Matthieu Gresil

Predictive modeling of electromechanical impedance spectroscopy for composite materials

The advancement of composite materials in aircraft structures has led to an increased need for effective structural health monitoring technologies that are able to detect and assess damage present in composite structures. The study presented in this article is interested in understanding self-sensing piezoelectric wafer sensors to conduct electromechanical impedance spectroscopy in glass fiber reinforced polymer composite to perform structural health monitoring. For this objective, multi-physics-based finite element method is used to model the electromechanical behavior of a free piezoelectric wafer active sensor and its interaction with the host structure on which it is bonded. The multi-physics-based modeling permits the input and output variables to be expressed directly in electric terms, while the two-way electromechanical conversion is done internally in the multi-physics-based finite element method formulation. The impedance responses are also studied in conditions when the sensor bonding layer is subject to degradation and when the sensor itself is subjected to breakage, respectively. To reach the goal of using the electromechanical impedance spectroscopy approach to detect damage, several damage models are generated on simplified orthotropic structure and laminated glass fiber reinforced polymer structures. The effects of the modeling are carefully studied through experimental validation. A good match has been observed for low and high frequencies.

Prediction of attenuated guided waves propagation in carbon fiber composites using Rayleigh damping model

In this work, a predictive model of attenuated guided wave propagation in carbon fiber–reinforced polymer using Rayleigh damping is developed. After a brief introduction, this article reviews the theory of guided waves in anisotropic composite materials. It follows with a discussion of the piezoelectric wafer active sensors, which are lightweight and inexpensive transducers for structural health monitoring applications. Experiments were performed on a carbon fiber–reinforced polymer panel to measure the dispersion curves and the piezoelectric wafer active sensors tuning curves. Lamb wave damping coefficient was modeled using the multi-physics finite element method and compared with experimental results. A discussion about the capability to simulate, with multi-physics finite element method commercial software, guided wave in composite material using the Rayleigh damping is developed. This article ends with conclusion, and suggestions for further work are also presented.

Full-Field Measurements for Determining Orthotropic Elastic Parameters of Woven Glass-Epoxy Composites Using Off-Axis Tensile Specimens

Using theoretical formulations to describe the general response of an orthogonally woven glass-epoxy composite subjected to off-axis tension loading, a simple experimental methodology incorporating stereovision and 3D digital image correlation (3D-DIC) into several optimization procedures is described that provides a direct approach for quantitatively determining all of the elastic properties. During each off-axis tensile loading experiment, axial strains are determined using both mechanical extensometry and 3D-DIC, with the 3D-DIC measurements also used to extract both the in-plane transverse normal strain and the shear strain fields. The effectiveness of various optimization procedures are then evaluated and compared by performing a series of off-axis tensile loading experiments to determine the material engineering constants, including E1, E2, G12, and v12 for the nominally transversely isotropic material. Results indicate excellent agreement between the extensometer measurements and the average axial strain obtained by 3D-DIC. Furthermore, direct comparison of the proposed optimization methods indicates that each method is robust and effective, especially when employing 3D-DIC to extract additional information to complete the elastic property characterization procedure.

Guided wave propagation in carbon composite laminate using piezoelectric wafer active sensors

Attenuation of Lamb waves, both fundamental symmetric and anti-symmetric modes, propagating through carbon fiber reinforced polymer (CFRP) was modeled using the multi-physics finite element methods (MP-FEM) and compared with experimental results. Composite plates typical of aerospace applications were used and provide actuation using integrated piezoelectric wafer active sensors (PWAS) transducer. The MP-FEM implementation was used to combine electro active sensing materials and structural composite materials. Simulation results obtained with appropriate level of Rayleigh damping are correlated with experimental measurements. Relation between viscous damping and Rayleigh damping were presented and a discussion about wave attenuation due to material damping and geometry spreading have been led. The Rayleigh damping model was used to compute the wave damping coefficient for several frequency and for S0 and A0 mode. The challenge has been examined and discussed when the guided Lamb wave propagation is multimodal.

Fatigue crack detection in thick steel structures with piezoelectric wafer active sensors

This paper presents a set of numerical and experimental results on the use of guided waves for structural health monitoring (SHM) of crack growth during a fatigue test in a thick steel plate used for civil engineering application. The capability of embedded piezoelectric wafer active sensors (PWAS) to perform in situ nondestructive evaluation (NDE) is explored. Numerical simulation and experimental tests are used to prove that PWAS can perform active SHM using guided wave pitch-catch method and passive SHM using acoustic emission (AE). Multi-physics finite element (MPFEM) codes are used to simulate the transmission and reception of guided waves in a 1-mm plate and their diffraction by a through hole. The MP-FEM approach permitted that the input and output variables be expressed directly in electric terms while the two-ways electromechanical conversion was done internally in the MP-FEM formulation. The analysis was repeated for several hole sizes and a damage index performances was tested. AE simulation was performed with the MP-FEM approach in a 13-mm plate in the shape of the compact tension (CT) fracture mechanics specimen. The AE event was simulated as a pulse of defined duration and amplitude. The electrical signal measured at a receiver PWAS was simulated. Daubechies wavelet transform was used to process the signal and identify its Lamb modes and FFT frequency contents. Experimental tests were performed with PWAS transducers acting as passive receivers of AE signals. The 8-mm thick flange of an I beam was instrumented on one side with PWAS transducers and on the other side with conventional AE transducers (PAC R15I) acting as comparison witnesses. An AE source was simulated using 0.5- mm pencil lead breaks; the PWAS transducers were able to pick up AE signal with good strength. Subsequently, PWAS transducers and R15I sensors were applied to a 13-mm CT specimen subjected to accelerated fatigue testing. The PWAS and R15I transducers signals were collected with PAC data acquisition system using the AE-win software. Comparative results of AE hits and source localization from the PWAS and R15I sensors are given. Active sensing in pitch catch mode was applied between the PWAS transducers installed on the CT specimen and damage indexes were calculated and correlated with physical crack growth as measured optically. The paper finishes with summary, conclusion, and suggestions for further work.

