Making public concerns tangible : an empirical study of German and UK citizens’ perception of data protection and data security

The problem of evaluating strength and fatigue life of critical engineering objects, the operational properties of which are characterized by multi-parametric nonstationary thermal-mechanical effects, is discussed. The main degradation mechanisms of structural materials (metals and their alloys) characteristic of such objects are considered. The main requirements for mathematical models of fatigue damage accumulation are formulated. To evaluate the stress-strained state (SSS) and fatigue life of critical engineering facilities (CEF) in the framework of modern achievements of mechanics of damaged media (MDM), a mathematical model is developed which describes the processes of cyclic thermal-plastic deformation and fatigue damage accumulation in structural alloys subject to multiaxial non-proportional paths of combined thermal-mechanical loading. The MDM model consists of three interconnected parts: thermal plasticity constitutive equations, accounting for their dependence on the failure process; an evolution equation of damage accumulation and a strength criterion of a damaged material. To qualitatively and quantitatively assess the constitutive relations of MDM for low-cycle modes of thermal-cyclic loading, the numerical and experimental results for the fatigue life of a notched compact sample in a non-uniaxial stress state under block modes of thermal-cyclic loading were compared, which supported the validity of the constitutive relations of the MDM model for thermal fatigue. An approach based on the Palmgren-Miner rule of linear summation of damage, when used for evaluating the fatigue life of structural elements, may result in both conservative and non-conservative estimates. This conclusion is confirmed by the experimental and theoretical studies of foreign and domestic authors. The results of numerical modeling of the fatigue durability of a compact specimen with an obtuse notch are presented for two loading histories. It is shown that several cycles of more intensive loading at the beginning of the strain history are the reason why the rule of linear summation of damage can overestimate or underestimate the value.

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Оценка усталостной долговечности материалов и конструкций при малоцикловом нагружении

Рассмотрено моделирование результатов испытаний металлов в условиях ползучести при нестационарном сложном напряженном состоянии. В качестве примера рассмотрены экспериментальные данные, полученные группой японских ученых при испытаниях трубчатых образцов из нержавеющей стали при температуре $650 ^{\circ}$С. В приведенной статье представлены результаты испытаний при четырех различных программах нагружения. Эти программы нагружения представляют собой различные комбинации кусочно-постоянных зависимостей касательного и нормального напряжений от времени. Проведено моделирование представленных данных с помощью теории упрочнения и теории течения, две используемые материальные константы определяются из условия минимального относительного интегрального расхождения экспериментальных и теоретических кривых ползучести. Проведено сопоставление результатов моделирования с результатами моделирования этих тех же экспериментальных данных, полученных другими исследователями с использованием других теорий. В этих других теориях использовано большое количество характеристик материала: от трех до девяти констант и дополнительно - одной материальной функции. Показано преимущество рассмотренных авторами данной статьи теории упрочнения и теории течения всего с двумя материальными константами в каждой по сравнению с другими использованными теориями.

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Моделирование ползучести металлов при нестационарном сложном напряженном состоянии

Modeling of non-stationary creep processes under multiple loading conditions by taking into account damage accumulation in a structural material

The behavior of metal tubular specimens under combined tension–torsion, torsion–compression and internal torsion pressures is studied experimentally. The tests are necessary for obtaining experimental data in order to study loss of stability and deformation of elastic–plastic shells caused by large deformations under complex stress conditions loaded along multi-link broken polygonal deformation trajectories, as well as for assessing the role of deformation anisotropy. In order to conduct tests under complex stress conditions (internal pressure loading in combination with other types of loading), the testing equipment was modified. Equipment of the test complex with a system for loading of tubular specimens with internal pressure ensures the conditions for achieving destructive stresses, caused by both internal pressure and torsion with tension. The Zwick/Roell Z100 testing machine equipped with the system generating internal pressure in hollow specimens makes it possible to expand significantly the types of tests on determining deformation and strength characteristics of materials. The results can be used to verify mathematical models and program codes for the numerical study of the processes of elastic–plastic deformation and loss of stability of shells of revolution under complex loading.

Experimental Studies of Elastic–Plastic Deformation of Structural Materials Under Conditions of Triaxial Loading

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A damaged medium model for describing the processof long-term strength of structural materials(metals and their alloys)

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Software implementation of viscoplastic deformationand damage accumulation processes in structuralalloys under thermal-mechanical loading

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Modeling fatigue life of polycrystalline structural alloysunder block-type nonsymmetrical low-cycle loading

A mathematical model describing the unsteady creep of metals under complex loading is proposed. The results of numerical simulation of creep of St.304 steel in complex regimes of block multiaxial cyclic deformation are given. The numerical calculation results obtained are compared with the data of full-scale experiments. Creep is simulated in complex deformation processes accompanied by the rotation of main regions of stress, strain, and creep strain tensors.

State Equations of Unsteady Creep under Complex Loading

The main regularities of the degradation of structural materials (metals and alloys) resulting in a decrease in creep-rupture strength were investigated. A mathematical model describing the viscoplastic deformation and damage accumulation in polycrystalline structural alloys in creep was developed using the equations of the mechanics of damaged media. The paper presents the results of experimental studies of the short-term creep of 12Kh18N9 steel and VZh-159 high-temperature alloy at constant temperature and different stresses set in the samples and the results of experimental studies of creep recovery in some structural steels. Deformation and damage accumulation were studied numerically and the results were compared with the data of full-scale experiments.

I. S. Tarasov

Papers

A damaged medium model for describing the processof long-term strength of structural materials(metals and their alloys)

Software implementation of viscoplastic deformationand damage accumulation processes in structuralalloys under thermal-mechanical loading

Modeling fatigue life of polycrystalline structural alloysunder block-type nonsymmetrical low-cycle loading

State Equations of Unsteady Creep under Complex Loading

Constitutive Relations of the Mechanics of a Damaged Medium for Evaluating the Creep-Rupture Strength of Structural Alloys