Frédéric Lachaud

• PhD, HDR
• Professor (Full) at Institut Superieur de l'Aeronautique et de l'Espace (ISAE-SUPAERO)

In the context of enhancing the sustainability of aerospace vehicles, the structures must be designed to anticipate the possibility of disassembly. Mandatory certification in aeronautics and the robustness of satellites require structures to maintain their integrity to ensure safety during their life, which can come into conflict with the need for...

To increase the environmental sustainability of products, the repair and refurbishment of damaged or obsolete components can be carried out using additive manufacturing (AM) processes. The Laser-powder directed energy deposition (LP-DED) process is an interesting candidate due to its many potential applications, particularly for the repair of metal...

Determining adhesive failure in adhesively bonded joints is still challenging in the field. While the three-point bending test (3PBT) (ISO 14679:1997) has been helpful in identifying critical forces and displacements related to bond strength, it only allows for a qualitative assessment of the bond line. Recently, a new quantitative methodology has...

div class="section abstract"> Ice adhesion characterization relies heavily on experimental data, especially when dealing with fracture parameters. In this paper, a complementary framework encompassing experimental testing with the numerical treatment of the fracture variables is proposed to provide a physical description of adhesive fracture propag...

Microscale residual stress may develop during the manufacturing of Carbon Fiber-Reinforced Polymer (CFRP) composites and negatively affect apparent macroscale mechanical properties. Accordingly, accurately capturing residual stress may be essential in computational methods used for composite material design. This work presents a new data-driven met...

Bonded repairs for aerospace composite structures are very promising thanks to the high strength recovery rate they can achieve while keeping a good strength to mass ratio. Flush repairs, i.e. scarf and stepped repairs, are the most suitable to repair load-carrying structures as they provide maximum repairs efficiency while keeping a smooth aerodyn...

The design phase of an engineering project, especially in aerospace, is often time and resource consuming and can cause it to fail before it has even entered its infancy. Being equipped with reliable tools that can reduce computational time and resources committed without significant sacrifices in accuracy is a priority, and research is pushing to...

An aerospace structure is built from the assembly of structural sub-components involving joining technologies such as welding, mechanical fastening or adhesive bonding. The function of joints is to ensure load transfer between the structural sub-components. The integrity of the structure directly depends on strength of these joints. In order to des...

In this work, the time-dependent mechanical behavior of a short carbon fiber-reinforced PEEK is investigated at temperatures near and above the glass transition temperature and for stresses below the damage threshold. An experimental procedure including creep/recovery tests and dynamic mechanical tests was carried out by varying stress levels, temp...

In the present work, a specific three-point bending test is applied to evaluate how the roughness can impact the bond strength (adherence) and the mechanism of interfacial failure initiation. The study is conducted using an aluminum alloy 2024-T3 as substrate and the DGEBA (polyepoxide bisphenol A diglycidyl ether) /DETA (diethylenetriamine) as adh...

The current work is intended to give an overview of issues related to the numerical simulation of adhesive spreading for liquid to semi-liquid adhesives. The advantages and limitations are presented in order to guide the choice of the suitable approach depending on the case under consideration. It is shown that methods are of two categories, whethe...

Dans le cadre de la technologie d'assemblage par collage, l'évaluation des propriétés interfaciales est essentielle afin de déterminer la réponse globale de l'assemblage collé. En ce qui concerne la caractérisation mécanique des assemblages collés, une grande gamme de tests est largement utilisée pour déterminer les propriétés des adhésifs (rupture...

In the framework of the adhesive bonding, the assessment of interfacial properties has an essential role in determining the adhesive joints' global responses. Various surface preparations are available for each type of metallic substrate. There are plenty of tests widely used for mechanical characterisation to determine the adhesive properties and...

Flax fibres reinforced polymer composites are more and more used in various fields such as transportation due to the low density of flax paired up with good mechanical properties. This calls for a better understanding and prediction of the mechanical behaviour of such composites. In this study, the mechanical behaviour of flax fibres fabric reinfor...

