Shear Stress Amplitude Research Articles

Static and cyclic performance of polyurethane foam adhesive bound soil–rubber mixtures under drained conditions

The major drawbacks of a railway track include noise, vibration, and aggravated track degradation. Resilient mats and asphalt have been increasingly used in recent years to mitigate this noise and vibration. However, these materials are quite expensive. Conventional asphalt is very stiff and brittle, making it more prone to cracking. The present work aims to develop a novel material that can be used as a base layer in ballasted and slab tracks. The current research proposes a sustainable and resilient base course layer comprising ground rubber (GR) and polyurethane foam adhesive (PFA). In this study, the performance of GR embedded in the sand is investigated. The use of PFA-treated sand with and without GR is then explored. The optimum dosage of PFA for soil and GR for treated and untreated soil is recommended based on static direct simple shear (SDSS) and cyclic direct simple shear (CDSS) tests. SDSS tests were performed to evaluate the monotonic performance of all mixtures. CDSS tests were performed to assess the long-term performance of these different mixes under repeated cyclic loading (50,000 load cycles) and varying cyclic shear stress amplitude. It is shown that PFA helps reduce the settlement and enhance soil shear strength, while GR increases the damping ratio of the soil. The optimum dosage of PFA is recommended 10%. The optimum GR content for untreated and PFA-treated soil is recommended 5 and 10%, respectively.

Dynamic properties of dredger fill involved coupling action of initial stress and principal stress rotation

GCTS hollow cylinder apparatus was used to perform a series of tests on dredger fill from Tianjin under different initial stress states. This cyclic loading mode can simulate the rotation of the principal stress direction induced by wave loading. The effects of the initial intermediate principal stress parameter, initial shear stress and initial orientation angle of principal stress on softening index of dredger fill were investigated. A stiffness softening model which can consider different initial stress states was established. The test results show that when two of the three initial stress parameters remain unchanged, the softening index decreased with the increase of any other parameter. Among them, the initial orientation angle of principal stress has a great influence on stiffness softening. Based on the regression analysis of the test data, the relationship between the generalized shear strain ratio and the number of cycles under different cyclic shear stress amplitudes is proposed. Subsequently, the dynamic strength characteristics of the dredger fill were studied. It is found that the dynamic strength decreased significantly with the increasing initial angle of the principal stress, which can be accurately described by the model proposed in this article.

Long-Term Response of Sand Subjected to Repetitive Simple Shear Loading: Shakedown, Ratcheting, and Terminal Void Ratio

Low-amplitude repetitive drained loading may hinder the long-term performance of engineered and natural systems. This study examines the volumetric and shear response of a uniform quarzitic sand subjected to repetitive drained simple shear loading under constant vertical stress while tracking the evolution of the secant stiffness and the small-strain shear modulus. We explore the effects of initial density, initial shear stress and cyclic shear stress amplitude to identify criteria that can be used to anticipate asymptotic volumetric and shear states. We analyze experimental results in reference to the sand response under monotonic simple shear loading. All specimens evolved toward some asymptotic terminal void ratio eT when subjected to simple shear cycles. Contractive specimens exhibited unceasing shear strain accumulation and ratcheting when the normalized shear stress exceeded τ*=(τo+Δτ)/τult>0.85; on the other hand, dense-dilative specimens exhibited ratcheting only when the normalized shear stress exceeded τ*=(τo+Δτ)/τult>1.25. The small-strain Gmax and the secant Gpp shear moduli increased during repetitive shear cycles to reflect early fabric changes followed by abrasion/fretting among enduring contacts. Results obtained in this study allow us to propose simple guidelines to predict the asymptotic shear and volumetric response of uniform sands subjected to repetitive simple shear loading for first-order engineering analyses.

Wall shear stress during impingement at the building platform can exceed nozzle wall shear stress in microvalve-based bioprinting.

