Non-uniform Interface Research Articles

Friction-induced vibration of a slider-on-rotating-disc system considering uniform and non-uniform friction characteristics with bi-stability

The friction-induced vibration of a novel slider-on-rotating-disc system is studied by a combination of numerical analysis on the theoretical model and experimental investigation on the test rig. In this system, the rotation of an L-shaped component couples with the friction-induced stick–slip vibration in the tangential direction and produces a state-dependent normal force. The numerical results of the dynamic responses by employing the Coulomb friction model and the friction model with Stribeck effect are both in good agreement with the experimental results, therefore the credibility of the numerical analysis on the theoretical dynamic model is validated. The bi-stability phenomenon, i.e., there is coexistence of a stable pure sliding response and a stable stick–slip limit cycle in a certain parameter range, is not only revealed in the numerical analysis but also observed experimentally. Moreover, a novel approach to constitute a non-uniform friction interface on the disc surface is explored for its efficacy in suppressing the friction-induced stick–slip vibration of the system also by both numerical analysis and experimental testing, namely, the disc surface is divided into sectors assigned with different friction properties. Both the numerical and experimental results show that the non-uniform friction interface of the disc with appropriate friction properties of these sectors can be an effective approach to diminish the range of the operating parameters where the stick–slip vibration occurs and thereby reduce the possibility of occurrence of stick–slip vibration in the system.

Dual mechanisms of fiber dispersion of CF/Sn50Pb50 composites fabricated by double-layer printing head 3D printing process

Abstract Fiber dispersion was one of the crucial factors, which influenced the mechanical properties of fiber reinforced metal matrix composites (FR-MMCs). The incomprehension of fiber dispersion mechanisms and the lack of control methods limited the developments and further applications of the 3D printed FR-MMCs. In this work, the tensile properties and microstructures of continuous carbon fiber reinforced SnPb matrix composites, which were fabricated by the double-layer printing head 3D printing process (DPP), were measured and observed. The dual mechanisms of capillarity pressure driving and nonuniform interface reaction driving in fiber dispersion were proposed. Besides, the dynamic of fiber dispersion was discussed. It was found that improving wicking performance could increase the dispersion of fibers. This research filled in the blank of fiber dispersion mechanisms of 3D printed FR-MMCs, and provided the methodological supports for further improving the performances of composites.

Supramolecular self-assembly of nickel (Ⅱ)-substituted α-Keggin-type polyoxometalate and polyaniline coated Fe2O3 hollow nanospindle for microwave absorption application

A general strategy has been developed here to supramolecular self-assembly of nickel (Ⅱ)-substituted α-Keggin-type polyoxometalate and polyaniline coated Fe2O3 hollow nanospindle (Fe2O3 hollow nanospindle@PANI/α-SiW11Ni composites) via electrostatic attraction and hydrothermal method. Fe3+ was first hydrolyzed and polymerized into Fe2O3, then dissolved into [Fe(H2PO4)x]3−x, resulting in hollow structure. The polyoxometalate existed in polyaniline as a proton-doped counter-ion form, rather than as a separate crystalline state. The protons and anions entered the PANI main chain and combined with N atoms of amines and imines on the PANI chain ((-NH‧+ ​= ​)/α-[SiW11Ni(H2O)O39]6-) to form poles and bipolar delocalization into π bonds of the whole polyaniline molecular chain, which leaded to conductance and polarization. The Fe2O3 hollow nanospindle@PANI/α-SiW11Ni composites were proven to be excellent microwave absorber in terms of reflection loss (RL) and bandwidth. The maximum RL value was up to −53.6 ​dB at 3.5 ​mm and 6.9 ​GHz. The broadest absorption bandwidth exceeding −10 dB was 6.3 ​GHz at a thickness of only 1.9 ​mm. Moreover, the ternary composites presented obvious multi-band absorption with the matching thickness range of 1.5–5 ​mm. The absorption peaks bandwidth reached as wide as 14.3 ​GHz, which included all C-Ku bands. The hollow and core-shell structures could provide non-uniform interface for the induced polarization loss and space for the reflecting and scattering of microwave. The carrier, pair-ion carrier and hydrogen bond network could lead to conduction loss. The magnetic losses were caused by eddy current effect and natural resonance. This work can lay a theoretical foundation for the design and performance regulation of new absorbing materials.

