Interface Roughness Research Articles

Effect of roughness on shear behavior of interface between cemented paste backfill and rock

The interaction between cemented paste backfill (CPB) and rock at their interface plays a crucial role in the stability of underground backfill structures. Considering the interface roughness could have a significant influence on the shear behavior and mechanical properties of the interface, a series of laboratory direct shear tests were carried out on the CPB-rock interface with various roughnesses. The results indicates that the interface roughness and normal stresses have a remarkable effect on the interfacial shear behavior, with typical stress-shear displacement curves that could be classified into three types depending on the peak and post-peak characteristics. Compared to the smooth interface, the shear strength increases with increasing roughness, owing to the enhancing interlocking effect, which is confirmed by digital image correlation (DIC) in micro views. In addition, the shear contraction observed at the smooth interface changes to shear dilatation at the rough interface, which is caused by wider distribution and higher adhesion of CPB asperities, as observes by using 3D laser scanning technology. Furthermore, a theoretical model for the shear strength, taking into account the influence of interface roughness, is developed to assess its effect on shear strength. The experimental results and the theoretical model presented in this paper will contribute to better understand the interaction mechanism and predict the shear strength of the interface.

Enhancement of electron transport mobility in GaAs/InGaAs asymmetrically doped narrow quantum well pHEMT structure

We study the effect of asymmetric doping concentrations on the electron mobility μ in GaAs/InGaAs-based single quantum well (SQW) as well as double quantum well (DQW) pseudomorphic high electron mobility transistor (pHEMT) structures. Unequal doping in the substrate and surface barriers (n d1 and n d2 ) causes asymmetric distributions of subband wave functions, ψ 0 and ψ 1, which influence the subband scattering rate matrix elements (SSRME), thereby affecting the subband mobility μ n . For narrow well widths (w w ), in SQW structures, mostly a single subband is occupied. We show that an increase in n d2 , keeping n d1 fixed, enhances μ nonlinearly. The interface roughness (ir-) scattering mostly dominates μ in thin wells (w w < 70 Å), while generally, μ is determined by ionized impurity (ii-) scattering and to some extent by alloy disorder (ad-) scattering. The influence of ir-scattering enhances, while ad-scattering diminishes, by reducing n d2 . For DQW, a double subband is occupied. In a symmetric DQW structure at resonance, n d1 = n d2 , ψ 0 and ψ 1 equally extend into both the wells. For a minor variation, say n d1 > n d2 , ψ 0 mostly lies in one well while ψ 1 is in the other well. In the case of n d1 < n d2 , the distribution reverts. The substantial changes in ψ 0 and ψ 1 influence the intra- and inter-SSRME differently through intersubband effects, leading to nonlinear μ n as a function of n d2 . Taking n d1 + n d2 = 3 × 1018 cm−3, we show that for w w1 = w w2 = 80 Å, a shallow dip in μ occurs at n d1 = n d2 = 1.5 × 1018 cm−3. Whereas, for w w1 = 60 Å and w w2 = 100 Å, the dip in μ occurs near the corresponding resonance, n d1 = 2.3 × 1018 cm−3 and n d2 = 0.7 × 1018 cm−3. Our results of nonlinear μ can be utilized for performance analysis of pHEMT.

Experimental and theoretical study of the shear strength of ice-rock interface

Frost heave failure of fractured rock is an important and challenging problem faced by geotechnical engineering structures in cold regions. The shear strength of the ice-rock interface is a critical parameter in understanding this type of failure. In this study, we conducted shear tests on ice-rock interfaces to examine effects of freezing temperature, normal stress, and interface roughness on the shear strength of the interface. Furthermore, we derived a theoretical model for the shear strength of the ice-rock interface considering these three influencing factors. Comparisons between the theoretical and experimental results confirmed that the shear stress at the ice-rock interface was composed of two components, i.e., the ice-rock particle bonding stress and the frictional stress caused by the rough interface. The freezing temperature mainly affected the bonding stress of ice-rock particles, while the normal stress and the roughness affected the frictional stress. The ice melting happened during the shearing process, leading to the appearance of a second or third peak in the stress-strain curve.

