Patrice Masson

Autonomous spherical mobile robot for child-development studies

This paper presents the design process of a spherical robot capable of autonomous motion, and demonstrates how it can become a tool in child-development studies. The robot, named Roball, is capable of intentional self-propelled movements and can generate various interplay situations using motion, messages, sounds, illuminated parts and other sensors. Such capabilities allow Roball to interact with young children in simple and interesting ways, and to provide the potential of contributing to the development of their language, affective, motor, intellectual and social skills. Trials done with 12-24-month-old children demonstrate how Roball can be used to study childrens interest in a self-propelled and intentional device. An experimental methodology to conduct such studies is presented: it is based on quantitative and qualitative techniques to evaluate interactions, thus enabling the identification of challenges and opportunities in child-robot interaction studies.

Methodology for optimal configuration in structural health monitoring of composite bonded joints

In this study, a structural health monitoring (SHM) strategy is proposed in order to detect disbonds in a composite lap-joint. The structure under study is composed of a carbon fiber reinforced polymer (CFRP) bonded to a titanium plate and artificial disbonds are simulated by inserting Teflon tapes of various dimensions within the joint. In situ inspection is ensured by piezoceramics bonded to the structure to generate and measure guided waves. Theoretical propagation and through-thickness stress distribution are first studied in order to determine damage sensitivity with respect to the mode and frequency of the generated guided wave. The optimal configuration of the system in terms of piezoceramic size, shape and inter-unit spacing is then validated using finite element modeling (FEM) in 3D. Experimental assessment of propagation characteristics is conducted using laser Doppler vibrometer (LDV) in order to justify theoretical and numerical assumptions and pitch–catch measurements are then performed to validate the efficient detection of the damage and accurate estimation of its size.

Structural health monitoring strategy for detection of interlaminar delamination in composite plates

In this paper, a structural health monitoring strategy for detecting interlaminar delamination in a carbon fiber reinforced polymer structure using Lamb waves is proposed. The delamination is simulated by inserting a Teflon tape between two transverse plies and the Lamb wave generation and measurement is enabled by using piezoceramic elements. The Lamb wave theoretical propagation and through thickness strain distribution are studied, in order to determine the optimal configuration of the final system in terms of mode and frequency selection, and piezoceramic sizing and spacing, for detection of cross-sectional delamination. Pitch and catch measurements are performed by comparing wave propagations for different frequencies and along damaged and undamaged paths of the structure, and the analysis of results is performed using the reassigned short time Fourier transform. It appears that in the low frequency range (below 300 kHz), the A0 mode is sensitive to the damage, while in the high frequency range, S1 and A1 modes are both very sensitive to the damage while the propagation of the S0 mode is not affected very much.

Active structural acoustic control using strain sensing

A new strategy based on the direct use of strain sensing is proposed for the minimization of the acoustic radiation from a vibrating plate. This strategy uses active structural acoustic control because it eliminates the need for far-field acoustic sensors. The cost function is defined as the radiated acoustic power and the discrete strain information is given directly, for example, by fiber optic sensors embedded in the structure. Two approaches are presented to express the cost function in terms of strain information. The first one is based on plate’s displacement reconstruction from the strain field while the second is based on integration by parts of the wave-number transform of the displacement. Proper concentration of the control effort is obtained with the cost function defined in the wave-number domain. Both approaches are first validated with respect to an analytical solution for the calculation of the radiated acoustic power from structural strain information. It is shown that good agreement is o...

Broadband generation of ultrasonic guided waves using piezoceramics and sub-band decomposition

Classically, damage detection or dispersion curve determination using piezoceramic-generated guided waves has been based on analysis of propagation properties of multiple narrowband excitation signals. However, dispersion and multimodal propagation impair the determination of propagation properties. More recently, it has been proposed to consider broadband excitations for both damage imaging and group velocity estimation. Among existing transducer technologies, although laser excitation is prone to practical limitations in terms of dimensions and generated amplitudes, it allows generation of noncontact, point-like broadband displacement. Thus, broadband generation of guided waves using piezoceramics can be envisioned. However, direct impulse response measurements are limited by the generated amplitude, leading to low SNR measurements. For this purpose, chirp excitations have been proposed using variable-frequency bursts, leading to phase and amplitude variations with respect to the frequency, such that this approach is not suitable for precise estimation of time of flight (ToF) or modal amplitude. In this paper, a sub-band decomposition technique that allows high-SNR measurements of impulse response in a given frequency range is proposed. Broadband excitation is decomposed over a given number of frequency sub-bands, generated by a piezoceramic element and measurement is performed using a laser Doppler vibrometer (LDV) or a piezoceramic sensor. Application to experimental estimation of group velocity and damage detection in pitchcatch configuration is proposed. It is shown that the proposed method allows damage estimation without a priori knowledge of the damage size, whereas narrowband techniques can fail at specific wavelengths.

