Random Dispersion Research Articles

Effective properties of an isotropic solid weakened by micro-cracks located at inter-granular boundaries

This study presents a new methodology for estimating the effective properties of solids containing cracks along the inter-granular boundaries, using analytical developments and numerical simulations. The latter are based on the generation of virtual microstructures of such type obtained by superimposing a Voronoï tessellation modeling the granular network with a random dispersion of overlapping spheres in 3-D, or disks in 2-D, which serve to locate the cracks at the inter-granular boundaries. The different features of this microstructure model are studied herein, especially the morphological effects induced by varying the size ratio between grains and spheres/disks. By means of full-field simulations, the effective thermal conductivities of the generated microstructures are estimated and compared with those of uniformly weakened solids (presenting uniform crack dispersion). For the latter microstructures, the Ponte-Castañeda and Willis (1995) upper bound turns out to be close to the full-field results. In addition, the full-field computations show that the spatial distribution of inter-granular cracks induces a dramatic degradation of the effective thermal conductivity. Modifying only the cut-off crack density in the mathematical expression of the Ponte Castañeda and Willis bound provides a relevant analytical estimate of the effective conductivity of solids weakened by inter-granular cracks. This cut-off crack density only depends on the microstructural parameters. This new estimate is shown to improve the one derived by Sevostianov and Kachanov (2019) and based on the differential scheme at least for the microstructures considered herein. Finally, new estimates of the moduli of elasticity for isotropic cracked solids weakened at inter-granular boundaries are also provided. The effective bulk modulus thus estimated for 3-D solids is shown to remain below the upper bound which can also be generated by injecting the effective conductivity predicted by full-field computations into the classical cross-property relations.

Study on the heat transfer reinforcement of glass fiber/epoxy resin composites by grafting and dispersing graphene oxide

The grafted-graphene oxide/glass fiber/epoxy resin (grafted-GO/GF/EP) and dispersed-graphene oxide/glass fiber/epoxy resin (dispersed-GO/GF/EP) composites were successfully prepared by grafting graphene oxide (GO) on glass fiber (GF) with coupling agent and random dispersion of GO. A scanning electron microscope (SEM) was employed to characterize the micro structure. The heat transfer RVE models of the grafted-GO/GF/EP and dispersed-GO/GF/EP composites were established respectively. Based on RVE heat transfer simulation model, the heat transfer characteristics of the grafted-GO/GF/EP and dispersed-GO/GF/EP composites were analyzed. The results show that under the condition of 0.1 vol% GO content and heated for 60 s, the thermal conductivities of dispersed-GO/GF/EP and grafted-GO/GF/EP composites are increased by 3.48% and 82.37% respectively. The dispersion of GO increases the heat transfer paths in EP and forms a connected GO-GO heat transfer network. However, with the increasing of GO content, the agglomeration of GO becomes more obvious. The dispersion and interfacial bonding of the GO/GF/EP composites were improved by coupling agent, which effectively reduced the interfacial thermal resistance and significantly improved the thermal conductivity of the composites.

The theoretical study of mechanical property and thermostability analysis of poly(vinyl alcohol)/graphene oxide nanofiber composites with different architecture: Molecular dynamics simulation

AbstractIn order to get a deep insight into the correlation between the structure and properties of composite materials, the models of polyvinyl alcohol (PVA)/graphene oxide nanofiber (GOF) composites with different architecture (including random dispersion of GOF in the composites (referred as R‐PVA/GOF composite); columnar cladding of GOF (referred as C‐PVA/GOF composite) and 3D core‐shell structure of GOF (referred as 3D‐PVA/GOF composite) were built, and the mechanical property and thermostability of these composites were analyzed by the molecular dynamic (MD) simulations. It was found that the morphology of GOF in composites had significant influence on its properties. The glass transition temperature (Tg) of C‐PVA/GOF composite was the largest compared to those of other materials (3D‐PVA/GOF composite; R‐PVA/GOF composite and pure PVA). Moreover, the modulus and tensile yield strength of these materials were ordered as follows: C‐PVA/GOF > 3D‐PVA/GOF > R‐PVA/GOF > PVA. The microstructure analysis of materials revealed that the different morphology of GOF affected not only its interactions with PVA but also the ability of components to form hydrogen bonds, the arrangement of PVA molecular chains and the fraction of the free volume in the system, leading to differences in the properties of composites with different structures.

Design of Laminated Composite Plates with Carbon Nanotube Inclusions against Buckling: Waviness and Agglomeration Effects.