Mechanical behavior and constitutive relationship of bond interface in steel plate-reinforced shield tunnels

In order to explore the mechanical properties and failure mechanism of the bond interface of steel plate reinforced shield tunnels, a series of uniaxial tensile and uniaxial shear experiments were conducted in this study. The impact of bond interface parameters on the mechanical properties of the reinforced interface was mainly analyzed, including the failure mode, ultimate bearing capacity, average bond strength, and stress-strain relationship of the bond interface. To enable numerical simulation of the mechanical behavior at the bond interface, a stress-strain constitutive relationship equation for the bond interface is established using the least squares method. The main conclusions are as follows: For steel plate-concrete interface bonded with epoxy resin, the shear resistance of the bond interface generally surpasses the tensile resistance under the same interface parameters. Tensile load predominate leads to the cohesive failure of the concrete while the interface layer remains undamaged. In contrast, shear load mainly results in the detachment between the steel plate and the interface layer. The ultimate bearing capacity and bond strength of the interface can be enhanced by decreasing the interface thickness or increasing the interface roughness. Moreover, an expansion bolt can further increase the mechanical property of the bond interface, and the improvement effect intensifies with higher expansion bolt grades. The stress–strain curve of the bond interface can be divided into three stages with elastic stage, softening stage and debond stage. The main difference of stress–strain curve under different bond interface parameters lies in the stage before the softening of the bond interface. The interface stress-strain curve is primarily influenced by the thickness of the bond interface and the grade of expansion bolts, whereas the roughness of the concrete surface has minimal effect.

Approximate symplectic approach for mistuned bladed disk dynamic problem

A blade disk system plays a crucial role in the energy conversion efficiency of turbomachinery. Generally, a bladed disk is designed as a tuned system, which implies that the dynamic behaviors of all the blades are identical. In practice, there are some differences between the blades, known as mistuning, that can result in localized vibration. Thus, in this study, an approximate symplectic method developed to reproduce the vibration localization in a mistuned bladed disk system, that can provide guidance for designing vibration control strategies for the system. Considering the morphological characteristics of the interface roughness and the dynamic/stickiness characteristics of the sliding joint surface, an improved dry friction model is established to describe the coupling effects between the blades. Considering the micro-dynamic behaviors of the multi-joint surfaces, the dynamic problem of the entire bladed disk system is formulated as a set of ordinary differential equations (ODEs). An approximate symplectic method is developed in the Hamiltonian framework to simulate the vibration of each blade in the mistuned bladed disk system. From the numerical results reported, the phenomenon of vibration localization in the mistuned bladed disk system is reproduced in the comparison with the results in the tuned bladed disk system. In addition, the influences of the initial positive pressure, contact angle, and roughness of the surfaces on the strength of the vibration localization are revealed in detail in the numerical simulations.

Effect of interface roughness on mechanical properties of layered cemented tailings backfill

Research on the roughness parameters of the layered interface of the layered cemented tailings backfill (LCTB) is of great significance to improve the cementation quality of layered layers and reduce the strength reduction rate caused by layering for the safety and stability of the mine structure. Using the sedimentation mechanism of tailing sand particles, different roughness interfaces with different solid densities (SDs) and number of layered layers were designed, and the influence mechanism of interface roughness on the cementation quality of layered layers was studied by using uniaxial compression test, surface roughness detection and particle size detection. The results show that the existence of stratified surfaces can significantly reduce the uniaxial compressive strength (UCS) of the LCTB, which is defined here as the Stratified reduction rate (SRR).When the number of stratified layers is constant, the strength reduction rate caused by stratified layers decreases with the increase of SD, and the increase of SD will increase the shear resistance of the coarse particles in the slurry, making it less prone to segregation and subsidence. As a result, the larger the proportion of coarse particle size distribution on the layered surface, the macroscopic surface roughness increases. The SRR has a good linear fitting relationship with surface roughness Ra, and the SRR decreases with the increase of Ra, indicating that to a certain extent, the greater the surface roughness of the stratified plane, the better the cementation quality of the delamination surface, and the weaker the reduction effect of the delamination on the strength of the LCTB.

