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The present study aims at investigating the effect of organic-modified nickel phyllosilicate (NiPS) particles on the structure–property relationships of epoxy (EP) composites. The organic-modified NiPS particles were synthesized using a facile sol–gel method and subsequently mixed into EP matrix by physical blending to improve its tribological, mechanical and thermal properties. Based on a series of tests and analyses, it was found that organic-modified NiPS particles playing a great role in improving the tribological properties under dry sliding. The steady-state friction coefficient was just decreased moderately, whereas the wear rate was dropped significantly to 0.36 × 10−5 mm3/N·m, showing a reduction up to ca. 95% in comparison with pure EP. According to the analysis of worn surfaces, the main mechanism of wear resistance was discussed. The elastic modulus for the EP composites was increased remarkably while the elongation at break decreased. However, the added organic-modified NiPS particles show a negligible influence on the tensile strength. Moreover, the incorporated NiPS particles could enhance the thermal stability of EP composites, showing the notably suppressed mass loss rate and added residual chars. This study provided a promising way for preparing the high-performance EP composites with organic-modified lamellar particles.

This is the peer reviewed version of the following article: [ Deng, Z, Liu, X, Chen, P, et al. Basalt-polypropylene fiber reinforced concrete for durable and sustainable pipe production. Part 1: Experimental program. Structural Concrete. 2022; 23: 311– 327. https://doi.org/10.1002/suco.202000759], which has been published in final form at https://onlinelibrary.wiley.com/doi/abs/10.1002/suco.202000759. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. An experimental program consisting in producing and testing reinforced concrete pipes (RCPs) under the three-edge bearing tests considering different types of reinforcement was carried out. Four types of RCPs were produced, these reinforced with: (1) polypropylene macrofibers; (2) basalt microfibers; (3) combination of both (hybrid reinforcement); and (4) plain concrete. The analysis of the crack patterns and both service and ultimate mechanical responses allowed concluding that the use of fibers do not lead to an effective increase of the first cracking load; however, both types of fibers allowed a better crack width control respect to the standard RCP. In this regard, basalt microfiber reinforced concrete led to a better response caused by concentrated loads (jacketing) whilst polypropylene macrofibers increased the concrete pipe performance in terms of bearing capacity and flexural crack control. The hybrid fiber reinforced concrete was found to be the most suitable alternative for increasing the load bearing capacity and the crack width control for service loads. These incipient experimental results permit to conclude that this type of hybrid basalt-polypropylene fiber reinforced concretes are an interesting alternative to traditional steel-cage RCPs. This work is supported by the National Key Research and Development Program of China (2018YFC1504802), Natural Science Foundation Project of Chongqing, Chongqing Science and Technology Commission (cstc2018jscxmszdX0071), Postgraduate Research Innovation Project of Chongqing (CYS19005, CYS18026). In addition, Prof. Albert de la Fuente also wants to express his gratitude to the Spanish Ministry of Science and Innovation for the financial support received under the scope of the project CREEF (PID2019-108978RB-C32).

Property of the semiconductors under high pressure is investigated by the density functional theory and paralleled to the foretelling of the linear elasticity theory. In addition, ternary alloys of PbSxSe1-x and PbSxTe1-x lattice matching PbS substrate for x = 0.5 compositions are studied. Furthermore, quaternary alloys PbxSn1-xSyTe1-y lattice matching PbS substrate for x and y = 0.5 compositions are studied. The six independent elastic parameters (Cij) are also calculated. Meanwhile, the results data are analyzed in high pressure. The mechanical response of all alloys to pressures 0, 50, and 100 kbar increases progress to decrease in (Cij) in separate rates. The rapprochement between the calculated results and the available published data for these alloys demonstrate that they had worthy accordance at zero pressure and the results at high pressure may be required as an acceptable reference.

The multiscale hybridization of ceramic nanoparticles incorporated into polymer matrices reinforced with hybrid fibers offers a new opportunity to develop high-performance, multifunctional composites, especially for applications in aeronautical structures. In this study, two different kinds of hybrid fibers were selected, woven carbon and glass fiber, while two different ceramic nanoparticles, alumina (Al2O3) and graphene nanoplatelets (GNPs), were chosen to incorporate into a polymer matrix (epoxy resin). To obtain good dispersion of additive nanoparticles within the resin matrix, the ultrasonication technique was implemented. The microstructure, XRD patterns, hardness, and tensile properties of the fabricated composites were investigated here. Microstructural characterization demonstrated a good dispersion of ceramic nanoparticles of Al2O3 and GNPs in the fabricated composites. The addition of GNPs/Al2O3 nanoparticles as additive reinforcements to the fiber-reinforced polymers (FRPs) induced a significant increase in the hardness and tensile strength. Generally, the FRPs with 3 wt.% nano-Al2O3 enhanced composites exhibit higher tensile strength as compared with all other sets of composites. Particularly, the tensile strength was improved from 133 MPa in the unreinforced specimen to 230 MPa in the reinforced specimen with 3 wt.% Al2O3. This can be attributed to the better distribution of nanoparticles in the resin polymer, which, in turn, induces proper stress transfer from the matrix to the fiber phase. The hybrid mode mechanism depends on the interaction among the mechanical properties of fiber, the physical and chemical evolution of resin, the bonding properties of the fiber/resin interface, and the service environment. Therefore, the hybrid mode of woven carbon and glass fibers at a volume fraction of 64% with additive nanoparticles of GNPs/Al2O3 within the resin was appropriate to produce aeronautical structures with extraordinary properties.

The mechanical response of graphene nanoribbons under uniaxial tension, as well as its dependence on the nanoribbon width, is presented by means of numerical simulations. Both armchair and zigzag edged graphene nanoribbons are considered. We discuss results obtained through two different theoretical approaches, viz. density functional methods and molecular dynamics atomistic simulations using empirical force fields especially designed to describe interactions within graphene sheets. Apart from the stress-strain curves, we calculate several elastic parameters, such as the Young’s modulus, the third-order elastic modulus, the intrinsic strength, the fracture strain, and the Poisson’s ratio versus strain, presenting their variation with the width of the nanoribbon.