In the present study, a buckling analysis of laminated composite rectangular plates reinforced with multiwalled carbon nanotube (MWCNT) inclusions is carried out using the finite element method (FEM). The rule of mixtures and the Halpin–Tsai model are employed to calculate the elastic modulus of the nanocomposite matrix. The effects of three critical factors, including random dispersion, waviness, and agglomeration of MWCNTs in the polymer matrix, on the material properties of the nanocomposite are analyzed. Then, the critical buckling loads of the composite plates are numerically determined for different design parameters, such as plate side-to-thickness ratio, elastic modulus ratio, boundary conditions, layup schemes, and fiber orientation angles. The influence of carbon nanotube fillers on the critical buckling load of a nanocomposite rectangular plate, considering the modified Halpin–Tsai micromechanical model, is demonstrated. The results are in good agreement with experimental and other theoretical data available in the open literature.

Moment approximation of individual-based models. Application to the study of the spatial dynamics of phytoplankton populations

The objective of this paper is to analyze the efficiency of a spatial moments model (SMM) in approximating an individual-based model (IBM) dedicated to the study of the aggregation phenomenon in a phytoplankton population. The dynamic system of spatial moments consists of a system of integro-differential equations derived from a phytoplankton IBM. The later is built on the basis of stochastic processes describing the dynamics of phytoplankton cells and their interactions. These processes are: (1) the movement of cells, which takes into account the random dispersion of cells in water and the attraction between cells due to their chemosensory abilities, (2) the demographical process (cell division or cell death) in which, the effect of local competition for nutrient resources on the cell’s division process is taken into account through the use of density dependent division rate.We solve numerically the SMM and then simulate the two models (IBM and SMM), for a set of scenarios chosen to analyze the aggregation and the different interactions in the population. The numerical results have led to the conclusion that in contrast to the mean-field model (MFM), the method of spatial moments is efficient to capture the dynamics of the IBM. Further, the SMM easily permits the prediction of long term behavior of phytoplankton cells and their spatial structure, namely that the aggregation behavior of the cells is very much related to their cellular diffusion and the perceptual radius.Concerning competition on resources, this process has a short and medium-term effect on aggregation, since regardless of its intensity, in the long term the population tends to be stable with formation of aggregates, as a result of the equilibrium between different mechanisms, including reproduction, competition, diffusion and cells attractions due to chemosensory abilities.

Highly Ordered Pt-Based Nanoparticles Directed by the Self-Assembly of Block Copolymers for the Oxygen Reduction Reaction.

Designing Pt-based nanoparticle (NP) catalysts is of great interest for the lowering of Pt usage and the enhancement of catalytic activity on the proton-exchange membrane fuel cells (PEMFCs). However, it is still challenging to develop well-arrayed catalyst NPs on supports over multiple-length scales. Herein, we presented a facile strategy of producing well-ordered Pt-based NPs toward oxygen reduction reaction (ORR) catalysts assisted by the self-assembly of block copolymers. In contrast to the conventional Pt/C ORR catalysts with a random dispersion on carbon, the as-prepared Pt, PtCo, and PtCo@Pt NPs in our work were hexagonally arranged with a uniform quasi-spherical shape and ordered distribution. The systematic study related to their ORR activities revealed that the PtCo@Pt core-shell NP arrays were more active and more durable than PtCo, Pt, and the commercial Pt/C catalyst. In the rotating-disk electrode test, a half-wave potential (E1/2) of 0.86 V versus RHE and a 4-e ORR mechanism were found for PtCo@Pt. Single-cell performance showed that the current density and the peak power density of PtCo@Pt achieved 0.86 A/cm2@0.7 V and 1.05 W/cm2, respectively, with a Pt loading of ∼0.15 mg/cm2 on the cathode. Also, they held 81.4 and 82.9% retention, respectively, after the durability test in the single-cell test. Density functional theory calculation results revealed that PtCo@Pt NPs had a lower d-band center and a weaker oxygen binding energy compared to Pt and PtCo, which contributed to the enhancement of the ORR activity.

Structuring BaTiO3 /PDMS Nanocomposite via Dielectrophoresis for Fractional Flow Reserve Measurement

This work focuses on the development of piezoelectric sensors for the fractional flow reserve (FFR) technique, a procedure based on the measurement of blood pressure within a vessel to evaluate the severity of coronary stenosis. Considering the medical application, biocompatibility is a mandatory requirement that justifies the selection of fillers and matrix. Two composites made of lead‐free barium titanate nanoparticles (BaTiO3) incorporated in polydimethylsiloxane (PDMS) elastomer are developed: the first composite with particles randomly dispersed and the second one with particles aligned along one direction, via an innovative technique known as dielectrophoresis. The experimental characterization indicates that the electroactive and dielectric properties are coherent with the models’ prediction, confirming that the alignment of the filler gives rise to considerably enhanced dielectric and piezoelectric proprieties relative to the random dispersion. Thermal stability together with X‐ray diffraction is conducted, demonstrating superior piezoelectric response of the structured sample under high‐temperature conditions. FFR application is then simulated by applying an arterial pulse‐shape stimulus on the developed sensor, which is finally integrated into a catheter and directly inserted in a simulation arm.

