14:30
S8 :SHM for Space structures and systems at Amphi Fournel (AF)
Chair: David Barnoncel and Dimitrios Zarouchas
14:30
20 mins
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Development of a Mechaplastronic approach for optimizing hydrogen tank composites with in-situ Structural Health Monitoring (SHM)
Mohammadali Shirinbayan, Marc Rebillat, Joseph Fitoussi, Nazih Mechbal
Abstract: The transportation industry is seeking new solutions and sources of clean energy that align with sustainable environments. Hydrogen, as a vector of energy, offers a high energy density and produces only water when used in fuel cells, making it an environmentally friendly alternative to fossil fuels. Hydrogen storage in gaseous form is typically achieved in type IV composite tanks. These tanks feature a thermosetting matrix, usually an epoxy reinforced with carbon fibers, which provides mechanical strength. Additionally, a polymer liner, onto which the composite is deposited via filament winding, ensures the hydrogen barrier function. A metal base is incorporated to facilitate the introduction of hydrogen into the tank. Type V hydrogen tanks are made from thermoplastic polymers and consist of a monolithic structure including an internal layer of unfilled polymer and a multilayer composite external layer made of the same thermoplastic matrix reinforced with continuous carbon fibres. The interface between the composite and the liner is thus assumed to be perfect. These tanks will be subjected to the different types of thermomechanical loads as type IV tanks: nominal pressure of 700 bars, burst pressure of 1750 bars, temperature ranging from -60°C to 85°C, fill-drain cycles, shocks, and impacts (figure 1).
Fig. 1. Extreme thermomechanical loadings during the using of H2 tanks
However, in terms of service life, the difficulty of damage detection and measurement and monitoring of physical quantities within composite structures still requires the development of specific and reliable technological tools and methods, such as the integration of sensors into the composite structure. The interest in integrating such a function lies in the potential for in-situ health monitoring of the structure from its implementation (Process Health Monitoring - PHM) to its service life (Structural Health Monitoring - SHM). Mastering this technology in all its aspects could significantly reduce maintenance costs and ensure better durability while optimizing the manufacturing process. The integration of sensors into hydrogen storage structures is essential to advancing the use of hydrogen as an energy carrier in transportation. Integrated sensors can provide an easy and effective means to monitor manufacturing quality and mechanical performance of the tanks during their service life. Indeed, these sensors contribute to several essential functions of so-called "smart tanks" currently in development. However, the integration of sensors is complex and poses several challenges such as type of sensors, the methodology of integration of the sensors. To overcome these challenges, the proposed methodology aims to establish a structured approach for selecting and/or optimizing the Process-Material-Sensor (PMS) trio to ensure the reliability of the mechanical and electronic functions integrated within hydrogen tanks. The proposed approach involves combining an experimental method with a numerical one. Additionally, it leverages cross-disciplinary skills, including:
• The characterization and modeling of the Mechanical behavior of materials and the optimization of tank performance.
• The processes involved in the manufacturing of hydrogen tanks (plastics engineering).
• The integration and use of sensors, particularly the analysis of electronic signals to correlate with the assessment of the tank's degradation state.
In this paper the development of a highly transversal global approach that called Mechaplastronic has been proposed. Indeed, it can be considered that optimizing the integration of sensors within a tank involves studying different types of intrusiveness:
A) Intrusiveness of the Fabrication Process on Electronic Functions: Firstly, when sensors are integrated within the materials or at their interfaces, they must be compatible with the fabrication process of the structure (Automated Fiber Placement (AFP) / Filament Winding). Therefore, it is necessary to study the impact of the process on the operating mechanisms of the sensors and the reliability of its electrical and magnetic properties. This involves optimizing the process parameters and the choice of materials.
B) Mutual Intrusiveness of Electronic and Mechanical Functions: The presence of sensors creates interfaces and stress concentrations that can weaken the structures. Therefore, it is important to study the effect of the presence of sensors on the mechanical properties of the structural materials (especially the composite). Conversely, the various thermomechanical stresses endured by the structure can affect the operation of the sensors.
