Prediction Of Shear Stress Research Articles

Welding versus adhesive bonding strength investigation

This paper was intended to investigate the strength of adhesive and welded connections to be used in a dynamic message sign (DMS). The tensile strength and shear strength were studied for both of the adhesive and welded specimens. A number of tensile specimens and shear specimens with variations in width and temperature were tested until failure according to the ASTM D638 and ASTM D1002, respectively. The specimens with a range of width from 13 mm to 38 mm were conditioned with temperatures between −56.67 °C and 93.33 °C. The effects of temperature and width on each of the strengths were evaluated by analysing the testing data in a graphical and statistical manner. As expected, all the tests revealed that the welded specimens have significantly higher strength compared to the adhesive specimens in tensile and shear loadings. For the adhesive specimens, due to the increment of temperature, the highest increments were found to be 31.9% and 30.4%. In addition to the tests, Response Surface Metamodels (RSMs) and practical design equations were developed with regression analysis of the testing data, so as to predict tensile and shear stresses of both adhesive and welded specimens in an efficient way. 3D plots generated from the RSMs showed a higher effect of the temperature and width on the ultimate tensile and shear strength for both adhesive and welded specimens, and the practical design equations were founded to be more reliable for the overall tensile and shear stress prediction compared to the RSMs.

Uncertainty Assessment of Entropy-Based Circular Channel Shear Stress Prediction Models Using a Novel Method

Entropy models have been recently adopted in many studies to evaluate the shear stress distribution in open-channel flows. Although the uncertainty of Shannon and Tsallis entropy models were analyzed separately in previous studies, the uncertainty of other entropy models and comparisons of their reliability remain an open question. In this study, a new method is presented to evaluate the uncertainty of four entropy models, Shannon, Shannon-Power Law (PL), Tsallis, and Renyi, in shear stress prediction of the circular channels. In the previous method, the model with the largest value of the percentage of observed data within the confidence bound (Nin) and the smallest value of Forecasting Range of Error Estimation (FREE) is the most reliable. Based on the new method, using the effect of Optimized Forecasting Range of Error Estimation (FREEopt) and Optimized Confidence Bound (OCB), a new statistic index called FREEopt-based OCB (FOCB) is introduced. The lower the value of FOCB, the more certain the model. Shannon and Shannon PL entropies had close values of the FOCB equal to 8.781 and 9.808, respectively, and had the highest certainty, followed by ρgRs and Tsallis models with close values of 14.491 and 14.895, respectively. However, Renyi entropy, with the value of FOCB equal to 57.726, had less certainty.

Disrupted osteocyte connectivity and pericellular fluid flow in bone with aging and defective TGF-β signaling

Skeletal fragility in the elderly does not simply result from a loss of bone mass. However, the mechanisms underlying the concurrent decline in bone mass, quality, and mechanosensitivity with age remain unclear. The important role of osteocytes in these processes and the age-related degeneration of the intricate lacunocanalicular network (LCN) in which osteocytes reside point to a primary role for osteocytes in bone aging. Since LCN complexity severely limits experimental dissection of these mechanisms in vivo, we used two in silico approaches to test the hypothesis that LCN degeneration, due to aging or an osteocyte-intrinsic defect in transforming growth factor beta (TGF-β) signaling (TβRIIocy-/-), is sufficient to compromise essential osteocyte responsibilities of mass transport and exposure to mechanical stimuli. Using reconstructed confocal images of bone with fluorescently labeled osteocytes, we found that osteocytes from aged and TβRIIocy-/- mice had 33 to 45% fewer, and more tortuous, canaliculi. Connectomic network analysis revealed that diminished canalicular density is sufficient to impair diffusion even with intact osteocyte numbers and overall LCN architecture. Computational fluid dynamics predicts that the corresponding drop in shear stress experienced by aged or TβRIIocy-/- osteocytes is highly sensitive to canalicular surface area but not tortuosity. Simulated expansion of the osteocyte pericellular space to mimic osteocyte perilacunar/canalicular remodeling restored predicted shear stress for aged osteocytes to young levels. Overall, these models show how loss of LCN volume through LCN pruning may lead to impaired fluid dynamics and osteocyte exposure to mechanostimulation. Furthermore, osteocytes emerge as targets of age-related therapeutic efforts to restore bone health and function.

