The load separation and η pl

Load separation is the theoretical basis for the single specimen J form and the incremental calculation of J-R and J _M -R curves. It is based on the assumption that the load can be represented as a multiplication of two separate functions; a crack geometry function and a material deformation function. Until recently, the main experimental basis for such an assumption was the approximate agreement between the experimental results of the single specimen J form and the energy rate interpretation of J in blunt notched bending geometries. The load separation assumption has been also implied in the growing crack records in order to develop the R-curve analysis. Both the crack geometry and material deformation functions were assumed to maintain their forms as the crack grows. Recently, an experimental study investigated the load separation in the test records of stationary crack specimens of different geometry, material, and constraint. The study showed that the load can be represented by a separable form for the entire plastic region except for a limited region at the early region of plastic behavior. Also, it was found that the load separation is not limited to a certain geometry, material, or constraint but it is a dominant property in the ductile fracture behavior of stationary crack specimens. The study also showed that the crack geometry function is a power law function. Hence _pl is a constant equal to the power law exponent of the geometry function.The objective of this study is to investigate the extension of load separation to growing crack records. Sets of test records from three different materials are used in this study. For each material three or four precracked specimen test records and one blunt notched record are analyzed for the compact specimen geometry. The study will discuss the main condition to have a separable behavior in a growing crack test record. It will also construct the geometry and deformation functions for the materials studied, these functions are compared with those obtained from stationary crack records.     

QUANTITATIVE X-RAY DETERMINATION OF η-PHASE IN WC-Co CEMENTED CARBIDES

根据烧结过程中Ｗ元素的质量守恒，推导出ＷＣ－Ｃｏ硬质合金中ＷＣ相和η相（Ｗ３Ｃｏ３Ｃ）含量间的关系式，进而导出了ＷＣ相和ηｌ相间的相对Ｋ值表达式，从而建立了一种用Ｘ射线衍射方法宣测定ＷＣ－Ｃｏ合金中η相含量的实用方法。     

原位Al_2O_(3pl)/Ce-TZP复合材料的显微结构与力学性能

研究了原位生长Ａｌ２Ｏ３片晶／Ｃｅ－ＴＺＰ复合材料的显微结构与力学性能．结果表明,只要烧结温度适当,引入原位Ａｌ２Ｏ３片晶可同时提高复合材料的强度和断裂韧性．在所研究的范围内,以含 １５ ｖｏｌ％Ａｌ２Ｏ３的复合材料有最好的强韧化效果,而增韧效果又比增强效果明显．如果烧结温度过低或者Ａｌ２Ｏ３含量过高,则复合材料的力学性能反而下降．原位Ａｌ２Ｏ３片晶／Ｃｅ－ＴＺＰ复合材料的强韧化机理为应力诱导相交增韧和片晶增韧,两者起到协同增韧的作用．     

Hydrosilation of Carbonyl-Containing Substrates Catalyzed by an Electrophilic η-Silane Iridium(III) Complex

Hydrosilation of a variety of ketones and aldehydes using the cationic iridium catalyst, (POCOP)Ir(H)(acetone)(+), 1, (POCOP = 2,6-bis(di-tert-butyl phosphinito)phenyl) is reported. With triethyl silane, all but exceptionally bulky ketones undergo quantitative reactions employing 0.5 mol% catalyst in 20-30 min at 25 °C. Hydrosilation of esters and amides results in over-reduction and cleavage of C-O and C-N bonds, respectively. The diastereoselectivity of hydrosilation of 4-tert-butyl cyclohexanone has been examined using numerous silanes and is highly temperature dependent. Using EtMe(2)SiH, analysis of the ratio of cis:trans hydrosilation products as a function of temperature yields values for ΔΔH(?) (ΔH(?) (trans) - ΔH(?) (cis)) and ΔΔS(?) (ΔS(?) (trans) - ΔS(?)(cis)) of -2.5 kcal/mol and -6.9 e.u., respectively. Mechanistic studies show that the ketone complex, (POCOP)Ir(H)(ketone)(+), is the catalyst resting state and is in equilibrium with low concentration of the silane complex, (POCOP)Ir(H)(HSiR(3))(+). The silane complex transfers R(3)Si(+) to ketone forming the oxocarbenium ion, R(3)SiOCR'(2) (+), which is reduced by the resulting neutral dihydride 3, (POCOP)Ir(H)(2), to yield product R(3)SiOCHR'(2) and (POCOP)IrH(+) which closes the catalytic cycle.     

Study of the load-separation principle and a procedure to estimate ηp-factor for structures with different geometries

The theoretical background of load separation principle has been reviewed. Based on dimensional analysis, experimental results and finite element analysis the conditions for the validity of this principle have been studied and a method has been suggested to estimate the load separation function, and hence to estimate the _p-factor and to determine the J-R resistance curve easily from records of a single specimen or structure.     

A setup with Cherenkov total absorption spectrometers with large aperture for slow π0- and η-meson detection

A setup for measuring full cross sections of π⁰- and η-mesons photoproduction reaction on nuclei near threshold is described. The γ-quanta from meson breakup are detected by two Cherenkov spectrometers with full absorbtion. The meson detection efficiency is calculated according to the Monte Carlo method and is − 10%.     

