Void Surface Research Articles

Image processing and artificial neural network based determination of surface mean texture depth on lab-controlled chip seal pavement samples

Because surface texture is nearly the sole indicator of pavement functional properties and highly correlated with critical operational characteristics of roadways like traffic noise and safety, the change in pavement surface texture because of traffic loadings and environment has to be evaluated routinely. There are numerous direct or indirect evaluation techniques in the market. However, most of these methods have some limitations like requiring lane closure or being expensive. In this study, a 2D image processing method was established to estimate the surface mean texture depth (MTD) of chip sealed pavements. We produced chip sealed pavement samples in the laboratory with different aggregate type, shape, and size ranging between 2 and 19 mm to cover wide range of live conditions. Two well-known conventional test methods, Sand Patch (SP) and Hydrotimer (HT), were used to determine MTDs of chip seal samples. Subsequently numerous photos were taken on surface of the samples with a camera for 2-D image processing that was done based on surface void ratio (SVR) approach. With the image processing, SVR of all samples were determined. At the point of whether there is a relationship or not, correlation analysis was made between the MTDs obtained with SP and HT and the data obtained by SVR approach with the artificial neural network method. The results show that the proposed SVR approach construed on 2D image processing method can be a reliable alternative to evaluate the surface texture of pavements.

Investigations on the rheological properties of cement mortar based on fine aggregate characteristic and its extended prediction model

The rheological property of mortar is significantly influenced by its contained fine aggregate morphology characteristic and capable predictive models are limited. This work aims to expand the film thickness theory by developing an index that integrally represents variations in grain shape, gradation, and mix proportions, and elucidates the impact and the mechanism of these multifactorial differences on rheological performance. The quantitative analysis of the aggregate gradation and particle shape differences were performed, which was used to assess the impact of these variations and different mix ratios on the rheological performance of mortars. A correlation between aggregate differences and film thickness was established using specific surface area and void ratio. The result shows that variations in aggregates are accurately assessed by image analysis and consistently reflected in specific surface area and void ratio metrics. Since variations in rheological performance are predominantly governed by differences in film thickness, the disparities among aggregates can be quantified in terms of their impact on rheological properties by considering specific surface area and void ratio, thus translating into variations of film thickness. The differences in rheological properties due to variations in grain shape, gradation, and mix proportions can be comprehensively represented and controlled through an expansion of the film thickness model.

Impact of Formwork Materials on Concrete Surface Quality

Given the functional and aesthetic quality expected from concrete surfaces, this study investigated the influence of different formwork materials on their surface density, porosity, voids, and elementary chemical composition by relying on X-ray Microtomography (μCT), Scanning Electronic Microscopy (SEM), and Energy Dispersive X-ray Spectroscopy (EDS). The formwork materials assessed were galvanized steel, regular plywood (pink), marine plywood, polyvinyl chloride (PVC), and silicone. μCT showed that distinct formwork affected the surface density of the concrete. In this case, specimens cast within silicone and marine plywood had similar pore volumes although different pore sizes, whereas PVC led to the highest pore volume with small pore sizes. Galvanized steel and regular plywood resulted in similar porosity. SEM showed that the concrete surfaces produced with marine plywood formwork had the highest void content. EDS identified surface products resulting from the contact of concrete with the different formwork materials, suggesting the potential migration of chemical elements. This research significantly contributes to optimizing formwork material selection and enhancing concrete quality and durability. Moreover, it establishes a foundation for further investigations into how formwork materials affect concrete surfaces and the pathological manifestations potentially arising from the molding process.

Cavitation damage in rubber-like silicone adhesives

In this work, the failure of rubber-like materials by cavitation is investigated. Under local triaxial loading states, as they can occur in confined geometries of adhesive bonds, the instantaneous formation of voids can be observed. Analytical results of cavitation in a commercial silicone adhesive are provided. The results show that cavitation voids can be distinguished from manufacturing voids by the inner surface of the void. The surface of the cavitation void is rugged and shows a complex fracture pattern. Pancake experiments have been conducted for different ratios of radius and thickness. To assess the fracture process of cavitation onset one macroscopic and two asymptotic solutions of the energy release rate of cavitation voids are proposed. The solutions are compared and their limitations for the analysis of cavitation onset are discussed.

