Large Shear Research Articles

Shear strengthening of RC beams with prestressed NSM CFRP: Influencing factors and analytical model

This study proposes the application of prestressed near-surface-mounted (NSM) carbon-fiber-reinforced polymer (CFRP) technique in the field of the shear-strengthening of bridges for the first time. Fourteen reinforced concrete (RC) beams shear strengthened with prestressed NSM CFRP were tested under static load. The effect of the CFRP prestressing level, spacing, angle, and end-anchorage measures on the shear-strengthening behavior was evaluated. The experimental results demonstrate that the ultimate shear capacity of prestressed NSM CFRP shear-strengthened beams increased by 65–127% when compared to that of the reference beams, and the width of shear cracks was effectively suppressed. The failure mode of prestressed NSM CFRP shear-strengthened beams without end-anchorage measures was web concrete cover separation, which can be suppressed using a CFRP U-jacket and through-beam screw. Increasing the CFRP prestressing level and percentage enhanced the ultimate shear capacity and cracking resistance of the strengthened beams. However, an excessively high CFRP percentage and prestress level combination resulted in large shear crack angles and decreased the shear contribution of CFRP and concrete. Finally, an analytical model based on the modified compression field theory (MCFT) was proposed to predict the flexural-shear load response of strengthened beams, which was in agreement with the experimental results.

Effects of Dynamic Flow Rates on the In Vitro Bio-Corrosion Behavior of Zn-Cu Alloy

In the complicated real physiological environment in vivo, body fluids and blood are constantly replenished and move dynamically, and therefore, the dynamic impacts of bodily fluids and blood need to be considered in the evaluation of biodegradable materials. However, little research has been conducted on the impact of dynamic flowing circumstances on the corrosion characteristics of zinc-based alloys, particularly at high flow rates. The effects of various flow rates on the bio-corrosion behavior of the Zn-Cu alloy are thoroughly explored in this study. A model is developed using finite element analysis to investigate the impacts of flow rates and fluid-induced shear stress. The results reveal that the corrosion process of the Zn-Cu alloy is significantly accelerated by a higher flow rate, and a large fluid-induced shear stress caused by the boundary effect is found to promote corrosion. Furthermore, the empirical power function between the average flare rates in Hank’s solution and the corrosion rates of the Zn-Cu alloy is established by numerical simulation. The results provide insightful theoretical and experimental guidance to improve and evaluate the efficacy and lifespan of biomedical zinc-based alloy implants.

On the shear strain associated with T1 precipitation in Al-Cu-Li(-Mg-Ag) alloys

The formation mechanism and the distribution arrangements of T1 precipitate plates in peak-aged samples of an Al-4Cu-1.2Li-0.3Mg-0.4Ag (wt.%) alloy are studied using atomic-resolution high-angle annular dark-field (HAADF) and annular bright-field (ABF) scanning transmission electron microscopy (STEM). The formation of a T1 plate of a single unit-cell thickness from the α-Al matrix is found to be associated with a large shear strain that is equivalent to the formation and glide of two different Shockley partial dislocations on two alternate {111}α planes. The T1 precipitate plates tend to cluster into various configurations, including T-shaped and V-shaped configurations comprising two plates of two different T1 variants, and X-shaped configurations consisting of three or four plates of two different variants. The signature of the shear strain is clearly visible in these configurations. A single T1 plate of one unit-cell thickness is elastically distorted in a T-shaped configuration, and the two T1 plates of the same variant in an X-shaped configuration are displaced with respect to each other. Different types of stair-rods are also formed in the intersection of the paired T1 plates in the V-shaped configurations.

A vector sum analysis method for stability evolution of expansive soil slope considering shear zone damage softening

