Core Heating Research Articles

Effect of Lead Core Heating on Residual Displacements of Lead Rubber Bearings Under Bi-Directional Earthquake Excitations

ABSTRACT This paper investigates the variation in residual displacements (RDs) of lead rubber bearings (LRBs) subjected to bi-directional earthquake excitations when lead core heating effect is of concern. Accordingly, several dynamic analyses were conducted considering isolator response with and without lead core heating effect. A wide range of isolation system properties, several characteristic strength to weight ratios, isolation periods and yield displacements were considered to construct the bi-linear force-displacement relations of LRBs. Ground motions were selected to represent different magnitudes and pulse characteristics. Results were also used to assess the efficacy of code suggested equations to estimate RDs of seismic isolators.

Hard X-rays from the deep solar atmosphere: An unusual UV burst with flare properties

Explosive transient events occur throughout the solar atmosphere. The differing manifestations range from coronal mass ejections to Ellermann bombs. The former may have negligible signatures in the lower atmosphere, and the latter may have negligible nonthermal emissions such as hard X-radiation. A solar flare generally involves a broad range of emission signatures. Using a suite of four space-borne telescopes, we report a solar event that combines aspects of simple UV bursts and hard X-ray emitting flares at the same time. The event is a compact C-class flare in active region AR11861, SOL2013-10-12T00:30. By fitting a combined isothermal and nonthermal model to the hard X-ray spectrum, we inferred plasma temperatures in excess of 15\,MK and a nonthermal power of about $3 xii and xxi emission lines, which are characteristic of emission from hotter plasma with a temperature over 1\,MK. Moreover, the event exhibited very limited signatures in the extreme-UV wavelengths. Our study indicates that a UV burst -- hard X-ray flare hybrid phenomenon exists in the low solar atmosphere. Plasma that heats to high temperatures coupled with particle acceleration by magnetic energy that is released directly in the lower atmosphere sheds light on the nature of active region core heating and on inferences of flare signatures.

A Scaling Relation for Core Heating by Giant Impacts and Implications for Dynamo Onset

AbstractAccretional heating of Earth's interior during formation is pivotal to its subsequent thermal and chemical evolution. In particular, impact heating of Earth's core is expected, but its amplitude and radial distribution within the core is unknown and could influence the onset of the geodynamo. The uncertainty is due, in part, to the lack of constraints on the temperature of the interior following formation due to the difficulty of preserving a record of such a high energy environment, and the assertion that super‐heating during formation would be rapidly lost through magma ocean cooling. Here we systematically investigate core heating due to giant impacts using a Smoothed Particle Hydrodynamics (SPH) code with simulations spanning a range of impact angles, velocities, and masses. From these simulations we derive a scaling relation for core heating that depends on the impact parameters and predicts the radial core temperature profile following the impact. Our findings show that a significant amount of heat is deposited into the core, with a canonical impact scenario resulting in an average core temperature increase of about 3000 K, approximately 500 K higher than that of the overlying mantle. In this case the heat distribution within the core produces a strong thermal stratification. We use a parameterized cooling model to estimate that the core could have cooled to an adiabatic state ∼290 Myr after a canonical impact, which is consistent with the observed time span between the age of the Moon and evidence for an active geodynamo.

Fire Behavior of Concrete-Filled Hollow Section Columns with High Strength Bar-Bundle as Core

Concrete-filled hollow section (CFHS) columns with a solid steel core have gained popularity in the construction of tall buildings due to their robust load-bearing capacity, slender design, ease of prefabrication, and exceptional structural fire resistance. In this research paper, we introduce an innovative approach aimed at enhancing the structural performance of these columns. Our method involves replacing the solid steel core with high-strength bar bundles and substituting concrete with grout to achieve superior fire resistance. These modified columns are referred to as “bar-bundle columns.” The paper presents the results of extensive fire tests conducted on three bar-bundle columns, each with different bar-bundle sizes, quantities, and configurations. Additionally, we determine the temperature-dependent material properties of the high-strength steel used for reinforcing bars and the thermal properties of the grout used as a filler through standard experimental tests, which are crucial for numerical simulations. An advanced nonlinear finite element model is describe which is capable of predicting the fire behavior of bar-bundle columns. Finally, this numerical model is employed to conduct parametric analyses and propose a simplified design model for bar-bundle columns under fire conditions.Our findings indicate that the bar-bundle configuration and using grout as a filler significantly delays the heating of the steel core, resulting in enhanced fire resistance when compared to CFHS columns with a solid steel core. The simplified method proposed in this study can be used to estimate the fire resistance of slender bar bundles, but further experimental testing could further refine and improve its accuracy.