Electrogravimetry and Structural Properties of Thin Silicon Layers Deposited in Sulfolane and Ionic Liquid Electrolytes.

Potentiostatic deposition of silicon is performed in sulfolane (SL) and ionic liquid (IL) electrolytes. Electrochemical quartz crystal microbalance with damping monitoring (EQCM-D) is used as main analytical tool for the characterization of the reduction process. The apparent molar mass (Mapp) is applied for in situ estimation of the layer contamination. By means of this approach, appropriate electrolyte composition and substrate type are selected to optimize the structural properties of the layers. The application of SL electrolyte results in silicon deposition with higher efficiency compared to the IL 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [BMP][TFSI]. This has been associated with the instability of the IL in the presence of silicon tetrachloride and the enhanced incorporation of IL decomposition products into the growing silicon deposit. X-ray photoelectron spectroscopy (XPS) analysis supports the results about the layer composition, as suggested from the microgravimetric experiments. Attention has been given to the impact of practically relevant substrates (i.e., Cu, Ni, and vitreous carbon) on the reduction process. An effective deposition can be carried out on the metal electrodes in both electrolytes due to accelerated reaction kinetics for these types of substrates. However, on vitreous carbon (VC), a successful reduction of SiCl4 can only be accomplished in the IL, while the electroreduction process in SL is dominated by the decomposition of the electrolyte. For short deposition times, the scanning electron microscopy (SEM) images display rough morphologies in the nanometer range, which evolve further to structures with increased length scale of the surface roughness. The development of a rough interface during deposition, resulting in QCM damping at advanced stages of the process, is interpreted by a model accounting for the resistive force caused by the interaction of the liquid with a nonuniform layer interface. By using this approach, the individual contributions of the surface roughness and viscoelastic effects to the measured damping values are estimated.

Aerothermal and aerodynamic performance of turbine blade squealer tip under the influence of guide vane passing wake

In this paper, the performance of the turbine blade squealer tip has been studied detailed aimed to highlight the impact of the upstream guide vane passing wake. The first stage of GE-E3 high-pressure turbine has been employed to perform the three-dimensional simulation and the computational domain has been scaled based on the domain scaling method. Boundary conditions are consistent with operating conditions of the annular cascade testing. Circumferential averaged and realistic non-uniform interface conditions have been used to obtain steady and unsteady characteristics respectively. The validation of the turbulent model and mesh independent test has been conducted detailed in previous work. Three squealer tips, including two widths and heights, have been designed and investigated to understand its influence. Results show that the aerothermal performance of the squealer tip is remarkably influenced by the upstream passing wake. Although steady and time-averaged results have a good agreement, the variation of instantaneous heat transfer coefficient (HTC) would be over 30%, especially on the Cavity Floor region. Changing the geometry of the squealer also has different impacts on both steady and unsteady performance. The unsteady aerodynamic has relatively small fluctuation within 10%, and the distribution of steady and time-averaged leakage flow as well as total pressure loss coefficient still have a satisfactory agreement.

Spatial scale dependent impact of non-uniform interface defect distribution on field effect mobility in SiC MOSFETs

Understanding the properties of SiO2/SiC interfaces is one of the key issues related to the development of SiC power devices. However, existing evaluation methods such as capacitance-voltage measurements do not directly provide microscopic assessments. Recently, the nanoscale imaging of interface defect density distributions has become possible using local deep level transient spectroscopy. This technique has shown that the defect density at a SiO2/SiC interface can have a non-uniform, clustered distribution. Prior numerical simulations by our group have also demonstrated that this inhomogeneous clustering of interface defects may reduce field effect mobility in SiC metal oxide field effect transistors. The present work examines the relationship between the spatial scale of the non-uniformity and reductions in field effect mobility and shows that an interface defect distribution containing smaller features will have a greater effect on field effect mobility.

