Search

International audience; Most of the research on hybrid natural fiber composites has been focused on non-structural applications. The aim of this research is to improve the understanding of how to use hybrid natural fiber composites for structural applications, such as in the aerospace and automotive industries. The joining of subassemblies with rivets, bolts, or screws is a prominent feature in these industries, which implies that the presence of holes in the structural members is unavoidable. The study of the effect of holes on the mechanical behavior of these members is therefore imperative, especially given that holes are stress risers. An important factor in the design of open-hole hybrid flax composites is their fatigue behavior under cyclic loading because it accounts for most failures in composite structures. The investigation of this behavior is reported in this study where three types of 16-ply symmetric hybrid composites that were manufactured using woven carbon (C) and unidirectional flax (F), namely, unidirectional (CF[0]), cross-ply (CF[0/90]) and angle-ply (CF[[Formula: see text] 45]) are employed. A circular hole was made in the center of each specimen using either an abrasive water jet or conventional drilling methods. The observed machining-induced critical defect was delamination, which manifested in three forms: peel-up, push-out, and secondary. Stepwise fatigue tests were conducted to determine the damage evolution and high-cycle fatigue strength of each layup. The damage evolution of the material was assessed via stiffness damage, thermographic methods, and dissipated energy per cycle. It was observed that CF[0] layups are unaffected by the machining process and they have an identical high-cycle fatigue strength. For the CF[0/90] and CF[[Formula: see text] 45] layups, conventional drilling specimens have a higher high-cycle fatigue strength than their abrasive water jet counterparts.

International audience; This work presents an experimental investigation of the post-fire flexural strength of Filament-wound Glass Fiber Reinforced Polymer (GFRP) tubes manufactured by CTRA Company. These tubes are assembled according to both the NFT57-900 and DIN-16966 standards’ recommendations. To this end, flexural tests have been carried out on butt-to-butt assembled tubes, before and after fire endurance tests. To gain a better insight into fire-induced damage mechanisms, thermal analysis (DSC and TGA), FTIR analysis tests, as well as Scanning Electron Microscope (SEM) observations have been conducted. The experimental results revealed that a water leakage was observed prior to the recommended threshold time by the International Maritime Organization (IMO) resolution. It has been also confirmed that flexural properties of the GFRP tube are degraded after the fire tests. Furthermore, a quantitative comparison for both filament tubes assembled according to the NFT and DIN standards confirms that the NFT ones depict higher resistance. Finally, damage investigation reveals that the main observed forms of damage occurring during this experiments are delamination and matrix cracking phenomena. The main novelties of this work are (a) extending the classic analysis carried out on simple composite plate to cover water-filled GFRP assembled tubes subject to fire endurance test, and (b) the experimental investigation of DIN and NFT butt welded joined pipes under three point loading prior and post fire endurance test.

International audience; This work aims to experimentally investigate the effect of the machining parameters (Spindle speed and feed) as well as the tool geometry on the drilling quality of ± 55° filament wound hybrid composite tubes consisting of mechanical and anti-corrosion layers. Drilling tests were performed with three different spindle speed (1000, 2000 and 3000 rpm) and five different feeds (0.05, 0.1, 0.15, 0.25 and 0.4 mm/rev). The average surface roughness Ra of both mechanical and anti-corrosion layers was also measured at two angles 0° and −45°. Furthermore, the delamination at the hole entry and exit as function of the feed was quantified by means of an optical microscopy. The experimental results revealed that the drilling of the filament wound layer generates a higher thrust force compared to anti corrosion layer. Moreover, it was found that the filament wound layer present a higher surface roughness than the anti-corrosion layer for all the investigated machining parameters. This result is confirmed by SEM observations and 3D surface topography. Finally, optical observations show that the delamination is predominant at the hole entry and increase with the increase in feed.

International audience

International audience

International audience

International audience

International audience; The three-dimensional printing of long fiber composites was developed in recent years, and the mechanical behavior of the printed composites requires further investigation. The joining of this type of material requires a hole; and with reference to the available literature, the bearing strength requires investigation. In this context, three manufacturing processes were used for hole generation: direct printing, conventional drilling, and abrasive waterjet drilling (AWJ). The holes obtained by these manufacturing processes were characterized using X-ray tomography and a roughness system. Open-hole quasi-static and fatigue tests were used to assess the mechanical behavior of hole manufacturing on the tensile sections. Single-shear bearing tests yielded the same trend as that observed with open holes, where conventional drilling demonstrated higher performance than the printed and AWJ specimens. The absence of delamination and higher drilling temperature sealed the surface, thus limiting the influence of voids.

