Re-entrant Type Research Articles

Effect of damage evolution on the auxetic behavior of 2D and 3D re-entrant type geometries

In this work, a mathematical formulation based on variational asymptotic method (VAM) has been proposed to determine the effect of damage on the auxetic properties of two-dimensional (2D) and three-dimensional (3D) re-entrant geometries. The influence of damage progression on the auxetic behavior was captured using a geometrically exact one-dimensional beam theory and an isotropic damage law, implemented in a nonlinear finite element framework. The effect of material degradation on the macroscale effective elastic properties such as the elastic modulus and Poisson’s ratio for the two-dimensional and three-dimensional re-entrant auxetic geometries was quantified. The mechanical behavior as predicted by the in-house Python-based implementation of the proposed VAM-based formulation is verified with the results from the commercial finite element solver Abaqus, wherein the user material subroutine was used to capture damage evolution. The numerical examples presented in this paper reveal that the macroscale auxetic behavior of the geometries was affected significantly by damage progression. The results of this research will provide insights into the design and analysis of auxetic materials for applications that warrant consideration of damage evolution.

Fundamental period equations for plan irregular moment-resisting frame buildings

The fundamental natural period of oscillation is a critical parameter in evaluating the design base shear of buildings. Worldwide seismic design codes typically employ height-based empirical formulas to estimate this period for various building categories, without distinguishing between regular and irregular buildings. This study proposes a formula specifically for reinforced concrete (RC) moment-resisting frame (MRF) buildings with dominant re-entrant corner type plan irregularity. A total of 190 re-entrant corner dominant building models with different shapes (C-, L-, T-, and PLUS-type), heights, and floor configurations were prepared, and eigenvalue analysis (EVA) was conducted. The fundamental natural period of oscillation for each model was evaluated and compared with the height-based formulas from seismic design codes and the period–height relationship proposed in existing literature. A nonlinear regression model, using a multi-variable power function, is proposed to estimate the fundamental natural period for these re-entrant corner dominant building models. This model considers the A/L ratio in both directions of the building, along with its height. Both unconstrained and constrained regression analyses were performed to derive a formula that best fits the fundamental natural period data. The study recommends that the unconstrained best-fit minus one standard deviation curve can conservatively define the fundamental natural period of oscillation for re-entrant corner dominant RC building models. The equation defining this curve has the potential to replace the existing seismic design code-based period-height formula.

Exploiting nonlinearities through geometric engineering to enhance the auxetic behaviour in re-entrant honeycomb metamaterials

Classical approaches to enhance auxeticity quite often involve exploring or designing newer architectures. In this work, simple geometrical features at the member level are engineered to exploit non-classical nonlinearities and improve the auxetic behaviour. The structural elements of the auxetic unit cell are here represented by thin strip-like beams, or thin-walled tubular beams. The resulting nonlinear stiffness enhances the auxeticity of the lattices, especially under large deformations. To quantify the influence of the proposed structural features on the resulting Poisson’s ratio, we use here variational asymptotic method (VAM) and geometrically exact beam theory. The numerical examples reveal that 2D re-entrant type micro-structures made of thin strips exhibit an improvement in terms of auxetic behaviour under compression. For the auxetic unit cell with thin circular tubes as members, Brazier’s effect associated with cross-sectional ovalisation improves the auxetic behaviour under tension; the enhancement is even more significant for the 3D re-entrant geometry. Thin strip-based auxetic unit cells were additively manufactured and tested under compression to verify the numerical observations. The experimentally measured values of the negative Poisson’s ratio are in close agreement with the numerical results, revealing a 66% increase due to the nonlinearity. Simulation results showcase these alternative approaches to improve the auxetic behaviour through simple geometric engineering of the lattice ribs.

