TEM analysis of high temperature annealed W nanostructure surfaces

Helium plasma irradiation and electron heating experiments were conducted using tungsten in the divertor simulator NAGDIS-II. Helium plasma irradiation to tungsten led to the formation of nanostructures on the surface, while the nanostructures were annihilated after the potential of the specimen was changed to positive for several 10 min so that electrons irradiated the sample without ion irradiation. The specimens were analyzed in detail by transmission electron microscope with the help of focused ion beam technique. It is revealed that the helium nano-bubbles still remained even after the nanostructures were disappeared from the surface. Porosity of the nanostructured tungsten was measured from the TEM images.     

Finite element analysis of thick annular and sector plates

A finite element displacement formulation based on Reissner's thick plate theory is presented for the bending analysis of annular and sector plates. An annular element and an annular sector element, associated with six and twenty degrees of freedom, respectively, are developed. One of the significant features of these elements, which include both bending and shear deformation effects and which conform with respect to all degrees of freedom considered, is the ability to satisfy exactly the condition of vanishing shear stress resultant along a free edge. Numerical results are presented for substantiating the proposed procedure.     

Thermal analysis of plates with circular inclusions

A least square boundary point matching method is employed to determine the temperature distributions and deformations of rectangular plates with circular elastic inclusions. Solutions for two problems have been obtained. The first problem is concerned with the determination of the temperature distribution in a finite rectangular plate having a circular inclusion and subjected to prescribed temperature distribution and thermal conditions along the edges. The plate is heated uniformly through the thickness. The second problem is concerned with the deflection and moment distribution in the same plate model with simply supported edges and prescribed temperature variation across the thickness but no temperature variation over the plate surface. Numerical results are presented.     

Hybrid method for vibration analysis of rectangular plates

This paper presents a semi-analytical approach for the dynamic analysis of rectangular plates. The mathematical model is developed using a hybrid combination of the finite element method and Sanders’ shell theory. The in-plane, membrane displacement components are modelled by bilinear polynomials and the out-of-plane, normal to mid-surface displacement component is modelled by an exponential function that represents a general form of the exact solution of the equations of motion. The displacement functions are obtained by exact solution of the equilibrium equations of the rectangular plates. The mass and stiffness matrices are then determined by exact analytical integration to establish the plate's dynamic equations. The effect of various geometrical parameters and boundary conditions on the dynamic responses of the rectangular plates has been explored in this work. The results are in satisfactory agreement with those of experiments and other theories.     

Three dimensional analysis of thermally loaded thick plates

A mixed three dimensional formulation is presented for the analysis of thermally loaded thick plates. The method developed follows the guidelines furnished by the Vlasov-Iyengar technique applicable to the analysis of mechanically loaded thick plates, in which the three dimensional governing equations are derived from the elasticity equations by using a MacLaurin series approach. The expressions for the components of displacement, stress, and heat flux as well as the temperature are obtained in a series form in terms of the linear partial differential operators operating on a set of initial functions, which are the solutions to the governing equations. The procedure to be followed in arriving at the solution is illustrated by solving the problem of the thermal bending of a clamped-supported thick square plate; it is found that the present solution deviates significantly from those of the lower order theories for large values of the thickness ratio.     

注N~+高速钢表面层精细组织结构的电镜分析

本文对N离子注入W18Cr4V高速钢前后的表面层精细组织结构用透射电镜进行了比较分析。N离子注入能量为100keV,注入剂量为1.7×10~(17)/cm~2和2×10~(17)/cm~2。电镜分析发现,经注N~+的高速钢表面层组织形貌发生了显著变化,α-Fe基体中产生了很多辐照损伤区域,孪晶结构消失,α-Fe出现多晶化的倾向,位错密度明显降低,而且残余碳化物破碎呈现龟裂状形貌。文章对上述变化的机理作了初步分析。     

Numerical analysis of circular elastic-plastic plates under cycles of pressure and temperature

A numerical approach is considered to compute neutral domains (ND) of elastic response for the so-called load control-program (LCP), i.e. for the relation ƒ(p,T) = 0, where p and T are pressure and temperature parameters, respectively. Elastic-plastic material with combined isotropic-kinematic strain-hardening is adopted. Material characteristics are assumed to be functions of temperature in incremental equations of the theory of plastic flow. Small strains are assumed but geometrical and equilibrium equations are derived for moderately large deflections. Distribution of temperature in the plate is assumed to be known in every point of the plate ξ, as the function (ξ, T). The method of solution lies in computation of a sequence of boundary-value problems, first along the LCP curve, then along the ND curve. The BV problem is solved by means of forward numerical integration. Coordinates of points on the ND curve are computed by use of an iterative procedure which bases on a directed search approach. Computations have been carried out for a sandwich annular plate for linear and piecewise LCP.     