Structural health monitoring with piezoelectric wafer active sensors exposed to irradiation effects

The increasing number, size, and complexity of nuclear facilities deployed worldwide are increasing the need to maintain readiness and develop innovative sensing materials to monitor important to safety structures (ITS) such as pressure vessels and piping (PVP) in a nuclear reactor. Technologies for the diagnosis and prognosis of PVP systems can improve verification of the health of the structure that can eventually reduce the likelihood of inadvertently failure. Recently investigated piezoelectric wafer active sensors (PWAS) open the possibilities to develop and deploy such system. Piezoelectric wafer active sensors are widely used in structural health monitoring (SHM) to determine the presence of cracks, delaminations, disbonds, and corrosion. Durability and survivability of PWAS under environmental exposures has been tested before. However the irradiation effects, pertinent to nuclear facilities for PWAS, have not been studied yet. This paper presents a study on PWAS that exposed to high energy gamma radiation. PWAS were irradiated using a Co-60 gamma source in an irradiator with different exposure times. The dose rate and total absorbed dose were calculated using Monte Carlo simulations (MCNPX). The PWAS material properties, electrical contact change were characterized through a series of tests. The electro-mechanical impedance spectrum (EMIS) of PWAS was measured before and after irradiation. This study not only provides the fundamental understanding of the PWAS irradiation survivability but also tests the potential of PWAS as irradiation sensors for nuclear applications.Copyright

Benchmark problems for predictive fem simulation of 1-D and 2-D guided waves for structural health monitoring with piezoelectric wafer active sensors

Predictive simulation of ultrasonic nondestructive evaluation and structural health monitoring (SHM) is challenging. This paper addresses this issue in the context of guided-waves with piezoelectric wafer active sensors (PWAS). The principle of guided wave with PWAS transducers is studied and an analytical model is developed to predict the waveform and theoretical frequency contents solution. Two benchmark problems, one 1-D and the other 2-D to achieve reliable and trustworthy predictive simulation of guided wave with finite element method have also been proposed.

Time-domain hybrid global-local concept for guided-wave propagation with piezoelectric wafer active sensor

This article presents a combined finite element method and analytical process to predict the one-dimensional guided-wave propagation for nondestructive evaluation and structural health monitoring application. Analytical methods can perform efficient modeling of wave propagation but are limited to simple geometries. In response to today’s most complex cases not covered by the simulation tools available, we aim to develop an efficient and accessible tool for structural health monitoring application. This tool will be based on a hybrid coupling between analytical solution and time-domain numerical codes. Using the principle of reciprocity, global analytical calculation is coupled with local finite element method analysis to utilize the advantages of both methods and obtain a rapid and accurate simulation method. The phenomenon of interaction between the ultrasonic wave, the defect, and the structure, leading to a complex signature, is efficiently simulated by this hybrid global–local approach and is able to predict the specific response signal actually received by sensor. The finite element mesh is used to describe the region around the defects/flaws. In contrast to other hybrid models already developed, the interaction between Lamb waves and defects is computed in the time domain using the explicit solver of the commercial finite element method software ABAQUS.

Thermal Diffusivity Mapping of Graphene Based Polymer Nanocomposites

Nanoparticle dispersion is widely recognised as a challenge in polymer nanocomposites fabrication. The dispersion quality can affect the physical and thermomechanical properties of the material system. Qualitative transmission electronic microscopy, often cumbersome, remains as the ‘gold standard’ for dispersion characterisation. However, quantifying dispersion at macroscopic level remains a difficult task. This paper presents a quantitative dispersion characterisation method using non-contact infrared thermography mapping that measures the thermal diffusivity (α) of the graphene nanocomposite and relates α to a dispersion index. The main advantage of the proposed method is its ability to evaluate dispersion over a large area at reduced effort and cost, in addition to measuring the thermal properties of the system. The actual resolution of this thermal mapping reaches 200 µm per pixel giving an accurate picture of graphene nanoplatelets (GNP) dispersion. The post-dispersion treatment shows an improvement in directional thermal conductivity of the composite of up to 400% increase at 5 wt% of GNP. The Maxwell-Garnet effective medium approximation is proposed to estimate thermal conductivity that compare favourably to measured data. The development of a broadly applicable dispersion quantification method will provide a better understanding of reinforcement mechanisms and effect on performance of large scale composite structures.

Guided Wave Propagation in Composite Laminates Using Piezoelectric Wafer Active Sensors

Piezoelectric wafer active sensors (PWAS) are lightweight and inexpensive transducers that enable a large class of structural health monitoring (SHM) applications such as: (a) embedded guided wave ultrasonics, i.e., pitch-catch, pulse-echo, phased arrays; (b) high-frequency modal sensing, i.e., electro-mechanical impedance method; and (c) passive detection. The focus of this paper is on the challenges posed by using PWAS transducers in the composite laminate structures as different from the metallic structures on which this methodology was initially developed. After a brief introduction, the paper reviews the PWAS-based SHM principles. It follows with a discussion of guided wave propagation in composites and PWAS tuning effects. Then, the mechanical effect is discussed on the integration of piezoelectric wafer inside the laminate using a compression after impact. Experiments were performed on a glass fiber laminate, employing PWAS to measure the attenuation coefficient. Finally, the paper presents some experimental and multi-physics finite element method (MP-FEM) results on guided wave propagation in composite laminate specimens.