Mechanical size effects at small characteristic dimensions are of intense current interest. In addition to the relevance for microfabrication, microscale compression molding provides a rich laboratory in which mechanical size effects manifest in interesting ways, especially as the characteristic molding dimension approaches the average grain size of the material being deformed. We investigate the effects of punch geometry and grain size on the mechanical response and gap filling behavior in micron scale compression molding. Micron scale long rectangular single-, double-, and triple- punch molding was conducted on polycrystalline Cu with varying grain sizes. Mechanical size effects were observed regarding the compression pressure and the material flow to fill the gaps between neighboring punches. The nominal compression pressure depended significantly on the punch width in single-punch molding and on the spacing between neighboring punches in double-punch molding. Analysis of double- and triple- punch molding data showed that both the punch geometry and the grain size of the molded Cu influence the Cu gap filling behavior in significant ways. Detailed microstructural examinations of molded Cu features were carried out to elucidate the underlying mechanisms. Our findings offer new data on micron scale plasticity and test cases for validating micron scale plasticity models.

Natural rubber (NR) foams reinforced by a physical hybrid of nanographene/carbon nanotubes were fabricated using a two-roll mill and compression molding process. The effects of nanographene (GNS) and carbon nanotubes (CNT) were investigated on the curing behavior, foam morphology, and mechanical and thermal properties of the NR nanocomposite foams. Microscope investigations showed that the GNS/CNT hybrid fillers acted as nucleation agents and increased the cell density and decreased the cell size and wall thickness. Simultaneously, the cell size distribution became narrower, containing more uniform multiple closed-cell pores. The rheometric results showed that the GNS/CNT hybrids accelerated the curing process and decreased the scorch time from 6.81 to 5.08 min and the curing time from 14.3 to 11.12 min. Other results showed that the GNS/CNT hybrid improved the foam’s curing behavior. The degradation temperature of the nanocomposites at 5 wt.% and 50 wt.% weight loss increased from 407 °C to 414 °C and from 339 °C to 346 °C, respectively, and the residual ash increased from 5.7 wt.% to 12.23 wt.% with increasing hybrid nanofiller content. As the amount of the GNS/CNT hybrids increased in the rubber matrix, the modulus also increased, and the Tg increased slightly from −45.77 °C to −38.69 °C. The mechanical properties of the NR nanocomposite foams, including the hardness, resilience, and compression, were also improved by incorporating GNS/CNT hybrid fillers. Overall, the incorporation of the nano hybrid fillers elevated the desirable properties of the rubber foam.

This paper presents the inclusion of explicit dual poroelastic mechanical behaviour as part of an existing dual porosity numerical model of multiphase, multicomponent chemical-gas transport. The dual poroelastic framework employed considers the pore structure changes occurring as a result of high pressure carbon dioxide injection into coal, particularly the adsorption-induced coal swelling that has been found to limit injectivity in field trials of carbon sequestration in coalbeds around the world. To address this issue, the surface stress of the fluid-solid interface is introduced into the constitutive relation for dual porosity effective stress in order to investigate the coal deformation and porosity changes related to adsorption behaviour. A new porosity model is presented, in which the impacts of gas flow and coal deformation are incorporated, and an interaction coefficient is proposed to explain the effect of fracture-matrix interactions on the porosity evolution. The model is verified and validated in this work against relevant analytical solutions and experimental results, and applied to study the gas flow behaviour and structural changes of coal. The results show that carbon dioxide injection not only causes coal swelling but also has the potential to change the internal pore structure of coal. The variation of fracture porosity is not monotonic as a competing result of effective stress and internal fracture-matrix interactions. However, the matrix porosity is found to increase during carbon dioxide injection, which seems to be a key contributor to the swelling phenomenon.

The paper discusses a perspective of the usage of various types of smart materials to enhance the operational properties of Gas Foil Bearings. The authors, referring to the current investigation on thermomechanical characteristics of the above-mentioned bearing type, have focused on the concept of using Shape Memory Alloys, Piezoelectric Transducers, Thermoelectric Modules and Thermocouples to improve both mechanical and thermal behavior of the bearings. Based on the available literature and the authors’ experience, the present work provides an overview of the known and perspective applications of smart materials to Gas Foil Bearings. In particular, a discussion on their capabilities, limitations and effectiveness is conducted, taking into account the unique characteristics and requirements of the studied type of bearings This research was funded by the National Science Center, Poland, within the project grant number 2017/27/B/ST8/01822 entitled “Mechanisms of stability loss in high-speed foil bearings—modeling and experimental validation of thermomechanical couplings”.

In this work we examine the driving force for edge dislocations to climb in α -Fe from atomistic and mesoscale viewpoints. We study the bias for the climb process depending on the dislocation orientation and the applied stress due to both the gradient of the chemical potential and the transport coefficients. Both terms are modified by the applied stress and therefore contribute to climb. Surprisingly, even though the vacancy migration barrier distribution is modified by the external stress as obtained by nudged-elastic band calculations, the mobilities resulting from a kinetic Monte Carlo model applied on the obtained energy landscape are indistinguishable, independently of the stress. Moreover, an object kinetic Monte Carlo (OKMC) model including the effect of the dislocation strain field to first order shows indeed a slight anisotropic component in the diffusion in more complex dislocation configurations. However, the OKMC results highlight the fact that the thermodynamic component is the dominant driving force. We conclude that in α -Fe under thermal conditions, the main source of bias is given by the difference in vacancy chemical potentials, which is small enough to hinder the process for dynamic atomistic simulations.