Slope stability analysis is a classical mechanical problem in geotechnical engineering and engineering geology. It is of great significance to study the stability evolution of expansive soil slopes for engineering construction in expansive soil areas. Most of the existing studies evaluate the slope stability by analyzing the limit equilibrium state of the slope, and the analysis method for the stability evolution considering the damage softening of the shear zone is lacking. In this study, the large deformation shear mechanical behavior of expansive soil was investigated by ring shear test. The damage softening characteristic of expansive soil in the shear zone was analyzed, and a shear damage model reflecting the damage softening behavior of expansive soil was derived based on the damage theory. Finally, by skillfully combining the vector sum method and the shear damage model, an analysis method for the stability evolution of the expansive soil slope considering the shear zone damage softening was proposed. The results show that the shear zone subjected to large displacement shear deformation exhibits an obvious damage softening phenomenon. The damage variable equation based on the logistic function can be well used to describe the shear damage characteristics of expansive soil, and the proposed shear damage model is in good agreement with the ring shear test results. The vector sum method considering the damage softening behavior of the shear zone can be well applied to analyze the stability evolution characteristics of the expansive soil slope. The stability factor of the expansive soil slope decreases with the increase of shear displacement, showing an obvious progressive failure behavior.

Influences of non-rubber components on the molecular network and viscoelasticity of natural rubber gum

The molecular network of natural rubber (NR) gum is determined by the interparticle diffusion when NR latex coagulates. However, the roles played by the non-rubber components (NRC) species on the heterogeneous network structure and on the viscoelasticity of NR gum have not been throughly investigated. Here, the molecular relaxation was studied by linear rheology. In addition, the inter- and intra-cycle nonlinearities under large amplitude oscillatory shear (LAOS) were studied for gums with extracted and added NRC. It was found that the high molecular weight free protein restricts the interdiffusion and improves the entanglement density, while the added lipid induces homogeneous distribution of NRC. The physical associations coming from free proteins increase the segment friction and retard the terminal relaxation. Onset of the strain softening was found to be induced by entangled network density. Both the elastic and viscous LAOS nonlinearities can be regulated by adjusting the NRC species. This work sheds light on the contributions of major NRC species on the network structure and nonlinear viscoelasticity of NR gum.

Failure behaviors of rainfall-induced shallow landslides: insights from a novel large angle-adjustable plane shear apparatus

Failure behaviors of rainfall-induced shallow landslides: insights from a novel large angle-adjustable plane shear apparatus

Enhanced Ion Acceleration Due To High‐Shear Tangential Discontinuities Upstream of Quasi‐Perpendicular Shocks

AbstractCollisionless shock waves are efficient ion accelerators. Previous numerical and observational studies have shown that quasi‐parallel (Q‖) shocks are more effective than quasi‐perpendicular (Q⊥) shocks at generating energetic ions under steady upstream conditions. Here, we use a local, 2D, hybrid particle‐in‐cell model to investigate how ion acceleration at super‐critical Q⊥ shocks is modulated when tangential discontinuities (TDs) with large magnetic shear are present in the upstream plasma. We show that such TDs can significantly increase the ion acceleration efficiency of 2D Q⊥ shocks, up to a level comparable to Q‖ shocks. Using data from the hybrid model and test particle simulations, we show that the enhanced energization is related to the magnetic field change associated with the discontinuity. When shock‐reflected ions cross the TD during their upstream gyromotion, the sharp field change causes the ions to propagate further upstream, and gain additional energy from the convection electric field associated with the upstream plasma flow. Our findings illustrate that the presence of upstream discontinuities can lead to bursts of energetic ions, even when they do not trigger the formation of foreshock transients. These results emphasize the importance of time‐variable upstream conditions when considering ion energization at shocks.

Energy Partition between Submesoscale Internal Waves and Quasigeostrophic Vortical Motion in the Pycnocline

Abstract Shipboard ADCP velocity and towed CTD chain density measurements from the eastern North Pacific pycnocline are used to segregate energy between linear internal waves (IW) and linear vortical motion [quasigeostrophy (QG)] in 2D wavenumber space spanning submesoscale horizontal wavelengths λx ∼ 1–50 km and finescale vertical wavelengths λz ∼ 7–100 m. Helmholtz decomposition and a new Burger number (Bu) decomposition yield similar results despite different methodologies. While these wavelengths are conventionally attributed to internal waves, both QG and IW contribute significantly at all measured scales. Partition between IW and QG total energies depends on Bu. For Bu < 0.01, available potential energy EP exceeds horizontal kinetic energy EK and is contributed mostly by QG. In contrast, energy is nearly equipartitioned between QG and IW for Bu ≫ 1. For Bu < 2, EK is contributed mainly by IW, and EP by QG, while, for Bu > 2, contributions are reversed. Finescale near-inertial IW dominate vertical shear variance, implying negligible QG contribution to vertical shear instability. In contrast, both QG and IW at the smallest λx ∼ 1 km contribute large horizontal shear variance, so that both may lead to horizontal shear instability, while QG, with its longer time scales, likely dominates isopycnal stirring. Both QG and IW contribute to vortex stretching at small vertical scales. For QG, the relative vorticity contribution to linear potential vorticity anomaly increases with decreasing horizontal and increasing vertical scales.

