Evolution Of Stress-strain State Research Articles

Algorithm for Designing a Removable Complete Denture (RCD) Based on the FEM Analysis of Its Service Life.

(1) Background: The paper addresses the computer simulation and prediction of the service life of the base of removable complete dentures (RCDs) under typical loads caused by biting and chewing food. For this purpose, the finite element method (FEM) was used. It is assumed that various blocks of teeth, such as incisors, canines, premolars and molars, are subjected to cyclic impacts during a human life. (2) Methods: Both symmetric and asymmetric mastication (two- and one-sided loads, respectively) cases were considered. The load level was assumed to be 100 N, which corresponds to the average muscular compression force of typical human jaws. (3) Results: The FEM analysis of the stress–strain state evolution for RCDs under cyclic loads was carried out. Maps of equivalent lines were drawn for the denture base in terms of its durability. A multi-axial criterion was implemented to determine the number of cycles prior to failure by the mechanism of a normal opening mode crack. The FEM-based assessment of the service life of RCDs enabled us to establish the critical stress concentration areas, thereby allowing for further planning for the correction of an occlusal scheme or teeth inclinations. As a result, the service life of RCDs under cyclic loading can be improved. (4) Conclusions: An algorithm for designing RCDs in the case of edentulism based on the FEM simulation using commercial software as part of the procedure is proposed.

Influence of internal factor on crack resistance of shell mold by investment models

The process of evolution of the stress-strain state (SSS) of a multilayer shell mold (SM) is modeled at properties change between layers during cooling of poured steel casting. A mathematical model was constructed and a theoretical study of the stress state of the SM was carried out in absence of connection between the layers in a multilayer composite. The article describes a complex three-component system: liquid metal, solid metal, and ceramic SM. Solid metal and SM are considered to be isotropic. To solve this problem, the authors used the theory of small elastic-plastic deformations and equations of thermal conductivity, as well as proven numerical methods. Evolution of SSS in SM was traced by time steps. Thickness of the solidifying metal was determined through the equation of interphase transition. The article considers the process of heating an axisymmetric SM when pouring liquid metal into it. Stress state was estimated by stresses and displacements that occur in SM. At SM contact with support filler (SF), SM surface move away from the SF is possible during cooling of liquid metal. In this case, contact problem is solved. Taking into account the compiled algorithm for solving the problem, calculations were performed for the case of complete sliding of layers using developed numerical schemes and software complexes. Obtained results of numerical calculations are clearly displayed by graphic illustrations in form of plots and graphs. Detailed analysis of the obtained results is given. There is inconsistency of the previously expressed idea about the applicability of sliding between layers in a multilayer composite from the position of reducing its stress state. The research results can be useful in calculations of other functional multilayer shell systems.

The Influence of Internal Factor on Crack Resistance of Shell Mold for Investment Models

The evolution of stress–strain state (SSS) of multilayer shell mold (SM) has been simulated upon variation of properties between the layers during cooling of casted steel. A mathematical model has been developed and the stress state of SM has been theoretically investigated in the case of absence of interrelation between the layers in multilayer composite material. The complex three-component system (liquid metal, solid metal, ceramic shell mold) has been analyzed. The solid metal and the SM are considered as isotropic. In order to solve the formulated problem, the theory of small elastic deformations and the equations of heat conductance have been applied as well as verified numerical methods. The SSS evolution in shell molds can be traced by time steps. The thickness of solidified metal is determined by the equation of interphase transition. Heating of axisymmetric SM during pouring of liquid metal is analyzed. The stress state has been estimated by stresses and displacements occurring in SM. During cooling of liquid metal at the contact between the shell mold and supporting filler (SF), the surface between them can be detached. In this case, the contact problem is solved. The calculations for the case of complete sliding of layers have been carried out with consideration of the compiled algorithm for problem solving by using the developed numerical schemes and software. The obtained numerical results are presented in the form of diagrams and plots. The obtained results have been analyzed in detail. The inconsistency of the previously proposed concept about applicability of sliding between the layers in multilayer composite material in terms of its strain state has been demonstrated. The experimental results can be useful for analysis of other functional multilayer shell systems.

Calculation of the transformation plasticity strain in the shape memory cylinder

A connected thermomechanical boundary problem for an infinite shape memory alloy cylinder loaded by an axial force and subjected to heating or cooling from the surface is solved. The evolution of stress-strain state is calculated for a process of the transformation plasticity. The mechanical properties of a material point are given by a micromechanical model accounting for the deformations due to elasticity, thermal expansion and phase transformation. The obtained problem was solved numerically using the iterative procedure with a variable iterative parameter. The influence of the surface temperature rate and radius of cylinder on the transformation plasticity is investigated. It is shown, that the elongation due to the transformation plasticity effect decreases with the increasing temperature rate. The elongation also decreases with the increasing cylinder diameter. This phenomenon can be explained by an inhomogeneity of the temperature and stress fields causing different conditions for the phase transformation in different points of the body. Stress in the local region can overtop more than twice the mean value.

