Martin Viens

Development of a low frequency shear horizontal piezoelectric transducer for the generation of plane SH waves

The shear horizontal guided wave fundamental mode (SH0) has the particularity of being the only non-dispersive plate guided wave mode. This characteristic makes this ultrasonic guided wave mode very attractive in non-destructive testing, facilitating signal processing for long range inspections. It is, however, difficult to generate only a single guided wave mode when using piezoelectric transduction. This work aims to develop a piezoelectric transducer capable of generating a virtually pure plane zeroth order shear horizontal wave. The chosen material was the PZT-5H for its dominant d15 piezoelectric constant, which makes it a perfect candidate for SH-wave generation. The transducer dimensions were optimised using an analytical model based on the Huygens’ principle of superposition and the dipole pattern of a shear point source. A 3D multiphysics finite element model was then used to validate the analytical model results. Experimental validation was finally conducted with a laser Doppler vibrometer (LDV) system. Excellent agreement between the analytical model, finite element model and experimental validation was seen.

On the performance of nondestructive testing methods in the hydroelectric turbine industry

Welded joints of turbine runners are one of the most critical parts of Francis turbines due to the presence of welding discontinuity and high stress. Because of thermal cycles, solidification, cooling distortion and residual stresses, welded joints always include discontinuities of different types and sizes. Some specific parameters will limit welding flaw dimensions in some or all direction based on the joint geometry, material and welding procedure. If discontinuities of critical size remain undetected, fatigue cracks might initiate and propagate in these zones because of dynamic in-service stresses leading to high repair costs and long down times. Therefore, reliable NDT methods and good knowledge of the probability of occurrence of welding flaws is important for fatigue life estimations. Every NDT method has its weaknesses; therefore, even after meticulous inspections it is likely for some discontinuities of critical sizes to remain in the welded joint. Our objective is to clarify the probability of detection and occurrence of different types of welding flaws in hydroelectric turbine runners. Furthermore, an overview of current nondestructive inspection methods and their capability in characterizing flaw dimensions will be discussed. Finally, advanced NDT techniques, for the characterization of welded joints integrity, will be proposed.

Selection of structural features for the systematic study of guided wave propagation and interaction with damage

Guided wave propagation and interaction with defects in aerospace structures is addressed in the literature only for specific and limited number of simple components and types of defects. The knowledge-gap based project between industrial and academic researchers presented in this paper aims at providing the industry with an extended knowledge base for a variety of generic structures that define a set of standards for guided wave propagation and interaction with damage or geometrical features. The knowledge base will contain metrics on guided waves propagation (in terms of velocity dispersion curves and attenuation) and their interaction with geometrical or damage features (spatial patterns, reflection and transmission coefficients). This paper presents the first step in this project, where structural features and design parameters (geometry, material, assembly configuration, surface finish, sealant, …) have been identified, extracted and filtered for their relevance from an extensive list of aerospace structures of interest. This list was created with the industrial partners, combining military and civil aircraft structures. Moreover, a list of in-service damage parameters (extent, depth, location, orientation, type …) has been identified, based on maintenance and in-service manuals, damage tolerance analysis reports, and following the analysis of part drawings. These structures of interest have then been rated by academic partners to extract the most relevant structures for experimental and numerical parametric studies. Based on this reduced list of structures, a set of simplified test articles has been proposed. This paper presents the detailed systematic process for selecting and designing the simplified test articles, together with the geometrical parameters to be varied in the study of guided wave propagation and interaction with both geometrical features and in-service damage. doi: 10.12783/SHM2015/246

Design of advanced automatic inspection system for turbine blade FPI analysis

Aircraft engine turbine blade is the most susceptible part to discontinuities as it works in the extremely high pressure and temperature. Among various types of NDT method, Fluorescent Penetrant Inspection (FPI) is comparably cheap and efficient thus suitable for detecting turbine blade surface discontinuities. In this paper, we have developed an Advanced Automatic Inspection System (AAIS) with Image Processing and Pattern Recognition techniques to aid human inspector. The system can automatically detect, measure and classify the discontinuities from turbine blade FPI images. The tests on the sample images provided by industrial partner have been performed to evaluate the system.

ÉquiNanos: innovative team for nanoparticle risk management

UNLABELLED Interactions between nanoparticles (NP), humans and the environment are not fully understood yet. Moreover, frameworks aiming at protecting human health have not been adapted to NP but are nonetheless applied to NP-related activities. Consequently, business organizations currently have to deal with NP-related risks despite the lack of a proven effective method of risk-management. To respond to these concerns and fulfill the needs of populations and industries, ÉquiNanos was created as a largely interdisciplinary provincial research team in Canada. ÉquiNanos consists of eight platforms with different areas of action, from adaptive decision-aid tool to public and legal governance, while including biological monitoring. ÉquiNanos resources aim at responding to the concerns of the Quebec nanotechnology industry and public health authorities. Our mandate is to understand the impact of NP on human health in order to protect the population against all potential risks emerging from these high-priority and rapidly expanding innovative technologies. FROM THE CLINICAL EDITOR In this paper by Canadian authors an important framework is discussed with the goal of acquiring more detailed information and establishing an infrastructure to evaluate the interaction between nanoparticles and living organisms, with the ultimate goal of safety and risk management of the rapidly growing fields of nanotechnology-based biological applications.

