Bar Of Cross Section Research Articles

Parametric finite-volume method for Saint Venant’s torsion of arbitrarily shaped cross sections

We extend our recent finite-volume based approach to the solution of Saint Venant’s torsion problems of bars and beams comprised of rectangular sections to enable analysis of arbitrary cross sections characterized by curved boundaries. This is accomplished by incorporating parametric mapping based on transfinite grid generation to enable discretization of the bar cross section by quadrilateral rather than rectangular subvolumes employed in the original version. The construction of the local stiffness matrix that relates the surface-averaged subvolume warping functions to the corresponding tractions is carried out in the reference plane such that the subvolume equilibrium in the physical plane is satisfied in a surface-averaged sense. This produces explicit expressions for the stiffness matrix elements that may be readily coded. Orthotropic subvolumes are intrinsic in the method’s construction so that bars with heterogeneous and composite microstructures may be analyzed. The convergence and accuracy of the parametric finite-volume method are assessed and verified upon comparison with exact elasticity solutions for cross sections with convex and concave boundaries. Examples involving structural applications of prismatic bars with curved boundaries illustrate the utility of the developed methodology. These include cross sections that resemble biological constructs with homogeneous and graded regions aimed at enhancing torsional rigidities, as well as homogeneous and graded elliptical cross sections with orthotropic shear moduli aimed at reducing and eliminating warping. We demonstrate for the first time that by laminating an elliptical cross section with alternating stiff and soft isotropic layers in a manner that mimics the required orthotropic moduli at the homogenized level, warping can be practically eliminated with sufficient microstructural refinement.

FLAT CARS COUPLING DYNAMICS WHEN TRANSPORTING LONG CARGO

Purpose. In connection with the tendency to intensify the transportation process under conditions of increased axial loads and train speeds the article aims to investigate the dynamic loading of the coupling of two flat cars with a long load, as well as to determine the dynamic forces of interaction under the action of quasi-static longitudinal forces. Methodology. The research is based on the method of mathematical and computer modeling of dynamic loading of longitudinal-and-flexural vibrations of a 22 m long stack of cargo, located on the coupling of two flat cars of 13-4012 model. The kinetic and potential energies of the system are compiled taking into account the kinetic and potential energies of the load, which are calculated using the known fundamental functions. To determine the fundamental functions, the problem of flexural vibrations of a load as a beam on two elastic supports was solved. To determine the fundamental functions for longitudinal displacements, the differential equation of free longitudinal vibrations of a bar of constant cross section was used. Theoretical studies were carried out when moving of flat cars with typical bogies 18-100 at speeds in the range from 60 to 100 km/h on a straight section of the railway track. Findings. During the study it was taken into account the movement of flat car coupling along a sinusoidal irregularity with a length of 25 m and different depths under the action of longitudinal compressive or tensile forces, as well as during running out. In the course of theoretical studies and after the modeling, taking into account the oscillation processes of the flat car and long cargo, in the presence of quasi-static longitudinal forces, the dependences of the main dynamic indicators on the movement speed were obtained. Originality. To determine the dynamic loading of the flat car coupling, a mathematical model of longitudinal-and-flexural vibrations in the vertical plane of the cargo stack-platform car coupling system has been developed. The proposed mathematical model makes it possible to theoretically determine the dynamic parameters of the system and ensure the development of methods for transporting long cargo in accordance with the safety requirements of train traffic. Practical value. As a result of the theoretical studies, a relevant and practically important problem of determining the loading of flat car coupling during the transportation of long cargo was solved, which will allow developing technical conditions for the implementation of resource-saving technologies.

Determination of stress concentration factors for shafts under tension

Abstract Computer-based design and optimization have become increasingly important in recent years. This paper has investigated the stress concentration factors (SCF) Kt for shoulder filleted shafts with a hole and without a hole. This study contains two types of shoulder filleted shafts, i. e., a stepped bar of circular cross section with shoulder filleted and a tube with filleted shafts under tension stresses. Investigations on SCF that have been carried out in experimental and theoretical studies, were updated and validated for 2 types of shafts. The charts have been converted into numerical value using high precision computer techniques. Dimensional ratios and SCF were determined using previous work charts. This study determines maximum stresses for shoulder filleted shafts by three dimensional finite element analysis (FEA) and artificial intelligence techniques. A set of SCF charts was converted into numerical values and this data was organized and stored in an Excel file. ANSYS models were created and applied the boundary conditions on the models. And also mesh optimizations were performed. Artificial neural networks (ANN) models were designed using previously collected and verified data. Previous works, ANSYS and ANN results were compared to each other. As a result, ANN model and chart results show a good agreement. The usage of ANN model does not require any mathematical formulae or converting the numerical data action for determining the Kt result for shafts. ANN model usage was identified as a very useful and practical method.