Experimental and numerical analysis of Cu/Al8011/Al1060 trilayered composite: a comprehensive study

This work studied the interface morphology, microstructure behavior, and mechanical properties of the fabricated trilayered Cu/Al8011/Al1060 composite. In this regard, the roll-casted Cu/Al8011 bimetal was subjected to the hot-roll-bonding process with Al1060 at a thickness reduction of 47%. As a result, the hot-roll-bonding broke the produced nonuniform continuous interface within the copper and aluminum during the roll-casting process. The corresponding interface from the copper side includes Al4Cu9, AlCu, and Al2Cu, respectively. Additionally, SEM-based in-situ tensile deformation revealed that the initiated cracks at the Cu/Al8011 interface propagated into the copper layer that led to its fracture before the aluminum. Based on the FEM results, the effective stress distribution of the Cu strip is not homogeneous at the deformation zone. Moreover, the thickness reduction of the Cu and Al layers was respectively lower and slightly higher than that of the trilayered composite, indicating that plastic deformation mainly occurred at the aluminum matrix due to its large plasticity amount.

Influence of Non-Uniform Interface Defect Clustering on Field-Effect Mobility in SiC MOSFETs Investigated by Local Deep Level Transient Spectroscopy and Device Simulation

It has recently been shown that interface defect density (Dit) at SiO2/SiC interfaces can have non-uniform clustered distribution through the measurement by local deep level transient spectroscopy (local DLTS). Here we investigate the influence of the non-uniform Dit clustering on the field-effect mobility in SiC metal-oxide-semiconductor field effect transistors (MOSFETs) by device simulation. We develop a three dimensional numerical model of a SiC MOSFET, which can incorporate actual Dit distributions measured by local DLTS. Our main result is that the impact of the non-uniform Dit clustering on field-effect mobility is negligible for a SiC MOSFET with high Dit formed by dry thermal oxidation but it becomes significant for that with lower Dit by post-oxidation annealing. The result indicates that channel mobility can be further improved by making Dit distribution uniform as well as reducing Dit.

Microstructure modification and corrosion improvement of [formula omitted] steel induced by pseudospark electron beam treatment

The pseudospark electron beam is a kind of pulsed electron beam characterized by fast and stable repetitive operations. It is able to achieve high rate of energy rise and plasma quenching. Thus, when used as an intense electron beam source for material processing, some unique properties are induced. The mechanism analysis of microstructure modification and corrosion improvement of AISI1045 steel treated by pseudospark electron beam are investigated. Results show that the amorphous phase is formed on the top surface of melted layer. The treated layer is several microns deep with nonuniform interface. Besides, material’s grain sizes are significantly reduced after pseudospark treatment. The average grain size in the heat affected zone is smaller than that in the melted zone, which is attribute to the combination effect of temperature-induced dynamic thermal stress fields and the highest temperature gradient. Furthermore, electrochemical impedance spectroscopy (EIS) and potential polarization analysis are used to study the corrosion behavior of samples pre and post pseudospark electron beam treatment. The improvement of corrosion resistance is due to the combination effects of the formation of austenite, the removement of impurities during the electron beam surface treatment process and the formation of the amorphous phase acted as a homogeneous passive film.

