Institut Clément Ader

PART ONE. PRINCIPLES OF CONSTRUCTION COMPOSITE MATERIALS, INTEREST AND PROPERTIES What is Composite Material Fibers and Matrix What can be Made Using Composite Materials? Typical Examples of Interest on the Use of Composite Materials Examples on Replacing Conventional Solutions with Composites Principal Physical Properties FABRICATION PROCESSES Molding Processes Other Forming Processes Practical Hints in the Manufacturing Processes PLY PROPERTIES Isotropy and Anisotropy Characteristics of the Reinforcement-Matrix Mixture Unidirectional Ply Woven Fabrics Mats and Reinforced Matrices Multidimensional Fabrics Metal Matrix Composites Tests SANDWICH STRUCTURES: What is a Sandwich Structure? Simplified Flexure A Few Special Aspects Fabrication and Design Problems Nondestructive Quality Control CONCEPTION AND DESIGN Design of a Composite Piece The Laminate Failure of Laminates Sizing of Laminates JOINING AND ASSEMBLY Riveting and Bolting Bonding Inserts COMPOSITE MATERIALS AND AEROSPACE CONSTRUCTION Aircraft Helicopters Propeller Blades for Airplanes Turbine Blades in Composites Space Applications COMPOSITE MATERIALS FOR OTHER APPLICATIONS: Composite Materials and the Manufacturing of Automobiles Composites in Naval Construction Sports and Recreation Other Applications PART TWO: MECHANICAL BEHAVIOR OF LAMINATED MATERIALS ANISOTROPIC ELASTIC MEDIA: Review of Notations Orthotropic Materials Transversely Isotropic Materials ELASTIC CONSTANTS OF UNIDIRECTIONAL COMPOSITES: Longitudinal Modulus Poisson Coefficient Transverse Modulus Shear Modulus Thermoelastic Properties ELASTIC CONSTANTS OF A PLY ALONG AN ARBITRARY DIRECTION: Compliance Coefficients Stiffness Coefficients Case of Thermomechanical Loading MECHANICAL BEHAVIOR OF THIN LAMINATED PLATES: Laminate with Miplane Symmetry Laminate without Miplane Symmetry PART THREE: JUSTIFICATIONS, COMPOSITE BEAMS, THICK PLATES ELASTIC COEFFICIENTS Elastic Coefficients in an Orthotropic Material Elastic Coefficients for a Transversely Isotropic Material Case of a Ply THE HILL-TSAI FRACTURE CRITERION: Isotropic Material: Von Mises Criterion Orthotropic Material: Hill-Tsai Criterion Evaluation of the Resistance of a Unidirectional Ply with Respect to the Direction of Loading COMPOSITE BEAMS IN FLEXURE: Flexure of Symmetric Beams with Isotropic Phases The Case of any Cross Section (Asymmetric) COMPOSITE BEAMS IN TORSION: Uniform Torsion Location of the Torsion Center FLEXURE OF THICK COMPOSITE PLATES: Preliminary Remarks Displacement Field Strains Constitutive Relations Equilibrium Equations Technical Formulation for Bending Examples PART FOUR: APPLICATIONS LEVEL 1 Simply Supported Sandwich Beam Poisson Coefficient of a Unidirectional Layer Helicopter Blade Transmission Shaft for Trucks Flywheel in Carbon/Epoxy Wing Tip Made of Carbon/Epoxy Carbon Fibers Coated with Nickel Tube Made of Glass/Epoxy Under Pressure Filament Wound Reservoir, Winding Angle Filament Wound Reservoir, Taking into Account the Heads Determination of the Volume Fraction of Fibers by Pyrolysis Lever Arm Made of Carbon/Peek Unidirectionals and Short Fibers Telegraphic Mast in Glass/Resin Unidirectional Ply of HR Carbon Manipulator Arm of Space Shuttle LEVEL 2 Sandwich Beam: Simplified Calculations of the Shear Coefficient Procedure for Calculation of a Laminate Kevlar/Epoxy Laminates: Evolution of Stiffness Depending on the Direction of the Load Residual Thermal Stresses Due to Curing of the Laminate Thermoelastic Behavior of a Tube Made of Filament Wound Glass/Polyester Polymeric Tube Loaded by Thermal Load and Creep First Ply Fracture of a Laminate. Ultimate Fracture Optimum Laminate for Isotropic Stress State Laminate Made of Identical Layers of Balanced Fabric Wing Spar in Carbon/Epoxy Determination of the Elastic Characteristics of a Carbon/Epoxy Unidirectional Layer from Tensile Test Sail Boat Shell in Glass/Polyester Determination of the in-Plane Shear Modulus of a Balanced Fabric Ply Quasi-Isotropic Laminate Orthotropic Plate in Pure Torsion Plate made by Resin Transfer Molding (RTM) Thermoelastic Behavior of a Balanced Fabric Ply LEVEL 3 Cylindrical Bonding Double Bonded Joint Composite Beam with Two Layers Buckling of a Sandwich Beam Shear Due to Bending in a Sandwich Beam Column Made of Stretched Polymer Cylindrical Bending of a Thick Orthotropic Plate under Uniform Loading Bending of a Sandwich Plate Bending Vibration of a Sandwich Beam Appendix 1: Stresses in the Plies of a Laminate of Carbon/Epoxy Loaded in its Plane Appendix 2: Buckling of Orthotropic Structures Bibliography