核辐射信号数字测量与分析方法研究

基于虚拟仪器的概念,设计了一套数字化辐射测量系统。使用该平台结合Si（Au）探测器和Cd（Zn）Te探测器进行了能量分辨率指标评估、单探测器多辐射类型并行测量分析及软件符合实验研究,并对结果进行了分析,评估了系统的优缺点。     

Reduced and selective integration techniques in the finite element analysis of plates

Efforts to develop effective plate bending finite elements by reduced integration techniques are described. The basis for the development is a ‘thick’ plate theory in which transverse shear strains are accounted for. The variables in the theory are all kinematic, namely, displacements and independent rotations. As only C⁰ continuity is required, isoparametric elements may be employed, which result in several advantages over thin plate elements. It is shown that the avoidance of shear ‘locking’ may be facilitated by reduced integration techniques. Both uniform and selective schemes are considered. Conditions under which selective schemes are invariant are identified, and they are found to have an advantage over uniform schemes in the present situation. It is pointed out that the present elements are not subject to the difficulties encountered by thin plate theory elements, concerning boundary conditions. For example, the polygonal approximation of curved, simply-supported edges is convergent. Other topics discussed are the equivalence with mixed methods, rank deficiency, convergence criteria and useful mass ‘lumping’ schemes for dynamics. Numerical results for several thin plate problems indicate the high degree of accuracy attainable by the present elements.     

Microstructural study of an irradiated high-nickel alloy by X-ray line profile analysis and TEM observations

The microstructure was investigated in previously deformed specimens of a high-nickel alloy with four levels of initial dislocation density, both before and after irradiation in BOR-60 reactor at 370–400°C and three displacement rates. The network dislocation density, dislocation loop radius and loop number density were determined by both X-ray line profile analysis and TEM observations. The dependence of dislocation structure parameters on irradiation conditions and initial network density was obtained.     

Simplified creep analysis of perforated plates under steady creep condition

A study is performed on the creep analysis of perforated plates based on the equivalent solid plate concept.A series of creep analyses by FEM for various materials, ligament efficiencies and loading conditions is performed on a perforated plate with a triangular penetration pattern of circular holes. Based on the results of the analysis, prediction methods for both the equivalent solid plate property and the stress-strain concentration around the hole are proposed.The prediction method for the equivalent solid plate property is compatible with the elastic property shown in the ASME B&PV Code Sec. III A-8000. The prediction method for the stress—strain concentration is based on Neuber's rule together with Hoff's analogy, and is compatible with the elastic peak stress multiplier in the ASME B&PV Code Sec. III A-8000.     

Method of initial functions in the analysis of thick circular plates

The method of initial functions has been used for the analysis of thick circular plates. In this method, the governing equations are derived from the three-dimensional elasticity equations in cylindrical polar coordinates using a Maclaurin series expansion in thickness coordinate for the unknowns. The formulation is in a form which is particularly amenable to consistent reduction to obtain approximate theories of any desired order. Numerical results obtained using this method are compared with those of elasticity solution for the case of a simply supported plate and for a plate subjected to self-equilibrating normal loads. Results are also given for clamped plates subjected to a uniformly distributed load.     

Combined grazing incidence RBS and TEM analysis of luminescent nano-SiGe/SiO2 multilayers

Multilayer structures with five periods of amorphous SiGe nanoparticles/SiO₂ layers with different thickness were deposited by Low Pressure Chemical Vapor Deposition and annealed to crystallize the SiGe nanoparticles. The use of grazing incidence RBS was necessary to obtain sufficient depth resolution to separate the signals arising from the individual layers only a few nm thick. The average size and areal density of the embedded SiGe nanoparticles as well as the oxide interlayer thickness were determined from the RBS spectra. Details of eventual composition changes and diffusion processes caused by the annealing processes were also studied. Transmission Electron Microscopy was used to obtain complementary information on the structural parameters of the samples in order to check the information yielded by RBS. The study revealed that annealing at 900 °C for 60 s, enough to crystallize the SiGe nanoparticles, leaves the structure unaltered if the interlayer thickness is around 15 nm or higher.     

Microstructural analysis of MTR fuel plates damaged by a coolant flow blockage

In 1975, as a result of a blockage of the coolant inlet flow, two plates of a fuel element of the BR2 reactor of the Belgian Nuclear Research Centre (SCK•CEN) were partially melted. The fuel element consisted of Al-clad plates with 90% ²³⁵U enriched UAl_x fuel dispersed in an Al matrix. The element had accumulated a burn up of 21% ²³⁵U before it was removed from the reactor. Recently, the damaged fuel plates were sent to the hot laboratory for detailed PIE.Microstructural changes and associated temperature markers were used to identify several stages in the progression to fuel melting. It was found that the temperature in the center of the fuel plate had increased above 900-950 °C before the reactor was scrammed. In view of the limited availability of such datasets, the results of this microstructural analysis provide valuable input in the analysis of accident scenarios for research reactors.     

