Interlayer Bond Research Articles

Nature of Interlayer Bonds in Two-Dimensional Materials

The role of interlayer bonds in the two-dimensional (2D) materials "beyond graphene" and so-called van der Waals heterostructures is vital, and understanding the nature of these bonds in terms of strength and type is essential due to a wide range of their prospective technological applications. However, this issue has not yet been properly addressed in the previous investigations devoted to 2D materials. In our work, by using first-principles calculations we perform a systematic study of the interlayer bonds and charge redistribution of several representative 2D materials that are traditionally referred as van der Waals systems. Our results demonstrate that one can distinguish three main types of inter-layer couplings in the considered 2D structures: one atom thick membranes bonded by London dispersion forces (graphene, hBN), systems with leading electrostatic interaction between layers (diselenides, InSe and bilayer silica) and materials with so-called dative or coordination chemical bonds between layers (ditelurides). We also propose a protocol for recognising the leading type of interlayer bonds in a system that includes comparison of interlayer distances, binding energies and redistribution of the charge densities in interlayer space. Such an approach is computationally cheap and can be used to further prediction of chemical and physical properties such as charge density waves (CDW), work function and chemical stability at ambient conditions.

Nanomaterials as Promising Additives for High-Performance 3D-Printed Concrete: A Critical Review.

Three-dimensional (3D) printed concrete (3DPC), as one of the subset of digital fabrication, has provided a revolution in the construction industry. Accordingly, scientists, experts, and researchers in both academic and industry communities are trying to improve the performance of 3DPC. The mix design of all kinds of concrete has always been the most crucial property to reach the best efficiency. Recently, many studies have been performed to incorporate nano- and micro-scale additives to ameliorate the properties of 3DPC. The current study aims to present the main design properties of 3DPC and completely cover both fresh and hardened state characteristics of 3DPC containing different nano- and micro-additives. Our observations illustrate that nanomaterials can be mainly utilized as a thickener to ameliorate the thixotropic behavior and the structural build-up of 3DPC, resulting in higher yield stress and better viscosity recovery. Furthermore, each nanomaterial, through its unique impact, can provide lower porosity and permeability as well as better mechanical strengths for 3DPC. Although much research investigate the fresh properties of 3DPC containing nano and micro additives, future studies are needed to provide better insight into the impact of these kinds of additives on the hardened characteristics of 3DPC. In addition, researchers may devote more research to address the effects of the additives discussed herein on the performance of other kinds of 3DPC such as lightweight, self-compacting, etc. It should be noted that the effect mechanism of nanomaterials on the inter-layer bond strength of 3DPC is another crucial issue that should be investigated in future studies. Furthermore, nano-scale fillers from source of waste and biomass can be attractive additives for future research to achieve high performance of sustainable 3D-printed concrete.

Experimental Study of the Effect of Tack Coats on Interlayer Bond Strength of Pavement

The performance and lifetime of the flexible asphalt pavement are mainly dependent on the interfacial bond strength between layer courses. To enhance the bond between layers, adhesive materials, such as tack coats, are used. The tack coat itself is a bituminous material, which is applied on an existing relatively non-absorbent surface to ensure a strong bond between the old and newly paved layer. The primary objective of this study was to evaluate the effects of various types of tack coat materials on interlayer bond strength and to determine the optimal application rate for each type. The tack coat types used in this paper were RC-70, RC-250, and CSS-1h. Both laboratory-prepared and field-constructed hot mix asphalt concrete pavements using the tack coats were tested for the binding strength between the layers. A direct shear test was used for the testing. The results obtained from the study showed that the optimum application rate for RC-70 was 0.1 L/m2, and for RC-250, it was 0.2 L/m2, while the optimum application rate for CSS-1h was 0.1 L/m2. From the field test, the optimum application rate of the RC-250 tack coat was 0.1 L/m2.