Development of digital technologies for the systems of remote mining safety monitoring

The article is devoted to development of methodology and digital technologies for assessing, forecasting and determining scenarios of geomechanical process evolution. A new digital technology is proposed for remote mining safety monitoring, which integrates a network personnel management system and expert subsystems for decision-making support taking into account geomechanical factors presenting risk of the mine roadway stability loss. Elements of the expert subsystems analyze data in real time, and are used to determine potential risks on basis of criteria and assessments of the production environment state in mines. It is proposed to identify the forecast safety indicators with the help of geomechanical models and by assessing scenarios of the “support-rocks” system stressstrain state evolution. In order the expert assessment of the rock massif and mine roadway stability, integral indicators of emergency potential risk for each geotechnical system elements are specified by values of informative parameters at a certain time point, as well as deviations rates of parameters from the equilibrium point over a period of time. Job safety is provided through the improved effectiveness of personnel interaction and its stricter disciplinary responsibility, as well as by making early decisions on keeping the mine roadways in a trouble-free condition.

The effect of contact influence on the opticomechanical properties of Panda-type fiber under thermocycling conditions

The mathematical model of the stress strain state evolution in polarization-maintaining Panda-type fiber in conditions of contact thermopower loading is developed. The influence of the position of the light-conducting core on the birefringence of the fiber is investigated. It is found that the temperature change in the thermal cycle has a minor effect on the stress strain state of the fiber. The impact of temperature change on the fiber optical characteristics is shown to increase with the deviation of its geometry from the design values.

Rock Mass as a Nonlinear Dynamic System. Mathematical Modeling of Stress-Strain State Evolution in the Rock Mass around a Mine Opening

The paper briefly reviews the fundamental (general) evolution properties of nonlinear dynamic systems. The stress-strain state evolution in a rock mass with mine openings has been numerically modeled, including the catastrophic stage of roof failure. The results of modeling the catastrophic failure of rock mass elements are analyzed in the framework of the theory of nonlinear dynamic systems. Solutions of solid mechanics equations are shown to exhibit all characteristic features of nonlinear dynamic system evolution, such as dynamic chaos, self-organized criticality, and catastrophic superfast stress-strain state evolution at the final stage of failure. The calculated seismic events comply with the Gutenberg-Richter law. The cut-off effect has been obtained in numerical computation (downward bending of the recurrence curve in the region of large-scale failure events). Prior to catastrophic failure, change of the probability density functions of stress fluctuations, related to the average trend, occurs, the slope of the recurrence curve of calculated seismic events becomes more gentle, seismic quiescence regions form in the central zones of the roof, and more active deformation begins at the periphery of the opening. These factors point to the increasing probability of a catastrophic event and can be considered as catastrophic failure precursors.

Numerical Models used for The Calculation of The Cable-Stayed Bridge at Km 0+540 over Danube-Black Sea Canal

Abstract Cable-stayed bridges are complex structures and for their design, the traditional calculation methods are hard, even impossible to use for a global analysis. Separate analyses for the each component of the bridge in a simplified manner can be conducted, but in this case the concurrence of the elements into the structure is not taken into account, leading to errors in estimating the structural response. For these structures, the construction method and the presence of the stays, which are elements having a nonlinear behaviour, implies to consider a nonlinear staged analysis including the second order effects in order to transmit form one stage to the other the stress-strain state. In the present time, thanks to the evolution and development of the calculation methods and computer analysis, cable-stayed bridges can be accurate analysed so that the obtained response is close to the behaviour of the structure during erection and later, in service. The aim of this paper is to present the results obtained using one of the finite element models and nonlinear staged analysis of the bridge at km 0+540 over Danube-Black Sea Canal near Agigea. Inside the paper, results related to the evolution of stress-strain state in principal structural elements of the bridge - pylons, stays and deck - during the execution and in final stage, in service are to be presented.

Evolution of Stress-Strain State in the Structural Heterogeneities Geomaterials under Uniaxial and Biaxial Loading

The aim of this study was to analyze distribution and development of stress-stress state in structured rock specimens subject to uniaxial and biaxial loading to failure using digital speckle correlation method. Within the experimental analysis of wave processes in the block-hierarchy structure of geomedia (uniaxial and biaxial compression and shearing of prismatic geomaterial specimens), the authors revealed the fact of initiation of low-frequency micro-deformation processes under slow (quasi-static) disturbances. The estimation of the deformation-wave behavior of geomaterials as the “summed” contributions made by elements of the scanned surfaces with different-oriented (in-phase and anti-phase) oscillations has been performed using the energy approach that is based on the scanning function R, analogous to the “center of mass” in the classical mechanics.

Evolution of stress-strain state in structured rock specimens under uniaxial loading

The comprehensive experimental studies into the change in the stress-strain state of rock specimens subjected to uniaxial loading until failure, using the automated digital speckle photography analysis shows that when the stress reaches 50% of the limit strength of the specimens, low-frequency micro-deformation processes begin in the specimens under slow (quasi-static) stiff loading. The amplitude of the deformation-wave processes depends on the level of the pre-set macro-loading. Wave packets are plotted for averaged microstrains obtained in sandstone and marble specimens under uniaxial compression. Fourier transforms are used to define the amplitude-frequency characteristics of four micro-deformation stages: elastic, nonlinearly elastic, post-peak and residual strength stages. Elastic oscillations with frequency 0.5–4 Hz appear at the pre-failure stage and continue at the post-peak loading stage.