Values Of Normal Stress Research Articles

Pengaruh Variasi Bentuk Permukaan Forging Dan Suhu Preheat Terhadap Kekuatan Tarik Friction Welding

Most of the railway facilities use steel as the constituent material. The method of joining (joining methods) of steel materials, especially in the railroad industry, the most widely used is the welding technique (welding) so that knowledge of the welding process is very important for welding enginers and metallurgists as well as for designers, fabricators, users of welding results. The purpose of this study was to determine the tensile strength of the joint resulting from the friction welding method with variations in the shape of the forging surface and preheat temperature. The shape of the forging surface is 8 mm, 10 mm and 12 mm. Variations in preheat temperature of 200 C, 400 C and 600 C. The results showed the highest tensile strength of the friction weld joint with an average tensile stress value of 407, 48 MPa on the forging surface shape of 12 mm and a preheat temperature of 600 C. And the tensile strength of the joint The lowest friction welding with an average tensile stress value of 120 MPa on the forging surface shape of 8 mm and a preheat temperature of 200 C.
 Keyword: friction welding, forgings, preheat temperature

Optimization of horizontal axis wind turbine blade using FEA

The need of renewable energy sources is growing. Wind energy is the important sources of renewable energy. In the wind energy sector Horizontal axis wind turbines are the major devices used for the production of electricity. Blade is the most important part of HAWT. Blade material is the most important factor in the performance of HAWT. The major structural properties are influenced in a wind turbine blade are Rigidity, fatigue and flexibility of materials and optimum aerodynamic shape. The main objective of this work is to optimize the blade material properties by finite element analysis with the structural factors in the risk area. The factors such as dynamic and elastic center of blades, positioning of center of gravity has been considered for the structural analysis. In this research the blade structure is consisted with 8, 10, 12, 14 layers of the fiber glass fabric and epoxy resin as matrix of composite reinforced polymer. In this research the fiber glass fabric and epoxy resin as matrix of composite reinforced polymer are consisted with 8, 10, 12, 14 layers. The maximum values of normal and tangential stress are considered for the static analysis. It was originated that when the risk area carries more number of layers and decreased the blade tip leads to increase resistance to static and dynamic loads. The aim of this study is to apply the finite element method on the wind turbine blade and enlightening the structure and reducing their cost of production.

Stress analysis of strain wave gear drives with four different geometries of wave generator

The comparison of strain wave gear drives with four different geometries of the wave generator is presented. The commonly used elliptical geometry of the wave generator is compared with a simplified geometry based on two rolling elements, a geometry based on four rollers, and a newly proposed parabolic geometry for the wave generator. The comparison will be performed in terms of the average maximum stresses caused in the flexible spline due to the rotation of the wave generator. The finite element method and fully-parameterized automatically-generated two-dimensional finite element models are being used in this work. The flexible spline and the ring gear are considered deformable elements whereas the wave generator is considered as a rigid element in the finite element model. The results show that the best mechanical performance in terms of lower average values of maximum von Mises and tensile stresses is achieved with the simplified and parabolic wave generator geometries. Although yielding slightly higher maximum von Mises and tensile stresses, the elliptical wave generator provides the lowest average maximum absolute compressive stress. The worst mechanical performance was obtained with the four roller wave generator.

Verification of Selected Failure Criteria for Adhesive Bonded Elements with Different Stiffness through the Use of Methacrylic Adhesive.

This study presents the testing results of methacrylic adhesive single-lap joints made from elements with different stiffness and of the adhesive itself, using cast specimens. Methods for the preparation and testing of material specimens of the adhesive joints have been presented. Moreover, an attempt was undertaken to determine the strength criterion and find out which of the presented calculation methods enables the most precise assessment of strength in the tested group of single-lap joints, that differ in terms of the adhered stiffness and thickness. For this purpose, C45 steel and 5754 aluminium flat bars were bonded. Stress distributions were determined for failure forces obtained in the experiment by means of three basic analytic and numerical methods. Stress and strain states were compared, indicating the highest consistency for the value of normal peel stresses acting in the direction perpendicular to the direction of the joint tension. Reduced stresses provided by the analyses reached values higher than those which were achieved during the specimen tension testing.