Computational fluid dynamics of the right atrium: Assessment of modelling criteria for the evaluation of dialysis catheters.

Central venous catheters are widely used in haemodialysis therapy, having to respect design requirements for appropriate performance. These are placed within the right atrium (RA); however, there is no prior computational study assessing different catheter designs while mimicking their native environment. Here, a computational fluid dynamics model of the RA, based on realistic geometry and transient physiological boundary conditions, was developed and validated. Symmetric, split and step catheter designs were virtually placed in the RA and their performance was evaluated by: assessing their interaction with the RA haemodynamic environment through prediction of flow vorticity and wall shear stress (WSS) magnitudes (1); and quantifying recirculation and tip shear stress (2). Haemodynamic predictions from our RA model showed good agreement with the literature. Catheter placement in the RA increased average vorticity, which could indicate alterations of normal blood flow, and altered WSS magnitudes and distribution, which could indicate changes in tissue mechanical properties. All designs had recirculation and elevated shear stress values, which can induce platelet activation and subsequently thrombosis. The symmetric design, however, had the lowest associated values (best performance), while step design catheters working in reverse mode were associated with worsened performance. Different tip placements also impacted on catheter performance. Our findings suggest that using a realistically anatomical RA model to study catheter performance and interaction with the haemodynamic environment is crucial, and that care needs to be given to correct tip placement within the RA for improved recirculation percentages and diminished shear stress values.

Influence of Subduction Zone Dynamics on Interface Shear Stress and Potential Relationship With Seismogenic Behavior

AbstractWhether tectonic convergence at subduction zones is accommodated predominantly through seismic or aseismic deformation, the former potentially generating large earthquakes, varies considerably between subduction margins. This margin‐scale variability has previously been linked to overriding plate deformation, trench migration, and their influence on the plate interface stress state. While these processes are linked to mantle‐scale dynamics, it is unclear how such dynamics influence interface stress. We systematically analyze the interface stress state in a suite of 2‐D thermo‐mechanical subduction models, where slabs display a range of morphologies that arise from diverse multiscale interactions with adjacent mantle and the overriding plate. We demonstrate that the thickness of the interface layer varies dynamically, in response to Poiseuille flow induced by slab bending or unbending, leading to associated effects on interface shear stress at typical seismogenic depth. Lower shear stress occurs when slab unbending is significant, which is commonly associated with trench retreat and draping of the slab as it impinges on the higher‐viscosity lower‐mantle. Conversely, higher shear stress is associated with limited slab unbending, which is promoted by negligible trench migration and vertically subducting slabs. We conclude that the diversity of slab dynamics may cause large variations in interface stress state between and maybe within margins. This is an additional variable that potentially controls seismogenic behavior, and we compare broad stress estimates for Circum‐Pacific margins to previous studies. Although predicted shear stress varies with observed seismogenic behavior, more detailed constraints on stress state are needed to test for correlation.

Predicting Shear Stress Parameters in Consolidated Drained Conditions Using Artificial Intelligence Methods

Using the direct shear stress test for estimating shear stress parameters is considered to be of great importance, mainly for enhancing and strengthening soils, assessing their bearing capacity, and predicting potential risks that could bring harm to foundations. However, conducting the test in consolidated drained conditions is quite expensive and time-consuming (e.g., up to three months in consolidated clay). To our knowledge, few researchers have suggested simple models in undrained conditions to experimentally estimate these parameters. However, in large projects and slope studies, testing in consolidated drained conditions is more important because these conditions mimic reality. The current study aims to suggest a new model for estimating shear stress parameters. The reliability of the approach was tested through comparing several models of multiple regression analysis, genetic programming, and artificial neural networks. These models were tested on 98 samples of Algiers soil. The results showed the efficiency of the artificial neural network method with two hidden layers, which provided the best appropriate model, and the most approached results to experimental data, as compared with the other models. Based on these findings, this study proposes a structural flowchart for effectively predicting shear stress parameters effectively in future studies.

