Pascal CASARI

• Professor
• Professor at Nantes Université

Aimed at the decarbonization of marine structures under harsh humid environments, the present study explores the cyclic hygroscopic aging behavior of balsa wood core bio‐composite sandwich structures with manufacturing defects in Glass‐Fiber Reinforced‐Polymer (GFRP) skins. Both experimental investigations and analytical predictions are presented....

The aim of this work is the data generation of aged mechanical properties following the Arrhenius equation and large deformation theory for a transversely isotropic bio‐based polyurethane foam, and the application of this dataset in the training process of different deep neural network architectures to evaluate their capacity to predict the full st...

For strengthening or rehabilitation of existing structures, patches of fiber-reinforced polymers (FRP) materials are being adhesively bonded to the existing metallic structures. So far, Carbon FRP (CFRP) are the main composite materials industrially implemented for metal structural reinforcement, due to their reliability and high mechanical perform...

This work investigates the moisture diffusion behavior of bio-based balsa wood and balsa core sandwich structures. All the special dog-bone balsa wood and sandwich specimens were immersed in water at room temperature to saturation, and the moisture absorption kinetics were identified analytically and numerically. It was found that the final saturat...

Afin de contribuer au progrès du protocole d'essai de mode II et de fatigue pour les stratifiés composites, une méthode d'essai rapide pour la croissance de la fissure de fatigue en mode II des joints adhésifs en CFRP a été mise au point avec une fréquence élevée de 5 Hz. La nouvelle technique d'impression 3D a été utilisée pour produire les charge...

The objective of this study is to assess, characterize, and forecast the aging effects on the mechanical properties of a vegetable‐based polyurethane foam (PUF) derived from castor oil under elevated relative humidity conditions and at two distinct load orientations (aligned with the expansion direction and perpendicular to it). Ten specimens were...

To contribute to the development of sustainable composites, this work investigates the effects of moisture on the key AE characteristics related to the damage mechanisms of a bio-based balsa wood core sandwich in 4-point bending tests, including cumulative counts, amplitude, peak frequency, and duration. Novel triple dog-bone balsa wood core sandwi...

The current dataset brings raw compression test information of a vegetable-based polyurethane foam (PUF) exposed to different temperatures over different periods of time. Such experimental dataset can provide researches with important information in the application of numerical and datadriven simulations. Also, it saves money and time once the expe...

Using fiber-reinforced composite patches for repairing damaged structures made of metal or/and concrete is an interesting and widely available solution on the market using synthetic materials. These repairing patches are bonded on the structures’ surfaces to increase their strength against internal stresses, as well as protect them from external ph...

A multi-layer structure by sandwiching rigid cellular PVC (polyvinyl chloride) foam between two GFRP (glass-fibre reinforced plastic) faces is studied in order to investigate the sample edge effects on fatigue life of the sandwich structure. Therefore, a new geometry of specimen is developed based on numerical simulation approach. Compared to the r...

In this work, 4-point bending fatigue performance including the fatigue damage evolution process, stiffness degradation process and fatigue lifetime of eco balsa cored composite sandwich structures have been investigated. An original triple dog-bone shape has been used to facilitate the observation of the induced laminate skin and core damages than...

The work focuses on the mechanical strength of composite structures with embedded electrical functionalities submitted to low energy impact. This material is defined for aeronautical applications as multilayers of glass fibre composite with flat electrical cable layers embedded. The main question is about the damage involved by the low energy impac...

The development of modern technologies requires the use of materials with high mechanical properties specific to their use, but with low densities. Composite materials with sandwich structure meet the above requirements, due to their low density, high strength, high rigidity and excellent durability. Despite of their advantages, sandwich structure...

In this work, moisture effects on strength/stiffness degradation of GFRP-balsa sandwich structures are studied with the help of active AE and IRT techniques. AE pencil lead breaking tests were conducted before 4-point bending tests to investigate the relationships between Moisture Content (MC) and AE wave propagation properties, including AE wave v...