The effects of surface topography and non-uniform wettability on fluid flow and interface slip in rough nanochannel

The flow of argon liquid in an asymmetric nanochannel with smooth and rough wall is investigated by molecular dynamics method. Considering the relationships of related factors which include characteristic dimensions, the number and the dense arrangement pattern of nanostructure, the effects of surface topography on fluid flow and interface slip are probed. The results show that the variation of the surface topography height has a significant influence on the fluid flow and interface slip. However, the effect of the variation of topography width is greatly related to the number and dense arrangement pattern of nanostructure. Surface topography causes an increase in interfacial resistance and more reduction in velocity slip at the rough wall, which even results in the forming of sticky boundary condition. The effect of non-uniform interface wettability of rough wall on the flow behavior and slip at the solid–liquid interface is investigated as well. The results show that the influence of non-uniform interface wettability on the flow in the hydrophobic channel is more obvious than that in the hydrophilic channel. Hydrophobic substrate with hydrophobic nanostructures has a smaller interfacial hydrodynamic resistance than that with hydrophilic nanostructures, which makes the average velocity and velocity slip become greater. Obviously, non-uniform interfacial wettability strengthens the effect of surface topography on the fluid flow and interface slip. It is possible to achieve effective velocity slip and obtain drag reduction by applying the non-uniform wettability of nanostructures under the same surface topography.

Nanoscale Mapping of Nonuniform Heterogeneous Nucleation Kinetics Mediated by Surface Chemistry.

Nucleation underlies the formation of many liquid-phase synthetic and natural materials with applications in materials chemistry, geochemistry, biophysics, and structural biology. Most liquid-phase nucleation processes are heterogeneous, occurring at specific nucleation sites at a solid-liquid interface; however, the chemical and topographical identity of these nucleation sites and how nucleation kinetics vary from site-to-site remain mysterious. Here we utilize in situ liquid cell electron microscopy to unveil counterintuitive nanoscale nonuniformities in heterogeneous nucleation kinetics on a macroscopically uniform solid-liquid interface. Time-resolved in situ electron microscopy imaging of silver nanoparticle nucleation at a water-silicon nitride interface showed apparently randomly located nucleation events at the interface. However, nanometric maps of local nucleation kinetics uncovered nanoscale interfacial domains with either slow or rapid nucleation. Interestingly, the interfacial domains vanished at high supersaturation ratio, giving way to rapid spatially uniform nucleation kinetics. Atomic force microscopy and nanoparticle labeling experiments revealed a topographically flat, chemically heterogeneous interface with nanoscale interfacial domains of functional groups similar in size to those observed in the nanometric nucleation maps. These results, along with a semiquantitative nucleation model, indicate that a chemically nonuniform interface presenting different free energy barriers to heterogeneous nucleation underlies our observations of nonuniform nucleation kinetics. Overall, our results introduce a new imaging modality, nanometric nucleation mapping, and provide important new insights into the impact of surface chemistry on microscopic spatial variations in heterogeneous nucleation kinetics that have not been previously observed.

Plastic Deformation and Fragmentation of Strained Actin Filaments

The assembly of actin filaments and filament networks generate forces that drive cell and vesicle movement. These structures and the comprising actin filaments must be mechanically stable to sustain these forces and maintain their structural integrity. Filaments in these dynamic structures must also be disassembled to recycle and replenish the pool of actin monomers available for polymerization. Actin-severing proteins such as cofilin and contractile myosin motor proteins fragment these nominally stable structures. We developed a mesoscopic-length-scale actin filament model to investigate force-induced filament fragmentation. We show that fragmentation in our model occurs at curvatures similar to previous measurements of fragmentation within (cofil)actin and actin-cofilactin boundaries. Boundaries between bare and cofilin-decorated segments are brittle and fragment at small bending and twisting deformations. Extending filaments disperses strain uniformly over subunit interfaces, and filaments fragment with no detectable partial rupture or plastic deformation. In contrast, bending or twisting filaments imposes nonuniform interface strain and leads to partial interface rupture, accelerating filament fragmentation. As a result, the rupture force under compressive loads is an order of magnitude lower than under tensile loads. Partial interface rupture may be a primary mechanism of accelerating actin filament fragmentation by other actin-destabilizing proteins.

