Piotr Kijanka

GPU-based local interaction simulation approach for simplified temperature effect modelling in Lamb wave propagation used for damage detection

Temperature has a significant effect on Lamb wave propagation. It is important to compensate for this effect when the method is considered for structural damage detection. The paper explores a newly proposed, very efficient numerical simulation tool for Lamb wave propagation modelling in aluminum plates exposed to temperature changes. A local interaction approach implemented with a parallel computing architecture and graphics cards is used for these numerical simulations. The numerical results are compared with the experimental data. The results demonstrate that the proposed approach could be used efficiently to produce a large database required for the development of various temperature compensation procedures in structural health monitoring applications. (Some figures may appear in colour only in the online journal)

Noncontact ultrasonic guided wave inspection of rails

This article describes a new system for high-speed and noncontact rail integrity evaluation being developed at the University of California at San Diego. A prototype using an ultrasonic air-coupled guided wave signal generation and air-coupled signal detection has been tested at the University of California at San Diego Rail Defect Farm. In addition to a real-time statistical analysis algorithm, the prototype uses a specialized filtering approach due to the inherently poor signal-to-noise ratio of the air-coupled ultrasonic measurements in rail steel. The laboratory results indicate that the prototype is able to detect internal rail defects with a high reliability. Extensions of the system are planned to add rail surface characterization to the internal rail defect detection. In addition to the description of the prototype and test results, numerical analyses of ultrasonic guided wave propagation in rails have been performed using a Local Interaction Simulation Approach algorithm and some of these results are shown. The numerical analysis has helped designing various aspects of the prototype for maximizing its sensitivity to defects.

Actuation stress modelling of piezoceramic transducers under variable temperature field

The article presents a two-dimensional temperature-dependent model of piezoceramic transducers used for Lamb wave–based damage detection applications. The effect of temperature on shear stress and normal stress components influencing wave actuation is analysed. Three models are analysed and compared, that is, static theoretical model and two numerical models, that is, static and dynamic. These models are analysed for two different piezoceramic transducers’ thicknesses. The results demonstrate that the effective transducer’s length is smaller than its physical in-plane dimension. The influence of the normal actuation stress component is significant for wave actuation. This component is dependent on temperature and transducer’s dimension.

Three-dimensional temperature effect modelling of piezoceramic transducers used for Lamb wave based damage detection

The paper presents a three-dimensional temperature-dependent model of surface-bonded, low-profile piezoceramic transducers (PZT) used for Lamb wave propagation. The effect of temperature on Lamb wave actuation, propagation and sensing is investigated. The major focus is on the study of actuation and sensing properties of PZT for various temperature levels. These properties are investigated through the electric field analysis of transducers. The temperature effect on transducer bond layers is also investigated. Numerically simulated amplitude responses are analysed for various temperatures and excitation frequencies. Numerical simulations are validated experimentally. The results demonstrate that temperature-dependent physical properties of PZT, bond layers and particularly host structures significantly affect the amplitude and phase of Lamb wave responses.

Enhanced nonlinear crack-wave interactions for structural damage detection based on Lamb waves

The paper presents a novel damage detection method that combines Lamb wave propagation with nonlinear acoustics. Low-frequency excitation is used to modulate Lamb waves in the presence of fatigue cracks. The work presented shows that the synchronization of the interrogating high-frequency Lamb wave with the low-frequency vibration is a key element of the proposed method. The main advantages of the proposed method are the lack of necessity for baseline measurements representing undamaged condition and lack of sensitivity to temperature variations. Numerical simulations and experimental measurements are performed to demonstrate the application of the proposed method to detect fatigue crack in aluminum beam.

Temperature effect modelling of piezoceramic transducers used for Lamb wave propagation in damage detection applications

Although damage detection using Lamb waves has been investigated for many years, real engineering applications are limited due to practical aspects related to implementation. Temperature effect is one of the major problems. It is well known that temperature variations influence Lamb wave propagation response parameters. In practice it is important to compensate for this effect. Experimental tests are often required to understand how temperature influences wave propagation. Numerical simulation can ease this task preventing many time-consuming experiments. Simulated Lamb wave responses can be used to develop new methods for temperature compensation. The effect of temperature variations on piezoceramic transducer responses is investigated using finite element modelling. The model takes into account temperature-dependent physical properties of low-profile PZT transducers and transducer bonding layers. The model is used to predict the S0 and A0 Lamb response in aluminium plate for the temperature range from -60 to +40°C. The study shows relevant changes in Lamb wave amplitude response caused by temperature fluctuations. This approach can provide the basis for temperature compensation in ultrasonic guided wave damage detection systems used for structural health monitoring applications.