This article proposes a synthesis and contribution at three levels: generation of dynamic equations of shell structures interacting with fluids, reduction of implicit resolution, and cross-applications to aerospace tanks and living systems. The synthesis of the equations is proposed around the four principles of thermodynamics at the level of discr...

This research deals with the development of a new semi-analytical model for composite-metal eccentric tensile bolted joints of casing structures. The model is based on a direct stiffness method considering structural elements , where flanges are modeled with axisymmetric shell elements, the bolt with a beam element and contact behavior with a speci...

In the framework of lightweight structures, the bonded joints appear as a suitable solution for increasing the mass-to-strength ratio. However, the full understanding of the interface debonding is a key obstacle to be overcome in critical systems. For characterizing adhesive-to-adherend interface crack initiation, the three-point bending test has b...

This study presents a numerical mesoscale approach to simulate the damage and failure mechanism of woven laminated composites under low velocity impact loading conditions. First, measurements were made on samples to obtain a realistic reproduction of the microstructure. This allows relating failure mechanisms in composite laminates with their geome...

The cohesive zone modelling (CZM) is extensively used for the simulation of delamination propagation of composite laminated materials. The Finite Element (FE) method is able to support the CZM. Nevertheless, a refined mesh in the cohesive zone is required to describe accurately the energy dissipation. A 1D-beam simplified analysis based on the macr...

Carbon fiber reinforced plastics (CFRP) are widely used in aircraft industry because of their high mechanical properties. However these properties considerably drop when composite materials are drilled and bolted. Thus, it is important to master the composite bolted joint behavior to avoid a structural failure. Experimental test on single lap bolte...

In this paper, the mechanisms of damage of an oxide/oxide ceramic matrix composite bearing are studied with a new experimental setup, the balanced quarter hole device (BQH). This test was designed to allow direct observation of the damage development on a material subjected to bearing failure. In a standard bearing experiment, real time monitoring...

Composite materials are increasingly used in the aeronautical field. The assembly of structures requires usually drilling of composite parts. Drilling of composite materials generates defects, mainly delamination at the exit of the hole. This major defect diminishes the structure strength. Delamination is directly related to the drilling thrust for...

Adhesive bondline mechanical behaviour is frequently described with cohesive zone models (CZM). For mode I loading condition these phenomenological laws simply represent the evolution of the peel stress as a function of the two adherends relative displacement normal to the joint. Generally, these laws are identified rather than really measured usin...

Bolting technologies have been commonly used to assemble structural members in order to carry loads. However, the main drawback of these joints is the local reduction of the strength-to-stress ratio. Compared to the bolted joints, adhesive bonding technology allows for the increase of static and fatigue strength while reducing the weight. The Finit...

Adhesive bonding modelling is often realised using cohesive zone models (CZM). For pure mode I loading, these laws represent the cohesive stress versus the interface displacement evolution designated as traction-separation laws (TSL). They enable the description of the interface irreversible phenomena such as damage and/or plasticity, while permitt...

In this paper, the potential static strength of hybrid (bolted/bonded)—termed “HBB”—joints with functionally graded adhesives (FGA) is theoretically investigated, in reference to the pure bolted joint, the pure bonded joint, and the HBB joint with homogeneous adhesive (HA). The investigation is performed on a particular in-plane tensile-loaded sing...

Adhesively bonded joints are often addressed through Finite Element (FE). However, analyses based on FE models are computationally expensive, especially when the number of adherends increases. Simplified approaches are suitable for intensive parametric studies. Firstly, a resolution approach for a 1D-beam simplified model of bonded joint stress ana...

The failure of fibers inside the yarns of 3D woven carbon/epoxy composites is investigated experimentally by estimating the critical energy release rate GC, through the analysis of Compact Tension (CT) and Single Edge Notched Beam (SENB) specimens. Close attention is paid to the specimen design as well as the tracking of the crack growth. Several d...