Thermal history based prediction of interlayer bond strength in parts manufactured by material extrusion additive manufacturing

Thermal history based prediction of interlayer bond strength in parts manufactured by material extrusion additive manufacturing

Using Fibre recovered from face mask waste to improve printability in 3D concrete printing

Surgical face mask usage has rapidly increased in the last two years due to the COVID-19 pandemic. This generates vast amounts of plastic waste, causing significant risks to the ecosystem. Thus, this study assesses the potential of using recycled fibre from face mask waste as fibre reinforcement in 3D concrete printing (3DCP) applications to improve printability while reducing landfill waste. The effect of recycled fibre from waste face masks on the rheological characteristics of printable mixes and the mechanical performance of printed elements was evaluated for different contents of shredded face masks (i.e., 1% and 2% by vol). The rheological properties like static and dynamic yield strengths, apparent viscosity, and thixotropic behaviour, along with compressive and flexural strength, were evaluated for 3D printed specimens and mechanical properties were compared to their mould-cast counterparts. Further, the variation in the interlayer bond strength and porosity due to different fibre dosages was also investigated. In addition, a comparative study on the fresh and hardened properties was performed for the printable mixes with polypropylene (PP) fibres and face masks. The addition of face masks significantly improved the rheological properties with good extrudability and buildability for all the dosages. Compared to face masks, mixes with PP fibres showed poor extrudability with higher fibre dosages. The compressive strength was increased by 41% for a 1% dosage of face masks when compared to the unreinforced concrete. Furthermore, the flexural strength when tested along the weaker interface, showed an increase of 74% and 82% for the addition of 1% and 2% face mask content. The interlayer bond strength of 1% face mask content showed 21% improvement and was observed to have the highest surface moisture content. The mechanical performance of face masks and PP fibres are observed to be comparable for 1% dosage. The mechanical properties of printed and mould-cast specimens were also observed to be similar.

A Bond-Based Peridynamic Model with Matrix Plasticity for Impact Damage Analysis of Composite Materials

The prediction of damage and failure to fiber-reinforced polymer composites in extreme environments, particularly when subjected to impact loading, is a crucial issue for the application and design of protective structures. In this paper, based on the prototype microelastic brittle (PMB) model and the LaRC05 composite materials failure model, we proposed a bond-based peridynamic (BB-PD) model with the introduction of plastic hardening of the resin matrix for fiber-reinforced polymer composites. The PD constitutive relationships of the matrix bond and interlayer bond under compressive loading are considered to include two stages of linear elasticity and plastic hardening, according to the stress-strain relationship of the resin matrix in the LaRC05 failure model. The proposed PD model is employed to simulate the damage behaviors of laminated composites subjected to impact loading. The corresponding ballistic impact tests of composite laminates were carried out to observe their damage behaviors. The PD prediction results are in good agreement with the ballistic experimental results, which can verify the correctness and accuracy of the PD model developed in this study in describing the impact damage behaviors of composite materials. In addition, the characteristics and degree of damage in composite laminates are analyzed and discussed based on this PD model. The difference in the impact resistance of composite laminates with different stacking sequences is also studied using the numerical simulation results.

Thermal conductivity of 2D diamond superstructures in interlayer-bonded twisted bilayer graphene

We report results from a systematic analysis of thermal transport in 2D diamond superstructures in interlayer-bonded twisted bilayer graphene (IB-TBG) based on molecular-dynamics simulations. We find that the introduction of interlayer C–C bonds in these bilayer structures causes an abrupt drop in the thermal conductivity of pristine, non-interlayer-bonded bilayer graphene, while further increase in the interlayer C–C bond density (2D diamond fraction) leads to a monotonic increase in the thermal conductivity of the resulting superstructures with increasing 2D diamond fraction toward the high thermal conductivity of 2D diamond (diamane). We also find that a similar trend is exhibited in the thermal conductivity of interlayer-bonded graphene bilayers with randomly distributed individual interlayer C–C bonds (RD-IBGs) as a function of interlayer C–C bond density, but with the thermal conductivity of the IB-TBG 2D diamond superstructures consistently exceeding that of RD-IBGs at a given interlayer bond density. We analyze the simulation results employing effective medium and percolation theories and explain the predicted thermal conductivity dependence on interlayer bond density on the basis of lattice distortions induced in the bilayer structures as a result of interlayer bonding. Our findings demonstrate that the thermal conductivity of IB-TBG 2D diamond superstructures and RD-IBGs can be precisely tuned by controlling interlayer C–C bond density and have important implications for the thermal management applications of interlayer-bonded few-layer graphene derivatives.

