Non-uniform Shear Stress Distribution Research Articles

Improved strain transfer model for flexible sensors based on non-uniform distribution of shear stress in each layer

The assumption of linear stress distribution for flexible sensors results in inaccurate strain transfer assessment because of low elastic moduli and thick layers, and the coating further constrains the deformation of the sensitive layer. A novel strain transfer model based on non-uniform distribution of shear stress is proposed to accurately characterize the strain of sensitive layer. The quadratic shear stress distribution is derived to calculate the strain transfer coefficient of each layer, replacing the linear attenuation of the shear stress. The average relative displacement of the sensitive layer was obtained through Hooke's law, thereby introducing the shear stress at the contact interface between the coating and the sensitive layer. Numerical simulations and experiments demonstrate that the substrate of the sensors is the primary factor causing strain transfer loss and the proposed model can accurately reflect the strain of the sensitive layer.

Numerical Simulation of the Shear Behaviour of Cement Grout

Cement grout is widely used in civil engineering and mining engineering. The shear behaviour of the cement grout plays an important role in determining the stability of the systems. To better understand the shear behaviour of the cement grout, numerical direct shear tests were conducted. Cylindrical cement grout samples with two different strengths were created and simulated. The numerical results were compared and validated with experimental results. It was found that, in the direct shear process, although the applied normal stress was constant, the normal stress on the contacted shear failure plane was variable. Before the shear strength point, the normal stress increased slightly. Then, it decreased gradually. Moreover, there was a nonuniform distribution of the normal stress on the contacted shear failure plane. This nonuniform distribution was more apparent when the shear displacement reached the shear strength point. Additionally, there was a shear stress distribution on the contacted shear failure plane. However, at the beginning of the direct shear test, the relative difference of the shear stresses was quite small. In this stage, the shear stress distribution can be assumed uniform on the contacted shear failure plane. However, once the shear displacement increased to around the shear strength point, the relative difference of the shear stresses was obvious. In this stage, there was an apparent nonuniform shear stress distribution on the contacted shear failure plane.

Orthotropic mode II shear test fixture: Iosipesque modification

In-plane strength and constitutive properties of composite materials is known as crucial problems. Although, several studies have been made for obtaining the in-plane mode II properties, the common test fixtures are blind in confrontation of shear zone. Furthermore, toughening mechanisms and consequently mode II fracture toughness cannot be evaluated, precisely. Also, proposing the convenient configuration of shear test fixture increase the accuracy of evaluation for the shear-zone energy dissipation, especially in orthotropic materials. Hence in the present research, a novel shear fixture configuration is proposed based on Iosipesque structural modification. Hereof, some arbitrary composite materials (e.g. graphite/epoxy and wood) were studies on the basis of DOE and E-691 ASTM. Furthermore, as the numerical method for indicating the comparison of the uniform and non-uniform shear stress distribution in the modified and common shear test fixture, a statistical procedure is used based on ASTM standard in addition to FEM analysis. The obtained results reveal that applying major amendments through the new scheme of the shear test fixture, would provide a remarkable precision and a reasonable estimation of the shear strength in comparison with the previous Iosipesque experiments.

The effects of carbon nanotube waviness and aspect ratio on the buckling behavior of functionally graded nanocomposite plates using a meshfree method

This work deals with the effects of waviness and aspect ratio on the buckling behavior of functionally graded carbon nanotube‐reinforced composite (FG‐CNTRC) plates subjected to in‐plane loads using reproducing kernel particle method (RKPM) based on modified first‐order shear deformation theory (FSDT). Wavy single‐walled carbon nanotubes (CNTs) are embedded in a polymer matrix and distributed in four types of distributions. The material properties of an FG‐CNTRC plate are assumed to be graded along the thickness direction of the plate and estimated through a micromechanical model based on the extended rule of mixture. The modified shear correction factors evaluated involving the nonuniform shear stress distribution through the thickness of the FG‐CNTRC plate. For the imposition of the essential boundary conditions the full transformation approach is utilized. The validity and accuracy of the RKPM method is established by a comparison with the obtained results of available literature data. Moreover, the effects of distribution, volume fraction, waviness, and aspect ratio of CNTs are investigated on the buckling behavior of FG‐CNTRC plates for various boundary conditions, plate width‐to‐thickness and aspect ratios. Detailed parametric studies demonstrate that the waviness and aspect ratio of CNTs have noticeable effects on buckling behavior of carbon nanotube‐reinforced composite (CNTRC) plates. POLYM. COMPOS., 38:E531–E541, 2017. © 2015 Society of Plastics Engineers