International audience; This article presents a comprehensive thermomechanical analysis and failure assessment in the drilling of glass fiber-reinforced polymer (GFRP) composites with different thicknesses using a CNC machine and cemented carbide drill with a diameter of 6 mm and point angles of ϕ = 118°. The temperature distribution through drilling was measured using two techniques. The first technique was based on contactless measurements using an IR Fluke camera. The second was based on contact measurements using two thermocouples inserted inside the drill bit. A Kistler dynamometer was used to measure the cutting forces. The delamination factors at the hole exit and hole entry were quantified by using the image processing technique. Multi-variable regression analysis and surface plots were performed to illustrate the significant coefficients and contribution of the machining variables (i.e., feed, speed, and laminate thickness) on machinability parameters (i.e., the thrust force, torque, temperatures, and delamination). It is concluded that the cutting time, as a function of machining variables, has significant control over the induced temperature and, thus, the force, torque, and delamination factor in drilling GFRP composites. The maximum temperature recorded by the IR camera is lower than that of the instrumented drill because the IR camera cannot directly measure the tool–work interaction zone during the drilling process. At the same cutting condition, it is observed that by increasing the thickness of the specimen, the temperature increased. Increasing the thickness from 2.6 to 7.7 had a significant effect on the heat distribution of the HAZ. At a smaller thickness, increasing the cutting speed from 400 to 1600 rpm decreased the maximum thrust force by 15%. The push-out delaminations of the GFRP laminate were accompanied by edge chipping, spalling, and uncut fibers, which were higher than those of the peel-up delaminations.

International audience; The building sector has been showing great interest in incorporating technologically advanced materials with lightweight, ecofriendly, high strength, and stiffness properties in flooring, roofing, and partition walls, etc. In addition to the mechanical properties, these materials should have good thermal properties as well. In response to these requirements, an attempt has been made to study the thermal behavior of green composite sandwich made of flax and agglomerated cork. Composite sandwiches were fabricated by using flax as skin reinforcement and agglomerated cork as core with different densities as 240, 280, and 340 kg m−3 using vacuum bagging method. Glass was also used as skin reinforcement for manufacturing composite sandwiches for comparison purpose. Experiments were conducted to predict thermal properties, viz. thermal conductivity, thermal expansion, flammability, and thermal stability. The experimental results show that the lowest thermal conductivity of 0.03 W m−1 K−1 was observed in flax-based composite sandwich having core density of 240 kg m−3; the lowest thermal expansion of 29.2 × 10−5 °C−1 was observed in glass-based composite sandwich having core density of 340 kg m−3; the highest value of time to ignition was 12 s, and minimum propagation rate was 0.25 mm s−1 in flax-based composite sandwich having core density of 340 kg m−3; The highest initial degradation temperature was 362 °C for glass-based skin and 263 °C for cork having density of 240 kg m−3.

In recent years, material scientists have been focusing on the utilization of materials from natural resources due to environmental concerns. In the same context, the aim of this work is to evaluate impact response, sound absorption behavior, and vibration damping characteristics of natural-based composite sandwich made of flax as skin reinforcement and agglomerated cork as core. Vacuum bagging method was used for manufacturing composite sandwiches with different cork densities of 240, 280, and 340 kg/m3. Composite sandwiches have also been manufactured by using glass as skin reinforcement for comparison. Low velocity impact test was conducted and found that glass fiber reinforced composite sandwich required 73–77% more energy to perforate when compared to the flax fiber reinforced composite sandwich irrespective of core density. Flax fiber reinforced composite sandwich has 45–96% higher sound absorption capacity and 27–32% higher vibration damping ratio than glass fiber reinforced composite sandwich irrespective of core density. This is due to multiscale structure and cellular nature of the flax fiber and the cork materials, respectively. These enhancements in sound and vibration are accomplished with just little forfeits in perforation energy. This study recommends that, if optimized, the natural-based composite sandwich could be an ecologically appealing answer for automobile and construction applications, where impact behavior is important, along with sound and vibration properties.

