Intrinsic Shear Research Articles

Exceptionally shear-stable and ultra-strong Ir-Ni-Ta high-temperature metallic glasses at micro/nano scales

Ir-Ni-Ta metallic glasses (MGs) exhibit an array of superior high-temperature properties, making them attractive for applications at high temperatures or in harsh environments. However, Ir-Ni-Ta bulk MGs are quite brittle and often fracture catastrophically even before plastic yielding, significantly undercutting their high-strength advantage. Here, we show that the Ir-Ni-Ta MGs are not intrinsically brittle, but rather malleable when the feature size is reduced to micro/nano-scales. All tested Ir-Ni-Ta MG micropillars with a diameter ranging from ~500 nm to ~5 µm display a large plastic strain above 25% (the maximum up to 35%), together with a yield strength up to 7 GPa, well exceeding the strength recorded in most metallic materials. The intrinsic shear stability of Ir-Ni-Ta MGs, as characterized by the normalized shear displacement during a shear event, is much larger than those malleable Zr- and Cu-based MGs. Our results suggest that Ir-Ni-Ta MGs are excellent candidates for micro/nanoscale structural applications used at high-temperature or extreme conditions.

Anisotropic Deformation Model for Hawkesbury Sandstone Incorporating Inherent Mobilised Shear Strength

An extensive study on modelling progressive Hawkesbury Sandstone degradation by anisotropic deformation subjected to monotonic loadings is presented and discussed in this study. Hawkesbury Sandstone was used due to its unique behaviour, which was initially assumed to be a uniform testing lithology with respect to grain size, compressive strength and stiffness. This study identified a theoretical approach to the anisotropic model of rock deformation. The model utilizes the stress-strain curve to derive the development of mobilised shear strength and applies it to the rock to simulate how it compresses in anisotropic. Monotonic loading tests were performed in triaxial conditions at variations of confining pressure, 4MPa and 8MPa. An increment of confining pressure was used to obtain elevation in the stress-strain curve. Progressive monotonic loading changed the mechanical characteristics of the rock; the level of the applied stress is compressed axially and then expanded laterally. During applied loading, the rock may experience damage or rock failure; the correlation between the magnitude of the mobilised shear strength and the axial stress associated with it is regarded as an intrinsic property in the rock mass. The stress-strain behaviour of rocks under anisotropic stress conditions can be predicted using this method. The mobilised minimum friction angle is used to determine the location of the mobilised shear strength envelope. The results reveal that the mobilised intrinsic shear strength is developed if the rock is forced to compaction. This is evidenced by the envelope rotating upward to the shear force envelopes during failing. Consequently, it can be deduced that the cementation (c') of the rock increases.

(Nanocarbons Division Best Poster Award - 3rd Place) Intrinsic Shear Strain in Graphene Heterostructures Detected Via Raman Spectroscopy

Graphene’s electronic band structure is extremely sensitive to small perturbations in its crystal lattice. Because of this it is vital to correctly characterize strain, doping and defects in graphene through nondestructive measurements. Characterization through Raman Spectroscopy allows this nondestructive measurement. Graphene on Transition Metal Dichalcogenides (TMDCs) show increased shear strain which is not caused by defects introduced through the transfer method. We prove this using Raman analysis of graphene samples on silicon oxide and TMDC. Graphene shows G peak splitting and shift indicative strain increasing on top of TMDC when compared to nearby graphene on silicon oxide.Acknowledgement: Authors acknowledge the JSNN, a member of the Southeastern Nanotechnology Infrastructure Corridor (SENIC) and National Nanotechnology Coordinated Infrastructure (NNCI), supported by the NSF (ECCS-1542174), The PSU Two-Dimensional Crystal Consortium – Materials Innovation Platform 2DCC-MIP, supported by NSF cooperative agreement (DMR- 1539916). Authors are grateful to Dr. S. Aravamudhan (JSNN) and Dr. J. Redwing (2DCC MIP).

