Values Of Tangential Stresses Research Articles

Investigation of stresses in a Kevlar (491PR-286) material disc by the Chebyshev pseudospectral method

In this study, a composite disc with Kevlar (491PR-286) material was modeled. Kevlar consists of very strong fibers of very light carbon origin. That is why they are used quite often in unmanned aerial vehicles and spacecraft. The disc has been subjected to thermal stress under a linearly increasing temperature distribution. The temperature limit conditions were applied as 25 °C, 50 °C, 75 °C, 100 °C, and 150 °C. The obtained findings were determined using a computer program, the psedudospectral Chebyshev method, and analytically in three different ways. The main difference between this study and other studies is that it investigates the thermal stresses occurring in circular discs using different methods. The results obtained are compared fairly among themselves and presented with graphs. It was determined that tangential stresses were higher than radial stresses at the studied temperature values. In the analytical study conducted, the radial stresses on the inner and outer surfaces of the disc were determined to be zero for the boundary conditions. Under the increasing temperature distribution from the inner surface to the outer surface, tangential stresses occurred as tensile stress on the inner part of the disc and compressive stress on the outer part. Under the decreasing temperature distribution from the inner surface to the outer surface, tangential stresses are pressed on the inner part of the disc, resulting in a tensile stress on the outer part. It is observed that with increasing temperature, there is an increase in radial and tangential stress values. At the end of the study, it was concluded that Kevlar (491PR-286) material discs can be used at high temperatures.

ДЕФОРМАЦИОННАЯ МОДЕЛЬ СОПРОТИВЛЕНИЯ БЕТОНА И ЖЕЛЕЗОБЕТОНА ОТ ДИСЛОКАЦИЙ ДО ТРЕЩИН

The article provides a model of "internal stresses" for concrete matrix of reinforced concrete structures from dislocations, microcracks to macrocracks. The energy theory on the surface of the sphere and the definition of the integral for the mean square value of tangential stresses from plasticity theory are used. An alternative to the general model of the "eight" in the form of a paraboloid from the summation of the volume sectors, levels - radii for the matrix of sliding planes (including octahedral and pure shear) is developed. In the environment of different materials, the model is constructed based on the structure of crystals and dislocations from microcracks to macrocracks, and its working assumptions are formulated. The important principle for displacement (deformation) processes of summation and reduction of relaxing stresses from the stress-strain diagram of concrete is taken into account. The internal total stresses at the rupture of the "figure of eight" (of two contour rings) are obtained for combinations of tetrahedrons or layers-strips from the tangle-paraboloid. The lower boundaries of concrete micro-cracking depend on stresses (deformations), growth rate, energy in crack advancement for a prism or a standard "figure of eight". Displacements from shear, opening widths and crack development heights are obtained from the criteria and connecting parameters in a "representative" volume of concrete. As a result, the dilatation moduli for the stages of the stress-strain state of reinforced concrete are determined, and the equality for the second stage and the dual console elements from the fracture mechanics are obtained.

Новый алгоритм обработки данных метода фотоупругости

The photoelasticity method is a reliable tool for studying the stress state of flat elements in building structures using the models made of optically sensitive materials. In this paper, the classical photoelasticity is considered. The experimental data obtained with the use of the method are presented as interferograms. A decoding procedure implies the obtaining of some normal and tangential stress values in the plane of the model. The polarization-projection installations that are used in optical methods are rather simple. However, the digital processing of the images obtained during the loaded model transmission requires high-intelligent software. Nowadays, national and international laboratories, working with polarization-optical methods, strive to develop digital photoelasticity. For some reasons, the authors of the presented work needed to develop their own algorithms for decoding experimental data of the photoelasticity method. This work is mainly devoted to a formulation of the problems to be solved. Some of them have already been solved, and the results obtained are presented here. The authors place special emphasis on the description of the algorithm for tracing of interference fringes based on the analysis of the image gradient.

ANALYTICAL AND NUMERICAL INVESTIGATION OF ELASTIC STRESSES IN THERMOPLASTIC MATRIX COMPOSITE DISCS UNDER TEMPERATURE EFFECT

In this study, elastic stress analysis was performed on thermoplastic composite discs. The modulus of elasticity of thermoplastic composite discs is also different from each other. Our goal is to study elastic stretching. The field of application of primitive stresses caused by uneven temperature distribution in engineering is quite large. Under the parabolic temperature distribution of the disks, radial stresses formed on the inner and outer parts of the disks were calculated by assuming that the modulus of elasticity does not change with temperature at temperatures of 30 °C, 60 °C, 90 °C, 120 °C on the inner and outer surfaces of the disk. During the study, analytical and numerical analysis was performed using a computer program and mathematically modeled ANSYS programs. Both methods give similar results. In other words, the differences analytical and numerical results can be ignored. At the end of this study, it was determined that the radial and tangential stress values were higher at high temperatures than at low temperatures. It has been established that tangential stresses are much larger than radial stresses. The purpose of this article is to study the behavior of the thermal load on two different thermoplastic disks.