Conventional milling during aircraft structural composite repair encourages defect generation and distortion, causing hindrance in milling depth control and thereby adversely affecting their mechanical behavior. Abrasive water jet (AWJ) milling can be an alternative to avoid these problems. In this study, carbon/epoxy laminates are milled using AWJ and machined surfaces are characterized at micro (surface texture) and macro (damage size) scales. Defects in the form of craters, ridges-valleys and broken fibers are identified and quantified. A new parameter “crater volume (Cv)” is proposed to quantify and qualify the machining quality in terms of induced damage. This introduces a novel approach to characterize the machined surface without ignoring the machining damage. Milled specimens with different damage levels are subjected to tensile and tension-tension fatigue tests instrumented with thermography and acoustic-emission transducers. Machined specimens with high Cv exhibited inferior fatigue behavior and X-ray tomography revealed that crack/fracture initiation occurred from the crater edges.

International audience; Abrasive Water Jet (AWJ) machining has proven to be an effective and versatile technique for milling various kinds of materials, even with low machinability such as aerospace grade titanium alloy Ti6Al4V. Many studies have been performed in order to master this technology and produce geometrically accurate shapes. However, in the context of bonding repairs which require surfaces free from foreign bodies, AWJ machining presents a significant drawback in form of abrasive grit embedment. The goal of this present work is then to investigate the effect of a post-AWJ machining cleaning operation using Plain Water Jet process (PWJ – i.e. without abrasive particles) on the surface quality and material properties. For this, several characterization techniques were employed. It was concluded that the contamination has been reduced by 65% without noticeable changes in depth of cut and crater volume. The AWJ milling operation produced surface and subsurface hardening as well as biaxial compressive residual stress, mostly piloted by the jet pressure. PWJ cleaning reduced the depth of hardening without clear modification in surface hardness.

International audience; Inconel 718 (IN718) is a precipitation hardened nickel-base super-alloy exhibiting poor machinability and used in the hot section of aircraft engines. These components are subjected to severe thermo-mechanical loads in a highly corrosive environment, limiting their service life due to cracks and wear. Due to their high added-value, repair of damaged IN718 components is an interesting alternative instead their replacement. Repair process involves material removal of the damaged zone and subsequent cavity refill. Nevertheless, material removal of IN718 by conventional methods is a challenging task. Abrasive Water Jet (AWJ), a non-conventional machining process, offers a potential alternative to mitigate IN718 machining problems. However, research on the impact of AWJ process parameters during IN718 milling on the surface and material integrity is limited in the literature. Furthermore, in repair context, no study proposes AWJ machining as material removal process. The present work focuses on a multi-scale characterization of the influence of AWJ process parameters (pressure, traverse speed, step-over distance and abrasive size) on surface roughness, depth of cut, abrasive embedment and residual stress, during milling of untreated IN718. Surface integrity characterization on the milled surfaces was conducted through 3D optical microscopy, profilometry and SEM techniques. Residual stress measurements were performed in longitudinal and transverse directions with respect to the machining path using XRD technique. The results showed that all milled surfaces presented abrasive embedment and a compressive residual stress state with similar values in both directions. Up to 15% of the area of a milled surface consisted of abrasive embedment. The tool path has not influenced the residual stresses. Furthermore, surface roughness is dependent on pressure and traverse speed; depth of cut is influenced by pressure, traverse speed and grit size; abrasive embedment depends on pressure, step-over distance and grit size; whilst, residual stresses are influenced by traverse speed and grit size.

The evolution of in-situ cutting temperature and machining forces during conventional drilling of multi-directional carbon fiber reinforced polymer (MD-CFRP) laminates using a novel inverted drilling setup is presented. The in-situ cutting temperature was measured using fiber Bragg grating (FBG) optical sensor embedded in the stationary drill. The effect of machining parameters such as spindle speed and feed rate on the temperatures and machining forces were studied that indicate the predominant effect of spindle speed on machining temperatures. The drilled MD-CFRP samples and drill bits were characterized by scanning electron microscopy (SEM) and micro-computed tomography ([Formula: see text]) techniques to assess machining-induced damage in the samples and tool wear in the drill bits. Exit-ply delamination was observed in MD-CFRP samples that aggravates with increase in cutting temperature and thrust force caused by evolving tool wear. The measured in-situ machining temperatures using the current experimental setup can be used to achieve better machining models.

