn. To validate the efficiency of theoretical and numerical results, three kinds of model tubular structure experiments filled in air (hollow), water and concrete, respectively, were performed based on lead zirconate titanate (PZT) transducer UGWs. The results showed that the UGWs propagation in different interfaces has the dispersion and multi-modes characters, which are not only related to the product of frequency and thickness, but also to the internal dielectric material parameters and interfacial boundary conditions.

Selective generation of ultrasonic guided waves in a bi-dimensional waveguide

Non-destructive testing and structural health monitoring systems based on ultrasonic guided waves propagation are particularly used in civil engineering or aerospace applications. Guided waves are commonly employed as they propagate through large distances and can inspect the entire cross-section of the structure. In order to optimize the sensitivity to a specific damage type, it is often preferable to generate a carefully selected pure mode. Although single-mode generation has been achieved for Lamb waves in infinite plate-like structures, such generation is much harder in a rectangular bar since less conventional modes propagate in finite cross-section waveguides. This article presents a general methodology for mode selective generation in a finite cross-section waveguide, using multiple transducers. Obtaining modal identification through conventional spatial Fourier transform on a longitudinal scan has proven to be inconvenient for waveguides with a two-dimensional cross-section. An alternative technique is proposed, consisting in the decomposition over the modal basis of the three displacement components measured across the bar width at the bar surface. The methodology is applied to the single-mode generation within an aluminum bar instrumented with eight piezoelectric transducers bonded to the surface. The modal basis is obtained with a semi-analytical finite element method. Numerical simulations and experiments using a three-dimensional laser Doppler vibrometer are conducted in order to validate the methodology.

Characterization of the Use of Low Frequency Ultrasonic Guided Waves to Detect Fouling Deposition in Pipelines.

The accumulation of fouling within a structure is a well-known and costly problem across many industries. The build-up is dependent on the environmental conditions surrounding the fouled structure. Many attempts have been made to detect fouling accumulation in critical engineering structures and to optimize the application of power ultrasonic fouling removal procedures, i.e., flow monitoring, ultrasonic guided waves and thermal imaging. In recent years, the use of ultrasonic guided waves has been identified as a promising technology to detect fouling deposition/growth. This technology also has the capability to assess structural health; an added value to the industry. The use of ultrasonic guided waves for structural health monitoring is established but fouling detection using ultrasonic guided waves is still in its infancy. The present study focuses on the characterization of fouling detection using ultrasonic guided waves. A 6.2-m long 6-inch schedule 40 carbon steel pipe has been used to study the effect of (Calcite) fouling on ultrasonic guided wave propagation within the structure. Parameters considered include frequency selection, number of cycles and dispersion at incremental fouling thickness. According to the studied conditions, a 0.5 dB/m drop in signal amplitude occurs for a fouling deposition of 1 mm. The findings demonstrate the potential to detect fouling build-up in lengthy pipes and to quantify its thickness by the reduction in amplitude found from further numerical investigation. This variable can be exploited to optimize the power ultrasonic fouling removal procedure.

The Energy Distribution Properties of the Guided Wave in the Underground Layered Pipeline Structure: Finite Element Simulation and Experimental Verification

Many layered pipe structures (LPSs) are covered under the soil, so it is important to investigate the guided wave propagation characteristics for underground LPSs in structural health monitoring (SHM). The paper aims to propose a finite element model to describe the ultrasonic guided wave propagation properties in (underground) layered pipeline. Firstly, a selection of suitable excitation frequency and mode of PZT-based guided waves is successfully finished. Secondly, finite element analysis (FEA) using ABAQUS software is applied to establish an (underground) layered pipe model with piezoceramic (PZT) transducers for generating the guided waves. The finite element analysis (FEA) results show that the soil have a significant impact on the generating modes. The analysis of reflection signal is difficult because of mode conversion. Thus, the energy method of guided wave is used in order to analyze properties of underground layer pipe. The soil impacts for layered pipe focus on the axial energy properties. Although a part of guided wave energy scatters into pipe layers even the soil which makes the behaviour description much more complicated, the remained guided wave energy is still sufficient enough for propagating in the pipe with the obvious frequency dispersion and mode conversion. An experimental system is established to verify the mentioned research, and the experimental and numerical results match well.

Pipeline Damage Detection Using Piezoceramic Transducers: Numerical Analyses with Experimental Validation.

This paper aims to set up a finite element model using piezoelectric elements to realize pipeline structure damage identification analysis. Ultrasonic guided wave propagation characteristics and damage identification of pipeline structures are analyzed by the ABAQUS software. The pulse-echo method using an L(0, 2) mode impulse guided wave with a central frequency of 70 kHz is applied to evaluate different size circumferential cracks. An experiment was performed for the validation of the numerical analysis results. Both of the results show that the proposed FEM model with piezoelectric elements can efficiently reveal the dynamic behaviors, which can be used in much more precise numerical simulations than the equivalent dynamic displacement loading method.

Fatigue evaluation of long cortical bone using ultrasonic guided waves

Bone fatigue fracture is a progressive disease due to stress concentration. This study aims to evaluate the long bone fatigue damage using the ultrasonic guided waves. Two-dimensional finite-difference time-domain method was employed to simulate the ultrasonic guided wave propagation in the long bone under different elastic modulus. The experiment was conducted on a 3.8 mm-thick bovine bone plate. The phase velocities of two fundamental guided modes, A1 and S1, were measured by using the axial transmission technique. Simulation shows that the phase velocities of guided modes A1 and S1 decrease with the increasing of the fatigue damage. After 20,000 cycles of fatigue loading on the bone plate, the average phase velocities of A1 and S1 modes were 6.6% and 5.3% respectively, lower than those of the intact bone. The study suggests that ultrasonic guided waves can be potentially used to evaluate the fatigue damage in long bones.