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International audience; This study focuses on the methodology of periodic open-cell composite foams manufacturing by rapid tooling as well as the thermal analysis of the obtained structure. A bimaterial is prepared by introducing a phase change material (paraffin wax) into metal foam. The aim is to provide a structural bimaterial to study its thermal behavior for energy storage and achieve an adapted geometry with the help of rapid tooling by three-dimensional printing (3DP). Concretely, the bimaterial melting process is experimentally studied in order to determine thermal behavior. The temperature variations and distributions of the bimaterial are analyzed and compared with the results of pure paraffin. Moreover, the effect of natural convection is analyzed and discussed. The results show that the periodic open-cell metal foam could be a potential solution to the problem of storage and recovery of energy.

The tribological performances of in-situ (TiB + TiC) / Ti1100 composites prepared by casting and the matrix alloy were tested by pin-on disc mode. The worn surface and wear debris were investigated by SEM. The models of the composites during the wear process were simulated by ABAQUS FEA software. The analysis shows the stress distributions inside the composites under the different shear stress. The wear mechanism of the composites is probed.

The cooling conditions used in the forming process of composite materials play an important role in the creation ofresidual stress. In this study, a new method for measuring residual stress in composite laminates is presented. Three cooling conditions were used to produce different residual stress levels. Residual stresses in [02/902]s and [08] laminate have been measured by the incremental holedrilling method combined with 3-D finite element modelling. A software which quickly calculates all the coefficients for each increment was developed. The automatic procedure can be used to calculate the calibration coefficient for any type oflaminate (ply number, mechanic characteristics,...) and whatever the number of increments and their depths. The different results show that this method provides access to the in-depth distribution and through thickness ofresidual stress in the laminate with a good accuracy and practicality.

Porous iron with woodlike microstructures was prepared from two kinds of wood templates through a developed biotemplating method in the present work. The biomorphic iron oxide was first produced through infiltration and sintering procedures, and was then reduced to the biomorphic iron in a hydrogen atmosphere at high temperatures (600C and 1000C). The morphologies of iron and iron oxide products were observed using SEM and FESEM, and their crystal structures were identified using X-ray diffraction. The results indicate that the pure iron phase can be obtained after the reduction process and the products faithfully retained the microstructures of the corresponding wood templates. [doi:10.2320/matertrans.48.878]

This work aims to numerically analyze the mechanical properties of thermoplastic composite laminates with the [0°/90°]4s, [±25°]s4 and [0°/±45°/90°]2s stacking sequences under three-point bending loading. Three-dimensional multilayer structural models of composite laminates are established and then orthotropic elastics, Hill yield criterion and isotropic hardening rule are applied on these structural models of composite laminates to conduct the bending mechanical deformation. Fine enough meshes and reasonable loads and boundary conditions can efficiently reduce the computing cost. Afterwards, three-dimensional fiber–matrix structural models with disordered fiber arrangements of 0°/90°, 25°/−25° and 0°/45° interlaminates at the free edges of composite laminates are also created, in which the boundary conditions are transferred step by step using a three-step structural submodeling. Once more, orthotropic elastics and isotropic hardening are applied on these fiber–matrix structural models. This work provides a good way to understand the bending mechanical behavior of thermoplastic composite laminates with different stacking sequences.

International audience; The present work aims to determine the residual stresses in carbon fiber/epoxy composite laminates, by means of the incremental hole-drilling method. Based on mechanical theories of composite laminates and an elastic plate with a circular hole, the relationship between the relaxed strains on the surface of laminates and the residual stresses in laminates was established. This newly deduced theoretical formula was adapted into the incremental hole-drilling method and allowed us to further study the residual stresses in the through-thickness direction for various composite laminates. Related numerical modeling of composite laminate with a hole was built to calibrate the coefficients within the formula. Experiments were conducted and the residual stresses in composite laminates [02/θ2]s are presented. The proposed approach was validated with the consistence between our results for cross-ply laminates and those in literature.