Solutions of the interfacial shear and normal stresses in plate flexural-strengthened beams based on different complementary strain energy assumptions

A series of solutions based on five different complementary strain energy assumptions (named as Assumptions A, B, C, D, E) are developed for the prediction of interfacial shear and normal stresses in plate flexural–strengthened beams. Basic differences between the Assumptions are that in the formulating of the energy, Assumption A includes the transverse normal and shear stress fields in the beam and in the plate, Assumption B includes the normal stresses but exclude the shear stresses, Assumption C includes the shear stresses but excludes the normal stresses, Assumptions D excludes the normal stresses and the shear stresses in the beam but include the shear stresses in the plate, and Assumption E excludes the normal and shear stresses in the beam and in the plate. The energy expressions of the five Assumptions are developed based on derived statically admissible stress fields and an a generalized 2D-Hooke’s law constitutive model. Through an energy variation principle, compatibility equations and boundary conditions of the interfacial stresses are obtained. Closed form and numerical solutions are then developed for the compatibility equations. By comparing against the interfacial stresses of 2D- and 3D- finite element analyses (FEA), it is observed that Assumptions A and B significantly underpredict the interfacial stresses, Assumption C excellently predicts the interfacial normal stresses, Assumptions D and E excellently predict both the interfacial shear and normal stresses, and Assumptions (C, D, E) excellently capture the FEA stress fields (those are strongly varied across the adhesive thickness). The present study is applicable to plate-strengthened beams with general force boundary conditions but it is limited to linearly elastic orthotropic/isotropic materials.

Predicting the near-wall velocity of wall turbulence using a neural network for particle image velocimetry

Near-wall velocity prediction for wall-bounded turbulence is useful for constructing a wall model and estimating dissipation and wall shear stress. A convolutional neural network is developed to improve the near-wall velocity prediction and spatial resolution for wall-bounded turbulent velocity fields obtained using particle image velocimetry (PIV). To establish the relationship between the low-resolution and high-resolution fields, this machine learning model is trained on a synthetic PIV dataset generated based on velocity fields obtained from the direct numerical simulation of turbulent channel flows at Reτ = 1000. Using a test dataset with a higher Reynolds number of Reτ = 5200, the performance of this model is assessed in terms of instantaneous fields, error analysis, velocity statistics, and energy spectra. The influences of the interrogation window, image resolution, and particle concentration on the performance of this network are also considered. We further apply this network to practical PIV data from a turbulent boundary layer at Reτ = 2200 to assess the network performance under real experimental conditions. The results indicate that the proposed machine-learning-based model can predict missing near-wall velocity fields and enhance the spatial resolution of PIV fields, but the accuracy for Reynolds shear stress prediction needs to be further improved. The presented approach shows the potential ability to predict the near-wall instantaneous velocity of high-Reynolds-number turbulence from low-Reynolds-number flow fields.

Effect of working temperature on the interfacial behavior of overmolded hybrid fiber reinforced polypropylene composites

In the present study, the interfacial behavior of overmolded hybrid fiber reinforced polypropylene composites (hybrid composites) in the working temperature range from 23 °C to 90 °C was studied by experimental and constitutive methods. Monotonic and cycle loading-unloading single-lap-shear tests were employed to determine the interfacial properties of hybrid composites. The experimental results show that both interfacial shear strength and shear stiffness decrease with increasing working temperature. A regression function was adopted to evaluate the decaying degree of interfacial properties with increasing working temperature. The shear stress-displacement relationship under monotonic loading exhibits nonlinear behavior after an initial elastic region. The envelope lines of shear stress-displacement of hybrid composites under cyclic loading indicate that the nonlinearity in the curve is caused by the plastic deformation of polypropylene in the interphase region. A constitutive model was built to describe the nonlinear shear stress-displacement relation of hybrid composites at different working temperatures. A full suite of temperature-dependent plastic parameters in the model was obtained from cyclic loading-unloading tensile tests. The predicted shear stress–displacement curves agreed well with experimental results from different working temperatures. In addition, the failure mode of hybrid composites varied with working temperature.