Modeling and analysis of electro-thermal processes in installations for induction heat treatment of aluminum cores of power cables

Introduction. The development of the electric power industry is directly related to the improvement of cable lines. Cable lines meet modern requirements for reliability, they are increasingly used. Problem. Currently, power cables with an aluminum multi-conductor core, which requires heat treatment - an annealing process at the stage of the technological manufacturing process, are widespread. This process makes it possible to desirably reduce the electrical resistance of the wire and increase its flexibility. For effective use of induction heating during annealing of an aluminum core, it is necessary to determine the optimal frequency of the power source of the inductor. Considering the long length of the inductor and the large number of its turns, the numerical calculation of the electromagnetic field, which is necessary for calculating the equivalent electrical parameters of the turns of the inductor and its efficiency, requires significant computer resources. The goal is to develop a computer model for calculating electro-thermal processes in an induction plant for heating (up to the annealing temperature) an aluminum core of a power cable moving in the magnetic field of a long multi-turn inductor, as well as obtaining frequency dependences of the equivalent R, L parameters of such an inductor and determining the optimal the value of the frequency of the power source, which corresponds to the maximum value of the electrical efficiency of the inductor. Methodology. The mathematical model was developed to analyze the coupled electromagnetic and thermal processes occurring in a core moving in a time-harmonic magnetic field of an inductor at a constant speed. The differential equations for the electromagnetic and temperature fields, taking into account the boundary conditions, represent a coupled electro-thermal problem that was solved numerically by the finite element method using the Comsol software package. For a detailed analysis of the electromagnetic processes in the inductor, an additional problem was considered at the level of the elementary cell, which includes one turn of the inductor and a fragment of the core located near this turn. Results. According to the results of the calculation of the electromagnetic field in the area of the elementary cell, the equivalent electrical parameters of one turn of the inductor and the entire multi-turn inductor were calculated depending on the frequency of the electric current. The frequency dependences of the electrical efficiency of the inductor were calculated. Originality. Taking into account the design features of the inductor (its long length and large number of turns), the method of multiscale modeling was used. Electro-thermal processes in the core were studied at the macro level, and the distribution of the electromagnetic field and electric current density in the cross-section of the massive copper turn of the inductor was calculated at the micro level – at the level of an elementary cell containing only one turn of the inductor. The frequency dependences of the equivalent R, L parameters of the inductor, taking into account the skin effect, the proximity effect, and the geometric effect, were obtained, and the quantitative influence of the electric current frequency on these effects was studied. Practical value. The dependence of the electrical efficiency of the inductor on the frequency of the power source was obtained and it was shown that for effective heating of an aluminum core with a diameter of 28 mm, the optimal value of the frequency is in the range of 1–2 kHz, and at the same time the electrical efficiency reaches values of ηind = 0.3–0.33, respectively.

Research on the Influence of Negative KERMA Factors on the Power Distribution of a Lead-Cooled Fast Reactor