Necessary Height of the Vertical Stiffeners in Steel Silos on Discrete Supports with Accounting of Imperfections

To ensure unloading of the whole amount of stored product by gravity, the steel silos are often placed on supporting frame structure. The values of stresses in the joints between the thin shell and supporting frame elements are extremely high. It can cause local loss of stability in the shell. To prevent it, many designers place stiffening elements above the supports. Here the question is how high should be the stiffening elements? The appropriate solution is that they should rise to that level till which the values of meridional normal stresses above the supports and in the middle between them are equalized. But where is this level? Many researchers worked on values and ways of distribution of normal meridional stresses above the supports of the cylindrical shells. As a result of their efforts are determined critical height Hcr of the shell and the ideal position HI of intermediate stiffening ring. But these heights are considerably different between each other. To which of them our vertical stiffening elements should achieve? Considering the nonlinear behaviour of the steel, the effects of changes in geometry during loading and imperfections caused by welding works, the author tried to obtain an answer to this question.

Effects of heat treatment on microstructure and mechanical properties of TiC/TiB composite bioinert ceramic coatings in-situ synthesized by laser cladding on Ti6Al4V

To improve the wear resistance of titanium alloy, in this work, TiC/TiB composite bioinert ceramic coatings were synthesized in-situ via laser cladding using Ti and B4C mixed powders as precursor materials. And to decrease the impact of the excessive residual tensile stress generated by the uneven temperature distribution on the performance of coatings, the coatings were then subsequently heated for 3 h at different temperatures (400 °C, 600 °C, and 800 °C) and then air cooled. The effects of heat treatment on the microstructure, residual stress, micro-hardness, fracture toughness, and wear resistance of the coatings were investigated. The results showed that phase compositions and microstructure of the heat-treated coatings were virtually identical to that of the untreated coatings; however, the precipitation of acicular TiB enhanced mechanical properties of the heat-treated coatings. In addition, the average residual tensile stress values of the coatings decreased as the heat treatment temperature increased, which improved fracture toughness of the coatings from 3.95 to 4.68 MPa m1/2. Moreover, wear resistance of the coatings was greatly enhanced by heat treatment; as the wear volume of the heat-treated coatings decreased by 50% at 800 °C compared with that of the untreated coatings. Lastly, the coatings showed good biocompatibility after being evaluated in vitro, and therefore had broad application prospects in the field of orthopedic implants.

INFLUENCE OF FRICTION REGIMES ON THE TRIBOTECHNICAL PROPERTIES OF COMPOSITES BASED ON PTFE AND CARBON FIBERS

The paper presents the results of tribotechnical tests of polymer composite materials based on polytetrafluoroethylene (PTFE) and carbon fibrous activated material UVIS-AK-P (SPC UVIKOM LLC) depending on the contact pressure in dry and boundary friction modes in various oils. I-20A industrial oil, Siboil TAD-17u transmission oil, and Rosneft Gidrotec HLP 46 hydraulic oil were used as liquid lubricants for the friction of polymeric materials. For tribotesting, a polymer composite with a content of 5 % wt. UVIS-AK-P, obtained using sequential mixing of filler with PTFE and the technology of joint activation of components in a planetary mill, is the most wear-resistant material according to the results of previous studies. It has been established that despite the heavy wear at increased bearing pressure during dry friction, unfilled PTFE does not undergo plastic deformation and maintains a low coefficient of friction practically unchanged. It has been found that the friction coefficient passes through a minimum during dry friction of a composite with CF at a load of 350 N. It is associated with the transition of the elastic contact of the interacting elements of the surfaces of the metal-polymer tribosystem to the plastic one with increasing load. During friction of PTFE in a lubricating oil environment, a significant decrease in mass wear, friction coefficient and temperature in the contact zone are observed due to the formation of secondary structures on the friction surfaces and the significant flexibility of PTFE. This increases the actual area of the tribocontact, which reduces the value of real normal contact stresses. During friction of polymer composite materials in the environment of lubricating oils, a decrease in the friction coefficient and the area of the friction track by 1.7-2.7 times was recorded as well. Deformations, groove formation and mass wear were not observed. It has been revealed that the greatest effect of increasing the wear resistance and permissible friction load and lowering the temperature in the friction zone of PTFE and composite is observed when using Siboil TAD-17u transmission oil. This is due to the presence of special antifriction additives in this oil brand and a decrease in the actual contact of the working surface of the polymer material with the lubricant, which helps to reduce the intensity of the destructive process in the surface layer while contacting with the lubricant.