This paper presents a review of the issues concerning sandwich structures for aeronautical applications. The main questions raised by designers are first recalled and the complexity of sandwich structure design for aeronautics is highlighted. Then a review of applications is presented, starting with early examples from the 1930s and the Second World War. The growth in the use of sandwich materials in civil and military applications is then developed. Recent research and innovations conclude the paper.

A comparative study of the crystallinity of Polyetheretherketone by using density, DSC, XRD, and Raman spectroscopy techniques. In this work, the microstructure of Polyetheretherketone is first analyzed with usual techniques such as density, Differential Scanning Calorimetry, X-ray Diffraction, and secondly, compared with Raman Spectroscopy. Assessing the degree of crystallinity of PEEK is challenging because of the different interpretation of the crystallinity according to each technique. The density measurement gives the highest most trusted absolute uncertainty for the degree of crystallinity, around 4%, compared to the other techniques. The Differential Scanning Calorimetry, usually used by the polymer community, overestimates up to 18% the degree of crystallinity due to a competitive phenomenon between crystallization and melting of PEEK over the same temperature range, and a fast crystallization. When Analyzing the X-ray Diffraction data, the degree of crystallinity is underestimated up to 11% as a consequence of the broad amorphous halo. Lastly, our investigation proves that Raman microspectroscopy is appropriate to determine the local crystallinity on the sample surface and compares 18 indicators in the same study. The 1651 cm-1 band shift has the highest correlation coefficient of 0.92 with the degree of crystallinity determined by density. This work attempts to correlate the results of degree of crystallinity of PEEK obtained by these four techniques in order to establish the best evaluation of this fundamental property for numerous applications.

Abstract Heat transfer and fluid flow in microchannels have been topics of intense research in the past decade. A critical review of the current state of research is presented with a focus on the future research needs. After providing a brief introduction, the paper addresses six topics related to transport phenomena in microchannels: single-phase gas flow, enhancement in single-phase liquid flow and flow boiling, flow boiling instability, condensation, electronics cooling, and microscale heat exchangers. After reviewing the current status, future research directions are suggested. Concerning gas phase convective heat transfer in microchannels, the antagonist role played by the slip velocity and the temperature jump that appear at the wall are now clearly understood and quantified. It has also been demonstrated that the shear work due to the slipping fluid increases the effect of viscous heating on heat transfer. On the other hand, very few experiments support the theoretical models and a significant effort should be made in this direction, especially for measurement of temperature fields within the gas in microchannels, implementing promising recent techniques such as molecular tagging thermometry (MTT). The single-phase liquid flow in microchannels has been established to behave similar to the macroscale flows. The current need is in the area of further enhancing the performance. Progress on implementation of flow boiling in microchannels is facing challenges due to its lower heat transfer coefficients and critical heat flux (CHF) limits. An immediate need for breakthrough research related to these two areas is identified. Discussion about passive and active methods to suppress flow boiling instabilities is presented. Future research focus on instability research is suggested on developing active closed loop feedback control methods, extending current models to better predict and enable superior control of flow instabilities. Innovative high-speed visualization and measurement techniques have led to microchannel condensation now being studied as a unique process with its own governing influences. Further work is required to develop widely applicable flow regime maps that can address many fluid types and geometries. With this, condensation heat transfer models can progress from primarily annular flow based models with some adjustments using dimensionless parameters to those that can directly account for transport in intermittent and other flows, and the varying influences of tube shape, surface tension and fluid property differences over much larger ranges than currently possible. Electronics cooling continues to be the main driver for improving thermal transport processes in microchannels, while efforts are warranted to develop high performance heat exchangers with microscale passages. Specific areas related to enhancement, novel configurations, nanostructures and practical implementation are expected to be the research focus in the coming years.