The interest in functionally graded adhesive (FGA) joints has been increasing in recent years. For example, FGAs offer the opportunity to optimize the strength of multi-material bonded joints by locally tailoring the adhesive properties and without modifying the design of the adherends to be joined. The development of dedicated stress analyses to p...

The demand for designing lightweight structures without any loss of strength or stiffness has conducted many engineers and researchers to seek for alternative joining methods. In this context, adhesive bonding may appear as an attractive joining method. However the interest of adhesive bonding remains while the structural integrity of the joint is...

The necessity of understanding the influence of cutting variables in orthogonal cutting of Carbon Fiber Reinforced Polymer (CFRP) is vital because of their significant influences to the quality of manufactured parts. In this present research work the influences of different cutting depths to the cutting and thrust forces have been analyzed and a co...

Functionally graded adhesive (FGA) joints involve a continuous variation of the adhesive properties along the overlap allowing for the homogenization of the stress distribution and load transfer, in order to increase the joint strength. The use of FGA joints made of dissimilar adherends under combined mechanical and thermal loads could then be an a...

In the context of increasing the strength-to-mass ratio of lightweight structures, the adhesively bonded joining technology appears to be an attractive solution. Nevertheless, the adhesive bonding method is important when the structural integrity of joints has to be ensured. In the literature, the cohesive zone models (CZMs) are shown to be able to...

Experimental and numerical modelling of the mechanical behavior of bonded joints as function of adhesive thickness.

Presentation associated with the related conference paper.

L’essai de flexion 3 points a été développé par Roche dans les années 80 [1]. La particularité de cet essai est qu’il ne consiste pas en un assemblage sandwich comme il est de coutume dans les essais d’adhérence des assemblages collés. Il consiste en un plot d’adhésif collé sur le substrat. Cet essai a été choisi, car il permet d’obtenir une ruptur...

The assembly of aeronautical parts requires the machining of composite materials. Drilling is the most important process in the assembly. When drilling composite materials, a number of defects are generating. A solution, to reduce these defects, is to drill using a step gundrill. In this paper, drilling of thick composite plates using a step gundri...

The load transfer in hybrid (bolted/bonded) – denoted HBB – single-lap joints is complicated due to the association of two different transfer modes (discrete and continuous) through elements with different stiffnesses. The Finite Element (FE) method can be used to address the stress analysis of those joints. However, analyses based on FE models are...

Composite material aircrafts are protected against lightning on the basis of complex and expansive lightning strike experimental plans aiming at designing optimal protections. The paper aims at reducing the number of lightning strike tests on protected and painted composite panels. An analytical calculation is presented that gives the characteristi...

The fracture toughness GC was identified on 3D woven carbon/epoxy composites, using CT and SENB specimens. The analysis relied on multiple instrumentation technics in order to track the crack growth and compared several data analysis methods to obtain a noise and linear-asumption independant process. Variation of GC with the specimen size and shape...

In hybrid composite/metallic structures, loads can be transmitted from one part to the other through localized contact pressures, i.e., bearing. Such structures may be rotating structures, which can accumulate as many as 10⁹ load cycles during their service life. Designing safe hybrid rotating structures thus requires a sound understanding of how c...

The use of composite materials machining is increasing more and more in aeronautical. Drilling process is in particular the most used process in the assembly of aeronautical structures. When drilling thick composite laminates, delamination occurs at the exit of the hole. These defects are assumed to be the major defects. They diminish the strength...

Short-carbon-fibre-reinforced polyether ether ketones are materials of great interest for the aeronautical industry. In this study, a design of experiment was carried out to understand the effect of process parameters on micro- and macro-scale properties of injection-moulded short-carbon-fibre-reinforced polyether ether ketone (90HMF40). Mould temp...

Fibre kinking is one of the main failure modes of composite laminates under compression loading. In this paper, the role of kinking in the failure of quasi-isotropic composites subjected to a bearing load is investigated. High-resolution CT scans show that kinking is largely involved in the events leading to laminate collapse, notably by triggering...