Вплив навантажень на формостійкість тришарової паркетної дошки

Досліджено вплив навантажень на формостійкість тришарової паркетної дошки, склеєної термопластичними полівінілацетатними клеями, залежно від їх величини під час експлуатації. На основі побудованої математичної моделі для прогнозування формостійкості тришарової паркетної дошки залежно від дії зовнішніх факторів під час експлуатації з використанням імітаційного моделювання досліджено пружно-деформаційний стан тришарової паркетної дошки, склеєної термопластичними полівілацетатними клеями. Побудовано графічні залежності радіальних та тангентальних напружень у тришаровій паркетній дошці і проаналізовано їх вплив на паркетну дошку під час експлуатації залежно від навантажень. Під час математичного та імітаційного моделювання тришарову паркетну дошку розглянуто як клейову конструкцію, що складається із трьох шарів, а саме: верхнього, середнього та нижнього, склеєних між собою термопластичними полівінілацетатними клеями із ступенем навантаження 3D. Кожний шар конструкції виготовлений із різних матеріалів, а саме: верхній шар – із твердолистяної породи деревини дуба, середній – із хвойної породи сосни та нижній – із фанери. Оскільки для матеріалу, з якого виготовлена конструкція, характерні різні фізико-механічні властивості, то відповідно, це матиме вплив на пружно-деформаційні процеси тришарової паркетної дошки під час навантажень та визначатиме формостійкість виробу. Встановлено, що за дії на тришарову паркетну дошку, склеєну термопластичними полівінілацетатними клеми, фізичних навантажень, тангентальні напруження будуть зростати у середньому шару, який виготовлений із ламелей деревини сосни та розміщений перпендикулярно до верхнього лицевого та нижнього основного шару. Мінімальне значення тангентальних напружень спостерігається у середині верхнього лицевого та нижнього шарів. Такий розподіл навантажень у тришаровій конструкції паркетної дошки, досягається завдяки нижньому шару, який виготовлений із фанери, та еластичності клейового з'єднання, яке формується термопластичними полівінілацетатними клеями. Це дає змогу компенсувати напруження у внутрішньому шарі тришарової паркетної дошки під час її експлуатації, цим самим покращити її формостійкість.

Экспериментальное исследование реологических свойств жидкого кристалла, модифицированного углеродными нанотрубками

The results of an experimental study of the rheological properties of a nematic liquid crystal MBBA modified with carbon nanotubes depending on the mass concentration of the filler are presented. The measurements were performed on the Physica MCR 501 rheometer (Anton Paar, Austria) by the method of oscillations in the controlled deformation mode. It is shown that the introduction of a modifier into a liquid crystal changes the temperature of the phase transition to the isotropic phase of Ti. The dependence of Ti on the concentration of the filler is constructed. The flow curves and the curves of the complex viscosity of the samples were measured in the concentration range from 0.015to 0.085 wt.%. It is shown that all flow curves can be approximated by one functional dependence: the rheological Tscheuschner equation. The parameters of the approximating curves are calculated. It is shown that the doped samples, in contrast to the dispersion medium, exhibit viscoelastic properties, the greater the greater the concentration of the filler. The dependences of the phase shift angle between tangential stresses and the strain value δ on the concentration of the modifier are investigated. It is shown that as the shear flow velocity increases, the values of δ →π/2, which corresponds to a purely viscous flow. The values of tangential stresses at which the transition to a viscous flow occurs, depending on the concentration of the modifier, are calculated..

Buckling Analysis on a Pipe Conveying Fluid under Two Stresses

Pressure pipes have broad applications in aviation, space flight, mechanical engineering, industrial and civil architecture etc. Instability destruction is their main failure mode. Firstly, in this paper, a complex fluid-solid coupling problem was simplified as a buckling problem of a pipe under two stresses which were along the pipe wall. The two stresses consisted of a compressive stress which was perpendicular to the pipe wall and a tangential stress which was parallel to the pipe wall. Secondly, the buckling performs of the pressured pipe were discussed by finite element analysis method under a working state and an off-working state, respectively. Some obtained conclusions were drawn as follows by the analysis in this paper.1). Provided the tangential stress is unchanged, by increasing compressive stress eigenvalue buckling critical load increases and nonlinear buckling critical load decreases.2). Provided the compressive stress is unchanged, when the direction of the tangential stress is same as that of the axial pressure, by increasing the absolute value of tangential stress the buckling critical load decreases; provided the compressive stress is unchanged, when the direction of the tangential stress is in the opposite direction of the axial pressure, by increasing the absolute value of tangential stress the buckling critical load increases.