[EN] Atomic force microscopy is an invaluable characterization tool in almost every biophysics laboratory. However, obtaining atomic/sub-nanometer resolution on single proteins has thus far remained elusive - a feat long achieved on hard substrates. In this regard, nanomechanical spectroscopy mapping may provide a viable approach to overcome this limitation. By complementing topography with mechanical properties measured locally, one may thus enhance spatial resolution at the single-protein level. In this work, we perform all-atom molecular dynamics simulations of the indentation process on a single immunoglobulin G (IgG) adsorbed on a graphene slab. Our simulations reveal three different stages as a function of strain: a noncontact regime - where the mechanical response is linked to the presence of the water environment - followed by an elastic response and a final plastic deformation regime. In the noncontact regime, we are able to identify hydrophobic/hydrophilic patches over the protein. This regime provides the most local mechanical information that allows one to discern different regions with similar height/topography and leads to the best spatial resolution. In the elastic regime, we conclude that the Young modulus is a well-defined property only within mechanically decoupled domains. This is caused by the fact that the elastic deformation is associated with a global reorganization of the domain. Differences in the mechanical response are large enough to clearly resolve domains within a single protein, such as the three subunits forming the IgG. Two events, unfolding or protein slipping, are observed in the plastic regime. Our simulations allow us to characterize these two processes and to provide a strategy to identify them in the force curves. Finally, we elaborate on possible challenges that could hamper the interpretation of such experiments/simulations and how to overcome them. All in all, our simulations provide a detailed picture of nanomechanical spectroscopy mapping on single proteins, showing its potential and the challenges that need to be overcome to unlock its full potential., Funding from a Marie Sklodowska-Curie Fellowship within the Horizon 2020 framework (Grant No. DLV-795286) and the Swiss National Science Foundation (Grant No. ). R.P. acknowledges support from the Spanish MINECO (Grant No. MAT2017-83273-R) and from the Ministerio de Ciencia e Innovación (MICINN) through the “María de Maeztu” Programme for Units of Excellence in R&D (Grant No. CEX2018-000805-M). R.G. acknowledges funding from the MICINN (Grant No. PID2019-106801GB-I00) and Comunidad de Madrid Grant No. S2018/NMT-4443 (Tec4Bio-CM). We thankfully acknowledge the computer resources, technical expertise, and assistance provided by the Red Española de Supercomputación (RES) at the Minotauro and CTE-Power9 supercomputers (BSC, Barcelona). We thank Dr. Alejandro Martín-González for fruitful discussions.

A significant increase is seen worldwide in the amounts of wood ashes (WAs) produced by the heating and power industry. This study investigates the potential utilisation of two different WAs as low-level cement replacements, in an untreated and a washed version. Phase development and mechanical response were investigated. Results indicated ettringite formation mainly to contribute to the strength development until excessive formation. Indications of an optimum SO3/C3A ratio for mixtures with a low-level cement replacement with WA was between 0.4 and 0.5. Washed WA originating from grate combustion appeared to be most promising of the tested WAs in cement-based materials

Soil reinforcement with natural or synthetic fibers enhances its mechanical behavior in various applications. Fiber-reinforced sands (FRS) can be relatively anisotropic because of the fiber self-weight and the compaction technique. However, the microscopic mechanisms underlying the anisotropy are still poorly understood. This study used a discrete element approach to analyze the microscopic mechanisms underlying the strength anisotropy of FRS due to fiber orientation. Analysis of contact networks revealed that the optimum fiber orientation angle is perpendicular to the main direction of strong contact force in direct shear testing. These fibers produced the largest increase in shear zone thickness, normal force around the fiber body, effective contact area, tensile force along fibers, and energy storage/dissipation. This study is valuable for further understanding of the mechanical behaviors of FRS.

Accelerated pavement testing (APT) is an effective method in evaluating pavement performance by applying wheel loading and speed under controlled conditions. This study aims to investigate the effects of wheel loading, speed and ambient temperature on the pavement responses at different directions and depths of pavement structure. A two-layer asphalt pavement structure was constructed on a base layer constructed 10 years ago. Strain gauges were installed both in the transversal and longitudinal directions of motion on the bottom of both layers. The response of the asphalt layers was monitored and the developed strains were recorded. The results show that maximum compressive strain increases with wheel load. In contrast, the maximum tensile strain decreases as load increases; this is probably due to the high confining pressure that occurs within the pavement structure when higher wheel load is applied. The maximum compressive and tensile strains decrease with wheel speed, because the asphalt mixture becomes stiffer at high wheel speed (frequency). The maximum compressive and tensile strains in the transversal direction increase with ambient temperature, because of the low stiffness of asphalt materials at high temperature, which appears to be the cause of rutting.

The interplay of interface and bulk dislocation nucleation and glide in determining the motion of twin boundaries, slip-twin interaction, and the mechanical (i.e., stress-strain) behavior of fcc metals is investigated in the current work with the help of molecular dynamics simulations. To this end, simulation cells containing twin boundaries are subject to loading in different directions relative to the twin boundary orientation. In particular, shear loading of the twin boundary results in significantly different behavior than in the other loading cases, and in particular to jerky stress flow. For example, twin boundary shear loading along &lang, 112 &rang, results in translational normal twin boundary motion, twinning or detwinning, and net hardening. On the other hand, such loading along &lang, 110 &rang, results in oscillatory normal twin boundary motion and no hardening. As shown here, this difference results from the different effect each type of loading has on lattice stacking order perpendicular to the twin boundary, and so on interface partial dislocation nucleation. In both cases, however, the observed stress fluctuation and "jerky flow" is due to fast partial dislocation nucleation and glide on the twin boundary. This is supported by the determination of the velocity and energy barriers to glide for twin boundary partials. In particular, twin boundary partial edge dislocations are significantly faster than corresponding screws as well as their bulk counterparts. In the last part of the work, the effect of variable twin boundary orientation in relation to the loading direction is investigated. In particular, a change away from pure normal loading to the twin plane toward mixed shear-normal loading results in a transition of dominant deformation mechanism from bulk dislocation nucleation/slip, to twin boundary motion.

International audience; The shiv derived from the shredded stem of the hemp plant [1], when mixed with a mineral binder and water, produces hemp concrete (or “hempcrete”), which is considered as an eco-material because of its remarkable environmental properties (favourable CO2 balance, easy management and disposal at the end of the product life, etc.) [2]. However, much like any agricultural product, its quality may be affected by the soil where the hemp has been grown, the weather conditions, and a variety of other factors. As these parameters are rather variable, the produced plant matter tends to be somewhat irregular, which can hamper the development of this type of building solution. The study at hand tests the characteristics of the hemp (particle size distribution, water absorption capacity, etc.), to assess the impact of the variability of these factors on the performance of the hempcrete made with the shiv. To begin with, the thirteen types of shiv used in the study were compared by multicriteria analysis, and then classified into three different groups.Next, nine types of shiv were selected, so that each of the three groups was represented. In identical conditions (i.e. the only variable being the type of shiv), specimen of hempcrete were made up in the lab for experimentation. The aim here was to validate the results of the study characterising the different types of shiv. The results show that there are three main types of mechanical response when the hempcrete is subjected to a compression test, where the material behaviour is characterised by small, medium or large strains. The large specific surface area of shiv is known to be responsible for weak binding at the interface between the binder and the plant particles, leading to total failure of the test piece. In addition, its high water absorption capacity, which is the likely cause of the “false set effect” associated with the elongated form of the particles, is identified as being responsible for the high rates of deformability found. It should be noted that in the latter case, the specimens behave like a succession of layers, which accounts for the significant levels of strain.By multicriteria analysis of the results for the hempcrete specimens, we found that they can be also classified into three groups, matching the three detected by the multicriteria analysis of the types of shiv from which they were made. Unlike the previously published literature, this study leads to the conclusion that shiv types with small particle sizes and high water absorption capacities do not produce the best performance.