Effect of Split and Re-Entrant Type Piston Bowl Geometry and Preheated Calophyllum Inophyllum Methyl Ester on the Conventional CI Engine Performance

Effect of Split and Re-Entrant Type Piston Bowl Geometry and Preheated Calophyllum Inophyllum Methyl Ester on the Conventional CI Engine Performance

Impact response analysis of stiffened sandwich functionally graded porous materials doubly-curved shell with re-entrant honeycomb auxetic core

Owing to unique deformation behavior and high capacity of energy absorption, auxetic structures have garnered significant research attention. To reveal the energy-absorbing properties of the auxetic structure, the impact response of stiffened sandwich functionally graded porous materials (FGPM) doubly-curved shell with re-entrant honeycomb auxetic core is studied by the established analytical model in the present work. The material properties in the thickness direction of FGPM face sheets are adjusted according to the volume fraction of constituents by power law and exponential law, while the core layer is made of the re-entrant honeycomb auxetic core with negative Poisson's ratio. On the basis of the Hertz theory for elastic impacts and the first-order shear deformation theory (FSDT), an analytical model is developed to study its impact phenomenon. Equations of motion are derived using Hamilton's principle, which are further solved analytically using Navier's technique of assuming unknown variables in the double trigonometric series. The time-dependent contact force is obtained by applying the spring-mass (SM) model consisting two-degrees-of freedom. Afterward, the transverse central displacements of the stiffened sandwich FGPM doubly-curved shell are calculated by adopting the Duhamel integration. The impact force and transverse displacements are compared with the previously published results, indicating that the theoretical results agree with the previously published results.Parametric analyses have been carried out to investigate the effect of variation of various parameters such as volume fraction exponents, radii of principal curvatures, porosity volume fraction, core layer inclined angle on the impact response of the sandwich shell. Additionally, the results show that compared with the traditional hexagonal honeycomb core type, the stiffened sandwich FGPM doubly-curved shell with re-entrant honeycomb core type has significant advantages in impact energy absorption. This work may provide an extensive reference and valuable guidance in the impact design and application of auxetic sandwich shell structures.

Co-optimization of operating parameters, fuel composition, and piston bowl geometry of gasoline compression ignition (GCI) engine at high loads

Focusing on the gasoline compression ignition (GCI) combustion mode, the operating parameters, fuel composition, and piston bowl geometry were collaboratively optimized at high loads to improve engine performance. A meliorative genetic algorithm coupled with a three-dimensional computational fluid dynamics (CFD) program was adopted as the optimization tool. The optimal GCI combustion strategy is summarized based on the optimization results, and the key parameters affecting engine performance at high loads are further analyzed. The results show that the employment of the open-type piston bowl, high-reactivity fuel, and late start of injection (SOI) is desirable for GCI engines at high loads. Under this strategy, fuel burns in multiple stages, which can reduce the heat release rate and advance the combustion phase. The width of the piston bowl is the geometric parameter with the most notable impact on GCI combustion. Due to the weaker turbulent kinetic energy and the smaller surface area, the larger piston bowl width is conducive to diminishing the heat transfer losses of the engine and promoting the oxidation of unburned hydrocarbon (HC) emissions. Relative to the optimal case, the strategy with the open-type piston bowl, high-reactivity fuel, and early SOI can reduce fuel consumption but results in a higher in-cylinder pressure rise rate and increased ringing intensity (RI). On the contrary, the re-entrant type piston bowl, low-reactivity fuel, and late SOI can significantly reduce the pressure rise rate and RI while deteriorating thermal efficiency.

Thermodynamic Performance of an Engine by Modifying Piston Bowl Geometries Fuelled by SME-100, LA-100, KB-100 Biodiesel Blends, and Diesel