Lightning strikes of composite materials induce two distinct kinds of direct effects: surface and bulk mechanical damage. Bulk damage includes fiber-resin debonding, transverse cracks, fiber rupture and ply delamination. It results from the mechanical stresses associated to physical processes which come with lightning strikes such as surface explos...

The Finite Element (FE) method is able to address the stress analysis of adhesively bonded joints. However, analyses based on FE models are computationally expansive and it would be profitable to develop simplified approaches enabling extensive parametric studies. Firstly, a 1D-beam simplified model for the bonded joint stress analysis assuming a l...

The machining of composite materials is a growing problem in the aeronautical field. In particular, the drilling of these materials, required to assemble different parts, is difficult to control and often leads to delamination at the exit of the laminates. This can affect the strength of the structure. In this paper, the drilling of thick composite...

The orthogonal cutting of composite T800/M21 is simulated using a dynamic explicit analysis. To simulate the cavity behavior in the inner ninety-degree plies, a three-dimensional model with an elastic homogenous damage-evolving material is used. Modified Matzenmiller failure criteria are applied to predict damage initiation and evolution in the stu...

Lightning strikes on thin monolithic composite materials such as aircraft fuselage skin induce two distinct kinds of direct effects: surface and bulk mechanical damage. Bulk damage includes fibre-resin debonding, transverse cracks, fibre rupture and ply delamination which are caused by mechanical stresses resulting from physical processes induced b...

Lightning strike threats are well accounted for by aircraft manufacturers, through rigorous procedures acknowledged by airworthiness authorities, but there still remains a significant potential for mass optimization of protections, especially regarding features adopted for composite structures. In a first paper we presented a method to design mecha...

Aeronautic Certification rules established for the metallic materials are not convenient for the composite structures concerning the resistance against impact. The computer-based design is a new methodology that is thought about to replace the experimental tests. It becomes necessary for numerical methods to be robust and predictive for impact. Thr...

Composite materials are increasingly used in aeronautics. The assembly of aircraft structures requires the machining of different parts. The drilling of thick composite plates is a particularly delicate operation because of the fast rise in the temperature of the tool and the material. This causes defects at the hole entry, on the wall of the hole,...

The composite materials are nowadays widely used in aeronautical domain. These materials are subjected to different types of loading that can damage a part of the structure. This diminishes the resistance of the structure to failure. In this paper, matrix cracking and delamination propagation in composite laminates are simulated as a part of damage...

The drilling process is widely used in the assembly of composite structures. The twist drill is the most commonly used cutter as for metallic structures. Delamination at the hole exit is considered as the major defect during drilling of composite laminates. A solution to minimize these defects at the exit of the hole is to drill using a pilot hole....

Low-velocity/low-energy edge impact and quasi-static experiments have been carried out on carbon fiber-reinforced plastic structures. A drop-weight testing machine has been used to impact four different uni-directional laminates at 10, 20 and 35-J impact energy levels. In parallel, a quasi-static study has been carried out to compare its results wi...

Energy absorption during crushing is evaluated using a thermodynamic based continuum damage model inspired from the Matzenmiller-Lubliner-Taylors model. It was found that for crash-worthiness applications, it is necessary to couple the progressive ruin of the material to a representation of the matter openings and debris generation. Element kill te...

The hole wall defects created during drilling of carbon fiber reinforced polymer laminates are analyzed. First, an analysis of the location of the defects on the wall is performed. It is shown that, using results of orthogonal cutting, it is possible to predict the location of the main defects. Then refined scanning electron microscopic observation...

Lightning strikes of composite materials induce two distinct kinds of direct effects: surface and bulk mechanical damage. Bulk damage includes fiber-resin debonding, transverse cracks, fiber rupture and ply delamination. It results from the mechanical stress associated to physical processes which come with lightning strikes such as surface explosio...

Computer based design using damage mechanics is thought about as a new methodology to replace tests and help deriving realistic while simple new rules for Aeronautic Certification of composite structures. Numerical methods and models must then be robust and predictive. Three different computational strategies are developed and compared: a Cohesive...

