The failure criterion based on hydrogen distribution ahead of the fatigue crack tip

The hydrogen effect on the fracture toughness and fatigue crack growth behaviour in themartensitic high strength steel is investigated. The secondary ion mass spectrometry method has beenemployed to analyse the distribution of hydrogen concentration in the zone of the crack tip and at its edges.Changes in hydrogen concentration are observed in the vicinity of the propagating crack tip and at a remotesite. The hydrogen peak H C is reduced and moves away from the fatigue crack tip with the increase of themaximum stress intensity factor max K . The concept of damage evolution is used to explain fatigue crackpropagation in connection with the hydrogen redistribution ahead of the crack tip. The physical failure criterionbased on the hydrogen peak in the vicinity of the fatigue crack tip and the maximum stress intensity factor hasbeen proposed. The criterion reflects changes in the hydrogen peak which resulted from the hydrogenredistribution due to the increase of the maximum stress intensity factor as the crack length increases underfatigue loading

Determination of fracture mechanics parameters on a base of local displacement measurements

New experimental technique for a determination of the stress intensity factor (SIF) and T-stressvalues is developed and verified. The approach assumes combining the crack compliance method and opticalinterferometric measurements of local deformation response on small crack length increment. Initialexperimental information has a form of in-plane displacement component values, which are measured byelectronic speckle-pattern interferometry at some specific points located near a crack tip. Required values offracture mechanics parameters follow from the first four coefficients of Williams’ series. A determination ofinitial experimental data at the nearest vicinity of notch tip is the main feature of the developed approach. Thatis why it is not necessary to involve complex numerical models, which include global geometrical parameters,loading and boundary conditions of the object under study, in a stage of experimental data interpretation. Anavailability of high-quality interference fringe patterns, which are free from rigid-body motions, serves as areliable indicator of real stress state around a crack tip. A verification of the technique is performed bycomparing experimental results with analogous data of FEM modelling. Experimentally determined mode I SIFfor DCB specimen with end crack is in 5 per cent agreement with the numerically simulated case. Proposedapproach is capable of estimating an influence of the notch radius on fracture mechanics parameters.Comparing SIF and T-stress obtained for U-notches of different radius both in actual and residual stress fieldconfirms this statement

Calculation of the energy J -integral for bodies with notches and cracks

Abstract. The approximate solutions for calculation of the energy J -integral of a body both with a notch and with a crack under elastic-plastic loading have been obtained. The crack is considered as the limit case of a sharp notch. The method is based on stress concentration analysis near a notch/crack tip and the modified Neuber's approach. The HRR-model and the method based on an equation of equilibrium were also employed to calculate the J -integral. The influence of the strain hardening exponent on the J -integral is discussed. New aspects of the two-parameter J * c -fracture criterion for a body with a short crack are studied. A theoretical investigation of the effect of the applied critical stress (or the crack length) on the strain fields ahead of the crack tip has been carried out

The effect of low-cycle fatigue on evolution of fracture mechanics parameters in residual stress field caused by cold hole expansion

Localized displacement measurements based on electronic speckle-pattern interferometry are used to obtain crack mouth opening displacement (CMOD), stress intensity factor (SIF) and T-stress values during crack growth around cold-expanded holes. The specimens with a central open hole are made from 2024 aluminium alloy. The expansion level is 5% of nominal interference. The results are obtained for the same stress range ??? = 350 MPa, but different stress ratio R = 0.4 and R = �1.0. A sequence of narrow notches, inserted under the constant external load, serves for crack modelling at different stages of cyclic loading. Initial experimental data represent in-plane displacement component values measured in the vicinity of the crack tip. The transition from in-plane displacement components to SIF and T-stress values follows from the relationships of modified version of the crack compliance method. The crack length curves of CMOD, SIF and Tstress profiles are obtained for different stages of cyclic loading. These data provide the construction of dependencies of fracture mechanics parameters for cracks of fixed lengths from the loading cycle numbe

Multiple filamentation Ti:Sapphire-laser pulses in water

The results of experimental studies of the spatial characteristics of multiple filamentation terawatt femtosecond Ti:Salaser in water are presented. With an increase in initial power laser pulses increases the number of filaments, the length of the field is increased filamentation and reducing the length of the filaments have been shown. The distribution of the filaments in the longitudinal direction of the field of multiple filamentation has a maximum cross-sectional filament is shifted from the center to the periphery of the beam at the end region of filamentation. The minimum diameter of the beam on the track corresponds to the position of the maximum number of filaments. After the point of maximum impulse essentially loses energy in the initial direction of propagation. Upon reaching the pulse power 2 104 Pcr of multiple filamentation area is formed of a hollow cone, the apex directed to the radiation source

Filamentation of collimated Ti:sapphire-laser pulses in water

The results of experimental studies of the spatial characteristics of multiple filamentation terawatt femtosecond Ti:Salaser in water are presented. With an increase in initial power laser pulses increases the number of filaments, the length of the field is increased filamentation and reducing the length of the filaments have been shown. The distribution of the filaments in the longitudinal direction of the field of multiple filamentation has a maximum cross-sectional filament is shifted from the center to the periphery of the beam at the end region of filamentation. The minimum diameter of the beam on the track corresponds to the position of the maximum number of filaments. After the point of maximum impulse essentially loses energy in the initial direction of propagation. Upon reaching the pulse power 2 104 Pcr of multiple filamentation area is formed of a hollow cone, the apex directed to the radiation source