The Use of PVDF Strain Sensing in Active Control of Structural Intensity in Beams

An investigation of structural intensity control associated with flexural vibration in beams using strain sensing is presented in this paper. The instantaneous intensity is completely taken into account in the control algorithm, i.e., all the terms are considered in the real-time control process and, in particular, the evanescent waves are considered in this approach. Previous work has shown the validity of the approach using an array of accelerometers to measure structural intensity. It is the purpose of this paper to present results on the use of strain sensing in the control of structural intensity. A finite difference approach using discrete PVDF strain sensors provides the structural intensity sensing scheme. A feedforward filtered-X LMS algorithm is adapted to this energy-based control problem, involving a nonpositive definite quadratic form in general. In this respect, the approach is limited to cases where the geometry is such that the intensity component will have the same sign for the control source and the primary disturbance. Experimental validation of the approach is conducted on a free–free beam covered with viscoelastic material and excited harmonically by a shaker. A comparison is made between classical acceleration control and structural intensity control and the performance of both approaches is presented. These results tend to indicate that intensity control allows the error sensors to be placed closer to the control source and the primary disturbance, while preserving a good control performance.

Compensation of piezoceramic bonding layer degradation for structural health monitoring

The compensation of the degradation of the bonding layer of piezoceramics used in structural health monitoring is addressed in this article. A simple admittance model is first used to measure and extract the variation of admittance parameters using the same acquisition chain which is used by the structural health monitoring system for damage monitoring. More precisely, the method uses measurable changes in physical transducer modal damping at frequencies around piezoceramic resonance to estimate the extent of degradation. Then, a finite element model is used to obtain calibration curves linking the variations in transducer modal damping to amplitude and phase of the ultrasonic signals generated or measured by the piezoceramics. Such calibration curves are obtained by simulating with the FEM the effect of varying the bonding layer coverage area and Young’s modulus on (a) admittance and (b) amplitude and phase of the ultrasonic signals. From this, a signal correction factor is developed for the dominant bonding layer coverage area degradation failure mode to compensate for the changes in amplitude and phase of guided waves generated and measured by degraded piezoceramic transducers. The measured modal damping determines the amount of bonding layer degradation from the simulated modal damping calibration curves and then the quantified bonding layer degradation amount selects the amplitude and phase correction to be applied to measured signals from the calibration curves. The benefits of the signal correction factor are demonstrated below piezoceramic resonance to improve damage imaging and localization using the Embedded Ultrasonic Structural Radar algorithm (delay and sum method) when a single transducer in a sparse array of transducers fixed to an aluminum plate is damaged due to the close proximity of drop-weight impacts. Up to a certain damage extent, the signal correction factor could allow an extension of the service life of the structural health monitoring system.

Correlation-based imaging technique using ultrasonic transmit-receive array for Non-Destructive Evaluation.

This paper describes a novel array post-processing method for Non-Destructive Evaluation (NDE) using phased-array ultrasonic probes. The approach uses the capture and processing of the full matrix of all transmit-receive time-domain signals from a transducer array as in the case of the Total Focusing Method (TFM), referred as the standard of imaging algorithms. The proposed technique is based on correlation of measured signals with theoretical propagated signals computed over a given grid of points. In that case, real-time imaging can be simply implemented using discrete signal product. The advantage of the present technique is to take into account transducer directivity, dynamics and complex propagation patterns, such that the number of required array elements for a given imaging performance can be greatly reduced. Numerical and experimental application to contact inspection of isotropic structure is presented and real-time implementation issues are discussed.

Investigation of active structural intensity control in finite beams: Theory and experiment

An investigation of structural intensity control is presented in this paper. As opposed to previous work, the instantaneous intensity is completely taken into account in the control algorithm, i.e., all the terms are considered in the real-time control process and, in particular, the evanescent waves are considered in this approach. A finite difference approach using five accelerometers is used as the sensing scheme. A feedforward filtered-X least mean square algorithm is adapted to this energy-based control problem, involving a nonpositive definite quadratic form in general. In this respect, the approach is limited to cases where the geometry is such that the intensity component will have the same sign for the control source and the primary disturbance. Results from numerical simulations are first presented to illustrate the benefit of using a cost function based on structural intensity. Experimental validation of the approach is conducted on a free-free beam covered with viscoelastic material. A comparison is made between classical acceleration control and structural intensity control and the performance of both approaches is presented. These results confirm that using intensity control allows the error sensors to be placed closer to the control source and the primary disturbance, while preserving a good control performance.

Dynamic and static assessment of piezoelectric embedded composites

The design of fully integrated structures, and especially of new generation composites with embedded sensors and actuators, now requires the development of adequate tools for predicting the static and the dynamic behavior of the structure as well as its life cycle. These tools will provide flexibility in assessing well-suited control strategies for optimum structural performance. As a first step towards the development of integrated computational tools for smart structures, this work validates both theoretically and experimentally the implementation under MSC/NASTRAN of a simplified multilayer tri-dimensional model based on the analogy between thermal strains and piezoelectric strains. Numerical results obtained from this model are first compared to results obtained from a reference finite element tri-dimensional piezoelectric code developed to assess the thermal analogy for different loading conditions. Experimental validation is also conducted on a clamped AS4/3501-6 carbon/epoxy composite beam structure excited at the clamped end by an embedded piezoelectric. Results obtained from vibration testing are assessed with the thermal analogy model using a large number of tri-dimensional elements in order to get a detailed representation of the different variables. Details for practical implementation of the embedment procedures are presented along with the adequate model prediction of the structures dynamic behavior.