Total Shear Research Articles

Flow displacement and decreased wall shear stress might be associated with the growth rate of an ascending aortic dilatation.

OBJECTIVESOur goal was to evaluate whether four-dimensional (4D) flow magnetic resonance imaging (MRI) can predict the growth rate of dilatation of the ascending aorta (AA) in patients with a tricuspid, normally functioning aortic valve.METHODSIn this prospective clinical study, aortic 4D flow MRI was performed at the Kuopio University Hospital on 30 patients diagnosed with AA dilatation (maximum diameter >40 mm) between August 2017 and July 2020. The MRI was repeated after a 1-year follow-up, with AA dimensions and 4D flow parameters analysed retrospectively at both time points. The standard error of measurement was used to assess the statistical significance of the growth rate of AA dilatation. Flow displacement (FD) was transformed to a class-scaled parameter using FD ≥5% as a threshold.RESULTSStatistically significant growth [median 2.1 mm (1.5–2.2 mm); P = 0.03] was detected in 6 male patients (20%); the AA diameter remained unchanged [0.2 mm (−0.3 to 0.9 mm)] in 24 patients (80%). An increased FD at the baseline was associated with significant growth during the 1-year follow-up in the proximal AA. An association was detected between decreased total wall shear stress and significant aortic growth in the inner curve of the sinotubular junction [529 mPa (449–664 mPa) vs 775 mPa (609–944 mPa); P = 0.03] and the anterior side of the proximal aortic arch [356 mPa (305–367 mPa) vs 493 mPa (390–586 mPa); P < 0.001].CONCLUSIONSFD and decreased wall shear stress seem to be associated with significant growth of AA dilatation at the 1-year follow-up. Thus, 4D flow MRI might be useful in assessing risk for AA diameter growth in patients with a tricuspid aortic valve.

Nitrogen and Phosphorus Diffusion Fluxes: Insight from High-Resolution Technology and Hydrodynamic Modeling

Nitrogen and phosphorus are key elements in controlling eutrophication in the aquatic system. Water and sediment samples were collected from Hongfeng Lake, a seasonally stratified reservoir in southwest China, in winter and summer. Diffusion fluxes of NH4+, NO3−, and labile P in summer using diffusive gradients in thin films technology were 3.4, −37.2, and 0.9 mg m−2 day−1, respectively, based on Fick’s first law. The diffusion flux of labile P was 2.05 mg m−2 day−1 in winter. The contributions fraction of the labile P diffusion flux from sediment to the overlying water were higher in winter than those in summer, because of the relatively lower external input, concentrations and higher diffusion fluxes in winter. After the external input decreased, all of the three diffusion fluxes were lower than the previous record. To understand the influence effect of hydrodynamics, environmental fluid dynamics code modeling was used to simulate the flow and temperature field in winter and summer. Modeling results showed that velocity in summer was higher than that in winter due to concentrated rainfall within the catchment. Moreover, the velocity and temperature in the euphotic zone were higher than that of the hypolimnion in summer. Less variation of velocity and temperature in vertical profile in winter than that in summer was observed, which may be attributable to the high specific heat capacity and the low heat conductivity of water. There was no significant correlation among velocity, hydrochemistry, nitrogen, and phosphorus concentrations. Hydrodynamics, solar radiation, and water depth affect the position of the thermocline, which was consequently to water temperature, hydrochemistry, dissolved nitrogen, and phosphorus concentration. Correlation analysis suggested that the higher bottom velocity and total bed shear may accelerate labile P, NH4+, and NO3− diffusion fluxes. These results provide evidence and suggestions for preventing and controlling reservoir eutrophication and water safety management.