It is well known that in microvalve-based bioprinting, the cells are subjected to wall shear stress, which can negatively affect their viability rate. We hypothesized that the wall shear stress during impingement at the building platform, hitherto not considered in microvalve-based bioprinting, can be even more critical for the processed cells than the wall shear stress inside the nozzle. To test our hypothesis, we used fluid mechanics numerical simulation based on finite volume method. In addition, viability of two functionally different cell types, HaCaT cell line and primary human umbilical vein endothelial cells (HUVECs), embedded in the cellladen hydrogel was assessed after bioprinting. Simulation results revealed that at low upstream pressure the kinetic energy was not sufficient to overcome the interfacial force for droplet formation and detachment. Oppositely, at relatively mid upstream pressure, a droplet and a ligament were formed, whereas at higher upstream pressure, a jet was formed between nozzle and platform. In the case of jet formation, the shear stress during impingement can exceed the wall shear stress in the nozzle. The amplitude of impingement shear stress depended on nozzle-to- platform distance. This was confirmed by evaluating cell viability which revealed an increase of up to 10% when increasing the nozzle-to-platform distance from 0.3 to 3 mm. In conclusion, the impingement-related shear stress can exceed the wall shear stress in the nozzle in microvalve-based bioprinting. However, this critical issue can be successfully addressed by adapting the distance between the nozzle and the building platform. Altogether, our results highlight impingement-related shear stress as another essential parameter to consider in devising bioprinting strategies.

Cyclic failure characteristics of silty sands with the presence of initial shear stress

Liquefaction of silty sands remains an outstanding issue since it continues to lead to catastrophic consequences in recent earthquake events. The cyclic characteristics, such as cyclic failure pattern and cyclic resistance, are the fundamental aspects of liquefaction analysis. The difficulty and uncertainty of characterization and evaluation of cyclic behavior and liquefaction resistance of silty sand mainly come from the complicated interactions of various influencing factors, such as packing density, confining pressure, initial shear stress, cyclic loading amplitude, soil properties, and soil fabric. This study presents a series of laboratory testing results to identify the cyclic failure patterns of silty sands considering different soil states, fines contents, initial static shear stress, etc. It is found that the failure patterns are related to the states of soils and the cyclic loading characteristics, i.e., the combination of initial shear stress and cyclic loading amplitude for silty sands with similar soil fabric, and that the cyclic resistance of silty sands is also a function of soil states and initial static shear stress for similar soil fabric. Critical state soil mechanics is implemented to characterize the cyclic failure patterns and cyclic resistance. Implications of the present study to the existing liquefaction assessment methods are also discussed.

An improved Artificial Neural Network for the direct prediction of fretting fatigue crack initiation lifetime

Fretting fatigue is a common type of problem in the aviation and other engineering fields. Due to its multiaxial characteristics, it leads to a shorter overall fatigue life compared to plain fatigue conditions. Fretting fatigue crack initiation lifetime is a crucial part of the total lifetime, and the currently dominant method for research on fatigue behavior is the combination of the theoretical and numerical models. With the advent of the era of data science, machine learning has been widely used to predict fatigue behavior, but there are no many applications in the field of fretting fatigue. This paper proposed an improved Artificial Neural Network (ANN) using Balancing Composite Motion Optimization (BCMO) for quick prediction of fretting fatigue crack initiation lifetime. Physical-mechanical reasoning parameters, axial stress amplitude, shear stress amplitude, half contact width, and half stick zone width are considered as input parameters, and fretting fatigue crack initiation lifetime is set as the output feature. The main aim of BCMO is to improve the robustness of the ANN based on the influential parameters, namely bias and weight. The provided results using ANN-BCMO are robust compared to ANN and traditional techniques from the literature. The Matlab code of improved ANN using BCMO can be found at https://github.com/Samir-Khatir/BCMO-ANN.git

Cyclic strain sweep testing-analysis to evaluate the mechanical characteristics of stabilized soils

