Variation Of Shear Stress Research Articles

Effect of thermal radiation on MHD three dimensional natural convective Couette flow in presence of thermo-diffusion and chemical reaction

This paper analyzes the effect of thermal radiation on MHD three dimensional natural convective Couette flow of an incompressible, viscous and electrically conducting fluid with uniform magnetic field. The plates are taken vertically upward. The magnetic field is applied normal to the plates. The governing equations are solved using simple perturbation technique. The effect of various parameters like M, Pr, R, Re, Gr, Gm etc. are studied graphically on dimensionless velocity, temperature and concentration. Also the variations in shear stress (τ), Nusselt number (Nu) and Sherwood number (Sh) for different physical parameters are presented in tables.

A n-order refined theory for free vibration of sandwich beams with functionally graded porous layers

In this paper, a simple n-order refined theory is developed for free vibration of a simply supported sandwich beam with functionally graded porous layers. The present theory is variationally consistent, uses the n-order polynomial term to represent the displacement field, and does not require a shear correction factor. The variation of shear stress is parabolic across the thickness and the condition at the top and bottom surface are shear stress-free. Equations of motion are derived from Hamilton's principle. In the solution of the governing equations, the Navier procedure is implemented. For porosity effect, four different porosity distributions namely O, X, V, and homogeneous distribution types are modelled; power-law variation of functionally graded face sheets is considered. Results show the effects of varying gradients, thickness to length ratios, effects of the porosity parameters and porosity types on free vibration of functionally graded sandwich beams for simply supported boundary conditions. The results of the present method were validated with existing literature for both hard (ceramic) core material and soft (metal) core material, and good agreement with the benchmarks is seen. The effect of hard-core and soft-core material on natural frequency is found to be contrasting in nature.

Acoustic Properties of the Otolith of the Large Yellow Croaker Larimichthys crocea (Perciformes: Sciaenidae).

The inner ears of fish contain three pairs of otoliths-lapilli, asterisci and sagittae-which play important roles in hearing and balance. However, acoustic properties and dynamic responses of fish otoliths are poorly understood. The large yellow croaker (Larimichthys crocea), like many species in the family Sciaenidae, is extremely sensitive to sound. The present study used L. crocea sagittae as the research subject and examined the variation in shear stress on sagittae under different acoustic stimuli. For the first time, the sound speed of the sagitta was measured using ultrasonic pulse-echo techniques, and the acoustic impedance and natural frequency of the sagitta were calculated. Larimichthys crocea adults (20-22 cm standard length, n = 10) had a sagitta density of 2781.5 ± 28.06 kg/m3, sound speed of 4828-6000 m/s and acoustic impedance range of 13.4-16.7 MPa·s/m, approximately 9-11 times that of seawater (1.48 MPa·s/m). The natural frequency of the sagitta was 76.4-95.5 kHz. The shape and structural details of sagittae were reconstructed by 3D scanner and the shear stress responses of sagittae under different acoustic stimulus were investigated based on a finite element model. The simulation results showed that the shear stress responses tended to increase and then decrease in the range of sciaenid hearing frequency from 200 to 1300 Hz, peaking at 800 Hz. The shear stress responses varied with the direction of acoustic stimulus and peaked when the incident direction was perpendicular to the inner surface of the otolith. These results provide important parameters that may be used to protect L. crocea from possible underwater noise damage, particularly during their spawning aggregations and over-wintering aggregations.

Endothelial mechanotransduction in cardiovascular development and regeneration: emerging approaches and animal models.

Living cells are exposed to multiple mechanical stimuli from the extracellular matrix or from surrounding cells. Mechanoreceptors are molecules that display status changes in response to mechanical stimulation, transforming physical cues into biological responses to help the cells adapt to dynamic changes of the microenvironment. Mechanical stimuli are responsible for shaping the tridimensional development and patterning of the organs in early embryonic stages. The development of the heart is one of the first morphogenetic events that occur in embryos. As the circulation is established, the vascular system is exposed to constant shear stress, which is the force created by the movement of blood. Both spatial and temporal variations in shear stress differentially modulate critical steps in heart development, such as trabeculation and compaction of the ventricular wall and the formation of the heart valves. Zebrafish embryos are small, transparent, have a short developmental period and allow for real-time visualization of a variety of fluorescently labeled proteins to recapitulate developmental dynamics. In this review, we will highlight the application of zebrafish models as a genetically tractable model for investigating cardiovascular development and regeneration. We will introduce our approaches to manipulate mechanical forces during critical stages of zebrafish heart development and in a model of vascular regeneration, as well as advances in imaging technologies to capture these processes at high resolution. Finally, we will discuss the role of molecules of the Plexin family and Piezo cation channels as major mechanosensors recently implicated in cardiac morphogenesis.