Simulation of Direct injection (DI) compressed ignition (CI) engine working on diesel thermodynamic cycle on diesel-Rk software carried out for evaluating the effect on thermal performance. The analysis of an engine was worked out by applying different bowl geometrical shapes and by testing with different fuels. Further same compositions were tested on an experimental test rig having a set-up of (compressed ignition, single cylinder, four strokes, air-cooled, direct injection) diesel engine at constant crank speed. Hemispherical (HCC), Shallow depth (SCC), Re-entrant (RCC), Double wedge shallow, and Toroidal (TCC) piston geometries were created in solid-work and analyzed with B-100 blend of SME (Soybean Methyl Ester), KB (Karanja Biodiesel), LA (Roselle Biodiesel) and diesel further they were analyzed and their effects have investigated experimentally and numerically at fully loaded condition, with a constant crank speed of 1500 rpm and by setting constant compression ratio at 17.5. BSFCs were higher by 21.03%, 12.97%, and 12.96% for SME100, KB100, and LA100 with hemispherical, toroidal, and re-entrant type combustion chambers compared with the diesel fuel. Indicated thermal efficiencies and ignition delay periods were reported slightly lower for different blends and pure biodiesel than diesel at specific load conditions whereas combustion durations were reported higher compared to diesel.

Experimental investigation of 3D-printed auxetic core sandwich structures under quasi-static and dynamic compression and bending loads

Auxiliary metamaterials designed according to the Negative Poisson’s Ratio (NPR) property are exciting structures due to their high impact strength, impact energy absorption abilities, and different damage mechanisms. These good mechanical features are suitable for aviation, automotive, and protective construction applications. These structures, whose most significant disadvantages are production difficulties, have become easier to produce with the development of 3D production technology and have been the subject of many studies in recent years. In this presented study, two conventional core geometries and three different auxetic geometries, commonly used in sandwich structures, were designed and produced with 3D printer technology. The strength and energy absorption capabilities of prototype sandwich structures investigated experimentally under bending loads with static and dynamic compression. Except for the re-entrant (RE) type core, the auxetic core foam sandwich structures demonstrate higher rigidity and load-carrying capacity than classical sinusoidal corrugated (SC) core and honeycomb (HC) core sandwich structures under both quasi-static and impact-loaded compression and three-point bending experiments. Double arrowhead (DAH) and tetrachiral (TC) auxetic cores outperformed honeycomb core in terms of specific quasi-static and impact load-bearing performance under compression by 1.5 ± 0.25 times. In three-point bending experiments under both quasi-static and impact loading conditions, the load-carrying capacity of the double arrowhead and tetrachiral auxetic cores was found to be more than 1,86 ± 0.38 times that of the honeycomb core sandwich panels.

Intuitive diagnosis of complex atrial tachycardia mechanisms using a novel histogram module of an ultra-high-resolution mapping system.

The LUMIPOINT™ software module was developed to aid the physician in determining the mechanism of individual atrial tachycardias (ATs). The purpose of this study was to assess the clinical utility of the SKYLINE™ histogram that is a part of LUMIPOINT™. This study included consecutive patients with iatrogenic sustained AT who underwent catheter ablation using conventional mapping (RHYTHMIA™). SKYLINE™ patterns were analyzed offline and classified into two types: (1) focal type (type-F) exhibiting a low-amplitude (relative activating surface area < 10%) plateau period and (2) reentrant type (type-R) showing no plateau period. How well the two patterns distinguished between focal and macroreentrant ATs as determined by conventional mapping was evaluated. We studied 101 iatrogenic ATs in 91 patients (female: 24, mean age: 67.3 ± 9.1years). Activation mapping revealed 79 (78.2%) macroreentrant, 6 (5.9%) localized reentrant, and 16 (15.8%) focal ATs. Among the 72 type-R ATs, the mechanism was truly a macroreentry in 70 ATs. However, one focal AT and one localized reentrant AT displayed a type-R pattern (pseudo-reentry pattern). In the 29 type-F ATs, nine macroreentrant ATs were recognized (pseudo-focal pattern). Using SKYLINE™ type-R to differentiate macroreentrant AT from AT with centrifugal activation (focal or localized reentry), the sensitivity and specificity were 88.6% and 90.9%, respectively. Even when the SKYLINE™ type did not match the mapping-based AT mechanism, all discrepancies were electrophysiologically explicable using the SKYLINE™ histograms. SKYLINE™ histograms are a useful tool for the intuitive diagnosis of AT mechanisms.

