Safran Ceramics (France)

In this paper, acoustic emission data fusion based on multiple measurements is presented for damage detection and identification in oxide-based ceramic matrix composites. Multi-AE (acoustic emission) sensor fusion is considered with the aim of a better identification of damage mechanisms. In this context, tensile tests were conducted on ceramic matrix composites, fabricated with 3M™ Nextel™ 610 fibers and aluminosilicate matrix, with two kinds of AE sensors. Redundant and complementary sensor data were merged to enhance AE system capability and reliability. Data fusion led to consistent signal clustering with an unsupervised procedure. A correlation between these clusters and the damage mechanisms was established thanks to in situ observations. The complementarity of the information from both sensors greatly improves the characterization of sources for their classification. Moreover, this complementarity allows features to be perceived more precisely than using only the information from one kind of sensor.

Digital image correlation (DIC), which consists in registering image pairs to measure displacement fields, can be tailored to analyze image sequences from videos taking advantage of a common reference image.In the present study it is no longer the first image of the sequence but rather a computed image from the entire video.The sought kinematics, which is separated in space and time, offers the opportunity to extract 'modes', each of which is a spatial displacement field multiplied by a scalar function of time only.These modes are not chosen a priori but rather computed from a specific formulation of DIC so that they capture the displacements at best.The exploited mathematical technique to achieve this modal representation is a form of proper generalized decomposition that makes use of the DIC variational formulation, where both spatial and temporal regularizations can be included.Two image videos acquired with an ultra-high speed camera at 5 and 10 million frames per second are analyzed to illustrate the proposed technique.Very large computation time gains are obtained with no noticeable differences in the kinematic measurements.Moreover, it is shown that motions have a lower complexity, i.e. require less modes, than the direct proper orthogonal decomposition (or principal component analysis) performed on the entire video.

Due to their high specific strength at elevated temperatures and resistance to oxidative environments, SiC-based fibers are of great interest for the reinforcement of ceramic matrix composites. They are however subjected to a slow crack growth (SCG) phenomenon causing their delayed failure under subcritical conditions. The testing of filaments, other than comprising handling difficulties, requires large sets of data (broadly dispersed), drawback alleviated by multifilament tow testing. The data available in the present paper correspond to a comprehensive mechanical characterization and static fatigue testing of various types of SiC-based fiber bundles. The initial non-linearity of load displacement curves were analyzed to reveal the tow structure originating from filament misalignment. Static fatigue tests were used to assess the lifetime prediction coefficients and its distribution parameters. These data may found interest for the interpretation of dispersion bundle testing can highlight under different solicitation mode. Such data are also prominent for the wealth of composite design and to guaranty long term performances over the broad application field offered.

This data article reports a systematic fractographic analysis of SiC-based filaments aiming at stress intensity factors assessment. A total of 11 fiber types (as-received or chlorinated Nicalon® and Tyranno® of all three generations) where therefore repeatedly tensile tested to generate the fracture surfaces. The tensile strengths were found to be independent to defect location (surface or internal). The well-known linear square root dependence of strength on mirror, mist or hackle outer radius was reaffirmed. These measurements reveal some residual tensile stresses on Nicalon® fibers, statement however questioned by the broad data scattering. Moreover, it is shown the surface etching treatment didn't affected (generating or releasing) such residual stress. A null y-intercept was consequently adopted to assess the characteristic stress intensity factors (KIC, mirror, mist or hackle constants). The toughness (KIC) estimated this way ranges from 1.0 to 1.9 MPa m1/2 and shows a clear dependency to substrate composition: higher values were extracted on oxygen-free fibers. The Am/KIC ratio, estimated to equal 1.8 and independent to substrate type, is a key parameter that would assist further fractographic investigations.

Abstract In this work, a novel process named Flexible Injection Process ( FIP ) was developed to manufacture near‐net shape oxide/oxide composites reinforced with 3D interlock fibers. This process uses a flexible membrane to apply pressure to promote transverse impregnation of the fibrous reinforcement by a slurry charged with sub‐micron ceramic particles. Due to the through‐thickness filtration and compaction, FIP process is much faster than typical in‐plane impregnation and results in composites with lower residual porosity than those produced by traditional processes. In this study, a mathematical modeling of the impregnation in FIP was developed and compared to experimental infiltration experiments. Furthermore, ceramic matrix composites ( CMC s) produced by FIP were compared to composites manufactured via an established RTM ‐like process. The two molding processes were compared to determine if the different flow behaviors have an impact on material densification, porosity formation, mechanical properties, and manufacturing time. CMC s produced by both methods resulted in similar microstructures, as determined by mercury intrusion porosimetry, even if FIP composites were marginally less porous. Finally, a comparison of mechanical properties resulting from the two manufacturing methods has shown a similar behavior. Thus, the main advantages of FIP molding were identified to be the shorter cycle time and the robustness of the impregnation compared to RTM ‐like processes.

