Effect of external stresses on efficiency of dislocation sinks in BCC (Fe, V) and FCC (Cu) crystals

The efficiency of linear sinks for selfpoint defects (SPDs) elastically interacting (dislocations) and not interacting with sinks with the density of 3 × 1014 m–2 is calculated for BCC (Fe, V) and FCC (Cu) crystals at the temperature 293 K using the object kinetic Monte Carlo technique, depending on type and value of applied mechanical load (up to 200 MPa) and types of linear sinks. Full straight dislocations in slip systems [111](1 0), [111](11 ), [100](001), and [100](011) for Fe and V and [100](001) for Cu are considered for dislocation sinks (DSs). Orientations of noninteracting linear sinks (NILSs) coincide with those of DSs. Interaction of SPDs with internal (dislocation) and external stress fields is calculated within the framework of anisotropic linear theory of elasticity. Relative changes in efficiency of different codirectional linear sinks (either interacting or not interacting with SPDs) under action of applied stress are approximately identical under low stress. Radiation creep rates are calculated for the considered crystals under uniaxial stress in the stationary regime of Frenkel pairs generation. The creep rate strongly depends on the loading direction and Burgers vector of dislocations in Fe and V, and it is almost independent of these parameters in Cu. At the same generation rate of Frenkel pairs, the radiation creep rate averaged over all loading directions is significantly higher in BCC (Fe, V) crystals containing dislocations with the Burgers vector a/2〈111〉 than in FCC (Cu) crystals

Dislocation sinks efficiency for self-point defects in iron and vanadium crystals

The effect of the dislocations stress fields on their sink efficiency for self-point defects (interstitial atoms and vacancies) is studied in the temperature range of 293–1000 K and at the dislocation density values of 1 × 1012–3 × 1014 m−2 in body-centered cubic (BCC) iron and vanadium crystals. Straight screw and edge dislocations in 〈111〉{110}, 〈111〉{112}, 〈100〉{100}, and 〈100〉{110} slip systems are considered. Defect diffusion is simulated via the object kinetic Monte Carlo method. The energies of the interaction of defects with dislocations are calculated within the anisotropic linear theory of elasticity. The dislocation sink efficiency is analytically represented as a function of temperature and dislocation density

Evaluation of metal plasticity by cold two-stage deformation

В роботі виконані дослідження впливу анізотропії механічних властивостей і величини використаного ресурсу пластичності, обумовлених попередньою пластичною деформацією металу, на його пластичність при подальшій пластичній деформації в заданому напрямку. При цьому використана тензорна модель процесу накопичення пошкоджень, в основі якої лежить гіпотеза про залежність інтенсивності накопичення пошкоджень від чутливості пластичності металу до схеми напруженого стану, яка описується поверхнею граничних деформацій, від історії деформування і направляючого тензора прирощень пластичних деформацій. Результати виконаних в роботі експериментальних досліджень підтвердили достовірність прийнятої моделі процесу накопичення пошкоджень.Subject. Plasticity of deformed metal depending on the amount of used resource of ductility at the previous stage of forming and deformation story at the subsequent stage. Subject-matter: Evaluation of ductility of deformed metal and its dependence on the size and nature of the preliminary plastic deformation. Purpose of the study is to test the reliability adopted in the tensor model of damage accumulation in the evaluation of plasticity deformed metal. To evaluate the plasticity of the metal is used strain tensor model of damage accumulation process, which is based on the hypothesis of the dependence of the damage accumulation intensity on the plasticity sensitivity the of the metal to the scheme stressed state, which is described by limiting the surface deformation of the deformation story and by guiding the plastic strain increment tensor. The experiments are carried out on a joint twisting stretch of solid cylindrical sample to a certain degree of deformation and subsequent stretching before breaking. Experiments on joint twisting stretch were carried out by a special program that provides complex loading. The difference between ultimate strain calculated from the accepted model and obtained in experimental studies does not exceed 9%. Application results. Tensor model of damage accumulation, adopted in this paper, can be used to assess the estimated longevity of parts made of metal forming techniques, depending on the features of plastic deformation in their manufacture and the stress-strain state, which will take place during the details operation. Findings. On the basis of experimental studies performed residual plasticity of the material pre-deformed specimens, was proved the accuracy of the tensor model of damage accumulation in the evaluation of deformed metal plasticity.В работе выполнены исследования влияния анизотропии механических свойств и величины использованного ресурса пластичности, обусловленных предшествующей пластической деформацией металла, на его пластичность при последующей пластической деформации в заданном направлении. При этом использована тензорная модель процесса накопления повреждений, в основе, которой лежит гипотезе о зависимости интенсивности накопления повреждений от чувствительности пластичности металла к схеме напряжённого состояния, которая описывается поверхностью предельных деформаций, от истории деформирования и направляющего тензора приращений пластических деформаций. Результаты выполненных в работе экспериментальных исследований подтвердили достоверность принятой модели процесса накопления повреждений

