The study of a defect evolution in iron under fatigue loading in gigacyclic fatigue regime

The work is devoted to the study of the damage accumulation in iron under gigacyclic fatigue (VHCF) regime. The study of the mechanical properties of the samples with different state of life time existing was carried out on the base of the acoustic resonance method. The damage accumulation (porosity of the samples) was studied by the hydrostatic weighing method. The obtained results show the accumulation of porosity in the volume of the sample during fatigue loading and corresponding decrease of the elastic properties. A statistical model of damage accumulation was proposed in order to describe the damage accumulation process. The model describes the influence of the sample surface on the location of fatigue crack initiatio

Theoretical and Experimental Investigation of the Dissipated and Stored Energy Ratio in Iron under Quasi-Static and Cyclic Loading

The problem of energy storing (cold work accumulation) in metals was intensively investigated both theoretically and experimentally during all last century but a general theoretical conception of the process was not created. This work is devoted to an experimental investigation of energy dissipation in metals under plastic deformation and to the development of a thermodynamic model to study the cold work accumulation under plastic deformation and failure. The proposed model is based on a statistical description of collective properties of mesoscopic defects and on dividing the plastic deformation into two parts (dissipative and structural). The structural plastic strain was considered as an independent thermodynamic variable that allowed us to determine the thermodynamic potential of the system. The derived constitutive relations were applied for numerical simulation of tensile and cyclic tests. The numerical results demonstrate a good agreement with experimental data.Экспериментально исследовано рассеяние энергии в металлах при пластическом де формировании и разработке термодинами­ческой модели для изучения накопления наклепа при пластическом деформировании и разрушении. Предлагаемая модель осно­вана на статистическом описании коллек­тивных свойств мезоскопических дефектов и на разделении пластической деформации на две части (диссипативную и общую). Общая пластическая деформация рассмат­ривалась как независимая термодинамическая переменная, что позволило опреде­лить термодинамический потенциал систе­мы. Полученные определяющие соотноше­ния применили для численного моделиро­вания результатов испытаний на растяжение и циклических испытаний. Численные ре­зультаты хорошо согласуются с эксперимен­тальными данными

Theoretical and Experimental Investigation of the Dissipated and Stored Energy Ratio in Iron under Quasi-Static and Cyclic Loading

The problem of energy storing (cold work accumulation) in metals was intensively investigated both theoretically and experimentally during all last century but a general theoretical conception of the process was not created. This work is devoted to an experimental investigation of energy dissipation in metals under plastic deformation and to the development of a thermodynamic model to study the cold work accumulation under plastic deformation and failure. The proposed model is based on a statistical description of collective properties of mesoscopic defects and on dividing the plastic deformation into two parts (dissipative and structural). The structural plastic strain was considered as an independent thermodynamic variable that allowed us to determine the thermodynamic potential of the system. The derived constitutive relations were applied for numerical simulation of tensile and cyclic tests. The numerical results demonstrate a good agreement with experimental data.Экспериментально исследовано рассеяние энергии в металлах при пластическом де формировании и разработке термодинами­ческой модели для изучения накопления наклепа при пластическом деформировании и разрушении. Предлагаемая модель осно­вана на статистическом описании коллек­тивных свойств мезоскопических дефектов и на разделении пластической деформации на две части (диссипативную и общую). Общая пластическая деформация рассмат­ривалась как независимая термодинамическая переменная, что позволило опреде­лить термодинамический потенциал систе­мы. Полученные определяющие соотноше­ния применили для численного моделиро­вания результатов испытаний на растяжение и циклических испытаний. Численные ре­зультаты хорошо согласуются с эксперимен­тальными данными

Self-Induced Quasistationary Magnetic Fields

The interaction of electromagnetic radiation with temporally dispersive magnetic solids of small dimensions may show very special resonant behaviors. The internal fields of such samples are characterized by magnetostatic-potential scalar wave functions. The oscillating modes have the energy orthogonality properties and unusual pseudo-electric (gauge) fields. Because of a phase factor, that makes the states single valued, a persistent magnetic current exists. This leads to appearance of an eigen-electric moment of a small disk sample. One of the intriguing features of the mode fields is dynamical symmetry breaking

Fracture characteristics of titanium VT1-0 and Zr–1 wt. % Nb alloy in different structures under gigacycle fatigue loading regime

Fatigue testing of ultrafine-grained, fine-grained and coarse-grained VT1-0 and Zr–1 wt. % Nb samples was performed under conditions of gigacycle fatigue regime. It was established that ultrafine-grained titanium and zirconium alloy samples initiate increasing fatigue strength of up to 1.3 times for titanium and 1.7 times for zirconium alloy within gigacycle region (109 cycles) comparable to fine-grained and coarse-grained samples. Analysis of fracture surface morphology has revealed the similar fractured structure in coarse-grained and ultrafine-grained titanium and zirconium alloy samples. Fractures in ultrafine-grained titanium and zirconium alloy samples exhibit quasi-brittle pattern

Collective Modes in the Microshear Ensemble as a Mechanism of the Failure Wave

Results of theoretical and experimental study of failure wave phenomena are presented. A description ofthefailure wavephenomenon wasproposed in terms ofa self-similar solutionfor the microshear density. The mechanisms offailure wave generation andpropagation were classified as a delayedfailure with the delay time corresponding to the time ofexcitation ofself-similar blow-up collective modes in a microshear ensemble. Experimental study of the mechanism of the failure wave generation andpropagation was carried out using afused quartz rod and included the Taylor test with high-speed framing. The results obtained confirmed the "delayed” mechanism of the failure wave generation and propagation.Представлены результаты теоретических и экспериментальных исследований явления волны разрушения. Предложено описание явления волны разрушения на основе авто­модельного решения для плотности микро­сдвигов. Механизмы возникновения и рас­пространения волны разрушения классифи­цировали как замедленное разрушение, при­ чем время задержки соответствовало времени возбуждения автомодельных взрывных коллективных колебаний во множестве микросдвигов. Экспериментальное исследо­вание механизма возникновения и распро­странения волны разрушения проводилось с использованием расплавленного кварцевого стержня и включало испытание по методу Тейлора с высокоскоростным фотографированием. Полученные результаты подтверди­ ли “замедленный” механизм возникновения и распространения волны разрушения

Experimental investigation of crack initiation and propagation in high- and gigacycle fatigue in titanium alloys by study of morphology of fracture

Fatigue (high- and gigacycle) crack initiation and its propagation in titanium alloys with coarse and fine grain structure are studied by fractography analysis of fracture surface. Fractured specimens were analyzed by interferometer microscope and electronic microscope to improve methods of monitoring of damage accumulation during fatigue test and verify the models for fatigue crack kinetics. Fatigue strength was estimated for high cycle fatigue (HCF) regime using the Luong method [1] by “in-situ” infrared scanning of the sample surface for the step-wise loading history for different grain size metals. Fine grain alloys demonstrated higher fatigue resistance for both HCF and gigacycle fatigue regimes. Fracture surface analysis for cylindrical samples was carried out using optical and electronic microscopy method. High resolution profilometry (interferometerprofiler New View 5010) data of fracture surface roughness allowed us to estimate scale invariance (the Hurst exponent) and to establish the existence of two characteristic areas of damage localization (different values of the Hurst exponent). Area 1 with diameter ~300 ?m has the pronounced roughness and is associated with damage localization hotspot. Area 2 shows less amplitude roughness, occupies the rest fracture surface and considered as the trace of the fatigue crack path corresponding to the Paris kinetics