Abstract Suspensions of ytterbium disilicate in isopropanol were prepared using iodine dispersant. Their zeta potential, electrical conductivity, and pH dependence with iodine concentration is detailed. Electrophoretic deposition was performed on silicon substrates at various voltages (100‐200 V) and times (until 10 minutes) and the growth dynamic was investigated. It was observed that the deposited mass reaches a maximum value for [I 2 ] = 0.2 g/L, and the coating microstructure becomes porous at higher iodine concentrations. Current density and voltage measurements allowed to correlate this behavior to the increase of free protons concentration in the suspension. In these conditions, it was proved that porosity increases with the increase in applied voltage, and a compaction occurs as the deposition time increases. This has been related to the coating resistance increase and subsequent decrease in effective voltage in the suspension. The denser coatings (20% of porosity) were obtained in the case of suspension without iodine, at the minimum applied voltage and for the longest deposition times.

Introducing thermal gradients to improve the Chemical Vapor Infiltration (CVI) process is a key strategy to overcome its principal drawback, namely, the presence of residual porosity in the central part of ceramic composite material preforms. The aim is to create an infiltration front starting from the least accessible part of the porous preform and progressing towards its surface. However, in practice, it may be quite difficult to evaluate the magnitude of the thermal gradient necessary for the achievement of this desired infiltration front. Modeling may bring solutions for the design of a successful processing situation. This paper reviews four distinct application examples, for which multi-physics numerical modeling studies have been developed and validated. These cases are also examined using analytical computations of a front infiltration criterion in order to discuss the influence of processing parameters on the quality of the process and of the resulting material.

Abstract In order to determine the thermo-mechanical properties of a complex 3D woven ceramic composite material, an experiment at high and inhomogeneous temperature and its dedicated full-field measurement procedure is developed. 3D tomographic images of the tested sample are captured at different stages of loading in a synchrotron beamline, and an infrared camera captures a side view of the sample as it rotates in the x-ray beam. A pin-hole projective model of the thermographic camera allows one to map the thermal field measured under numerous orientations onto a 3D mesh of the sample built from an initial tomographic image or a model. The projective model has to be calibrated, and an original procedure is proposed thanks to an integrated digital image correlation algorithm based on the ‘silhouette’ of the sample (as only the protruding edges outlining the sample shape can be seen clearly). This procedure is illustrated with an experimental case study.

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The tomography of an object with limited angle can be addressed through Iterative Reconstruction Reprojection (IRR) procedure, wherein a standard reconstruction procedure is used together with a “filtering” of the image at each iteration. It is here proposed to use as a filter a phase-field—or Cahn -Hilliard—regularization interlaced with a filtered back-projection reconstruction. This reconstruction procedure is tested on a cone-beam tomography of a 3D woven ceramic composite material, and is shown to retrieve a reconstructed volume with very low artifacts in spite of a large missing angle interval (up to 28%).

The Liquid Silicon Infiltration (LSI) process is used to decrease residual porosity of SiC/SiC composite materials. However, it is not fully mastered since the mechanisms involved at 1500 °C under high vacuum are complex to analyze, especially without direct observation. Previous work had demonstrated the feasibility of using X-ray radiography to observe the front rise of silicon in a SiC/SiC composite material during the LSI process. 2D observations, as a first approach, could give a basic understanding of the mechanisms but raised several interrogations due to the superposition of these phenomena along the thickness preventing any quantification. The setup has been improved in order to make X-ray tomography using a fully integrated DC motor in place of the rotation stage commonly used. The sets of X-ray tomographs confirm two successive fillings. First, the molten silicon rapidly and non uniformly invades the accessible intergranular micro porosity of the powder. Then, the liquid slowly fills the remaining isolated powder areas. Once the SiC matrix is fully saturated, the liquid fills the bigger porosities such as cracks and intra yarn macro porosities. In addition, this 3D analysis enabled to give a better comprehension of the non uniform wetting front in the SiC matrix powder. During the 1st step, the accessibility of the powder was known to have a major effect on the speed of progression. Also, the cracks network plays a key role in the filling of the isolated areas in the powder matrix.

The present work concerns the study of the interface fracture energy between a SiC/SiC Ceramic Matrix Composite and an environmental barrier coating. Four-point flexural tests with no precrack were conducted. These tests enable for the stable propagation of two interfacial cracks. They were carried out at room temperature and were instrumented with visible light cameras. This instrumentation allowed for the analysis of the tests thanks to digital image correlation as well as comparisons between experimental and numerical results to locate crack tips and to calculate the interface fracture energy using numerical methods based on linear elastic fracture mechanics. The limits of the method as well as the uncertainties associated with the crack length and the fracture energy were assessed.