Numerical simulation of ballistic impact on aluminium 5083-H116 plate with Johnson cook plasticity model

Nowadays, a numerical simulation study using finite element method is very famous among the engineers and scientists, because it not only reduces the cost of the entire project but also saves a lot more time. The results of the numerical simulations needed to validate through experiments. So, we can say that numerical simulation studies reduce the no. Of experiments taken, if it cannot eliminate. In this research, a ballistic impact on the aluminium AA5083-H116 plate by using a rigid steel projectile is examined through numerical simulations in LS-Dyna Solver by using Johnson-Cook (J-C) failure model, which uses a 3-Dimensional nonlinear dynamic finite element code which is explicit in nature. The J-C plasticity model is used for simulation because it can capture large strain, strain rate hardening, and fracture encountered at high-velocity ballistic impacts. The aluminium plate is impacted by a rigid projectile with six different velocities. In the deformed plate, the variation of pressure on the plate at different points during impact, residual projectile velocity and the variation of axial and shear stresses are evaluated and studied. The results obtained from this research may be used to understand the failure behaviour of aluminium alloys, which can be used in the design and fabrication of lightweight bulletproof vehicle outer surface, thin armour portable shelters, and in other engineering applications.

Buckling analysis of functionally graded plates using HSDT in conjunction with the stress function method

In this article, the mechanical buckling analysis of simply-supported functionally graded plates is carried out using a higher shear deformation theory (HSDT) in conjunction with the stress function method. The proposed formulation is variationally consistent, does not use a shear correction factor and gives rise to a variation of transverse shear stress such that the transverse shear stresses vary parabolically through the thickness satisfying the surface conditions without stress of shear. The properties of the plate are supposed to vary across the thickness according to a simple power law variation in terms of volume fraction of the constituents of the material. Numerical results are obtained to study the influences of the power law index and the geometric ratio on the critical buckling load.

Trigonometric zigzag theory for free vibration and transient responses of cross-ply laminated composite plates

In this article, an application of the non-polynomial zigzag theory is presented to analytically derive the free vibration and transient responses of multilayered laminated composites and sandwich plates. The non-linear variations of the transverse shear stresses are incorporated in the mathematical model with the help of a trigonometric function, namely the secant function. The inter-laminar continuity conditions are artificially enforced at the layer interfaces that reduce the total number of field variables to five like the first-order shear deformation theory (FSDT). The present kinematic field yields more accurate results than the FSDT and also removes the requirement of any shear correction factor. The governing equilibrium equations of motion are obtained using Hamilton's principle and solved with Navier's solution technique. The responses from the coupled ordinary differential equations in time are obtained with the Newmark's time integration scheme. Numerical problems on the diaphragm supported laminated composites, and soft-core-sandwich plates are solved analytically to derive the free vibration and transient responses by taking into consideration the several geometrical and material features of the plate structures. The responses are also compared with the benchmark elasticity solutions and solutions reported in the literature from other shear deformation models. An exhaustive study on the transient analysis is presented by solving several problems of laminated composite plates that are subjected to various time-dependent loads and various forms of blast loads.

Flexural behavior of porous functionally graded plates using a novel higher order theory

In this paper, the flexural response of functionally graded plates with porosities is investigated using a novel higher order shear deformation theory, which considers the influence of thickness stretching. This theory fulfills the nullity conditions at the top and bottom of the plate for the transverse shear stresses, thus avoids the need of a shear correction factor. The effective material properties are computed through the rule of mixtures. The principle of virtual displacements is employed to derive the equilibrium equations. The Navier’s method is adopted to obtain the solutions in closed form for simply supported boundary conditions. The accuracy and consistency of the developed theory are established with numerical results of perfect and porous functionally graded plates available in the open literature. The dimensionless transverse displacements and stresses have been reported. The effect of even, uneven and logarithmically-uneven porosity distributions with different porosity volume fraction, gradation index, side-to thickness ratios and aspect ratios are studied. The numerical results show that, the increase of volume fraction of porosity increases the dimensionless transverse deflections and axial stresses, and decreases the transverse shear stresses. No variation of transverse shear stresses observed for a completely ceramic and metallic plate for all kinds of porosity models. The provided numerical results can be used to evaluate various plate theories and also to compare the results of other analytical methods and finite element methods.