For high-performance foiling yachts, cavitation is often a limiting factor for take-off and top speed. The present work investigates solutions to control the onset of cavitation thanks to a combination of leading edge and trailing edge flaps. Numerical and experiments in a hydrodynamic tunnel are conducted in order to assess the effect of specific...

This work focuses on moisture effects on mechanical properties of GFRP-balsa sandwich structure experimentally and numerically. Firstly, relationships between Moisture Content (MC) and Acoustic Emission (AE) wave velocity have been demonstrated by Hsu-Nielsen tests during the water immersion tests. And then, a new methodology was proposed to predic...

In this work, Non-Destructive Testing (NDT) techniques (Munoz V et al., 2016), including Acoustic Emission (AE) and InfraRed Thermography (IRT), were coupled to investigate the bending behavior and damage mechanisms of GFRP-balsa sandwich structures. Post-mortem examinations by microscope were also compared with NDT observations to characterize the...

In this paper deep investigations and full characterization of SA 70 epoxy’s properties as a bulk material and as an adhesive in a bonded assembly, are performed. Those properties are essential for an industrial or a supplier and whose determination is not at all obvious. Double lap bonded steel-SA 70 epoxy assemblies were prepared and then thermal...

The bending behavior of foam core sandwich composites has increasingly attracted attention and application in industries such as shipbuilding, aircraft, and wind turbine industries. The main objective of this research work is the assessment of shear strain in a foam core beam by means of optical fiber sensors during a bending test. Experimental stu...

Dans ce travail, un enregistrement des signaux acoustiques et thermiques est couplé aux essais de flexion pour investiguer les mécanismes d'endommagement de la structure sandwich GFRP-balsa sous flexion 4 points en statique. Une approche tenant compte de la corrélation entre le mouvement vertical du pixel dans les images de température et le déplac...

In this paper, an analysis of the evolution of microcracking of Non-Crimp Fabric (NCF) polymer matrix laminates under hygrothermal loading is presented. These composites are reinforced with biaxial NCF styles ([+45/-45], [0/90], etc.) and manufactured by Liquid Resin Infusion (LRI). The samples are subjected to accelerated hygrothermal cycles that...

The present study focuses on providing enhanced monitoring methods to control balsa cored sandwich composites structures used in naval and construction industry. It demonstrates that AE wave velocity and amplitude attenuation property can be useful parameters to reflect the variation of moisture content and stiffness of a sandwich structure. Conclu...

This paper develops a simple and versatile analytical method for characterizing residual stress associated with the deposition of thick, thin, single and multilayer coatings. This study is of great importance, since the generation of residual stress can lead to the formation of significant defects in the coating. To illustrate the effectiveness of...

The reinforcement efficiency on a composite depends on the effective transfer of the stress between matrix and fiber. This work presents an experimental and comparative study of fiber-matrix bond strength for fiber-matrix interface between glass fibers and carbon fibers added to the slag-based geopolymer matrix. This analysis was performed by pull-...

The development of modern technologies requires the use of materials with high mechanical properties and lightest weight structure. With their low density, high strength, high rigidity and excellent durability, the sandwich structures are one of the best materials to meet these requirements. Despite of these advantages, sandwich structure is rather...

This work focuses on the rapid determination of Acoustic Emission (AE) wave propagation velocity in composite laminate and sandwich structures using a closed-form formula. Firstly, a classical closed-form model proposed in the literature is extended to determine the acoustic wave velocity in any direction in a composite laminate or sandwich structu...

The efficiency of an optical sensor embedded in a composite structure strongly depends on the interfacial adhesion between the optical fiber coating and the surrounding solid material and on the environment humidity. Moisture diffusion can induce a decrease of the mechanical stiffness and strength of organic matrix composites. The present work repo...

The forming process of thermoplastic composites inevitably leads to the development of residual stresses. This study proposes a model to predict the residual stresses at the ply scale of a thermoplastic composite laminate. It accounts for the heat transfer, crystallization kinetics and mechanical behaviour of the laminate. The model is applied to t...