The accurate calculation of reactor core heating is vital for the design and safety analysis of reactor physics. However, negative KERMA factors may be produced when processing and evaluating libraries of the nuclear data files ENDF/B-VII.1 and ENDF/B-VIII.0 with the NJOY2016 code, and the continuous-energy neutron cross-section library ENDF71x with MCNP also has the same problem. Negative KERMA factors may lead to an unreasonable reactor heating rate. Therefore, it is important to investigate the influence of negative KERMA factors on the calculation of the heating rate. It was also found that negative KERMA factors can be avoided with the CENDL-3.2 library for some nuclides. Many negative KERMA nuclides are found for structural materials; there are many non-fuel regions in fast reactors, and these negative KERMA factors may have a more important impact on the power distribution in non-fuel regions. In this study, the impact of negative KERMA factors on power calculation was analyzed by using the RBEC-M benchmark and replacing the neutron cross-section library containing negative KERMA factors with one containing normal KERMA factors that were generated based on CENDL-3.2. For the RBEC-M benchmark, the deviation in the maximum neutron heating rate between the negative KERMA library and the normal library was 6.46%, and this appeared in the reflector region. In the core region, negative KERMA factors had little influence on the heating rate, and the deviations in the heating rate in most assemblies were within 1% because the heating was mainly caused by fission. However, in the reflector zone, where gamma heating was dominant, the total heating rate varied on account of the gamma heating rate. Therefore, negative KERMA factors for neutrons have little influence on the calculation of fast reactor heating according to the RBEC-M benchmark.

Effectiveness of near-fault pulse models in determining behavior of isolated buildings based on lead core heating

Yüksek genlikli, uzun periyotlu pulslar içeren yakın-fay depremleri, sismik yalıtımlı binalar için yıkıcı bir potansiyele sahiptir. Tarihi yakın-fay deprem kayıtlarının sayısı kapsamlı çalışmalar için yeterli olmadığından; bu kayıtları simüle etmek için sentetik puls modelleri kullanılabilmektedir. Geliştirilen farklı puls modellerinin etkinliği, sismik yalıtımlı yapılar için araştırılmış; ancak bu çalışmalarda, yakın-fay depremlerindeki etkilerinin önemli düzeylere çıkabildiği bilinen kurşun çekirdek ısınması göz önüne alınmamıştır. Bu çalışmada, puls modellerinin taban yalıtımlı binaların yakın-fay depremleri etkisinde kurşun çekirdek ısınmasına bağlı sismik tepkisini belirlemedeki başarısını araştırmak amacıyla, tarihi yakın-fay depremleri ve sentetik olarak üretilmiş eşdeğer yer hareketi kayıtları etkisinde zaman tanım alanında doğrusal olmayan analizler gerçekleştirilmiştir. Sonuçlar, puls modelleri ile genel davranışın belirlenebilesine karşın kurşun çekirdek ısınmasına bağlı olarak farkların ortaya çıkabileceğini göstermiştir.

Light Fueled High-Throughput Binary Droplet Splitting and Transport on High-Energy Substrate.

High-throughput droplet splitting and controllable transport of generated microdroplets on open surfaces are crucial in a broad spectrum of applications. Herein, a light strategy for controlling high-throughput splitting of binary droplets and transport of generated microdroplets on a high-energy substrate endowed by a localized photothermal effect is reported. Strong Marangoni flow as a result of the surface tension gradient and limited inward flow at the droplet bottom as a result of the significant viscous effect are together responsible for binary droplet splitting. The temperature gradients across the generated microdroplets established at the core heating zone are responsible for their transport away from the laser-acted zone. Remarkably, assisted by hydrophobic stripes on a high-energy substrate, high-throughput binary droplet splitting and controllable transport of generated microdroplets can be realized. Successful applications in biosample droplets and parallelized microreactions highlight the promising potential of this light strategy in open droplet microfluidics, biological assays and diagnosis, etc.

Optical and scintillation properties of Yb-doped La2Hf2O7 crystal grown by core heating method for fiber reading remote-dosimetry system

(La0.99Yb0.01)2Hf2O7 (Yb:LaHO) crystal has been developed by the core heating method as a near-infrared-emitting oxide scintillator for a fiber reading remote-dosimetry system under the high-dose-rate region. This system consists of a scintillator, a long silica optical fiber and a detector unit. Near-infrared-emitting photons can be separated from significant fiber-derived noise mainly observed in the UV–blue range. The noise is generated in the optical fiber itself by gamma-rays and charged particles. The Yb:LaHO crystal had a maximum emission peak at 975 nm when excited by X-rays and a transmittance of approximately 29% at 977 nm. The afterglow intensity of the Yb:LaHO crystal under X-rays was 11% that of Cr:α-Al2O3 (ruby) crystal. We demonstrated the applicability of the remote-dosimetry system with the Yb:LaHO crystal irradiated with gamma rays from a 60Co source with an activity of ∼77 TBq. The signal-to-noise ratio (SNR) of the Yb:LaHO crystal was 1.9 times higher than that of the ruby crystal at ∼ 1 kGy/h, and the lowest limit of the dynamic range was comparable between the Yb:LaHO and ruby crystals. The results of the SNR and afterglow intensity showed that the Yb:LaHO crystal is a more suitable scintillator than the ruby crystal for fiber reading remote-dosimetry systems.