A broad variability characterizes the lifetime of SiC-based bundles under static fatigue conditions at intermediate temperature and ambient air, challenging the accuracy of its prediction. The same is true, in a lower extend, with tensile properties, in apparent discrepancy with the bundle theory based on weakest link theory. The data presented here focus on lifetime scattering, evaluated on different fiber types (6 in total, Nicalon® or Tyranno®). It is hosted at http://dx.doi.org/10.17632/96xg3wmppf.1 and related to the research article "Static fatigue of SiC-based multifilament tows at intermediate temperature: the time to failure variability" (Mazerat et al., 2020) [1]. The insufficiency of classically invoked external and discrete bias (fiber sticking phenomenon for instance) was compared to a devoted Monte Carlo algorithm, attributing to each filament a strength (random) and a stress (homogeneous). Introduction of a stress inconsistency from tow to tow, experimentally observed through section variability, was revealed to overpass such biasing approach. This article can be referred to for the interpretation or prediction of CMC lifetime to guaranty long term performances over the broad offered application field.

This research work applied the hydrothermal process for the surface treatment of ceramic fibres in replacement of conventional process using strong acids.

The assessment of service life of composite thermo-structural parts is a primary issue for the aeronautic industry. To this end, a unified damage model for woven composites undergoing both static and fatigue loadings is presented here. Its specificity resides in its rate damage evolution law, which enables to predict the behaviour of the material under cyclic or random fatigue loadings.

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Abstract SiC‐based fibers are subjected to slow crack growth, a crack growth mechanism activated by stresses and the chemical environment, as identified by static fatigue testing. Such tests can be performed on filaments or bundles. Although both types of specimens show a similar lifetime variation, testing of bundles is often preferred. This work compares the scatter of lifetimes predicted for filaments and for tows using a dedicated Monte Carlo simulation tool relying on the following hypotheses: The stress applied to a single filament can be defined, whereas the size of its most critical flaw cannot; on a bundle, neither the applied stress nor the strength of the critical filament (which triggers the cascade failure and the tow failure) can be defined. Depending on the parallelism of fibers inside the bundle and their strength dispersion, the lifetime scatter can be narrower for filaments compared to tows or vice versa.

Many manufacturing processes of fibrous composites involve fiber movement to obtain a targeted fibrous preform before the resin is injected or polymerized. The ability of the fibers to move within the yarn can be named “cohesion.” To obtain a correct preform, it is of great importance to know and master yarn cohesion. As there is currently no available method to characterize yarn cohesion upstream, the process parameters have very often to be tuned using lengthy trial and error strategies. This paper proposes to address this issue, demonstrating that the yarn cantilever bending test is a very promising and efficient candidate to characterize and quantify yarn cohesion. In addition, the test can be easily performed in an industrial context and is sensitive enough to discriminate small variations in cohesion, even small discrepancies resulting from the yarn manufacturing process. Above all, thanks to real manufacturing tests on different yarns, this paper shows that the upstream identification of cohesion using the proposed cantilever bending test achieves the goal of predicting the yarn processability.

Contributions Sara Jimenez Alfaro: did contribute to writing, simulation, modelling Hyung-Jun Chang: did contribute to writing, modelling Dominique Leguillon: did contribute to modelling Sébastien Denneullin: did contribute to modelling, data Funding sources S. Jimenez-Alfaro acknowledges the Iberdrola Foundation under the Marie Skłodowska-Curie Grant Agreement No 101034297. She also acknowledges the support of the Ministerio de Ciencia e Innovación of Spain for his postdoctoral fellowship under reference JDC2023-050492-I. Data structure and information The .csv documents include the raw data of Figures 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19 y 20 in the manuscript. The .zip includes an executable file to test the code: Codes in the folder ccma_multifibers_pycodes: data - CSV raw data for reproducing the figures workflows toughcmc.py - central part of the code where the main functions are called. ccma_multifibers_pycodes - rest of the Python functions are stored toughcmc_fem.py - where the finite element method is executed using the solver FEniCSx, versión 7.3. datsim_dmoyf25_Vf10_pene_adim0_xpyp.json - main data related to the example of the executable file. In this case the example contains positive horizontal and vertical distances between the fibers. mesh_xpyp.py - code that builds the mesh of the example before any crack is generated. We use the gmsh software. mesh_xnyp.py, mesh_xpyn.py - Additional functions for other cases where either the horizontal or the vertical distance is negative. evaluate_on_points.py - Auxiliary function that is used to evaluate some functions in the finite element code at certain nodes of the mesh. Paper Description Achieving greater engine efficiency by increasing gas temperatures is a key challenge set by the European Commission for the aerospace industry by 2050. However, traditional metal alloys may fail under such extreme conditions. Ceramic matrix composites (CMCs) have emerged as a promising alternative, particularly short-fiber CMCs, which offer enhanced performance in components with complex geometries. This paper presents a novel computational framework to predict the fracture toughness of short-fiber CMCs based on the Coupled Criterion approach. The influence of various composite parameters has been systematically analyzed and validated against existing experimental data, demonstrating the model's reliability and potential as a robust design tool for next-generation aerospace applications.

Modeling of damage behavior of an environmental barrier coated ceramic matrix composite under thermal loadings and comparison with experimental tests