Optimization study of diesel jet controlled compression ignition (JCCI) with dual-direct injection system and reentrant type combustion chamber

Optimization study of diesel jet controlled compression ignition (JCCI) with dual-direct injection system and reentrant type combustion chamber

Spindle vibration mitigation utilizing additively manufactured auxetic materials

This paper presents novel spindle holders fabricated by using auxetic materials for spindle vibration mitigation. Unlike traditional spindle vibration suppression methods using anti-vibration tool holders or software-based dampers, auxetic material-based spindle holders enhance energy absorption and vibration damping under cyclic loading, providing sufficient stiffness and compactness. The re-entrant hexagon type auxetic structures commonly used in auxetic design were fabricated by various additive manufacturing (AM) processes such as fused deposition modeling (FDM) using carbon fiber-reinforced polymer (CFRP), powder bed fusion process (PBF) using titanium (Ti). Static and dynamic behaviors of two auxetic materials (CFRP Auxetic, Ti Auxetic) were characterized by finite element analysis (FEA), and were experimentally identified by characterizing stiffness, damping, frequency response function, vibration power transmissibility, vibration spectrum and power spectral density, and those results were compared with those of the control group to quantitatively characterize how auxetic materials impact on spindle vibration mitigation and improve spindle operations. As a result, the auxetic material-based spindle holders have high damping characteristics and showed a decrease in the spindle vibration magnitude compared to the control group. Also, it was confirmed that the auxetic material-based spindle holder can effectively suppress the spindle vibration when the spindle is idling or machining, as an alternative vibration damper. The development of the AM processes toward high part accuracy will enable further development of auxetic structures for spindle vibration mitigation.

Computational study of effect of Ceramic coatings and piston bowl depth on heat fluxes of Re-entrant type piston

The current research article investigates the variation of heat flux with geometric modification on the re-entrant type piston bowl by varying bowl depth by computational domain. The contribution of ceramic coating on heat flux is also investigated in this research report. Computational study was carried out by using ANSYS 19.2 software in order to obtain the augmented results. The variation of piston bowl depth of Re-entrant type piston is accomplished as there is a novel need to study the variation in heat flux of piston at different bowl depths. The impact of the thickness of the ceramic coating is also evaluated. The focus of this article is to study the effects of combustion on the piston of a compression ignition engine. It was noticed that with the decrease of bowl depth and addition of ceramic coating there is a decrease in heat flux. Around 27.75% depreciation in the heat flux was noticed for the uncoated piston with a bowl depth of 15mm in comparison with 27 mm bowl depth and a 25% decrement with the addition of a ceramic coating of 0.4 mm and also a 55% decrement in the heat flux was observed with 1mm coating to the piston with 15 mm bowl depth in reference to 27 mm bowl depth of respective coating thickness. Disparity of maximum heat flux and heat losses with increasing bowl depth is also analyzed in the inquiry.

Computational optimization of the piston bowl geometry for the different combustion regimes of the dual-mode dual-fuel (DMDF) concept through an improved genetic algorithm