Numerical and Analytical Calculations for Modeling and Designing Drilling Wicks or Rotary Cutters Based of Functionally Graded Materials

Drilling tools or drilling pipes, such as drill bit and mill drill, are often subjected to various forces, including essentially tangential forces, centered on their axis of rotation. The main objective of this work is to find analytical and numerical solutions of the distribution of stress field, deformation, and displacement, when such tools are subjected to such forces. It will be assumed that the instrument in the chosen model in this work is a rotating hollow cylinder constructed from a Functional Graded Material (FGM). Because of the graduation of the FGM, the mechanical and elastic properties such as Young’s modulus, density, and Poisson’s ratio vary in the radial direction according to a power law function. By choosing that the inhomogeneity parameter is between -0.5 and 0.5, we have established the differential equation which describes the equilibrium of the hollow cylinder in rotation under an axial load. The calculations performed have allowed finding an analytical solution which was compared with numerical solutions obtained by using the shooting method and the fourth-order Runge-Kutta algorithm. These analytical and numerical results have shown that the values of tangential stresses are greater than the radial stresses. The radial stresses and tangential and vertical stresses progressively increase with the axial force Fz. The force Fz affects more tangential stresses that the radial stresses. The tangential stress, tangential deformations, and displacements are higher on the inner walls of the cylinder than on the exterior surfaces. The results obtained are very important and can be applied in the modeling and designing wicks and drilling strawberries in order to reduce their rapid wear and damage.

Влияние угла профиля передней поверхности резца на степень деформации сдвига

It is established that cutting with gear-cutting and thread-cutting tools is not free that results in the increase of loading upon tool tips and their quick wear. The layers of metal cut are subjected to considerable shear deformation and also to other kinds of deformation. In this connection the wear character of a tool and its properties will change. There is considered a process of chip removal by trapezoidal and triangular cutters (as in case of metal cutting off with teeth of a hob may be used not three but two tool tips) and the impact of a cutting face profile angle upon a shear deformation degree is also considered. There are shown analytical dependences for the definition of angles of a chip flow, a relative shear, a deformation degree of a shear and a value of tangential stresses in the cutting area taking into account the influence of the strength of material machined, width and thickness of a layer cut and a friction factor. The dependences are checked up at cutting with a trapezoidal cutter.

On the necessity of using critical distance model in mixed mode brittle fracture prediction of V-notched Brazilian disk specimens under negative mode І conditions

Fracture load is experimentally measured for round-tip V-notched Brazilian disk (RV-BD) specimen made of PMMA and loaded under mixed mode І/ІІ with negative mode І components. The experimental results are obtained for 90° notch angle and various notch tip radii. The experimental observations show that in some cases, fracture does not initiate from the notch border and it occurs from the edge of the central square hole of the specimen, which is not usually expected. It is shown by the finite element (FE) analysis that although the notch is under mixed mode І/ІІ loading with negative mode І conditions and the notch bisector line experiences compressive stresses, the notch round border is divided into two compressive and tensile sides, suggesting that two critical points may exist on the notch border. Moreover, the FE analysis shows that in some cases, the value of tangential stress on the notch border is larger than that on the edge of the central square hole; but according to the maximum tangential stress (MTS) criterion, which is based on the Theory of Critical Distances (TCD), because the value of tangential stress at the critical distance from the notch border is lower than that on the edge of the hole, fracture is not expected to occur from the notch border. In such cases, the experimental observations are consistent well with predictions of the MTS criterion for the fracture initiation points. The results demonstrate the necessity of using the critical distance in brittle failure prediction of engineering components weakened by blunt V-notches.

Optimization of Wind-Up Tension of Webs Preventing Wrinkles and Slippage

This paper describes the optimization method of wind-up tension to prevent wound roll defects, mainly star defects and slippage, based on the optimum design technique. Hakiel’s nonlinear model with air entrainment effects is applied to analyze in-roll stress distributions in the radial and tangential directions (1987, “Nonlinear Model for Wound Roll Stresses,” Tappi J., 70(5), pp. 113–117). It is well known experimentally that a decrease in the wind-up tension prevents star defects due to negative tangential stress under winding. Thus, in the present optimization method, wind-up tension is gradually decreased in the radial direction to minimize the averaged value of tangential stresses under the constraint of non-negative tangential stresses. Furthermore, the relation of the slippage between wound film layers and in-roll stress of a roll is considered. Successive quadratic programming, which is the typical mathematical programming method, is used as the optimization technique. Wind-up tension is expressed by the third-order spline curve of a radial coordinate. The liner function with respect to the radial coordinate is used as the original wind-up tension. The optimized wind-up tensions are obtained for various winding conditions, and we confirmed that the in-roll stress distributions were very much improved for preventing wrinkles and slippage by the optimization method proposed.

Strength properties of rocks under a nonuniform triaxial dynamic load

1. In the case of nonuniform dynamic loading of rock to pressures comparable to the strength, the limit equilibrium of the rock can be described satisfactorily by the Coulomb-Mohr plasticity condition in effective stresses. 2. Cohesion and internal friction in rock increase with increase of the loading rate, varying from the limit static to the limit dynamic value. 3. An irreversible change in the strength properties of rocks depends on the degree of nonuniformity of the state of stress, determining the development of dilatation in the rock, which reduces cohesion-in rock and has practically no effect on internal friction, which ultimately leads to a considerable decrease of the limit values of tangential stresses. 4. A prescribed change of the strength properties of rocks can be achieved by appropriate selection of the time parameters of loading, magnitude, and nonuniformity of threedimensional stresses.