Inhomogeneous Structure Research Articles

Heat physical properties of polymer composites based on polychlortrifluoroethylene filled with thermally expanded graphite

Based on research and comparative analysis of heat physical (specific heat capacity cp, thermal coefficient of linear expansion a) properties of systems polychlorotrifluoroethylene (PCTFE) - nanodispersed thermally expanded graphite (TEG) and PCTFE - nanomodified silicon dioxide (SiO2) TEG (30% SiO2 for 70% TEG) the influence of the structural-morphological state of the components and their concentration, the level of interfacial interaction on the physical properties of nanocomposites has been studied.
 It is established that the double effect of the modified nanofiller on the crystalline component of the matrix structure is that a more developed crystal structure is formed in the polymer-modified nanofiller interaction zones and, conversely, some amorphization in the peripheral zones. At the same time, increasing the concentration of the modified nanofiller leads to competition from the growth of neighboring crystallites and the ability to fix macromolecules “from both ends” on the particles of the modified nanofiller. Whereas in the case of unmodified dispersed TEG the existence of such competing factors led to their mutual compensation and, as a consequence, stabilization of reflex temperatures after reaching the percolation threshold and exceeding the percolation threshold, in the case of modified nanofiller when polymer-filler interactions percolation of the second factor predominates, which leads to a decrease in the temperatures of the corresponding reflexes almost to their values, which correspond to a pure matrix.
 The work found that depending on the nanofiller concentration, the structure of the matrix and the system as a whole shows a transformation in the size of the inhomogeneity and change in the size of the inhomogeneity of the system structure is associated with the transition from inhomogeneity as the size of crystallites, the growth of which is activated by nanofiller at low concentrations, through the percolation threshold, to inhomogeneities associated with coagulation of nanoparticles at concentrations exceeding the percolation threshold. Thus the case of nanofillers, it is not advisable to use concentrations that significantly exceed the percolation threshold, as this leads to coagulation of the filler particles and the corresponding loosening of the matrix.
 It is also shown that modification of the nanofiller (TRG/30%SiO2) increases intermolecular interaction in the filler-matrix system. Depending on the concentration of the filler, the structure of the matrix and the system as a whole demonstrates dynamic transformations in the size of the heterogeneity of the structure. Also, research results show that modified nanofiller is more active against the polymer matrix than unmodified, which is a consequence of the fact of the double action of the modified nanofiller on the matrix structure is manifested, which consists in the formation of a strong crystalline structure in the zones of influence of the nanofiller and amorphization of the matrix in the peripheral zones

Achieving ultrahigh cryogenic yield strength and sufficient ductility in a medium-entropy alloy via bimodal grain design

This work proposes an efficient strengthening and toughening method. A CrCoNi medium-entropy alloy (MEA) with a bimodal grained structure can be designed by controlling intermediate-temperature-annealing after cold rolling. The bimodal grained MEA consists of ultrafine-grained domain and fine-grained domain (volume fractioñ37%), showing an ultrahigh yield strength (YS) of 1600 MPa and a remarkable uniform elongation of 19% at cryogenic temperature, whose cryogenic YS improves by ∼2.5 times compared to that of coarse-grained counterpart. The inhomogeneity of the bimodal grained structure can significantly improve the YS while maintaining stable strain hardening ability, and activate multiple deformation mechanisms including significant dislocation activities, massive stacking faults, deformation nanotwins, and Lomer-Cottrell locks. Our results demonstrate that tailoring bimodal grained structures can enrich the applications of MEAs in cryogenic engineering.