This paper presents a structural health monitoring (SHM) method for in situ damage detection and localization in carbon fiber reinforced plates (CFRPs). The detection is achieved using the electromechanical impedance (EMI) technique employing piezoelectric transducers as high-frequency modal sensors. Numerical simulations based on the finite elemen...

The damage tolerance methodology is used here to compare impact damage from experimental testing and virtual (numerical) testing. The first part of the study aims to identify links between experimental internal (delaminated area) and external measurable damage (dent depth) for a typical aeronautical T800S/M21e laminate. Effects of the mass/velocity...

The Low through-the-Thickness Strengths of Composites make them Prone to Delamination and Brutal Rupture. for Primary Aircraft Structural Components, it is Necessary to Predict Failure with Adequate Criteria for any Structure of Various Thicknesses and in Zones of Material or Geometric Discontinuities. the Purpose of the Present Work is to Evaluate...

Composite corners are generally tested under four point-bending to identify Inter-Laminar Tensile Strength design values. Hereafter several lay-ups have been defined in order to characterize very different damage evolution processes. Damage monitoring has been performed with the help of Digital Image Correlation, Acoustic Emission and Fast Video Re...

Piezoelectric sensors are widely used for structure health monitoring technique. In particular, electromechanical impedance techniques give simple and low-cost solutions for detecting damage in composite structures. The purpose of the method proposed in this article is to generate a damage localization map based on both indicators computed from ele...

The Finite Element (FE) method could be able to address the stress analysis of bonded joints. Nevertheless, analyses based on FE models are mainly computationally cost expensive and it would be profitable to develop simplified approaches, enabling extensive parametric studies. Firstly, a one-dimensional 1D-bar and 1D-beam simplified models for the...

Piezoelectric sensors are widely used for Structure Health Monitoring (SHM) technique due to their high-frequency capability. In particular, electromechanical impedance (EMI) techniques give simple and low cost solutions for detecting damage in composite structures. For example, damage indicators computed from EMI deviations between the pristine st...

Presentation of computation strategies for the coupled experimental / numerical simulation of composite joints

Variations of injection-moulding parameters have a great impact on mechanical and damaging properties of short-fibre reinforced thermoplastics. The aim of the study is to predict the behaviour and damaging of an injected specimen under monotonic quasi-static tensile loading depending on injection parameters thanks to a design of experiments carried...

This paper presents a study of Finite Element Model Matching, based on the use of displacement field measurements. The wealth of information provided by full-field measurement techniques is extremely useful in experimental mechanics, because it is without contact. This study is a three-dimensional mechanical problem. An investigation of the seconda...

A continuum damage model inspired from the Matzenmiller-Lubliner-Taylor's model, has been derived to predict damage induced in T800S/M21GC sample plates during low velocity impacts. It was found that for crashworthiness applications, it is necessary to couple the progressive ruin of the material to a representation of the matter openings. Element k...

This study presents the influence of the manufacturing parameters of the injection-transfer process over tensile properties of Discontinuous Carbon Fiber Reinforced Composite (DCFRC) manufactured by this process. The matrix is epoxy and the fiber volume rate is 56%. The material studied is considered as a long fiber composite since fibers are longe...

This research activity report is mainly based on the last 14 years work for understanding and modeling the nonlinear mechanical behavior of aeronautical composite materials. Being initiated during my PhD, this work is an extent of it, oriented to the analysis of damage phenomena (initiation and propagation) under static or rapid dynamic loadings fo...

Composite materials are widely used in aeronautical structures. Assembling the various parts involved requires machining operations, especially drilling. When drilling, a number of defects that diminish the structure breaking strength are propagated. Delamination on hole exit is considered to be the main such defect, this being directly related to...

Résumé Les travaux portant sur le procédé de fabrication par injection de matériaux composites à fibres longues discontinues et à matrice thermodurcissable sont peu nombreux. Cette étude présente l'influence de la longueur des fibres sur les propriétés mécaniques en traction d'un matériau composite carbone/époxy à fibres mi longues discontinues fab...