Effect of Minimum Quantity Lubrication to Prediction of Cutting Temperature Distribution in Turning Material AISI-1045

This paper presents a prediction of cutting temperature in turning process, using a continuous cutting model of Johnson-Cook (J-C). An method to predict the temperature distribution in orthogonal cutting is based on the constituent model of various material and the mechanics of their cutting process. In this method, the average temperature at the primary shear zone (PSZ) and the secondary shear zone (SSZ) were determined for various materials, based on a constitutive model and a chip-formation model using measurements of cutting force and chip thicknes. The J-C model constants were taken from Hopkinson pressure bar tests. Cutting conditions, cutting forces and chip thickness were used to predict shear stress. Experimental cutting heat results with the same cutting parameters using the minimum lubrication method (MQL) were recorded through the Testo-871 thermal camera. The thermal distribution results between the two methods has a difference in value, as well as distribution. From the difference, we have analyzed some of the causes, finding the effect of the minimum quantity lubrication parameters on the difference.

Bond investigations of prestressed, near-surface-mounted, ribbed memory-steel bars with full bond length

The effectiveness of iron-based shape memory alloy (Fe-SMA, ‘memory-steel’) reinforcements has been proven in several studies and site applications. Due to the novelty of ribbed memory-steel reinforcement bars, limited research has been performed on their application in structural engineering, however. In this study, the bond behaviour of memory-steel bars in a near-surface-mounted configuration designed for prestressed strengthening of concrete structures was investigated. Memory-steel bars were installed on concrete blocks and activated by resistive heating before being subjected to pull-out load. The effects of heating and hence prestressing, bar ductility, bond length and rigidity of the fixation were studied based on obtained prestress, crack development, slip and bar strain. During activation of the bars, a longitudinal splitting crack with insignificant crack width occured. Two failure modes were observed during subsequent external loading, including tensile rupture of the bar when less ductile material was used, or bond failure when material with higher ductility was under investigation. Initial prestressing did not result in a reduced bond capacity. Based on the differential equation of bond behaviour, an analytical calculation procedure was developed that enables prediction of bond shear stress, slip, bar strain, pull-out load, as well as the use of a non-linear material behaviour.

An accurate solution for stress fields strongly varied across the adhesive thickness in soffit plate-strengthened beams

A closed form solution and a finite difference formulation are developed for an accurate prediction of adhesive shear and normal stresses in soffit plate flexural-strengthened beams. First, three statically admissible stress fields (i.e., longitudinal normal, transverse shear and normal stresses) are derived and expressed in terms of four unknown interfacial shear and normal stresses. Then, a modified complementary strain energy is written in which the energy contributions of the transverse normal stress fields in the beam and in the plate, and the transverse shear stresses in the beam are omitted. Based on an energy variational principle, compatibility equations and corresponding boundary conditions are obtained. A closed form solution and a finite difference formulation are finally developed. Through validations, the adhesive shear and normal stresses near the plate ends predicted by the present study are in excellently agreements with those provided in several experimental and numerical studies. Also, the present study excellently captures stress fields strongly varied across the adhesive thickness, especially the transverse normal stresses. Based on the present theory, a parametric study is conducted to quantify the effects of the plate longitudinal modulus and the thickness on the interfacial shear and normal stresses. The parametric study indicates that the peak normal stresses are significantly higher than the peak shear stresses in the adhesive layer. The present study is applicable to predict the adhesive shear and normal stresses highly concentrated near the plate ends in plate-strengthened beams with general applied loads and force boundary conditions.