Abstract The identification of the mechanical behavior of adhesives is necessary to describe the development of residual stresses during their curing, which might impact their mechanical strength and lead to early failure of the bonding. A simple characterization and modeling approach is therefore developed and presented, which permits to monitor a...

Reducing the CO2 emissions is one of the major objectives in aerospace engineering. In this regard, XSun startup is developing an autonomous solar drone, SolarXOne. The latter is independent on one hand in decision with an autopilot and on the other hand in energy using solar cells and batteries. This paper aims at presenting the mechanical behavio...

In this study, the hygro–thermo–mechanical responses of balsa core sandwich structured composite was investigated by using experimental, analytical and numerical results. These investigations were performed on two types of specimen conditions: dry and moisture saturation sandwich composite specimens that are composed of E-glass/polyester skins bond...

Thermo-mechanical properties of sandwich composite materials used in marine applications have been analyzed as a function of the burning duration with various moisture contents. Dry and wet coupons with glass reinforced polymer skins and balsa wood core (saturated with water) were submitted to fire. The mass loss kinetics and the post-combustion me...

In this work, a collaborative experimental study has been conducted to assess the effect an imposed internal pressure has on the controlling the hydrodynamic performance of a compliant composite hydrofoil. It was expected that the internal pressure together with composite structures be suitable to control the hydrodynamic forces as well as cavitati...

This research investigates the fluid-structure interaction and hydroelastic response of a composite hydrofoil using an innovative joint experimental and numerical method. The main novelties are, first, the use of a state-of-the-art strain measurement technique, via a fully-distributed-optical fiber sensor directly embedded within the com- posite pl...

Characterizing the thermomechanical properties of thermoplastic resins and associated composites is of outmost importance to understand the development of process-induced stresses. To that extent, the characterization of a low viscosity PA66 matrix is proposed thanks to a homemade volumetric dilatometer named PvT-XT and a dynamic mechanical analyse...

Research has increased in the development of new families of multiaxial composite materials to meet high performance criteria such as strength and durability. The last decade has seen the emergence of a new generation of composite materials of the Non-Crimp Fabric type (NCF). These are materials consist of multiaxial non-woven reinforcements, and s...

This work investigates the effect of relative humidity (RH) and temperature on drying phenomenon of a siloxane coating during the sol-gel process. An experimental approach was taken, due to a lack of available data in existing literature. Dynamic Vapor Sorption, Fourier Transform Infra-Red spectroscopy and X-ray Photoelectron Spectroscopy analyses...

A new method which allows the development of Low Pressure Cold Sprayed copper coatings on PEEK (Poly-Ether-Ether-Ketone) based composites reinforced by carbon fibers is investigated. Due to the solid state and high velocities of impacting particles, cold spraying involves a high erosion on composite materials, leading to an absence of coatings and...

Les peintures sont classiquement utilisées dans le domaine des énergies marines renouvelables pour protéger les structures acier de la corrosion. Afin d’améliorer l’adhérence et donc la durabilité de ces revêtements, des traitements de surface peuvent être employés. Habituellement, celui-ci est réalisé par sablage. Dans cette étude, des traitements...

Fatigue behavior of sandwich structures with honeycomb core and GFRP skins is studied and failure mode is investigated through tomographic observations. The first S/N curves are presented. The second part discusses the failure modes observed during fatigue tests and responsible for stiffness decrease during fatigue tests.

To reduce maintenance and to increase the corrosion protection and lifetime of maritimestructures while complying with environmental standards, multilayer coatings are applied to protectsteel sections. A new generation of hybrid sol-gel and/or HiPIMS Ni-based thin films appear toconstitute an efficient pre-treatment before the anti-corrosion paint...

The design and qualification of composite repairs for pipelines usually requires hydrostatic tests for the determination of the failure pressure. In this work, the use of a shaft blister test to assess the failure pressure of composite repairs is proposed. Blister tests were conducted to investigate the interfacial debonding of a composite plate bo...

