Values Of Normal Stress Research Articles

Analytical Method to Determine Vertical Stresses within a Granular Material Contained in Right Vertical Prisms

In the design of large and tall storage containers/structures such as silos, hoppers, and mine stopes, it is often required to determine the stresses within the container, especially at the bottom where stresses are the highest. Due to arching, where a substantial fraction of the self-weight of the granular material is carried by the wall, the vertical stress at the bottom of the container is significantly less than what is given by the product of the height and unit weight. Few analytical expressions published in the literature can be used to determine the vertical stresses taking into account the arching effect and on the basis of equilibrium considerations. The objective of this paper is to propose a new analytical method for determining the vertical stresses in a long container, assuming plane strain conditions. The method is extended to containers with rectangular and circular cross sections and is used to accommodate a surcharge at the top of the granular material. The values of vertical normal stresses computed for long-strip square, and circular cross sections are in very good agreement with those computed from Marston’s theory, which was recently validated against numerical and laboratory models for providing satisfactory estimates of average vertical stresses within mine stopes. The results from the proposed model also compare well with elastoplastic numerical model results, provided K and δ are assumed to be as follows: (a) K=K0 and δ=2/3ϕ or (b) K=Ka and δ=ϕ. More than the expressions, the method itself would pave the way to future applications in similar and generalized problems related to storage structures with sloping walls.

Experimental investigation of tornado-like vortex dynamics with swirl ratio: The mean and turbulent flow fields

An experimental simulation of tornado-like vortices is conducted in a small tornado vortex simulator in order to study the effect of swirl ratio on flow characteristics. Particle Image Velocimetry (PIV) method is employed to quantitatively determine the tornado-vortex velocity field for swirl ratios ranging from 0.08 to 1. The radial and tangential components of velocity as well as the core radius of the tornado increase with increase in swirl ratio. The location of the maximum radial and tangential velocities is adjacent to the ground where the tornado vortex interacts with the surface. The values of normal and shear turbulent stresses indicate the existence of a laminar core for small swirl. As expected the shear stresses increase with swirl ratio as the vortex becomes turbulent. The highest turbulent production corresponds to the critical case of vortex touchdown.

A new method to solve crack problems based on gradient elasticity

ABSTRACT A new constant displacement discontinuity method is presented for the numerical solution of cracks of the three fundamental deformation modes I, II and III lying either in the plane or in the half-plane. This method is based on the strain-gradient elasticity theory in its simplest possible Grade-2 (G2) variant for the solution of classical crack problems. The assumption of the G2 expression for the stresses results to a more accurate average stress value at the mid-point of the straight displacement discontinuity since it takes into account the stress-gradient effect and gives considerably better predictions of the stress intensity factors compared to the compared to the classical elasticity solution. Moreover, the proposed method preserves the simplicity and hence the high speed of computations. For brevity of this paper we present here the specific case of mode-II cracks perpendicular to the free-surface of the half-plane. Validation of the method is made against analytical solution.

Photoelastic Stress Analysis Error Quantification in Vasculature Models for Robot Feedback Control

Real-time and accurate stress calculation in walls of vasculature is a desired goal in order to provide feedback control for catheter insertion robots without changing catheter stiffness and lumen. This feedback source also has applications in endovascular surgery simulation. In order to address this need, we consider photoelastic effect, as birefringence produced by light retardation relates to the stress inside photoelastic materials. In this research, a polariscope was designed for urethane elastomer vasculature models, the photoelastic coefficient of urethane elastomer was measured, and a camera system was calibrated to quantify and reduce error in the measurement system. An average error of 3.9% was found in stress measurements for the pressure range of 60-189 mmHg inside the urethane elastomer model. This result was applied to correct stress distribution images, using the average stress value as a reference and preserving local maxima and minima of stress. This enabled us to accurately calculate stress in vasculature models during human blood pressure simulation (HBPS), and enables the comparison, in a closed loop, of stress produced by HBPS and by catheter motion when driven by a robot, as well as to measure the stress produced by medical tools on the vascular model wall.

The G2 constant displacement discontinuity method – Part I: Solution of plane crack problems

A new constant displacement discontinuity element was presented in a previous paper applied initially for the numerical solution of either isolated straight cracks or for co-linear cracks of the three fundamental deformation modes I, II and III due to the special form of the solution. It was based on the strain-gradient elasticity theory in its simplest possible Grade-2 variant. The assumption of the G2 expression for the stresses has resulted to a better average stress value at the mid-point of the straight displacement discontinuity compared to the classical elasticity solution. This new element gave considerably better predictions of the stress intensity factors compared to the constant displacement discontinuity element and the linear displacement discontinuity element. Moreover, it preserved the simplicity and hence the high speed of computations. In this Part I, the solution for this element is extended for the analysis of cracks of arbitrary shape in an infinite plane isotropic elastic body and it is validated against three known analytical solutions.