Texture and Differential Stress Development in W/Ni-Co Composite after Rotary Swaging.

Knowledge of texture and residual stresses in tungsten heavy pseudoalloys is substantial for the microstructure optimization. These characteristics were determined in cold and warm rotary swaged W/NiCo composite with help of neutron diffraction. The results were discussed in view of the observed microstructure and mechanical properties. The investigated bars consisted of tungsten agglomerates (bcc lattice) surrounded by NiCo-based matrix (fcc lattice). No preferential crystallographic orientation was found in the as-sintered bar. A strong texture was formed in both the tungsten agglomerates (<101> fiber texture parallel to the swaging axis) and in the NiCo-based matrix (<111> fiber texture) after rotary swaging. Although usually of double-fiber texture, the <001> fiber of the fcc structures was nearly missing in the matrix. Further, the cold-swaged bar exhibited substantially stronger texture for both phases which corresponds to the higher measured ultimate tensile strength. The residual stress differences were employed for characterization of the stress state of the bars. The largest residual stress difference (≈400 MPa) was found at the center of the bar deformed at room temperature. The hoop stresses were non-symmetrical with respect to the swaging axis, which was likely caused by the elliptical cross section of the as-sintered bar.

Studies on Stress Corrosion Cracking of Vit 105 Bulk Metallic Glass

The project “Stress Corrosion Cracking of Zr-based Bulk Metallic Glasses” (SCC of Zr-BMG) within PP1594 mainly dealt with mechanical-corrosive interactions and failure of this class of metastable materials. It focussed on one of the most application-relevant Zr-BMG, Vit(reloy) 105 with composition Zr52.5Cu17.9Ni14.6Al10Ti5 (at.-%). Even though this BMG is known as extraordinary glass former, the metallurgical processing is still a critical issue. In contrast to conventional processing, i.e. melting of master alloys from pure elements, a different route using binary pre-alloys for the master alloys production was applied and led to superior mechanical properties upon mechanical testing under tensile and 3-point-bending (3PB) conditions in air. As a reference and for a detailed understanding of failure, fracture and cracking of Zr-base BMG in air, notched specimen 3PB experiments with in-situ microscopic observation were done and the still controversial interpretation of the mechanical behaviour of BMG in the framework of fracture mechanics was addressed. The specimen from the in-situ 3PB-tests served for TEM investigations on the structural nature of shear bands in BMG on the atomistic scale. Altogether, complete crack paths could be observed and analysed and based on this, details of the shear-band driven crack growth are described. While in first SCC studies using a newly developed setup full cross section (3PB) bars were investigated, in recent in situ experiments notched specimen were tested in 0.01 M NaCl yielding strong evidence for a catastrophic failure due to hydrogen embrittlement (HE). The known susceptibility to pitting corrosion in halide containing environments is only the initial stage for failure under SCC conditions. Once pitting is initiated, the local electrode potential is severely reduced. Further, the hydrolysis reaction of oxidised Zr4+ to zirconyl ions ZrO2+ during local BMG dissolution produces H+ and thus, a local acidic environment that enables proton reduction and hydrogen absorption in the stressed BMG region. The peculiar failure and fracture surface characteristics as well as the proven local reduction of the pH value in the vicinity of the notch during in-situ experiments clearly account for the proposed HE-SCC failure mechanism.

A general approach to minimal mass tensegrity

This work is motivated by the fundamental questions in engineering mechanics: Does continuum guarantee a minimal mass structure? What is a more mass efficient way to design structures? Moreover, what are the fundamental laws of the new approach? This paper provides a general unified approach for the minimal mass design of any solid or hollow bar tensegrity structures with any given external forces subject to the structure equilibrium conditions and the maximum stress constraints of structure members (strings yield, bars yield or buckle) in a compact matrix form. The methodology yields several nonlinear programming problems. Local stability is assured by checking the modes of failure of all the structure members, and global stability is guaranteed by solving a linear matrix inequality with the derived stiffness matrix. To further reduce mass, the choice of the cross-section of bars are also discussed. For practical problems, joint mass is considered as a penalty to the total structure mass. The principles developed in this paper demonstrates a fundamental insight into both materials and structures.