Comprehensive Characterization of Polymeric Composites Reinforced with Silica Microparticles Using Leftover Materials of Fused Filament Fabrication 3D Printing.

Silica exhibits properties such that its addition into polymeric materials can result in an enhanced overall quality and improved characteristics and as a result silica has been widely used as a filler material for improving the rheological properties of polymeric materials. The usage of polymers in three-dimensional printing technology has grown exponentially, which has increased the amount of waste produced during this process. Several polymers, such as polypropylene (PP), polyvinyl alcohol (PVA), polylactic acid (PLA), and nylon, are applied in this emerging technology. In this study, the effect of the addition of silica as a filler on the mechanical, thermal, and bulk density properties of the composites prepared from the aforementioned polymeric waste was studied. In addition, the morphology of the composite materials was characterized via scanning electron microscopy. The composite samples were prepared with various silica concentrations using a twin extruder followed by hot compression. Generally, the addition of silica increased the tensile strength of the polymers. For instance, the tensile strength of PVA with 5 wt% filler increased by 76 MPa, whereas those of PP and PLA with 10 wt% filler increased by 7.15 and 121.03 MPa, respectively. The crystallinity of the prepared composite samples ranged from 14% to 35%, which is expected in a composite system. Morphological analysis revealed the random dispersion of silica particles and agglomerate formation at high silica concentrations. The bulk density of the samples decreased with increased amount of filler addition. The addition of silica influenced the changes in the characteristics of the polymeric materials. Furthermore, the properties presented in this study can be used to further study the engineering design, transportation, and production processes, promoting the recycling and reuse of such waste in the same technology with the desired properties.

Dispersed nickel-cobalt double metal hydroxide self-assembled with polystyrene sulfonic acid polyelectrolyte for the preparation of carbon solid solid supercapacitors with wide temperature range and long cycle stability

Although polyelectrolytes with good electrochemical compatibility have been widely used in all solid-state supercapacitors, the random dispersion of polymer chains results in a narrow operating temperature range, which limits its further application. Herein, through the electrostatic attraction assembly strategy, the negatively charged polystyrene sulfonic acid (PSS) and the positively charged layered nickel-cobalt double hydroxide (NiCo-LDH) nanosheets are synthesized into PSS/NiCo-LDH composite electrolyte. Meanwhile, the polyelectrolyte shows a wide temperature application range (20–80 °C) and excellent electrochemical cycle stability in solid supercapacitor (capacitance retention rate reaches 96.2% after 5000 cycles) based on activated-carbon electrodes. The remarkable thermal stability and electrochemical performance are mainly attributed to the addition of NiCo-LDH, which is not only limit the thermal decomposition of PSS molecular chains, but also accelerate the migration rate of electrolyte ions. This work opens a way for the preparation of polyelectrolyte with wide temperature range and long cycle stability for application in solid-state supercapacitors.

Ectoparasites infecting Mugil curema (Mugiliformes: Mugilidae) in Amapá state estuary, in the northern Brazilian coast region.

In fish, one of the most important interactions is that occur between parasite species and environment. Wild fish interactions with parasites of different taxa can result in diseases for fish and consequently damages to the fishing industry. This study investigated the ectoparasite fauna in Mugil curema (Valenciennes, 1836), in Amapá state estuary, in Brazilian coast region. The parasite prevalence was 51.4%, and a total of 282 parasites were collected among Ligophorus brasiliensis (Abdallah, Azevedo & Luque 2009), Excorallana longicornis (Lemos de Castro, 1960), larvae of Gnathia sp. and Ergasilus atafonensis (Amado & Rocha, 1995), but L. brasiliensis was the dominant parasite. The parasites presented highly aggregated dispersion, except for Gnathia sp. that had a random dispersion. There was a predominance of hosts non-parasitized and parasitized by one species. The relative condition factor did not differ between parasitized and non-parasitized fish. The body size of hosts did not influence the parasite abundance. The community of ectoparasites consisted of low species richness with low infection levels. This is the first study on parasites of fish from the coast of the State of Amapá and is the first report of Gnathia sp. for M. curema.