Computational modeling of shear forces and experimental validation of endothelial cell responses in an orbital well shaker system

Vascular endothelial cells are continuously exposed to hemodynamic shear stress. Intensity and type of shear stress are highly relevant to vascular physiology and pathology. Here, we modeled shear stress distribution in a tissue culture well (R = 17.5 mm, fill volume 2 ml) under orbital translation using computational fluid dynamics with the finite element method. Free surface distribution, wall shear stress, inclination angle, drag force, and oscillatory index on the bottom surface were modeled. Obtained results predict nonuniform shear stress distribution during cycle, with higher oscillatory shear index, higher drag force values, higher circular component, and larger inclination angle of the shear stress at the periphery of the well compared with the center of the well. The oscillatory index, inclination angle, and drag force are new quantitative parameters modeled in this system, which provide a better understanding of the hydrodynamic conditions experienced and reflect the pulsatile character of blood flow in vivo. Validation experiments revealed that endothelial cells at the well periphery aligned under flow and increased Kruppel-like Factor 4 (KLF-4), cyclooxygenase-2 (COX-2) expression and endothelial nitric oxide synthase (eNOS) phosphorylation. In contrast, endothelial cells at the center of the well did not show clear directional alignment, did not induce the expression of KLF-4 and COX-2 nor increased eNOS phosphorylation. In conclusion, this improved computational modeling predicts that the orbital shaker model generates different hydrodynamic conditions at the periphery versus the center of the well eliciting divergent endothelial cell responses. The possibility of generating different hydrodynamic conditions in the same well makes this model highly attractive to study responses of distinct regions of the same endothelial monolayer to different types of shear stresses thereby better reflecting in vivo conditions.

Time dependent finite element analysis of steel-concrete composite beams considering partial interaction

A finite element computer code for short-term analysis of steel-concrete composite structures is extended to study long-term effects under service loads, in the present work. Long-term effects are important in engineering design because they influence stress and strain distribution of the structural system and therefore contribute to the increment of deflections in these structures. For creep analysis, a rheological model based on a Kelvin chain, with elements placed in series, was employed. The parameters of the Kelvin chain were obtained using Dirichlet series. Creep and shrinkage models, proposed by the CEB FIP 90, were used. The shear-lag phenomenon that takes place at the concrete slab is usually neglected or not properly taken into account in the formulation of beam-column finite elements. Therefore, in this work, a three-dimensional numerical model based on the assemblage of shell finite elements for representing the steel beam and the concrete slab is used. Stud shear connectors are represented for special beam-column elements to simulate the partial interaction at the slab-beam interface. The two-dimensional representation of the concrete slab permits to capture the non-uniform shear stress distribution in the horizontal plane of the slab due to shear-lag phenomenon. The model is validated with experimental results of two full-scale continuous composite beams previously studied by other authors. Results are given in terms of displacements, bending moments and cracking patterns in order to shown the influence of long-term effects in the structural response and also the potentiality of the present numerical code.

A Dynamic-induced Direct-shear Model for Dynamic Triggering of Frictional Slip on Simulated Granular Gouges

This study presents a dynamic-induced direct-shear model to investigate the dynamic triggering of frictional slip on simulated granular gouges. An incident P-wave is generated as a shear load and a normal stress is constantly applied on the gouge layer. The shear stress accumulates in the incident stage and the frictional slip occurs in the slip stage without the effect of the reflected wave. The experimental results show a non-uniform shear stress distribution along the gouge layer, which may be induced by a shear load induced torque and by normal stress vibration along the layer. The shear stress at the trailing edge strongly affects the frictional slip along the P-wave loading direction, while the rebound stress at the leading edge propagates along the opposite direction. The frictional slip is triggered when the maximum shear stress at the trailing edge reaches a critical value. The normal stress influences the maximum shear stress at the trailing edge, the maximum slip displacement and the slip velocity. The advantages and the limitations of this model are discussed at the end.

