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•Dynamic moduli measured by IDT and UC tests are compared.•Stress–strain states of IDT and UC tests are investigated.•Stress of IDT and UC tests present an exponential relationship ...with temperature.•UC test shows a good strain control at low and medium temperatures.
Dynamic modulus is an essential parameter for the performance characterisation of asphalt materials for performance prediction and pavement design. The Indirect Tensile (IDT) test and the Uniaxial Compression (UC) test are both well-known experiments performed in the laboratory to characterise the dynamic modulus of asphalt mixtures over a range of temperatures and loading frequencies. A considerable amount of research has investigated the difference between two test modes, while few studies analysed the fundamental difference in stress–strain distributions for the two test setups. This work aims at comparing the effect of the two test methods on dynamic modulus of asphalt mixtures, as well as stress–strain state. For these purposes, two types of mixtures commonly employed to build road surface layers, namely Asphalt Concrete (AC) and Stone Mastic Asphalt (SMA), were created and tested. The specimens were prepared with a gyratory compactor. The master curves of dynamic modulus and the stress–strain states obtained from the two testing procedures were compared. The dynamic modulus and phase angle results are almost identical for medium frequency and temperature, whereas the results exhibit significant discrepancies for lower and higher frequency values. AC 11 and SMA 11 mixtures show differences in comparison between the two tests. Moreover, the strains measured by the IDT test are variable and the strains obtained from the UC test stabilise around 40 με. Similarly, both tests have poor strain control at 40 °C. The values of normalised stresses measured by the IDT test are approximately 3.26 and 2.34 times greater than the ones measured by the UC test for AC 11 and SMA 11 mixtures, respectively. In general, the results of the mechanical characterisation of the asphalt mixtures conducted using both tests are similar. The IDT test has the advantage of sample size for sample preparation methods in both laboratory and field, and the UC test has a better deformation control at low and medium temperatures.
•The CFRP starts to work with the main reinforcement immediately after application.•The previous loading has the influence on the efficiency of strengthening with CFRP.•Lower values of preloading ...increase the strengthening effect.
This paper presents results obtained from test carried out to investigate the behavior of columns strengthened with CFRP laminates subjected to eccentrically applied axial loading. It is noted that when strengthening existing structures, it is often not possible to fully unload them and as a result the structural elements being strengthened are pre-loaded. In this research 10 large scale column specimens, strengthened with CFRP are investigated. Attention is focused on investigating the effect of pre-loading acting at the moment of strengthening on the recorded behavior. Each sample is initially loaded with eccentrically applied axial force, equal to 30%, 50% and 70% of the ultimate capacity. Once strengthened, the specimens were incrementally loaded until the destruction, values of strains and deflections were recorded on each loading stage. Strength, deformability and ductility parameters of columns were determined and thoroughly analyzed. Comparative analysis was carried out and the effectiveness of the strengthening is determined. It was identified, that the higher levels of initial loading decrease the strengthening effect from 31.8% to 15 % when for 30% and 70% preloading, respectively. Also, for samples with high pre-loading level the ultimate displacement at ultimate load reduced. It is important to note the increase of stiffness and decrease of deflections due to CFRP-strengthening. The presence on initial loading slightly decreases the ductility of CFRP strengthened columns (by 9–12 %). Specific features of CFRP effectiveness should be taken into account in engineering practice.
In this paper, the Variational Iteration Method (VIM) or Extended Kantorovich Method (EKM) is formulated for the first time for flexible porous functionally graded (PFGM) plates with different ...boundary conditions and geometric nonlinearity according to the theory of Theodore von Karman. Its accuracy and efficiency are demonstrated. The plate is subjected to a uniform transversal load and temperature field. The displacement field of the plate is approximated based on the classical plate theory (CTP) or Kirchhoff's plate theory. The governing equations are derived using Hamilton's principle. Modified Coupled Stress Theory (MCST) is used to account for size-dependent effects. The material properties vary with thickness and are temperature dependent. Four porosity distribution patterns are considered in this study. Several examples are solved to demonstrate the proposed algorithm. The results obtained are compared with solutions obtained by the Bubnov-Galerkin Method (BGM) in higher approximations, the Finite Difference Method (FDM) of second order accuracy, as well as with results obtained by the Finite Element Method (FEM) of other authors. The results include an analysis of the effect of size dependent parameters, porosity type pattern, porosity index, functionally graded index, temperature field and different types of boundary conditions on the stress–strain state and bending deflection of plates.
Electrolysis units are widely used in different branches of industry. They are high-pressure tanks, each having a chamber and electrodes placed therein, which are arranged in assemblies, a cover as ...well as an inlet and outlet pipes. High requirements are imposed on their technical characteristics, confirming the urgency of the problem of improving calculation methods. To simulate the kinetics of the thermally stressed state in elements of power plants with complex rheological characteristics of the material and taking into account its damageability, a special technique and software complex have been developed on the basis of the finite element method, which allow solving a wide class of nonlinear nonstationary problems in a three-dimensional formulation with simultaneous consideration of all operating factors. The kinetics of the crack was studied using the method of calculating the survivability of structural elements, which is based on the principles of brittle fracture mechanics, while the plastic zone at the crack tip is assumed to be small compared to the crack size, and the crack kinetics is determined by the stress intensity factors at crack tips. The technique is based on calculating the kinetics of the crack to its critical dimensions, when an avalanche-like destruction of a structural element occurs, or a crack grows through the thickness of the element. The kinetics of a semi-elliptical crack emerging on the inner surface of the cell wall was studied under the action of static and cyclic loading. With the use of the developed technique, computational studies of the thermal stress state of the upper part of the electrolyser cell were carried out. The results obtained show that the cylindrical part of the cover is the most loaded. There have been carried out studies of the development of an internal surface semi-elliptical crack, which originated in this zone. It was found that with a small number of cycles per year, the crack will grow for a long time to a certain depth, then the rate of its growth from static loading will increase so quickly that the growth of the crack from cyclic loading can be neglected.