Infrastructure such as roadways, airfield pavements, and railways are primarily subjected to cyclic loading conditions. Subgrade soils for such infrastructure systems are often stabilized to meet and improve mechanical properties with the goal of achieving acceptable performance over the life of pavement or rail system under cyclic loading. This requires understanding the behavior of stabilized soils under cyclic loading as well as monotonic compressive strength as is typically done. This paper discusses a simple and fundamentally sound test method used to investigate the behavior of stabilized soils under cyclic loading. Cylindrical specimens compacted using a Harvard miniature compaction apparatus are subjected to oscillatory torsional loading applied in the strain amplitude sweep mode. To characterize the response of the stabilized soils under cyclic loading, four parameters resulting from the testing were examined: peak shear stress amplitude, dynamic shear modulus, phase angle, and dissipated strain energy. This test method was applied to a simulant soil that was treated using three different additives and cured in two ways. The results of the analysis of the test method using the four parameters showed that the coefficient of variation was in a range of 10–20%, which infers good repeatability. A high sensitivity to the type of stabilizing agents and curing conditions was observed. The energy dissipation response during strain-sweep cyclic loading showed unique time-varying hysteresis loops when different stabilizing agents and curing conditions were used. Furthermore, the method identified two critical strain amplitudes—one indicating the onset of significant nonlinear behavior and the other representing the failure of specimens. Both strain amplitudes were distinctively different from the cases when varying the stabilization methods.

Dynamic Characteristics of Post-Cyclic Saturated Loess

Damage to soil structure caused by strong earthquakes is one of the main reasons for post-earthquake geohazard development. To investigate the nonlinear dynamic behaviors of the post-earthquake loess, a pre-shock reconsolidation test was designed to simulate the process of the loess undergoing earthquake and post-earthquake reconsolidation in a natural state. Furthermore, dynamic triaxial tests of the specimens before and after pre-shock action and consolidation stabilization with different over-consolidation ratios (OCR) were conducted to investigate the variety of the dynamic modulus and damping ratio of the saturated loess. The influence of pre-shock and reconsolidation on the dynamic behaviors was determined. Moreover, the mechanism of the changes after pre-shock and consolidation was discussed by combining the microstructure test results of soil samples before and after pre-shock and reconsolidation. The results suggest that the kinetic stiffness of the pre-shock saturated loess decreases significantly under the same consolidation conditions. The growth of the damping ratio-dynamic strain curve increases, and the deformation potential of the loess has a remarkable growth. With an increase in OCR, the dynamic elastic modulus after pre-shock increases continuously; however, the damping ratio decreases significantly. The dynamic stiffness increases and the deformation potential weakens significantly. The strong earthquake leads to the weakening of interparticle cementation, pore penetration, and structural reorganization in the local area, causes connecting of the macropores, and produces microfractures in the soil, which makes a significant decrease in the dynamic shear modulus ratio and an increase in the damping ratio of the loess, leading to the enhancement of soil dynamic nonlinearity and the attenuation of the dynamic strength. Moreover, the compaction effect of reconsolidation on the soil increases the interparticle friction and heals some microfractures, which leads to an increase in soil stiffness. This makes the maximum dynamic shear modulus and the maximum dynamic shear stress amplitude of the post-cyclic saturated loess perform at the same level compared with the natural loess without shock when the OCR equals three. However, the dynamic shear modulus and the damping ratio of the post-cyclic saturated loess are close to the natural loess when the OCR equals two.

Characterization of dislocation microstructures in near-[formula omitted] single crystal copper using high-voltage scanning transmission electron microscopy

Metallic structures are prone to failure caused primarily by fatigue-related damage to the structural material. Fatigue behavior is strongly correlated with dislocation structures in metals. Therefore, investigating the formation of dislocation structures is essential for understanding the fatigue process. The dislocation structure in face-centered cubic crystals has a strong orientation dependence. However, the detailed characteristics and evolution process of dislocation structures of fatigued [1‾11] single crystal copper are still insufficient. This study investigated dislocation structures in near-[1‾11] single crystal copper cyclically deformed at room temperature under different constant plastic shear strain amplitude (γpl) to analyze the formation mechanism of dislocation structures and their relationship with fatigue behavior. Characteristic dislocation structures were characterized by adopting multiple planes using a high-voltage scanning transmission electron microscope. With increasing shear strain amplitude, a vein-like structure along the (1‾11) plane gradually developed into a wall structure. When γpl ≥ 1 × 10−3, deformation bands and cell bands were formed to accommodate the higher plastic strain. The state of cell-band development significantly affected the cyclic softening of the single crystal copper. A positive linear relationship existed between the shear stress amplitude and the reciprocal of the cell width.