Predicting the values of average stresses during the ice–water phase transition in mesoporous silicon-based structures in the temperature range 233...273 K

Theoretical model has been developed for predicting the average stress values during melting of water frozen in silicon-based mesoporous structures in the temperature range 233...273 K, caused by the difference in the thermal expansion coeffi cients of the heterogeneity elements in the materials studied. Numerical calculations were carried out using and dependences of the average stress tensor components on the volumetric water content in the mesoporous silicon matrix were investigated.

Testing methods for shear strength of bond line between concrete and different types of engineered wood

This paper identified a reliable testing method for determining the shear strength of bond lines between concrete and engineered wood. The identification was carried out based on analytical derivations and experimental tests on concrete (compressive strength of 24.8 MPa) and engineered wood composite connections glued by two types of epoxy. Forty specimens were tested under two commonly used test setups, i.e. 20 double-shear tests on timber-concrete composite specimens with a bond length of 50 mm and another 20 compression-shear tests on specimens with a bond length of 300 mm. The result analysis showed that there was no significant statistical difference between the shear strength of the bond lines (around 2.3 MPa) as well as between the failure modes obtained (dominated by concrete failure), regardless of the considered bond lengths and adhesive types investigated. The analysis used a quasi-non-linear fracture mechanics model, considering the boundary conditions of the tests. The analytical model revealed that the ultimate shear stress is approximately uniformly distributed both in the double-shear and in the compression-shear tests, so the spatially averaged shear stress value can approximate the critical shear stress of the bond line with sufficient accuracy. However, if the failure occurred in the wood or the strength of the concrete was higher, the shear stress distribution at ultimate load in the compression-shear tests with a bond length of 300 mm would not be uniform. The maximum shear stress value, which is significantly larger than the average one, occurred at the fixed (or supporting) end of the bond line. Even so, in the shear tests with a bond length of 50 mm, the average ultimate shear stress value was still close to the shear strength with a difference smaller than 5%. Hence, a bond length of 50 mm is recommended for determining the shear strength of a bond line between normal strength concrete and engineered wood when using a push-out shear test setup.

Інженерна методика розрахунку елементів із комбінованої клеєної деревини

Extensive world experience in the implementation of building structures made of timber, in particular glued timber, for various purposes confirms the feasibility of their use. This is facilitated by the fact that glued timber effectively accumulates the positive properties of timber as a structural material level the shortcomings of solid timber. One of the types of constructions of glued timber are constructions of combined glued timber. Taking into account the structure and features of elements of combined glued timber of rectangular cross section, for a detailed analysis of the stress-strain state, a method is proposed, which consists in applying to standard formulas for calculating the reduced cross-sectional characteristics: reduced area, reduced moment of inertia, reduced moment of resistance. To calculation, the elements of combined glued timber of rectangular cross section according to the second limit state (serviceability), it is proposed to use the reduced modulus of elasticity of the section to the boards of the outer layers. To analyze the proposed method, a number of numerical studies of beams of combined and glued timber of the same strength class using analytical calculation methods and using the finite element method in the software package LIRA-CAD, using three-dimensional and flat finite elements. Numerical studies show that the results of calculations of beams of combined glued and glued timber of the same strength class differ within 20% in the direction of increasing the values of deflections and normal stresses in the elements of combined glued timber. Finite element calculations in the software package LIRA-CAD beams of combined and glued timber of the same strength class modeled volumetric and flat showed almost complete coincidence of results with a discrepancy of up to 2%, which suggests the need to significantly simplify the modeling, set elements from glued timber with flat finite elements. It is confirmed that the analytical calculation of beams of combined glued timber is recommended to be carried out according to the proposed method. The proposed technique allows to take into account the thickness and mechanical characteristics for the strength class of each board of which the glued cross section of the element, which significantly expands the range of use of combined glued timber. The high level of coincidence (within 5%) of the proposed analytical method with determination of the given cross-sectional characteristics with the results obtained by the finite element method for different cross-sections and spans of beams is confirmed, which allows to assert the expediency of its application in engineering calculations. In addition, the modeling of structures made of combined glued timber is possible with rod elements with the provision of the reduced modulus of elasticity according to the proposed method, which greatly simplifies the calculation of complex rod systems.