Model for predicting the variation of shear stress in unsaturated soils during strain-softening

Several of the geotechnical structures constructed with unsaturated soils undergo a large deformation prior to reaching failure conditions (e.g., progressive failure of a soil slope). During this process, the shear stress in soils typically increases initially and then reduces with an increase in the shear strain. The prediction of the stress–strain relationship is critical for reasonable interpretation of the mechanical behavior of those geo-structures that undergo large deformation. This paper introduces a model based on the disturbed state concept (DSC) to predict the variation of shear stress in unsaturated soils during the strain-softening process under consolidated drained triaxial compression condition. In this model, the apparent stress–strain relationship is formulated as a weighted average of a hyperbolic hardening response extending the pre-peak state stress–strain curve and a linear response extending the critical state stress–strain curve with an assumed disturbance function as the weight. The prediction procedure is described in detail and the proposed model is validated using several sets of published data on unsaturated soils varying from coarse- to fine-grained soils. Finally, a comprehensive error analysis is undertaken based on an index of agreement approach.

Effect of stress concentration near grips on the tensile strength of composites

Strength of a unidirectional composite along the fibers is the most important characteristic for the design calculation of composite products, being, however most difficult for correct determination in the experiment. The main problem is attributed to the shape and methods of fixing the specimen, providing the minimum impact of the stress concentration near the grips on the strength. The impossibility of direct use of standard self-tightening grips due to lateral crushing of the sample led to the necessity of using either samples with glued pads, or special grips with a constant transverse force. Specimens with fillets should not be used for unidirectionally reinforced plastics. When using standardized specimens in the form of rectangular strips with abruptly varying shear stresses applied to their lateral surface which results a significant concentration of tensile stresses, the incorrect result can be gained. We present the calculated values of the stress concentration factor (SCF) near the grips using a simplified model of shear analysis and the finite element method (FEM). Since the strength reduction factor is always less than the theoretical stress concentration factor, a phenomenological parameter of the material with the dimension of length, as a characteristic size of the stress averaging zone should be introduced to assess the strength value. Three methods are proposed to find this characteristic size according to the results of testing specimens of different kind: 1) smooth with various thicknesses; 2) smooth with various thicknesses and with holes in which the failure occurs at the hole, away from the grips; 3) with a series of holes with a decreasing radius, to find that small radius, the influence of which on the strength decrease is equivalent to the influence of grips. Proceeding from the experimentally determined characteristic size, the dependences of the strength on the specimen thickness, on the ratio of Young’s and shear modulus, on the length of the grips and the working zone, and on the degree of stress smoothing near the grip edges are calculated. The proposed calculation and experimental technique provided more accurate assess of the «true» tensile strength of the composites, which can be approximately 10 % higher than that determined on the specimens of large thickness. Taking this correction for the effect of grips into account, it appeared possible to reduce the safety factor, and, hence, to reduce the mass of composite structures.

Effect of a Bio-Based Dispersing Aid (Einar® 101) on PLA-Arbocel® Biocomposites: Evaluation of the Interfacial Shear Stress on the Final Mechanical Properties.

In this paper, the production and the characterization of poly (lactic) acid (PLA)-based composites containing different amounts (from 10 wt.% to 25 wt.%) of ultra-short cellulose fibers (Arbocel 600 BE/PU) have been investigated. On the basis of a previous study, it was observed that the addition of the cellulose fibers led to an embrittlement of the composite. Consequently, in order to obtain a composite with enhanced impact resistance and elongation at break, the effect of the Einar 101 addition (a bio-based dispersing aid additive) was analyzed. The role of the adhesion between the fiber and the matrix, coupled with a better fiber dispersion, was thus evaluated. Also, the consequences on the final mechanical properties (tensile and impact test) caused by the Einar addition were investigated. Analytical models were also applied in order to obtain an evaluation of the variation of the interfacial shear stress (IFSS) (strictly correlated to the fiber-matrix adhesion) caused by the Einar introduction. Furthermore, due to the very low aspect ratio of the Arbocel fibers, a suitable Bader and Boyer model variation was adopted in order to have a better quantitative estimation of the IFSS value.