Interply slip plays an important role in composite forming processes, the resulting product geometry, final fiber orientations and fiber stresses. This interply slip will depend on fiber/resin properties, the fibers distribution, the reinforcement architecture and the process conditions. In this paper, a new model, based on Reynolds equation for th...

Self-healing polymer composites are part of a class of materials which have the capability to repair themselves when damaged. They are often tested by inflicting damage onto them and then performing a mechanical test to initiate and measure self-healing. Self-healing efficiency is commonly defined as the ratio of a recovered property value to its o...

In the first part of this paper, a viscoelastic model is used to numerically study the cellular foam core fatigue behaviour. Material’s temperature evolution is quantified with a numerical/experimental confrontation. In the second part, the slamming phenomenon is discussed by measuring the panel flexural strain on a racing sailboat during navigatio...

Polymer metallization using cold spray method, due to low process temperature, is a potential candidate to form electrically conducting polymers as well as composites and improve the mechanical properties of their surface (abrasion, corrosion, etc.). Low Pressure Cold Sprayed copper coatings on PEEK (Poly-Ether-Ether-Ketone) based composites reinfo...

Polyamide based composites are increasingly used in automobile industry. During their lifetime, they are subjected to aggressive environments including moisture which acts as a plasticizer of the polymer network, affecting its mechanical behaviour. Besides, the heterogeneous in-depth moisture content induces a differential hygroscopic swelling that...

The main objective of the present study was to develop a fire thermal model able to predict the evolution of the temperature gradient across a sandwich composite structure when exposed to fire. Thermal response of sandwich panels, with glass/polyester skins and balsa core, was investigated under severe temperature conditions as samples were exposed...

Thermoforming allows the manufacture of structural parts for the automotive and aeronautical domains using long fiber thermoplastic prepregs with short cycle times. During this operation, several sheets of molten prepregs are stacked and subjected to large macroscale strains, mainly via in-plane shear, out-of-plane consolidation or dilatation, and...

The forming process of thermoplastic laminates inevitably lead to the development of process induced – or residual, stresses. These stresses may induce several phenomena in the final part, including dimensional alteration, health degradation and microcrack initiation at several scales. The accurate prediction of the residual stresses is therefore a...

This work aims at highlighting some microstructure-properties relationships; namely: the effect of the microstructure on the diffusive behavior of composites tubes obtained by filament winding technique. Composites tubes are made from either glass or carbon fibers impregnated with the same epoxy matrix cured at 150℃. Specimens were rings cut from t...

The study deals with the experimental and numerical characterisation of the impact response of multifunctional composite structures embedding two layers of electrical cable. Experimental characterisations are carried out with a drop weight tower and reveal internal tension-shear fibre failure at the interface with the embedded cables, with no exter...

La prédiction des contraintes résiduelles de fabrication durant le refroidissement de composites thermoplastiques représente actuellement toujours un challenge pour la communauté scientifique. Une détermination précise de ces contraintes est nécessaire afin d'optimiser les paramètres procédé permettant de limiter leur effet sur la santé finale de l...

The purpose of this study is to investigate the influence of a spatially moving load and edge effects on the fatigue life of the foam-cored sandwich structures. A spatially moving load can be observed in structures subjected to slamming. A new geometry of specimen is developed to reduce the influence of edge effects in the test specimen. Numerical...

The renewable marine energies represent a major economic and political development. The majority of renewable marine structures developers have preferred carbon or a combination between glass and carbonfor MRE systems. The reliability of these components, in a very severe environment, is crucial to the profitability of marine energy systems. These...

This work concerns the study of a double-lap bonded assembly subjected to an impact during its exposure to fire. Numerical simulations have been carried out using ABAQUS. They have shown that the most sensitive zone is the adhesive which shows an early deterioration. The adherent deteriorates less quickly but especially in the areas of the glue. Mo...

The prediction of process induced stresses during the cooling of thermoplastic composites still represents a challenge for the scientific community. However, a precise determination of these stresses is necessary in order to optimize the process conditions and thus lower the stresses effects on the final part health. A model is presented here, that...