Thermal stability and decomposition mechanisms of hexatetracarbon: Tight-binding molecular dynamics and density functional theory study

In this work, we carry out molecular dynamics and ab initio modeling to determine the thermal decomposition channels and thermal stability of the recently proposed 2D carbon allotrope, hexatetracarbon (HTC). To take into account the role of edges in the initialization of decay, we considered finite size cluster models of HTC passivated by hydrogen. Four models were selected for the study: [Formula: see text], [Formula: see text] [Formula: see text] and [Formula: see text]. Molecular dynamics and hyperdynamics was carried out using the NTBM non-orthogonal tight-binding model. For ab initio calculations, we used the electron density functional theory with the B3LYP three-parameter hybrid functional and the 6-311G[Formula: see text] electronic basis set. Prismane [Formula: see text] demonstrated the highest stability due to the high energy barrier of 1.5 eV preserving its decomposition. Larger clusters possessed lower barriers in the 0.65–0.9 eV range. We concluded that the HTC edges are unstable at room temperatures. However, the destruction of some interlayer bonds can result in strain relaxation and increase of stability. We believe that HTC could exist at room temperatures in the form of nanosized quantum dots that appeared from bilayer graphene under high pressure.

Fabrication, Interlayer Bonding and Mechanical Characterization of Four Layered AA7075/SiC Functionally Graded Material

Fabrication, Interlayer Bonding and Mechanical Characterization of Four Layered AA7075/SiC Functionally Graded Material

The effect of multiaxial geocomposite reinforcement on fatigue performance and crack propagation delay in double-layered asphalt beams

The presented study investigates the effect of a recently developed multiaxial geocomposite made of polypropylene geogrid and non-woven fabric on the delay of crack propagation, based on four-point bending tests of large asphalt concrete beams – both for reinforced and non-reinforced specimens. Several approaches are described in this study, including analysis of stiffness modulus decrease and analysis of crack propagation using dissipated energy. The study also includes investigation of the impact of reinforcement on shear resistance of the inter-layer bond. The reinforced system displays reduced decrease in stiffness during cyclic loading; it is able to bear loads over a longer period, in contrast to the unreinforced system. An increase in fatigue life by a factor of 10–22 is possible, as compared to the unreinforced system. The factor of relative increase in the number of cycles to the first initiation of crack in lower asphalt layer when reinforcement is introduced ranges from 5 to 10.

Evaluation of the Effect of Interlayer Bonding Condition on the Deterioration of Asphalt Pavement

In this study, to investigate the effect of interlayer bonding condition on the deterioration of asphalt pavement, we conducted numerical analysis based on multi-layer elastic theory, verification of numerical analysis results by experiments on a full-scale test track, and comparison of the progress of deterioration based on accelerated loading tests conducted on the test pavement. Firstly, the analysis indicated that stronger tensile strain could occur on the upper side of the interlayer when the interlayer bonding weakens. Furthermore, the test pavement simulating interlayer debonding showed the same strain tendency as the analysis. These results suggest that if the interlayer debonding continues, the pavement may suffer early fatigue failure. On the other hand, there are some results that are not consistent with those of the analysis, such as the magnitude of deflection in the test pavement; thus, further investigation is required. Furthermore, because of the accelerated loading on the test pavement, the sections where the layers were debonded immediately after construction became bonded. Since the deflection of the test pavement did not change significantly from that immediately after construction, and no conspicuous damage such as cracks was observed on the road surface, it is considered necessary to continue follow-up surveys.

Research status and prospect of machine learning in construction 3D printing

3D printing brings new opportunities for the development of civil engineering. Machine learning (ML) is also widely used in various fields of 3D printing. To describe the main research issues and potential future applications of ML for construction 3D printing, it is essential to comprehensively overview the current research topics. This paper aims to review, summarize, analyze, and introduce the research progress of ML applications in construction 3D printing, followed by a discussion of the current challenges and future research scope. Firstly, the classification and working principle of 3D printing and ML technology were introduced. Secondly, in the aspects of the design of construction materials, control of printing process, and quality inspection of construction components, the application status of ML in construction 3D printing was discussed. Based on this, in terms of interlayer bond performance enhancement, real-time status monitoring, and anisotropic behavior control, the future potential and challenges of ML in construction 3D printing were summarized, to provide a reference for promoting the realization of high-efficiency, intelligence, and sustainability in the field of civil engineering.