The cold bending method is a type of curved glass curtain wall construction method that has been used in practical engineering for a short time. It has the advantages of simple operation, high efficiency and low cost. However, the mechanical response and properties of glass panes caused by cold bending have not been solved effectively. To study the mechanical response and the properties of cold formed laminated tempered glass panes after applying with a wind load, cold bending and load tests of 9 laminated tempered glass panes were conducted by the orthogonal experimental design method. The effects of cold bending curvature, glass pane thickness and interlayer thickness were considered. In this paper, the response law of cold bending stress to the curvature and the relationship among the influencing factors were analyzed. The variation process of stress, the deflection of cold-formed glass panes under uniform load and the characteristics affected by cold-formed stress and deformation were studied. The results show that the cold bending stress is distributed in a saddle shape, and the curvature has the greatest influence on the cold bending stress, followed by the thickness of the glass panes. The influence of the interlayer thickness is small. The maximum stress appears near the corner of the short side direction adjacent to the cold bending corner. The cold bending stress increases linearly with increasing cold bending curvature. The cold bending stress and deformation have little effect on the change process of the later stage load effect.

Based on the experimental method of projectile penetration into the concrete target, different excitation by deceleration of polymer bonded explosives (PBXs) was achieved by controlling the length of steel pillars behind PBXs. A series of impact tests were conducted to study the mechanical response of PBXs with different initial densities under different excitation by deceleration. A physical model was developed to describe the viscoelastic-plastic deformation of PBXs. The plastic part was added on the basis of the viscoelastic statistical crack mechanical model (Visco-SCRAM) model, and the compaction behavior of charge in different environments was characterized based on the Heckel compaction equation. The model was implemented in LS-DYNA, and the simulation results were verified by the experiments. The dynamic mechanical behavior of PBXs under different excitation by deceleration was studied from the macroscopic and mesoscale aspects. The stress curves, strain curves, the density change and the interaction between particles in deceleration environment were predicted. After comparison and analysis, the dynamic response law of the charge in the penetrating process was obtained. Macroscopic responses along with mesoscale modeling results are significantly important to have a better understanding of deformation mechanisms of PBXs.

Uneven settlement of high-speed railway subgrade leads to the irregularity of high-speed railway line, which seriously affects high-speed train operation. The skylight point of high-speed railway operation is short and the maintenance time is limited. Therefore, how to quickly lift and repair the ballastless track slab in the subsidence section is an urgent problem to be solved in the maintenance of high-speed railways. The two-component non-aqueous reactive polymer material has the advantages of strong expansive force, fast reaction speed, and wide application range, which is extremely suitable for the repair of high-speed railway track slab subsidence and lifting. In this study, the expansion force characteristics of different density polymer materials and the stress-deformation curves at corresponding density are tested in laboratory to propose the mechanical parameters of polymer. Then, a three-dimensional finite element (FE) model of high-speed railway train ballastless-track subgrade is established based on ABAQUS. The mechanical characteristics of CRTS III ballastless track under different repair materials, different elevation, and different density of polymer grouting materials are analyzed. The results show that, under the dynamic load of the train, the stress value of polymer repairing material is less than that of cement slurry, presenting a compressive stress state, which is similar to that of the complete subgrade surface. In addition, within a certain thickness range, increasing the thickness of polymer is beneficial to reducing the difference of stress variation between polymer filling layer and complete pavement. Once beyond this range, the thickness of polymer has little effect on the force variation.

International audience; The hysteresis observed in the mechanical response of rubbers (especially filled rubbers) is classically assumed to be fully due to viscosity. Complete energy balances carried out during cyclic deformation show that viscosity is not systematically the preponderant contribution to the hysteresis loop the mechanical energy brought to the material is not entirely dissipated into heat but can be predominantly used by the material to change its microstructure. Predicting changes in temperature, and consequently the self-heating, is therefore not possible from the mechanical response only. This has been evidenced by defining a ratio in terms of energy. A new way of interpretation of the rubber resistance can therefore by found through its ability to store mechanical energy.

Materials and design 183, 108153 (2019). doi:10.1016/j.matdes.2019.108153, Published by Elsevier Science, Amsterdam [u.a.]

The continuing demand on device miniaturization has motivated the interest in micro metal forming technologies for manufacturing metal parts with sub-mm characteristic dimensions. In this work, axisymmetric reverse extrusion experiments were conducted on Cu 110 and Al 1100 alloy rod specimens with widely varying initial grain sizes, achieved through equal channel angular pressing (ECAP) and post annealing. Accompanying crystal plasticity finite element (CPFE) simulations were carried out. At a characteristic extrusion dimension (CED) of ∼100 µm, defined by the sidewall thickness of the extruded cup-shaped structures, the deformation characteristics of the reverse extrusion process were investigated. Specifically, the characteristic plastic strain for extrusion and the influence of initial grain size on the extrusion mechanical response and shape of extruded parts were examined in detail through scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD), in combination with CPFE simulations. The mechanical response of extrusion showed deviations from continuum scaling behavior as the CED became small as compared to the initial grain size. The present study serves as a baseline for further studies of metal forming at the meso to micro scales.