Engineering methodology for checking the local stability of the wall of steel I-beams in distributed stress fields

For many years, normative methods have been developed and applied for the core schematic of the calculation of load-bearing structures. With the increase in computing power of computers and the development of computer programs, it becomes possible to consider design situations for the load-bearing structures modeled in three dimensional form. The results of the calculation of mechanical systems of three-dimensional finite element models in computer complexes are presented in the form of distribution fields: stresses, deformations, displacements. Stresses can be distributed on the plane for plate models or in volume for models of volumetric finite elements. For correct work with the results of calculations of three-dimensional computer models, normative methods of calculation need a quality update and adaptation to new levels of design automation. In the paper, discusses the procedure for determining the average stress values in the wall of a finite element model of a steel beam, broken into compartments, while checking local stability. The author calculated the steel I-beam of an overlapping beam with a span of 18 meters in the SCAD Office computing complex. The beam geometry is modeled from finite casing elements with zero Gaussian curvature. The article discusses an example of determining the average stress values in an ordinary beam compartment. In the example, the procedure for determining the average stresses in the wall of the steel beam by the distributed fields for the subsequent substitution of the local stability test into the normative condition is indicated. It is proposed to determine the average values of stresses in proportion to the distribution area in the finite elements along the compartment or section of the compartment, in horizontal rows. In the considered method, it is sufficient to determine the average values of stresses for two horizontal rows, then it is proposed to linearly interpolate or extrapolate the required stress along the height of the cross section. The article proposes an engineering method for testing local stability for use in the practice of design.

Modelling analysis of high effect of roll hoop main on the strength of student car formula chassis

Purpose: To analyse the strength of materials by means of optimization, find the best value of the strength test of mutually influential materials with a variation of roll-hoop height. Design/methodology/approach: The research began with the design of a threedimensional model by varying the height of the roll-hoop on chassis types: A, B, C, D, E, F, G, H ,and I. The height of the main roll hoop at each chassis is: 502, 504, 506 508, 510, 512, 514, 516 and 518 mm. Then by using the student version of Autodesk Inventor, a simulation is made to test: Deflection, Normal stress, Shear stress (T-x / T-y) and Torsional stress. The results of this test are used to analyse the types of chassis that have been designed so that the best chassis design is obtained. Findings: The results obtained in this study are the value of Normal stress decreases with increasing roll-hoop height, and applies inversely to the torsional stress value. Deflection values tend to be stable with increasing roll-hoop height, while Shear stress T-x and T-y values tend to fluctuate. Research limitations/implications: The chassis material uses carbon steel which has mechanical property values in accordance with 2015 FSAE Standard regulations. Practical implications: The optimization results of the design of the roll hoop height on the chassis show that the chassis type B with the main roll hoop height of 504 mm is the best with the lowest deflection value and the difference in tension according to the FSAE rules. Originality/value: The research that has been done only tests the strength of the ingredients separately. In this study trying to analyse the strength of the material by way of optimization to find the best value from the strength test of material that influence each other with a variation of roll-hoop height.

Experimental validation for the application of the flat jack test in cob walls

The flat jack test is one of the most applied investigation techniques in the field of cultural heritage conservation. The purpose of the experimental campaign presented in this paper was to assess the feasibility of the technique to measure the average compressive levels of stress in existing cob walls and determine their mechanical properties. It was observed that the single flat jack test tended to overestimate the average value of stress by a factor of two. Therefore, it is advised to apply a value of Ke=0.51 to correct the average compressive stress values obtained with the use of this technique.