Oral Administration of FT-4202, an Allosteric Activator of Pyruvate Kinase-R, Has Potent Anti-Sickling Effects in a Sickle Cell Anemia (SCA) Mouse Model, Resulting in Improved RBC Survival and Hemoglobin Levels

Introduction: Sickle cell anemia (SCA) results from a mutant β-globin gene that produces abnormal hemoglobin S (HbS). HbS polymerizes upon deoxygenation, resulting in red blood cell (RBC) sickling and membrane damage, leading to vaso-occlusions and hemolysis. Additionally, sickle RBCs contain less ATP and more 2,3-diphosphoglycerate (2,3-DPG) than normal RBCs; 2,3,DPG allosterically reduces hemoglobin (Hb) oxygen (O2)-affinity [i.e. increases P50], promoting faster unloading of O2, which potentiates HbS polymerization and RBC sickling. FT-4202, a selective and orally bioavailable allosteric activator of RBC pyruvate kinase (PKR), decreases 2,3-DPG and increases ATP in normal human RBCs (Blood, 2019, 134, Supplement 1:616). We hypothesized that oral administration of FT-4202 to SCA mice will increase HbS O2-affinity, and thereby decrease RBC sickling and membrane damage. Methods: Berkeley SCA mice were given 500-1000 mg/kg/day FT-4202 in chow (FT-4202 group) or control chow (control group) in 4 cohorts for 2 weeks (total 17-18 mice/group). In all cohorts, the health status, weight, and average chow consumption of each mouse was determined 3 times/week. Three cohorts were injected with sulfo-NHS-biotin 1 week into treatment (10-11 mice/group), and RBC survival assessed over the next week with serial micro-bleeds while on treatment. The 4th cohort was only bled at 2 week time-point to obtain P50 (Hemox Analyzer) and Hb levels (Hemavet). At experiment termination, all cohorts were terminally bled to determine (a) RBC levels of 2,3-DPG and ATP, (c) plasma levels of FT-4202 by LC-MS/MS, (d) the proportion of irreversibly sickled RBC (ISC) on blood smears (Image-J analysis), (e) the kinetics of experimentally-induced sickling (Lorrca®Oxygenscan) and (f) membrane deformability (Lorrca®Ektacytometry). Results: SCA mice on FT-4202 consumed a similar amount of food, and had similar weights and survival, compared to SCA mice on control chow throughout the 2-week period. As hypothesized, HbS O2 affinity increased, reflected by a decrease in P50 from 29.6 ± 0.62 mmHg (mean ± SEM) in the control group to 27.6 ± 0.58 mmHg in the FT-4202 group (p<0.03). Determinations of 2,3-DPG, ATP and FT-4202 are ongoing and will be presented. As expected, this increased HbS O2-affinity in the FT-4202 group reduced RBC sickling and membrane damage. At 2 weeks, the proportion of ISCs on blood smears was reduced in the FT-4202 group to 2.4 ± 0.3% vs. 5.9 ± 1.4% in the control group (p<0.02). The sickle RBC half-life increased to 1.8 ± 0.07 days in FT-4202 group vs. 1.4 ± 0.1 days in the control group, a 28% increase in RBC survival (p<0.01, Figure 1A). Hence, Hb levels in the FT-4202 group increased from 9.1 ± 0.2 g/dL before treatment, to 10.8 ± 0.3 g/dL 2 weeks after treatment (p<0.001), while Hb levels in the control group remained unchanged (Figure 1B). The reticulocytes remained unchanged in both groups before and after treatment. When sickle RBCs were de-oxygenated from an ambient pO2 of ~150 mmHg to a pO2 of 10-15 mmHg, followed by their re-oxygenation to ambient pO2 at a constant shear stress of 30 Pa (Oxygenscan), the point of sickling (PoS; pO2 level when the EI becomes 95% of the EI at ambient O2) decreased on average from 37% pO2 in the control group, to 30% pO2 in the FT-4202 group (p<0.002, Figure 1C), with a significantly improved Elongation Index at the point of minimum pO2 (EImin), (p<0.05). Next, RBC membrane deformability was measured under ambient pO2 (normoxic conditions), but varying shear stress after the de-oxygenation/re-oxygenation cycle on the Oxygenscan. Sickle RBCs from the FT-4202 group were significantly more deformable [i.e. had a higher Elongation Index (EI)] compared to control sickle RBCs (p<0.01, Figure 1D), as shear stress increased to ≥3 Pa, demonstrating that FT-4202 sickle RBCs sustained significantly less membrane damage following sickling and un-sickling. Conclusion: A 2-week oral FT-4202 administration was well tolerated by SCA mice and demonstrated beneficial biological effects: improved RBC membrane deformability and sickling parameters, with a shift in the PoS to lower pO2, and increased RBC survival and Hb levels. A parallel human phase-I study in healthy subjects and sickle cell disease patients to assess the safety and PK/PD of FT-4202 is ongoing (NCT03815695). Overall, our results suggest that FT-4202 can be a potentially useful orally available agent with significant anti-sickling effect. Disclosures Drake: Forma Therapeutics: Other: Shareholder of Forma Therapeutics. Fulzele:FORMA Therapeutics, Inc: Current Employment, Other: Shareholder of Forma Therapeutics. Guichard:FORMA Therapeutics, Inc: Current Employment, Other: Shareholder of Forma Therapeutics; AstraZeneca: Other: Shareholder. Malik:Aruvant Sciences, Forma Therapeutics, Inc.: Consultancy; Aruvant Sciences, CSL Behring: Patents & Royalties.