International audience; Leather materials are subjected to various deformation states during their elaboration and their use as a final product. Although the mechanical response of leathers under tension has been studied in the literature for decades, scarce information is available on the nature of their elasticity and more generally on their thermomechanical behavior. In the present study, four leathers were tested under uniaxial loading conditions while temperature changes were measured at the specimen surface using infrared thermography. Two types of tests were 2 performed at constant ambient temperature: monotonous displacement-controlled tests until failure, and cyclic load-unload tests with increasing amplitudes. The heat sources at the origin of the temperature changes were also determined by using a version of the heat diffusion equation applicable to homogeneous tests. Results enabled us to discuss the nature of thermoelastic couplings in leathers. Intrinsic dissipation caused by mechanical irreversibility was also detected and quantified. Distinct responses are evidenced depending on the type of leather tested.

The study explores the use of a composite, graphitic carbon (GC) – sulfur (S) based cathode in laminated structural batteries. Specifically, failure by delamination is studied with regards to the applicability of a double-walled tube architecture obtained by coating the inner surfaces of hollow carbon nanofibers with sulfur. Differences between the material responses of various LiXS (X ∈ (0, 2)) compounds under bulk-like and interface confined conditions are discussed in terms of the shear response of physically and chemically bonded interfaces, formed with non-functionalized and H/OH/O-functionalized GC surfaces. The study indicates that only a chemically bonded interface with non-functionalized GC yields bulk-compatible mechanical behavior, with the exception of concentrations of X ∈ (0.8, 1.1). To strengthen the interface at low Li concentrations, at which a pronounced inhomogeneity in mass density in terms of interface debonding occurs, a modified transition layer was tested. The results indicate a distinct improvement in terms of homogeneity of mass density and plastic strain localization. The effect of delithiation at high rates on the interface structural stability is investigated at different concentrations of Li in structures of initially uniform Li distribution. According to the results, delamination failure is likely to occur.

Biodiesel has emerged as one of the major sources of renewable energy in automotive applications substituting the convention diesel. However, the compatibility of biodiesel and rubber components remains a major concern. Indeed, it is found that biodiesel tends to swell rubber components resulting to their faster degradation. Thus, studies focusing on the compatibility of newly developed biodiesel are essential for rubber durability. Along this line, the main purpose of the present study is to investigate the swelling characteristics of rubber in cottonseed oil biodiesel. Two types of unfilled and filled rubbers are considered: natural rubber (NR) and polychloroprene rubber (CR). For filled rubbers, two carbon black contents are used: 25 and 40 phr. The rubber samples are immersed in conventional diesel fuel, biodiesel and diesel-biodiesel blends for 1000 hours at room temperature (25 °C). The evolutions of rubber mechanical properties such as hardness, tensile modulus and tensile strength are investigated as well as the macroscopic stress-strain characteristics. For both rubbers, it is found that the decrease in the mechanical properties becomes more significant as the biodiesel content increases. Finally, a continuum model predicting equilibrium swelling proposed by Ch’ng [S.Y. Ch’ng. Coupling between diffusion of biodiesel and large deformation in elastomers: from experimental investigation to constitutive modeling. Ph.D. Thesis. University of Malaya, Malaysia. 2014] is adopted to simulate the effect of carbon black on the stress-free equilibrium swelling of rubber.

International audience; Defect-free joints were friction stir welded (FSW) from AZ31 Mg alloy sheets by employing optimum welding parameters for the tool geometry used. Microstructure, texture and mechanical response of the welded joints were studied to identify susceptibility of crack initiation in the different weld zones and to understand the overall fracture behavior of these welds. Uniaxial tensile testing conducted orthogonal to the welding direction at temperatures of 25, 100, 200, and 300 °C revealed that cracks initiated mainly on the tool’s advancing side (AS) of the weld between thermo-mechanically affected zone (TMAZ) and stir zone (SZ). Such cracks were found to propagate preferentially along this interfacial region leading to complete fracture. This finding may be linked to the inhomogeneous plastic deformation in the weld resulting in strong texture and microhardness gradients at the interface region between the TMAZ (AS) and the SZ. On the other hand, in tensile samples machined along the welding direction and containing stir zone microstructure, second phase particles were identified as the preferred sites for cracks initiation.

Polytetrafluoroethylene/aluminum/molybdenum oxide (PTFE/Al/MoO3) reactive composites of a volume ratio of 60:16:24 were studied in this research. Quasi-static compression, dynamic compression and drop-weight experiments were performed to explore the mechanical response and the shear-induced initiation properties of the composites. Mesoscale images of the specimens after sintering demonstrate that PTFE, Al and MoO3 powders were evenly mixed and no chemical reaction occurred after the materials were stirred, pressed and sintered. The yield stress and compressive strength of PTFE/Al/MoO3 specimens are sensitive to strain rate within the range of 10&minus, 3~3 &times, 103 s&minus, 1, and the yield stress shows a bilinear dependence on the logarithm values of strain rate. The established Johnson-Cook constitutive model based on the experimental data can describe the mechanical response of PTFE/Al/MoO3 material well. Drop-weight tests show that the PTFE/Al/MoO3 specimens can react violently when impacted, with the characteristic drop height (H50) calculated as 51.57 cm. The recovered specimens show that the reaction started from the outer edge of the specimen with the largest shear force and the most concentrated shear deformation, indicating a shear-induced initiation mechanism. The reaction products of PTFE/Al/MoO3 specimens were AlF3, Al2O3, Mo and C, demonstrating that redox reaction occurred between PTFE and Al, and between Al and MoO3.

Degradable polymers are limited by their often-insufficient mechanical and thermal properties, which limit their usage to single-use packaging items at room temperature and in dry conditions. In this respect, the present work deals with the manufacture of custom-built Poly Lactic Acids (PLAs), which are designed to be compostable, suitable for food contact and are characterized by a good compromise between mechanical properties and thermal stability. A commercial grade PLA was, therefore, compounded in a twin-screw co-rotating extruder by the use of specific additives: maleated and glycidyl methacrylate PLAs as compatibilizers/chain extenders and microlamellar talc as mineral filler/nucleation promoter. After pelletizing, the resulting compounds were melt-processed by injection and compression molding. Differential scanning calorimetry, flexural tests in static machine and top-hat cylindrical flat indentations were performed to evaluate the thermal and mechanical response of the molded components. The experimental findings show that crystallization of the PLA can be controlled by fine-tuning the compound formulation as well as by properly setting the processing parameters. In addition, achievement of the appropriate crystallization degree in the polymer can lead to molded components, which exhibit improved mechanical strength and high thermal stability.