Focusing on the dual-mode dual-fuel (DMDF) combustion concept, a combined optimization of the piston bowl geometry with the fuel injection strategy was conducted at various loads. An improved genetic algorithm was introduced in this study, which is superior in searching for the global optimal solutions. The optimal piston bowl shape coupled with the corresponding injection strategy was summarized at the various loads. The results show that the piston bowl geometry optimization can further improve the thermal efficiency with 1.4%, 4.4%, and 1.4% percentage points for the low, mid, and high loads, respectively. An indicated thermal efficiency up to 51.8% can be realized at mid load. Meanwhile, for all the optimal cases, NOx and soot emissions can meet the Euro VI limits.At low and mid loads, both the open and re-entrant type piston bowl can be equipped, while the high load only prefers the open type piston bowl for the DMDF mode. The re-entrant type or deep piston bowls are superior in organizing strong in-cylinder flow, which is beneficial for the fuel/air mixing. The open type or shallow piston bowls are helpful for reducing the heat transfer losses owing to the less heat transfer surface area. Furthermore, a correlation analysis was conducted to investigate the sensitivity of engine performance to the piston geometric parameters and injection parameters. It is concluded that the fuel injection event becomes more important for managing the engine performance as load increases. Among the injection parameters, the influence of the fuel injection timings and injection pressure on engine performance is more obvious. The piston geometric parameters play more significant roles in the heat transfer losses than the injection parameters for all loads. Among the geometric parameters, the most influential parameters are the width and open extent of the piston bowl. The heat transfer loss energy fraction can be well decreased with a wider and more open piston bowl.

Auxetic structures fabricated by material extrusion: an experimental investigation of gradient parameters

Purpose This paper aims to focus on studying the influence of gradient parameters, namely, thickness coefficient, length coefficient and height ratio of auxetic structure on responses such as strength, stiffness and specific energy absorption (SEA) under compressive loading. Optimization of significant parameters is also performed to maximize responses. Further, efforts have also been made to develop regression models for strength, stiffness and SEA of auxetic structure. Design/methodology/approach Central composite design of response surface methodology is used for planning experiments. Auxetic structures of acrylonitrile butadiene styrene (ABS) and poly-lactic acid (PLA) materials are fabricated by the material extrusion (ME) technique of additive manufacturing. Fabricated structures are tested under in-plane uniaxial compressive loading. Grey relational analysis is used for the optimization of gradient parameters of the unit cell of auxetic structure to maximize responses and minimize weight and time of fabrication. Findings From the analysis of variance of experimental data, it is found that the compressive strength of auxetic structures increases with a decrease in length coefficient and height ratio. In the case of ABS structures, stiffness increases with a decrease in thickness coefficient and length coefficient, while in the case of PLA structures, stiffness increases with a decrease in length coefficient and height ratio. SEA is influenced by length coefficient and thickness coefficient in ABS and PLA structures, respectively. Based on the analysis, statistical non-linear quadratic models are developed to predict strength, stiffness and SEA. Optimal configuration of auxetic structure is determined to maximize strength, stiffness, SEA and minimize weight and time of fabrication. Research limitations/implications The present study is limited to re-entrant type of auxetic structures made of ABS and PLA materials only under compressive loading. Also, results from the current study are valid within a selected range of gradient parameters. The findings of the present study are useful in the optimal selection of gradient parameters for the fabrication of auxetic structures of maximum strength, stiffness and SEA with minimum weight and time of fabrication. These outcomes have wide applications in domains such as automotive, aerospace, sports and marine sectors. Originality/value Limited literature is available on studying the influence of gradient parameters of ME manufactured auxetic structure of ABS and PLA materials on responses, namely, strength, stiffness and SEA under compressive loading. Also, no work has been reported on studying the influence of gradient parameters on mechanical properties, weight and time of fabrication of auxetic structures. The present study is an attempt to fulfil the above research gaps.

Effects of materials and microstructures on pool boiling of saturated water from metallic surfaces

Pool boiling experiments using horizontal, flat, and upwards facing aluminum, stainless steel, and copper, heating surfaces are conducted in distilled water. The wettability, measured by the static contact angle (CA), and the critical heat flux (CHF) are found to vary significantly among the three surfaces. The Boehmite treated aluminum, stainless steel, and copper surfaces have a CHF of 1850, 1375, and 1015 kW/m2, respectively. Powder Injection Molding (PIM) and High-Temperature Conductive Microporous Coating (Cu-HTCMC) are also applied on the copper heating surface to create various microstructures, and their pool boiling performances are compared to that of a plain copper surface. The PIM and Cu-HTCMC reduce the contact angle and increase the CHF value. However, the Cu-HTCMC causes an increase in CHF well beyond the expected value, and it is believed to be due to the porous coating structures and reentrant type cavities within the microporous coating.