The proposed methodology, aiming to control the different potential intrusiveness and their interactions within a hydrogen tank, can be schematized as illustrated in figure 2.
Fig. 2. Methodology of developing smart H2 tanks
Thus, this study aims to enhance the understanding of the performance of critical areas in H2 tanks. The entirety of this study's results, along with the understanding of the phenomena involved, particularly damage, constitutes an important experimental and numerical foundation.
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14:50
20 mins
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Insights into the Effects of Piezoelectric Wafer Active Sensor Bonding Degradation on Ultrasonic Guided Wave Surveys: Application, and Path Forward for Structural Health Monitoring of Reusable Launch Vehicles
Jesus Eiras, Loïc Mastromatteo, Ludovic Gavérina, Jean-Michel Roche
Abstract: In today’s Reusable Launch Vehicles (RLVs) market, ensuring the structural integrity of critical components between launches is paramount. To meet this demand, Structural Health Monitoring (SHM) systems are being increasingly considered as essential tools for optimizing maintenance tasks and warranting the safety of RLV operations. Ultrasonic Guided Wave-based Structural Health Monitoring is widely used in aerospace applications to assess structural integrity. Central to this technique are Piezoelectric Wafer Active Sensors (PWAS), which transmit and receive ultrasonic waves. However, during the operation of RLVs, electronic hardware is exposed to harsh environmental conditions, presenting significant durability challenges. As the electronic hardware is subjected to extreme conditions such as high and low temperatures, transient and dynamic loads, or radiation, the effectiveness of SHM systems can be compromised over time. Accelerated durability testing under representative environments is important to understand the mechanisms of degradation and forestall the failure of the SHM hardware. These challenges include issues such as bonding degradation and sensor property loss, which can compromise the effectiveness of SHM systems in accurately assessing the structural health of RLVs. Evaluating and understanding these nuances plays a pivotal role in setting acceptance criteria for durability tests conducted on SHM hardware. In this study, we focus on the effects of degraded bonding on electromechanical impedance measurements and ultrasonic guided wave testing. We conduct these assessments at both the sensor unit level and across an array of sensors using Finite Element simulations. These simulations are designed to mimic the effects of a degraded bonding layer, providing valuable insights into how bonding degradation influences the performance of Structural Health Monitoring (SHM) systems.
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15:10
20 mins
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Simulation of ultrasonic SHM system based on Fiber Bragg Gratings on optical fibers
Nina Kergosien, Arnaud Recoquillay, Antoine Gallet, Guillaume Laffont
Abstract: This paper is dedicated to the modelling of Fiber Bragg Gratings (FBG) acting as ultrasound receivers using the so-called edge filtering technique. The model is based on a one-way coupling between the structure and the FBG, neglecting the influence of the sensor on wave propagation while enabling fast computations. First validations of the model are also included.
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15:30
20 mins
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Robust self-referenced defect detection applied to woven composite parts of complex shape
Clément Fisher, Arnaud Recoquillay, Oscar D'Almeida
Abstract: In the context of Structural Health Monitoring (SHM), the use of guided waves is often limited by the need for a reference state for data analysis. This reference state is often shown in the literature to be temperature dependent, but this is also true for other environmental and operational conditions such as sensor ageing.
This paper presents a new self-referencing methodology that is robust to fluctuations in environmental and operational parameters. It is based on the principle of instantaneous reference state, or instantaneous baseline, i.e. the comparison of simultaneous measurements on structures with a high degree of structural similarity with respect to guided waves. This method can identify defects that have a small impact on the measurements, despite the presence of other internal and external variations.