Influence of the thermal effect on quasi-static shear characteristics of calcareous soil: an experimental study

In principle, the mechanical properties of soil particles are irreversibly changed after particles are subjected to heating. Accordingly, this study performed ring-shear tests on calcareous sand samples subjected to high temperatures to qualitatively investigate the influence exerted by the degradation of the calcareous sand, caused by the thermal effect, on the large displacement shear characteristics of the samples. The effects of the shear velocity and normal stress on the quasi-static shear behavior of the calcareous sand samples were analyzed. The influence of the thermal effect on the quasi-static shear flow behavior of the samples is primarily reflected in the change in the particle mineral composition, particle hardness, and sample density. These variations result in changes in the shear strength, residual shear stress, macroscopic friction coefficient, and other shear characteristics of the calcareous sand samples. Both the shear velocity and the high temperature affect the fluctuation amplitude of the residual shear stress. The results have great theoretical and practical significance in terms of explaining the instability mechanism of a slope. Moreover, a feasible and effective technique is proposed to investigate the large-displacement shear behavior of soil subjected to the thermal effect exerted by a long-runout landslide.

A standardizable approach for Tooth Flank Fracture

Ultrasonic scanning of large spiral bevel gears and the subsequent fracture analyses of early-stage tooth flank fractures imply a mode II crack initiation under surface-parallel, orthogonal shear stresses. An iteration of the Dang Van criterion is presented that focuses exclusively on surface-parallel material planes, yielding a standardizable approach for the study of tooth flank fracture in spiral bevel gears. It is shown that Dang Van’s shear stress amplitude and maximum hydrostatic stress along a surface-perpendicular path can adequately be described by the Hertzian orthogonal shear stress amplitude and Lang’s compressive residual stress. The fatigue properties along the same path are estimated from Thomas’ hardness model and augmented by ISO-inspired lifetime, size and conversion factors. The article closes with a comparison between the commonly used Witzig-Boiadjiev, Hertter-Wirth, DNV subsurface fatigue and the herein proposed, rationalized Dang Van criterion.

A contribution to the identification of the critical plane using the maximum variance method

The goal of the present paper is to propose a new critical plane search strategy based on the Maximum Variance Method of the resolved shear stress, to build a computationally efficient algorithm. For this, it is considered that the maximum variance of the shear stress resolved can be obtained by calculating the eigenvalues and eigenvectors of the covariance matrix of the resolved shear stress amplitudes in two perpendicular directions of a material plane. The evaluation of this strategy for different random multiaxial loading conditions shows that it compares very well with experimental data published in the literature.

Laboratory Rat Thrombi Lose One-Third of Their Stiffness When Exposed to Large Oscillating Shear Stress Amplitudes: Contrasting Behavior to Human Clots

Rats impress by their high platelet count resulting in hypercoagulability, which protects the animals from severe bleeding. However, platelets also import numerous stiff junction points into the fibrous system of a clot, also enhancing the pre-stress of the fibrin fibers, which lowers their deformability. Clot deformation is clinically important since large strains are present in the arterial tree (caused by the propagation of pressure and pulse waves), and a clot is considered “safe” when it can deform over a long range of strain amplitudes. We tested clot formation and the behavior of fully formed blood clots of laboratory rats at large sinusoidal shear stress amplitudes by rheometry and compared outcomes to human reference data. We found that fiber density (by scanning electron microscopy) and clot stiffness (by rheometry) was pronounced compared to humans and differed with sexual dimorphism and with rat strain. Using our large amplitude oscillation (LAOS) protocol, we detected that rat clots yielded with a frustrated attempt to stiffen instead of showing the macroscopic stiffening response that is typical for human clots. We attribute this behavior to the appearance of multiple microfractures until, finally, a few leading fibers uptake the load. Rat clots also failed to align fibers in shear direction to initiate affine deformation. The rat clot phenotype differs substantially from the human one, which must be considered in research and toxicological testing. If microfractures in the fiber meshwork are concentrated in vivo, parts of a clot may break off and be washed away. However, homogenously distributed microfractures may open pores and allow the penetration of plasminogen activators. What occurs in the rat vasculature depends on the on-site clot composition.