Shell-Model Study of Nuclear Weak Rates relevant to Astrophysical Processes in Stars

New shell-model Hamiltonians which can successfully describe spin responses in nuclei are used to evaluate nuclear weak rates in stellar environments. The e-capture and β-decay rates for the nuclear pair with 31Mg-31Al, in the island of inversion, which have been pointed out to be important for the cooling of neutron star crusts, are studied by shell-model calculations with the effective interaction in sd-pf shell obtained by the extended Kuo-Krenciglowa (EKK) method. The weak rates induced by the Gamow-Teller transitions between the low-lying states in the nuclear pair lead to a nuclear Urca process. The spin-dipole strengths and e-capture rates for 78Ni are evaluated by shell-model with full pf-sdg shells including up to 5p-5h excitations outside filling configurations of 78Ni. The e-capture rates obtained are compared with RPA calculations and the effective rate formula. Weak rates for the second-forbidden transition in 20Ne are evaluated by the multipole expansion method of Walecka as well as the Behrens-Bühring method within sd-shell. Difference in the rates between the two methods is found to be rather small as far as the conserved-vector-current (CVC) relation is satisfied. Possible important contributions of the forbidden transition to the heating of the ONeMg core by double e-captures on 20Ne in a late stage of the evolution of the core and implications on the final fate of the core, whether core-collapse or thermonuclear explosion, are discussed.

ECRF stray radiation studies in preparation of the operations of JT-60SA

JT-60SA tokamak is equipped with an ECRF system since the beginning of its operational phase. Starting from two gyrotrons units during the Integrated Commissioning, applicable for core heating, assisted breakdown and assisted Wall Conditioning, the system capabilities will be progressively extended from the Initial Research phase for wider applications. The development of the full current plasma H mode scenario 2 (inductive, type I ELM, Ip=5.5 MA, BT=2.25 T, q95=3) is among the first scientific objectives of the research program. In preparation of this, predictive modelling of the current ramp-up in scaled versions of scenario 2 is being done, based on parameters previously published. In this scenario the ECRF power is injected from an early phase of the discharge. Such modelling provides the kinetic profiles giving the opportunity to estimate the expected amount of EC stray radiation during the ramp-up phase when the EC power absorption might be less than 100% and consequently the potential risk of damage of the in-vessel components is higher.

Dependence of resistivity gradient guiding of laser-driven relativistic electron beams on laser intensity and duration

A laser-driven relativistic electron beam (REB) has a large beam divergence. For the efficient heating of material by REB, for example, core heating in fast ignition, beam guiding from its generation point to the heating material to be heated by suppressing spatial divergence in a perpendicular direction to keep its intensity sufficiently high is indispensable. We evaluated the dependences of the REB guiding performance in the resistivity gradient guiding scheme [A. P. L. Robinson and M. Sherlock, “Magnetic collimation of fast electrons produced by ultraintense laser irradiation by structuring the target composition,” Phys. Plasmas 14, 083105 (2007)] on laser intensity and duration, from the present petawatt laser parameters to the fast ignition-relevant laser parameters, in terms of the temperature dependence of resistivity and energy deposition of the REB. The REB transport simulations in solid materials show that for a fast ignition-relevant laser condition, a nickel cylinder works as a guiding material; an REB transport efficiency of 40% is obtained for a 100-μm propagation. The simulation results show that the resistive gradient guiding scheme is one of possible candidates for improving core heating efficiency.