Accurate modeling of gas microvection is crucial for a lot of MEMS applications (microheat exchangers, pressure gauges, fluidic microactuators for active control of aerodynamic flows, mass flow and temperature microsensors, micropumps, and microsystems for mixing or separation for local gas analysis, mass spectrometers, vacuum, and dosing valves…). Gas flows in microsystems are often in the slip flow regime, characterized by a moderate rarefaction with a Knudsen number of the order of 10−2–10−1. In this regime, velocity slip and temperature jump at the walls play a major role in heat transfer. This paper presents a state of the art review on convective heat transfer in microchannels, focusing on rarefaction effects in the slip flow regime. Analytical and numerical models are compared for various microchannel geometries and heat transfer conditions (constant heat flux or constant wall temperature). The validity of simplifying assumptions is detailed and the role played by the kind of velocity slip and temperature jump boundary conditions is shown. The influence of specific effects, such as viscous dissipation, axial conduction and variable fluid properties is also discussed.

The crystallization degree in semi-crystalline thermoplastics plays an important role in determining the final properties of structural composite material (e.g. toughness, stiffness and solvent resistance). The main purpose of this work is to study different induced degrees of crystallinity in carbon fiber (CF) reinforced polyphenylene sulfide (PPS) composites, by using three different cooling rates during hot compression molding processing (51%, 58% and 62% of crystallinity). In this study, the morphology, thermal and mechanical properties of the produced laminates were investigated and compared. The results showed an increase in the storage modulus (9.8%), Young's modulus (9.2%) and ILSS (14.2%) for the lower cooling rates. Evidences of fiber/interface improvement and crystallites nucleation on the fiber reinforcement surface were also identified.

The huge and rapid progress in electric drives offers new opportunities to improve the performances of aircraft at all levels: fuel burn, environmental footprint, safety, integration and production, serviceability, and maintainability. Actuation for safety-critical applications like flight-controls, landing gears, and even engines is one of the major consumers of non-propulsive power. Conventional actuation with centralized hydraulic power generation and distribution and control of power by throttling has been well established for decades, but offers a limited potential of evolution. In this context, electric drives become more and more attractive to remove the natural drawbacks of conventional actuation and to offer new opportunities for improving performance. This paper takes the stock, at both the signal and power levels, of the evolution of actuation for safety-critical applications in aerospace. It focuses on the recent advances and the remaining challenges to be taken toward full electrical actuation for commercial and military aircraft, helicopters, and launchers. It logically starts by emphasizing the specificity of safety-critical actuation for aerospace. The following section addresses in details the evolution of aerospace actuation from mechanically-signaled and hydraulically-supplied to all electric, with special emphasis on research and development programs and on solutions entered into service. Finally, the last section reviews the challenges to be taken to generalize the use of all-electric actuators for future aircraft programs.

Recently, it has been demonstrated that a vibro-impact type nonlinear energy sink (VI-NES) can be used efficiently to mitigate vibration of a linear oscillator (LO) under transient loading. The objective of this paper is to investigate theoretically and experimentally the potential of a VI-NES to mitigate vibrations of an LO subjected to a harmonic excitation (nevertheless, the presentation of an optimal VI-NES is beyond the scope of this paper). Due to the small mass ratio between the LO and the flying mass of the NES, the obtained equations of motion are analyzed using the method of multiple scales in the case of 1:1 resonance. It is shown that in addition to periodic response, system with VI-NES can exhibit strongly modulated response (SMR). Experimentally, the whole system is embedded on an electrodynamic shaker. The VI-NES is realized with a ball which is free to move in a cavity with a predesigned gap. The mass of the ball is less than 1% of the mass of the LO. The experiment confirms the existence of periodic and SMR regimes. A good agreement between theoretical and experimental results is observed.