The influence of size, shape and vessel geometry on nanoparticle distribution

Nanoparticles (NPs) are emerging as promising carrier platforms for targeted drug delivery and imaging probes. To evaluate the delivery efficiency, it is important to predict the distribution of NPs within blood vessels. NP size, shape and vessel geometry are believed to influence its biodistribution in circulation. Whereas, the effect of size on nanoparticle distribution has been extensively studied, little is known about the shape and vessel geometry effect. This paper describes a computational model for NP transport and distribution in a mimetic branched blood vessel using combined NP Brownian dynamics and continuum fluid mechanics approaches. The simulation results indicate that NPs with smaller size and rod shape have higher binding capabilities as a result of smaller drag force and larger contact area. The binding dynamics of rod-shaped NPs is found to be dependent on their initial contact points and orientations to the wall. Higher concentration of NPs is observed in the bifurcation area compared to the straight section of the branched vessel. Moreover, it is found that Péclet number plays an important role in determining the fraction of NPs deposited in the branched region and the straight section. Simulation results also indicate that NP binding decreases with increased shear rate. Dynamic NP re-distribution from low to high shear rates is observed due to the non-uniform shear stress distribution over the branched channel. This study would provide valuable information for NP distribution in a complex vascular network.

Strain-based strength model for direct punching shear of interior slab–column connections

A strength model was developed to predict the direct punching shear strength of interior slab–column connections without shear reinforcement. At slab–column connections damaged by flexural cracking, it was assumed that the punching shear force was resisted mainly by the compression zone of the critical section. The punching shear strength at the critical section was determined at the intersection between the shear capacity curve and the demand curve. The shear capacity was defined by the material failure criteria of concrete, addressing the effect of the slab flexural stresses on the shear stress capacity of concrete. The shear demand was defined as a shear force required to develop the flexural moment of the slab. For the application of the proposed model to design practice, a simplified strength model was also developed, introducing two modification factors involving in the size effect and non-uniform shear stress distribution. For verification, the proposed strength model was applied to existing test specimens tested by other researchers.

Wind effects on retention time in highway ponds

The paper presents results from an experimental and numerical study of wind-induced flows and transportation patterns in highway wet detention ponds. The study presented here is part of a general investigation on road runoff and pollution in respect to wet detention ponds. The objective is to evaluate the quality of long term simulations based on historical rain series of the pollutant discharges from roads and highways. The idea of this paper is to evaluate the effects of wind on the retention time and compare the retention time for the situation of a spatial uniform wind shear stress with the situation of a "real" spatial non-uniform shear stress distribution on the surface of the pond. The result of this paper shows that wind plays a dominant role for the retention time and flow pattern. Furthermore, the results shows that the differences in retention time between the use of uniform and non-uniform wind field distributions are not significant to this study.

Geosynthetics reinforcement application for tsunami reconstruction: Evaluation of interface parameters with silty sand and weathered clay

Great attention is directed to rebuild livelihoods and rehabilitate coastal communities affected by the Tsunami in the Indian Ocean in South Asia. It takes years of effort of different engineering disciplines to recover from recent devastations caused by the Tsunami. Geosynthetics can play important and vital roles in the protection, mitigation and rehabilitation efforts in affected coastal areas. Geosynthetics can be applied for reinforcement, filtration, drainage, protection, lining, and containment. Particularly, geotextiles can be used effectively for erosion protection and for reinforcement of earth embankments to resist failure during the occurrence of earthquakes associated with tsunami. Presented in this paper is the interaction behavior at pullout interfaces of high strength geotextile confined in weathered clay and silty sand. The interface parameters which are needed for both finite element and conventional analyses of geotextile-reinforced earth structures such as the local shear stress/shear displacement, the interface interaction coefficient and the in-soil stress/strain of the reinforcement have been successfully interpreted by the newly proposed method considering the softening behavior and non-uniform distribution of shear stress along the extensible reinforcement. Results from this study indicate that the interpretation of pullout tests using conventional methods underestimated both the shear stiffness and the peak shear strength at the pullout interface of extensible reinforcement.