Research on ultrasonic assisted press-fit assembly of small interference fits

Interference fits are widely used in aerospace, precision instruments and other fields. Press-fit assembly is one of the traditional assembly methods for interference fitting parts. Wear during assembly will affect the performance of interference components and the service life of marine equipment. Ultrasonic assisted press-fit can significantly reduce the press-mounting force of an interference fit. However, its effect on connection quality is rarely studied. The mechanism of ultrasonic assisted press-fit is unclear. In this paper, ultrasonic assisted press-fit was simulated and experimentally studied. The effects of ultrasonic vibration on heat generation, press-mounting force, connection strength, and interface wear were analyzed and discussed. Through analogy analysis with similar ultrasonic assisted machining processes, the mechanism of ultrasonic assisted press-fit was revealed. The results show that the superimposed ultrasonic vibration can effectively reduce the joining force (up to 33.5%), and increase the connection coefficient from 10% to 40%. This is due to stress superposition, friction reduction and acoustic softening that reduces interface wear. The increase of the interface roughness Rz from 3.681 to 4.586 μm confirms this analysis. Furthermore, the ultrasonic vibration can effectively reduce the material plastic flow of contact interface. This study reveals the significant advantages of ultrasonic assisted press-fit assembly (UAPA) method and provided a basis to understand the underlying mechanisms of UAPA.

Effect of substrate heterogeneity and topology on epithelial tissue growth dynamics.

Tissue growth kinetics and interface dynamics depend on the properties of the tissueenvironment and cell-cell interactions. In cellular environments, substrate heterogeneity and geometry arise from a variety factors, such as the structure of the extracellular matrix and nutrient concentration. We used the CellSim3D model, a kinetic cell division simulator, to investigate the growth kinetics and interface roughness dynamics of epithelial tissue growth on heterogeneous substrates with varying topologies. The results show that the presence of quenched disorder has a clear effect on the colony morphology and the roughness scaling of the interface in the moving interface regime. In a medium with quenched disorder, the tissue interface has a smaller interface roughness exponent, α, and a larger growth exponent, β. The scaling exponents also depend on the topology of the substrate and cannot be categorized by well-known universality classes.

A-C/GeTe superlattices: Effect of interfacial impedance adaptation modeling on the thermal properties

Recently, nanostructuration has been proposed to improve the performance of phase change memories. This is the case of superlattices composed of amorphous carbon and crystalline germanium telluride, which we have investigated by molecular dynamics. For this, a modified Stillinger–Weber potential is adapted to reproduce their stiffness contrast/impedance ratio. In order to study the effect of the interface interaction, two sets of parameters are used to model the interfaces with different interactions between the two materials using the properties of the softer material or the average properties between the two creating an adaptation of impedance across the layers. The effects of interface roughness and carbon diffusion at grain boundaries are studied. Using equilibrium molecular dynamics as well as the propagation of wave-packets, we show first that without impedance adaptation, the anisotropy is high, and the roughness has a marked impact on the properties. However, the introduction of impedance adaptation destroys those effects on the thermal conductivity. Finally, we show that the periodic texturing of the interface increases the transmission of in-plane transverse phonons.

A new method for constructing three dimensional rough surface topography with expected bearing capacity

Surface bearing ratio tp(c) or tp curve is often used to evaluate the bearing contact performance of rough surfaces, but currently it is difficult to invert the surface topography with the expected surface bearing ratio tp(c). Combining the definition of tp curve and the key coefficients in random process theory, roughness characteristic parameters (RCP) that directly regulate tp curve are found out to provide parameters for the active design model with expected tp(c). By calculating the surface height matrix satisfying the expected tp(c) and RCP with genetic algorithm, the active design method of surface topography gets constructed. Surface tp curves of grinding, shot peening, barrel finishing and active design are compared to verify the reliability of the method and the versatility of RCP. The results show: 1) RCP of tp curve are Sa (arithmetic mean height), Sq (root mean square height), Ssk (skew), Sku (kurtosis), Sp (maximum peak height) and Sv (maximum pit depth); 2) The surface topography of the expected tp(c) is basically consistent with the measured tp curve. The maximum relative errors of tp(c) and Sa are 5%, 1%, respectively. And the average relative errors are only 1.4% and 0.5%. The regulatory parameters influence in RCP on the surface bearing capacity is ranked as follows: Sa, Ssk, Sku, Sv, Sp. The new active design model provides method for constructing the expected bearing capacity surface and roughness interface mechanics’ study.