The effect of permeability on the erosion threshold of fine-grained sediments

The erosion of marine sediments, although difficult to predict, can lead to important implications in offshore engineering, sedimentology and coastal management. Continued research is, therefore, warranted to compile high-quality erosion data from which to develop models to better predict the erosion resistance of different types of marine sediments. In this paper, dimensional analysis is performed to express the threshold shear stress as a function of a selection of soil properties that are commonly linked to the erosion process of sediments. To identify the dominant dimensionless group, an experimental investigation on the erosion threshold was carried out using fine-grained sediments that were systematically prepared to ensure variations in (i) particle size distribution (i.e. fines content), (ii) bulk density, and (iii) hydraulic permeability. The samples included silica, carbonate and marine sediments, each of which are expected to have limited or no clay-mineral content.The measurements were analysed and compared with existing literature and predictive models. It was found that marine sediment samples with limited fines content showed good agreement with the empirical Shields curve, irrespective of particle size distribution, bulk density and permeability. In contrast, for finer marine sediment it was found that variations in these soil properties modify the threshold shear stress away from the Shields curve. Across each of these parameters only permeability appeared to independently correlate with the observed range of threshold measurements. Motivated by this finding, a model is introduced to predict the threshold shear stress as a function of permeability and the reference erosion rate that is used to define when the threshold is reached. The resulting expression is shown to quantitatively explain the experimental data and is found to also agree with existing data from the literature for quartz sediments with a wide range in fines content. An apparent advantage of the new model is that it is consistent with existing studies that identify variations in threshold shear stress due to changes in bulk soil parameters – including fines content and bulk density – since each of these parameters also affect permeability.

Permeability Evolution of Two-Dimensional Fracture Networks During Shear Under Constant Normal Stiffness Boundary Conditions