Influence of non-uniform distribution of shear stress on aerobic biofilms

This work deals with the detachment of biofilm subjected to a shear stress. Biofilms are developed on plates, under very low shear stress for one month and then subjected to an erosion test for 2 h in a Couette–Taylor reactor (CTR). During the erosion test, the plate was fixed on the external cylinder of the CTR. The presence of the plate modifies the velocity field in the CTR. A first zone close to the facing step region is characterized by the detachment of the stream lines. A second zone, downstream, is characterized by a pure shear flow: the distribution of the shear stress is uniform; the residual biofilm mass was measured and the detachment can be classically related to the magnitude of shear stress. In the first zone, the recirculating flow induces a strong non-uniform distribution of shear stress. The residual biofilm mass was also measured and found to be much lower than in the uniform shear stress zone, whereas the magnitude of shear stress is of the same order or even smaller. The assumption of elastic rheology for the biofilm enables the strong detachment observed in the region subjected to non-uniform shear stress to be explained.

A volumetric model for growth of arterial walls with arbitrary geometry and loads

Stress and deformation in arterial wall tissue are factors which may influence significantly its response and evolution. In this work we develop models based on nonlinear elasticity and finite element numerical solutions for the mechanical behaviour and the remodelling of the soft tissue of arteries, including anisotropy induced by the presence of collagen fibres. Remodelling and growth in particular constitute important features in order to interpret stenosis and atherosclerosis. The main object of this work is to model accurately volumetric growth, induced by fluid shear stress in the intima and local wall stress in arteries with patient-specific geometry and loads. The model is implemented in a nonlinear finite element setting which may be applied to realistic 3D geometries obtained from in vivo measurements. The capabilities of this method are demonstrated in several examples. Firstly a stenotic process on an idealised geometry induced by a non-uniform shear stress distribution is considered. Following the growth of a right coronary artery from an in vivo reconstructed geometry is presented. Finally, experimental measurements for growth under hypertension for rat carotid arteries are modelled.

Analysis of damage localization for ductile metal in process of shear band propagation

Abstract Distribution of localized damage in shear band can't be predicted theoretically based on classical elastoplastic theory. The average damage variable in shear band was considered to be a non-local variable. Based on non-local theory, an analytical expression for the localized damage in strain-softening region of shear band in the process of shear band propagation was presented using boundary condition and symmetry of local damage variable, etc. The results show that dynamic shear softening modulus, dynamic shear strength and shear elastic modulus influence the distribution of the localized damage in shear band. Internal length of ductile metal only governs the thickness of shear band. In the strain-softening region of shear band, the local damage variable along shear band's tangential and normal directions is non-linear and highly non-uniform. The non-uniformities in the normal and tangential directions of shear band stem from the interactions and interplaying among microstructures and the non-uniform distribution of shear stress, respectively. At the tail of the strain-softening region, the maximum value of local damage variable reaches 1. This means that material at this position fractures completely. At the tip of shear band and upper as well as lower boundaries, no damage occurs. Local damage variable increases as dynamic shear softening modulus decreases or shear elastic modulus increases, leading to difficulty in identification or detection of damage for less ductile metal material at higher strain rates.