Physical and frictional properties of non-treated and steam exploded barley, canola, oat and wheat straw grinds

During storage and handling, accurate knowledge of the physical and frictional behaviors of biomass grinds is essential for the efficient design of equipment. Therefore, experiments were performed on non-treated and steam exploded barley, canola, oat and wheat straw grinds to determine their coefficient of internal friction and cohesion at three hammer mill screen sizes of 6.4, 3.2 and 1.6 mm, three normal stress values of 9.8, 19.6 and 39.2 kPa at 10% moisture content (wb). At any specific hammer mill screen size, the geometric mean particle size and bulk density of non-treated straw was significantly larger than steam exploded straw. The bulk density of ground straw significantly increased with a decrease in hammer mill screen sizes. The steam exploded straw grinds resulted in higher coefficient of internal friction compared to non-treated straw grinds primarily because of lower bulk densities. The coefficient of friction for non-treated barley, canola, oat and wheat straw were in the range of 0.505 to 0.584, 0.661 to 0.665, 0.498 to 0.590, and 0.532 to 0.591, respectively. Similarly, the coefficient of friction for steam exploded barley, canola, oat and wheat straw were in the range of 0.562 to 0.738, 0.708 to 0.841, 0.660 to 0.860, and 0.616 to 1.036, respectively, which were higher than non-treated straw of the kind. Power, logarithmic or exponential equations were developed to predict the coefficient of internal friction and cohesion with respect to average geometric mean particle sizes for non-treated and steam explode barley, canola, oat and wheat straw grinds.

The theoretical shear strength of fcc crystals under superimposed triaxial stress

The influence of a triaxial stress applied normally to shear planes and shear direction during affine shear deformation of face-centered cubic crystals on the theoretical shear strength is studied for the 〈 1 1 2 ¯ 〉 { 1 1 1 } shear system using first-principles methods. The applied relaxation procedure guarantees that the modeled system is subjected to a superposition of shear, normal and in-plane stresses with individually adjustable in-plane and normal stress values. The theoretical shear strengths of individual elements prove to be qualitatively different functions of the superimposed stresses. In the special case of hydrostatic loading, however, these functions are qualitatively uniform. This behavior is discussed in terms of the electronic structure.

Interlaminar shear stress distribution between nested layers of plain weave composites

During the manufacture of woven fabric composites, fabric layup and lateral compression may cause fabric layers to nest with each other and compact altering the mechanical behavior of the composite. In this work, nesting and layer compaction were geometrically defined and their mechanistic impact on the interlaminar shear distribution was analyzed. Neighboring layers of plain weaves were geometrically modeled to nest with one another via a relative in-plane horizontal translation, an out-of-plane vertical translation, forcing them into valleys of neighboring layers, and vertical compaction. The normal stress distribution within each layer was mapped and used to obtain the interlaminar shear stress distribution between layers utilizing a strain energy density approach. Four-point flexural tests were carried out and the average value of the normal stress in different layers at failure was used to evaluate the interlaminar shear strength. It was found that nesting reduces the interlaminar shear stress between layers, while compaction of nested layers reduces the variation in the stress distribution within the layer itself. Failure occurs when the interlaminar shear stress exceeds the shear strength of the matrix material between the layers. POLYM. COMPOS., 31:1838–1845, 2010. © 2010 Society of Plastics Engineers

Simple General Solution for Interfacial Stresses in Plated Beams

The flexural strength of a reinforced concrete, metallic or timber beam can be increased by bonding a thin plate, made of steel or fiber-reinforced polymer, to its tension face. A main failure mode of such plated beams involves debonding of the plate end from the beam and such plate-end debonding depends strongly on the interfacial stresses between the beam and the plate. Consequently, many analytical solutions have been developed for the interfacial stresses of specific plated beam problems, with almost all of them being for simply supported plated straight beams of constant section subjected to simple loadings. The existing analytical solutions are therefore neither general enough nor simple enough for direct exploitation in assessing the risk of plate-end debonding failure. This paper corrects this deficiency by presenting a simple, accurate yet general solution for interfacial stresses. The solution is applicable to plated beams of all geometric (e.g., curved beams), sectional (e.g., tapered beams), loading (e.g., a linearly varying distributed load), and boundary conditions (e.g., continuous beams). The accuracy of the solution is demonstrated through comparisons with finite element results. The paper also presents simple and accurate approximations for the peak values of interfacial shear and normal stresses at the plate end. In these approximate expressions, only the sectional forces and properties of the plate end section are involved, which greatly facilitates their direct exploitation in predicting debonding failure.