Dynamic crack growth mechanism and lifetime assessment in plasma sprayed thermal barrier system upon temperature cycling

Abstract Failure of plasma-sprayed thermal barrier coatings (TBCs) is very complicated upon temperature cycling, therefore, to ascertain the crack propagation behavior is beneficial to understand the failure mechanism and life prediction of TBCs. In this paper, a finite element model is developed by coupling the dynamic growth of thermally grown oxide and dynamic crack propagation to explore the failure of TBCs induced by the instability of the interface between top coat (TC) and bond coat (BC). The thermal cyclic lifetime is deduced by obtaining the thermal cycles corresponding to the occurrence of complete delamination. The influence of the non-uniformity of the interface on thermal cyclic lifetime is quantitatively evaluated. Sensitivity studies including the effects of constituent properties and crack distance to the interface on the thermal cyclic lifetime are further examined. The results show that the incipient cracks usually nucleate above the valley due to the large tensile stress, and the shear stress near the peak plays a very crucial role. The crack growth involves three stages with different fracture dominated-mode. The crack propagation behavior obtained by simulation is in line with that observed by experiments. The TBCs system with a uniform interface exhibits a longer thermal cyclic lifetime compared to the non-uniform interface. Coating optimization methods proposed in this work may provide an alternative option for developing a TBCs system with longer service lifetime.

Low-coherent fiber-optic interferometry for in situ monitoring the corrosion-induced expansion of pre-stressed concrete cylinder pipes

The corrosion-induced expansion of pre-stressed concrete cylinder pipes shapes a major determining factor in the durability of most pipeline systems. However, a structure extended in a very large span and accompanied by a slow corrosion-induced structural damage is still a challenge in practice. Here, a low-coherent fiber-optic interferometry is proposed for in situ measuring the corrosion-induced expansion by directly circling the sensing optical fiber on the outer surface of the pipe. Since the accuracy of the absolute deformation measurement by the low-coherent fiber-optic interferometry can reach 3–5 μm, we are able to improve the sensitivity by choosing the length of the sensing fiber. In the experiment, we employ 50-m sensing fiber; therefore, a resolution of about 0.1 microstrains had been approached. We chose 12 places along the pipeline as the corrosion-induced expansion monitoring points. On monitoring for about half a year, a non-uniform interface in structure, such as the repaired places, was found as a key factor of the corrosion-induced expansion development, which could be a reference for the further health care of the pipeline structures.

Nonuniform interface failure of steel-concrete composite structures bonded using epoxy resin mortar

The connection between steel and concrete determines the overall mechanical properties of the composite structure. Compared with the conventional method of connecting materials by using metal connectors, using an adhesive to connect steel-concrete composite structures is more advantageous. In this study, high-speed cameras and a conventional data acquisition system were used to perform a push-out test on steel-concrete composite structure specimens connected using epoxy resin mortar. The study obtained the failure mode, interface strength, and ductility index of the specimen. The results revealed that the failure modes of the specimens were damage in the concrete at the interface of the adhesive, indicating that the adhesive material has a good bond strength; with the improvement in the concrete strength grade, the limited load increases along with the strain, but the ductility decreases. In this paper, digital image correlation (DIC) technology was used to analyze the strain development of the concrete interface, and the results revealed that the strain distribution at the interface was nonuniform. Compared with the conventional strain gauge test method and elastic mechanics theory, the results of DIC measurement indicate that the DIC technology can reveal the nonuniform failure process and failure mechanism of the interface.

Coating two-dimensional MoS2 with polymer creates a corrosive non-uniform interface

Two-dimensional (2D) materials and soft materials are both susceptible to mechanical instabilities, such as buckling, wrinkling, folding and creasing, especially when located on surfaces. Here, we report that weak van der Waals interactions cause the interface between 2D molybdenum disulphide (MoS2) and a soft poly(methyl methacrylate) coating to demonstrate mechanical instability and delamination. The resulting non-uniform and buckled interface greatly hampers the ability of the coating to protect the MoS2 substrate. Also, the corrosion rate of 2D MoS2 and quench rate of intrinsic luminescence in 2D MoS2 were significantly accelerated by the soft coating. Owing to the formation of corrosive cavities at the interface, the geometry and size of the flakes became the dominating factor, and a critical size of 2D flakes for such interfacial instability was determined based on elasticity theory. Such hazardous corrosion in a 2D material caused by a soft coating raises concern for their use in electronic packaging, and for the processing of van der Waals-layered materials for future applications.