Numerical and experimental investigation of FDM fabricated re-entrant auxetic structures of ABS and PLA materials under compressive loading

Purpose Auxetic structures are one type of mechanical meta-materials mainly used for energy absorption applications because of their unique negative Poisson’s ratio. This study is focused on numerical and experimental investigations of fused deposition modeling (FDM) fabricated re-entrant auxetic structures of acrylonitrile butadiene styrene (ABS) and poly-lactic acid (PLA) materials under compressive loading. Influence of geometric parameters, namely, re-entrant angle, height and arm-length on strength, stiffness and specific energy absorption (SEA) of auxetic structures under compressive loading. Optimization of significant parameters is also performed to maximize these responses and minimize weight and time of fabrication. Further, efforts have also been made to develop predictive models for strength, stiffness and SEA of auxetic structures. Design/methodology/approach A full factorial design of experiment is used for planning experiments. Auxetic structures of ABS and PLA are fabricated by FDM technique of additive manufacturing within the constrained range of geometric parameters. Analysis of variance is performed to identify the influence of geometric parameters on responses. To optimize the geometric parameters Gray relational analysis is used. Deformation of auxetic structures is studied under compressive loading. A numerical investigation is also performed by building nonlinear finite element models of auxetic structures. Findings From the analysis of results, it is found that re-entrant angle, height and arm-length with their interactions are significant parameters influencing responses, namely, strength, stiffness and SEA of the auxetic structures of ABS and PLA materials. Based on the analysis, statistical nonlinear quadratic models are developed to predict these responses. Optimal configurations of auxetic structure of ABS and PLA are determined to maximize strength, stiffness, SEA and minimize weight and time of fabrication. From the study of deformation of auxetic structures, it is found that ABS structures have higher energy absorption, whereas PLA structures have better stiffness. Results of finite element analysis (FEA) are found in good agreement with experimental results. Research limitations/implications The present study is limited to re-entrant type of auxetic structures of ABS and PLA materials only under compressive loading. Also, results from the present study are valid within the selected range of geometric parameters. The findings of the present study are useful in maximizing strength, stiffness and SEA of auxetic structures that have wide applications in the automotive, aerospace, sports and marine sector. Originality/value No literature is available on studying the influence of geometric parameters, namely, re-entrant angle, height and arm-length of auxetic structure on strength, stiffness and SEA under compressive loading. Also, a comparative study of feedstock materials, namely, ABS and PLA, is also not reported. The present work attempts to fulfill the above research gaps.

INTERRELATION OF SERUM ALBUMIN CONFORMATIONAL AND PHASE STATES IN SALT SOLUTIONS AS STUDIED BY EPR SPIN LABELING

The use of serum albumins (SA) in model systems in the study of the biological activity of chemical compounds and nanomaterials, as well as the physicochemical properties, in particular, phase properties of biological fluids, including the nucleoplasm and cytoplasm of living cells, requires a deeper understanding of the relationship of conformational (structural-dynamic) states of protein molecules with phase states of protein dispersions in a wide range of temperatures and compositions. The joint plotting and analysis of the protein stability curve and phase diagrams of protein solutions commonly used in the study of this relationship are significantly complicated by this protein’s elevated tendency to aggregate. In this paper, an experimental-theoretical approach, based on the application of the electron spin resonance (ESR) of spin labels (maleimido-TEMPO and dichlortriasine-TEMPO spin labels) covalently bound to the protein and sensitive to changes in both the structural-dynamic state of protein molecules and the phase state of protein dispersions, is proposed for studying this relationship. Data on the mobility characteristics of the spin labels (correlation times, state functions, equilibrium constants), indicating the state of intra- and intermolecular interactions of SA molecules, are presented. Transitions in temperature dependences of these characteristics on the temperature and concentration of NaCl, CaCl2, (NH4)2SO4, sucrose, polyethylene glycol, and heavy water have been shown to reflect the interconversions of protein conformers and their aggregates as well as liquid-liquid phase transitions, including those of a reentrant type. Based on the results, a phase diagram of the SA dispersion describing liquid-liquid phase transitions in the temperature range of cold and thermal denaturation and taking into account the role of native protein conformers, their aggregates and transitions between them in the physiological interval has been proposed.