Improved analytical solution for slip and interfacial stress in composite steel-concrete beam bonded with an adhesive

In this paper, an improved theoretical interfacial stress and slip analysis is presented for simply supported composite steel-concrete beam bonded with an adhesive. The adherend shear deformations have been included in the present theoretical analyses by assuming a linear shear stress through the thickness of the adherends, while all existing solutions neglect this effect. Remarkable effect of shear deformations of elements has been noted in the results. It is observed that large shear is concentrated and slip at the edges of the composite steel-concrete. Comparing with some experimental results from references, analytical advantage of this improvement is possible to determine the normal and shear stress to estimate exact prediction of normal and shear stress interfacial along span between concrete and steel beam. The exact prediction of these stresses will be very important to make an accurate analysis of the mode of fracture. It is shown that both the normal and shear stresses at the interface are influenced by the material and geometry parameters of the composite steel-concrete beam. This research is helpful for the understanding on mechanical behavior of the connection and design of such structures.

The Influence of Surface Stress Fluctuation on Saltation Sand Transport Around Threshold

AbstractMultiscale wind velocity fluctuation and complex inertial response of sand saltation to wind variations give rise to intermittent and nonuniform sand transport, which greatly challenges the prediction of transport rate under wind conditions around saltation threshold. In this paper, three‐dimensional sand saltation within simulation domain of wind tunnel scale is modeled based on large eddy simulation of turbulent wind. Special attention is paid to the prediction of surface shear stress and consequently aerodynamic entrainment. When the wall stress model considering the influence of large‐scale turbulent structures was employed in case of relatively small resistance level for calculating particle aerodynamic entrainment, the model results predict sand transport below the impact threshold. The sand transport rate in this regime increases exponentially with mean wall stress, in contrast to the standard power law‐like behavior above the impact threshold. Aerodynamic entrainment and strong transport events lag behind high‐speed fluids sweep on a large scale even in wind tunnel, but the spatiotemporal variability of small‐scale sand transport is still unclear and quite complex due to transport inertia.

Predicting River Embankment Failure Caused by Toe Scour Considering 1D and 2D Hydraulic Models: A Case Study of Da-An River, Taiwan

Physically based numerical models can predict scour depth at embankments located in bend reaches. However, methodologies for utilizing these numerical models to assess the risk of reinforced concrete embankment failure are rarely investigated. Therefore, a new assessment methodology is proposed to predict the riverbank failure caused by bend scour. The methodology is primarily based on a bend scour simulation model that integrates a one-dimensional (1D) hydraulic model, a two-dimensional (2D) hydrodynamic finite-volume model, and an empirical equation of bend scour prediction. The model was first applied to the Shuiwei Embankment located in a river bend reach of Da-An River in Taiwan and verified against results from the 1D hydraulic model and field data. The model was then used to simulate 2D flow field and the temporal evolution of bend scour depth under different return period flood events to examine the relationships between river discharge, water level, shear stress, and bend scour depth. The influence of shear stress on the stability of toe protections was also investigated. The field data (from two events) and numerical solutions (four scenarios) were assessed to conceive two empirical equations for predicting shear stress and bend scour depth. A new assessment methodology was proposed using these two equations to predict the risk of river embankment failure during flood periods. The proposed methodology can be easily applied in other disaster-prone regions to mitigate the effects of disasters caused by bend scouring.