Assessment of shear-resisting mechanisms of steel-fibre-reinforced concrete beams

The shear strength of 14 reinforced concrete beams, all devoid of shear reinforcement, is experimentally investigated. An analytical model is also formulated, by introducing the three main resisting mechanisms in shear, based on the contributions of the concrete compressive zone, aggregate interlock along the inclined cracks and steel fibres (dowel action is neglected). Hooked-end steel fibres 35 mm and 60 mm long are used at volume fractions ranging from 0.75 to 1.5% in the former case, and from 0.5 to 1.0% in the latter case. In all, the shear capacity resulting from the tests is higher than that predicted by the lower bound limit proposed by G. Parra-Montesinos in 2006 and by American Concrete Institute and Indian standard building codes (ACI 318 and IS 456) for fibrous concrete beams. The efficacy of the proposed model is also compared with the 12 other models proposed in the literature. The contribution of shear-resisting mechanisms, namely, compressed concrete, aggregate interlock and steel fibre, is found to be approximately 67, 15 and 18%, respectively, of the total shear strength. The effect of fibre factor (F) and longitudinal reinforcement (ρ) on the contribution of various shear-resisting mechanisms have been rigorously studied and presented.

Cenozoic Dextral Shearing Along the Arusan Sector of the Great Kavir–Doruneh Fault System (Central Iran)

AbstractThe structural analysis of large intracontinental wrench faults is fundamental for deciphering the long‐term evolution of continental crust in complex areas in terms of their geodynamic evolution and large‐scale crustal block displacements. In this contribution, we demonstrate a pre‐Miocene dextral activity of the present‐day left‐lateral Great Kavir ‐ Doruneh Fault System (GKDFS, Central Iran), one of the major intracontinental active strike‐slip faults extending from the Afghan border to the Nain region between Central Iran and the Sanandaj‐Sirjan Zone. We document important dextral shearing recorded along a segment of the GKDFS, the Arusan Fault System (AFS), located east of Jandaq, close to the present‐day active trace of the GKDFS. The AFS include several ENE‐WSW striking strands exposed for a length of more than 50 km, which couple pre‐Cretaceous ophiolites and metamorphic basement units with the Cretaceous succession of the Khur basin. The fault shows transpressional structures consistent with a dextral shear including thrusts and en échelon folds affecting the Cretaceous carbonate units. Paleostress reconstruction based on mesoscopic fault analysis and related folds geometry allowed to establish vorticity parameters indicating that deformation occurred close to a total simple shear regime with a calculated Wk between 0.9 and 1. The enormous Meso‐Cenozoic dextral displacements occurred along the AFS and along the entire GKDFS are attested by the up to several hundreds of kilometers offset of the Paleotethys suture zone, from NE Iran to the western border of Central Iran.

Optimization performance parameters short carbon fiber reinforced Polyamide66 composite spur gear with addendum variation

Addendum variation effects on the Short Carbon Fiber (SCF) reinforced Polyamide66 (PA66) composite spur gear. By using percentage variations of 00,10,20,30,40,50,60 by weight of SCF in PA66. The addendum variation coefficients are considered in steps from a lower negative value to a higher positive value. The lower limit value is called an undercutting limit, and the higher value is called a peaking limit. Different addendum variation values of −0.4, −0.2, 0, +0.2 and + 0.4 mm and different percentage of SCF in PA 66. The performance parameters of spur gears like total deformation, Von-Mises, maximum principle, shear stress, and factor of safety are evaluated by using FEM analysis. The results show that when the addendum decreases, Von-Mises, maximum principal stress decrease, and total deformation, Shear stress, FOS increases. When the addendum increases, Von-Mises, shear stress, FOS decreases, and total deformation, maximum principal stress increases. Maximum principal stresses at the gear root on the tensile side were used to assess the bending strength of the gear. High deformation causes high shear stresses and is useful for the selection of gear material of particular applications. Based on the analysis results, Von-Mises stress and cyclic loading were instrumental in predicting deformation and gear failure.