Experimental and CFD analysis of Re-entrant Combustion Chamber on Diesel Enriched with Hydrogen

In view of global warming and diminution of sources for traditional fuels, investigators paid their attention towards finding the substitutes in all sectors such as agriculture, transportation and industries. One of the best alternative and unique option for overcoming these limitations is usage of hydrogen gas as fuel for petroleum-based engines. Further to have better quality of fuel and air mixture formation, a significant part is played by the geometry of the combustion chamber. To have quality burning of the fuel, an effort is targeted to investigate the impact of re-entrant chambers over the conventional type without and with hydrogen enrichment at distinct flows of diesel. Initially, experiments were conducted on toroidal chamber geometry of the piston bowl with diesel and with hydrogen enrichment. With a reduction of 30.65%, 44.11% and 18.78% in emission particulates of UHC, CO and smoke density correspondingly with addition of hydrogen as that of with diesel at peak load, further there is growth in NOx emissions about 10.16%. The variations of emission particulates with replacement of modified geometry, i.e. re-entrant type are detected as further reduced. To validate the reduction in emission trends, CFD simulations are carried out on fuel mass fraction and the findings presented.

Designing Re-Entrant Geometry: Construction of a Superamphiphobic Surface with Large-Sized Particles.

Re-entrant geometries can effectively trap air pockets beneath coating surfaces, prevent the penetration of low surface tension organic liquids, and achieve superamphiphobic performance. However, the creation of re-entrant geometries through particle-based spray coating remains a challenge. In the past decade, various studies have focused on the preparation of superamphiphobic coatings using ultrafine nanoparticles (10-15 nm) using conventional spray-coating methods. In this work, we aim to fabricate a spray-coated superamphiphobic surface using large particles with a hierarchical structure. The study systematically investigated the wetting behaviors of liquids with different topographies obtained using large particles (i.e., smooth, micro, nano, and micro/nanostructures) by different coating methods. The findings suggested that compared with the typical colloid template method, the surface obtained using the spray-coating method showed much greater roughness, which greatly enhanced the oleophobicity of the coating. Furthermore, only hierarchically monodisperse hollow SiO2 spheres (MDH-SiO2) showed excellent superamphiphobicity, which was independent of the hollow sphere size. While maintaining the coating roughness, by applying solid C@SiO2 as a reference sample, the important role of the hollow structure of MDH-SiO2 at the solid-liquid-air interface was confirmed. Nanosphere-surrounded hollow structures were shown to serve as a re-entrant type structure, preventing the imbibition of the liquid, finally leading to a stable Cassie state. This design strategy may provide useful guidelines for the fabrication of large particle-based spray-coated superamphiphobic surfaces.

Compression Properties of 3d Printed Honeycomb and Re-Entrant Sandwich Core Materials

In the presented paper, honeycomb (cellular) and re-entrant (auxetic) structures were produced with different thermoplastic filaments on FDM type 3D printer and their compression properties were tested. Samples were prepared from PP, ABS, PLA and PA thermoplastic polymers. The samples were subjected to quasi-static compression in edgewise and flatwise direction and their stress-strain relationships were established. For a proper strain evaluation, digital-image correlation was applied to measure full-field displacements on the sample surfaces and their and their compressive-deformation behaviour in both elastic and plastic regime up to the densification were evaluated. It was shown through compression tests in flatwise and edgewise directions re-entrant type of auxetic cores components exhibit higher compression failure stresses compared to those of cellular honeycomb core components. The stress strain curves of the re-entrant core failure show a higher energy absorbance of the honeycomb cores for the same polymer types