Inconel 718 (IN718) is a precipitation hardened nickel-base super-alloy exhibiting high strength and good corrosion resistance at elevated temperatures and on the downside it is characterized by poor machinability. Abrasive Water Jet (AWJ) process, offers a potential method to machining difficult-to-cut materials such as IN718. The present work investigates the influence of Abrasive Water Jet parameters on surface roughness, topography, depth of cut and residual stress when milling IN718. Surface characterization was conducted through 3D optical microscopy and SEM techniques. Residual stresses were measured in longitudinal and transverse directions with respect to the machining path using X-ray diffraction (XRD) technique. The obtained results showed that milled surfaces have a homogeneous texture with embedded abrasive particles and high surface roughness. AWJ process introduced high compressive residual stresses with similar order of level in both directions (X and Y). In addition, it was observed that jet pressure is the most influencing parameter on roughness and depth of cut, whilst traverse speed and step-over distance had a significant effect on the residual stress. Based on the experimental analysis, an empirical model to predict the depth of cut was proposed. The validation of the proposed model, has shown around 5% error in the predicted and actual pocket depth.

International audience; Abrasive water jet (AWJ) milling process, though being an effective alternative to conventional machining for difficult-to-machine materials, induces abrasive embedment which is an issue for repair application by structural bonding. In this context, the effectiveness of cleaning Ti6Al4V specimens by Plain Water Jet (PWJ) post AWJ milling is studied. For this, Ti6Al4V specimens are milled by AWJ process with varying parameters to create several levels of surface quality and contamination. Different characterization techniques have been used to perform a multi-scale analysis of the machined surfaces and surface quality has been quantified by an innovative criterion called “crater volume” (Cv). Then the specimens are subjected to PWJ cleaning operation (using a single set of parameters chosen after preliminary study). Finally, surface texture analysis and contamination quantification is performed and compared with the AWJ milled surfaces. The results revealed that PWJ cleaning reduced the surface contamination by 65% without any significant change in Cv, surface texture and topology. However, it was found that it was impossible to dislodge deeply embedded particles. The comparison of pre and post-cleaning contamination levels also revealed that PWJ cleaning process efficiency depends on the AWJ milling parameters (mainly pressure).

Due to the expensive price of their structures, both in terms of material and manufacturing costs, aerospace manufacturers prefer to perform repair operations as much as possible in case of damage. In this context, the damaged area is removed by conventional or non-conventional milling processes, depending on the material constitutive of the structure to repair. However, all these techniques present issues in case of aerospace grade materials (e.g. Carbon Fibers Reinforced Plastics—CFRPs—or titanium alloys) machining such as excessive tool wear, thermal damage or use of corrosive products. In this context, Abrasive Water Jet (AWJ) machining has proven to be a good alternative to these processes. However, some issues have still to be faced when machining with AWJ. This review presents the influence of the machining parameters on the material removal features (viz. depth of cut and Material Removal Rate) and on the types and expanse of the machine-induced defects and damage when using AWJ for machining of CFRP and metallic materials (mainly aerospace grade titanium alloy Ti6Al4V). Moreover, the link between the machining process and the modifications in the mechanical behaviour are also discussed.

In aerospace industry, polymers reinforced with carbon fibre offer several advantages, such as weight/strength ratio and corrosion resistance. However, the manufacturing process is complex, especially the machining of composite materials, due to their specific properties and characteristics. The detection and prediction of surface finishing and occurrence of defects during manufacturing using non-destructive techniques is industrially useful, in terms of fomenting automated manufacturing systems to increase productivity and quality control. Acoustic emission signal processing is being successful in mechanical tests for determining material defects, more recently used as a method for manufacturing evaluation of machined parts. This paper focused in the machining process of CFRP plate, in terms of surface finishing evaluation with comprehension of process phenomenology using analyses of temperature and acoustic emission signal features. The aim of this paper is to show the possibility of online monitoring of the cutting process and to understand mechanism behind variables of control, with comparisons of different milling parameters and focusing in their impacts in acoustic emission signals and surface finishing, with suggestions of evaluation and prediction methods of machined surface quality using mainly acoustic emission signals.