Abstract The tribo-characteristics of metal forming at high temperatures have not yet been well understood due to the complex nature of thermal, microstructural, interaction, and process parameters. This is a review paper on the effects of temperature, coating, and lubrication to the tribological characteristics in hot forming as well as the tribometers for different metal forming processes at elevated temperatures mainly based on the experimental work. The tribological behaviors of oxides in hot forming, such as rolling and stamping, were reviewed and presented. Some commonly used surface coatings and lubricants in hot forming were given. Many types of tribometer were selected and presented and some of them provided a great potential to characterize friction and wear at elevated temperatures. Nevertheless, more testing conditions should be further investigated by developing new tribometers. Eventually, experimental results obtained from reliable tribometers could be used in theory and model developments for different forming processes and materials at high temperatures. The review also showed the great potential in further investigations and innovation in tribology.

Chapter 6

In the aerospace field, electromechanical actuators are increasingly being implemented in place of conventional hydraulic actuators. For safety-critical embedded actuation applications like flight controls, the use of electromechanical actuators introduces specific issues related to thermal balance, reflected inertia, parasitic motion due to compliance and response to failure. Unfortunately, the physical effects governing the actuator behaviour are multidisciplinary, coupled and nonlinear. Although numerous multi-domain and system-level simulation packages are now available on the market, these effects are rarely addressed as a whole because of a lack of scientific approaches for model architecting, multi-purpose incremental modelling and judicious model implementation. In this publication, virtual prototyping of electromechanical actuators is addressed using the Bond-Graph formalism. New approaches are proposed to enable incremental modelling, thermal balance analysis, response to free-run or jamming faults, impact of compliance on parasitic motion, and influence of temperature. A special focus is placed on friction and compliance of the mechanical transmission with fault injection and temperature dependence. Aileron actuation is used to highlight the proposals for control design, energy consumption and thermal analysis, power network pollution analysis and fault response.

Most of the norms used in the field of digital image (and volume) correlation to register two images (or volumes) lead to ill-posed problems. One of the frequent solutions is to enforce a restricted kinematics requiring a compromise between the richness of the solution (i.e., the spatial resolution) and the measurement uncertainty. An alternative route is to use a displacement norm that permits to alleviate this compromise by the means of a mechanical regularization used when the gray levels do not give enough information. It is then possible to compute a displacement vector for each pixel or voxel, inducing lower residuals (in terms of experimental data) while decreasing the noise sensitivity. The resolution performance of these different approaches is discussed, and compared for the analysis of a tensile test on a cast iron specimen based on a pair of tomographic images. As representative reconstructed volumes lead to a large number of degrees of freedom, a dedicated GPU computational strategy has been developed and implemented.

In many engineering optimization problems, the number of function evaluations is often very limited because of the computational cost to run one high-fidelity numerical simulation. Using a classic optimization algorithm, such as a derivative-based algorithm or an evolutionary algorithm, directly on a computational model is not suitable in this case. A common approach to addressing this challenge is to use black-box surrogate modelling techniques. The most popular surrogate-based optimization algorithm is the efficient global optimization (EGO) algorithm, which is an iterative sampling algorithm that adds one (or many) point(s) per iteration. This algorithm is often based on an infill sampling criterion, called expected improvement, which represents a trade-off between promising and uncertain areas. Many studies have shown the efficiency of EGO, particularly when the number of input variables is relatively low. However, its performance on high-dimensional problems is still poor since the Kriging models used are time-consuming to build. To deal with this issue, this article introduces a surrogate-based optimization method that is suited to high-dimensional problems. The method first uses the ‘locating the regional extreme’ criterion, which incorporates minimizing the surrogate model while also maximizing the expected improvement criterion. Then, it replaces the Kriging models by the KPLS(+K) models (Kriging combined with the partial least squares method), which are more suitable for high-dimensional problems. Finally, the proposed approach is validated by a comparison with alternative methods existing in the literature on some analytical functions and on 12-dimensional and 50-dimensional instances of the benchmark automotive problem ‘MOPTA08’.