Empirical Shear Strength Criterion for Rock Joints Based on Joint Surface Degradation Characteristics During Shearing

Joint surface morphology has essential implications for joint shear behaviors. In this paper, constant normal load (CNL) direct shear tests were performed on 150 artificial rock joint specimens to study the joint surface degradation process under various initial joint roughness coefficient (JRCinitial), joint wall compressive strength (JCS), and normal stress (σn) values. The experimental results revealed that with increases in JRCinitial, JCS, and σn, the joint surface exhibited different levels of increased degradation. With increasing shear displacement, the JRC continued to decline and finally tended to stabilize to a constant value, and we divided the degradation process into an initial weakening phase, a rapid weakening phase, and a constant weakening phase. Based on regression analyses, a JRC degradation model was presented to evaluate the JRC values of rock joints under various displacements, and a new empirical equation was introduced to predict peak shear displacement. Additionally, a piecewise function for the different shear displacement stages was proposed to calculate JRCmobilized by replacing JRC in the JRC–JCS model, and the variation in the friction angle $$\phi$$ at various stages was discussed. Finally, a modified constitutive model was developed to predict shear strength versus displacement curves. The predicted results indicated that the new proposed model performs better than previous models.

Experimental Study of Shear Behavior of Rock Joints under Two Types of Boundary Conditions: Constant Normal Load and Constant Normal Stiffness

Shear destruction of rock mass along weakened planes is one of the main reasons of the failure of career boards, underground workings and rock slopes. The paper deals with laboratory testing of rock joints under direct shear loading. Special test and measurement complex was created to study deformation and strength characteristics of rock joints. Test specimens were made from single slab of sandstone of homogeneous structure. Shear tests have been conducted under constant normal load (CNL) and constant normal stiffness (CNS) boundary conditions at three values of normal compressive stress: 0.5 MPa, 1.2 MPa and 1.8 MPa. The analysis of test results allowed to reveal patterns of changes of deformation-strength properties of rock joints depending on the level of normal load, boundary conditions and roughness values. The ultimate shear stress is always higher under CNS boundary condition than CNL for the same values of normal compressive stress. Shear stress practically retains constant value after reaching the ultimate stress under CNL boundary conditions and it decreases under CNS conditions. The values of ultimate shear stresses, shear modulus and the length of linear section on “shear stress–shear displacement” curve increases with increasing surface roughness at the equal levels of normal compressive stress.

Failure Criteria for Isotropic Rocks Using a Smooth Approximation of Modified Mohr–Coulomb Failure Function

It is reported that strength of rocks is a function of three-dimensional (3D) stress state as observed from the large sets of experimental results under the true-triaxial condition. Triaxial compression test data in general is readily available for rocks, but in practice true-triaxial facilities are seldom used. This creates a requirement for 3D failure criterion, which can be used to predict the true-triaxial strength using simple triaxial compression test data. We have proposed three criteria by altering the deviatoric function of modified Mohr–Coulomb criterion (Singh et al. in Int J Rock Mech Min Sci 48(4):546–555, 2011). The proposed criteria represent the behaviour of rock from lower to very high confining pressures. The criteria have unique yield surfaces. The yield surface changes its shape with the change in the mean stress. It is observed beyond certain value of the mean stress; the yield surfaces converge to von-Mises yield surface which means the shape of the yield surface is independent of pressure beyond the certain value of mean normal stress. The criteria require three parameters that can be easily calculated from the triaxial compression test results. The proposed criteria also satisfy the Drucker stability postulate, hence could be adopted as a plastic potential function. For the assessment of the criteria, true-triaxial data from twelve rocks are considered. Results of the criteria are compared with the modified Mohr–Coulomb criteria both 2D and 3D proposed by Singh et al. (Int J Rock Mech Min Sci 48(4):546–555, 2011). Performance of the new failure criteria for the considered rocks are observed to be better than the modified Mohr–Coulomb criteria (2D and 3D).