Plane Wave SH0 Piezoceramic Transduction Optimized Using Geometrical Parameters

Structural health monitoring is a prominent alternative to the scheduled maintenance of safety-critical components. The nondispersive nature as well as the through-thickness mode shape of the fundamental shear horizontal guided wave mode (SH0) make it a particularly attractive candidate for ultrasonic guided wave structural health monitoring. However, plane wave excitation of SH0 at a high level of purity remains challenging because of the existence of the fundamental Lamb modes (A0 and S0) below the cutoff frequency thickness product of high-order modes. This paper presents a piezoelectric transducer concept optimized for plane SH0 wave transduction based on the transducer geometry. The transducer parameter exploration was initially performed using a simple analytical model. A 3D multiphysics finite element model was then used to refine the transducer design. Finally, an experimental validation was conducted with a 3D laser Doppler vibrometer system. The analytical model, the finite element model, and the experimental measurement showed excellent agreement. The modal selectivity of SH0 within a 20∘ beam opening angle at the design frequency of 425 kHz in a 1.59 mm aluminum plate was 23 dB, and the angle of the 6 dB wavefront was 86∘.

Feasibility of high frequency guided wave crack monitoring

Ultrasonic guided waves are particularly interesting for SHM applications because they have the ability to propagate long distances with minimal attenuation. Using the baseline subtraction approach, the signal from a defect free structure is subtracted from the actual monitoring signal to detect and characterize defects. Low frequency guided wave SHM and the interaction of the fundamental guided wave modes with various types of defect are well documented in the literature. There are, however, only a very limited number of studies on high order modes. High frequency guided waves may enable the detection of smaller cracks relative to conventional low frequency guided wave SHM. The main difficulty at high frequency is the existence of several modes with different velocities. This study investigates the scattering of high frequency Lamb waves around a through-thickness hole with a view to developing a highly sensitive SHM system for safety-critical components. A 3D finite element model of a 305 × 305 × 1.6 mm aluminum plate was used to determine the scattered field generated by cracks on the circumference of a through-thickness hole in the middle of the plate. Crack properties such as orientation, length and depth were studied. A subset of the finite element simulations were validated against experimental results. The experimental setup comprised a classic contact piezoelectric transducer bonded on the side of the plate and a laser interferometer detector.

Scattering of high order guided wave modes around a through-thickness circular hole

Ultrasonic guided waves have the ability to propagate long distances with minimal attenuation, which makes them particularly interesting in structural health monitoring (SHM) applications. Using the baseline subtraction approach, the signal from a defect-free structure is compared with the actual monitoring signal to detect and locate defects. There are many scientific publications on low-frequency guided waves for SHM purposes, and the interaction between guided wave fundamental modes and defects is also well documented. There is however a very limited number of studies on high order modes. High-frequency guided waves may enable the detection of smaller cracks related to conventional low-frequency guided wave SHM. The main difficulty at high frequency is the existence of several modes with different velocities. This study investigates the scattering of high order guided wave modes around a through-thickness hole with a view to developing a highly sensitive SHM method. A 3D finite element model of a 305 m...

The effect of martensitic stainless steel microstructure on the ultrasonic inspection of turbine runner joints

Martensitic stainless steel runners are widely used in the hydroelectric turbine industry because of their good mechanical properties, cavitation and corrosion resistance. The high downtime cost and limited in-service inspection possibility of these turbine runners increase the need for accurate fatigue models to estimate the life of these equipment. One of the key inputs of these models is the distribution of flaw size and their location near highly stressed area. The critical area is generally located near the welded joint and flaw sizes are estimated using the outcome of nondestructive inspection. In such case, more reliable NDT results will lead to less uncertainty in the life estimation and hence unfavorable consequences, such as unexpected failure during service or non-essential down time for unnecessary inspections, are avoided. Turbine runner welded joints are inspected using ultrasonic refracted shear waves. Considering the dependence of the refracted angle to the shear wave velocity in the mater...

HBAR‐Spectroscopy Used for Materials Characterization

Resonance spectra of a High‐overtone Bulk Acoustic Resonator (HBAR), consisting of a substrate plate and a piezoelectric transducer, can be used to evaluate density, elastic constants and mechanical loss of the substrate material. It is shown that density and elastic constants can be determined independently from the spacing of the parallel resonant frequencies whereas mechanical loss can be assessed from the parallel resonance Q‐value. The accuracy of the presented method is evaluated though a series of numerical simulations based on an equivalent circuit model. Application to the characterization of some industrial materials is discussed.