Drift-diffusion simulation of leakage currents in unintentionally doped organic semiconductors with non-uniform interfaces

Organic electronic devices frequently employ intrinsic semiconductors as active layer. The choice of different materials for the charge injecting and extracting interfaces gives rise to a finite contact potential. Injection of holes against the built-in electrical field results in a diffusion-limited exponential current–voltage characteristic at low bias. Leakage currents, however, seek paths with preferable negative built-in voltages arising from non-uniform interface properties. Along such paths holes are spilled into the intrinsic layer from the charge extracting contact whose Fermi energy is pinned in the lower half of the semiconductor’s band gap. We show here that the drift movement of holes opposed by diffusion can lead to a sublinear increase in the injected current with voltage. Charge injection is assisted by a built-in electrical field, depending mainly on the dopant density and the potential barrier at the injecting contact. Variability of these important properties can arise unintentionally, e.g., due to ambient processing, and low bias currents can serve as simple monitor. As a model system, measured current voltage characteristics of ambient processed poly(3-hexylthiophene-2,5-diyl) (P3HT) films are compared to numeric simulations solving the coupled nonlinear Poisson and drift-diffusion differential equations illustrating the basic principle.

Theoretical study of the effective modulus of a composite considering the orientation distribution of the fillers and the interfacial damage

In the manufacturing process of a filler-reinforced composite, the fillers in the matrix are aligned due to the shear flow occurring during the drawing stage, and the interface between the matrix and the fillers form various imperfections that lead to debonding and slip under mechanical loading. Hence, there have been numerous micromechanics studies to predict effective moduli of the composites in the presence of partial alignment of fillers and interface imperfections. In this study, we present an improved theory that overcomes two limitations in the existing micromechanics based approaches. First, we find that the interface damage tensor, which has been developed to model the weakened interface between matrix and fillers, has singularities that cause non-physical predictions (such as infinite or negative effective moduli). We correct the mathematical mistakes to remove singularities and derive analytic expressions of the damage tensor for ellipsoidal inclusions. Second, we reveal that the previous theory on the effective moduli with axisymmetric filler orientation distribution fails because the longitudinal and transverse moduli do not converge in the limit of random orientation distribution. With appropriate corrections, we derive an analytic expression for the orientation average of arbitrary transversely isotropic 4th order tensor under general axisymmetric orientation distribution. We apply the improved method to compute the effective moduli of a representative composite with non-uniform filler orientation and interface damage.

Spin transfer torque magnetization reversal in a hard/soft composite structures

Current induced magnetization manipulation in a spin valve structure where the free layer is a magnetic hard/soft composite structure is studied using micromagnetic simulations. In this structure where the hard layers has strong perpendicular magnetic anisotropy, a domain wall can be nucleated in the soft layer due to the spin transfer torque effect. Depending on the magnetic properties of the layers and the current intensity the domain wall can induce the free layer reversal or be pinned by the hard layer. For these non-uniform magnetic configurations both bulk and interface spin transfer torques need to be considered. The potential reduction of the critical current observed in this geometry is of potential technological interest.

Frequency and Area Dependence of High-K/Ge MOS Capacitors

This paper investigates the capacitance-voltage (C-V) measurements of Ge/Al2O3/ZrO2/TiN MOS capacitors at different frequencies for square devices with different side lengths (10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 100 μm). The results show that the series resistance corrected capacitance (CC) for accumulation region is dependent on frequency, devices substrate and area. CC increases at a faster pace when a lower frequency (1KHz) is used than at a higher frequency (1MHz). Substantial decrease of CC per unit area is reported in Ge/High-K in comparison to Si/High-K devices when device area is increased. This decrease is attributed to the large non-uniform interface defect density and high leakage current associated with Ge.