Low cost modelling tools for the design of additively manufactured acoustic materials

Additive manufacturing (AM) methods have unlocked new capabilities in the design of acoustic materials and their topologies. This has enabled the design of devices with breakthrough performance in sound absorption and insulation while achieving subwavelength characteristics. However, material fabrication through AM presents its own challenges. These challenges include inherent defects which can be specific to the printing method employed. Examples of defects in low-cost AM include void formation, surface roughness and poor bonding between layers. Each of these features of AM have different acoustic impacts which may degrade the performance of a design. To optimize the production of additively manufactured acoustic materials it is imperative that designers can exploit features, such as surface roughness, to enhance rather than degrade the overall material performance. The aim of this paper is to investigate the effects of surface roughness in extrusion-based AM on acoustic material performance. A novel, low-cost numerical methodology is used to capture the influence of surface roughness in a subwavelength acoustic absorber. With this approach the impact of roughness can be captured in the design process. The intention is to develop efficient low-cost design methodologies that can be exploited for industrial development of novel additively manufactured acoustic materials.

Compact multilayer selective absorbers based on amorphous carbon for solar-thermal conversion

In addressing the energy crisis and climate change, environmentally sustainable materials and structures with heightened absorption and enhanced photothermal conversion efficiency are urgently demanded. In this study, a series of ultrabroadband, omnidirectional, and near-perfect solar radiation absorbers based on amorphous carbon (a-C) were fabricated by magnetron sputtering. These absorbers, featuring 4, 6, and 8-layer compact multilayer thin film structures, exhibited measured absorption of 96.8 %, 96.5 %, and 96.6 % in the range of 300–2500 nm, respectively. The high absorption efficiency delves into the synergistic effects of intrinsic absorption of a-C and enhanced absorption through thin film interference. Through microstructure analysis, the reduced absorption compared to design originates from the optical thickness mismatch caused by the unstable growth rate of a-C. In addition, the absorbers show very slight variations in absorption within 40° and maintain a high absorption of more than 80 % in the incident angle of 60°. For samples with different air annealing temperatures from 100 to 250 °C, the microstructure, morphology, and optical properties were systematically investigated. The appearance of oxygen channels due to surface defects or voids leads to the oxidation reaction of the diffused Ti atoms at high temperature. Notably, the proposed absorber can be fabricated by a lithography-free method, paving a way for large-area application of a-C.

A generalized machine learning framework to estimate fatigue life across materials with minimal data

In this research, a generalized machine learning (ML) framework is proposed to estimate the fatigue life of epoxy polymers and additively manufactured AlSi10Mg alloy materials, leveraging their failure surface void characteristics. An extreme gradient boosting algorithm-based ML framework encompassing Synthetic Minority Over-sampling TEchnique (SMOTE), categorical data encoding, and external loop cross-validation is developed to evaluate the fatigue life across materials. The influence of different training strategies based on materials, input features, encoding method, and data standardization on the model performance is explored. Additionally, the importance of anti-data-leakage and anti-overfitting measures over the ML model performance is addressed. The result shows that the data-leakage-free, external loop cross-validated model can estimate the fatigue life of selective epoxy polymers and metal alloys with an average R2 of 0.71 ± 0.06 using a mere 12 to 27 experimental data points per material category. Whereas the model trained with data-leakage and overfitting results in high R2 of 0.9.

Electrochemical Performance of Coal-Based Needle Coke Anode for Lithium Ion Batteries

Lithium-ion capacitors (LICs) with the capability of high energy and high power are considered to be attractive for advanced energy storage applications. However, the design and fabrication of suitable electrode materials with desirab-le properties by a facile approach using cost-effective precursors are still a great challenge. In this work, we have utilized needle cokes, an commercial carbon material with high carbon content and soft carbon structure, as a single carbon source for anode material. A lithium-ion battery fabricated using four kinds of needle cokes exhibits a maximum high energy density of 1357mAhg-1. Systematic characterization analysis demonstrates that unique characteristics of the green coke including large interlayer spacing, turbostratic and disordered microstructures that are composed of surface defects, nanopores or voids, and graphitic domains. That contribute synergistically to the outstanding performance of the needle coke-based LIC. More importantly, anode materials from a single source is an effective way for high value-added utilization of needle coke at the commercial level.