This work studies the behavior of a multidirectional laminate under Mode II loading. We describe the process of delamination in a reinforced composite of glass/epoxy. The stacking sequence (plies orientation [± θ] was selected to minimize the coupling effects. The Mode II interlaminar test under three-point bending and cantilever flexure using ENF (End Notch Flexure) and ELS (End Load Split) specimens, respectively, was performed and analyzed. The test procedures and the results of strain-energy-release rate study for crack initiation are presented. The fracture process and the mechanical behavior of the two types of specimens are analyzed. The analysis clearly shows a close link between the angle θ, the ratio a/L, and the thickness h of the specimen. Fracture by delamination can be obtained only with an optimal choice of these parameters. The analysis of the states of stresses at the tip of crack allows us to explain the phenomenon of bifurcation between plies and is confirmed by the experimental results.

International audience; Due to their remarkable mechanical properties, carbon nanotube (CNT) reinforced aluminum (Al) matrix composites have attracted a wide range of research interests. This work attempts to experimentally and numerically investigate the relationship between the micro-structures and mechanical behavior of CNT/Al composites. Three-dimensional (3D) computational structural modeling of CNT/Al composites is performed, in which the size, morphology, orientation, location and volume fraction of CNTs are reproduced to be similar to those of the actual micro-structures of CNT/Al composites. The strengthening of the mechanical properties of the constituent materials of CNT/Al composites and reasonable load and boundary conditions are studied based on the models of CNT/Al composites developed. The tensile mechanical behavior of CNT/Al composites is numerically evaluated and experimentally verified. Results show that the enhanced mechanical properties of CNT/Al composites can be attributed to three factors: CNT reinforcements, matrix grain refinement and layered architectures. Through the microscopic structural modeling methods presented herein, the effects of model size, interfacial behavior, volume fraction of CNTs and layered structures on the mechanical behaviors of CNT/Al composites can be reproduced to understand the strengthening and deformation mechanisms of CNT/Al composites.

International audience; The literature concerning ± laminates under mode II (propagation mode) loading encounters a difficulty in calculation of the structural dimensions. Indeed, it is rare to have a specimen geometry which fully satisfies the conditions for application of the Linear Elastic Fracture Mechanics (LEFM). Thus, the aim of this work is the optimisation of the specimen geometry which allows the characterisation of mode II by the approach of the LEFM concept. The results obtained show an interaction between the geometrical characteristics of the specimen (thickness h), the angle of orientation of the plies () and the characterisation of delamination. The experimental results are in good agreement with the analytical predictions. The use of the acoustic emission allows us to observe that delamination is only one final stage in a process of damage which starts well before.

International audience; Dynamic response of open-cell metal foam under low-velocity impact loading is important in applications involving impact resistance and energy absorption, etc. Assuming that metal foam is a conceptually continuous material, the macroscopic mechanical behaviors, both static and dynamic, must be studied. Within the dynamic mechanical properties of metal foam, impact response becomes the renewed interest to understand the characteristics of impact deformation. The present work aims to experimentally and numerically analyze the low-velocity impact response of open-cell metal foam. A series of low-velocity drop impact tests are realized on the open-cell metal foam samples with different relative densities and at different impact velocity. Afterwards, a well compiled program in Python controls the whole multiple drop impact process on each sample of metal foam. Corresponding numerical modeling and the simulation for single impact analysis are continuously carried out with the finite element (FE) program ABAQUS/Explicit. Proper meshing technique, loading and boundary conditions are conducted on all the foam models, and at the same time, the required mechanical properties: elastic module, Poisson's ratio, uniaxial stress-strain response and strain-rate dependence are utilized. In conclusion, the simulated results provide the good agreements with the experimental results in the case of low-velocity impact testing of open-cell metal foam. Experimental procedure and numerical simulation offer good approaches to improve the impact resistance and energy absorption of the open-cell metal foam.