Variable Saturation Inductor-Based Full Bridge Converter With Wide ZVS Range and Reduced Duty Cycle Loss

A phase-shifted full-bridge (PSFB) converter is widely used in various applications due to its soft-switching characteristics. However, one of the recognized shortcomings of the PSFB converter is that it cannot simultaneously have a wide soft switching range and a small secondary-side duty cycle loss. The shortcoming hinders the high frequency and high efficiency of the converter. In this article, the change of the energy demand of the converter on the external series inductor with input voltage and load is analyzed. On this basis, a variable saturation inductor with controllable energy is proposed to meet the energy demand and solve the problem of core heating. The controllable change characteristics of the inductor energy are studied directly instead of the controllable change of the inductance value. By adjusting the inductor energy, the PSFB can not only achieve soft switching under light loads, but also reduce duty cycle loss under heavy loads. Theoretical analysis and experimental verification are carried out on the soft switching and duty cycle loss of the converter. Since the transformer ratio can be increased due to thesmaller duty cycle loss. The efficiency of the converter can be further improved.

Active control of amplitude and phase of high-power RF systems in EAST ICRF heating experiments

The EAST ICRF system operating space has been extended in power and phase control with a low-level RF system for the new double-strap antenna. Then the multi-step power and periodic phase scanning experiment were conducted in L-mode plasma, respectively. In the power scanning experiment, the stored energy, radiation power, plasma impedance and the antenna's temperature all have positive responses during the short ramp-ups of PL,ICRF. The core ion temperature increased from 1 keV to 1.5 keV and the core heating area expanded from |Z|≤5cm to |Z|≤10cm during the injection of ICRF waves. In the phasing scanning experiment, in addition to the same conclusions as the previous relatively phasing scanning experiment, the superposition effect of the fluctuation of stored energy, radiation power and neutron yield caused by phasing change with dual antenna, resulting in the amplitude and phase shift, was also observed. The active control of RF output facilitates the precise control of plasma profiles and greatly benefits future experimental exploration.

Carotid body hyperexcitability underlies heat-induced hyperventilation in exercising humans.

Physical activity is the most common source of heat strain for humans. The thermal strain of physical activity causes overbreathing (hyperventilation) and this has adverse physiological repercussions. The mechanisms underlying heat-induced hyperventilation during exercise are unknown, but recent evidence supports a primary role of carotid body hyperexcitability (increased tonic activity and sensitivity) underpinning hyperventilation in passively heated humans. In a repeated-measures crossover design, 12 healthy participants (6 female) completed two low-intensity cycling exercise conditions (25% maximal aerobic power) in randomized order, one with core temperature (TC) kept relatively stable near thermoneutrality, and the other with progressive heat strain to +2°C TC. To provide a complete examination of carotid body function under graded heat strain, carotid body tonic activity was assessed indirectly by transient hyperoxia, and its sensitivity estimated by responses to both isocapnic and poikilocapnic hypoxia. Carotid body tonic activity was increased by 220 ± 110% during cycling alone, and by 400 ± 290% with supplemental thermal strain to +1°C TC, and 600 ± 290% at +2°C TC (interaction, P = 0.0031). During exercise with heat stress at both +1°C and +2°C TC, carotid body suppression by hyperoxia decreased ventilation below the rates observed during exercise without heat stress (P < 0.0147). Carotid body sensitivity was increased by up to 230 ± 190% with exercise alone, and by 290 ± 250% with supplemental heating to +1°C TC and 510 ± 470% at +2°C TC (interaction, P = 0.0012). These data indicate that the carotid body is further activated and sensitized by heat strain during exercise and this largely explains the added drive to breathe.NEW & NOTEWORTHY Physical activity is the most common way humans increase their core temperature, and excess breathing in the heat can limit heat tolerance and performance, and may increase the risk of heat-related injury. Dose-dependent increases in carotid body tonic activity and sensitivity with core heating provide compelling evidence that carotid body hyperexcitability is the primary cause of heat-induced hyperventilation during exercise.