Enhanced shear and veer in the Taiwan Strait during typhoon passage

During typhoon passage extreme wind conditions pose a challenge to the structural integrity of wind turbines. Particularly, wind shear and wind veer can influence wind turbine loads. This study investigates how Taiwan’s central mountain range affects wind shear and wind veer in the Taiwan Strait during three westward-moving typhoon cases. The typhoons are simulated with the Weather Research and Forecasting (WRF) model. We find that wind speed, shear, and veer vary over different regions in the Taiwan Strait. In large areas, the simulated wind shear is larger than modeled over the open ocean. In particular, mountain blockage leads to a spatially confined area of several 1000 km2 downstream of Taiwan, that exhibits over several hours strongly modified shear and veer in all three analyzed cases. Shear exponents up to 0.75 and veer between 0.2 and 0.6° m−1 suggest that turbine loads are impacted by the vertical change in the wind field in this area. The shear exponent and wind veer vary strongly with height in the downstream area of Taiwan’s central mountain range. The location of the area with large wind shear and wind veer differs between the three simulated typhoon cases and primarily depends on the latitude of the typhoon track relative to the central mountain range.

Convective Phenomenes in the Context of Meso-β-scale Convective Structures

This review article presents the results of radar studies of convective phenomena in Moldavia and the North Caucasus using Eulerian (ECS) and Lagrangian (LCS) coordinate systems. Application of the Lagrangian approach allowed us to exclude the influence of the tropospheric displacement and to obtain integral grid patterns of thunderstorm-hail processes. These structures are especially well manifested at small wind shears (up to 1 m/sec/km). At large shears, the mesh structures are transformed predominantly into linear structures. The methodology for obtaining integral pictures of radio echoes of thunderstorm processes is described. Intersections of linear elements, which we call faces, occur at nodes. The latter plays a particularly important role in the dynamics and kinematics of convective storms. The latter play a particularly important role in the dynamics and kinematics of convective storms. The development of storms occurs along the facets and at the nodes of meso-β-scale convective structures (MMCS), which explains the mechanisms of splitting and merging of storms: in the first case the facets diverge, in the second case they converge. The relations of motion vectors for different types of storms are obtained. It is shown that the direction of the radio echo canopy coincides with the storm motion trajectory; the evolution vector (propagation) for the most powerful storms deviates from the storm displacement direction by 80°–135°. The structure of the updated band within which the Flanking Line is formed for supercells and multicells is studied. Mnemonic rules have been derived that allow one to infer from instantaneous patterns of anvil orientation and the mutual location of storms whether they are converging or diverging, and to identify left- or right-moving storms. A hypothesis on the internal structure of the cold front of the 2nd kind is stated. The main conclusion of the work is that the evolution of storms is determined by the configuration of meso-β-scale convective structures. This explains various convective phenomena from unified positions. The results are applicable in works on modification of convective cloudiness, for ultra-short-term forecasts of dangerous phenomena, storm warnings of the population, rescue services, etc.

Brittle Damage Processes Around Equi‐Dimensional Pores or Cavities in Rocks: Implications for the Brittle‐Ductile Transition