The accelerated formation of bainite in presence of martensite is opening a new processing window for the steel industry. However, for a feasible industrial implementation, it is necessary to determine the mechanical behaviour of the steels developed under such conditions. This study focuses on analysing the effects of the formation of athermal martensite, followed by the formation of bainitic ferrite, on the mechanical response of a low-C high-Si steel. For this purpose, microhardness measurements and tensile tests have been performed on specimens that were thermally treated either above or below the martensite-start temperature (Ms). Specimens isothermally treated below Ms exhibit a good combination of mechanical properties, comparable with that of the specimens heat treated by conventional treatments above Ms, where there was no prior formation of martensite. Investigations show an increase of the yield stress and a decrease of the ultimate tensile strength as the isothermal holding temperature is decreased below Ms. The formation of prior athermal martensite and its tempering during the isothermal holding leads to the strengthening of the specimens isothermally heat treated below Ms at the expense of slightly decreasing their strain hardening capacity.

In the present work, a hybrid micro macro-approach was adopted to investigate the material behavior of the A5XXX-O object of the Benchmark 3 of Numisheet2018. Starting from the provided uniaxial stress-strain curve and in house microstructure measurements, a mean eld approach, by using the VPSC7c code, was used to perform numerical experiments in order to derive the anisotropic macroscopic behavior of the aluminum alloy. Then, at the macroscale, a constitutive model was built on coupling a non-quadratic yield surface function with a damage model developed in the framework of the continuum damage mechanics. Finally, by using MSC.Marc2017.1, finite element simulations of uniaxial and Nakajima bulging tests were performed with the purpose of obtaining the Fracture Formin gLimit Curve for the aluminum alloy under investigation.

This paper presents a crystal plasticity model to predict the tensile response and crack initiation in a mixed ferrite-martensite material with a low volume fraction of pro-eutectoid ferrite, representative of a welding-induced intercritical heat-affected zone. It is shown that small volume fractions of ferrite can have a significant effect on material strength and ductility depending on the ferrite grain orientation. For relatively soft ferrite grains, microcracks can grow across interferrite ligaments with damage accumulating in the ferrite, leading to a reduction in strength and strain hardening, but with little influence on ductility; in contrast, relatively hard ferrite grains act to accelerate microcrack initiation, leading to reduced ductility, with negligible influence on strain hardening up to the maximum load. This publication has emanated from research conducted with the financial support of Science Foundation Ireland under grant no. 14/IA/2604 and the College of Engineering and Informatics at NUI Galway. The authors are grateful to the Irish Center for High‐End Computing (ICHEC) for supporting the computational work (uleng040b). The authors are grateful for the helpful discussions with the Mechanics team (NUI Galway and UL). The assistance of Mr Edward Meade of the Bernal Institute at UL is also gratefully acknowledged. peer-reviewed

A simple two-dimensional Unit cell (UC) with three different mesoscopic phases may be geometrically modeled as a combination of two concentric circles or squares embedded in a square. In this paper, a two-dimensional three-phase UC with a similar design is developed and utilized for modeling the full deformation and failure response of cement based quasi-brittle cementitious composites under compression. It was identified from the numerical investigation that the three-phase design greatly improved the prediction capability of the UC in suitably capturing the material nonlinearity observed experimentally. HighlightsSuccessfully developed and implemented the three-phase unit cell approach for the mechanical characterization of cementitious composites.Captured the non-linear deformation behavior in good correlation with experiments.Established the effectiveness of the three-phase unit cell approach in capturing the non-linearity of the materials considered without sacrificing the simplicity of the unit cell model.Different parametric studies were also conducted to identify the influence of certain phase characteristics of the unit cell for the materials considered.

Aluminum laminates are among the main components of beverage packaging. These layered material systems are coupled to paperboard plies except in the cap opening area, where the human force limit sets a requirement on the material properties to allow open-ability and the mechanical characteristics are of particular interest. Experimental investigations have been carried out on this composite and on its components by either traditional or full-field measurement techniques. The interpretation of the collected data has been supported by the simulation of the performed tests considering either a homogenized material model or the individual laminate layers. However, different results may be recovered from similar samples due to physical factors like the material processing route and the embedded defectiveness. In turn, the conclusions may vary depending on the model assumptions. This contribution focuses on the physical effects and on the modeling of the large localized deformation induced by material singularities. This topic is discussed at the light of some experimental results.

The mechanical properties of structurally-defined magnetoactive polymer (co)networks synthesized from well-defined poly(2-dimethylamino)ethyl methacrylate (poly(DMAEMA)) homopolymers and diblock copolymers of poly(DMAEMA) with the hydrophobic n-butyl methacrylate (BuMA) were measured in compression. Magnetic nanoparticle composition varied from 0 to 30% wt and caused a 6-fold increase in the Young's modulus of the homopolymer networks (2.91 vs. 18.62 kPa) and a 12-fold increase in the modulus of diblock copolymer networks (0.76 vs. 9.1 kPa), with homopolymers being stiffer. Mathematical modeling revealed an exponential constitutive equation to predict accurately the mechanical response of the polymers. Furthermore, experiments were performed for the poroelastic behavior of the materials and their hydraulic conductivity was found to be independent of magnetic loading and network structure. In conclusion, the incorporation of magnetic nanoparticles strengthened the (co)network structure, while the synthetic approach employed for the DMAEMA-b-BuMA formation retained the linear, non-crosslinked architecture of BuMA, resulting in less stiff structures. This journal is © The Royal Society of Chemistry 2015. 5 20011 20019 20011-20019

The effect of prolonged hydration of Portland cement paste on engineering behavior was investigated using dynamic mechanical thermo-analysis (DMTA) methods. Specimens ranged in age from 3 days to 45 years. Compacts of hydrated cement powders and normally hydrated paste specimens were tested. Age dependent nanostructural characteristics of C–S–H were shown to influence the mechanical response of cement paste. Evidence was provided to support the use of compacts as structural models for hydrated cement paste. Details of ageing effects on the DMTA parameters (storage modulus and internal friction) as a function of temperature and porosity are reported.