Tuning of exchange bias by regulating the microstructural parameters in Ni81Fe19 (5, 8, 11, 14, 17, and 20 nm)/Ir7Mn93(10 nm) bilayers probed using magnetoresistance

The investigation and tunning of positive exchange bias (PEB) and negative exchange bias (NEB) are reported at room temperature (RT) and low temperature (20 K), respectively, in a series of top-pinned Ni81Fe19(tFM = 5, 8, 11, 14, 17, and 20 nm)/Ir7Mn93(10 nm) polycrystalline heterostructure thin films grown in the presence of a 1 kOe in situ magnetic field by systematically controlling the microstructural parameters such as thickness, roughness, and crystallite/grain size. On decreasing the thickness (roughness) of NiFe from 20 nm (0.49 nm) to 5 nm (0.28 nm), an enhancement in PEB and NEB is observed from +12 to +22 Oe and −300 to −556 Oe at RT and 20 K, respectively. It is observed that both exchange bias and coercivity substantially depend on the atomic scale roughness of the interface width (NiFe/IrMn). The representative plane-view of transmission electron microscopy (TEM) measurements revealed the enhanced antiferromagnet (AF) grain size on decreasing the thickness of ferromagnetic, whereas cross-sectional TEM studies exhibited the sharp interfaces in the bilayer samples after magnetic annealing. A unique correlation between the training mechanism and the degree of asymmetry is established. Further, the training measurement data are fitted with various theoretical models that support the fact that not only interfacial but also bulk AF spins play a vital role in the exchange bias. Thus, the present study reveals the microstructural insights by varying the thickness of NiFe to address the unresolved issues of the EB by directly correlating it with interface roughness and the crystallite/grain size of AF in it, probed using the magnetoresistance technique.

Determination of SIFs and application of a SIF-based fracture criterion for concrete-rock interface under sustained loading

This study proposes an effective method to determine the stress intensity factors (SIFs) of the interface crack considering the viscoelasticities of the bilateral materials and verifies the feasibility of the initial fracture toughness-based fracture criterion for the concrete-rock interface under sustained loading. Firstly, low-level sustained loading tests were conducted on the composite concrete-rock specimens with respect to two interface roughness degrees and two sustained load levels less than the initial cracking load. Then, an implicit creep equation was employed to characterise the viscoelasticities of bilateral materials and then calculate the mechanical responses of the concrete-rock interface in the low-level sustained loading test. The SIFs of the interface crack under sustained loading were determined by using the elastic strain energy density ahead of the crack tip. By averaging the SIFs over the radius of the core region of the crack tip, the representative SIFs under sustained loading were obtained. The test results indicated that the SIFs showed decreasing tendencies under sustained loading, and the initial fracture toughness can be considered as a material property of the concrete-rock interface. The initial fracture toughness-based fracture criterion was verified to be feasible to determine the initial cracking status of the concrete-rock interface under sustained loading. In addition, due to the reductions of the SIFs under sustained loading, additional loads were required to compensate the losses of the SIFs, leading to the enhancement of the initial cracking loads after experiencing the sustained loading.

Uniform, Strain-Free, Large-Scale Graphene and h-BN Monolayers Enabled by Hydrogel Substrates.

Translation of the unique properties of 2D monolayers from non-scalable micron-sized samples to macroscopic scale is a longstanding challenge obstructed by the substrate-induced strains, interface nonuniformities, and sample-to-sample variations inherent to the scalable fabrication methods. So far, the most successful strategies to reduce strain in graphene are the reduction of the interface roughness and lattice mismatch by using hexagonal boron nitride (h-BN), with the drawback of limited uniformity and applicability to other 2D monolayers, and liquid water, which is not compatible with electronic devices. This work demonstrates a new class of substrates based on hydrogels that overcome these limitations and excel h-BN and water substrates at strain relaxation enabling superiorly uniform and reproducible centimeter-sized sheets of unstrained monolayers. The ultimate strain relaxation and uniformity are rationalized by the extreme structural adaptability of the hydrogel surface owing to its high liquid content and low Young's modulus, and are universal to all 2D materials irrespective of their crystalline structure. Such platforms can be integrated into field effect transistors and demonstrate enhanced charge carrier mobilities in graphene. These results present a universal strategy for attaining uniform and strain-free sheets of 2D materials and underline the opportunities enabled by interfacing them with soft matter.