Utilization of viscoelatic models with non-linear springs and dashpots in delamination study of multilayered beams

This paper analyzes delamination of multilayered inhomogeneous beam structure by utilization a non-linear viscoelastic mechanical model. The non-linear time-dependent response is treated by a non-linear spring and a non-linear dashpot connected in series to a system of two linear springs and two linear dashpots. The model is under stress that is a linear function of time. The constitutive law of the model representing a non-linear dependence between stress, strain and time is derived. The main goal of the paper is to obtain a solution of the strain energy release rate for the delamination in the multilayered inhomogeneous beam by applying the non-linear viscoelastic model. Solutions are derived by using the complementary strain energy and by analyzing the balance of the energy with taking into account the non-linear viscoelastic behaviour. For this purpose, the constitutive law of the non-linear viscoelastic mechanical model is used. The solutions are applied to obtain results for multilayered beams with non-linear variation of material properties in longitudinal direction. The influence of different parameters on the time-dependent strain energy release rate is assessed. The study indicates the effectiveness of the viscoelastic mechanical models with non-linear springs and dashpots in time-dependent delamination analyses of multilayered inhomogeneous beam structures.

Illustrating the atomic structure and formation mechanism of ion tracks in polyethylene terephthalate with molecular dynamics simulations

This work reports molecular dynamics (MD) simulations of the formation of detailed ion track structures at the atomic scale in polymers. To simulate the initial chemical reactions and the subsequent thermal movement of polymer molecules, an adapted thermal spike model was implemented using a charge-implicit reactive force field potential. The MD simulation reproduces the physical–chemical process of ion track formation observed in the experiment, e.g., the bond breakage and creation, gas production and release, carbonization effect, and the relative radial density distributions, which are consistent with small angle X-ray scattering results of ion tracks in polyethylene terephthalate generated with 15.9 keV nm−1 Au and 10.9 keV nm−1 Xe ions, respectively. Based on the MD simulation, the ion tracks in polymers show a heavily-damaged core region with an inhomogeneous nanoporous structure, and a surrounding transition region with the mass density increasing gradually back to the same value as the pristine sample.

Influence of ultrasonic vibrations during drilling of carbon-fiber-reinforced polyetherimide composites

Carbon-fiber-reinforced polyetherimide (CFRP) is an advanced composite material that has a high strength-to-weight ratio, better fatigue, high mechanical strength, low friction coefficient and low weight. Drilling of composite is difficult due to the anisotropic and inhomogeneous structure of fiber and matrix that affects micro and macro geometrical damages. Conventional drilling of CFRP composite causes high temperature, cutting force, torque, fiber pull-out, damaged surface topology, microcracks and delamination. The present study leverages rotary ultrasonic-assisted drilling of CFRP composites and comparison with rotary drilling and normal drilling. The influence of different drilling parameters was investigated on cutting force, temperature, torque, surface roughness, material removal rate and microcracks produced at the drilled edge surface. It was observed that a rotational speed of 2500 rpm, 10 mm/min of feedrate, 420 µm of diamond grit sizes and ultrasonic power of 100 % for minimizing the cutting force, surface roughness, and torque. The rotary ultrasonic-assisted drilling of CFPR composite produces a precise cut with smooth surface morphology as compared to rotary drilling and normal drilling of composites. The application of rotary ultrasonic-assisted drilling using diamond-impregnated hollow tools can be leveraged for various industrial applications to avoid microcracks and fiber delamination.

Transmission strings: a technique for spatially mapping exoplanet atmospheres around their terminators

ABSTRACT Exoplanet transmission spectra, which measure the absorption of light passing through a planet’s atmosphere during transit, are most often assessed globally, resulting in a single spectrum per planetary atmosphere. However, the inherent 3D nature of planetary atmospheres, via thermal, chemical, and dynamical processes, can imprint inhomogeneous structure and properties in the observables. In this work, we devise a technique for spatially mapping the atmospheres of exoplanets in transmission. Our approach relaxes the assumption that transit light curves are created from circular stars occulted by circular planets, and instead we allow for flexibility in the planet’s sky-projected shape. We define the planet’s radius to be a single-valued function of angle around its limb, and we refer to this mathematical object as a transmission string. These transmission strings are parametrized in terms of Fourier series, a choice motivated by these series having adjustable complexity, generating physically practical shapes, while being reducible to the classical circular case. The utility of our technique is primarily intended for high-precision multiwavelength light curves, from which inferences of transmission spectra can be made as a function of angle around a planet’s terminator, enabling analysis of the multidimensional physics at play in exoplanet atmospheres. More generally, the technique can be applied to any transit light curve to derive the shape of the transiting body. The algorithm we develop is available as an open-source package, called harmonica1.