Parameter Estimation and Application of Anisotropic Yield Criteria for Cylindrical Aluminum Extrusions: Theoretical Developments and StereoDIC Measurements

Theoretical and experimental studies are presented to characterize the anisotropic plastic response under torsion loading of two nominally identical aluminum Al6061-T6 extruded round bars. Theoretical models are developed using isotropic (Von Mises 1913) and anisotropic (Barlat 1991) yield criteria, along with isotropic strain hardening formulae, to model post-yield behavior under simple torsion loading. For the case of simple shear loading, incremental plasticity theory is used to determine the theoretical elastic, plastic, and total shear strains. A set of experiments are performed to calibrate Barlat’s 1991 yield function. Several specimens are extracted at different orientations to the longitudinal direction of each round Al6061-T6 bar and tested under uniaxial tension and simple torsion to optimally determine all anisotropic (Barlat 1991) yield function parameters. During loading, Stereo Digital Image Correlation (DIC) is used to quantify surface deformations for the torsion experiments and a baseline tension specimen to identify and correct measurement anomalies. Results show the isotropic yield model either underestimates or overestimates the experimental shear strains for both extrusions. Conversely, results using the Barlat 1991 anisotropic yield criteria are in excellent agreement with experimental measurements for both extrusions. The presence of significant differences in the anisotropic parameters for nominally similar extrusions confirms that plastic anisotropy is essential for the accurate prediction of mechanical behavior in longitudinally extruded Al6061-T6 bars.

Shear strengthening of reinforced concrete beams with high-strength steel wire and engineered cementitious composites

Engineered cementitious composite (ECC) is a type of high-performance fibre-reinforced cementitious composite with good ductility and excellent crack control ability. It has attracted increasing attention as a structural repair material in severely corrosive environments. However, the strength improvement is limited when ECC is used alone for shear strengthening of existing reinforced concrete (RC) members, although its shear capacity is much higher than that of other brittle cementitious materials such as cement mortar. This study proposes a novel shear strengthening method for RC beams with both high load-carrying capacity and good durability through the combination of high-strength steel wire and an ECC layer. The shear behaviours of the beams were tested under static loading. The test results showed that the shear strength and the ultimate displacement were significantly improved through shear strengthening. A large number of fine cracks appeared on the ECC layer before the failure of the beams. The load-carrying capacity was reduced by pre-damage owing to the important role of the shear resistance of the concrete with respect to the total shear capacity. The shear strength of the strengthened beams cannot be accurately predicted by the current design code owing to the ignorance of the shear resistance of ECC.

Performance of Six- and Ten-story Reinforced Concrete Buildings Designed by using Modified Partial Capacity Design (M-PCD) Method with 70% Shear Force Ratio

One design alternative of earthquake resistant building is Partial Capacity Design (PCD) method. Unlike the commonly used capacity design method, PCD allows a safe failure mechanism which is called partial sidesway mechanism. In this mechanism, all beams and some columns are allowed to experience plastic damages while some selected columns are designed to remain elastic (called elastic columns). A new approach to predict the required strengths needed to design each structural member, called modified-PCD (M-PCD) is proposed. In this research six- and ten-story reinforced concrete buildings were designed using M-PCD, and their seismic performances are investigated. The base shear force resisted by the elastic columns was set to approximately 70% of the total base shear. Both nonlinear static procedure (NSP) and nonlinear dynamic procedure (NDP) are used to analyze the structures. The results show that the expected partial side sway mechanism is observed, and the drifts of the buildings are acceptable.

Aneurysm Wall Enhancement Is Associated With Decreased Intrasaccular IL-10 and Morphological Features of Instability.