Numerical frameworks for fretting fatigue life analysis: Modeling, validation and experimental comparison

A comparison of four numerical frameworks employed for the fretting fatigue life estimation of standard metallic specimens is presented. The frictional contact frameworks are: a Node-To-Node contact formulation using the boundary element method, a Node-To-Segment and a Segment-To-Segment contact formulations coupled to the finite element method, and a dual mortar formulation. The analysis procedure, repeated using each framework, is performed in three steps. The first step is the evaluation of the stress history during one loading cycle of a standard fretting fatigue setup which includes normal load, bulk load and shear load. In the second step, a critical plane approach is used to obtain the shear stress amplitude and the maximum normal stress. The final step is to employ a criterion to estimate the fatigue life. Based on previous works, the Fatemi–Socie method is selected. The validation of the stresses computed by the numerical models are carried-out using analytical formulae while the fatigue life estimations are compared to experimental data. A discussion on the performance of each framework is also provided.

Chemically reactive accelerating radiative flow of Eyring Powell nanofluid with microorganisms and buoyancy forces

Recently, the nanofluids report multidisciplinary applications in the various era of engineering like engine cooling, solar energy production, cooling of engineering devices, diesel generator performance etc. Owing to such novel applications, the aim of current communication is to report the significances of bio-convection for unsteady Eyring Powell nanofluid due to bidirectional oscillatory stretching surface. The enrollment of buoyancy forces and magnetic impact are worked out to inspect the stability and thermal on set of nanofluids. Heat transformation features are explored by utilizing thermal radiation. Further, the characteristics of chemical reaction and activation energy have been considered for physical significance. Unlike traditional approach, the governing equations are not altered into ordinary set of equation but only diminish the independent variables. This task makes the non-dimensional equations in highly complicated from which the convergent technique via HAM is successfully implemented. The physical outcomes of dominant variables on profiles of microorganisms, concentration, temperature, velocity and skin frictions are conferred graphically while local motile density, Sherwood and Nusselt numbers are deliberated through different tables. It is noted that the amplitude of bidirectional shear stresses and velocities periodically get increase for higher material parameter. This analysis emphasized that concentration distribution augments for rising values of activation energy variable, whereas conflicting situation occurs for temperature difference parameter. Moreover, motile microorganism's distributions are diminished by improved values of bio-convected Peclet and bio-convected Lewis numbers.

A hybrid ANN-multiaxial fatigue nonlocal model to estimate fretting fatigue life for aeronautical Al alloys

A new hybrid model (M3I) based on Artificial Neural Network (ANN) and on a non-local multiaxial fatigue analysis has been proposed to predict fretting fatigue life. The inputs for the ANN were: (i) the shear stress amplitude, (ii) the maximum normal stress, both on the material critical plane, and (iii) the critical distance size. To train and validate the analysis available fretting fatigue data on Al alloy were chosen. The M3I not only yielded accurate life estimates, but also assimilated the effects of the mean normal stress, of the stress gradient and of the contact size on life.

Experimental Investigation on the Deformation and Noncoaxial Characteristics of Fiber-Reinforced Aeolian Soil under Traffic Load