Effects of Dry Density and Grain Size Distribution on Soil-Water Characteristic Curves of Sandy Soils

The unsaturated soil mechanics is receiving increasing attention from researchers and as well as from practicing engineers. However, the requirement of sophisticated devices to measure unsaturated soil properties and time consumption have made the geotechnical engineers keep away from implication of the unsaturated soil mechanics for solving practical geotechnical problems. The application of the conventional laboratory devices with some modifications to measure unsaturated soil properties can promote the application of unsaturated soil mechanics into engineering practice. Therefore, in the present study, a conventional direct shear device was modified to measure unsaturated shear strength parameters at low suction. Specially, for the analysis of rain-induced slope failures, it is important to measure unsaturated shear strength parameters at low suction where slopes become unstable. The modified device was used to measure unsaturated shear strength of two silty soils at low suction values (0 ~ 50 kPa) that were achieved by following drying path and wetting path of soil-water characteristic curves (SWCCs) of soils. The results revealed that the internal friction angle of soil was not significantly affected by the suction and as well as the drying-wetting SWCCs of soils. The apparent cohesion of soil increased with a decreasing rate as the suction increased. Further, the apparent cohesion obtained from soil in wetting was greater than that obtained from soil in drying. Shear stress-shear displacement curves obtained from soil specimens subjected to the same net normal stress and different suction values showed a higher initial stiffness and a greater peak stress as the suction increased. In addition, it was observed that soil became more dilative with the increase of suction. A soil in wetting exhibited slightly higher peak shear stress and more contractive volume change behaviour than that of in drying at the same net normal stress and the suction.

Hydroxyapatite ceramics coating on magnesium alloy via a double layered capsule hydrothermal hot-pressing

Hydroxyapatite (HA: Ca10(PO4)6(OH)2) ceramic coating on magnesium (Mg) alloy (AZ31; Mg–3Al–1Zn) was achieved simultaneously by using a double layered capsule hydrothermal hot-pressing (DC-HHP) method at the low temperature as low as 150°C with no special surface treatment on the surface of the Mg alloy. A mixture of calcium hydrogen phosphate dehydrate (DCPD) and calcium hydroxide (Ca(OH)2) was used as a starting powder material for solidifying HA. Pull-out tests were conducted in order to obtain an estimate of adhesive properties for the HA coating to the Mg alloy. Average value of maximum shear stress was determined to 6.1 ± 1.0 MPa. After the pull-out fracture tests, it was revealed that HA ceramics remained on the surface of the Mg alloy. The Mg alloy could be bonded to HA ceramics with good adhesive properties.

Impact of volume fiber on distribution of thermal stress residual near fiber/epoxy interface using axisymmetric model

Thermal residual stresses are important in composite materials. The aim of this work is the computation of thermal residual stresses by finite element method and the effect of volume fraction on their distribution. In this work, two cases are considered by using an epoxy matrix with respectively glass and carbon fibers with a different volume fiber using an axisymmetric model. From the results of the numerical calculation, it is shown that the stresses are important and thus should be taken into account. The interface is affected by thermal stresses. The normal stresses and shear stress value have an influence on the behavior of the material. Hence, on the performance of composites during service, is an information of significance for the designers.

A traversing system to measure bottom boundary layer hydraulic properties

This study describes a new convenient and robust system developed to measure benthic boundary layer properties, with emphasis placed on the determination of bed shear stress and roughness height distribution within estuarine systems by using velocity measurements. This system consisted of a remotely operated motorised traverser that allowed a single ADV to collect data between 0 and 1 m above the bed. As a case study, we applied the proposed traversing system to investigate bottom boundary layer (BBL) hydraulic properties within Coombabah Creek, Queensland, Australia. Four commonly-employed techniques: (1) Log-Profile (LP); (2) Reynolds stress (RS); (3) Turbulent Kinetic Energy (TKE); and (4) Inertial Dissipation (ID) used to estimate bed shear stresses from velocity measurements were compared. Bed shear stresses estimated with these four methods agreed reasonably well; of these, the LP method was found to be most useful and reliable. Additionally, the LP method permits the calculation of roughness height, which the other three methods do not. An average value of bed shear stress of 0.46 N/m 2, roughness height of 4.3 mm, and drag coefficient of 0.0054 were observed within Coombabah Creek. Results are consistent with that reported for several other silty bed estuaries.