Local numerical modelling of ultrasonic guided waves in linear and nonlinear media

Nonlinear ultrasonic techniques provide improved damage sensitivity compared to linear approaches. The combination of attractive properties of guided waves, such as Lamb waves, with unique features of higher harmonic generation provides great potential for characterization of incipient damage, particularly in plate-like structures. Nonlinear ultrasonic structural health monitoring techniques use interrogation signals at frequencies other than the excitation frequency to detect changes in structural integrity. Signal processing techniques used in non-destructive evaluation are frequently supported by modeling and numerical simulations in order to facilitate problem solution. This paper discusses known and newly-developed local computational strategies for simulating elastic waves, and attempts characterization of their numerical properties in the context of linear and nonlinear media. A hybrid numerical approach combining advantages of the Local Interaction Simulation Approach (LISA) and Cellular Automata for Elastodynamics (CAFE) is proposed for unique treatment of arbitrary strain-stress relations. The iteration equations of the method are derived directly from physical principles employing stress and displacement continuity, leading to an accurate description of the propagation in arbitrarily complex media. Numerical analysis of guided wave propagation, based on the newly developed hybrid approach, is presented and discussed in the paper for linear and nonlinear media. Comparisons to Finite Elements (FE) are also discussed.

Nonlinear dispersion effects in elastic plates: numerical modelling and validation

Nonlinear features of elastic wave propagation have attracted significant attention recently. The particular interest herein relates to complex wave-structure interactions, which provide potential new opportunities for feature discovery and identification in a variety of applications. Due to significant complexity associated with wave propagation in nonlinear media, numerical modeling and simulations are employed to facilitate design and development of new measurement, monitoring and characterization systems. However, since very high spatio- temporal accuracy of numerical models is required, it is critical to evaluate their spectral properties and tune discretization parameters for compromise between accuracy and calculation time. Moreover, nonlinearities in structures give rise to various effects that are not present in linear systems, e.g. wave-wave interactions, higher harmonics generation, synchronism and | recently reported | shifts to dispersion characteristics. This paper discusses local computational model based on a new HYBRID approach for wave propagation in nonlinear media. The proposed approach combines advantages of the Local Interaction Simulation Approach (LISA) and Cellular Automata for Elastodynamics (CAFE). The methods are investigated in the context of their accuracy for predicting nonlinear wavefields, in particular shifts to dispersion characteristics for finite amplitude waves and secondary wavefields. The results are validated against Finite Element (FE) calculations for guided waves in copper plate. Critical modes i.e., modes determining accuracy of a model at given excitation frequency - are identified and guidelines for numerical model parameters are proposed.

Simulation of guided wave propagation near numerical Brillouin zones

Attractive properties of guided waves provides very unique potential for characterization of incipient damage, particularly in plate-like structures. Among other properties, guided waves can propagate over long distances and can be used to monitor hidden structural features and components. On the other hand, guided propagation brings substantial challenges for data analysis. Signal processing techniques are frequently supported by numerical simulations in order to facilitate problem solution. When employing numerical models additional sources of errors are introduced. These can play significant role for design and development of a wave-based monitoring strategy. Hence, the paper presents an investigation of numerical models for guided waves generation, propagation and sensing. Numerical dispersion analysis, for guided waves in plates, based on the LISA approach is presented and discussed in the paper. Both dispersion and modal amplitudes characteristics are analysed. It is shown that wave propagation in a numerical model resembles propagation in a periodic medium. Consequently, Lamb wave propagation close to numerical Brillouin zone is investigated and characterized.

Damage location by ultrasonic Lamb waves and piezoelectric rosettes

An approach based on Macro-Fiber Composite (MFC) transducer rosettes and ultrasonic guided waves is proposed for damage location in plate-like structures. By using the directivity behaviour of the three MFC sensors in each rosette, the direction of an incoming wave generated by scattering from damage can be estimated without knowledge of the wave velocity in monitored structures. Two rosettes suffice to identify the location of a scatterer in a planar structure. The technique does not have any drawbacks of time-of-flight triangulation that requires information on wave velocity and thus complicates damage location when testing anisotropic materials, tapered sections, or any structure under temperature fluctuations. The effectiveness of the piezoelectric rosette method is tested experimentally using an aluminium plate with a simulated damage subjected to temperature variation.