Determination of stress concentration factors for shafts under tension

Abstract Computer-based design and optimization have become increasingly important in recent years. This paper has investigated the stress concentration factors (SCF) Kt for shoulder filleted shafts with a hole and without a hole. This study contains two types of shoulder filleted shafts, i. e., a stepped bar of circular cross section with shoulder filleted and a tube with filleted shafts under tension stresses. Investigations on SCF that have been carried out in experimental and theoretical studies, were updated and validated for 2 types of shafts. The charts have been converted into numerical value using high precision computer techniques. Dimensional ratios and SCF were determined using previous work charts. This study determines maximum stresses for shoulder filleted shafts by three dimensional finite element analysis (FEA) and artificial intelligence techniques. A set of SCF charts was converted into numerical values and this data was organized and stored in an Excel file. ANSYS models were created and applied the boundary conditions on the models. And also mesh optimizations were performed. Artificial neural networks (ANN) models were designed using previously collected and verified data. Previous works, ANSYS and ANN results were compared to each other. As a result, ANN model and chart results show a good agreement. The usage of ANN model does not require any mathematical formulae or converting the numerical data action for determining the Kt result for shafts. ANN model usage was identified as a very useful and practical method.

In-plane backward and zero group velocity guided modes in rigid and soft strips.

Elastic waves guided along bars of rectangular cross sections exhibit complex dispersion. This paper studies in-plane modes propagating at low frequencies in thin isotropic rectangular waveguides through experiments and numerical simulations. These modes result from the coupling at the edge between the first order shear horizontal mode SH0 of phase velocity equal to the shear velocity VT and the first order symmetrical Lamb mode S0 of phase velocity equal to the plate velocity VP. In the low frequency domain, the dispersion curves of these modes are close to those of Lamb modes propagating in plates of bulk wave velocities VP and VT. The dispersion curves of backward modes and the associated zero group velocity (ZGV) resonances are measured in a metal tape using noncontact laser ultrasonic techniques. Numerical calculations of in-plane modes in a soft ribbon of Poisson's ratio ν≈0.5 confirm that, due to very low shear velocity, backward waves and ZGV modes exist at frequencies that are hundreds of times lower than ZGV resonances in metal tapes of the same geometry. The results are compared to theoretical dispersion curves calculated using the method provided in Krushynska and Meleshko [J. Acoust. Soc. Am. 129, 1324-1335 (2011)].

Use moded bar of variable cross section in vibration analysis of telescopic boom system of truck-mounted cranes

Use moded bar of variable cross section in vibration analysis of telescopic boom system of truck-mounted cranes

Material Improvement of Mild Steel S355J2C by Hot Rotary Swaging

Rotary swaging reduces the cross section of bars and tubes and usually acts as a cold forming technology. The induced work hardening leads to products with high ultimate tensile strength and low ductility. In contrast, hot forming processes result in parts with higher ductility and lower ultimate tensile strength but with finer grain compared to cold formed material. Fine grained materials have great significance due to a better tradeoff between strength and ductility. In this study, hot rotary swaging is examined to produce fine grain material from mild steel S355J2C. The experiments prove that hot rotary swaging produces parts with higher ductility than cold-formed parts. Due to the fine grain, the achieved high ultimate tensile strength is comparable to the cold drawn raw material. The highest ultimate tensile strength is achieved by combining fine grain with work hardening, when hot forming is followed by cold forming. In this way, the ultimate tensile strength of mild steel could be improved from Rm = 700 MPa to Rm = 1250MPa which is a typical value of high-alloyed steel.

Численное исследование закритической работы стержней кольцевого поперечного сечения при внецентренном сжатии

Analysis results of hollow circular cross-section bars under bending and axial compression by the finite element method in different formulations with considering of overall buckling described. Qualitative comparison of the data obtained with the data of laboratory tests is made. Analysis parameters allowing achieving an optimal balance between analysis accuracy and speed are given.

Evaluation of some process parameters for production of investment bar castings

This investigation aims at evaluating some process parameters for the production of aluminium alloy investment castings using polystyrene as pattern material and Plaster of Paris as investment slurry. The process parameters considered are the shell thickness, casting thickness and pouring temperature and the effect of varying these parameters on the mechanical properties of aluminium silicon magnesium alloy (A356) produced through the investment casting method is being investigated in this work. The effects of these variables were studied using design of experiments (D.O.E) via Taguchi’s L9 orthogonal array method. The castings produced were subjected to mechanical tests such as tensile strength, impact strength and hardness test using Monsanto tensometer and Avery impact and Avery hardness testing machines respectively. The results obtained were analysed using Minitab software 17. The results showed that the tensile strength, impact strength and hardness were optimum when the shell thickness was 5 mm, pouring temperature was 665 o C and the bar cross section was 64 mm 2 respectively. The investigation concludes that investment shell of thin thickness, casting thickness of smaller bar sections and lower pouring temperatures in the range of 665 o C - 690 o C were the most suitable parameters that produced optimum results with better mechanical properties in this study. Keywords: Investment casting, Polystyrene pattern, Plaster of Paris slurry

