Low Shear Resistance Research Articles

Discrete element analysis of earthquake surface fault rupture through layered media

The influence of soil inhomogeneity on earthquake surface fault rupture is analyzed using the discrete element method (DEM). Particle assemblages are produced with layers having contrasting relative density. Similar to that observed in homogenous soil simulations, loose layers tend to absorb the localized shear deformation from underlying dense layers and disperse it over a broader area. However, the rupture can re-localize as it moves into an overlying dense layer. The ground surface deformations produced by fault rupture through layered soils are bounded by the ground surface deformation produced in homogeneous soil. The presence of a thin layer does not significantly alter the path of fault rupture propagation of a steeply dipping dip-slip fault. Conversely, a loose thin layer within dense soil can divert the path of fault rupture propagation during shallow reverse fault rupture by providing a kinematically compatible path of low shear resistance. Stresses are homogenized within the simulations to highlight the capability of DEM to capture the response of granular materials in scenarios that are difficult to achieve physically in the laboratory.

Hexagonal boron nitride (h-BN) nanosheets as lubricant additive to 5CB liquid crystal for friction and wear reduction

The h-BN nanosheets (h-BNn) was used as an additive to 4-n-pentyl-4′-cyanobiphyl liquid crystal (5CB), and its influence on tribological performance was investigated on a ball-on-disc tribometer for steel/steel contacts. Micron h-BN (h-BNμ) was used as a reference additive, and it is found that h-BNn has superior lubricating effects than h-BNμ. When h-BNn concentration is 0.01 wt%, compared to pure 5CB, the friction coefficient and the wear scar diameter on the ball reduced by 15.5% and 33.8%, respectively. Raman spectra analysis shows that h-BNn entered sliding interface, forming a low shear resistance protective layer on wear surfaces.

Orthogonal tests of the lubricating performance of SnO2 nanoparticles in poly-alfa-olefine oil

The tribological properties of SnO2 nanofluids were investigated using ball-on-plate reciprocating sliding wear tests. It was found that the coefficient of friction was reduced by 34.9% using 3 wt% SnO2 nanoparticles. The wear width and wear depth were reduced by 42% and 50.1%, respectively, using 2 wt% SnO2 nanoparticles. In the orthogonal tests, the frequency had the greatest influence on the friction and wear loss. Additionally, the optimal working conditions were a normal load of 50 N, a motion frequency of 1 Hz, and a surface roughness of 500–600 nm. Additionally, the excellent tribological performance of SnO2 nanofluids could be attributed to the formation of a tribo-film with a low shearing resistance due to the oleic acid and a protective layer due to the embedment of SnO2 nanoparticles.

Microstructure effects on the machinability behaviour of Ti6Al4V produced by Selective Laser Melting and Electron Beam Melting process

Additive Manufacturing (AM) is gaining widespread attention over the last decade in the areas of product development and prototyping, across aerospace and medical domains. Nevertheless, the built parts are near-net shaped that usually require a machining finish to improve the surface quality and operational life.The current study aims to document the machinability behaviour of the Ti6Al4V parts fabricated by the AM process, which is based on powder bed fusion, namely, Selective Laser Melting (SLM) and Electron Beam Melting (EBM). Further, machinability parameters are correlated with the microstructure and mechanical properties of the material. Face milling operation is performed under finishing conditions to study the response on the cutting forces. The effect of Hot Isostatic Pressing (HIP) and the influence of the build direction on microstructure and machinability have been investigated for the two AM processes. The effect of crystallographic textures and microstructure morphology of α and reconstructed prior β phases on the mechanical properties was studied using shear tests. It was observed that the SLM process primarily produced homogenous and fine α lath structures with less grain boundary α (αGB) grains, leading to low shear resistance and hence generated low cutting forces. On the other hand, the EBM process produced microstructures with variable morphologies, including more grain boundary alpha (αGB) grains and widmenstatten structures which resulted in a higher shear resistance and forces. The results show a striking influence of the microstructure induced by the type of the AM process, build orientation, and the subsequent heat treatment on the shear resistance and their ability to be machined. Further, the crystallographic textures were not strong for both processes and seem not to impact the machining process. The results highlight a strong “process – property” link which demands optimization of the cutting process for the type of the AM process and the resulting microstructure.