Heat-induced amorphous aggregates assembly of soy protein modulate in vitro digestibility of potato starch

This research focused on the characteristics of amorphous aggregates derived from soy protein (SPAA), and their effects on the structural, physicochemical, and digestive properties of potato starch (PS). The SPAA induced by different heating temperatures at pH 7.0 formed an inhomogeneous spherical structure. The presence of SPAA could improve the degree of short-range order of starch, increase thermal stability, reduce pasting viscosity and breakdown, and setback viscosity values of PS. For the PS complexed with SPAAs under simulated cooking conditions, the fraction of digested starch at 300 min (C300) decreased by 6–14 %, and rapid digestible starch content (RDS) decreased by 18–25 %, while the slowly digestible starch (SDS) and resistant starch (RS) increased by 0.4–3 % and 15–23 %, respectively. The SPAA at higher temperature treatment (SPAA130) reduced digestive rate coefficient (k) values more significantly than SPAA at a lower temperature (SPAA70, SPAA90, SPAA110). And the SPAA had no inhibitory effect on α-amylase. The results of this study would significantly contribute to expanding the theoretical information about protein regulation in starch digestion and promoting the development of healthy foods with digestion-resistant properties.

Coherent propagation of vortex rings at extremely high Reynolds numbers

We take advantage of the extremely small kinematic viscosity of superfluid $^4$ He to investigate the propagation of macroscopic vortex rings at Reynolds numbers between $2 \times 10^4$ and $4 \times 10^6$ . These inhomogeneous flow structures are thermally generated by releasing short power pulses into a small volume of liquid, open to the surrounding bath through a vertical tube $2$ mm in diameter. We study specifically the ring behaviour between $1.30$ and $1.80$ K using the flow visualization and second sound attenuation techniques. From the obtained data sets, containing more than $2600$ realizations, we find that the rings remain well-defined in space and time for distances up to at least $40$ tube diameters, and that their circulation depends significantly on the travelled distance, in a way similar to that observed for turbulent vortex rings propagating in Newtonian fluids. Additionally, the ring velocity and circulation appear to be influenced solely by a single, experimentally accessible parameter, combining the liquid temperature with the magnitude and duration of the power pulse. Overall, our results support the view that macroscopic vortex rings moving in superfluid $^4$ He closely resemble their Newtonian analogues, at least in the absence of significant thermal effects and at sufficiently large flow scales.

How Thin and Efficient Can a Metasurface Reflector Be? Universal Bounds on Reflection for Any Direction and Polarization

AbstractLight reflection plays a crucial role in a number of modern technologies. In this paper, analytical expressions for maximal reflected power in any direction and for any polarization are given for generic planar structures made of a single material represented by a complex scalar susceptibility. The problem of optimal light‐matter interactions to maximize reflection is formulated as the solution of an optimization problem in terms of the induced currents, subject to energy conservation and passivity, which admits a global upper bound by using Lagrangian duality. The derived upper bounds apply to a broad range of planar structures, including metasurfaces, gratings, homogenized films, photonic crystal slabs, and more generally, any inhomogeneous planar structure irrespective of its geometrical details. These bounds also set the limit on the minimum possible thickness, for a given lossy material, to achieve a desired reflectance. Moreover, the results allow the discovery of parameter regions where large improvements in the efficiency of a reflective structure are possible compared to existing designs. Examples are given of the implications of these findings for the design of superior and compact reflective components made of real, imperfect (i.e., lossy) materials, such as ultra‐thin and efficient gratings, polarization converters, and light‐weight mirrors for solar/laser sails.