Stress Distributions and Pullout Responses of Extensible and Inextensible Reinforcement in Soil Using Different Normal Loading Methods

Abstract In design of reinforced soil structures, pullout capacity of reinforcement in an anchorage zone is an important parameter for stability analysis. This parameter is generally quantified by conducting laboratory or field pullout tests. In the laboratory pullout test, the reinforcement is embedded in the soil mass at a normal stress, which is commonly applied by a pressurized airbag or a hydraulic jack through a rigid plate, and then a horizontal tensile force is applied to the reinforcement. This article reports an experimental study conducted to evaluate the effect of the load application method using an airbag with and without stiff wooden plates on the vertical stress distribution and the pullout capacities and deformations of extensible (geogrid) and inextensible reinforcement (steel strip) in the soil in a large pullout box. This study monitored the distributions of the vertical earth pressures at the top and bottom of the soil mass in the pullout box, and at the level of reinforcement using earth pressure cells. The measured earth pressures show that the airbag with stiff plates resulted in a nonuniform pressure distribution, whereas the tests with an airbag directly on the soil had an approximately uniform pressure distribution. The nonuniform pressure distribution resulting from the airbag with stiff plates reduced the pullout resistance of the reinforcement as compared with that using the same airbag without stiff plates. The nonuniform pressure distribution effect was more significant for narrow inextensible reinforcements than wide extensile reinforcements. The test results also show that the displacements in the cross section of the same transverse bar were not equal when the normal load was applied through stiff plates.

Assessment of head loss coefficients for water turbine intake trash-racks by numerical modeling

In this work, numerical simulations of fluid flow around trash-rack for different bar cross sections are conducted to investigate cross section influence on head losses. Comparison with experimental data is conducted to validate the usage of numerical simulations which enable investigation of great number of trash-rack configurations. In previous experimental studies researchers mostly focused on trash-rack parameters (bar spacing, bar length, inclinations etc.) where bar cross section was mainly rectangular or streamlined shape. Therefore, 2D simulations for different cross sections are carried out for a range of trash-rack configurations in order to provide better insight how it affects energy losses. It is shown that head loss reduction due to change in cross section is greatly dependent on trash-rack configuration, therefore optimization of simplified real water turbine trash-rack is also conducted to produce the cross section that generates smallest head losses for given configuration.

Analytical and Numerical Shape Optimization of a Class of Structures under Mass Constraints and Self-Weight

AbstractThis paper first extends a classical solution concerning the shape optimization of a hanging bar. The well-known solution determines the optimal cross section of a homogeneous bar that mini...

Searching for shear forces flows in arbitrary cross-sections of thin-walled bars: numerical algorithm and software implementation

Development of a general computer program for the design and verification of thin-walled bar structural members remains an actual task. Despite the prevailing influence of normal stresses on the stress-strain state of thin-walled bars design and verification of thin-walled structural members should be performed taking into account not only normal stresses, but also shear stresses.Therefore, in the paper a thin-walled bar of an arbitrary cross-section which is undergone to the general load case is considered as investigated object. The main research question is development of mathematical support and knoware for numerical solution for the shear stresses problem with orientation on software implementation in a computer-aided design system for thin-walled bar structures.The problem of shear stresses outside longitudinal edges of an arbitrary cross-section (including open-closed multi-contour cross-sections) of a thin-walled bar subjected to the general load case has been considered in the paper. The formulated problem has been reduced to the searching problem for unknown shear forces flows that have the least value of the Castigliano’s functional. Besides, constraints-equalities of shear forces flows equilibrium formulated for cross-section branch points, as well as equilibrium equation formulated for the whole cross-section relating to longitudinal axes of the thin-walled bar have been taken into account.A detailed numerical algorithm intended to solve the formulated problem has been proposed by the paper. The algorithm is oriented on software implementation in systems of computer-aided design of thin-walled bar structures. Developed algorithm has been implemented in SCAD Office environment by the program TONUS. Numerical examples for calculation of thin-walled bars with open and open-closed multi-contour cross-sections have been considered in order to validate developed algorithm and verify calculation accuracy for sectorial cross-section geometrical properties and shear stresses caused by warping torque and shear forces. Validity of the calculation results obtained using developed software has been proven by considered examples.