Correlation between the formation of tribofilm and repassivation in biomedical titanium alloys during tribocorrosion

Titanium alloys are widely used in the field of orthopaedics, however, poor tribological performance arising from the low shear resistance and weak protection of the oxide layer limits their applicability. In this work, the tribocorrosion behaviour of novel β and α + β biomedical titanium alloys were studied in bovine serum solution under open circuit potential. Ti-5Mo-Fe-3Sn and Ti-6Al-4V ELI alloys were found to have the capability to repassivate when testing at a slower sliding speed. Scanning and transmission electron microscopy results revealed that the repassivation was mainly associated with the greater tribofilm formation on the worn surface, rather than an oxide film. The tribolayer performed as a solid lubricating film, which stabilised the coefficient of friction.

Study on the effect of grain morphology on shear strength in granular materials via GPU based discrete element method simulations

The majority of publications in DEM use simplified particle shapes, in this study we use polyhedral shapes to determine the effect of particle shape on shear strength via a direct-shear test. Grain aspect ratio was found to be the primary determinant of shear strength with elongated polyhedra having a lower shear resistance. Grain irregularity also had a significant effect, shapes with isotropic contacts angles had the highest shear strength. The variability of granular material behavior due to shape was demonstrated by non-convex shapes re-orientating to jam in certain cases. Shapes with multi-stable packed orientations were found to offer the highest resistance to reordering under localized vibration.

Numerical characterization of slope rock mass through considerations of hydraulic and mechanical properties

In this paper, the slope rock mass is numerically characterized by considering hydraulic and mechanical properties using two distinct element models. The flow rate and permeability are calculated from localized fluxes through rock masses with varied fracture orientations and scales. Flow models suggest that rock mass permeability is predominantly controlled by fracture size. High rock mass permeability is simulated when the fractures are enlarged. Hydraulic anisotropy is captured when the difference in the fracture size is amplified. The mechanical properties of the slope rock mass are characterized through numerical shearing tests. In general, high permeability corresponds to low shearing resistance of the rock mass. The fractures obliquely distributed to shearing direction lead to additional shearing resistance. Enlarged fractures reflect high conductivity of the rock mass structure and decrease the shearing resistance. Mechanical anisotropy of the rock mass is also captured and attributed to the difference in the fracture size. The relations between hydraulic and mechanical properties are examined, and negative exponential relations are fitted between rock mass cohesion and permeability. The research introduces permeability as reference to slope rock mass characterization and provides reliable methods to this challenging issue.

Superior Wear-Resistance of Ti3C2Tx Multilayer Coatings.

Owing to MXenes' tunable mechanical properties induced by their structural and chemical diversity, MXenes are believed to compete with state-of-the-art 2D nanomaterials such as graphene regarding their tribological performance. Their nanolaminate structure offers weak interlayer interactions and an easy-to-shear ability to render them excellent candidates for solid lubrication. However, the acting friction and wear mechanisms are yet to be explored. To elucidate these mechanisms, 100-nm-thick homogeneous multilayer Ti3C2Tx coatings are deposited on technologically relevant stainless steel by electrospraying. Using ball-on-disk tribometry (Si3N4 counterbody) with acting contact pressures of about 300 MPa, their long-term friction and wear performance under dry conditions are studied. MXene-coated specimens demonstrate a 6-fold friction reduction and an ultralow wear rate (4 × 10-9 mm3 N-1 m-1) over 100 000 sliding cycles, outperforming state-of-the-art 2D nanomaterials by at least 200% regarding their wear life. High-resolution characterization verified the formation of a beneficial tribolayer consisting of thermally/mechanically degraded MXenes and amorphous/nanocrystalline iron oxides. The transfer of this tribolayer to the counterbody transforms the initial steel/Si3N4 contact to tribolayer/tribolayer contact with low shear resistance. MXene pileups at the wear track's reversal points continuously supply the tribological contact with fresh, lubricious nanosheets, thus enabling an ultra-wear-resistant and low-friction performance.

Experimental evaluations on tribological performance of oil-based WS2 nanofluid applied on steel/brass friction pairs

The present research evaluated the tribological performance of oil-based WS2 nanofluids applied on steel-brass friction pairs. It was found that the coefficient of friction could be reduced by up to 39%, and the wear width and depth could be reduced by up to 28.7% and 66.4% using 1 wt% WS2 nanofluid. While using the WS2 nanofluids, almost no adhesive wear was detected on the worn surfaces. By analyzing the chemical compositions, carbon percentage increased after engaging the oleic acid which suggested tribo-films with low shear resistance were formed. In addition, elements of sulfur and tungsten were found within the wear track lubricated by WS2 nanofluids. It was believed that the WS2 nanoparticles were involved in the formation of the tribo-layers and mixed with the oleic acid tribo-films to improve the tribological behavior. Moreover, the tribo-layers produced by the WS2 nanoparticles could provide solid lubricating and mending effects on the mating surfaces.