Intra-aneurysmal flow patterns and wall shear stresses calculated with computational flow dynamics in an anterior communicating artery aneurysm depend on knowledge of patient-specific inflow rates

To evaluate if knowledge of patient-specific inflow data in computational fluid dynamics simulations is required for the accurate calculation of intra-aneurysmal flow patterns and wall shear stress in an aneurysm of the anterior communicating artery (AcomA). 3D digital subtraction angiography (3D-DSA) and phase contrast magnetic resonance (pcMRI) images were obtained in a 71-year old patient with an unruptured aneurysm of the anterior communicating artery (AcomA). A baseline computational flow dynamics simulation was performed using inflow boundary conditions measured with pcMRI. Intra-aneurysmal flow patterns, maximum, minimum and average values of wall shear stress and wall shear stress histograms were calculated. Five additional computational flow dynamics simulations were performed, in which simulated inflow from the right and left A1 segment was varied, while keeping the total inflow constant. Intra-aneurysmal flow patterns measured with pcMRI were qualitatively compared to intra-aneurysmal flow patterns derived from the simulations. Intra-aneurysmal flow patterns calculated in the baseline simulation were in good qualitative agreement with pcMRI measurements. Intra-aneurysmal flow patterns and wall shear stress changed considerably when inflow conditions were altered. Changes in the flow distribution between right and left A1 segments caused variations of the averaged wall shear stress as high as 43%. Intra-aneurysmal flow patterns and wall shear stress in an AcomA aneurysm calculated with computational flow dynamics depended strongly on the flow distribution between A1 segments. Patient-specific flow data measured with pcMRI obtained prior to computational flow dynamics are necessary for an accurate simulation of intra-aneurysmal flow patterns and calculation of wall shear stress in AcomA aneurysms. Further studies may indicate if wall shear stress calculated with computational flow dynamics can predict aneurysm growth and/or rupture.

Standardization of the strength of large-lump soils

Today’s continuous increase in prices paid for mineral fuel, and stringency of requirements to protect the environment from pollution by hot-house gases throughout the entire world is promoting growing interest in the development of water power. In Russia, for example, construction is therefore being planned for a number of new HPP, and prospects for resumption of construction on the Rogunskaya HPP in Tadzhikistan and the Kambartin HPP in Kirgizia are being actively revisited. High dams, including those built of earthen materials are a component part in all large-scale HPP. The most important problem encountered for these dams is the assurance of their reliability and safety; this is achieved primarily by the strength of the soils employed. Large-lump soils, the volumes of which are frequently very large, are some of the basic materials utilized for the construction of high earthen dams. Thus, the volume of soils in the Nurek and Rogunskaya (designed by the Sredazgidroproekt) Dams is 54.2 and 72.1 million m3, respectively. Although man has used conventional soils as a construction material for several thousands of years, large-lump soils, the size of individual lumps of which reaches 500 mm and more, has come into use only recently since the middle of the last century after the appearance of heavy-duty construction equipment capable of excavating and transporting them, and placing and compacting them in a structure [1, 2]. The two basic types of large-lump spoils are gravellyconglomerate mixtures, and a quarried mass of broken stone. Here, the strength of large-lump soils has been standardized only for sandy and gravelly-sandy soils for hydraulicked dams, whereupon standardization has been to a large degree conditional for densities that vary over a rather broad range. It is also possible to note that the design strength for these soils has also been established with insufficient accuracy; this has necessitated its substantial reduction in Construction Rule and Regulation 2.06.05–84 as compared with Construction Rule and Regulation II-53–73 (Table 1). As for large-lump soils in rolled filled dams, the Constructions Rules and Regulations recommend the density be determined from results of direct tests of the soils, or their standard mixtures. Strength investigations for large-lump soils are very labor-intensive, and require considerable time; tests with these soils are therefore conducted only within the framework of plans for specific large-scale structures, and in very limited volumes. Due to the high labor intensiveness and duration of direct strength tests for large-lump soils, these investigations for each specific case are, as a rule, restricted to the testing of only a small number of specimens (3 – 5) for different normal-stress values o. Experimental data are reduced in o – o coordinates. The resultant o = f(o) line or curve also serves as the basis for determination of the desired strength parameters tan o and c. Here, the standard strength is assumed equal to the average value. Moreover, the design strength is generally conditional in nature, since it is impossible here to satisfy requirements of the Construction Rules and Regulations regarding its level of significance, for which the 90-percentile strength, or strength corresponding to a confidence level of 0.95 is adopted. A large number of points would be required for this purpose. And mainly, all test points on the experimental o = f(o) curve are, as a rule, obtained during the testPower Technology and Engineering Vol. 43, No. 2, 2009