International audience; Machining of composite materials is a challenging task due to the heterogeneity and anisotropy of composite structures. The induced defects reduce integrity of the machined surface as well as the loading capacity of the composite structure in service. Therefore, it is necessary to quantify the damage induced during trimming and correlate the quality of the machined surface to mechanical properties. The correlation of the surface roughness criteria, widely used in literature, to the mechanical behavior raise several contradictions. For this reason, new parameters for the characterization of themachined surface are proposed and correlated to the mechanical behavior under compressive loading. In this context, carbon fiber-reinforced plastic laminates are conventionally trimmed, and the machining damage is characterized using scanning electron microscope observations, X-ray tomography, and 3D optical topography. The results reveal that crater volume and maximum depth of damage quantify the machining damage more realistic compared to the classical surface roughness criteria.

International audience; Conventional machining of carbon fiber reinforced plastic composites (CFRPs) generates minute chips that get suspended in air causing a hazard compromising operator safety. This study investigates the influence of cutting parameters (feed speed, cutting speed, radial depth of cut, tool geometry and tool wear) during trimming of CFRP on the form and quantity of harmful particles dispersed. Also, performance of two classical PCD tool geometries (two straight flutes, two helix flutes) have been compared with newly designed (in collaboration with ASAHI Company) four serrated straight flutes for the purpose of dust emission reduction. The quantification of the number of harmful particles was estimated using laser spectroscopic dust monitor. The results reveal that, trimming with a combination of higher feed speed and lower cutting speed can reduce the dispersion of harmful particles. Further, the four serrated straight flutes recorded the least number of harmful particles compared to the conventional tools.

Machining and especially drilling of multi-stacks is a challenge task. In fact, drilling of multi-layers generates several damages such as burr at the hole exit and the decohesion of the interface of the layers. It is important to note that the decohesion phenomenon favors the accumulation of the chips at the interface of the layers. In this case, it will not be possible to use the automated system (such as robots) for drilling and fastening in the aeronautical field. This work gives focuses on the numerical and an experimental study during drilling of a multi-stack made of titanium alloy (Ti/Ti), which is usually encountered during the assembly of the aircraft door at Boeing Company. The impact of the machining parameters on the thrust force, responsible of the decohesion of the layers as well as the burr size, has been investigated experimentally and numerically. The proposed model is based on the behavior law of Johnson-Cook for the titanium parts and the cohesive zone for the interface. The main experimental and numerical results have shown that the feed rate and the thickness of the bottom layer have a great influence on the size of the decohesion zone. However, the burr at the hole exit is strongly influenced by the feed rate.

The present work aims to numerically investigate the pressure behaviour of adhesively bonded interlocked composites tubes. To this end, a finite element model has been investigated based on the meso-model (interface and ply) concept. The identification of the model parameters has been carried-out through fracture mechanical tests and cyclic tensile tests on [±45] and [±80] specimens. The mathematical models as well as the experimental tests of both interface and ply are presented. It has been proved through numerical outcomes that the joined tube outer diameter is proportional to the applied pressure.

International audience; The goal is to study the influence of abrasive water jet (AWJ) machining parameters (jet pressure, traverse speed and scan step) on the cutting depth of 3D woven Carbon Fibres Reinforced Polymer (CFRP) composite. The original material linked to this non-conventional milling process has not been treated yet. The depths of cut were measured and characterized as a function of the machining parameters. Finally, two prediction models for the cutting depth are proposed and validated experimentally.An increase in cutting depth with the pressure and a decrease as the traverse speed and/or the scan step increase were observed. The first prediction model, based on the pocket depth measurements, has a mean error of 5%. However, the error increases (up to 23%) when the pocket becomes shallow (lesser than 1 mm). The second prediction model, based on the algebraic sum of elementary passes modelled with Gaussian bells, shows at first a mean error of 12%. A correction was performed depending on the erosion regime piloted by the depth of the elementary trench constitutive of the pocket. This enhancement, performed thanks to the primary jet diameters measurements with high speed camera, has improved the second model with a mean error of 5% (error