High-resolution vessel wall imaging plays an increasingly important role in assessing the risk of aneurysm rupture. To introduce an approach toward the validation of the wall enhancement as a direct surrogate parameter for aneurysm stability. A total of 19 patients harboring 22 incidental intracranial aneurysms were enrolled in this study. The aneurysms were dichotomized according to their aneurysm-to-pituitary stalk contrast ratio using a cutoff value of 0.5 (nonenhancing<0.5; enhancing≥0.5). We evaluated the association of aneurysm wall enhancement with morphological characteristics, hemodynamic features, and inflammatory chemokines directly measured inside the aneurysm. Differences in plasma concentration of chemokines and inflammatory molecules, morphological, and hemodynamic parameters were analyzed using the Welch test or Mann-Whitney U test. The concentration ΔIL-10 in the lumen of intracranial aneurysms with low wall enhancement was significantly increased compared to aneurysms with strong aneurysm wall enhancement (P=.014). The analysis of morphological and hemodynamic parameters showed significantly increased values for aneurysm volume (P=.03), aneurysm area (P=.044), maximal diameter (P=.049), and nonsphericity index (P=.021) for intracranial aneurysms with strong aneurysm wall enhancement. None of the hemodynamic parameters reached statistical significance; however, the total viscous shear force computed over the region of low wall shear stress showed a strong tendency toward significance (P=.053). Aneurysmal wall enhancement shows strong associations with decreased intrasaccular IL-10 and established morphological indicators of aneurysm instability.

Factors Determining Shear‐Parallel Versus Low‐Angle Shear Band Localization in Shear Deformations: Laboratory Experiments and Numerical Simulations

AbstractUnderstanding the mechanics of shear localization in materials is a key to interpreting a wide range of failure‐assisted geophysical processes. This paper addresses a crucial problem of shear band formation in ductile shear zones undergoing simple shear movement. We studied ductile shear zones in two geological terrains of Eastern India and observed extensive micro‐ to macro‐scale shear‐parallel deformation bands (C‐bands) in them. However, laboratory‐scale simple shear experiments on wet sand (Coulomb) and putty (viscoplastic) failed to produce C‐bands. They developed shear bands in conjugate sets: low‐angle R1 (10°–15°) and high‐angle R2 (65°–75°) and single sets of low‐angle shear bands (LSB), respectively. These contrasting findings between field and experiments motivate us to address the question‐ under what conditions can shear bands localize parallel to the bulk shear direction? With the help of 2D numerical models, based on viscoplastic rheology, we demonstrate C‐band and LSB formation as two competing mechanisms of shear localization, mediated by a combined effect of the shear zone parameters: geometric (shear zone thickness), kinematic (bulk shear rate) and rheological (bulk viscosity). Finally, two non‐dimensional factors: (a) dynamic (Ω: global shear stress /cohesive strength [Ci]) and (b) geometric (δ: effective thickness [Wc]/total shear zone thickness [W]) are recognized to show the fields of LSB and C‐bands formation. We also provide a theoretical analysis of the shear band orientation as a function of the dynamic and geometric parameters.

Characterization of seismic energy during fault-slip induced by fluid injection using coupled and dynamic X-FEM analysis

Fluid injection into a rock mass from industrial processes can lead to reactivation of pre-existing faults at great depths. When the shear behaviour involves dynamic rupture, perceivable seismic events could be induced that may raise public concern. This seismicity can be caused by injection-induced fluid pressure in the rock mass causing slip on faults. This study provides a method to distinguish between aseismic and seismic fault movement induced by anthropogenic fluid injection with the aim of gaining an insight into the difference in seismic source parameters between the two types of fault behaviour, i.e., seismic and aseismic. This was achieved by using a two-dimensional fully coupled fluid and mechanical loading extended finite element model (X-FEM) with a dynamic analysis module. This code considers fluid flow along the fault as well as into the rock mass and uses a directly proportional equivalent injected flow rate into the fault as the input. This model was validated by comparing the resultant pressure and normal and shear displacements calculated at the centre of the fault against observations from a decametre-scale in-situ experiment. The main results were that not only the mechanics of the fault could be simulated using this approach, but the simulation correctly predicted the onset of seismicity and transition to dynamic analysis and at similar seismic magnitudes to observations. In terms of the difference in seismic source parameters between seismic and aseismic fault movements, it was shown that while the seismic shear movement to total shear movement is approximately 1%, the dynamic analysis produces approximately 75% of the total near field energy released in the simulation. This indicates the necessity of distinguishing dynamic and quasi-static shear movements in the numerical simulation of fluid injection-induced seismicity in order to quantify magnitude and seismic energy released accurately and to assess the risk of seismicity properly, since aseismic fault movements do not cause any damage to facilities on the surface. These results are important, since they demonstrate the applicability of this X-FEM approach in accurately predicting the mechanics of fault reactivation and the resultant seismicity, aiding in the design and scheduling of fluid injection and in the optimization of operational parameters.