Tribological properties of Al2O3/WS2 oil-based composite lubricant utilized on steel-brass frictional couples

The tribological properties of Al2O3/WS2 composite lubricant were examined by using a ball-on-plate reciprocating sliding wear test configuration utilizing PAO6 base fluid and oleic acid as surfactant. The morphology and chemical composition of the wear tracks were examined by using a scanning electron microscope and a x-ray energy dispersive spectrometer. It was found that the coefficient of friction was reduced by 46.6% after adding 0.5 wt% Al2O3/WS2 composite particles. The wear width and wear depth were reduced by 37% and 59.6% after adding 3 wt% Al2O3/WS2 composite particles. In orthogonal tests, it was proposed that the best tribological performance of Al2O3/WS2 composite lubricant could be achieved while using the normal load of 50 N, frequency of 2 Hz and temperature of 65 °C. Frequency could be considered as the primary factor affecting the tribological properties of compsite lubricant. The excellent lubricating performance could be attributed to the formation of WS2 tribo-film with low shearing resistance, and a portion of the Al2O3 particles were embedded by external force to prevent surface contact between the steel ball and brass plate.

Enhanced oil recovery mechanisms of polymer flooding in a heterogeneous oil reservoir

Abstract Taking reservoir rocks and fluids of the Daqing, Dagang and Changqing oilfields as research objects, the EOR mechanisms and technical approach of polymer flooding were discussed. By comparing the displacement performances of ordinary polymer, glycerol, polymer in “sheet-net” structure and heterogeneous weak gel at the same viscosity and concentration, the relationship between the viscosity of polymer displacement agents and displacement performance was demonstrated, and the method of improving polymer flooding effect was worked out. The main mechanism of polymer flooding to increase oil recovery is the swept volume expansion of water injection due to polymer retention in porous media. The viscosity of polymer agents has no positive correlation with polymer flooding effect. Although polymer of “sheet-net” structure has strong capacity in increasing viscosity, it has poor compatibility with pore throat structure of reservoir rock, low injectivity and low shear resistance. Heterogeneous weak gel system has higher adsorption and capture capacity in porous media, which is easy to retain in porous media, and can effectively establish seepage resistance in high permeability layers (zones). Compared with polymer solutions with the same viscosity or concentration, it has stronger ability to expand swept volume. Long term injection of polymer flooding agents will inevitably lead to fluid entry profile reversal, and thus worsening of polymer flooding effect. Alternate injection of high retention and low or non-retention displacement agents can further improve the displacement effect of polymer flooding agents.

Experimental analysis on tribological properties and lubricating mechanisms of oil-based Al2O3 nanofluids applied on steel-brass frictional pairs

The present research studied the tribological properties of Al2O3 nanofluids applied on steel-brass contacts. It was found that the coefficient of friction could be stabilized and reduced by approximately 40.7% after adding Al2O3 nanoparticles. The wear width and wear depth could be reduced by up to 39.6% and 69.3% while using 1 wt% Al2O3 nanofluid. By examining the worn surfaces, Al2O3 nanoparticles were embedded into brass by external load to form a hard case, which could protect the brass surfaces from wear loss. In addition, some black spots with low shear resistance containing high carbon content were formed which were the result of the presence of oleic acid. In summary, the excellent lubricating performance of Al2O3 nanofluids was mainly associated with the physical embedment of Al2O3 nanoparticles and tribo-films of oleic acid. The results obtained in this research can be used to enhance the performance and extend the service life of some engineering components such as journal bearings with inner brass bushings.

The Tribo-Induced Effect of Shielding Action of Ethanolamines and Compounds of Cholesterol under the Dynamic Contact of Metals in Plastic Lubricants

The effect of the integrated shielding of plastic lubricants containing ethanolamines and liquid-crystalline cholesterol compounds induced during the frictional interaction of mating surfaces is found. It is shown that this effect of the protective antiwear properties of plastic lubricants significantly increases upon using intermediate refining fractions as a base—oil distillates, which form lubricant layers with low shear resistance due to the presence of natural surfactants and have high antiwear properties in the process of dynamic contact and interaction with ethanolamines and cholesterol compounds in contrast to refined mineral oils.