Effects of surface voids on free convection via concentrated double-pipe

Effects of surface voids on free convection via concentrated double-pipe

Using fractal voids to understand Mode I compressive fracture in brittle materials – A two-dimensional analysis

Unlike cases of direct or indirect tensile loading, analysis of Mode I fracture in cases of compressive loading must necessarily consider two-dimensional flaw geometries. The consequent analytical complications have resulted in little theoretical evolution towards understanding Mode I fracture in compressive loading. Researchers have recently observed that the linear elastic (LE) stress fields surrounding two-dimensional flaws in compression appear to have indicative value regarding Mode I fracture, but no rational framework has yet been proposed for their interpretation. Herein it is demonstrated that by idealizing void surfaces as fractal, and using what will be called the “small flaw assumption,” LE stress fields can be interpreted to obtain significant insight regarding brittle Mode I compressive fracture. Using fractal voids, a rational and consistent explanation for the satisfaction of the stress and energy criteria at the surface of two-dimensional flaws is presented. The discussion resolves many typical theoretical issues in the literature in a manner consistent with fundamental Griffith theory, and accounts for size and shape effects. The framework further enables the computationally efficient prediction of peak KI values associated with the propagation of line cracks from two-dimensional flaws from a brittle medium subject to macroscopic uniaxial compression via LE stress fields.

Plasma-enhanced atomic layer deposition of silicon nitride thin films with different substrate biasing using Diiodosilane precursor

In this work, we report on Plasma-Enhanced Atomic Layer Deposition (PE-ALD) of SiNx films using Diiodosilane (DIS) precursor and N2-H2 plasma. Systematic studies as a function of DIS dosing time, plasma duration, plasma composition and deposition temperature are investigated. The material properties have been studied using X-ray photoelectron spectroscopy (XPS), X-Ray Reflectometry (XRR), Atomic Force Microscopy (AFM) and High-Resolution Transmission Electron Microscopy (HR-TEM). The optimal deposition parameters for achieving high-quality SiNx with a high growth per cycle (GPC) are first determined. We show that DIS offers a wide temperature window for SiNx deposition starting from 110 °C up to 300 °C, paving the way for a large choice of SiN-based applications. The impact of substrate biasing on SiNx film deposition and properties is also investigated. We show that high ion energies during the nitridation step can cause surface damage and void formation, thus affecting the SiNx quality. Overall, these results highlight the importance of this novel precursor for growing SiNx using PE-ALD and the possible swapping of the material properties by fine control of the substrate biasing, which can help to go far beyond the existing SiNx limitations.

Inception of vented water trees in high voltage XLPE cable insulation: Effect of inorganic contaminations inside the semiconductive material

AbstractWet‐design AC subsea power cables are currently rated up to a maximum voltage of 72.5 kV. These high voltage (HV) cables are cost‐effective alternatives to subsea cables kept dry by a protective lead sheath and exhibit superior properties for dynamic applications. However, several vented water trees, degradation phenomena reducing the cable lifetime, are observed in a HV XLPE insulated cable subjected to wet aging in the laboratory. The water trees initiate from a smooth and clean XLPE insulation/semiconductive screen interface. In this paper, we show that voids in the range 15–150 μm are observed in the conductor screen, 50–320 μm from the water tree inception sites. Degradation of the semiconductive material is observed, in the form of porous regions that connect the voids to the water tree inception sites. NaCl impurities are detected on the void surfaces and in the porous regions. These features are proposed to be the pre‐requisites for the formation of the vented water trees observed in this type of cable. The mechanism responsible for the formation of the void and porous regions in the semiconductive cable screen is discussed based on the observations.