Tridimensional nonhydrostatic transient rip currents in a wave-resolving model

Flash rips and surf eddies are transient horizontal structures of the order of 10 to 100 m, which can be generated in the surfzone in the absence of bathymetric irregularities. They are traditionally evaluated in a depth averaged setting which involves intrinsic horizontal shear instabilities and the direct generation of vorticity by short-crested waves. In this article, we revisit the processes of surf eddy generation with a new three-dimensional wave resolution model (CROCO) and provide a plausible demonstration of new 3D non-hydrostatic instability and turbulent cascade. We first present a quick overview of a compressible free surface approach suitable for nearshore dynamics. Its ability to simulate the propagation of surface gravity waves and nearshore wave-driven circulation is validated by two laboratory experiments. Next, we present a real world application from Grand Popo Beach, Benin, forced by waves with frequency and directional spreading. The generation of surf eddies by the 3D model differs from depth-averaged models, due to the vertical shear associated with shallow breaking waves. In this case, the generation of eddies from both horizontal shear instability and the breaking of short-crested waves is hampered, the former by stretching the alongshore current and the latter by inhibiting the inverse energy cascade. Instead, the vertical shear flow is subjected to forced wave group variability and Kelvin–Helmholtz type instability at an inflection point. Primary and secondary instabilities generate spanwise and streamwise vorticity connecting small-scale eddies to larger horizontal surfzone structures. Streamwise filaments, appearing as 5 m wide ribs or mini-rips, can extend beyond the surfzone but with moderate energy. These results appear consistent with the velocity spectra and observed patterns of tracers and suspended sediments at Grand Popo Beach. The timescale associated with the mean shear-induced turbulence is several times the wave period and suggests an intermediate range between breaker-induced turbulence and large-scale surf eddies.

Printability and bio-functionality of a shear thinning methacrylated xanthan–gelatin composite bioink

3D bioprinting is a recent technique that can create complex cell seeded scaffolds and therefore holds great promise to revolutionize the biomedical sector by combining materials and structures that more closely mimic the 3D cell environment in tissues. The most commonly used biomaterials for printing are hydrogels, however, many of the hydrogels used still present issues of printability, stability, or poor cell-material interactions. We propose that bioinks with intrinsic self-assembling and shear thinning properties, such as xanthan gum, can be methacrylated (XGMA) and combined with a bio-functional material such as gelatin methacryloyl (GelMa) to create a stable, cell-interactive bioink with improved properties for 3D bioprinting. These biomaterials have reduced viscosity under high shear and recover their viscosity rapidly after the shear is removed, retaining their shape, which translates to easier extrusion whilst maintaining accurate fidelity after printing. This was confirmed in printing studies, with measured normalized strand widths of 1.2 obtained for high gel concentrations (5+5 % XGMA-GelMA). Furthermore, the introduction of a secondary photo-cross-linking method allowed tuning of the mechanical properties of the hydrogel with stiffness between 15 and 30 kPa, as well as improving the stability of the hydrogel with retention of 75 % of its mass after 90 d. The hydrogel was shown to be biocompatible and bio-active with 97 % cell viability, and cell spreading after 7 d of culture for low gel concentrations (3+3 % XGMA-GelMA). Shear stresses were relatively low while printing (1 kPa) as a result of the shear thinning property of the material, which supported cell viability during extrusion. Finally, printed hydrogels retained high cell viability for lower gel concentrations, and showed improved cell viability for more concentrated hydrogels when compared to cells cultured in bulk hydrogels, presumably due to improved nutrient/oxygen diffusion and cell migration. In conclusion, stability and formulation of a XGMA-GelMA shear thinning composite hydrogel has been optimized to create a bio-functional bioink, with improved printability, and in vitro culture stability via secondary photo-induced cross-linking, making this composite a promising bioink for 3D bioprinting.

A novel evaluation method for thin films mechanical characterizations using cutting system

In this study, we suggest a nano-cutting system to determine the shear strength of the thin films using fracture mechanics analysis of the diamond blade. Based on Merchant's cutting model, we analyze the thin films cutting process with regard to shear angle and resistant forces as initiation of the yield in the chip to establish a direct correlation between the cutting forces and the shear strength. Validating the proposed method was conducted using homogenous polycarbonate disk showing similar shear strengths between different cutting directions. Next, we examined a thin copper electroplated film used in traces of printed circuit board. A thin copper film was examined and found the intrinsic shear strength (307.5 MPa) and adhesion force (44 N/m) between the film and substrate. The result was comparable with tensile strength values reported in the literatures. Finally, we used SEM to visually verify the feasibility of nano-cutting technique to determine thin film properties.