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15:50
20 mins
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Low energy impact detection and localization in composite panel using ultrasound guided wave: towards monitoring with Fiber Bragg Grating sensors
Guillemette Ribay, Rudy Desmarchelier, Nicolas Roussel, Arnaud Recoquillay, Oscar d' Almeida
Abstract: Composite material tends to replace metallic ones in aeronautic structures to meet the need to reduce aircraft weight and fuel consumption. However, aeronautic structures are subject to severe environmental conditions and in particular to impacts during use: hail, birds.... These impacts can result in structural damage. In order to guarantee their integrity, aircrafts are subject to costly ground checks. An alternative would be to carry out continuous monitoring of these structures to detect anomalies and trigger maintenance operations only when necessary [1]. The work presented in this paper therefore aims at developing a Structural Health Monitoring technique able to detect impacts.
In particular, the aim is to detect low-energy impacts on composite structures likely to create precursor defects invisible to the naked eye, and to locate them, as damage in specific areas of the structure may have more severe consequences. In addition, we want to use a SHM system that is as non-invasive as possible by using a small number of optical Fiber Bragg Grating sensors (FBG). FBGs are indeed capable of measuring ultrasonic elastic waves in composite structures [2]. The structure studied in this work is a composite panel of variable thickness, whose mechanical properties (and hence the elastic wave propagation in the panel) are anisotropic. Using a ‘conventional’ low-frequency FBG interrogator, low energy impacts were easily detected even in the presence of added white noise. However, the low frequency content of the measured signals made it difficult to locate the impacts properly. Prior to further impact localization experiments with a high frequency interrogation system developed internally, a careful analysis of the possibilities of such a method was carried out.
Among the various impact localization methods proposed in the literature, we chose the gridsearch technique for its robustness [3]. It consists in extracting the time-of-flight of impact echoes that are then used to calculate a cost function at any point on a grid covering the area to be monitored. The estimated impact position is that where the cost function reaches its minimum. This algorithm is based on the assumption that the energy propagation velocity of elastic waves is known.
The first part of the work consisted in evaluating the effectiveness of this technique using simulated data in a simplified configuration, based on CIVA-SHM software [4], taking into account the varying thickness of the panel. The material parameters required as input for the simulation were determined by comparing the wave fields measured by laser interferometry with those simulated. The impact is assumed to generate predominantly the bending mode qA0, due to its asymmetry with respect to the plate midplane. After characterizing guided wave propagation in the composite structure, the localization algorithm is applied to simulated data using the mean theoretical energy velocity. In these simulations, receivers are considered omnidirectional like circular piezo-electric wafer sensors, and the impact is supposed to act as an omnidirectional artificial source. In this composite panel, it was shown that the source frequency content needs to be above 20kHz to achieve centimeter-precision localization with the grid search algorithm. In addition, due to the reflection properties of the qA0 mode on free edges of the composite panel, the distance of the receivers from the edges has an impact on localization accuracy. By placing the receivers as close as possible to the edges, and approximately 30cm apart, the accuracy was found to be maximum (cf orange crosses in figure 1) ; accuracy is reduced for receivers that are further apart.
Lastly, measurements were performed on the composite panel using 4 FBGs glued with salol to its surface, with an interrogation system developed internally for ultrasonic measurements. The system is based on the so-called edge-filtering technique [5]: for each FBG to be used, the interrogator comprises a tunable laser source (OSICS TLS-AG, EXFO), an optical circulator leading the laser beam to the FBG and then leading the reflected laser beam to a photodiode. The laser beam is locked on the slope of the Bragg reflection peak. When an elastic wave propagates through the structure, the glued FBG undergoes a similar strain, inducing a shift in the reflection peak at the same frequency as the elastic wave. The reflected laser power thus changes accordingly, which can be measured at a high sampling rate (>MHz) by the photodiode coupled with an Analog to Digital Converter. After appropriate wavelet-transform filtering, the signature of metallic ball impacts as well as Hsu-Nielsen tests obtained with the 4 FBGs enabled us to retrieve their position with very good accuracy (maximum error of 1.5cm), thus validating the method (figure 1).
Figure 1: Localization of a Hsu-Nielsen test on a 70cmx35cm composite panel.