Flow structures and shear-stress predictions in the turbulent channel flow over an anisotropic porous wall

This article identifies the main coherent structures driving the flow dynamics in the turbulent channel flow over anisotropic porous walls. Two different cases have been analyzed where the drag increases or decreases with respect to a channel with isotropic porous walls. Higher order dynamic mode decomposition (HODMD) is applied to analyze these data, identifying 20 and 15 high amplitude modes in the drag increasing (DI) and drag reducing (DR) cases, respectively, which well reflects the largest flow complexity in the former case. The frequency of 13 modes and the three-dimensional structure of the modes are similar in the DR and DI cases, suggesting the need of using more complex analyses to deepen our physical insight of these flows. The spatio-temporal HODMD analysis identifies a periodic solution along the spanwise direction (as imposed by the boundary conditions). The wavenumbers related to the modes with highest amplitude are β = 0 and β = 3 (Lz = 2 3 π ). The rollers, groups of spanwise correlated structures, are mostly identified in the DI case near the wall, with β = 0, while the presence of the streaks, streamwise correlated structures are mostly identified in the DR case. Although, in areas far away from the wall it is possible to identify these two types of structures with β = 3 in both cases, depending on the temporal frequency of the DMD modes, the rollers and the streaks are related to high and low frequency DMD modes, respectively. Finally, a model is constructed to predict the temporal evolution of the wall shear, using the 6 most relevant DMD modes interacting near the channel wall: 6 low frequency modes for DR and 3 low and 3 high frequency modes for DI. In the DR case the wall shear is predicted for almost 300 time units with relative error ∼ 2%, however, this error is larger in the DI case, ∼ 6%, suggesting the need of using a larger number of modes to represent this more complex flow.

Depth-Averaged von Kármán Coefficient in Sediment-Laden Flows Using a Turbulent Kinetic Energy Balance

AbstractPrecise prediction of bed shear stress (τ0) and velocity profile in open channels is critical in various applications. This paper deliberates on the depth-averaged von Karman coefficient in...

Investigation of New Tsallis-Based Equation to Predict Shear Stress Distribution in Circular and Trapezoidal Channels

In this study, the entropy concept is employed to estimate the shear stress distribution in a circular channel with flat bed and trapezoidal channel. Using the principle of maximum entropy, the shear stress distribution is derived by maximizing the Tsallis entropy by assuming averaged shear stress as a random variable. The derived shear stress equation can describe the variation of shear stress along the wetted perimeter of channel. The developed model of shear stress distribution is tested with some credible experimental data and is also compared with equations obtained by other researchers based on the Shannon entropy concept. The present model has shown good agreement with the observed data and performed better than the Shannon-based model in both cross-sections with better results of several computed quantitative criteria. The model precision in estimating shear stress in the trapezoidal channel with mean root mean square error (RMSE) of 0.0158 was higher than the circular channel with flat bed with RMSE of 0.0679.

Improved phase-field-based lattice Boltzmann models with a filtered collision operator

In this study, a phase-field lattice Boltzmann model based on the Allen–Cahn equation with a filtered collision operator and high-order corrections in the equilibrium distribution functions is presented. Here, we show that in addition to producing numerical results consistent with prior numerical methods, analytic solutions, and experiments with the density ratio of 1000, previous numerical deficiencies are resolved. Specifically, the new model is characterized by robustness at low viscosity, accurate prediction of shear stress at interfaces, and removal of artificial dense bubbles and rarefied droplets, etc.

Correcting interface turbulence viscosity using CFD modeling for predicting stratified gas–liquid flow shear stress in horizontal pipes

Abstract The prediction of different shear stresses is one of the great challenges of turbulent–turbulentstratified two-phase flow in horizontal pipes. In this work, VOF method, near-wall differential viscosity and local turbulence viscosity distribution coefficient function are introduced and offer an efficient tool to correct the interface turbulence viscosity. The results show that the new method can better predict the shear stresses, liquid holdup and pressure drop of stratified two-phase flow. The fitting relationship between interfacial and wall friction factor ( f i ∕ f W ) is in good agreement with the experimental data. It is found that f i ∕ f W is predicted with a relative error of 12.62% by the new method, which is much less than that by any other method when the gas and liquid superficial Reynolds numbers are 8000 ≤ Re S G ≤ 90000 and 5000 ≤ Re S L ≤ 170000. It provides a reliable method for achieving the closure of stratified flow to predict the shear stresses.