Electrochemical-Mechanical Coupling Experiments on Solid-State Battery Materials and Interfaces

The interaction of mechanical and electrochemical effects in the areas of thermodynamics, kinetics, and transport are known, but accurately measuring those couplings can be complicated by the difficulty of getting a uniform stress at a solid-solid interface where surface roughness, voids and inclusion result in inhomogeneous contacts.1 This is a particular challenge for solid-state batteries where both the active material and electrolyte are in the solid phase. In addition, cycling of metal anodes (e.g., Na and Li) results in processes such as dendrite and void formation in which electrochemical and mechanical can be amplified.2 This talk will focus on two improvements to typical experiments in which electrochemical-mechanical coupling strongly influences results: (1) The use of a solid-state reference electrode for solid Na / solid electrolyte interfacial studies, and (2) the use of a nanoindentation platform to assess electrochemical-mechanical coupling behaviors in thin-film solid-state materials.For topic (1), we will discuss our use of a solid Na metal reference electrode to inform the cycling of Na metal against a Na-β″-Al2O3 solid electrolyte using cycling protocols of commercial relevance (e.g., 5 mAh/cm2, <5 MPa external pressure).2 Our work identifies the current density at which stripping shifts from stable to unstable, and shows that large (100s of mV) of interfacial overpotential can persist for hours in some stripping test protocols, which, according to models indicates that >80% of the initial electrochemical active interfacial area has been lost. We will also present recent results on how the applied pressure affects the interfacial behavior of Na metal / Na-β″-Al2O3 interfaces, as well as the role of applied pressure and the cycling protocol for an interface that starts as only current collector / Na-β″-Al2O3.For topic (2), we will present on our electrochemical-mechanical coupling studies of thin-film (i.e., <1 um thick) V2O5 samples on an Ohara Li+-conducting glass ceramic disc. This platform allows us to simultaneously control electrochemical behavior (e.g., Li insertion and removal, current) and the applied force, to study thermodynamic and kinetic electrochemical-mechanical couplings. This platform enables the application of a uniform stress on the thin-film V2O5 sample.1. Joule 7, 652–674, April 19, 2023.2. ACS Appl. Mater. Interfaces 2023, 15, 42, 49213–49222

Highly Fluorinated Nanospace in Porous Organic Salts with High Water Stability/Capability and Proton Conductivity.

Water in hydrophobic nanospaces shows specific dynamic properties different from bulk water. The investigation of these properties is important in various research fields, including materials science, chemistry, and biology. The elucidation of the correlation between properties of water and hydrophobic nanospaces requires nanospaces covered only with simple hydrophobic group (e.g., fluorine) without impurities such as metals. This work successfully fabricated all-organic diamondoid porous organic salts (d-POSs) with highly fluorinated nanospaces, wherein hydrophobic fluorine atoms are densely exposed on the void surfaces, by combining fluorine substituted triphenylmethylamine (TPMA) derivatives with tetrahedral tetrasulfonic acid. This d-POSs with a highly fluorinated nanospace significantly improved their water stability, retaining their crystal structure even when immersed in water over one week. Moreover, this highly hydrophobic and fluorinated nanospace adsorbs 160 mL(STP)/g of water vapor at Pe/P0=0.90; this is the first hydrophobic nanospace, which water molecules can enter, in an all-organic porous material. Furthermore, this highly fluorinated nanospace exhibits very high proton conductivity (1.34×10-2 S/cm) at 90 °C and 95 % RH. POSs with tailorable nanospaces may significantly advance the elucidation of the properties of specific "water" in pure hydrophobic environments.