An orientation-stretch coupled model for entangled comb polymers

A semi-empirical constitutive equation is suggested for the model comb polymer with the purpose to simultaneously describe the intrinsic medium amplitude oscillatory shear (MAOS) behaviors and transient behaviors in start-up elongational experiments. The molecular stress and hierarchical relaxation of comb polymers are discussed on the basis of the orientation-stretch coupled conformation tensor of both backbone and arm, which are governed by the same evolution equation with different relaxation times. The discrete Baumgaertel–Schausberger–Winter spectrum is adopted for the backbone relaxation. The model has four parameters that are fully determined from the linear spectrum. The equation set is solved analytically by the perturbation method under MAOS and solved numerically under start-up extensional flows. The predictions on the nonlinear rheological behaviors are well consistent with the experiments.

Atomic nonaffinity as a predictor of plasticity in amorphous solids

Structural heterogeneity of amorphous solids present difficult challenges that stymie the prediction of plastic events, which are intimately connected to their mechanical behavior. Based on a perturbation analysis of the potential energy landscape, we derive the atomic nonaffinity as an indicator with intrinsic orientation, which quantifies the contribution of an individual atom to the total nonaffine modulus of the system. We find that the atomic nonaffinity can efficiently characterize the locations of the shear transformation zones, with a predicative capacity comparable to the best indicators. More importantly, the atomic nonaffinity, combining the sign of third order derivative of energy with respect to coordinates, reveals an intrinsic softest shear orientation. By analyzing the angle between this orientation and the shear loading direction, it is possible to predict the protocol-dependent response of plastic events. Employing the new method, the distribution of orientations of shear transformation zones in a model two-dimensional amorphous solids can be measured. The resulting plastic events can be understood from a simple model of independent plastic events occurring at variously oriented shear transformation zones. These results shed light on the characterization and prediction of the mechanical response of amorphous solids.

On the non-classical crystallographic slip in Tin+1AlCn MAX phases

In this work, we investigate the effect of atomic stacking on non-classical (non-Schmid) crystallographic slip in a class of atomically layered ternary carbides referred to as MAX phases with general formula Mn+1AXn, where the value of n represents the stacking sequence. To this end, we have carried out compression tests on single crystal micropillars of Ti3AlC2 with a range of crystallographic orientations and compared the results with that of Ti2AlC. Our results show that similar to Ti2AlC, Ti3AlC2 also exhibits non-classical crystallographic slip, wherein the crystallographic slip depends on both the resolved shear stress and the stress normal to the slip plane. However, for crystallographic slip, the intrinsic critical resolved shear stress in Ti3AlC2 is greater than Ti2AlC, while the frictional resistance in Ti3AlC2 is smaller than Ti2AlC. The implications of these findings on the macroscopic response of polycrystalline aggregates of these two MAX phases is also discussed.

On the low reinforcing efficiency of carbon nanotubes in high-performance polymer fibres

Driven by the exceptionally high mechanical properties of carbon nanotubes (CNTs), over the years an extensive research effort has been devoted to the reinforcement of high-performance polymer fibres with CNTs. However, to date, improvements in the strength of these fibres have been rather modest even for relatively high CNT contents. After a brief review of CNT reinforced polymer fibres, here, analytical and numerical finite element models will be used to show that these experimental findings are to be expected based on the intrinsic mechanical properties of these polymer fibres and CNTs, their aspect ratio and interfacial characteristics. Results show that for realistic CNT contents and aspect ratios, the extraordinary strength of CNTs cannot be easily fully exploited in high-performance polymer fibres like Dyneema®or Kevlar®. Even if CNTs are perfectly aligned, bonded and dispersed, the low intrinsic shear strength of these highly anisotropic polymer fibres limits effective stress transfer and nanotube reinforcement.