Bending and buckling of a class of nonlinear fiber composite rods

An investigation of the mechanics of bending and buckling is carried out for a class of nonlinear fiber composite rods composed of embedded unidirectional fibers parallel to the rod axis. The specific class of composite considered is one in which the fibers interact with the matrix through a nonlinear Needleman-type cohesive zone [Needleman, A., 1987. A continuum model for void nucleation by inclusion debonding. ASME J. Appl. Mech. 54, 525–531; Needleman, A., 1992. Micromechanical modelling of interfacial decohesion. Ultramicroscopy 40, 203–214]. The primary decohesive mechanism active in bending and buckling of these composite rods is shear slip along the fiber–matrix interfaces allowing the use of a previously developed constitutive relation for antiplane shear response [Levy, A.J., 2000b. The fiber composite with nonlinear interface—part II: antiplane shear. ASME J. Appl. Mech. 67, 733–739]. The formulation requires the specification of a potential interface force–slip law that is assumed to permit interface failure in shear. Four cases of the bending and shearing of beams (concentrated or uniform load on a cantilever or a simply supported beam) are analyzed, each of which exhibits qualitatively distinct response. For certain values of interface parameters, the beam deflection or its gradient at a fixed location can change discontinuously with load. Furthermore, for interface parameter values within a certain range, singular surfaces will exist in uniformly loaded beams where there is a non-uniform distribution of shear stress along the beam length. These singular surfaces divide the beam into regions of maximal and minimal fiber slip and propagate with a rate that varies inversely as the square of the applied load. For other parameter values, singular surfaces will not exist and fiber slip will be diffuse. For the class of nonlinear composite considered, bifurcation and imperfection buckling of pinned–pinned columns is analyzed. For bifurcation buckling, a nonlinear eigenvalue problem is derived and the solution is obtained by Galerkin's method. It is demonstrated that critical loads are influenced by the initial slope, and hence the linear portion, of the interface force–slip relation but the post-buckling response, which in some sense resembles that of plastic buckling, is affected by the entire interface constitutive relation. Imperfection buckling is analyzed in a similar manner by assuming a slight initial curvature of the rod. Sensitivity of the response to imperfection magnitude is discussed as well.

Assessment of fibre-matrix adhesion and interfacial properties using the pull-out test

Fibre--matrix adhesion is assessed using a technique based on the fibre pull-out test. The fibre-matrix adhesion can be characterized in terms of the interfacial shear (bond) strength, r;. The non-uniform shear stress distribution at the fibre-matrix interface is taken into account. The technique also allows other interfacial properties such as the matrix shrinkage pressure Po and the interfacial coefficient of friction μ to be evaluated from a single set of pull-out test data. Analysis of new experimental data for glass fibre-nylon 66 and glass fibre-nylon 11 composite systems is presented to illustrate application of the technique. The issue of the effect of loading configuration and specimen geometry on the pull-out test is then considered. This is to facilitate proper analysis of experimental data, to ensure a high success rate in the pull-out experiment and to minimize specimen failure by fibre fracture and other non pull-out modes.

Analysis of the Iosipescu shear test as applied to unidirectional carbon-fibre reinforced composites

Intralaminar shear properties of unidirectional carbon-fibre reinforced epoxy and PEEK composites were investigated using the Iosipescu shear test. The apparent shear strength and shear moduli were measured using specimens with two different fibre orientations. Finite element analysis was applied to determine the stress distribution within the Iosipescu specimen. Using numerical correction factors to account for the non-uniform shear stress distribution in the gauge-section of Iosipescu specimens, the actual shear moduli were established. The Iosipescu shear test also provided a reasonable estimate of the shear strength.

Finite Element Analysis of Postbuckled Shear Webs

An isolated panel subjected to shear distortion is capable of carrying a shear force well in excess of that causing initial shear buckling, even when the boundary flanges have no bending strength. A finite element method (FEM) analysis confirms the view that the postsbuckling strength is attributable to a nonuniform shear-stress distribution along the boundaries, varying from the critical stress in one corner up to the shear-yield stress in the tension corner with no need for any diagonal tension. The presence of flanges with bending strength does permit the development of diagonal tension. However, light flanges give no increase in shear resistance. Impractically heavy flanges are shown to be capable of developing true diagonal tension, giving an increase in total shear capacity. The FEM analysis is applied to plate girders for which test results are known and is shown to provide reliable predictions.

SHAP EEFFECTS ON RESISTANCE TO UNIFORM FLOW IN OPEN CHANNELS

The effects of the shape of the cross-section on flow resistance in open channels has received considerable attention from hydraulic engineers for many years. Many investigators have tried to introduce parameters to represent the cross-section shape effect but their results have been inconclusive. Some of the techniques previously used to deal with this problem are reviewed and their shortcomings are discussed. A new method for dealing with shape effect is developed in this paper from considerations of dimensional analysis and using the experimental data of TRACY and LESTER and of SHIH and GRIGG. This method, which is referred to as KAZEMIPOUR'S method, employs new parameters more representative of the effect of cross-sectional shape on flow resistance in open channels than those previously used and offers solutions more rational than those previously proposed. The shape factor developed is ϕ = ϕ 1/ϕ 2, where ϕ 1, equal to , reflects the effects of non-uniform distribution of shear stress on the boundary ...