Tuning of SiO2/Si interface by a hybrid plasma process combining oxidation and atom-migration

As a common oxide-semiconductor interface, SiO2/Si plays an important role in silicon-based electronics and optoelectronics. In order to effectively obtain an ultra-smooth and thin SiO2/Si interface, a hybrid tuning process based on inductively coupled plasma (ICP) was proposed, which combined oxidation (plasma-OX) and atom-migration manufacturing (plasma-AMM). In plasma-OX process, a thick oxide film was rapidly prepared on Si wafer surface in 2 min, which included a SiO2 layer on the top and a SiOx (x < 2) layer between the top layer and the bulk crystalline silicon (c-Si). In subsequent plasma-AMM process, ICP steadily delivered energy to the Si wafer surface and induced the migration of unsaturated Si from SiOx layer to c-Si, which enhanced the crystallization of silicon wafer. The roughness of SiO2/Si interface was reduced to Sa 0.171 nm at 620 W in 5 min. However, a 2–3 nm thickness SiOx layer still existed, and several defects causing by residual thermal stress can be observed. Further optimizing plasma-AMM process by setting multi-step slow cooling, the SiOx layer can be almost completely decomposed. The interface roughness Sa was reduced to <0.1 nm and the interface thickness was reduced to 1–2 atom layer. Both OX and AMM process were conducted in the same setup, which is convenient for switching. This study proposed and demonstrated the feasibility of a hybrid plasma tuning process, which provided an efficient tuning technology at atomic level for semiconductor interface.

Growth and optical performance of short-period W/Al and polished W/Si/Al/Si multilayers

Short-period multilayer mirrors are used in wavelength-dispersive x-ray fluorescence to reflect and disperse elements in the O-Kα– Al-Kα range. In this work, we investigated sputter-deposited 2.5 nm W/Al with 20 periods. Our results show that W/Al is a poor reflector due to a combination of high interfacial roughness and strong W–Al intermixing. To address this, we introduced 0.5 nm Si seed layers at the W-on-Al and Al-on-W interfaces each consecutive period, while reducing the Al thickness from ∼2.0 to ∼1.0 nm. The Si seed layers significantly reduced interfacial roughness and W–Al intermixing, which led to an increase in the reflectance of the first Bragg peak at λ = 0.154 nm. To further reduce interfacial roughness, ion beam polishing of the top Si layer was applied at each period. The resulting structure of W/Si/Al/Si with ion beam polishing showed that the reflection coefficient of the first Bragg peak at λ = 0.154 nm was comparable to that of standard W/Si. These findings demonstrate the effectiveness of seed layers combined with polishing techniques in synthesizing smooth, high-reflectance multilayers containing two materials that are otherwise challenging to synthesize.

Nonequilibrium interfacial properties of chemically driven fluids.

Chemically driven fluids can demix to form condensed droplets that exhibit phase behaviors not observed at equilibrium. In particular, nonequilibrium interfacial properties can emerge when the chemical reactions are driven differentially between the interior and exterior of the phase-separated droplets. Here, we use a minimal model to study changes in the interfacial tension between coexisting phases away from equilibrium. Simulations of both droplet nucleation and interface roughness indicate that the nonequilibrium interfacial tension can either be increased or decreased relative to its equilibrium value, depending on whether the driven chemical reactions are accelerated or decelerated within the droplets. Finally, we show that these observations can be understood using a predictive theory based on an effective thermodynamic equilibrium.