Highly Fluorinated Nanospace in Porous Organic Salts with High Water Stability/Capability and Proton Conductivity

AbstractWater in hydrophobic nanospaces shows specific dynamic properties different from bulk water. The investigation of these properties is important in various research fields, including materials science, chemistry, and biology. The elucidation of the correlation between properties of water and hydrophobic nanospaces requires nanospaces covered only with simple hydrophobic group (e.g., fluorine) without impurities such as metals. This work successfully fabricated all‐organic diamondoid porous organic salts (d‐POSs) with highly fluorinated nanospaces, wherein hydrophobic fluorine atoms are densely exposed on the void surfaces, by combining fluorine substituted triphenylmethylamine (TPMA) derivatives with tetrahedral tetrasulfonic acid. This d‐POSs with a highly fluorinated nanospace significantly improved their water stability, retaining their crystal structure even when immersed in water over one week. Moreover, this highly hydrophobic and fluorinated nanospace adsorbs 160 mL(STP)/g of water vapor at Pe/P0=0.90; this is the first hydrophobic nanospace, which water molecules can enter, in an all‐organic porous material. Furthermore, this highly fluorinated nanospace exhibits very high proton conductivity (1.34×10−2 S/cm) at 90 °C and 95 % RH. POSs with tailorable nanospaces may significantly advance the elucidation of the properties of specific “water” in pure hydrophobic environments.

Influence of calcination temperature on the 3D nanoscale topography of LaMnO3 thin films: A comprehensive surface analysis

In this paper, we present a comprehensive study on the 3D nanoscale topography of LaMnO3 thin films, focusing on the influence of calcination temperature on surface morphology. The study reveals significant structural, chemical, and morphological changes as a function of the calcination temperature. XRD analysis confirmed the formation of the orthorhombic LaMnO3 structure at 700 °C, 750 °C, and 800 °C, with increasing unit cell volume and crystallite size observed at higher temperatures. FTIR spectra identified characteristic functional groups associated with molecular vibrations, indicating the perovskite structure. SEM imaging showed grain growth with temperature, while EDS analysis confirmed compound formation and substrate interactions. AFM analysis revealed increased surface roughness with temperature, attributed to nucleation and crystal growth. Morphological and microtextural analyses further detailed changes in surface features, peaks, valleys, and voids. Fractal characterization highlighted variations in surface texture with temperature, with a decrease in dominant wavelength indicating changes in microtexture complexity. Overall, the findings provide insights into the temperature-dependent properties of LaMnO3 thin films, essential for optimizing growth conditions and understanding their potential applications in various fields.

Enhancing lead-free photovoltaic performance: Minimizing buried surface voids in tin perovskite films through weakly polar solvent pre-treatment strategy

Buried interfacial voids have always been a notorious phenomenon observed in the fabrication of lead perovskite films. The existence of interfacial voids at the buried interface will capture the carrier, suppress carrier transport efficiencies, and affect the stability of photovoltaic devices. However, the impact of these buried interfacial voids on tin perovskites, a promising avenue for advancing lead-free photovoltaics, has been largely overlooked. Here, we utilize an innovative weakly polar solvent pre-treatment strategy (WPSPS) to mitigate buried interfacial voids of tin perovskites. Our investigation reveals the presence of numerous voids in tin perovskites during annealing, attributed to trapped dimethyl sulfoxide (DMSO) used in film formation. The WPSPS method facilitates accelerated DMSO evaporation, effectively reducing residual DMSO. Interestingly, the WPSPS shifts the energy level of PEDOT:PSS downward, making it more aligned with the perovskite. This alignment enhances the efficiency of charge carrier transport. As the result, tin perovskite film quality is significantly improved, achieving a maximum power conversion efficiency approaching 12% with only an 8.3% efficiency loss after 1700 h of stability tests, which compares well with the state-of-the-art stability of tin-based perovskite solar cells.

Topological constraints-induced radiation shielding efficiency of SiO2 α-cristobalite polymorphism: Signatures from Hirshfeld pseudo-surfaces

