Conditions Of Complex Stressed State Research Articles

Development of the strength statistical characteristics of materials, which takes into account the features of their brittle fracture

The object of the research is the algorithm for determining the finding of the most probable, mean value, dispersion and coefficient of failure loading variation of a stochastically defective plate under conditions of comprehensive tensile-compression. The material of the plate is considered as a continuous medium in which evenly distributed defects such as rectilinear cracks that do not interact with each other. It is isotropic and has the same crack resistance. Let’s believe that the plate consists of primary elements, each of which can be weakened by one defect. To predict the strength and failure conditions of plates made of such material, it is natural to use, on the one hand, the results of the theory of limit equilibrium of individual determined defects and their development, and on the other hand, probabilistic-statistical methods that take into account the randomness of defects. This comprehensive approach makes it possible to calculate the statistical characteristics of strength and fracture based on data on the structure of the material defect and its resistance to the emergence and development of cracks. The main content of this paper is the algorithm for calculating and research the strength statistical characteristics of stochastically defective plate structural elements taking into account some deterministic features of their brittle fracture. Based on the deterministic failure criterion, which takes into account the initial direction of crack propagation, the ratio is obtained to find the most probable, mean value, dispersion and coefficient of variation of failure loading. The dependences of the specified strength statistical characteristics on the type of applied loading, the number of defects (body size) and structural inhomogeneity of the material, as well as the effect of taking into account the initial direction of crack propagation are investigated. The obtained results allow to more adequately assessing the reliability of structural materials under conditions of complex stress state, taking into account the stochastic of their structure. This is due to the fact that the use of the approach to determine the limit applied stresses, which takes into account the initial direction of the crack propagation, improves the algorithm for finding strength statistical characteristics.

Обгрунтування застосування неліній-ної моделі в’язкопружності типу моделі Работнова в задачах повзучості

The relationship between the components of the strain tensor, stress tensor and time is given by the defining equations of the hereditary type, which are written based on the hypothesis of proportionality of the deviators. Thin-walled tubular low-pressure polyethylene elements are considered as the object of research. The scope of the model is substantiated based on the hypothesis of the existence of a single diagram of instantaneous deformation and a single diagram of long-term deformation. The invariance of the tensile and torsion diagrams with respect to the stress state is checked. The region of nonlinear elastic deformation is determined. The defining equations of the model contain a set of functions and coefficients determined from the basic experiments. A method for determining the parameters of heredity kernels of nonlinear viscoelastic materials under complex stress state has been developed. The nonlinearity of viscoelastic properties is given by equations of the Rabotnov's model type. The method is based on the relations between the creep kernels obtained under conditions of complex stress state and the creep kernels under one-dimensional stress state. The method is tested experimentally on the problems of calculating creep deformations under combined loading of thin-walled tubular elements made of low-pressure polyethylene.

How to Use a Tensor Measure of Accumulated Fatigue Damage for Analyzing the Fatigue Life of Carbon Fibre-Reinforced Plastics under a Complex Stress State

A phenomenological model describing fatigue damage accumulation by using a tensor measure of the accumulated damage caused by different cyclic stresses is presented for estimating numerically the fatigue life of carbon fibre-reinforced plastics operating under complex stress state conditions. A procedure for calculating the fatigue life by using the presented model is given. An example demonstrating acceptable agreement between experimental and calculated data is presented.

До задачі розрахунку релаксації напружень у тонкостінних трубчастих елементах із лінійно- в’язкопружних матеріалів

The relaxation of isotropic homogeneous and non-aging linear-viscoelastic materials under conditions of complex stress state is considered. Thin-walled tubular specimens of High Density Polyethylene (HDPE) for creep under a single-axial stretching, with a pure twist and combined load tension and torsion are considered as base experiments, tests. The solution is obtained by generalizing the initial one-dimensional viscoelasticity model to a complex stressed state, constructed using the hypothesis of the proportionality of deviators. The heredity kernels are given by the Rabotnov’s fractional-exponential function. The dependence between the kernels of intensity and volumetric creep is established, which determine the scalar properties of linear viscoelastic materials in the conditions of a complex stressed state in the defining equations of the type of equations of small elastic-plastic deformations, and the kernels of longitudinal and transverse creep defining the hereditary properties of linear-viscoelastic materials under the conditions of the uniaxial tension. The problems of stress relaxation calculation of thin walled tubes under combined tension with torsion have been solved and experimentally approved.