In this paper, an original approach is proposed to calculate the static load distribution and the axial stiffness of a planetary roller screw (PRS) mechanism. Assuming that the external loading is shared equally over an arbitrary number of rollers, only a sector of the system is represented to save on computing time. The approach consists in using a structure of bars, beams, and nonlinear springs to model the different components of the mechanism and their interactions. This nonlinear model describes the details of the mechanism and captures the shape of the nut as well as the bending deformation of the roller. All materials are assumed to operate in the elastic range. The load distribution and the axial stiffness are determined in three specific configurations of the system for both compressive and tensile loads. Further, the influence of the shape of the nut is studied in the case of the inverted PRS. The results obtained from this approach are also compared to those computed with a three-dimensional finite-element (3D FE) model. Finally, since the calculations appear to be very accurate, a parametric study is conducted to show the impact of the bending of the roller on the load distribution.

The migration of neutrally buoyant finite sized particles in a Newtonian square channel flow is investigated in the limit of very low solid volumetric concentration, within a wide range of channel Reynolds numbers Re = [0.07-120]. In situ microscope measurements of particle distributions, taken far from the channel inlet (at a distance several thousand times the channel height), revealed that particles are preferentially located near the channel walls at Re > 10 and near the channel center at Re < 1. Whereas the cross-streamline particle motion is governed by inertia-induced lift forces at high inertia, it seems to be controlled by shear-induced particle interactions at low (but finite) Reynolds numbers, despite the low solid volume fraction (<1%). The transition between both regimes is observed in the range Re = [1-10]. In order to exclude the effect of multi-body interactions, the trajectories of single freely moving particles are calculated thanks to numerical simulations based on the force coupling method. With the deployed numerical tool, the complete particle trajectories are accessible within a reasonable computational time only in the inertial regime (Re > 10). In this regime, we show that (i) the particle undergoes cross-streamline migration followed by a cross-lateral migration (parallel to the wall) in agreement with previous observations, and (ii) the stable equilibrium positions are located at the midline of the channel faces while the diagonal equilibrium positions are unstable. At low flow inertia, the first instants of the numerical simulations (carried at Re = O(1)) reveal that the cross-streamline migration of a single particle is oriented towards the channel wall, suggesting that the particle preferential positions around the channel center, observed in the experiments, are rather due to multi-body interactions.

SUMMARY This paper proposes a novel technique to reduce the computational burden associated with the simulation of localized failure. The proposed methodology affords the simulation of damage initiation and propagation while concentrating the computational effort where it is most needed, that is, in the localization zones. To do so, a local/global technique is devised where the global (slave) problem (far from the zones undergoing severe damage and cracking) is solved for in a reduced space computed by the classical proper orthogonal decomposition while the local (master) degrees of freedom (associated with the part of the structure where most of the damage is taking place) are fully resolved. Both domains are coupled through a local/global technique. This method circumvents the difficulties associated with model order reduction for the simulation of highly nonlinear mechanical failure and offers an alternative or complementary approach to the development of multiscale fracture simulators. Copyright © 2011 John Wiley & Sons, Ltd.

In this paper, the dynamic response of a harmonically forced linear oscillator (LO) strongly coupled to a nonlinear energy sink (NES) is investigated both theoretically and experimentally. The system studied comprises an LO with an embedded, purely cubic NES. The behavior of the system is analyzed in the vicinity of 1:1 resonance. The complexification-averaging technique is used to obtain modulation equations and the associated fixed points. These modulation equations are analyzed using asymptotic expansion to study the regimes related to relaxation oscillation of the slow flow, called strongly modulated response (SMR). The zones where SMR occurs are computed using a mapping procedure. The slow invariant manifolds (SIM) are used to derive a proper optimization procedure. It is shown that there is an optimal zone in the forcing amplitude-nonlinear stiffness parameter plane, where SMR occurs without having a high amplitude detached resonance tongue. Two experimental setups are presented. One is not optimized and has a relatively high mass ratio (≈13%) and the other one is optimized and exhibits strong mass asymmetry (mass ratio ≈1%). Different frequency response curves and associated zones of SMR are obtained for various forcing amplitudes. The reported experimental results confirm the design procedure and the possible application of NES for vibration mitigation under periodic forcing.