International audience; The present work aims to experimentally investigate the fire behaviour of water-filled E glass reinforced thermoset resin hybrid filament-wound composites tubes under static pressure. Heretofore, fire endurance tests have been conducted on single and adhesively bonded tubes manufactured by CTRA Company. Furthermore, internal pressure tests until failure have been performed on the burnt single and burnt joined tubes in order to quantify their abilities to contain the fluid after being exposed to heat flux. A comparison between the pressure behaviour of exposed to fire (burnt) and non-exposed tubes (single and joined) was also inspected. The identification of the fire-induced damage mechanisms of the tubes was performed through optical microscopy, Scanning Electron Microscopy (SEM) and X-ray tomographic observations. Finally, the thermal analysis was carried-out on burnt specimens in order to better understand the multiphysical phenomenon taking place during the fire endurance tests. The experimental results have revealed that the combustion process of both single and joined tubes was described in four steps namely tube heating, resin degradation, ignition and flame decay. Moreover, it was found that no leakage was witnessed on the tubes (single and joined) outer surfaces during the fire endurance tests. The comparison between the pressure behaviour of the burnt single tube and the burnt joined one has proved that the single tube is much resistant under internal pressure loading than the burnt joined tube. Finally, the fire-induced damage included matrix cracking and delamination between the tube plies which was noticed from microscopic observations.

International audience; Repair of damaged aircraft structural parts is a regular maintenance activity carried out to preserve airworthiness while being economically viable. Conventional repair techniques used have negative impact on the repair quality and environment due to dust emission. For eliminating aforementioned problem, this study investigates controlled depth abrasive water jet (AWJ) milling for repair procedure of 3D woven CFRP composite structures used in the new aircraft engine developed by Safran Aircraft Engines. The aim is to identify and quantify the damage and surface contamination induced by AWJ milling. For this, the influence of milling parameters on the damage and surface contamination is investigated through full factorial experimental study. Several characterisation techniques like 3D optical profilometry, Scanning Electron Microscopy and X-ray tomography combined with image processing were used for a multi-scale analysis of the machined surface damage and contamination. In fact, the machining quality was quantified using an innovative criterion called “crater volume” (Cv). The obtained results have shown surface contamination by embedded abrasive particles and presence of bare and broken fibres, cracks, craters. The results show that the rate of contamination is influenced by the jet pressure and the scan step and the Cv is influenced by the jet exposure time.

A finite element (FE) model for exit-ply delamination during drilling carbon fiber reinforced polymers (CFRPs) laminates is presented. The current FE model is developed to predict critical thrust force at the onset of delamination for 1 and 2 plies under the twist drill for various cutting temperatures. The interface behavior for delamination onset is modeled using surface based cohesive zone model (CZM). The numerical predictions for critical thrust force are compared with experimental thrust forces for various number of plies under the twist drill over a range of cutting temperature. Thrust force predictions were found to match with experimental data.

International audience; This work aims to study experimentally and numerically the pressure behaviour of filament wound adhesively bonded interlocked tube under internal pressure tests. To this end, a series of hydraulic pressure tests were carried-out on E glass reinforced Vinylester 411 adhesively bonded tubes. The experimental results have revealed that a leakage was witnessed on the bonding area. Furthermore, the post-mortem X-ray tomography tests on specimens, subjected to internal pressure loading, provided a better understanding of the failure mechanisms resulting from the applied pressure. Based on these results, a finite element model was developed taking into account the nonlinearity behaviour of the adhesive layer. In fact, the aforementioned model intend a compliant prediction of the pressure behaviour of the joined tube as well as the damage propagation in the bonding zone. A perfect correlation of the experimental and the numerical outcomes has been obtained.

International audience; Cutting forces are critically important in cutting operations because they correlate strongly with cutting performance such as surface accuracy, tool wear, tool breakage, cutting temperature, self-excited, and forced vibrations. The drilling operation of titanium alloys is considered by manufactures as complex and difficult in view of the mechanical and thermal properties of this material. In fact, titanium has a very small coefficient of conduction which leaves a high temperature at the area of contact between the tool and the workpiece, which decreases the cutting forces and increases the wear of the tool. For this, more research has focused on the prediction of cutting forces during the drilling of titanium in order to improve the machinability of this material as well as the wear of the tool. Many efforts have been made by researchers to better understand the drilling process and to formulate theoretical cutting forces models to predict and to simulate the phenomenon. This paper presents a numerical model for prediction of cutting forces and torque during a drilling operation including the effect of the regenerative chatter and of the cutting process damping. The corresponding algorithm allows understanding the interaction between the tool and the workpiece and identifying numerically the three-dimensional evolution of the cutting force components and cutting torque generated by the drilling process of a titanium alloy. Verification tests are conducted on a vertical machine for titanium alloy Ti6Al4V and the effectiveness of the model and the algorithm is verified by the good agreement of simulation result with that of cutting tests under different cutting conditions.