Simplified Equations for Shear Strength of Composite Concrete-Filled Steel Tubes

Shear strength of filled composite members, namely, circular or rectangular concrete-filled steel tubes (CFST) have been investigated in past research. Results established the relative contributions of the steel tube and concrete infill to the total shear strength and showed that the concrete contribution depends on the development of a compression strut in the concrete infill when shear-span values are low. While experimental results and numerical models are available in the literature, simple equations that empirically encompass this behavior are preferable for design purposes. This paper provides an overview of the technical approach that has been followed to propose such equations for consideration and possible implementation in future editions of design specifications. The shear strength obtained using the proposed equation is compared with the shear test database from the existing literature and found to be safe; it accurately captures the contribution of the steel tube to the total shear strength and conservatively approximates that of the concrete.

Anisotropic constitutive model coupled with damage for Sn-rich solder: Application to SnAgCuSb solder under tensile conditions

With the rapid development of microelectronics and nanoelectronics, Moore law has significantly slowed down and More than Moore based system in packaging (SiP) is expected to be more and more important, at least for next one to two decades. Mechanical behaviors of interconnect materials such as solders are critical for yield in processes and reliability in testing and operation. Based on the framework of crystal plastic theory and continuum damage mechanics, an anisotropic constitutive model coupled with damage was developed to describe the deformation behaviors of Sn-rich solder. In the proposed model, the inelastic shear rate function was presented by hyperbolic sinusoidal form and power law form. For the damage evolution law, the total shear strain was chosen as the damage function variable. The proposed model was implemented into the general finite element software ABAQUS by forward Euler integration procedure. Some simulation examples were performed to verify the proposed model by comparing the simulation results with the experiments at uniaxial tensile conditions with SnAgCuSb solder chosen as the Sn-rich solder. The tensile stress-strain curves of the simulation results agreed well with the experiments at small strain under different temperatures and strain rates. The simulated stress-rupture stages showed reasonable accuracy with the experiments under four representative tensile conditions. Different tensile stress-strain curves of single grains with orientation of (0-0-0)°, (0-45-0)°, and (0-90-0)° were obtained under the same loading conditions, with an inverse relationship between the tensile strength and elongation. This relationship was in accordance with a referable literature. All these results indicate that the proposed model can describe the deformation behaviors of SnAgCuSb solder well under the tensile conditions in consideration of the mechanical anisotropy and the damage evolution.

Research on Low Shear Rheological Properties of Annulus Drilling Fluid For Cementing in Kuqa Piedmont

Aiming at the frequent leakage of cementing casing in the fourth and fifth spuds of ultra deep natural gas wells in Kuqa Piedmont structural belt, Tarim Basin, the actual shear rate of annulus drilling fluid during casing running is analyzed. According to the he Ba rheological model, the test data at full shear rate (1.70–1021.40 s–1) and low shear rate (1.70–340.50 s–1) are used, The total shear and low shear rheological parameters of oil-based drilling fluid are fitted respectively, and the difference of exciting pressure under total shear and low shear rate is analyzed. It is found that the actual drilling fluid shear rate is much lower than the high value of conventional total shear rate of 1021.40 s–1; Under full shear and low shear rate, the rheological parameters vary greatly with temperature and pressure; The casing activation pressure at full shear rate is less than that at low shear rate. With the increase of well depth, the difference between full shear and low shear rate is greater. The results show that for natural gas wells with narrow safety pressure window, the test data should be selected to fit the corresponding rheological parameters according to the actual low shear rate range of drilling fluid, and on this basis, the casing running speed should be reasonably designed according to the allowable casing running exciting pressure, so as to reduce the leakage during casing running.