Reaction wetting behaviour of improved Ti-based brazing fillers on carbon/carbon composites at 1423–1573 K

Ti-based brazing fillers for carbon/carbon composite (C/C) connections are very promising; however, there is a lack of research on this topic. The wetting behaviour and mechanism of Ti-Cu-Si fillers on C/C at 1423–1573 K were investigated in this study. When the temperature was less than 1473 K, the contact angle decreased with time because of TiC layer formation, which exhibited a large interfacial ideal adhesion work (Wad) of 9.815 J/m2. However, the contact angle increased abnormally over time when the temperature exceeded 1473 K. This nonwetting behaviour can be attributed to the formation of SiC and Ti3SiC2 phases, which naturally increased the interfacial energy and surface roughness and decreased Wad (Wad of TiCu/SiC was reduced to 3.669 J/m2), and this hinders the spread of the liquid on the C/C substrate. These results suggest that increasing the temperature does not necessarily imply an improvement in wettability, thereby providing a new idea for developing high-temperature solders for C/C welding.

Shear bond between existing concrete and high‐strength fiber reinforced overlay: Influence of substrate strength and interface roughness

AbstractBonded concrete overlays are widely used for strengthening and repair of concrete members. The aim of a concrete repair is to restore the load‐carrying capacity and stiffness of a concrete member, and to extend the service life of a structure. The bond between substrate and overlay is one of the main factors concerning the serviceability of a composite member consisting of concrete of different ages. This paper aims at better evaluating, through an extensive experimental program, the shear bond strength between existing concrete and a subsequently applied fiber reinforced overlay. The main purposes of this test program are to study the influence of the substrate strength and of the substrate surface roughness on the interface bond strength between a substrate and overlay concrete. A refinement of a novel bond test, proposed by some of the authors of this paper, is also implemented. Results indicate that there is an increase in the bond strength with an increase in the substrate compressive strength. On the other hand, the results suggest that, for the substrate strength classes investigated, the surface roughness does not influence the interface bond strength.

Structural, electrical, morphological, and interfacial characteristics of lattice-matched InAlN/GaN HEMT structure on SiC substrate

This work highlights the influence of surface properties, on the characteristics of InAlN/GaN based high electron mobility transistor (HEMT) structures grown on the SiC substrate by metalorganic vapor phase epitaxy. The growth parameters, i.e., reactor pressure and V/III ratio were tuned to improve the morphological and two-dimensional electron gas (2DEG) characteristics of the HEMT structure. It was found that V/III ratio plays a significant role in improving surface morphology and 2DEG properties without altering average indium composition. It was also found that 2DEG properties are highly sensitive to surface morphology and its features. The step flow smooth surface morphology with very low surface and interface roughness was observed in optimized lattice-matched InAlN/GaN HEMT structures. The sheet resistance of ∼170 Ω/sq with good 2DEG concentration (∼2.4 × 1013 cm−2) and 2DEG mobility (∼1500 cm2/V s) was achieved in the optimized lattice-matched InAlN/GaN HEMT structure. A comparison between different barrier-based HEMT structures, i.e., lattice-matched InAlN/GaN and strained AlGaN/GaN, was also discussed. Their structural, electrical, morphological, and interfacial characteristics were compared.

A simple formula for coherent specular reflection loss of underwater sound from rough ocean surfaces

The interaction of underwater sound with rough sea surfaces affects its propagation. The interaction may involve several coupled mechanisms: (1) a rough air-sea interface scatters and spreads the incident sound energy over a range of angles, (2) entrapped sub-surface air bubbles absorb and scatter sound energy, and (3) medium of bubble clouds refract sound energy upwards. In this paper, we ignore the effect of bubbles and consider the effect of rough air-sea interface only. We further limit our consideration to the coherent component in the specular direction. Two simple closed-form formulas are often used to model the coherent reflection loss from rough ocean surfaces. One is derived from perturbation approximation and suitable for smaller grazing angles. The other is from Kirchhoff approximation and suitable for larger grazing angles. More accurate approximations over a wide-range of grazing angles require numerical evaluation of integrals or complex special functions. In this work, we simplify and adapt earlier results by other authors to obtain a simple expression that transits from the perturbation to the Kirchhoff formulas as grazing angle increases. The new simple analytical formula is easy to use and compares well with results from complex numerical methods.