Testing of Thin-Walled Tubular Workpieces

In accordance with the Russian Federation State program called “Industrial growth and improving competitiveness” it becomes more wide-spread to use thin-walled makes for pieces, modern materials with new treating methods in mechanical engineering, in automobile production and modern aviation industry. As well as requirements for quality and mechanical characteristics of finished products constantly grow. In relation to these standards, methods of intensive irreversible deformation under conditions of complex stressed state are used with increasing frequency. Study of the following parameters has a great practical importance: loaded capability of the makes during exploitation and work material strength performance under complex production process. Such strain tasks are frequently counted as most complex and demand experimental verification because of geometric and physical task nonlinearity.The current study proposes testing method for thin-walled tubular workpieces which combines implementation simplicity with a wide range of strain-stressed state charts.

Investigation of the regularities of deformation of heat-resistant steels under conditions of creep in the complex stressed state

We study the regularities of deformation of 1Kh18N9T steel under long-term static loading along different paths of radial loading with regard for the influence of the type of stressed state. The viscoplastic properties of 08Kh18N10T-VD steel subjected to stepwise static loading under conditions of complex stressed state are analyzed.

Specific features of the fracture of elastoplastic cracked bodies under triaxial loading and the effect of hydrogen

By using the energy approach of fracture mechanics, the deformation and force criteria of the state of limiting equilibrium are analytically established for bodies subjected to the combined action of loading and hydrogen. The proposed criteria are well justified from the physical point of view because they consider the case of simultaneous realization of three macromechanisms of fracture and exhaustion of plasticity in the entire process zone. Hence, they can be used for the evaluation of the residual strength of structural elements operating under the conditions of complex stressed state and the action of hydrogen.

Strength criteria for wood under the conditions of complex stressed state

We propose strength criteria for wood under the conditions of complex stressed state. Various modes of fracture of wood, such as fracture along and across tracheids, crushing across tracheids, and buckling of tracheids, are analyzed. The local conditions of fracture of wood taking into account the action of normal and tangential stresses in the critical plane are formulated. The accumulated numerical results are in good agreement with the experimental data.

Assessment of Viscoplastic Properties of Titanium Alloys

The paper presents findings of the study of viscoplastic properties of several titanium alloys subjected to cyclic loading under complex stress state conditions. The applicability of elastic viscoplastic models to structural materials has been experimentally verified.

Change in the deformation and strength properties of coal during interaction with surfactant solutions

Features of the change in strength and deformation properties of coal during the action of adsorption-active media, especially under the conditions of a complex stress state, are not always evident and, consequently, cannot be taken adequately into account when performing work utilizing the physicochemical treatment of rock masses and coal in order to increase the safety and efficiency of mining production processes. Taking into account the importance of such data for intensification of the change in properties and state of the host rock during mining, including even finding the optimal conditions for coal destruction, they studied the singularities of adsorption-active fluid interaction with coal under complex stress state conditions. The deformation curves for brown coal and coal of grade T obtained under simple uniaxial compression conditions are represented.

Failure criteria for anisotropic graphite in a complex stress-state conditions

Failure criteria for anisotropic graphite in a complex stress-state conditions

Method for studying mechanical properties of composite materials under complex stress-state conditions

Method for studying mechanical properties of composite materials under complex stress-state conditions

The stress-strain state of individual grains in polycrystalline silicon iron

1. The development of inhomogeneous elastic strain in the grains of silicon iron result in strengthening of the microsources of increased and decreased strains; the level of inhomogeneity exceeds by far the difference in the elastic moduli for the individual grains which fact can be explained by the large role of intergranular interaction. 2. The significant difference between the calculated and experimental Poisson's coefficients for the different grains shows that practically all the microvolumes under uniaxial tension are in complex stress state conditions. 3. The nucleation principles of plastic strain in individual grains are determined not only by the elastic strain distribution and the strength properties of the individual grains but also to a large degree by the cooperative strain, owing to the fact that individual microvolumes are plastically strained sooner than others.

Plasticity and strength of metals under complex stress-state conditions

Plasticity and strength of metals under complex stress-state conditions