AbstractIn the Earth's upper crust, rocks deform mostly by means of brittle fracturing processes. At the micro‐scale these processes involve the formation and growth of microcracks in the vicinity of defects such as open fissures, pores and other cavities. Large defects can produce strong enough perturbations of the stress field to activate and/or intensify brittle damage around them. Here we considered the ideal cases of smooth cylindrical and spherical pores inside an infinite solid body subjected to remote triaxial compressive stresses (i.e., the intermediate and minimum principal stresses are assumed equal). We first established the resulting local stress field around one of those large pores and then verified whether certain brittle damage processes could be activated in these conditions. We mainly considered the formation of tensile microcracks and micro shear bands. The former requires the presence of tensile stresses in some regions around the pore, while the latter needs sufficiently large shear stresses on pre‐existing optimally inclined microcracks to overcome their frictional resistance to sliding. We find that shear driven deformation remains localized in the vicinity of the pore. On the other hand, dilatational, tensile cracks can propagate large distances away from the pore but cannot form at and above some threshold ratio of the least to the largest principal stresses. Faulting associated with interacting tensile cracks is therefore suppressed with increasing depth. Our analysis leads to conclusions generally consistent with published experimental observations and provides some clues to discuss the physical cause of the brittle‐ductile transition in rocks.

Dynamic shear resistance and its dependence on geometrical imperfection of high entropy Cantor alloy and BJAM 316L stainless steel

This paper examines the adiabatic shear resistance of recently popular Cantor alloy and Binder Jetting Additive Manufacturing (BJAM) 316L, with emphasis on their dependence on geometrical imperfection. A series of shear tests were conducted by using the long Split Hopkinson bar and shear compression specimen (SCS). Both alloys present strain rate dependent shear behaviour with the large dynamic shear failure strain of about 104 %–132 %. Microstructural characterizations reveal that both Cantor and BJAM 316L alloys fail by adiabatic shear band. Introduced by the varying notch root radius, the sharpness significantly affects the dynamic shear resistance of the Cantor and BJAM 316L alloys. The linear functions are proposed to describe the drop of critical strain and energy density with the designed inverse root radius.

Thermal-hydraulic performance of TPMS-based regenerators in combined cycle aero-engine

The existing regenerator structure in aero-engine cannot satisfy the requirements with the development of hypersonic vehicles. The triply periodic minimal surface (TPMS) with superior thermal and mechanical performances has great potential for the regenerator. However, the study on TPMS structures as heat exchangers with high compactness and high power-to-weight ratio is still lacking. This study presents a complete workflow for evaluating the performances of TPMS heat exchangers. Based on this workflow, the thermal–hydraulic performances of Diamond, Fischer-Koch S (FKS), and printed circuit heat exchangers (PCHE) at different Reynolds numbers are investigated. Compared with the PCHE, the performance evaluation criteria of Diamond and FKS structures increased by 11.3–26% and 10.9–32.5%, respectively. This can be mainly attributed to the intensive turbulent mixing, large wall shear stress and high specific surface area of the TPMS structures. The thermal–hydraulic performance is also well explained by the field synergy principle. Based on the developed thermal and hydraulic correlations, the TPMS regenerators are designed and the results indicate that the power-to-weight ratio is improved by about 4 times with half volume of a PCHE. In summary, the TPMS regenerators can save space, reduce weight, and increase payload of aircrafts and have great application potential in the field of aerospace.

Effects of filler content on non-linear viscoelasticity of high fluorine content fluoroelastomer mixture investigated through large amplitude oscillatory shear tests

Effects of filler content on non-linear viscoelasticity of high fluorine content fluoroelastomer mixture investigated through large amplitude oscillatory shear tests

Does spinopelvic alignment affect femoral head cartilage and the proximal femoral physis in slipped capital femoral epiphysis? A finite element analysis

BackgroundSlipped capital femoral epiphysis is a prevalent pediatric hip disorder. Recent studies suggest the spine's sagittal profile may influence the proximal femoral growth plate's slippage, an aspect not extensively explored. This study utilizes finite element analysis to investigate how various spinopelvic alignments affect shear stress and growth plate slip. MethodsA finite element model was developed from CT scans of a healthy adult male lumbar spine, pelvis, and femurs. The model was subjected to various sagittal alignments through reorientation. Simulations of two-leg stance, one-leg stance, walking heel strike, ascending stairs heel strike, and descending stairs heel strike were conducted. Parameters measured included hip joint contact area, stress, and maximum growth plate Tresca (shear) stress. FindingsPosterior pelvic tilt cases indicated larger shear stresses compared to the anterior pelvic tilt variants except in two leg stance. Two leg stance resulted in decreases in the posterior tilted pelvi variants hip contact and growth plate Tresca stress compared to anterior tilted pelvi, however a combination of posterior pelvic tilt and high pelvic incidence indicated larger shear stresses on the growth plate. One leg stance and heal strike resulted in higher shear stress on the growth plate in posterior pelvic tilt variants compared to anterior pelvic tilt, with a combination of posterior pelvic tilt and high pelvic incidence resulting in the largest shear. InterpretationOur findings suggest that posterior pelvic tilt and high pelvic incidence may lead to increased shear stress at the growth plate. Activities performed in patients with these alignments may predispose to biomechanical loading that shears the growth plate, potentially leading to slip.