Dynamics of wall jet flow under external pulsation

The present study aims to identify the dominant coherent structures in the wall jet flow subjected to external pulsation at Reynolds number 2600 (based on average jet exit velocity and nozzle diameter). The forcing frequency is varied between St = 0 and 0.99 (St is the Strouhal number). Quadrant analysis is employed to identify the relative contribution of different quadrant motions to the total Reynolds shear stress. Unlike boundary layer flows and channel flows, two distinct regions (inner shear region and outer shear region) are observed in the wall jet flows, and the characteristics of different quadrant motions change in these regions. About 70% of the total shear stress is contributed from the first and fourth quadrants in the outer shear region. We observe that ejection motion is more energetic than sweep motion in the downstream direction, although less frequent. The ejection motion is observed to be more violent for St = 0.44 than for the other frequencies. A proper orthogonal decomposition (POD) analysis reveals while the modal structures exist in different regions of the wall for different jet pulsation; there are no dominant modes (30 modes are required to recover about 75% of the total energy), and the energy is fairly distributed over a large number of modes. However, the POD analyses are capable of capturing the response of the wall jet to different jet pulsations. The most dominant and strongest modal structures are found nearer to the impingement region of the wall when St = 0.44 and the jet tends to laminarize for St &amp;gt; 0.9.

Numerical Simulation of the Geothechnical Effects on Local Scour in Inclined Pier Group with FLow-3D Softaware

When the bridge piers are located in front of the water flow, vortices are formed against it and due to their activity, the materials of the river bed are eroded around the bridge piers and the scouring hole is created. If the foundation depth and bridge pier piles are insufficient, the bridge will fail.The study of total shear stress in the flow bed at different leveling of the pile caps shows that the highest shear stress is created when the pile cap position is at the same level as the river bed; by installing the pile cap at a lower level than the river bed, the maximum shear stress decreases. This may be due to the fact that in this case, the distance between the pier group increases and the presence of the second pier decreases the flow rate in the pier group and different pier in the one pier group acts as the two independent piers in the formation of the flow pattern. By comparing the final longitudinal sections of the scouring at different leveling of the pile cap, it is concluded that the largest reduction in scouring depth occurs in aerofoil-shaped pile caps and pile caps with the sharper nose and better aerodynamic shapes are good options to control the horseshoe vortices and will reduce the scouring depth around the inclined pier group.

Observed Near-Inertial Waves in the Northern South China Sea

Characteristics of near-inertial waves (NIWs) induced by the tropical storm Noul in the South China Sea are analyzed based on in situ observations, remote sensing, and analysis data. Remote sensing sea level anomaly data suggests that the NIWs were influenced by a southwestward moving anticyclonic eddy. The NIWs had comparable spectral density with internal tides, with a horizontal velocity of 0.14–0.21 m/s. The near-inertial kinetic energy had a maximum value of 7.5 J/m3 and propagated downward with vertical group speed of 10 m/day. Downward propagation of near-inertial energy concentrated in smaller wavenumber bands overwhelmed upward propagation energy. The e-folding time of NIWs ranged from 4 to 11 days, and the larger e-folding time resulted from the mesoscale eddies with negative vorticity. Modified by background relative vorticity, the observed NIWs had both red-shifted and blue-shifted frequencies. The upward propagating NIWs had larger vertical phase speeds and wavelengths than downward propagating NIWs. There was energy transfer from the mesoscale field to NIWs with a maximum value of 8.5 × 10−9 m2 s−3 when total shear and relative vorticity of geostrophic currents were commensurate. Our results suggest that mesoscale eddies are a significant factor influencing the generation and propagation of NIWs in the South China Sea.