Ultra-High Performance Fiber Reinforced Concretes (UHPFRC) have demonstrated their potential to contain the explosion of maintenance costs (Economy and Environment) for civil engineering structures, due to their extremely low permeability associated with the outstanding mechanical properties. Substitution of Embodied- Energy (EE)-costly components of UHPFRC such as clinker and steel fibers, is the next step towards sustainability, to make it even more efficient and more environment- friendly. In this study, a strain hardening UHPFRC mix with two main modifications has been developed in which (1) 75% of steel fibers have been replaced by ultra-high molecular weight polyethylene (UHMWPE, henceforth referred to as PE) fibers and (2) 50% volume of cement type CEM I have been replaced with limestone filler. The effect of the fiber orientation and the specimen thickness on the mechanical properties of such mixes have been investigated. The mechanical properties have been investigated using direct tensile test, and 4-point bending test. Finally, the dramatic effect of fiber orientation on the ultimate strength and deformability has been demonstrated. Moreover, the results confirm that the specimen thickness affects the deformation capacity of the specimens. Finally, improvements in terms of reduction of EE of the proposed mixes are highlighted.

International audience; Elasticity of the child rib cortical bone is poorly known due to the difficulties in obtaining specimens to perform conventional tests. It was shown on the femoral cortical bone that elasticity is strongly correlated with density for both children and adults through a unique relationship. Thus, it is assumed that the relationships between the elasticity and density of adult rib cortical bones could be expanded to include that of children. This study estimated in vivo the elasticity of the child rib cortical bone using quantitative computed tomography (QCT). Twenty-eight children (from 1 to 18 y.o.) were considered. Calibrated QCT images were prescribed for various thoracic pathologies. The Hounsfield units were converted to bone mineral density (BMD). A relationship between the BMD and the elasticity of the rib cortical bone was applied to estimate the elasticity of children’s ribs in vivo. The estimated elasticity increases with growth (7.1 ± 2.5 GPa at 1 y.o. up to 11.6 ± 1.9 GPa at 18 y.o.). This data is in agreement with the few previous values obtained using direct measurements. This methodology paves the way for in vivo assessment of the elasticity of the child cortical bone based on calibrated QCT images.

Fibrin is a protein polymer that forms a 3D filamentous network, a major structural component of protective physiological blood clots as well as life threatening pathological thrombi. It plays an important role in wound healing, tissue regeneration and is widely employed in surgery as a sealant and in tissue engineering as a scaffold. The goal of this study was to establish correlations between structural changes and mechanical responses of fibrin networks exposed to compressive loads. Rheological measurements revealed nonlinear changes of fibrin network viscoelastic properties under dynamic compression, resulting in network softening followed by its dramatic hardening. Repeated compression/decompression enhanced fibrin clot stiffening. Combining fibrin network rheology with simultaneous confocal microscopy provided direct evidence of structural modulations underlying nonlinear viscoelasticity of compressed fibrin networks. Fibrin clot softening in response to compression strongly correlated with fiber buckling and bending, while hardening was associated with fibrin network densification. Our results suggest a complex interplay of entropic and enthalpic mechanisms accompanying structural changes and accounting for the nonlinear mechanical response in fibrin networks undergoing compressive deformations. These findings provide new insight into the fibrin clot structural mechanics and can be useful for designing fibrin-based biomaterials with modulated viscoelastic properties.

The translaminar fracture toughness of fibre-reinforced composites is a size-dependent property which governs the damage tolerance and failure of these materials. This paper presents the development, implementation and validation of an original analytical model to predict the tensile translaminar (fibre-dominated) toughness of composite plies and bundles, as well as the associated size effect. The model considers, as energy dissipation mechanisms, debonding and pull-out of bundles from quasi-fractal fracture surfaces; the corresponding lengths are stochastic variables predicted by the model, based on the respective bundle strength distributions and fracture mechanics. Parametric studies show that composites are toughened by stronger fibres with large strength variability, and intermediate values of interfacial toughness and friction. Predictions are validated against four different composite ply systems tested in the literature, proving the model’s ability to capture not only size effects, but also the influence of different fibres and resins.

International audience; The environmental and economic concerns have raised the popularity of biodiesel as a potential replacement for conventional fuel. However, the incompatibility of engineering rubber components with biodiesel affects significantly the performance of the components. Majority of the compatibility studies focus on evaluating the degradation of mechanical properties of the rubbers due to contamination of different types of biodiesel. Nevertheless, the resulting mechanical responses of swollen rubbers, in particularly under cyclic and fatigue loading conditions, are rarely investigated. In engineering applications where elastomeric components are concurrently subjected to fluctuating mechanical loading and contamination of hostile liquids such as biodiesel, it is crucial to investigate the mechanical responses of these components for durability analysis. In this view, the present study aims to investigate the effect of swelling, due to biodiesel diffusion in the elastomers, on the macroscopic mechanical responses under cyclic loading conditions. Simple stress-free immersion tests are conducted on elastomers and the resulting mechanical responses are evaluated. The focus of the present work is on the effect of biodiesel diffusion on the inelastic responses classically observed in elastomers under cyclic loading conditions, i.e. stress-softening, hysteresis and stress relaxation. The results show that the above inelastic responses decrease significantly when the swelling level increases.

Twinning is an important deformation mechanism in hexagonal close-packed (hcp) metals such as Mg, Zr, Ti, and Be. Twinning in hcp materials is a multiscale process that depends on microstructural and mechanical response details at the mesoscale, microscale, and atomic scales. Twinning can generally be understood as a two-step process, a nucleation step followed by propagation. The nucleation of twins is governed by both material details such as the defect configurations at potential nucleation sites within grain boundaries, as well as the highly local mechanical field near grain boundaries. These two factors, the material and mechanical, must align for a successful nucleation event. In this article, we present a stochastic constitutive law for nucleation of twins and describe its implementation into a homogenized crystal plasticity simulation. Twin nucleation relies on the dissociation of grain boundary defects under stress into the required twinning partials. This dissociation is considered to follow a Poisson process where the parameters of the Poisson distribution are related to the properties of the grain boundaries. The rate of the process is a direct function of the local stress concentration at the grain boundary. These stress concentrations are randomly sampled from a distribution calibrated to full-field crystal plasticity simulations. � 2013 TMS (outside the USA).