In marine construction, ship hulls are subjected to high fatigue stresses due to the impact of waves and their cyclic solicitations. However, fatigue behavior evaluation of the constitutive materials of the hull is based on standard tests. The objective of this study is to take a critical view of the current standard test method set to investigate...

In marine construction, ship hulls are subjected to high fatigue stresses due to the impact of waves and their repetitive actions. However, fatigue life data of the constitutive materials of hull are based on standard test [1]. This paper explains the design of a sandwich specimen under fatigue from 4-points bending test. Following the work from [2...

In this work, we demonstrate that current fatigue characterization tests with high density foam suffer from edge effects within the specimen, probably leading to early failures. Then a new specimen is designed to avoid this artifact. With this developed geometry, the stress is concentrated in the center of the specimen and not in the edge as given...

Moisture diffusion can induce a decrease of the mechanical stiffness of organic matrix composites. Recently, optical sensors have been used in order to measure the hygroscopic strains of organic matrix composites. In this study, the Bragg wavelength shift (λb) has been recorded at room temperature. The measurement have been achieved at higher tempe...

Foam-cored sandwich yacht hulls are subjected to high core shear stresses during slamming events. As slamming is repetitive by nature, failures observed on boats may be due to fatigue. This study aims to investigate possible improvements to fatigue testing of both foam core materials and sandwich specimens. In general test setup induces differences...

The present work investigates the internal stresses induced by moisture absorption in sandwich composite material. Moisture absorption effect was analyzed for balsa core specimens and sandwich structures composed of E-glass/polyester face sheets bonded to a balsa core. These materials were immersed in distilled water at 40 °C and the kinetic of moi...

Cure shrinkage in the thermoset matrix is the major source of cure-induced defects in composite parts for industrial applications. Thus, its correct determination is very important to optimize the composite fabrication process. In general, volume chemical shrinkage of resin is tested and assuming it is isotropic, rule of mixture or a homogenization...

This study is focused on the finite element analysis of the hygro-elastic stresses experienced by unidirec- tional composite structures instrumented by Fiber Bragg Grating (FBG) sensors. One of the significant advantages of this method is that by taking into account the complex geometry of elaborated specimen and their different constituents with h...

This study is devoted to the identification of the moisture expansion coefficients of composite materials by means of a novel measurement technique. This method is based on the insertion of Fibre Bragg Grating (FBG) sensors between composite layers. The sensor enables to measure the hygroscopic strain induced by moisture diffusion in the plane of t...

Environmental concern has resulted in a renewed interest in bio-based materials. Among them, plant fibers are perceived as an environmentally friendly substitute to glass fibers for the reinforcement of composites, particularly in automotive engineering. Due to their wide availability, low cost, low density, high-specific mechanical properties, and...

Natural fibers have good properties to be used as reinforcement in composite materials. The main issue is their hydrophilic behavior. So we propose here to investigate the diffusion phenomenon in such fibres. First, a brief characterization of four vegetal fibers has been achieved. We show that all fibers have a similar composition and structure de...

Thermal expansion is an important property to define the end use application, and to model residual stresses and related problems in a composite part. Thus its accurate determination is essential. In laminated composites, this parameter depends largely on the orientation of fibres, fibre fraction, type of resin and reinforcement, etc. In this artic...

In this work, moisture penetration in glass fiber-reinforced polymers was systematically investigated through both experiments and theoretical approaches. The diffusivities of the neat resin and those of unidirectional composite plates containing various glass fiber volume fractions have been identified through the analysis of hygro-thermal aging t...

The efficiency of an optical sensor embedded in a composite structure strongly depends on the interfacial adhesion between the optical fiber coating and the surrounding solid material. The present paper reports on the study of the interfacial adhesion of an optical fiber embedded in a composite material. A simple system composed of optical fibers e...

This study is devoted to the identification of the moisture expansion coefficients of composite materials by means of a novel measurement technique. This method is based on the insertion of Fibre Bragg Grating (FBG) sensors between composite layers. The sensor enables to measure the hygroscopic strain induced by moisture diffusion in the plane of t...