An elastic–inelastic model for dry friction with a smooth transition

A model for dry friction is developed based on a model of a shearing layer with a smooth elastic–inelastic transition. The resulting model for friction has a single history-dependent variable that characterizes elastic shear strain in the layer and is determined by integrating an evolution equation for its rate. The model uses an experimentally determined functional form for the coefficient of friction which decreases with increased shearing rate. The shear stress applied to the shearing layer is proportional to the normal compressive stress for transient response and the proportionality function becomes the coefficient of friction for steady-state response. The model also predicts the observed result that the transitional total shear strain for a jump in total shearing rate remains in a specified range for a large range of applied shear rate and is independent of the applied normal stress.

Sand-sand and sand-steel interface grain-scale behavior under shearing

The behavior of a sand-steel interface can be different than the shearing behavior of a sand. This study focuses on the effect of shear loading on a sand-to-sand and a sand-steel interface as well as on particle breakage. A series of ring shear and simple shear tests were conducted to measure the effects of particle shape and surface roughness characteristics before and after shearing at the shear zones within a sand-to-sand and at a sand-steel plate interface. It was found that sand density had a large effect on the interface shearing behavior. While interface sliding began at a shear displacement of 0.9 mm (corresponding to 22% of the total shear displacement) in dense specimens, this occurred at a much higher displacement of 5.6 mm (62% of total displacement) in loose sand at rough steel interface. Sliding displacement prevailed at the sand-steel plate interface in simple shear tests as the sand sample became denser. Critical states were observed in the sand-to-sand ring shear tests after shear displacements of 65–79 mm and 87–98 mm in medium-dense and loose samples, respectively. Comparing sand-to-sand and sand-steel interface results indicated that sand-steel interface behaves less dilative with the critical state occurring at much smaller shear displacements of about 12–14 mm at the interface compared to that occurring within the sand at 65–79 mm. Both loose and dense sands reached a residual strength of 98 kPa at a shear displacement of 7 mm in simple shear tests. The inter-particle shear resistance and particle crushing, combined with particle rearrangement/rotation were the mechanisms which developed shear resistance. An interface friction angle of 27° was subsequently mobilized at the critical states of the simple shear tests, while particle crushing and abrasion resulted in a slightly elevated (by 2°) interface friction angle in the ring shear tests. The difference between sand-steel interface and sand-to-sand interaction mechanism highly influenced particle damage induced by particle fracturing and abrasion. As a result of particle crushing, roughness and aspect ratio of sand particles sheared at the interface with a steel plate reduced by respectively 39.7% and 12–14% sheared at normal stresses of 50 to 200 kPa. In particular, particles' circularity increased from 0.685 to 0.817, indicating symmetrically rounded particles. The maximum size of particles in all tests reduced to about 16.9–18.1% of the original maximum particle size (Dmax = 0.85 mm). While the skewness of particles sheared within the sand increased from −0.231 to 0.656 (indicating increased surface roughness), those of particles collected from the sand-steel interface decreased to −1.31 reflecting smoother particle surfaces.

The micro/macro mechanical approach of reinforced braid composite used in tribology

Self-lubricant composite is a flourish scope of technology that merits academic and industry attention, as it is a specific part which essentially employed in acute operation conditions. In the present study, the mechanical properties of the self-lubricating composite of two-dimensional (2D) and three-dimensional (3D) braid were investigated. The composites contained Polytetrafluoroethylene (PTFE) fibers as a lubricant and glass, carbon, and Kevlar as a reinforcement, hierarchically incorporated into the structure. In order to study the composite behavior as well as to determine the modulus and hardness of the sample, an indentation test, which is very similar in loading to abrasion tests, was applied. A microband test was also conducted to assess the adhesion between the resin and the PTFE fiber. Shear punch tests were performed to evaluate the total shear strength and impact test to estimate energy absorption and impact strength. The results showed that PTFE/epoxy matrix has poor adhesion. Composites with higher PTFE volume fraction had good energy absorption and, at the same time, low shear strength. The higher modulus of carbon composites was concerned.