International audience; The extraordinary properties of nanofibrous structure have gained ever-increasing appeal as an attractive candidate in a myriad of applications, especially for the water filtration. This type of structure has permeability due to its porous structure. Electrospinning is one of the most viable approaches in fabricating nanofibrous web that exhibits novel and outstanding performance in membrane separation as compared to those produced through conventional methods. Thus, the optimization of electrospinning processes is actively pursued by many researchers in order to obtain the best structure suitable for real-life applications. In this study, the surface morphology analysis and mechanical characterization of nanofibrous structure are addressed. For this purpose, polyvinylidene fluoride (PVDF) is considered. The polymeric nanofibrous structures are fabricated through electrospinning technique. Parameters such as polymer concentration and applied voltage for electrospinning process were varied and the resulting morphology of the structure were observed using SEM. In addition, the macroscopic mechanical responses of the structure were probed by means of tensile tests with special attention given to membrane anisotropy and behavior under cyclic loading.

In the exploration of planetary materials using robotic probes, one of the key priorities is to establish fundamental level understandings on the mechanical response of materials under different levels of loading. In this context, though a number of strength characterisation tools are applied in the space industry, whole-field visualization of stress and temperature distribution on rock samples and their potential relevance to fracture under external loading is not yet well exploited. In this work, we apply two types of tomography namely (i) IR tomography and (ii) PSAT tomography to understand the variation of temperature and shear stress distribution respectively anywhere on the samples at point scale. Sandstone is used as a simulant material here. Potential links between the tomography measures and the fracture strength of the sandstone are revealed in this work. This publication was made possible by NPRP grant # 6-1010-2-413 from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors. Scopus

cited By 25; International audience; Evolution of atomic mobility in a Ti 40Zr 25Ni 8Cu 9Be 18 bulk metallic glass was studied by dynamic mechanical analysis (DMA) in different states: as-cast, after structural relaxation, after crystallization and after deformation (cold-rolled). Characteristics of Ti 40Zr 25Ni 8Cu 9Be 18 bulk metallic glass are similar to that observed in other based bulk metallic glasses in the amorphous state: at low temperature, the material is mainly elastic and the mechanical response is independent of driving frequency, while on the other hand, the visco-elastic component becomes very large in the glass transition region. Structural relaxation and crystallization induce a decrease in the visco-elastic component, suggesting that atomic mobility is reduced. In contrast, atomic mobility is increased by a plastic deformation (i.e. cold-rolling). The higher is the cold-rolling ratio, the higher is the visco-elastic component. The experimental results were analyzed in the framework of quasi-point defects theory, which is based on the existence of defects in amorphous materials (polymer, bulk metallic glasses and other non-crystalline solids). © 2012 Elsevier Ltd. All rights reserved.

International audience; Motivated by environmental and economic factors, biodiesel has been introduced to partially replace the diminishing stock of petroleum-based fuel. However, the use of biodiesel such as palm biodiesel is placing additional demands on automotive components, e.g. rubber components, due to a compatibility issue in the fuel system. In engineering applications where hostile environments are involved, the long-term mechanical response of rubber components is affected by interactions existed between diffusion of liquids into the material and fluctuating multiaxial loading. Hence, it is crucial to investigate the durability of rubber components in this aggressive environment. A number of studies on static immersion tests to investigate the diffusion of liquids in stress-free rubber can be found in the literature. However, studies focusing on the coupling between diffusion and large deformation in rubber, and the resulting swelling and mechanical response under cyclic loading conditions are less common. In the present work, a compression device for the investigation of interaction between diffusion of palm biodiesel and large compressive strain in rubber is developed. The apparatus is comprised of four rectangular stainless steel plates with spacer bars in between, which are designed such that pre-compression can be introduced on the rubber specimens while they are immersed into biodiesel. This allows diffusion and large strain to take place simultaneously. Different pre-compressive strains and biodiesel blends are considered. At the end of each immersion period, the resulting swelling behavior and mechanical response of rubber specimens under cyclic loading conditions are investigated. The features of this compression device are discussed and perspectives are drawn.

Radiation-induced segregation (RIS) in desensitized type 304 stainless steel (SS) was investigated using a combination of electrochemical potentiokinetic reactivation (EPR) test and atomic force microscopy (AFM). Desensitized type 304 SS was irradiated to 0.43 dpa (displacement per atom) using 4.8 MeV protons at 300 degrees C. The maximum attack in the EPR test for the irradiated desensitized SS was measured at a depth of 70 mu m from the surface. Grain boundaries and twin boundaries got attacked and pit-like features within the grains were observed after the EPR test at the depth of 70 mu m. The depth of attack, as measured by AFM, was higher at grain boundaries and pit-like features as compared to twin boundaries. It has been shown that the chromium depletion due to RIS takes place at the carbide-matrix as well as at the carbide-carbide interfaces at grain boundaries. The width of attack at grain boundaries after the EPR test of the irradiated desensitized specimen appeared larger due to the dislodgement of carbides at grain boundaries. (C) 2011 Elsevier B.V. All rights reserved.

The primary objective of this work is to characterize and compare the dynamic mechanical behavior of asphalt concrete mixes with styrene butadiene styrene (SBS) polymer and crumb rubber modified asphalt binders with the behavior of mixes with unmodified viscosity grade asphalt binders. Asphalt binders are characterized for their physical and rheological properties. Simple performance tests like dynamic modulus, dynamic and static creep tests are carried out at varying temperatures and time. Dynamic modulus master curves constructed using numerical optimization technique is used to explain the time and temperature dependency of modified and unmodified asphalt binder mixes. Creep parameters estimated through regression analysis explained the permanent deformation characteristics of asphalt concrete mixes. From the dynamic mechanical characterization studies, it is found that asphalt concrete mixes with SBS polymer modified asphalt binder showed significantly higher values of dynamic modulus and reduced rate of deformation at higher temperatures when compared to asphalt concrete mixes with crumb rubber and unmodified asphalt binders. From the concept of energy dissipation, it is found that SBS polymer modification substantially reduces the energy loss at higher temperatures. Multi-factorial analysis of variance carried out using generalized liner model showed that temperature, frequency and asphalt binder type significant influences the mechanical response of asphalt concrete mixes. The mechanical response of SBS polymer modified asphalt binders are significantly correlated with the rutting resistance of asphalt concrete mixes. � 2011 Elsevier B.V.