Modulational instability in optical fibers with randomly kicked normal dispersion

We study modulational instability (MI) in optical fibers with random group velocity dispersion (GVD) generated by sharply localized perturbations of a normal GVD fiber that are either randomly or periodically placed along the fiber and that have random strength. This perturbation leads to the appearance of low frequency MI side lobes that grow with the strength of the perturbations, whereas they are faded by randomness in their position. If the random perturbations exhibit a finite average value, they can be compared with periodically perturbed fibers, where Arnold tongues appear. In that case, increased randomness in the strengths of the variations tends to affect the Arnold tongues less than increased randomness in their positions.

Propagation of coherent shear waves in scattering elastic media.

We measure the reflection and transmission of shear waves by slabs of random dispersions of hard, dense spheres in a viscoelastic matrix. By modeling the slab as a Fabry-Pérot interferometer, we determine the effective wave number of coherent shear waves in this scattering medium and its effective mass density. We evidence the effect of the resonant rigid-body translation and rotation of the spheres on the propagation. We validate a vectorial model of multiple scattering for volume fractions of spheres up to 10%, revealing the signature of two modes of propagation.

Composite structural modeling and mechanical behavior of whisker reinforced Cu matrix composites

To study the effect of TiB whisker on the mechanical properties of copper matrix composites (CMCs), a 3D microscopic TiB/Cu finite element model was established. By using the geometric features of TiB whisker obtained from the scanning electron microscopes (SEM), random dispersions of the length, the diameter, the positions and the volume fractions of TiB whiskers were numerically reconstructed in line with their actual microscopic structures. Brittle fractures of whisker, ductile damage and failure behaviors of matrix, and whisker–matrix interfacial behaviors are introduced in the model to simulate the mechanical behavior of TiB/Cu. The results show that when the length of TiB whisker exceeds 6d, the tensile strength of TiB/Cu tend to be stable at 320 MPa and the elongation tend to be stable at 0.086, where d is the diameter of TiB whisker. The effective length of whisker in TiB/Cu is 6d. Damage mechanisms in TiB/Cu were revealed by analyzing the average stress in the end and the middle of TiB whisker, and the simulation results were consistent with the experimental observations. This work provides a theoretical basis for the selection and optimization of parameters of reinforcement phase in preparation of TiB/Cu.

Nano-scale simulation of directional solidification in TWIP stainless steels: A focus on plastic deformation mechanisms

In this study, in order to understand the nanostructure of FeCrNi steels in the laser powder bed fusion (LPBF) process, directional solidification was simulated using large-scale molecular dynamics simulation (LSMDS). For this purpose an atomic box with a dimension of 70×40×60(nm3) including random dispersion of Fe, Cr and Ni was created. Then, two different fixed temperatures were considered for the left and right side of the box during cooling from the liquid molten state. For evaluation of the uniformity in mechanical properties, uniaxial tensile tests were performed in the parallel and perpendicular directions. Extensive twinning induced plasticity (TWIP) occurred along side Shockley partial dislocations (DLs) evolution in both directions, while different ultimate tensile strengths (UTS) were obtained as a sign of non-uniform tensile behavior. Different plastic deformation mechanisms at the nano-scale including stacking faults (SFs) interaction with each other/grain boundaries (GBs)/twin boundaries (TBs), formation of defective coherent twins (DCTs), dynamic Hall-Petch, shear stress gradient (back stress), and a new mechanism for dynamic recrystallization at room temperature are discussed in detail.

Development of active packaging films based on poly (butylene adipate-co-terephthalate) and silver–montmorillonite for shelf life extension of sea bream

This paper is a continuation of our previous study focusing on the development of active food packaging films and presents the results of their potential application in the sea bream storage. Intended for fish packaging, active nanocomposite films based on poly (butylene adipate-co-terephthalate) and silver–montmorillonite (PBAT/Ag-MMT) with 2, 3 and 5 wt. % of Ag-MMT were successfully prepared and characterized by several techniques which confirmed the formation of exfoliated nanocomposite structures with a random dispersion of spherically shaped Ag nanoparticles on the whole of the polymer matrix. PBAT/Ag-MMT films exhibited a sharp reduction in their water and oxygen permeabilities. The kinetic study of the silver ions migration confirmed that the release was mainly ensured by diffusion. Due to this controlled release, these packaging films displayed a long-lasting antibacterial activity. Furthermore, the results of their use as sea bream packaging films confirmed their great potential for maintaining the freshness and quality of the fish and extending its shelf life for a period of 15 days.