Structural analysis of DC magnetron sputtered and spin coated thin films using RBS, TEM and X-ray reflectivity methods

Metallic thin films such as Au, Cr, Ag, etc., on silicon substrate have many technologically important applications as contact layers in microelectronic industry, as reflecting mirrors in synchrotron radiation research, etc. The native oxide layer on crystalline silicon surface inhibits wetting of few nm thick Au or Ag on native oxide/silicon systems. To obtain continuous thin metallic films (a few nm thick), a Cr layer was first deposited as a adhesion layer on the Si substrate. In this paper, Rutherford backscattering analysis (RBS) of Si/Cr/SiO₂/Si, Si/Au/SiO₂/Si, Si/Au/Cr/SiO₂/Si and Polystyrene (PS) polymer coated on some of these bi- or tri-layer structures has been reported. The X-ray reflectometry and transmission electron microscopy studies were carried out to complement the RBS measurements. The thickness, surface and interface roughness, and crystalline quality have been determined.     

In situ oxidation of zirconium binary alloys by environmental SEM and analysis by AFM, FIB, and TEM

Binary Zr-alloys containing 1%Fe and 1% Ni (large precipitates) and 1% Cr and 0.6% Nb (small precipitates), as well as a pure Zr sample were exposed in situ at 130 Pa water vapour pressure at 415 °C in an environmental SEM. The surface topography and composition of each sample was characterised before in situ experiments, during and after oxidation. After oxidation the surface was characterised by SEM and EDS, AFM and TEM combined with EDS. Focused ion beam was used to prepare cross sections of the metal-oxide interface and for the preparation of TEM thin foils.The oxidation behaviour of precipitates for these alloying elements can be characterised into two large families, those which show a rapid oxidation and those which induce a delayed oxidation in comparison with the Zr-matrix.At 415 °C after 1 h of oxidation for Zr1%Fe and Zr1%Ni, the formation of protrusions could be detected at the surface, being related to underlying SPP in the oxide. On Zr1%Cr and Zr0.6%Nb unoxidised SPPs were observed in the oxide, close to the metal-oxide interface. These SPPs were, however, oxidised close to the outer surface of the oxide. The surface roughness was increased for all materials after in situ oxidation, however, only for Zr1%Fe and Zr1%Ni protrusions appeared on the surface during oxidation. It was subsequently demonstrated that these latter correspond to the position of SPPs. For Zr1%Fe the surface roughness increased more than in the other materials and on these protrusions small iron oxide crystals have been observed at the surface. These observations confirm that Fe has a different behaviour compared to the other SPP forming elements, and it diffuses out to the free surface of the material.These alloying elements being the constituents of the commercial alloys (Fe and Cr for Zircaloy-4; Fe, Cr and Ni for Zircaloy-2 and Nb for all Nb-containing alloys), this study allows to separate their individual influence and can allow a subsequent comparison to the behaviour of those more complex alloys.     

Buckling sensitivity analysis of cracked thin plates under membrane tension or compression loading

Thin-walled structural components such as plates and shells are commonly used in practical applications such as aerospace, naval, nuclear power plant, pressure vessels, mechanical and civil engineering structures and so on, and the safety assessment of such structures must carefully consider all the phenomena which can decrease the bearing capacity of such elements. Among them, the presence of cracks in thin-walled structures can heavily affects their safety factor with respect to the more common modes of failure such as buckling or fracture. For very thin plate, buckling collapse under compression or even under tension, apart fracture or plastic failure in this last case, can easily take place: the presence of flaws such as through-the-thickness cracks can sensibly modify such ultimate loads. In the paper the effects of cracks’ length and orientation on the buckling loads of rectangular elastic thin-plates - characterised by different boundary conditions and by various Poisson's ratio - under tension and compression, is considered. For tensioned flawed plates a fracture-buckling and a plastic-buckling collapse maps are obtained. After a short explanation of the buckling phenomena in plates, several FE numerical parametric analyses results are presented in terms of critical load multiplier in compression or in tension in cracked plates. The obtained results are discussed and some interesting and useful conclusions regarding the sensitivity to cracks’ presence of buckling loads of thin plates under compression or tension (or fracture in this last case) are explained. The interesting case of tensioned cracked plates is considered by studying the easiest collapse between fracture, plastic flow and buckling: in such cases some failure-type maps are finally determined.     

A high precision triangular plate bending element for the analysis of thick plates

A high precision triangular plate bending element for the analysis of thick plates is developed in thin paper. The element has three nodes and 12 degrees of freedom per node. Explicit expressions for stiffness coefficients are derived. The superiority of the element is demonstrated by the accuracy of the results obtained by applying it to some typical thick plate problems.     

TEM and PAS study of neutron irradiated VVER-type RPV steels

Conventional transmission electron microscopy and positron lifetime and Doppler broadening positron annihilation spectroscopy techniques have been used to investigate the radiation-induced microstructural changes in surveillance specimens of VVER-type reactor pressure vessel (RPV) steels, and RPV steels irradiated in the research reactor. Defects visible in transmission electron microscopy consist of black dots, dislocation loops and precipitates concentrated along the dislocation substructure. Their size and density depend on the neutron flux and fluence. The parallel set of thermally aged specimens, specimens recovery annealed after irradiation and specimens irradiated in a lower neutron flux was investigated too. No defects discernible in transmission electron microscopy were found after accelerated irradiation in the research reactor. In addition to visible defects, the small-volume vacancy clusters were identified by positron annihilation spectroscopy.