Roles of a strain relaxation and an oxygen vacancy on nanoscale inhomogeneities in VO2 thin film

We investigated structural and electronic inhomogeneities in a VO2 thin film grown on a (001)-oriented TiO2 substrate by exploiting nano-scale and macroscopic probing techniques. A compressive strain along the out-of-plane direction becomes additionally relaxed via microcracks which form a micron-sized rectangular pattern. A large inhomogeneity in the dielectric response is observed near the crack, and this signifies a strong coupling between electronic and lattice degrees of freedom. Interestingly, the strong inhomogeneity is observed also inside of the rectangular pattern, and it shows a gradient along one crystalline axis. We attribute such peculiar inhomogeneity observed in a relatively large length scale possibly to a combined effect of the strain relaxation and an oxygen vacancy distribution. As the nano-scale inhomogeneities in structural and electronic properties will eventually determine macroscopic responsivities, this work can be a good guide in designing VO2 thin films with appropriate controls of the strain and the chemical composition to realize better functionalities.

Prediction of the Destruction of Materials with Inhomogeneous Structures

Structural and metallurgical factors that cause the differences in the fracture resistance of steels and alloys are studied, which is necessary for predicting the destruction of media with an inhomogeneous structure. The prospects for digitalization of measuring the parameters of the structure and fracture surfaces using Big Data algorithms are considered.

The Impact of Apparent Frequency-Dependent Soil Properties on Electrical Grounding Characteristics

The purpose of this work is to estimate and reduce errors that can occur if apparent frequency-dependent soil properties are used for calculations of the grounding potential rise and exact inhomogeneous soil structure is neglected. Such estimation would help evaluate, which level of complexity is needed for measurement techniques when soil properties are used for grounding design. Simulations have shown that errors associated with the usage of apparent soil properties for electrical grounding characteristics can be avoided if the depth of investigation is chosen appropriately (except for specific cases). A measurement approach was proposed that takes into account which instruments are available for measurements. The approach was verified by measurements with inhomogeneous soils. In addition, it was found that to avoid the high-frequency effects in measurements of soil properties, it is convenient to limit the depth of investigation (rather than dipole size). It has also been demonstrated that soil inhomogeneities can lead to differences in apparent soil properties at higher frequencies (for the same low-frequency resistivity).

Analytical modelling of heat accumulation in laser based additive manufacturing processes of metals

The flexibility of additive manufacturing processes results from the principle of subsequently adding small amounts of material in individual layers or beads on top of each other. The periodic input of energy required to melt the material can lead to an accumulation of heat, which increases the temperature of the part and changes the local temperature distribution in the melt pool. This heat accumulation results in local shape deviations of the part and can lead to inhomogeneous solidification conditions coinciding with inhomogeneous grain structures and potentially inhomogeneous mechanical properties or build failures. To produce high quality parts with homogeneous properties and to reduce unproductive dwell times, a comprehensive knowledge of the heat accumulation phenomena is required. The present work considers an explicit analytical description of the heat accumulation effect, which allows for a mathematical analysis of the influence of all contributing process parameters on the temperature increase of the part. The analytical equations were derived from simplified heat conduction equations and validated by comparison with temperature measurements from literature. The calculated temperature increase shows a good agreement with measurements observed during additive manufacturing of different materials and alloys in case of cladding or building volumes with direct energy deposition (DED) and laser powder bed fusion (LPBF). Finally, the obtained analytical solution is used to derive optimization strategies aiming to reduce heat accumulation while simultaneously increasing productivity. • Analytical equations for the prediction of the temperature increase. • Analytical description of the heat accumulation in cladding and volume building with DED and LPBF • Validation for titanium-, inconel-, steel-, and aluminum-alloys • Identification of conditions that lead to a convergence of heat accumulation • Mathematical identification of the key factors, which influence heat accumulation. • Derivation of optimization strategies to increase productivity

Study of Light Diffraction on Electrically Controlled Multilayer Inhomogeneous Structures with Smooth Optical Inhomogeneity Based on Photopolymerizing Compositions with Nematic Liquid Crystals