The permeability evolution of fractal-based two-dimensional discrete fracture networks (DFNs) during shearing under constant normal stiffness (CNS) boundary conditions is numerically modeled and analyzed based on a fully coupled hydromechanical (HM) model. The effects of fractal dimension, boundary normal stiffness and hydraulic pressure on the evolutions of mechanical behaviors, aperture distributions and permeability are quantitatively investigated. The results show that with increasing confining pressure from 0 to 30 MPa, the permeability decreases from the magnitude of 10−13 m2 to 10−16 m2, which is generally consistent with previous models reported in the literature. With the increment of shear displacement from 0 to 500 mm, the variations in shear stress, normal stress and normal displacement exhibit the same patterns with the conceptual model. As shear advances, the permeability evolution exhibits a three-stage behavior. In the first stage, the permeability decreases due to the compaction of fractures induced by the increasing shear stress from 0 to the peak value. In the second stage, the permeability holds almost constant values under constant normal load (CNL) boundary conditions, whereas that under CNS boundary conditions decreases by approximately one order of magnitude. Under CNS boundary conditions, although the aperture of shearing fracture increases enhancing its own permeability, the apertures of surrounding fractures are compacted due to the simultaneous increases in the normal and shear stresses, which result in the decrease in the total permeability of DFNs. When the fractal dimension increases from 1.4 to 1.5, the permeability increases following exponential functions in the early stage of shear, which fail to characterize the permeability in the residual stage due to the complex flow path distributions. At the start of shear, the ratio of permeability perpendicular to the shear direction to that parallel to shear decreases approximately from 1.0 to 0.5 and then gradually decreases from 0.5 to 0.3 in the residual stage. The hydraulic pressure tends to open up the fractures and enhances the permeability. The magnitude in permeability enhancement is of approximately the same order with the increase in the hydraulic pressure.

Effect of C60-SiO2 hybrid nanoparticles on thermophysical and tribological properties of a multigrade engine oil: an experimental study

In this study, the thermophysical and tribological properties of a hybrid nanofluid containing fullerene-silica nanoparticles in a multigrade engine oil have been investigated. The nanoparticles were suspended in SAE 5W30 engine oil with a volume fraction of 0.1 to 1% using the two-step method. The results showed that thermal conductivity of nanofluid increased by approximately 9% at 1% volume fraction, and at ambient temperature, rather than the base oil. Investigation of shear stress variations for base fluid and nanofluids at different concentrations revealed that the rheological behavior of the nano-oil is non-Newtonian and shear thinning. Also, the results represented that by increasing the concentration, the nanofluid dynamic viscosity had an erratic trend. The highest increase was 14% and occurred at 1% volume fraction and 5 °C. Also, the behavior of nanofluids against temperature was in accordance with the conventional fluids. Besides, viscosity decreased after the enhancement of temperature in all volume fractions. The wear test was carried out using a pin-on-disk device based on the ASTMG99 standard. The results revealed that the wear rate decreased by 18% in comparison with the base oil at concentration of 1% and temperature of 25 °C. Finally, in order to predict the viscosity of nanofluid, a precise equation was presented based on the experimental data in terms of three variables of temperature, volume fraction and shear rate by using response surface methodology (RSM). Two-degree polynomial function with R2 = 0.9983 has been employed as the optimal function to model the viscosity of nanolubricant.

Theoretical "t-z" Curves for Piles in Radially Inhomogeneous Soil

Accurate estimates of pile settlement are key for efficient design of axially loaded piles. Calculations of pile settlement can be simplified using one-dimensional “t-z” curves describing pile settlement at a certain depth as a function of side friction. In the realm of this simplified framework, theoretical “t-z” curves can be derived by substituting an attenuation function describing the variation of shear stress with distance from the pile, into a soil constitutive model relating shear strain to shear stress, then integrating with respect to distance to get the settlement at the pile circumference due to an applied shear stress. A handful of analytical “t-z” curves are available in the literature using the concentric cylinder model to define an attenuation function; these include solutions for linear-elastic, power-law and hyperbolic constitutive models. However, radially homogeneous soil has often been assumed, ignoring the effect of the pile installation resulting in unconservative calculations of pile settlement. This paper considers the installation of the pile, resulting in a radially variable shear modulus distribution in the surrounding soil. A radial inhomogeneity correction factor has been developed for selected constitutive models based on two simplified functions for the soil inhomogeneity, which can be applied to the previously derived “t-z” curves produced assuming radially homogeneous soil. The performance of this simplified method is investigated.