International audience; In this work, we demonstrated a novel surface-enhanced Raman scattering (SERS) substrate inspired by natural nanostructures of butterfly wing scales. By facile and low-cost procedures, we synthesized the substrate composed of tin dioxide (SnO2) and silver (Ag) nanoparticles (NPs). Micrographs and composition analyses exhibited the morphologies of Ag-Biomorphic SnO2 which inherited the natural three-dimension (3D) periodic nanostructures, and characterized the elemental information of the nanocomposites. SERS spectra were measured by using rhodamine 6G (R6G) as analyte molecules. The satisfying sensibility (with the enhancement factor about 106) and good reproducibility of this SERS-active substrate revealed the effectiveness of our work. It is expected that this substrate would be a potential candidate for relative applications.

International audience; The weathering of hemp fiber influences their appearance and mechanical properties. The aim of this study is to better understand the mechanism of aging of hemp fiber exposed to different conditions (moisture, heat and UV aging). A xenon aging test machine was used to simulate and accelerate the natural ageing. The influence of each aging condition on the mechanical properties of hemp fiber is investigated by micro tensile tests. The microstructures and water absorption of these natural fibers were analyzed by means of SEM and gravimetric methods. Humidity absorption of hemp fibers depends on the relative humidity, not concerning the temperature. Temperature accelerates the saturation of fibers. All aging process reduced the mechanical properties of hemp fibers. After 4 weeks exposure, fibers aged by UV has the worst mechanical properties compared to humidity and temperature aging.

International audience; The objective of this paper is to study the influence of residual stresses due to fabrication conditions on the thermomechanical behavior of carbon/epoxy laminate structures (cross ply). These studied laminates have undergone various cycles of thermal aging. The addition of a post-cure cycle after the end of the initial cycle makes it possible to reduce the residual stresses level. The incremental hole-drilling method is used to measure the residual strain in the laminates. These measured strains and the numerical calibration coefficients obtained by the finite element method allow to calculating the residual stress distribution in composite depth. The obtained results show that heat treatments of composite structures do not lead to an important reduction the initial residual stress due the fabrication conditions.

International audience; Residual stresses occur during most manufacturing processes (from shrinkage of the resin, difference of thermal expansion coefficients, etc.). Residual stresses may cause local yielding and damage initiation and propagation, and can severely affect performances of a composite structure component. The aim of this work is to investigate the influence of residual stresses on the mechanical behavior of carbon/epoxy cross-ply laminates under tensile and torsion loading. The residual stresses field was determined using the incremental blind-hole drilling technique combined with the finite element analysis. The effect of various cure cycles on the residual stress level is analysed. The quantitative effect of the residual stresses on the mechanical behaviour and the damage initiation and growth is studied by using acoustic emission technique.

Residual stresses play an important role on the mechanical behavior of composite laminate. The development of new methods to determine the residual stresses gradient within the laminates is necessary. This article presents the adaptation of the compliance method in the case of composite laminates carbon/epoxy [02/902]s. The incremental drilling of a constant width groove allows for each increment to measure the strains (using strain gages) and displacements (using an optical device) of particularly points of the structure surface. These experimental data are compared with results given by a finite elements simulation. This comparison allows to raise the residual stresses in the composite laminate.

High-performance composite are fabricated by hot isostatic pressing of matrix and fibers. The cooling conditions in the forming process (Resin Transfer Molding, Structural Resin Injection Molding, Laying-up) play an important part in the thermal residual stress distribution. The existence of residual stresses, combined with mechanical loads, could considerably decrease the durability of laminate structures by leading matrix cracking, fibres breaking and interface delamination initiation. The objective of this study is to investigate the influence of residual stresses on the mechanical behavior of composite laminates. Incremental hole-drilling method combined with 3D FE analysis is used to performed the internal strains in laminate plates [0 2 /90 2 ] s polymerized with different cooling conditions (fast, normal and slow). The emission acoustic events system was used during static tensile tests and the signal interpretations are given by a schematic classification in order to estimated the damage initiation between interfaces. The results of this study show that the general level of the residual stresses changes appreciably with the conditions processing and prove that this new method gives a new prospect for the study of the residual stresses distribution in advanced composites parts.