Study of Light Diffraction on Electrically Controlled Multilayer Inhomogeneous Structures with Smooth Optical Inhomogeneity Based on Photopolymerizing Compositions with Nematic Liquid Crystals

In-situ temperature monitoring during rotary ultrasonic-assisted drilling of fiber-reinforced composites

Drilling polyetherimide composite is difficult due to the anisotropic and inhomogeneous structure of fiber and matrix. Drilling of fiber-reinforced composites is a thermo-mechanical friction procedure required in various aerospace and automotive applications. The major reason for component rejection during manufacturing processes is due to thermal damage and temperature elevation defects such as delamination and fiber pullout caused during drilling. This work aims to propose a rotary ultrasonic-assisted drilling technique for composite materials to reduce thermal damage using diamond-impregnated tools. The influence of drilling parameters such as rotational speed, feed rate, abrasive grit size, and ultrasonic power was monitored on temperature elevations. The temperature was monitored using thermocouples located at different distances of 1.0, 2.0, and 3.0 mm from the main drilled hole. The response surface methodology was used for the design of experiments during the drilling of composite material and optimization of process parameters was carried out using analysis of variance. Rotational speed and abrasive grit size were observed to have the highest contribution of 42% and 37% for temperature elevations respectively. It was witnessed that temperature increases with an increase in rotational speed, feedrate, and abrasive grit size. Increasing the ultrasonic power during drilling temperature can be minimized. The temperature elevations at the tool-composite interface can be reduced by leveraging the application of rotary ultrasonic-assisted drilling.

Visualizing Structural and Chemical Transformations of an Industrial Cu/ZnO/Al2O3 Pre‐catalyst during Activation and CO2 Reduction

AbstractThe typical industrial catalyst used for methanol synthesis is a multi‐component catalyst based on Cu/ZnO/Al2O3. The synergies between various phases of this catalyst play a vital role in defining the overall catalytic function and performance. To gain insights into the role and interaction between the relevant components and phases, ex situ and in situ transmission electron microscopy (TEM) was deployed to investigate the structures and phases of an industrial Cu/ZnO/Al2O3 in its precursor, activated and reaction states. High structural inhomogeneity in this material is revealed, i. e. the presence of various phases with different morphologies and compositions. It is shown how structural and compositional changes occur during hydrogen treatment and how compositional inhomogeneity in the starting material translates into differences in the local composition of the activated and working catalyst. The formation of defective metallic copper particles (stacking faults and twins) that are in an intimate contact with zinc oxide (poorly crystalline, partially reduced ZnOx and crystalline ZnO), alumina, Zn−Al oxide and carbon‐zinc‐oxygen containing phases (such as zinc formate) is observed. It is also uncovered that alumina plays a potentially important role in stabilizing cationic zinc species. This work provides atomic‐level insight into the relevant state of an industrial methanol synthesis catalyst and the associated synergistic interplay between the involved phases in reactive atmosphere.

Discrete exterior calculus for photonic crystal waveguides

AbstractThe discrete exterior calculus (DEC) is very promising, though not yet widely used, discretization method for photonic crystal (PC) waveguides. It can be seen as a generalization of the finite difference time domain (FDTD) method. The DEC enables efficient time evolution by construction and fits well for nonhomogeneous computational domains and obstacles of curved surfaces. These properties are typically present in applications of PC waveguides that are constructed as periodic structures of inhomogeneities in a computational domain. We present a two‐dimensional DEC discretization for PC waveguides and demonstrate it with a selection of numerical experiments typical in the application area. We also make a numerical comparison of the method with the FDTD method that is a mainstream method for simulating PC structures. Numerical results demonstrate the advantages of the DEC method.

Controlled Synthesis of Single-Crystalline Ni-Rich Cathodes for High-Performance Lithium-Ion Batteries.