Numerical simulation of steel corrosion in chloride contaminated concrete

Corrosion is one of the main reasons for the degradation of reinforced concrete structures, especially of those exposed to a chloride-contaminated environment. To study the effect of chloride ions on the corrosion of steel embedded in concrete, two electrochemical parameters, namely, the anodic Tafel slope and potential, were theoretically analyzed and semi-empirically modified by the concentration of chloride ions in concrete. Subsequently, a numerical model that couples the mass transport and electrochemical corrosion process was established to simulate the transport of chloride ions and the evolution of steel corrosion that occurred simultaneously in the concrete. Based on the proposed numerical model that incorporated the appropriate electrochemical parameters, the corrosion current density and corrosion potential were obtained numerically and they coincided well with the experimental data. Finally, the proposed model was applied to study the chloride ion distribution as well as the corrosion current density around the cross-section and circumference of the steel bar in concrete members with single or multiple steel bars. The results indicate that the proposed numerical modelling method can be used to predict the corrosion-initiation time, as well as the development of the morphology of the corrosion profile of steel bars in concrete structures.

Influence of loading cracks on the carbonation resistance of RC elements

In reinforced concrete (RC) structures, carbonation induced corrosion is one of the most significant durability issues. A very important factor that affects the carbonation process is the appearance of cracks in RC structures. According to the current state of the art, cracks have not yet been considered as a parameter in carbonation models which are used for defining the service life of concrete structures. The main objective of this research is to analyse the influence of cracked concrete cover as reinforcement protection. The analysis was carried out using own experimental results and the application of available standards and novel predictions regarding carbonation depth. For that purpose, prismatic RC samples without cracks and with different crack widths (0.05, 0.10, 0.15, 0.20 and 0.30 mm) were made and subjected to accelerated carbonation. The influence of carbonation depth on the corrosion of cracked and uncracked samples was analysed by observing the reduction of the reinforcement cross section. The compressive and tensile stress influence on carbonation resistance was also evaluated. The conducted analysis showed that even with low crack widths (0.05 mm) the maximum carbonation depth was significantly higher compared with uncracked samples. It was also shown that reduction in the reinforcing bar cross section after 28 days of exposure to 2% CO2 was between 0.05% and 0.13%, depending on the crack width. The results showed that compressive stress increase had no significant effect in the carbonation depth of samples.

A prototype for SANDD: A highly-segmented pulse-shape-sensitive plastic scintillator detector incorporating silicon photomultiplier arrays

We report the first clear observation of neutron/gamma-ray pulse-shape sensitivity of a fully-instrumented 8 $\times$ 8 array of plastic scintillator segments coupled to two 5 cm $\times$ 5 cm 64-channel SiPM arrays as part of a study of the key metrics of a prototype antineutrino detector module designed for directional sensitivity. SANDD (a Segmented AntiNeutrino Directional Detector) will eventually comprise a central module of 64 elongated segments of $^{6}$Li-doped pulse-shape-sensitive scintillator rods, each with a square cross section of 5.4 mm $\times$ 5.4 mm, surrounded by larger cross section bars of the same material. The most important metrics with the potential to impact the performance of the central module of SANDD are neutron and gamma-ray pulse-shape sensitivity using silicon photomultipliers (SiPMs), particle identification via scintillator rod multiplicity, and energy and position resolution. As a first step, we constructed a prototype detector to investigate the performance of a central SANDD-like module using two 64-channel SiPM arrays and rods of undoped pulse-shape-sensitive plastic scintillator.

Mechanical Properties of Cast-in Anchor Bolts Manufactured of Reinforcing Tempcore Steel.

The tempcore process is implemented in rolling mills to produce high strength reinforcing steel. Besides being used as reinforcement, rebars are also used as the base material for the manufacturing of anchor bolts. The mechanical properties of reinforcement bars used in Europe are assessed in accordance with Eurocode without the recommendations for cast-in anchor bolts. The material properties of Tempcore rebars are not homogenous over the bar cross section. The European Assessment Document (EAD) for the cast-in anchor bolts does not exactly specify the mechanical properties of the thread part. The aim of these experiments is to show the different mechanical properties of rebars and their thread parts. The experiments were performed on rebars modified by peeling to characterize the reduction of diameter in a thread part. As a possible way to predict mechanical properties in a non-destructive way, the hardness tests were performed. Next, the application of the correlation relationship between hardness and tensile strength has been determined. The paper formulates preliminary recommendations for assessment of the cast-in anchor bolts in practice.