Demonstration of the Strengthening Effect of Rapid Polymeric Chain Movement and Print Temperature on the Interlayer Bond

Demonstration of the Strengthening Effect of Rapid Polymeric Chain Movement and Print Temperature on the Interlayer Bond

Design, fabrication and characterization of MoS2self-lubricating pure MoS2Coatings for space applications using PVD magnetron sputtering

Tribological components cost just a fraction of the whole spacecraft, but they often lead to failures that partially or completely disrupt the spacecraft. Mechanical components used in space applications have to withstand extreme and severe environmental conditions such as very high or very low cryogenic temperatures, high vacuum, corrosive elements and radiation. MoS2 is the most widely used lubricating material in space applications. It possesses a lamellar structure with strong covalent bonds within layers and simultaneously weak van der Wall’s interlayer bonds, resulting in easy shearing of the crystals in the direction parallel to the basal planes, hence acting as a good solid lubricant.In this research, a thin film nano scale coating of MoS2 was deposited on steel using Physical Vapour Deposition (PVD). The PVD technique used was the RF magnetron sputtering process. Material characterization was performed using X-Ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Raman spectroscopy. According to the results, the developed MoS2 nano coatings have a polycrystalline structure with basal planes that are oriented perpendicular to the substrate surface.

Diagnosis of fatigue cracks in structural elements manufactured by additive manufacturing

Recently, the production of metal structural elements using additive processes is gaining popularity. They allow the production of an element of any geometry and structure, while reducing the mass of the produced part. Unfortunately, the AM technology causes structural elements to be burdened with numerous defects in the form of porosity, unmelted powder, weak interlayer bonds or residual stresses, etc. These defects translate into the possibility of an early, uncontrolled fatigue crack. For this reason, it is important to find ways to quickly detect damage caused by random variable loads. The work presents methods of diagnosing cracks and fatigue damage in structural elements produced using 3D printing. The division of research methods allowing for the detection of defects in structural elements and the characteristics of the most popular methods, taking into account their advantages and limitations, were presented. Methods appropriate for a given type of material, test conditions and damages are indicated. The most important methods of diagnosing defects in printed elements include: penetrating, ultrasonic, radiographic, eddy current and thermal imaging methods.

Mechanical properties of AlMgB14-related boron carbide structures. A first principle study

We examine the effects produced by replacing B–B interlayer bonds by C–C bonds in AlMgB14-related boron network on its mechanical properties. The elastic constants, Vickers hardness and shear strength are evaluated by means of first principle computer simulations on the basis of density functional theory. The results of simulations suggest a possibility of existence of several orthorhombic boron carbide phases with strongly enhanced mechanical properties with the Young's modulus and Vickers hardness being within the range of 550–600 GPa and 43–50 GPa, respectively.

Influence of structuration rate, with hydration accelerating admixture, on the physical and mechanical properties of concrete for 3D printing

The effects of the concave exponential evolution of structuration rate (Athix) with aluminum sulfate-based hydration accelerating admixture on the physical and mechanical properties of concretes for 3D printing were investigated. Three printable concrete mixes were produced. The results showed that Athix did not have major implications on the physical and mechanical properties while using multiple batches for printing. However, it changed the behavior of critical deformation and interlayer adhesion. In some cases, it provided greater compressive strengths and favored physical/chemical interlayer bond, which points to the possibility of increasing the printing window.

Digital Twins Solve the Mystery of Raman Spectra of Parental and Reduced Graphene Oxides.