International audience; In this study, mechanical behavior and damage of thick laminated carbon/epoxy composite are investigated through static and fatigue three-point bending tests. In order to supply a maximum of information about the mechanical behavior of these materials, which have been little studied in the literature, and to provide an accurate description of the different mechanisms involved during their damage process, three non-destructive evaluation and monitoring techniques were used in this study. The acoustic emission for damage assessment, identification, and their threshold detection, the infrared thermography for fatigue damage evaluation and fatigue limit estimation and the digital image correlation for strain and displacement fields measurements.

Abrasive water jet (AWJ) process has been certified in some aerospace companies for repair applications. However, there is no information in the literature on the influence of the induced damage on the mechanical behaviour of complex materials such as 3D woven CFRP composite. To fill this gap, three texturing levels have been produced and quantified using both surface roughness (Ra) and “crater volume” (Cv) criteria. The specimens have been subjected to tensile static and tension-tension fatigue tests. Contrarily to Ra measurements, a linear correlation was highlighted between the increase in Cv and the degradation of the specimens’ mechanical performances (ultimate tensile stress and fatigue limit). The damage scenario of the textured specimens has been identified via acoustic emission activity, thermal maps and X-ray tomography pictures. Wider cracks and a more intense acoustic activity leading to a greater rise in temperature have been observed when Cv increases (worse quality). However, the small alterations in mechanical properties consecutive to AWJ texturing prove that this technique can be used for surface preparation of 3D woven CFRP parts prior to bounding without damaging them. Moreover, an innovative method, based on the damage accumulation, has been proposed and accurately estimates the endurance limit of the specimens.

International audience

This work denotes an insight into an experimental and numerical investigation of adhesively bonded tubular specimens. A series of tensile tests have been conducted on joined E glass reinforced thermoset resins to study the effect of the resin nature on mechanical behaviour. It has been proved through experimental outcomes that E glass/Vinylester 411 resin tube presents the best tensile properties in comparison with others resins. Therefore, the mechanical behaviour of this specimen has been investigated under uniaxial loading. The damage mechanisms resulting from this experimental test have been identified by means of the X-ray tomography and scanning electron microscope. A numerical model has been undertaken in order to predict the mechanical behaviour and the damage propagation of adhesively bonded tubular specimens. It has been proved that experimental and numerical results are in perfect agreement.

In this work, the influence of multi-walled carbon nanotube is presented on laser drilling of multi-walled carbon nanotube–doped glass/epoxy polymeric nanocomposite. Multi-walled carbon nanotubes were dispersed in polymer matrix to improve the thermal conductivity and heat transfer characteristics of materials, which also reduces the divergence in decomposition temperature of matrix and glass fiber. Effect of carbon nanotube on laser drilling–induced damages was assessed by considering heat-affected zone, taper angle, and surface roughness as output parameters. Scanning acoustic microscopy showed the useful technique to examine the laser drilling damage around the hole by providing ply-by-ply damage analysis. In addition, scanning electron microscope provided more details to better analyze the machining quality of laser-drilled hole. Energy dispersive X-ray analysis provided the elemental analysis of charred material which is deposited on the hole wall. Obtained results indicate that the quality of hole was improved significantly due to addition of multi-walled carbon nanotube in polymer matrix.