Исследована зависимость напряженно-деформированного состояния костной ткани от ее плотности вблизи дентального имплантата. Расчеты выполнены методом граничных элементов в постановке плоской ...деформации для модели, состоящей из цилиндрического имплантата и окружающих костных тканей. Костная ткань рассматривается как изотропный и однородный упругий материал. Моделирование влияния плотности костной ткани на напряженно-деформированное состояние при квазистатическом приложении нагрузки выполняется посредством изменения модуля упругости кости. Установлено, что при увеличении модуля упругости губчатой костной ткани максимальные эквивалентные напряжения в этой костной ткани возрастают. Напряжения в кортикальной костной ткани при увеличении модуля упругости губчатой кости снижаются за счет уменьшения нагрузки, передаваемой на эту часть кости. Напряжения в губчатой кости снижаются при увеличении модуля упругости кортикальной кости. Уровень максимальных напряжений в кортикальной кости возрастает при увеличении модуля упругости этой костной ткани. Максимальные напряжения в кортикальной костной ткани наблюдаются вблизи шейки имплантата.
The dependence of the stress-strain state of the bone tissue on its density near the dental implant has been studied. The computations were performed by the boundary element method for the plane-deformed state of a model consisting of a cylindrical implant and surrounding bone tissues. Bone tissue is considered as an isotropic and homogeneous elastic material. Simulation the effect of bone density on the stress-strain state when applying a quasi-static load is performed by changing of elasticity modulus of the bone. It has been established that with the increasing in the spongy bone tissue elastic modulus, the maximum equivalent stresses in this bone tissue increase. Stresses in the cortical bone tissue decrease with the increasing in the spongy bone elastic modulus due to the decreasing in the load transferred to this bone part. Stresses in the spongy bone decrease with the increasing in the cortical bone layer elasticity modulus. The level of maximum stress in the cortical layer of the bone increases with the increasing of this bone tissue elastic modulus. The maximum of stresses in the cortical bone tissue are observed near the implant neck.
The authors deal with the structures of buildings in the form of shallow shells with some damage. The derivation of equations is given taking into account the geometric nonlinearity of the work of a ...thin-walled structure. A technique for solving systems of equations using the Bubnov - Galyorkin method is given. The work of the structure with various ways of fixing the edges is simulated. Damage is specified by changing the modulus of elasticity in an arbitrary section of the structure. The influence of the shape and location of the defect on the value of the critical load is investigated. The results of the studies carried out are given in a dimensionless form and illustrated by graphs, which makes it convenient to use them in engineering calculations. Recommendations are given for correcting the shape and thickness of coating structures in the form of shallow shells in order to maintain their bearing capacity in the event of defects. The proposed method can be used to determine and investigate the stress-strain state of structures in the form of shallow shells, taking into account the geometric nonlinearity of work in the presence of defects in them. The constructed graphs of the dependence of the critical load on various parameters make it possible to evaluate the operation of structures, taking into account changes in various factors at various stages of the structure's operation. The use of varying characteristics of the reduction in the modulus of elasticity, which appears because of the occurrence of a defect, shows results that are close to real conditions.
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•k-Ga2O3 is grown epitaxially on α-Al2O3 with 100 || 1¯21¯0, 010 || 1¯010 and 001 || 0001 orientation relationships.•Analytical expressions for describing the stress-strain state and ...piezoelectric polarizations in films of κ-Ga2O3/α-Al2O3 and κ-(AlxGa1–x)2O3/κ-Al2O3 heterostructures taking into account materials anisotropy and various growth orientations are presented.•Heterostructure growth orientations can be used to design mechanical and electrical properties of κ-Ga2O3 film, for example, κ-Ga2O3/α-Al2O3 heterostructures with exotic(101¯8), (101¯3), and (21¯1¯5) growth planes, and κ-(AlxGa1–x)2O3/κ-Al2O3 heterostructures with ordinary (010) and (100) growth planes can be characterized by a low level of internal stresses and low or zero values of strain-induced piezoelectric polarization in the film.
The experimental data on orientation relationships for halide vapor phase epitaxy (HVPE) κ-Ga2O3 film grown on (0001) α-Al2O3 substrate and the theoretical model that describes growth orientation dependences of stress–strain state and piezoelectric polarization in κ-(AlxGa1-x)2O3 films with orthorhombic crystal structure grown on α-Al2O3 and κ-Al2O3 substrates are presented. Two possibilities for variation in films growth orientation for κ-Ga2O3/α-Al2O3 and κ-(AlxGa1–x)2O3/κ-Al2O3 heterostructures with inclination axes about either 100 or 010 crystallographic directions are considered. The changes in elastic strain field and piezoelectric polarization in the film caused by the differences in values of lattice parameters, elastic, and piezoelectric constants are demonstrated. The growth planes for κ-Ga2O3/α-Al2O3 and κ-(AlxGa1–x)2O3/κ-Al2O3 heterostructures that are characterized by low internal stresses and low or zero values of piezoelectric polarization are found.
The reported paper presents a field pattern of sliding lines in a plastic zone of flow chip formation in the process of cutting metals considered for front and rear angles on the cutting blade other ...than zero. Equations of sliding lines for these conditions are proposed. Using calculation data, plasticity zone border lines are plotted for positive and negative front angles. The paper suggests methods and calculation data on average stress and plane stress state components in nodal points of the plastic zone of chip formation. The study provides data for plotting distribution diagrams of normal and tangential stresses of contact stresses on work surfaces of a cutting blade.
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