On the buckling analysis of functionally graded sandwich beams using a unified beam theory

In this paper, a unified beam theory is developed and applied to study the buckling response of two types of functionally graded sandwich beams. In the first type (Type A), the sandwich beam has a hardcore whereas in the second type (Type B), the sandwich beam has a softcore. In both the type of beams, face sheets are made up of functionally graded material. The material properties of face sheets are varied through the thickness according to the power-law distribution. A unified beam theory developed in the present study uses polynomial and non-polynomial type shape functions in-terms of thickness coordinate to account for the effect of shear deformation. The present theory is built upon classical beam theory and shows a realistic variation of transverse shear stresses through the thickness of the beam. The governing equations are deduced based on the principle of virtual work. Analytical solutions for simply supported sandwich beams subjected to axial force are presented. The critical buckling load factors of two types of FG sandwich beams are investigated. The numerical results are obtained for various power law coefficients and face-core-face thickness ratios. The validity of the present theory is proved by comparing the present results with various available solutions in the literature.

Study on vibration mechanism induced by skidding in pure rolling contact

Skidding in a rolling bearing often causes unexpected surface wear and uneven vibration. To explore the fundamental interaction mechanisms, an investigation is conducted experimentally and numerically on the tribo-dynamic responses of a simplified sliding-rolling contact. Vibration analyses show that the tangential vibration contains not only the rotational frequency of the roller but also the higher harmonics excited by the sliding-rolling contact. Surface contact stress analysis is also carried out with a twin-discs model. Results show that, with sliding occurring in the rolling contact, the unstable shear stress variation is induced and becomes the root cause of the tangential vibration. Further wear checks reveal that the wear failure under sliding-rolling contact coincides with the shear effect of contact interfaces.

Effects of root morphological traits on soil detachment for ten herbaceous species in the Loess Plateau

Plant root systems can greatly reduce soil loss, and their effects on soil erosion differ across species due to their varied root traits. The purpose of this study was to determine the effects of root morphology traits of herbaceous plants on the soil detachment process. Ten herbaceous plants (dominant species) in the Loess Plateau were selected, and 300 undisturbed soil samples (including living roots from the selected herbages) were scoured with flowing water to measure their soil detachment capacities under six levels of shear stress (4.98 to 16.37 Pa). Then, the root traits of each soil sample were measured, and the rill erodibility and critical shear stress were estimated based on the Water Erosion Prediction Project (WEPP) model. The results showed that root morphology traits varied greatly among the ten selected herbages. Accordingly, resulting variations in soil detachment capacity (0.030 to 3.297 kg m−2 s−1), rill erodibility (0.004 to 0.447 s m−1), and critical shear stress (4.73 to 1.13 Pa) were also observed. Plants with fibrous roots were more effective than those with tap roots in reducing soil detachment. Their mean soil detachment capacity and rill erodibility were 93.2% and 93.4% lower, respectively, and their mean critical shear stress was 1.15 times greater than that of the herbaceous plants with tap root systems. Of all the root traits, root surface area density (RSAD) was the primary root trait affecting the soil detachment, and it estimated the soil detachment capacity well (R2 = 0.91, normalized squared error (NSE) = 0.82). Additionally, an equation with few factors (soil aggregate and RSAD) was suggested to simulate the soil detachment capacity when the plant root parameters and soil properties were limited.

Estimating Arterial Cyclic Strain from the Spacing of Endothelial Nuclei

BackgroundThe non-uniform distribution of atherosclerosis within the arterial system is widely attributed to variation in haemodynamic wall shear stress. It may also depend on variation in pressure-induced stresses and strains within the arterial wall; these have been less widely investigated, at least in part because of a lack of suitable techniques.ObjectivesHere we show that local arterial strain can be determined from impressions left by endothelial cells on the surface of vascular corrosion casts made at different pressures, even though only one pressure can be examined in each vessel. The pattern of pits in the cast caused by protruding endothelial nuclei was subject to “retro-deformation” to identify the pattern that would have occurred in the absence of applied stresses.MethodsRetaining the nearest-neighbour pairs found under this condition, changes in nearest-neighbour vectors were calculated for the pattern seen in the cast, and the ratio of mean changes at different pressures determined. This approach removes errors in simple nearest-neighbour analyses caused by the nearest neighbour changing as deformation occurs.ResultsThe accuracy, precision and robustness of the approach were validated using simulations. The method was implemented using confocal microscopy of casts of the rabbit aorta made at systolic and diastolic pressures; results agreed well with the ratio of the macroscopic dimensions of the casts.ConclusionsApplying the new technique to areas around arterial branches could support or refute the hypothesis that the development of atherosclerosis is influenced by mural strain, and the method may be applicable to other tissues.