New SiC microcantilever electric connection array for single molecule electrical investigation

In this paper, we present an optimized fabrication process to obtain arrays of RF magnetron sputtered SiC microcantilevers showing a controlled and defined curvature. Thin amorphous SiC films with a rms roughness of 1.04 nm and an electrical resistivity of 502 Ω cm are obtained. By optimizing sputtering conditions, we have defined an in-depth stress distribution leading to an average stress value of −1.8 GPa that allows obtaining reproducible cantilevers curvature value between 10.5 and 16 μm. TMAH Si wet etching has also been optimized to define homogeneous curvature and to limit undercut problems. First electrical characterization at ambient atmosphere leads to an in-between cantilevers resistance of 100 kΩ.

A Comparative Numerical Study of the Stress States in Flat and Cylindrical Lap Joints

The stress states along the bondline in flat and cylindrical lap joints are analysed with the finite element method. The cross section of both specimen configurations is the same and is modelled with the same two-dimensional finite element mesh. The simulations are performed for the plane strain and axisymmetric cases which correspond to the flat and cylindrical specimens, respectively. The elastic properties of the adhesive are varied in a wide range and the influence on the stress distribution is analysed and compared for the two configurations. The most uniform stress state is obtained for the cylindrical specimen with the smallest diameter and the derived diagrams can be used for error prediction if average stress values are used for the estimation of elastic properties or failure loads.

圧力式ホモジナイザーにおける内部流れと乳化効果の研究(流体工学,流体機械)

The homogenizer is extensively used to emulsify, disperse the products in various industrial fields including: food, chemical, pharmaceutical and biotechnology. The homogenizer basically consists of a high-pressure plunger pump usually with triple plungers to minimize pressure fluctuations and a homogenizing valve with a narrow gap. However, the flow within the homogenizing valve is not clarified theoretically. If the flow pattern within the homogenizing valve could be solved, a more efficient and stabilized emulsification could be carried out. In this paper, the influence of shape modification of the homogenizing valve was investigated in the emulsification effect. The experiments using a small homogenizer are conducted. We studied the influence of the flow pattern (velocity distributions, pressure distributions, shear stress) on the drop size distribution obtained in the experiment, and investigated the relation between the average value of wall shear stress and the emulsification effect in the homogenizing valve. The flow patterns were investigated using a Computational Fluid Dynamic model of the flow in the homogenizing valve. The purpose of this paper is to clarify the effects of differences in the shapes of valves on the results of emulsification.

Some Mechanical Properties of Safflower Stalk

General physical properties, bending stress, modulus of elasticity, compressive strength, shearing stress, and specific shearing energy were determined for safflower (Carthamus tinctorius L.) stalks. Test specimens were taken from two locations of the stalk: from the bottom and from the top region. Experiments were conducted in five different moisture contents of stalk. The bending stress decreased with increasing moisture content. The average bending stress value varied between 54.02 and 13.81 MPa. The modulus of elasticity in bending decreased with increases at the moisture content and the modulus of elasticity increased towards the top region. The average modulus of elasticity varied between 439.49- 95.62 MPa. The modulus of tangent in compressing decreased as the moisture content increased. The average tangent modulus varied between 31.39-6.35 daNmm-1. The shearing stress and the specific shearing energy increased with increasing moisture content. The maximum shearing stress and the specific shearing energy were 1.37 MPa and 94.64 mJmm-2, respectively. Both the shearing stress and specific shearing energy were found to be higher in the bottom region of the stalk.

Numerical Simulation of Mechanically Mixed Layer Formation at Local Contacts of an Automotive Brake System

Processes taking place at local contacts in an automotive brake system are analyzed on the basis of computer simulation with the method of movable cellular automata. The conditions of a mechanically mixed layer (MML) formation on the tribosurfaces and the influence of the layer on the friction coefficient are investigated. The results show that the MML formation leads to the stabilization of the coefficient of friction at a convenient range (0.3–0.4) for brake application. The presence of graphite particles in the MML decreases the critical value of local normal stress for switching from stick-slip to smooth relative motion with MML formation.