Digital Twins concept presents a new trend in virtual material science, common to all computational techniques. Digital twins, virtual devices and intellectual products, presenting the main constituents of the concept, are considered in detail on the example of a complex problem, which concerns an amazing identity of the D-G-doublet Raman spectra of parental and reduced graphene oxides. Digital twins, presenting different aspects of the GO and rGO structure and properties, were virtually synthesized using a spin-density algorithm emerging from the Hartree-Fock approximation. Virtual device presents AM1 version of the semi-empirical unrestricted HF approximation. The equilibrium structure of the twins as well as virtual one-phonon harmonic spectra of IR absorption and Raman scattering constitute a set of intellectual products. It was established that in both cases the D-G doublets owe their origin to the sp3 and sp2 C-C stretchings, respectively. This outwardly similar community reveals different grounds. Thus, multilayer packing of individual rGO molecules in stacks provides the existence of the sp3 D band in addition to sp2 G one. The latter is related to stretchings of the main pool of sp2 C-C bonds, while the sp3 constituent presents out-of-plane stretchings of dynamically stimulated interlayer bonds. In the GO case, the sp3 D component, corresponding to stretchings of the main pool of sp3 C-C bonds, is accompanied by an sp2 G component, which is related to stretchings of the remaining sp2 C-C bonds provided with the spin-influenced prohibition of the 100% oxidative reaction in graphene domain basal plane.

Mechanical behavior of bonded interface between steam-cured concrete and SCC under direct shear test: Experimental and numerical studies

The interlayer damage of slab ballastless track for high-speed railway has become a weak link that affects the safe operation of track structure. Under the combined action of the train self-weight load and wheel-rail friction, the track plate presents complex stress state. Meanwhile, the interlayer defects and bond state have a great influence on the damage mechanism of track plate. The failure mechanism of concrete-concrete interface under combined stress has been focused on, but it is still not well quantitatively investigated at the grain scale. In this paper, the discrete element method (DEM) combined with digital speckle and acoustic emission monitoring technology is used to conduct the direct shear tests on bonded samples composed of steam-cured concrete and self-compacting concrete (SCC) with different bond interface characteristics. On this basis, it is quantitatively analyzed the effects of interfacial bond strength and interfacial morphological characteristics on the compressive-shear mechanical properties and damage patterns of bonded samples, and the deterioration mechanism of the interface is explained from a mesoscopic perspective. The results show that the compression-shear mechanical response and damage features of the bonded samples are the result of the combined effect of bond strength and morphological characteristics of the interface. The increase of bond strength makes the samples change from shear cracking damage along the interface to tensile cracking damage inside the concrete. The bonded area ratio (BAR) of the interface maintains a good positive linear correlation with the shear strength, and the increase of BAR makes the brittle failure more obvious in the post-peak stage. The increase of interface roughness coefficient (IRC) makes more compressive stress concentration areas form in the interface, which enhances the shear strength of the bonded sample to a certain extent.

The impacts of stress on the macromolecular structure of anthracites: Implications for the mechanochemical effects

Despite the vast research studying the influence of stress on the physical structure, little is known whether and how stress works on the chemical structure in coals. In the present study, some insights are given by investigating the macromolecular structure evolution characteristics and mechanism of a Chinese anthracite (Ro,max = 3.6%) during deformation experiments at temperatures of 300–400 °C, confining pressure of 150 MPa, and strain rates of 2.5–20*10−6 s−1. Additional heat treatments (without stress) were also performed at the same temperature range. Revealed by vitrinite reflectance, XRD, and Raman spectroscopy, a smaller and less ordered macromolecular structure was observed within experimental conditions. Upon heating alone, Ro,max and stacking diameter (La) increased together, while stacking height (Lc) and structure ordering (ID/IG and FWHM of D and G peaks) decreased with increasing temperature, indicating structure rearrangement and relaxation. In contrast, the macromolecular structure in deformation experiments showed a two-stage evolution with decreasing strain rate. Stage 1 was characterized by the obvious decreases in Ro,max, La, and Lc, but minor changes in Raman spectra, implying stress might break in-plane and inter-layer chemical bonds at high strain rates. Stage 2 was identified by the relative increases in Ro,max, La, and FWHM of D peak, in combination with Lc, mainly indicating the generation of structural defects at low strain rates allows the aromatic layer to accommodate the stress without breakage. Our results suggest stress can act on the macromolecules directly by breaking or distorting the chemical bonds depending on the strain rate.