The aim of this paper was to study the influence of the nature coating and the machining parameters on the temperature of machining and tool wear of a new drilled 3D woven composite material used in carter fan of aircraft engine. For this various frictional contacts (tool/composite) have been analyzed for three types of cutting tools. The first tool is coated with a diamond layer and the other tools are coated with two new nano-composite multi-layers referenced as TiN/AlTiN/CrAlSiN and TiN/TiAlSiN/AlTiSiN. In addition, for the quantification of the in-situ temperature of drilling, an original technique based on the in-situ instrumentation of the cutting tool by optical fiber with four Braggs sensors is proposed. The evolution of the temperature of machining as a function of the machining parameters and frictional contacts were investigated. Also, the wear mechanisms were quantified in function of the number of drilled holes using Scanning Electron Microscopy (SEM). The results have shown that the feed rate and the nature of coating were the main factors which affect the temperature of machining. However, the spindle speed did not have any impact on the temperature of machining. It was also found that, when the drilling is conducted with a small feed (0.025 mm/rev) with TiN/TiAlSiN/AlTiSiN coating the temperature of machining was greater than the glass transition temperature of the composite. Moreover, tool wear mechanisms were found driven by abrasion phenomenon on the flank face and cutting edge.

International audience; The main purpose of this study is to provide a thorough experimental investigation of fatigue damage mechanisms and evolution in thick carbon/epoxy laminate subjected to bending load. The use of X-ray computed tomography (CT) in this study has allowed the visualization of all damage present in the studied laminates, which made it possible to identify, quantify and locate them precisely and therefore, to identify the physical origin of residual strength decrease and acoustic emissions (AE). Furthermore, the results of the AE analysis have provided very valuable information about the nature and evolution of damage. However, the determination of the depth and size of internal damage was not possible with this technique. The displacement field measured by digital image correlation (DIC) made it possible to determine and monitor the strain field evolution during the experiments. The combination of the results of the three non-destructive techniques used in this work has allowed better characterization of fatigue damage evolution in the studied laminates, and provide a complete and accurate description of the different mechanisms involved during their damage process.

The main objective of this paper is to study the effect of water absorption on the flexural strength of new green sandwich composite material made of flax as skin reinforcement and agglomerated cork as core. In this work, three different types of skin reinforcements and three different densities of agglomerated cork core have been used for the manufacturing of sandwich composites. The manufactured sandwich composites were subjected to three-point bending tests under both dry and wet conditions. The three-point bending results confirmed a decrease in the specific flexural strength by 14-42 % in wet samples due to water absorption. Also, the increase in core density leads to an increase in flexural strength both in dry and wet conditions. During testing under dry conditions, the specific flexural strength of flax reinforced sandwich composite was found to be superior because of the higher strength to weight ratio factor of flax fiber when compared to a glass reinforced sandwich composite and glass/flax reinforced hybrid sandwich composite. Due to the hydrophilic nature of flax fibers, flax reinforced sandwich composite has a reduced specific flexural strength in wet conditions when compared to glass reinforced sandwich composite and glass/flax reinforced hybrid sandwich composite.

International audience; The aim of this paper is to study the influence of the process parameters (cutting speed and feed) of the conventional trimming on cutting forces, machining temperatures, tool wear and machining quality of Carbon Fibers Reinforced Plastics (CFRP) using PCD tool. The machining quality was characterized using three different techniques such as Scanning Electron Microscopy (SEM), 3D optical topography and X-ray tomography. The originality of this work is based mainly on the multi-scale characterization of the machined surfaces. In fact, a new parameter based on the measurement of the volume of craters is proposed and compared to the surface roughness criterion (Sa) and the X-ray tomography images. The obtained results show that, with the crater volume criterion as well as the X-ray tomography images, the effect of the machining parameters and the wear of the tool on the textured surfaces are well correlated to surface roughness criterion (Sa). In addition, it was observed that the feed speed and tool wear were the major factors affecting the cutting forces and the machining temperatures.

The present study investigates the effects of machining parameters and the tool coating during drilling of a GLARE® hybrid aerospace material on the cutting forces, hole quality and the generation of harmful dust particles. The drilling tests were conducted using twist drills with diamond-like carbon (DLC), Cristall coating and without coating. Obtained results indicate that feed, in contrast to spindle speed, has an important effect on thrust force and torque. In addition, when DLC coated tools are used less surface deviation was detected in comparison with uncoated and Cristall coated drills. Moreover, dust measurement in terms of total number of particles, harmful particles and mass particles generated during drilling of GLARE® laminates was investigated. The results reveal that, the number of harmful particles in the air was found to be dependent on machining parameters. In fact, a lower spindle speed promotes the reduction of the number of harmful particles in the air by 50% compared to that observed at higher spindle speed.