Structure and Shear Response of Janus Colloid-Polymer Mixtures in Solution.

We investigate the structure and rheological properties of dilute colloid-polymer mixtures at rest and under shear via molecular simulations that take into account hydrodynamic interactions. Mixtures of amphiphilic Janus colloids (JCs) and hydrophobic/amphiphilic polymers are considered for various solvent qualities and polymer concentrations. Free polymers, small polymer droplets, and hybrid aggregates coexist in mixtures with slightly hydrophobic homopolymers. As the solvent quality worsens, all polymers aggregate into small droplets, covered and stabilized by the JCs. In mixtures with amphiphilic polymers, we observe the coexistence of free polymers, purely polymeric micelles, and hybrid aggregates. At low shear rates, all mixtures exhibit a Newtonian-like response with intrinsic shear viscosities that are up to 2 times as large as of pure suspensions of nonadsorbing colloids at the same concentration. Furthermore, the mean aggregation number increases slightly due to the flow-enhanced collision of aggregates. At larger shear rates, however, the aggregates break up, the polymers align in the flow direction, and the mixtures exhibit shear-thinning. This shear-induced breakup occurs at stronger shear compared to pure JC suspensions, indicating that the adsorbed polymers reinforce the hybrid aggregates.

Stability, flocculation, and rheological behavior of silica suspension-augmented polyacrylamide and the possibility to improve polymer flooding functionality

In this study, the characterization and rheological behavior of silica suspensions in aqueous/polymeric media are investigated. The variation of silica nanoparticles size and concentration, polymer molecular weight and concentration, pH, valency, and concentration of electrolytes are considered for this purpose. The findings show that bridging flocculation of dispersed silica nanoparticle-augmented polymer solution increases with nanoparticle concentration, nanoparticle diameter, the charge of electrolyte, and electrolyte concentration. In contrast, it decreases with an increase in pH and polymer concentration. Also, the intrinsic shear viscosity of aqueous polymer solution increases with molecular weight, unlike the behavior of polymer solution in the presence of silica nanoparticles. The shear viscosity and the rate of bridging flocculation of the silica nanoparticle-augmented polymer solution primarily increase until it reaches a maximum and finally decreases with further increasing polymer molecular weight. In polymer high molecular weight and high concentration, the repulsion due to steric stabilization overcomes the interaction between two adsorbed polymer chains resulting in a stable form of suspension. By utilizing the proper conditions, core flooding experiments are designed and implemented to enhance the hydrolyzed polyacrylamide polymer flooding efficiency. Around 20–52% higher recovery was obtained for the silica nanoparticle-augmented polymer solutions with respect to the polymer flooding.

Electronic theoretical study on the influence of shear deformation on the electronic structure and optical properties of Li absorbed silicene

Based on the density functional theory, the influence of shear deformation on the electronic structure and optical properties of Li absorbed silicene system is studied by using the first-principles calculations. In the current research scope, it was found that after silicene adsorbs Li atoms, the silicene around the Li atoms has different degrees of distortion, and the band gap of the silicene increases. The calculation of binding energy shows that the shear deformation has little effect on the structural stability of Li absorbed silicene system. After intrinsic silicene shear deformation, the band gap increases with the increase of shear deformation.The band gap of Li absorbed silicene system decreases with the increase of shear deformation. The shear deformation causes the maximum absorption peak and the maximum reflection peak of the adsorption system to red shift.

High Temperature Microtribological Studies of MoS2 Lubrication for Low Earth Orbit

Molybdenum disulfide is one of the most common lubricant coatings for space systems but it displays enormous susceptibility to environmental conditions making it hard to predict performance throughout the entire lifetime. The majority of mechanisms for space operate in low Earth orbit where temperatures typically reach 120 °C along with exposure to highly reactive atomic oxygen which can be detrimental to lubricant performance. In the present study, a MoS2 lubricant coating is tested using friction force microscopy under different environmental conditions including air and dry nitrogen environments with temperatures ranging from 25 °C to 120 °C. The increased temperature was found to be beneficial for friction behaviour in air up to 100 °C as ambient humidity is removed from the contact, but higher temperatures become detrimental as increased reactivity leads to oxidation. These competing effects resulted in a minimum coefficient of friction at 110 °C in the air environment. The high temperature also increases the wear of the coatings as the intrinsic shear strength decreases with thermal energy which in turn disrupts tribofilm formation leading to increased friction. The run-in duration and magnitude are both found to decrease with temperature as the energy barrier to optimal reconfiguration is reduced. Finally, contextualization of the present findings for mechanisms operating in low earth orbit is discussed.