Effect of Steel Fiber Reinforced in FRP Confined Concrete by Using Numerical Analysis

The models are predicting and analyzing on compressive and flexural testing by considering fiber reinforcement embedded in confinement concrete. In this work, steel 4340 fiber with high aspect ratio was developed in unique random spline shape and randomly disperse in confinement concrete. Fibers designed in 15.5mm of average length and amount were varied in range of 50 to 200 and 250 to 1000 for compressive and flexural testing, respectively. Both varied orientation and random dispersion of fiber were developed using MATLAB before embedded and analyzed in Ansys Workbench. The finite element model was validated in initial results on plain concrete prior study in influence of confining and fibers to structure. The model proposed showed that confining reinforcement increasing ductility and large deflections in structure testing. In addition, fibers as reinforcement slightly increases in strength for both compressive and flexural in certain number. These method reinforcement was help warning of failure prior to complete failure that use in construction material.

Boron nitride-epoxy inverse “nacre-like” nanocomposite coatings with superior anticorrosion performance

Embedding 2D nanomaterials in polymer matrix is a fascinating strategy to construct anticorrosive coatings with superior barrier performance. However, this is extremely limited by the uncontrolled dispersion and arrangement of 2D nanomaterials in coating matrix. Here, we present a promising approach to prepare self-aligned boron nitride-epoxy composite coating, where the random distribution mode of boron nitride nanosheets is transformed into ordered dispersion and orientation through an electrophoretic deposition technique. Electrochemical results confirm that the impedance modulus of the resultant bioinspired composite coatings are 4 and 2 orders of magnitude than those of the blank and random dispersion coatings.

Binding Site Effect in Metal‐Organic Frameworks for Property Regulation of Metal Nanoparticles

Metal nanoparticles (MNPs) supported on metal–organic frameworks (MOFs) have exhibited excellent performance in various catalytic reactions. As a class of crystal catalysts, the roles played by MOFs different positions in regulating the MNPs properties are distinct. It is therefore meaningful to clarify the influence of different positions of MOFs on MNPs to help reveal the structure–activity relationship. However, the random dispersion of MNPs in the MOFs matrixes is usually an obstacle existing in the traditional preparation methods. Herein, a facile strategy is developed to precisely control the MNPs growth behavior on the target binding sites of MOFs. The MNPs on edges of MOFs show significantly improved hydrogen evolution reaction performance in comparison to those on the planes of MOFs, mainly because the electronic structure of MNPs is regulated by special interface originating from MNPs growth on the edges of MOFs, which provides high density of unsaturated copper ions. The effect of different binding sites of MOFs on MNPs properties is clarified, which is highly desired for fine‐tuning the structures and properties of the MOF composites.

ZnO/PDMS nanocomposite generator: Interphase influence in the nanocomposite electro-mechanical properties and output voltage

Nanocomposite generators convert mechanical energy into electrical energy and are attractive low-power solutions for self-powered sensors and wearables. Homogeneous dispersion, high concentration, and orientation of the embedded filler strategies have been assumed to maximize the voltage output in nanocomposite generators. This work contrast these assumptions by studying the dominance of the interphase in low filler concentrations (¡10%) and random dispersions in a ZnO/PDMS nanocomposite generator with high peak-to-peak voltage generation capabilities (≈150V). The interphase in the nanocomposite was studied by the analysis of the random dispersion of the nanocomposite through the estimation of the effective volume fraction (ϕagg) which allowed us to identify three levels of interaction: individual interphases, interacting interphases, and overlapping between NPs and interphases. The interacting interphase is responsible here for the high generated voltage. In addition, the impact of the interphase was studied by applying lumped element (LE) and interphasial power-law (IPL) models that capture the measured voltages and the electromechanical film properties. The obtained results justify that engineering of interphases could be a design strategy for high voltage generation.

Mining terrain curvatures approximation using the polynomials and a subsidence trough profile fragmentation

In an article a method of average course obtaining of measured mining terrain curvatures has been presented. Terrain curvatures values are very important for building objects located on mining areas and which have a considerable length or/and a great cubature. Curvatures observed graph has an irregular course and that’s why there is a need of their average course determination in order to obtain the most probable value. Measured curvatures approximation by use of the polynomial various orders has been done. Additionally, a whole profile of subsidence trough into the parts has been divided. Subsidence trough fragmentation allowed for a better fit of the curvatures average values to the observed values. A right polynomial order and a trough segments proper number taking into account value of variability coefficient of curvatures random dispersion have been chosen. Geodesic surveys, based on which a graph of measured curvatures has been obtained, in the Upper Silesian Coal Basin (Poland) have been done. There was conducted a mining exploitation of hard coal deposits by use of the longwall system with a roof rocks cave-in.