Aerodynamic flow field analysis of vortex interactions on multi-swept wing configurations

The underlying flow physics of vortex breakdown and vortex-vortex interactions at moderate to high angles of attack is not well understood. This lack of understanding is a challenge to the development of optimized wing designs for fighter aircraft. The goal of this study is to gain insight into the breakdown of vortices on multi-swept wing configurations. Two generic models were considered, one with a gradual vortex breakdown and one with a rapid (abrupt) breakdown. Aerodynamic forces were calculated from the US Air Force Academy (USAFA) subsonic wind tunnel to validate the experimental setup using computational fluid dynamics (CFD) and previous work. Stereoscopic particle imaging velocimetry (SPIV) was used to visualize vortex-vortex interactions, measure vortex strengths, and identify vortex breakdown locations. The measured lift and drag forces showed flow physics that agreed with previous experiments and CFD, supporting the validity of the new experimental setup. Analysis of SPIV and CFD data improved our understanding of the different types of vortex interactions observed for both models. The only difference between the models was the location of the secondary sweep angle on the chord. The C4L80 model, with a secondary sweep angle at 40% of the root chord, had a large shear layer along the leading edge, which led to vortex merging and gradual vortex breakdown at lower angles of attack than its counterpart. The C6L80 model, with a secondary sweep angle at 60% of the root chord, had no such shear layer and instead developed strong, isolated vortices that were characterized by vortex braiding and abrupt breakdown at high angles of attack. These vortices were entrained into the main vortex at the leading edge of the strake (inboard vortex), creating a balanced vortex system that enhanced lift and delayed the onset of gradual vortex breakdown seen in the C4L80 model.

Nonlinear viscoelasticity of Melaleuca alternifolia essential oil Pickering emulsion stabilized with cellulose nanofibrils

Pickering emulsions are suitable technological approaches to stabilize the bioactive compounds of essential oils (EOs) with economic interests for the pharmaceutical, cosmetic and food industries using atoxic and renewable stabilizers, such as cellulose nanostructures. The Melaleuca alternifolia essential oil (MaEO) is recognized for its pronounced antimicrobial performance, which has attracted your interest in developing eco-friendly antiseptic products. In this contribution, we report the nonlinear viscoelasticity behavior of MaEO-in-water Pickering emulsions stabilized by cellulose nanofibrils (CNF) using Large Amplitude Oscillatory Shear (LAOS) tests. The rheological characterizations by Fourier Transform (FT) rheology spectroscopy and Lissajous plots enabled the correlation of the viscous and elastic behaviors with the physical processes involving the deformation of the emulsion. Also, the internal structure of the emulsion was elucidated by fluorescence optical microscopy. Several findings relative to the effects of the shear deformation amplitude over the nonlinear viscoelasticity of the emulsified system are reported here, which are essential to the industrial processes used to develop technological products.

On the undrained shear behavior of sand mixtures with non-plastic fines subjected to large shear displacement