МАТЕМАТИЧНЕ МОДЕЛЮВАННЯ ТА РЕГУЛЮВАННЯ ПРОЦЕСІВ КОМПЛЕКСНОЇ ЕЛЕКТРОТЕРМООБРОБКИ АЛЮМІНІЄВОЇ ЖИЛИ СИЛОВОГО КАБЕЛЮ

In the work using the finite element method, a three-dimensional computer model of the processes of electrothermal treatment of an aluminum core of a power cable in an electric furnace and a thermostat was developed, and the pat-terns of changes in the temperature field in such a core were determined under different modes of implementation of the so-called "annealing" processes, that is, the restoration of the necessary electrical properties in it , in particular, an increase in specific electrical conductivity and plasticity. Calculations based on the developed mathematical model and the obtained regularities are consistent with the results of practical measurements of electrical conductivity and plastic-ity of experimental samples of aluminum cores of cables manufactured by YUZHCABLE WORKS, PJSC, Kharkiv. However, the analysis of the patterns of changes in the temperature field in the volume of aluminum cores of cables during their continuous electric heating to the required temperatures of both the outer and inner layers of the core wound on a spool showed that the difference in their temperatures can exceed 500 С. Such nonuniformity of the tem-perature field of the core and long-term overheating of its outer layers leads to unacceptable losses of electricity and reduces the positive result of the processes of such heat treatment of the core, in particular, regarding the increase of its electrical conductivity. It is substantiated that in order to reduce the loss of electricity and the nonuniformity of the temperature field in the aluminum core, it is necessary to reduce the duration of electric heating of the aluminum core to the temperature of its upper layers, necessary for annealing, and then move the drum with such a core to a thermo-stat without electronic heating elements. In such a thermostat, the temperature of the outer layers will decrease, and the temperature of the inner layers will continue to increase. The work shows that after some time (≈ 60 min), the tempera-ture distribution in the core will become almost uniform, and the total losses of electricity and the nonuniformity of the temperature field in the volume of the core will become smaller. Based on the results of the calculations, recommenda-tions were developed for the selection of appropriate modes of heat treatment of aluminum cores wound on a spool, with acceptable energy consumption and overheating of the upper layers of the core. Ref. 8, fig. 4.

Effects of Lead Core Heating on the Response of Isolated-Base and Fixed-Base Regular and Irregular Reinforced Concrete Structures

In this study, the seismic behavior of isolated- and fixed-base regular and irregular reinforced concrete structures was investigated. For this purpose, a three-dimensional, eight-story reference building model without any irregularity was designed in accordance with the Turkish Building Earthquake Code (TBEC-2018). Later, the building models with irregularities were created using the reference building model. In the building models with seismic isolators and fixed supports, fiber hinges were used for columns and beams to model nonlinear behavior. Moreover, nonlinear behavior at the isolation level was taken into account in building models with seismic isolators. Eleven different earthquake records were scaled using the geometric scaling method. Bi-directional nonlinear response history analysis (NRHA) was performed simultaneously for both horizontal components of the earthquake records in all building models. In addition to boundary analyses (Lower Bound and Upper Bound), which do not take into account the strength loss defined by the codes, analyses considering the strength loss as a result of heating in the lead core due to cyclical motion (Temperature Including) were carried out for building models with seismic isolators. In the analyses, displacement, acceleration, story drift ratio, base shear ratio, and damage mechanisms in the columns and beams obtained from the fixed-base and isolated-base structures were compared. In addition, the results of the analysis, in which the loss of strength due to temperature increase due to cyclical motion in the lead core is taken into account, were compared with the results obtained from the boundary analysis. As a result of the study, it was deduced that significant improvements were observed in the structural behavior of all regular and irregular models with seismic isolators under earthquake effects.