THE STRESS ANALYSIS ON TWO DIFFERENT ADHESIVELY BONDED T-JOINTS VIA 3D NONLINEAR FINITE ELEMENT METHOD

Adhesively bonded joints are formed in different configurations. T- adhesively bonded joint is one of these configurations and has an important position in industrial applications. The purpose of this study was to numerically study the stress distributions, strength, damage evolution of different T-joints with or without adhesive filling at the curvature of the L-shaped adherends under tensile load via 3D nonlinear finite element method. Here, type-I T-joint is the first model without adhesive filling at the curvature of the L-shaped adherends and type-II T-joint is the second model with adhesive filling at the curvature of the L-shaped adherends. In this study, FM73 and 3M 2214 adhesives and AA2024-T3 aluminum alloy adherends have been used to create two different T-joints numerically. Numerical analysis results have shown that the presence of filler adhesive has a direct influence on joint strength. It has also been observed that ABCD interface is the most critical region in terms of damage occurrence, while is AB and BC lines on the ABCD interface are the most critical lines. In addition, it was observed upon comparing the stress distributions of lines AB and BC that the shear and normal stress values decreased in lines AB and BC of the type-II T-joints. Therefore, it can be put forth that the strength of Type-II T-joints is greater in comparison with the strength of type-I T-joints and the use of a type-II T-joints is more suitable for loads which are close to the fracture load of the T-joints.

Numerical investigation of partially liquefied vitreous dynamics as two-phase viscoelastic-Newtonian fluid flow in a planar cavity due to oscillatory motion

In this paper a numerical solver is developed in the OpenFOAM to capture the interface effects and dynamic characteristics of two-phase viscoelastic-Newtonian fluid flow for single and multi-mode viscoelastic models in linear and non-linear regimes. The code is based on finite volume method and the PIMPLE algorithm is used to couple the velocity and pressure terms. The dynamic mesh technique is used to model the movement of the computational domain and a modified classic volume-of-fluid approach is employed to capture the interface effects. In order to enhance the stability of the numerical procedure the discrete elastic split stress method is employed and introduced into the momentum equation.The present numerical model is validated in the linear regime by comparing the results with those of the analytical solution for which excellent agreement is observed. The main objective of this study is to investigate the effects of various angular frequencies, amplitudes and volume fractions on the flow dynamics of partial vitreous liquefaction in a two-dimensional model of the vitreous chamber subjected to sinusoidal motions. Concentric and eccentric configurations of the liquefaction are considered with the initial circular shape inside a cavity. Numerical results are obtained for the velocity field, shear stress, normal stress difference and streamline pattern and it is discussed how the partial vitreous liquefaction responds to the different oscillatory movements in comparison with a normal, healthy vitreous gel. It is observed that in concentric cases, the maximum values of shear stress and tangential velocity intensify by increasing angular frequency and their locations move from the wall into the domain of the cavity. In eccentric configurations significant interface deformations are observed. Moreover, the results indicate that the shear and normal stress values in the eccentric cases are higher compared to those in the concentric configurations.

LDV-based measurement of 2D dynamic stress fields in transparent solids

Laser Doppler Vibrometer (LDV) has been performed as a tool to observe stress fields of ultrasound longitudinal wave inside transparent solids due to its high sensitivity and intuitiveness. Besides, this method is only sensitive to dynamic stress and has no response to static stress, so it has the advantage of not being affected by residual stress in transparent solids. However, this method has limitations. LDV cannot directly detect shear wave, and for longitudinal wave, it can only obtain an approximate value of normal stress. In this paper, we analyze the limitations, and achieve observing shear wave by adding a rotatable linear polarizer to the optical system. Furthermore, the complete photo-elastic tensor can be obtained from the process of measuring longitudinal wave, and then the absolute 2D dynamic stress fields can be calculated. To check the applicability of our method, we compared LDV with the results of numerical analysis and dynamic photoelasticity, respectively.

Study of stress-strain behavior of a compressed elastic strip

The paper considers the plane strain of a compressed elastic strip made from incompressible material. The deviation of the cross-section contour from the rectangle, as well as the intensity of the force applied to the upper and the lower edge of the section are known up to small parameters. The authors have carried out a study of the problem solution analyticity with respect to small near zero parameters. With the help of the perturbation method, they have found a solution for a particular case of the function describing the deviations up to the second order of smallness. It has been shown that if an experimental research is carried out and the applied force meets the condition described, the average stress and displacement values will differ from those typical for homogeneous state only by a second order infinitesimal.