In future work, the method could be improved by taking into account the theoretical time-of-flight variations with thickness and direction in the structure. Moreover, it would be interesting to model the Bragg grating response [6], in order to carry out a simulation study of the optimal positioning of these receivers taking into account their directivity.
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16:10
20 mins
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Ultrasonic Solution for Structural Health Monitoring Using Embedded Wireless Non Destructive Testing
Marianne Sagnard, Cyrus Rocher, Giovanni Mazzini, Antoine Bernard, Simon Clément, Frédéric Jean, Frédéric Giral
Abstract: To reduce the cost of space launches, the French National Space Agency (CNES), and ArianeGroup are collaborating on a program to develop future European reusable space launchers. Within this framework, PYTHEAS Technology is pioneering an embedded Non-Destructive Testing (eNDT) solution to ensure that critical components of the launcher are free of damage before each new launch.
Current eNDT systems are primarily wired, which poses significant challenges. The Structural Health Monitoring (SHM) devices often need to be deployed in hard-to-reach areas where wiring is impractical. Even in accessible areas, the weight of the cables is a critical consideration since the overall weight of the launcher must be minimized. Additionally, cables can introduce stress and potential damage to the system, complicating maintenance efforts.
To address these challenges, PYTHEAS Technology has developed an eNDT solution that uses a network of piezoelectric transducers embedded in the structure. This system detects, localizes, and characterizes potential structural damages by propagating guided waves. The method relies on comparing the baseline ultrasound signature of the structure with deviations observed in new ultrasound cartography. While effective in aerospace applications, the current solution's major drawback is the reliance on long cables, which can extend up to ten meters per transducer.
Therefore, PYTHEAS Technology is improving its SHM system to significantly reduce the number of wires, aiming for a partially wireless and batteryless solution. By enabling remote interrogation of the transducers without using a radiofrequency link, the system avoids unwanted electromagnetic interactions, enhancing overall efficiency and reliability.
The developed solution is based on the following architecture. One piezoelectric transducer, called “master”, is wired to an acquisition system. This connection enables both the power supply and the reception of acquired data. The other transducers, called the “nodes”, are wireless and have the ability to harvest energy from received guided waves and to store it in a capacitive reservoir. The master generates a wave, which is transmitted to the nodes within the plate. The excitation (frequency, amplitude) is generated to maximize theenergy transfer from the master to the nodes. Once the reservoir is charged, the system switches to SHM mode: each node successively transmits an ultrasonic guided wave through the structure to the master, that can be used to detect and to localize damages. The master saves the received signals acquired from the guided waves and stores them so the post-processing can be performed on a computer or on a dedicated acquisition system.
The first measurement is carried-out on a healthy structure and kept as reference. Subsequently, the structure is periodically interrogated to verify its integrity. After defining the previously described architecture, electronic boards were designed: one for the master and another one for the nodes. Both boards were initially modelled and simulated. The charging time is estimated at about five second, the survival time (namely the duration during which the system can transmit signals without external power) is 12 seconds and the overall interrogation cycle is less than a minute, with the possibility to average the measurements by sending up to ten pulses.
To facilitate the complete validation of the wireless and batteryless SHM system, three prototyping boards were manufactured. Using a protoboard allows for a compliant proof of concept with the flexibility to easily change the components if needed. The main drawback of the protoboard is its large size compared to the size of the transducers. As a consequence, they are installed next to the structure under test to avoid adding mass to the structure and the consequences it would have on wave propagation.
The tests demonstrate the capacity of the nodes to be charged using ultrasounds. The duration of the charging phase as well as the survival time are consistent with the numerical simulations. After switching from loading to SHM mode, the system demonstrated the capability to transmit up to 10 pulses before depleting the stored energy completely.
The use of one cycle allows to precisely timestamp the effect of the damage on the response. The frequency has been chosen to primarily excite the first symmetric harmonic (S0) of the Lamb wave.
The next steps of this development are to miniaturize the electronic cards and to fix them directly on the transducers, and to increase the distances over which the system can be deployed.
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