Seismic characteristics of hybrid cold-formed steel wall panels

The current standards for seismic design of cold-formed steel (CFS) structures are only limited to the lateral force-resisting systems which are not appropriate for mid-rise constructions due to their low shear resistance. Therefore, innovative hybrid CFS systems have recently been proposed and developed in response to the needs of CFS provisions as well as lightweight steel industry in mid-rise construction. This paper presents an experimental program on lateral cyclic behaviour of six full-scale hybrid wall panels with truss structural design and aims to investigate and characterize the seismic performance of this new CFS solution. The performance of the wall panels is compared in terms of seismic characteristics and response modification factor (R factor). A comprehensive comparison between lateral strength to weight ratio of the hybrid panels of this study and 87 previously tested CFS walls is also carried out to investigate the capability of using hybrid walls in modular lightweight steel buildings. The cyclic results demonstrate that the seismic performance of specimens with appropriate truss frame is satisfactory considering their shear strength, ductility and R factor values. The high strength to weight ratio of the hybrid walls of this study compared to the previously tested CFS panels also indicates the hybrid panels are well appropriate for modular lightweight buildings in seismic regions.

Experimental Investigation and Performance Evaluation of Modified Viscoelastic Surfactant (VES) as a New Thickening Fracturing Fluid.

In hydraulic fracturing, fracturing fluids are used to create fractures in a hydrocarbon reservoir throughout transported proppant into the fractures. The application of many fields proves that conventional fracturing fluid has the disadvantages of residue(s), which causes serious clogging of the reservoir’s formations and, thus, leads to reduce the permeability in these hydrocarbon reservoirs. The development of clean (and cost-effective) fracturing fluid is a main driver of the hydraulic fracturing process. Presently, viscoelastic surfactant (VES)-fluid is one of the most widely used fracturing fluids in the hydraulic fracturing development of unconventional reservoirs, due to its non-residue(s) characteristics. However, conventional single-chain VES-fluid has a low temperature and shear resistance. In this study, two modified VES-fluid are developed as new thickening fracturing fluids, which consist of more single-chain coupled by hydrotropes (i.e., ionic organic salts) through non-covalent interaction. This new development is achieved by the formulation of mixing long chain cationic surfactant cetyltrimethylammonium bromide (CTAB) with organic acids, which are citric acid (CA) and maleic acid (MA) at a molar ratio of (3:1) and (2:1), respectively. As an innovative approach CTAB and CA are combined to obtain a solution (i.e., CTAB-based VES-fluid) with optimal properties for fracturing and this behaviour of the CTAB-based VES-fluid is experimentally corroborated. A rheometer was used to evaluate the visco-elasticity and shear rate & temperature resistance, while sand-carrying suspension capability was investigated by measuring the settling velocity of the transported proppant in the fluid. Moreover, the gel breaking capability was investigated by determining the viscosity of broken VES-fluid after mixing with ethanol, and the degree of core damage (i.e., permeability performance) caused by VES-fluid was evaluated while using core-flooding test. The experimental results show that, at pH-value (), 30 (mM) VES-fluid (i.e., CTAB-CA) possesses the highest visco-elasticity as the apparent viscosity at zero shear-rate reached nearly to 10 (mPa·s). Moreover, the apparent viscosity of the 30 (mM) CTAB-CA VES-fluid remains 60 (mPa·s) at (90 C) and 170 (s) after shearing for 2-h, indicating that CTAB-CA fluid has excellent temperature and shear resistance. Furthermore, excellent sand suspension and gel breaking ability of 30 (mM) CTAB-CA VES-fluid at 90 (C) was shown; as the sand suspension velocity is 1.67 (mm/s) and complete gel breaking was achieved within 2 h after mixing with the ethanol at the ratio of 10:1. The core flooding experiments indicate that the core damage rate caused by the CTAB-CA VES-fluid is (), which indicate that it does not cause much damage. Based on the experimental results, it is expected that CTAB-CA VES-fluid under high-temperature will make the proposed new VES-fluid an attractive thickening fracturing fluid.

Laboratory Experimental Research on Foamed Warm Mix Asphalt Mixture Road Property

To verify the foamed warm mix asphalt mixture road property, the article formed foaming warm mix asphalt mixture, Sasobi-LM warm mix asphalt mixture, ordinary hot mix asphalt mixture test piece, comparative analysis of different asphalt mixture The resistance of high temperature to rutting, shear resistance, resistance of low temperature crack, water stability and fatigue properties, and comparative economic analysis. The results show that the resistance of low temperature crack, water stability and shear resistance of foamed warm asphalt mixture surpass Sasobi-LM warm asphalt mixture, but slightly lower than ordinary asphalt mixture; The resistance of high temperature rutting and fatigue resistance of the mixture is lower than that of Sasobi-LM warm mix asphalt mixture; through economic analysis, the economical efficiency of foamed warm mix asphalt mixture surpasses the economical efficiency of the Sasobi-LM warm mix asphalt mixture, lower than the ordinary hot mix asphalt mixture, it is recommended to choose construction in special areas.