Fluidized landslides pose significant hazards owing to the catastrophic failure and flow-like behavior with high mobility and long traveling distances. Non-plastic fines can be abundant in many fluidized landslides with 30%–40% content of relatively fine-grained particles. However, the role of fine particles in the initiation and movement of these landslides is not well understood. To investigate the effects of non-plastic fines content (FC) on the undrained shear behavior of the mixture, undrained ring shear tests were performed on mixtures of silica sand (D50 = 0.16 mm) with varying weight proportions of non-plastic fines (D50 = 0.035 mm) with different initial densities. We showed that liquefaction potential increased as fines content increased and initial density decreased. Peak strength (τp), steady-state strength (τss), and total dissipated shear energy to the steady state (Wss) increased against increasing density of the sample. Given the same initial density, τp, τss, and Wss decreased with the increases of FC. Using intergranular void ratio (es) and equivalent intergranular void ratio (es⁎), we found that plots of τp, τss, and Wss against es⁎ merged to a relatively narrow domain, indicating es⁎ can serve as a comprehensive indicator for evaluating the FC's effects on undrained shear behavior. An optimum es⁎ existed for the mixtures, which corresponds to the minimal brittleness index IB, that is used for analyzing liquefaction associated with post-failure behavior. The Wss in the log scale continuously decreased with increasing es⁎. We inferred that the addition of fine particles could change the inter-particle force transfer. When the FC increases, a greater proportion of fines can actively engage in the forces transferring structure as active fine particles, resulting in increasing liquefaction potential and reducing the energy dissipation throughout the entire shearing process of the saturated mixtures, thereby facilitating the fluidization and mobility of landslides. This study provides an evaluation of the full liquefaction process of fines-rich mixtures and further explains the fines' role in the high mobility of fluidized landslides based on the energy dissipation view.

Seismic response of combined piled raft foundation using advanced liquefaction model

The design of earthquake resistant structures founded on combined piled raft foundation (CPRF) mainly depends on raft-pile-soil interaction (RPSI). This interaction become more complex for these heavy structures, if founded on the liquefiable soil. The CPRF is considered to be useful foundation in practice to support such heavy structure; in which both raft and pile increase the bearing capacity of the soil. Where raft reduces the liquefaction induced settlement and piles help to transfer the load of the structure to the non-liquefiable soil layer. The aim of this paper is to carry out the 3D nonlinear finite difference analysis of CPRF considering the RPSI. A recently developed constitutive model i.e. CycLiq for the liquefaction modelling of the soil is utilized to represent the behaviour of sand in inelastic range which consider the cyclic behaviour and large post-liquefaction shear deformation of sand. The validation of the model is carried out with the centrifuge data. The effect of CPRF over the raft and pile group is carried out for harmonic excitation with varying frequency and earthquake motion with varying PGA. The study provides important observations and insights that were not previously evident. The findings emphasize the need to consider frequency effects, geometrical nonlinearity, and material nonlinearity in the design of NPP structures. Additionally, the study introduces the application of the CycLiq liquefaction model and the development of a user-defined material for FLAC3D. Further, the outcome shows the useful conclusion on the importance of CPRF foundation over the conventional foundation i.e. raft and pile group in the liquefiable soil. It is found that excitation frequency, ground motion PGA, porosity of sand and pile spacing of CPRF have great effects on the response.

Optimized submerged batch fermentation for metabolic switching in Streptomyces yanglinensis 3-10 providing platform for reveromycin A and B biosynthesis, engineering, and production.

The cultivation system requires that the approach providing biomass for all types of metabolic analysis is of excellent quality and reliability. This study was conducted to enhance the efficiency and yield of antifungal substance (AFS) production in Streptomyces yanglinensis 3-10 by optimizing operation conditions of aeration, agitation, carbon source, and incubation time in a fermenter. Dissolved oxygen (DO) and pH were found to play significant roles in AFS production. The optimum pH for the production of AFS in S. yanglinensis 3-10 was found to be 6.5. As the AFS synthesis is generally thought to be an aerobic process, DO plays a significant role. The synthesis of bioactive compounds can vary depending on how DO affects growth rate. This study validates that the high growth rate and antifungal activity required a minimum DO concentration of approximately 20% saturation. The DO supply in a fermenter can be raised once agitation and aeration have been adjusted. Consequently, DO can stimulate the development of bacteria and enzyme production. A large shearing effect could result from the extreme agitation, harming the cell and deactivating its products. The highest inhibition zone diameter (IZD) was obtained with 3% starch, making starch a more efficient carbon source than glucose. Temperature is another important factor affecting AFS production. The needed fermentation time would increase and AFS production would be reduced by the too-low operating temperature. Furthermore, large-scale fermenters are challenging to manage at temperatures that are far below from room temperature. According to this research, 28°C is the ideal temperature for the fermentation of S. yanglinensis 3-10. The current study deals with the optimization of submerged batch fermentation involving the modification of operation conditions to effectively enhance the efficiency and yield of AFS production in S. yanglinensis 3-10.