The cumulative plastic deformation of a foundation associated with traffic loading causes subgrade instability, and eventually, failure of retaining structures. In the present study, hollow torsional shear tests were conducted on fiber-reinforced aeolian soil involving varying fiber contents, cyclic deviator stresses, cyclic shear stresses, and consolidation confining pressures using the Small-Strain Hollow Cylinder Apparatus, developed by GDS Instruments Ltd. (GDS SS-HCA). This enabled an investigation of the deformation characteristics and noncoaxial angle changes of fiber-reinforced aeolian soil under a heart-shaped stress path. The results indicate that fiber-reinforced soil deformation under cyclic loading involves axial (ɛz), radial (ɛr), circumferential (ɛθ), and shear (γzθ) strains, and deformation increases with increasing the cyclic number. The strain increases rapidly during the first 200 cycles and then gradually. The axial deformation decreases with increasing fiber content when the fiber content is less than 2‰ and increases when the content is more than 2‰. The plastic strain and total deformation decrease with increasing confining pressure but increase as the cyclic dynamic stress and cyclic shear stress amplitudes increase. Functional equations of the cumulative axial plastic strain and vibration numbers are proposed. The relationships between the model parameters, including the fiber content and cyclic torsional shear stress, are analyzed. The principal stress axis rotation causes variations between the major principal strain increment and the principal stress directions, representing the noncoaxial angle (β). The noncoaxial angle fluctuates during each loading cycle, exhibiting a V shape, for principal stress axis angles (ασ) from −90° to −45° and −45° to 30°, and decreasing at angles varying from 30° to 90°, with a maximum noncoaxial angle of approximately 30° per cycle.

Modelling of third body effect on rolling contact fatigue damage

The contact problem for a rolling elastic sphere and an elastic half-space covered with a viscoelastic layer (third body) is considered. The layer properties in normal and tangential directions are described by the Maxwell model. Based on the macroscopic approach of the contact fatigue damage accumulation the rate of damage accumulation in an elastic half-space is assumed depending on the amplitude values of the principal shear stresses or the equivalent von Mises stress. The influence of the relative longitudinal slippage, the sliding friction coefficient and the properties of the intermediate layer on the internal stresses and at the depth of contact fatigue cracks initiation is studied. The results indicate that the maximum damage can occur both on the surface of the elastic half-space and at a certain depth. The increase of the friction coefficient or relative longitudinal slippage leads to reaching the maximum value of the principal shear stress amplitude on the surface of the half-space, which results in contact fatigue surface fracture (wear). The results also demonstrate that the presence of a viscoelastic layer leads to a decrease of the principal shear stress amplitude within the elastic half-space.

Multiaxial high-cycle fatigue failure and life prediction based on critical plane method

Multiaxial high-cycle fatigue failure criterion and life prediction is important for structural components under complex low stress. A new multiaxial high-cycle fatigue damage parameter based on the plane of maximum shear stress is proposed, which includes the maximum shear stress amplitude, normal stress amplitude and maximum equivalent normal stress. The maximum equivalent normal stress is defined in the form of SWT stress function considering the influence of mean stress. The feasibility of the proposed failure criterion and life prediction model is verified by test data of different materials. The predicted results show that the life prediction error of the proposed fatigue model is basically within three times by comparing with McDiarmid, Matake, Crossland and Papadopoulos fatigue models.

Effect of Solid Volume Concentration on Rheological Properties of Chengdu Clay Slurry

The determination of rheological model about the debris flow is the basis of the simulation of mud flow impact distance and sedimentary fan. By using a mcr301 rheometer, rheological experiments of Chengdu clay slurry with different solid volume concentrations were carried out and the effect of solid volume concentration on shear stress were analyzed. Then the rheological process of Chengdu clay slurry with different solid volume concentration was fitted on the basis of the power law model, the Bingham model and the H–B model. The conclusions are drawn as follows: Chengdu clay mud is a typical shear-thinning non-Newtonian body. The influence of solid concentration on the flow curve is different. When the solid volume concentration is not less than 34% and the shear rate is less than 1.0 s−1, the shear stress increases rapidly as the shear rate increases. Meanwhile, when the shear rate is greater than 1.0 s−1 the shear stress decreases with the increase in the shear rate. When the solid volume concentration is less than 31.6% and the shear rate is less than 1.0 s−1, the shear stress increases with the increase in the shear rate, while when the shear rate is more than 1.0 s−1, the shear stress is less affected by shear rate. In the range of low shear rate (less than 1.0 s−1), the increase amplitude of shear stress (slope of semi logarithmic coordinate flow curve) increases as the solid volume content increases. The flow curve of Chengdu clay mud can be reflected in the whole process by using the Herschel and Bulkley model. It is the best mathematical model to fit the rheological process of Chengdu clay mud. According to the above results, the effect of solid volume concentration on the yield stress of the H–B model is analyzed.