Investigation of the Effects of Superstructure Damping Ratio on Buildings with Lead Rubber Bearings under Earthquake Effect

Kurşun çekirdekli elastomer (KÇE) yalıtım birimleri yüksek enerji sönümleme kapasiteleri nedeniyle en çok kullanılan sismik yalıtım birimleri arasında yer almaktadır. Bununla birlikte, yapılan deneysel çalışmalar; kurşun çekirdekte tersinir yükler altında meydana gelen sıcaklık artışının, kurşunun akma dayanımını düşürerek karakteristik dayanımda azalmaya yol açtığını ve bu etkiyi dikkate almanın önemli olduğunu ortaya koymaktadır. Sismik yalıtımlı binalarda yalıtım sisteminin yanı sıra, üstyapı da kendi iç sönümü sayesinde bir dereceye kadar enerji sönümleme özelliğine sahiptir. Ancak, bu yapıların tasarımlarında ve bu tür yapıları ele alan araştırma çalışmalarında üstyapı için farklı sönüm oranlarının kullanıldığı görülmektedir. Bu çalışmada, üstyapı sönümünün, (i) taban ankastre betonarme binalara benzer şekilde % 5 alınması, (ii) % 2 gibi daha küçük bir değer alınması ya da (iii) tamamen ihmal edilmesi durumunda sismik yalıtımlı binaların kurşun çekirdek ısınmasına bağlı davranışlarının değişimi incelenmiştir. Sismik yalıtımlı betonarme bir bina, OpenSees programında, kurşun çekirdek ısınmasının dayanım üzerindeki etkisi göz önünde bulundurularak modellenmiş ve zaman tanım alanında yapılan doğrusal olmayan analizlerden elde edilen kat ivmeleri, kurşun çekirdekteki sıcaklık artışı, yalıtım birimi kesme kuvvetleri ve deplasmanları gibi tepkiler incelenmiştir. Sonuçlar, özellikle kat ivmelerinin önemli ölçüde değişebildiğini ve farklı üstyapı sönüm oranlarıyla elde edilen kat ivmelerinin farklı sınır aralıklarında olabileceğini ortaya koymuştur.

Development of Self-Shielded Flux-Cored Wires for Arc Welding of Low-Alloy Steels

Current aspects of the developing of modern self-shielding flux-cored wires composition for arc welding of low-alloyed steels are considered. Advantages and disadvantages of flux-cored wires of carbonate-fluorite, oxide and oxide-fluoride types of are shown in comparison. The effectiveness of gas shielding of molten metal at welding with self-shielding flux-cored wires of carbonate-fluorite type is analyzed considering the thermal properties of their cores. It is shown that to improve reliability of gas shielding at welding using the wires of this type it is important not only to ensure generation of sufficiently large volume of shielding gases at thermal destruction of the wire core, but also to control this process, providing gas evolution at all stages of heating and melting of the wire. The results of complex thermal analysis of the wire core mixtures containing, for example, lithium carbonate show substantially large heat losses for heating and melting of the wire core, which are accompanied by the development of energy-intensive processes of thermal destruction of core components. It is shown that the limitation of lithium carbonate content in the wire at the level of not more than 2 wt. % allows not only to preserve welding arc burning stability at the acceptable level but also to provide effective gas shielding of molten metal and easy separation of slag crust. The control of thermochemical reactions in the core is achieved by selection of its proper composition to ensure favorable melting of flux-cored wire and electrode metal transfer to the welding pool. Results of metallographic examinations of distribution and composition of non-metallic inclusions in metal of the welds made with wires of the oxide and oxide-fluoride types are presented. Main properties of the developed self-shielding flux-cored wires and recommendations on welding are given in conjunction with prospective fields of their application.

Temperature-dependent performance of LRBs and its effect on seismic responses of isolated bridges under near-fault earthquake excitations

As the widely used seismic isolators in engineering structures, the mechanical property of lead rubber bearings (LRBs) is vital to the seismic performance of isolated structures. Due to cyclic loadings, the temperature of lead core raises, causing the performance degradation of LRBs. This paper investigates the seismic performance of isolated bridges with consideration of the temperature-dependent behavior of LRBs, and the seismic responses of isolated bridges are quantified based on both the energy and deformation. The analytical results indicate that the absorbed energy and shearing strain of bearings increase when considering the effect of lead core heating under seismic loadings, and these variations cannot be ignored. Besides, the relative variations of energies and deformations of isolated bridges are unrelated to the period of the velocity pulse of near-fault ground motion. The temperature-dependent behavior of LRBs under seismic loadings is suggested to be taken into account in the seismic design of isolated bridges. Otherwise, the seismic damage risk of isolated bridges will be underestimated significantly.