Frictional properties of polymer binders for Li-ion batteries

In this work, the frictional properties of various polymer binders were studied using atomic force microscopy to enhance the mechanical integrity of the silicon (Si) anode for lithium-ion batteries (LIBs). The binders used include polyacrylic acid (PAA), polyacrylonitrile (PAN), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), and polyvinylidene fluoride. The interfacial shear strength of the polymer binder was determined against Si to understand the contact shearing and sliding behaviors. The results showed that due to electrolyte immersion, the intrinsic interfacial shear strengths and pressure coefficients decreased by factors of 1.3–7.5 and 1.6–23.7, respectively. Decreases in mechanical and adhesion properties in the electrolyte may be responsible for the decrease in the frictional properties. The results also showed that topography-induced friction fluctuation became significant in the electrolyte due to an increase in the slope of the surface asperities, which is associated with polymer swelling. The Si anodes of LIBs containing polymer binders with relatively large intrinsic interfacial shear strengths and pressure coefficients in the electrolyte (PAA, PAN, PVA, and CMC) had high capacity retention. Given that a polymer binder with high interfacial shear strength helps maintain the mechanical integrity of the Si anode, PAA with high intrinsic interfacial shear strength may be preferred when the stress level is low during lithiation, while PVA with a large pressure coefficient may be advantageous when the stress level is high during lithiation. The outcome of this work suggests that the interfacial shear strength is a better polymer binder performance indicator than just considering mechanical and adhesion properties.

Thermophysical rock properties of the crystalline Gonghe Basin Complex (Northeastern Qinghai–Tibet-Plateau, China) basement rocks

The basement of the Gonghe Basin complex (GBC) mainly consists of plutonic rocks, which, in general are suitable for geothermal applications. Knowledge of the rock properties of the deep basement formations is of fundamental importance for unconventional geothermal applications such as enhanced geothermal systems. An outcrop analogue study at the margin of the GBC was conducted to improve the understanding of the petrophysical rock properties and enhance the data availability for numeric simulation and resource assessment approaches. In total 148 samples were derived from 21 sampling locations at the margin of the GBC area and mountain ranges within. Lithologically, the sample set was divided in three sample types: (1) syenogranite, (2) granite and biotite granite, (3) granodiorite. Petrophysical properties such as grain density, bulk density, porosity, intrinsic matrix permeability, compressional and shear wave velocities as well as thermal properties like thermal conductivity and thermal diffusivity were analyzed on oven-dry specimens under laboratory conditions (ambient temperature, atmospheric pressure). Unconfined compressive strength was additionally measured on selected samples. The resulting dataset shows averaged bulk densities ranging between 2.59 and 2.73 g cm−3 and porosities from 0.2 to 1.7%. Matrix permeability is lower than 1 × 10–18 m2. Averaged thermal conductivity ranges from 2.34 to 3.19 W m−1 K−1, compressional wave velocity from 3.6 to 6.2 km s−1 and unconfined compressive strength from 128 to 241 MPa. Petrophysical data are correlated with mineral content and grain size to show the influence of petrography on petrophysical properties. Although the petrophysical rock properties were analyzed at laboratory conditions and therefore deviate from in situ properties at reservoir conditions, the presented dataset enhances the knowledge of petrophysical rock properties within the study area for further geothermal applications. A first prediction of in situ reservoir conditions was performed on laboratory data based on empirically determined pressure and temperature dependencies of thermal conductivity, thermal diffusivity, specific heat capacity and compressional wave velocity.