Performance Effects of Adding a Parallel Capacitor to a Pulse Inductive Plasma Accelerator Powertrain

Pulsed inductive plasma accelerators are electrodeless space propulsion devices where a capacitor is charged to an initial voltage and then discharged through a coil as a high-current pulse that inductively couples energy into the propellant. The field produced by this pulse ionizes the propellant, producing a plasma near the face of the coil. Once a plasma is formed if can be accelerated and expelled at a high exhaust velocity by the Lorentz force arising from the interaction of an induced plasma current and the magnetic field. While there are many coil geometries that can be employed to inductively accelerate a plasma, in this paper the discussion is limit to planar geometries where the coil take the shape of a flat spiral. A recent review of the developmental history of planar-geometry pulsed inductive thrusters can be found in Ref. [1]. Two concepts that have employed this geometry are the Pulsed Inductive Thruster (PIT) and the Faraday Accelerator with Radio-frequency Assisted Discharge (FARAD)

Endoscopic ultrasound—guided fine needle aspiration in the diagnosis of mediastinal masses of unknown origin

The ability of endosonography to diagnose a variety of gastrointestinal pathology has been significantly advanced with the introduction of endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) biopsy. EUS-FNA technology can also be applied to the evaluation of non-GI disorders. The role of EUS-FNA to establish the diagnosis of unexplained mediastinal masses has not been previously described. The aim of this study was to determine the diagnostic accuracy, impact on subsequent workup, and role of EUS-FNA in treating mediastinal masses of unknown cause. METHODS : A total of 26 patients (15 men and 11 women, mean age 61 yr, range 39–77 yr) underwent EUS-FNA in patients presenting with unexplained mediastinal masses at four tertiary referral centers. Presenting symptoms included: chest pain (10 patients), dysphagia (eight), cough (seven), fever (six), night sweats (three), and no symptoms/abnormal x-ray (five patients). Five of 26 patients had prior history of cancer (three lung, one tracheal, and one esophageal). RESULTS : Final diagnosis using EUS-FNA, surgery, autopsy, other diagnostic study, or long-term follow-up was available in all patients. EUS-FNA results were classified under three disease categories: 1) infectious, 2) benign/inflammatory, and 3) malignant. Final diagnosis included infectious in five patents, benign/inflammatory in nine, and malignant in 12. EUS-FNA was successful in 21 of 26 patients (81%) for all disease categories (infectious 60%, benign/inflammatory 78%, and malignant 92%). EUS-FNA was successful in directing subsequent workup in 77% (20 of 26) and therapy in 73% (19 of 26). Mean EUS-FNA passes for adequate tissue sampling was lower of nonmalignant disease categories (3.0 and 3.4) versus malignant disease (4.4). No complications were seen during the course of this study. CONCLUSIONS : EUS-FNA in patients presenting with idiopathic mediastinal masses establishes the diagnosis in the vast majority of cases, particularly for those with malignant disease. The emergence of transesophageal EUS-FNA of the mediastinum provides the ability to alter subsequent workup and therapy, obviating the need for more invasive diagnostic studies such as thoracotomy.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72588/1/j.1572-0241.2002.06023.x.pd