Controlling role of Ta-d pumice on the coseismic landslides triggered by 2018 Hokkaido Eastern Iburi Earthquake

The 2018 Hokkaido Eastern Iburi Earthquake triggered massive landslides in the pyroclastic fall deposits. Most of them are shallow debris slides. Based on the field reconnaissance, the shallow debris slides were further categorized into three types: steep translational sliding, gentle translational sliding, and mobilization of V-shaped convergent sliding masses. The three types of shallow landslides were investigated in depth through longitudinal sections, vertical stratigraphic sections, and in situ hardness tests. All three types of shallow landslides were found to initiate from the liquefied failure of the weak Ta-d pumice layer and further evolve to the overall mobilization of the superimposed pyroclastic fall deposits along the liquefied sliding zone. To testify the controlling role and to study the shear behavior as well as the anti-liquefaction strength of the weak Ta-d pumice layer, a series of laboratory tests (basic physical tests and triaxial tests) were conducted on the soils around the sliding zone. The test results indicate that the medium sandy Ta-d pumice MS and the fragile Ta-d pumice CS have lower shear resistance and anti-liquefaction strength than other layers and they can be easily liquefied under intense ground motion. One paleosol layer underlying the Ta-d pumice shows low permeability and enables weathering and soil erosion of the Ta-d pumice, resulting in the widespread existence of the fragile and medium sandy pumice layers in Ta-d. In addition, the positive relationship between coseismic landslide density and Ta-d pumice thickness demonstrates the controlling role of the Ta-d on Iburi landslide occurrence from a macro perspective.

Improving waxy rice starch functionality through branching enzyme and glucoamylase: Role of amylose as a viable substrate

The low solubility, gel strength and shear resistance of waxy rice limit utility in large-scale and widespread food applications. Herein, functional properties of waxy rice starch (WRS) have been improved through sequential branching enzyme (BE) and glucoamylase (GA) treatment with wheat amylose (WA), rice amylose (RA) and corn amylose (CA) as the substrate. The results suggest that, compared to the BE treatment, the sequential GA→BE treatment significantly improves the WRS properties. Among the three substrates, WA appears to be suited highly for the WRS through the GA→BE treatment. GABE-WRS/WA had the highest content of α-1,6-glucosidic linkages, increased number of short chains, shortest average chain length, increased crystallinity, enhanced solubility, paste clarity and swelling power, elevated gelatinization temperature and enthalpy, increased viscosity, strongest gels, and highest shear-resistance. Overall, the sequential GA→BE treatment appears to be suitable to modify the functional properties of waxy rice starch toward developing more palatable and large-scale food products.

Performance of a test embankment on very soft clayey soil improved with drain-to-drain vacuum preloading technology

Vacuum consolidation of soils is a technology that, to date, has not been implemented in the Valley of Mexico, where clays are highly compressible and have very low shear resistance and low permeability. This paper describes the experience of a test embankment, in which the drain-to-drain vacuum preloading was assessed. The evaluation includes the description of the subsoil conditions, characteristics of the embankment, construction process and instrumentation that was installed. The test lasted approximately one year with a vacuum applied for six months. The monitoring results showed that the vacuum distributed along the vertical drains and on the surface soil layers accelerated the consolidation, reduced the lateral displacements toward the outside of the platform and increased the effective stress of the soil to a depth similar to the length of the drains. However, there were vacuum pressure losses of approximately 30% between the pumps and end of the horizontal flexible pipes that distribute the vacuum. These losses of vacuum pressure affected the soil consolidation process.

Evaluation of EPS wall effectiveness to mitigate shallow foundation deformation induced by reverse faulting

A comprehensive study is presented to illustrate the effect of an expanded polystyrene sheet (EPS) wall for absorbing fault rupture and its effects on shallow embedded foundations. Numerical modeling has been thoroughly validated through centrifuge test results. Various embedment depths and fault dip angles were considered to specify the critical foundation position on the soil surface. Furthermore, the impact of vertical trenching of an EPS wall, next to a rigid foundation, was investigated to mitigate surface foundation deformation. Results indicated that, due to high compressibility and low shear resistance that is not time dependent, an EPS wall panel protects the foundation by absorbing fault induced shear strains in the soil stratum. The effectiveness of such walls depends mainly on the geometry, location and mechanical characteristics of the walls, foundation location, bedrock fault offset, and fault dip angle.