An investigation into the effects of block size on the mechanical behaviors of bimsoils using variable-angle shear experiments

Shear resistance is critical to the stability of bimsoils (block-in-matrix soils), although the shear mechanical behaviors of bimsoil have been widely studied, the effect of rock block size on the rock–soil interactions, block occlusion and the interlocking effect during shearing are still not well understood. This work aims to investigate the effect of block size on the macro–meso shear failure mechanism of bimsoils using a specially designed variable-angle shear testing. Compaction test with different hammer counts was used to prepare the bimsoil samples having different rock block proportions and sizes, to roughly ensure the same compactness of soil matrix. Macroscopic shear force–displacement analysis combined with the mesoscopic 3-D laser technique was used to reveal the internal shear failure mechanism. The results show that block size has obvious effect on the shear strength parameters and morphology of shear failure plane. The peak shear force increases with the increase of block size, and the occlusion and interlocking phenomena become severe for the sample with relatively large block size. An index of fractal dimension was used to establish the relationship between block size and shear strength parameters, it suggests that the fractal dimension of the fracture surface is large for the samples having larger block size, and the shear strength of bimsoil is strongly related to the morphology of fracture surface. The improvement of shear strength for bimsoil was the results of interactions between soil matrix and rock blocks and induced by the intrinsic shear fracture mechanism.

Integrative experimental and numerical study of ASR affected nuclear concrete containments

The alkali silica reaction (ASR) is a complex multifaceted deleterious one with broad implications on the structural integrity of a nuclear concrete containment (NCC). When compounded with seismic excitation, the structural assessment is even more complex, specially when its intrinsic shear strength is not yet well understood. This paper will highlight 3 years of a holistic research on the pre-cited problem, highlighting the interaction of various tasks, while details can be found in referenced publications. The reported work is broken into four integrated parts: (a) Design of a reactive concrete mix representative of the one in an NCC and likely to expand sufficiently within 6 months; (b) Specimens expansion monitoring in terms of different dimensions and reinforcement ratios for a year; (c) Large-scale testing of shear specimens to evaluate both material (no reinforcement) and structural (with reinforcement) components to assess impact of ASR; and (d) 3D probabilistic nonlinear seismic analyses of an NCC subjected to 40 years of ASR expansion followed by multiple dynamic excitation. It will be shown that the true shear strength of concrete material is affected by ASR, and that this reduction will reduce the seismic resistance of an NCC.

A branched hydrophobicity associated with polyacrylamide based on silica: synthesis and solution properties

A branched hydrophobicity associated with polyacrylamide based on silica was synthesized successfully. The structure of the polymer was characterized by Fourier Transform Infrared Spectrometer (FT-IR), 1H Nuclear Magnetic Resonance (1H NMR) and Scanning Electron Microscopy (SEM). Several properties such as intrinsic viscosity, temperature resistance, salt tolerance, shear resistance and viscoelasticity of the polymer were evaluated. Experiment results had demonstrated that the introduction of vinyltriethoxysilane (VTS-SiO2) and branching molecular structure could endow the polymer with excellent temperature tolerance capability, salt and shear resistant capability.

The shear strength of Opalinus Clay shale in the remoulded state

The Opalinus Clay shale formation is considered as a potential host geomaterial for the Swiss deep geological repository for radioactive waste. It presents different facies and it is characterised by a multi-scale heterogeneous composition, by a typical fissile structure with well-defined bedding planes and by anisotropic hydro-mechanical behaviour. This peculiar complexity makes it difficult to assign a unique set of geomechanical parameters to the material. This paper presents an experimental study aimed at characterising the lowest values of the shear strength parameters. In this sense, the shear behaviour was investigated on remoulded samples where the fabric and the diagenetic bonds of the intact material were eliminated. The results of a triaxial test campaign belonging to different facies of Opalinus Clay shale (“shaly” and “sandy” facies) are presented. Furthermore, with the aim to study the mechanical properties of fault zones in Opalinus Clay, the effect of large cumulated shear displacements on shear strength was also investigated. Ring shear tests were performed to determine the residual shear strength. The main geotechnical property which discriminates the different facies of Opalinus Clay is the grain-size distribution; in this sense, well-defined correlations between this intrinsic characteristic and shear strength angles of the remoulded material are presented.