Single-crystalline LiNi0.8Co0.1Mn0.1O2 (NCM811) has been considered as one of the most promising cathode materials. It addresses the pulverization issue present in its polycrystalline counterpart by eliminating intergranular cracks. However, synthesis of high-performance single-crystalline NCM is still a challenge owing to the lower structure stability of NCM811 at high calcination temperatures (≥900 °C), which is often required to grow single crystals. Herein, we report a synthesis process for microsized single-crystalline NCM811 particles with exposed (010) facets on their lateral sides [named as SC-NCM(010)], which includes the preparation of a well-dispersed microblock-like Ni0.8Co0.1Mn0.1(OH)2 precursor through coprecipitation assisted with addition of PVP and Na2SiO3 and subsequent lithiation of the precursor at 800 °C. The SC-NCM(010) cathode exhibits an excellent capacity retention rate (91.6% after 200 cycles at 1 C, 4.3 V) and a high rate capability (152.2 mAh/g at 20 C, 4.4 V), much superior to those of polycrystalline NCM811 cathodes. However, despite the removal of interparticle boundaries, when cycled between 2.8 and 4.5 V, the SC-NCM(010) cathode still suffers from structural changes including lattice gliding and intragranular cracking. These structural changes are correlated with the interior structural inhomogeneity, which is evidenced by the coexistence of H2 and H3 phases in the fully deintercalated state.

Study on mesoscopic failure mechanism of grout-infilled sandstone under uniaxial compression using an improved AE localization technique

In this paper, to study the influence of grouting on meso-failure mechanism, acoustic emission (AE) localization technique was used to monitor the micro-cracking during the uniaxial compression tests on single flawed sandstone specimens with or without grouting. Due to the inhomogeneous geometrical structure of the flawed specimens, the mesoscopic damage evolution is also inhomogeneous during the loading process. As a result, the wave velocity of the specimens varied temporally and spatially, which greatly increased the difficulty in accurate AE localization. To solve this problem, the wave velocities versus the axial load for the studied sandstone were first measured, and the stress concentration effect near the flaw was also theoretically analyzed. Accordingly, the localization arithmetic was also improved to match the complex wave velocity field. Results show that compared to the specimens without grouting, more microcracks (particularly the shear microcracks) are induced in the grout-infilled specimens prior to the final failure of the specimens. Moreover, the effect of grouting on microcrack initiation also varies with the oblique angle of the flaw. For θ (flaw inclination) ≤30°, grouting significantly increases the shear microcrack at macrocrack propagation stage which states that the axial tensile cracking was limited by the supporting effect of the grout material and made the failure mode trend to shear mode. For θ = 45° and 60°, grouting improved the ratio of shear microcrack during the whole failure process, indicating that the direction of maximum shear stress is close to the flaw direction. Hence, failure develops in stable shear mode. For θ = 75° and 90°, the primary microcrack generated during the first macrocrack initiation changed to shear mode, but the grouting has little influence on the subsequent crack propagation. So that, the reinforcement effect is poor in this set of specimens.

A tough shape memory hydrogel strain sensor based on gelatin grafted polypyrrole

Developing shape memory hydrogel strain sensors with both high mechanical property and stable electrical performance is a challenge. Here, a hydrogel based on gelatin was reported as a strain sensor. The hydrogel was developed by gelatin grafted polypyrrole, polyacrylamide and tannic acid. The gelatin moieties were exploited to form a water-soluble conductive polymer, endowing the hydrogel with shape memory behavior and addressing the challenge of low conductivity induced by structural inhomogeneity and aggregation of conductive nanomaterials. Tannic acid was introduced to provide hydrogen-bonding and π−π stacking interactions to promote hydrogel mechanical properties. The hydrogel achieved a maximum tensile strength of 1.44 ± 0.11 MPa, maximum toughness of 2581 ± 453 kJ/m3 and maximum conductivity of 0.58 ± 0.10 S/m. Results demonstrated that the hydrogel showed shape memory property and can respond to and discern different motions. This achievement offers an opportunity to facilitate significant shape memory conductive hydrogel strain sensor with both high mechanical property and stable electrical performance.