The paper presents a synergetic and comprehensive investigation into γ-radiation shields properties on SiO2 α-cristobalite subject varying external pressures (0<p < 9.1 GPa). Utilizing crystallographic methods involving γ-rays and Hirshfeld pseudo-surface (HPSs) analyses, we explore the structural responses of SiO2 α-cristobalite to external pressure and its consequent impact on MAC and LAC. The study encompasses a broad energy range (0.015<E < 15.0 MeV), employing online tool for analysis. Our findings reveal that the fundamental shielding characteristics of SiO2 α-cristobalite, including (5.809<MAC<0.021 cm2/g), (3.10 × 1023<Neff< 3.74 × 1023 e/g), (10.32<Zeff<12.43), and (10.79<Zeq<11.56), remain reliable across different polymorphic forms within the energy domain and varying pressures. The LAC values exhibit a clear dependency on both incident photon energies where it's LAC ∈ [0.042 to 11.776] cm−1 as pressure elevated on the crystal. This relationship underscores the influence of pressure-induced changes in crystal density on LAC values. Additionally, changes in lattice parameters (4.975<a<4.599 Å) and bond lengths under pressure contribute to this observed variation in the LAC values. Further analysis of the topological constraints (TCs) (i.e., 1.603<Si⋯O < 1.610 Å, 111.42°<O⋯Si⋯O < 112.00°, and 146.49°<Si⋯O⋯Si < 127.80° bending and twisting angles respectively) reveals defined correlations with LAC values.HPS topological analyses were also employed shed light on valuable insights into the mutual forces of interaction between atoms in the crystal unit cell. Changes in external stress lead to transformations in the HPSs, reflecting the impact of pressure on topological constraints. The evolution of HPS volume (i.e., 179.59-35.24 Å3) and area (i.e., 205.73-161.51 Å2) as well as void's volume (i.e., 10.20-0.17 Å3) and surface area (i.e., 46.10-3.12 Å2) within the crystal lattice is also observed, indicating a direct relationship between HPSs, crystal compactness, electron density and radiation effectiveness. These signatures have been correlated with TCs and thus on the γ-rays shield effectiveness.

Cryogenic incipient plasticity in bicrystalline copper with a spherical void and sigma 5 STGB by molecular dynamics simulation

Grain Boundaries and voids are common defects in nanocrystalline metals, playing pivotal roles in plastic deformation. This study conducted molecular dynamics simulation to explore the incipient plasticity of Σ5 STGB bicrystalline Cu with a spherical void, alongside its constituent monocrystals at 10 K. The results reveal homogeneous nucleation of an elliptical 1/6<112> Shockley partial dislocation loop in the monocrystals. In the void-free Σ5 STGB bicrystal, initial dislocation nucleates homogeneously in grain interior rather than from the Σ5 STGB, forming a Shockley partial dislocation loop. In the monocrystals with a large spherical void, four initial dislocations nucleate from void surface on four slip systems. In the Σ5 STGB bicrystals with a spherical void, when the void diameter is 0.5 nm, the initial dislocation is an arc-shaped Shockley partial dislocation nucleated from the Σ5 STGB. For void diameters larger than 0.5 nm, initial dislocations nucleate from void surface. Through this study, the conditions for the nucleation, number, and morphology of initial dislocations are further understood, facilitating the evaluation of subsequent plastic deformation. This research contributes theoretical underpinnings for improving the mechanical properties and designing high-performance nanocrystalline metals.

Embrittlement of notched duplex stainless steel: Role of hydrogen-assisted void growth and cleavage

The micro-degradation processes related to the ductile-brittle transition are crucial for revealing hydrogen embrittlement mechanisms. This study investigates the evolution and transition of hydrogen-assisted damages in notched duplex stainless steel using a combination of microstructural characterization, numerical simulations, and mechanistic models. The results show that the brittle area of the fracture surface increases rapidly with decreasing cathodic potential, accompanied by the fractography transition in a sequence of voids, voids mixed with quasi-cleavage, and quasi-cleavage. While hydrogen-assisted dislocation emission from the void surface and stress concentration at the phase boundary promote nanovoid growth, hydrogen-enhanced plasticity facilitates preferential void growth along the ferrite block. At higher hydrogen concentrations, ferrite cleavage cracking may originate from prolate voids and hydrogen-augmented Cottrell dislocation reactions, reducing plastic strain near the crack tip and hence diminishing the formation of vacancies as void nuclei. Previous studies have focused on the statistics of hydrogen's effect on void size. This work demonstrates the dislocation mechanism of hydrogen-assisted void growth and provides new insights into the development of micro-mechanism-based models to predict hydrogen embrittlement.