Additive manufacturing (AM) continues to rise in popularity due to its various advantages over traditional manufacturing processes. AM interests industry, but achieving repeatable production quality remains problematic for many AM technologies. Thus, modeling different process variables in AM using machine learning can be highly beneficial in creating useful knowledge of the process. Such developed artificial neural network (ANN) models would aid designers and manufacturers to make informed decisions about their products and processes. However, it is challenging to define an appropriate ANN topology that captures the AM system behavior. Toward that goal, an approach combining dimensional analysis conceptual modeling (DACM) and classical ANNs is proposed to create a new type of knowledge-based ANN (KB-ANN). This approach integrates existing literature and expert knowledge of the AM process to define a topology for the KB-ANN model. The proposed KB-ANN is a hybrid learning network that encompasses topological zones derived from knowledge of the process and other zones where missing knowledge is modeled using classical ANNs. The usefulness of the method is demonstrated using a case study to model wall thickness, part height, and total part mass in a fused deposition modeling (FDM) process. The KB-ANN-based model for FDM has the same performance with better generalization capabilities using fewer weights trained, when compared to a classical ANN.

ABSTRACT We report on the main results of a collaborative work devoted to the study of the uncertainties associated with Digital image correlation techniques (DIC). More specifically, the dependence of displacement measurement uncertainties with both image characteristics and DIC parameters is emphasised. A previous work [Bornert et al . (2009) Assessment of digital image correlation measurement errors: methodology and results. Exp. Mech. 49, 353–370] dedicated to situations with spatially fluctuating displacement fields demonstrated the existence of an ‘ultimate error’ regime, insensitive to the mismatch between the shape function and the real displacement field. The present work is focused on this ultimate error. To ensure that there is no mismatch error, synthetic images of in‐plane rigid body translation have been analysed. Several DIC softwares developed by or in use in the French community have been used to explore the effects of a large number of settings. The discrepancies between DIC evaluated displacements and prescribed ones have been statistically analysed in terms of random errors and systematic bias, in correlation with the fractional part τ of the displacement component expressed in pixels. Main results are as follows: (i) bias amplitude is almost always insensitive to subset size, (ii) standard deviation of random error increases with noise level and decreases with subset size and (iii) DIC formulations can be split up into two main families regarding bias sensitivity to noise. For the first one, bias amplitude increases with noise while it remains nearly constant for the second one. In addition, for the first family, a strong dependence of random error with τ is observed for noisy images.

Irreversible deformation in relation to the microstructure was investigated for a polycrystalline Ni-based superalloy (Alloy 718) from room temperature to 650 °C using high-resolution digital image correlation (HR-DIC) techniques. Interrupted tensile tests were performed under a protective atmosphere to ensure the stability of the speckle pattern to track kinematics fields from surface analyses. In-plane strain localization was captured using HR-DIC on scanning electron microscopy (SEM) images. A statistical analysis of different strain localization events in relation to the microstructural features was conducted, i.e., intragranular slip localization, slip localization parallel to and near Σ3-twin boundaries (Σ3-TB), and grain boundary sliding (GBS). Alloy 718 exhibited slip localization at room temperature and 350 °C. Intense strain localization develops parallel and in the vicinity of Σ3-TB from the onset of the microplasticity. Few intense slip stimulated-grain boundary sliding events were found due to slip localization on both grains adjacent to the grain boundary. At 650 °C, Alloy 718 experienced grain boundary sliding at the onset of the yield without particular slip localization in adjacent grains. At lower temperatures, strain localization parallel to and near Σ3-TB was intense, and intragranular slip localization intensified with increasing macroscopic deformation. Particular microstructural configurations were found at 650 °C leading to premature damage: (i) sub-surface cavitation at grain boundaries, and (ii) grain boundary cracking due to intense shearing near a Σ3-TB.