Моделирование и прогнозирование комплексных экологических ситуаций на примере Черкасской области

Збільшення антропогенного тиску на навколишнє середовище вимагає комплексного підходу до прийняття рішень з метою контролю та прогнозування його забруднення. Слід брати до уваги вплив багатьох факторів, які можуть мати значний вплив, і велика кількість інформації, яку необхідно враховувати в процесі прийняття рішень. Тому актуальним завданням є створення методів та програмних засобів для обробки всієї наявної інформації та надання обґрунтованих рекомендацій для прийняття ефективних рішень, особливо в екологічно несприятливому регіоні, наприклад, у Черкаській області.The increase in anthropogenic pressure on the environment requires an integrated approach to decision-making in order to control and predict its pollution. The influence of many factors that can have a significant impact and large amounts of information that must be considered in the decision-making process should be taken into account. Therefore, the creation of methods and software tools for processing all the available information and giving reasonable recommendations for making effective decisions, especially in an environmentally unfriendly region such as the Cherkasy region, is an urgent task.Повышение антропогенной нагрузки на окружающую среду требует комплексного подхода к принятию решений с целью контроля и прогнозирования ее загрязнения. Влияние многих факторов, которые могут оказать значительное влияние, и большое количество информации, которая должна учитываться в процессе принятия решений, должны быть приняты во внимание. Поэтому создание методов и программных средств для обработки всей доступной информации и предоставления разумных рекомендаций для принятия эффективных решений, особенно в экологически неблагоприятном регионе, таком как Черкасская область, является актуальной задачей

Use of Polarization Lidar for Investigation of Meteorological Formations

This paper presents the results of theoretical and experimental, investigations of depolarization characteristics of different meteorological formations. Experimental investigations are carried out with a monostatic lidar. The ruby laser radiation is polarized in a vertical plane. The radiation reflected is accepted by a lens system of 150 rom in diameter and a viewing angle of 12' and further it is divided by Wollaston prism into the components polarized orthogonally. In this case the principal plane of the prism is exposed parallel with the laser polarization plane. Investigations show the degree of radiation polarization, reflected from water clouds, to be changed within 1/0.7 (seldom up to 0.6) depending on their density. In most cases a signal reflected from the cloud leading edge is polarized completely. The time shift is observed between polarized and crosspolarized components of a Fignal, reflected from a cloud, depending on the density of a meteorological object. While penetrating into the cloud depth a degree of polarization decreases up to 0.8-0.7, and the character of this decrease is different for various types of clouds. For crystal clouds the shift between the components of the reflected signal is not observed and the magnitude of polarization degree amounts to 0.1/0.3 in comparison with water clouds. The polarization degree of radiation reflected by fog is not less than 0.6, and that in the rains of average intensity (about 5 mm/h) is always about 1. The authors have suggested an algorithm of numerical solution of nonstationary transfer equation in the vector form to forecast the influence of multiple scattering effects on polarization characteristics of the lidar light signal. The method of statistical simulation (Monte-Carlo technique) forms the basis of the algorithm. Numerical estimates obtained for a model of stratocumulus at lambda = 0.6943 microns under boundary conditions close to the conditions of natural experiment being discussed proved to be in a good agreement with the results of observation. Specifically, Fig. 1 shows the profiles of polarization (p) versus depth (L) of the following drop formations: fog (curve 1) with horizontal meteorological visibility of 4 km two stratocumulus at a height of 1100 m with the attenuation factors delta = 0.01m(exp -1) (curve 2) and delta = 0.05m(exp -1) (curve 3). Curve 3 shows the results of numerical estimates and the value of their statistical error

First Observation of CP Violation in B0->D(*)CP h0 Decays by a Combined Time-Dependent Analysis of BaBar and Belle Data

We report a measurement of the time-dependent CP asymmetry of B0->D(*)CP h0 decays, where the light neutral hadron h0 is a pi0, eta or omega meson, and the neutral D meson is reconstructed in the CP eigenstates K+ K-, K0S pi0 or K0S omega. The measurement is performed combining the final data samples collected at the Y(4S) resonance by the BaBar and Belle experiments at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. The data samples contain ( 471 +/- 3 ) x 10^6 BB pairs recorded by the BaBar detector and ( 772 +/- 11 ) x 10^6, BB pairs recorded by the Belle detector. We measure the CP asymmetry parameters -eta_f S = +0.66 +/- 0.10 (stat.) +/- 0.06 (syst.) and C = -0.02 +/- 0.07 (stat.) +/- 0.03 (syst.). These results correspond to the first observation of CP violation in B0->D(*)CP h0 decays. The hypothesis of no mixing-induced CP violation is excluded in these decays at the level of 5.4 standard deviations.Comment: 9 pages, 2 figures, submitted to Physical Review Letter

Belle II Technical Design Report

The Belle detector at the KEKB electron-positron collider has collected almost 1 billion Y(4S) events in its decade of operation. Super-KEKB, an upgrade of KEKB is under construction, to increase the luminosity by two orders of magnitude during a three-year shutdown, with an ultimate goal of 8E35 /cm^2 /s luminosity. To exploit the increased luminosity, an upgrade of the Belle detector has been proposed. A new international collaboration Belle-II, is being formed. The Technical Design Report presents physics motivation, basic methods of the accelerator upgrade, as well as key improvements of the detector.Comment: Edited by: Z. Dole\v{z}al and S. Un