On η5 -π-Complexes of C70 and Some of its Cyclopentadienyl Derivatives with Li Atoms: MNDO Simulation

Abstract

The molecular and electronic structure of hypothetical η⁵ -complexes of C₇₀ and its cyclopentadienyl derivatives such as C₇₀R₅, C₇₀R₁₀ and C₆₀X₁₀ (R = H, Cl, Br; X = B, N, Al, P) with Li are discussed. It was proposed that atoms R were attached to the α-positions of one (two) polar pentagon(s) of prolated shape fullerene (D_5n)-C₇₀, and atoms X substituted atoms C in same sites. It was established that the complexes under consideration were more stable systems in comparison with unsubstituted C₇₀. The MNDO method was used. The results obtained are generalizing theoretical studies of electron stucture of similar complexes of fullerene C₆₀ and its derivatives such as C₆₀R₅ and C₅₅X₅.     

Atomic structure of hardening precipitates in an Al–Mg–Zn–Cu alloy determined by HAADF-STEM and first-principles calculations: relation to η-MgZn2

The structures of two nanoscale plate precipitates prevalent at maximum strength and over-aged conditions in a 7449 Al–Mg–Zn–Cu alloy were investigated. Models derived from images of high angle annular dark field scanning transmission electron microscopy were supported by first-principles calculations. Both structures are closely linked to the η-MgZn₂ Laves phase through similar layers of a rhombohedral atomic subunit. The finest plate contains one such layer together with a layer of an orthorhombic unit. The second plate contains rhombohedral layers only, normally four, but rotated relatively to form different stacking variants, one of which may be likened to η. For both structures, the same atomic planes describe the main interface with Al. Both plates could be described in space group P3. The unit cells comprise interface and arbitrary numbers of {111}Al (habit) planes. Eight Al-planes were included in the first-principles calculations. The enthalpy indicates high layer/unit stability. The plate thickness can be understood by a simple mismatch formulation.     

Investigation of mechanical and corrosion properties of an Al–Zn–Mg–Cu alloy under various ageing conditions and interface analysis of η′ precipitate

The mechanical and corrosion properties under various ageing treatment conditions were investigated in an Al–6.0Zn–2.3Mg–1.8Cu–0.1Zr (wt.%) alloy. The results showed that the retrogression and re-ageing (RRA) were capable of providing higher strength and improved corrosion resistance in comparison with the conventional T6 and T74 ageing. The optimised ageing process had been found to be 120 °C/24 h + 180 °C/60 min + 120 °C/24 h for the experimental alloy. The results obtained from the high resolution transmission electron microscopy (HRTEM) interface analysis revealed that a semi-coherent stress field between the η′ precipitate and the Al matrix was critical in controlling the strength of the Al–Zn–Mg–Cu alloy heat-treated under different conditions. Furthermore, Transition Matrix calculation showed that the η′ phases had only two zone axes: [1̅21̅3]_η′ and [108̅2̅3]_η′, which were parallel to the [112]_Al zone axis, when being precipitated from the Al matrix. Therefore, the orientation relationships between the η′ precipitates and the Al matrix under the [112]_Al zone axis could be described as: [1̅21̅3]_η′//[112]_Al;(12̅12)_η′//(11̅)_Al and [108̅2̅3]_η′//[112]_Al;(12̅12)_η′//(111̅)_Al. Consequently, a new diffraction pattern model from η′ precipitates in two variants under the [112]_Al zone axis had been established, which was in a good agreement with the experimental data.     

Orientation relationships, interfaces, and microstructure of η-Cu6Sn5 formed in the early-stage reaction between Cu and molten Sn

A very thin η-Cu₆Sn₅ layer has been formed by dipping thin Cu foil into molten Sn at 240 °C for 1 s and quenching in ice water. After removing electrolytically the Sn on the surface, the η-Cu₆Sn₅ grains on the Sn side are shown to have a worm-type shape 0.3-0.5 μm wide and up to 2 μm long. Transmission electron microscopy (TEM) analysis shows that the η-Cu₆Sn₅ grains on the Cu side can be as small as 5 nm, indicating that the η-Cu₆Sn₅ /Cu interface is the nucleation side.The orientation relationships between η-Cu₆Sn₅ and Cu are determined by TEM. The η-Cu₆Sn₅ (112?0) surface is the interface with both the Cu (001) and (1?11) surfaces, and a common orientation relationship of (0001)_η//(110)_Cu is present on both interfaces. The match of atoms between η-Cu₆Sn₅ and Cu on the interfaces is analyzed.     

Formation and Acid–Base Surface Properties of Highly Dispersed η-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanopowders

Highly dispersed η-Al₂O₃-based nanopowders have been prepared via glycine–nitrate combustion followed by heat treatment in air. The resultant materials have been characterized by X-ray diffraction, Fourier transform IR spectroscopy, scanning electron microscopy, simultaneous thermal analysis, and other techniques. We have optimized the glycine-to-nitrate ratio (G/N = 0.2) and found heat treatment conditions for combustion products (isothermal holding at a temperature of 700°C for 6 h) that allow one to obtain single- phase nanocrystalline η-Al₂O₃ powders with an average particle size of 5 ± 1 nm and specific surface area of 54 ± 5 m²/g. The acid–base surface properties of the η-Al₂O₃ nanopowder have been analyzed using pyridine sorption–desorption processes as an example. The specific concentrations of weak, intermediate, and strong Lewis acid centers on the surface of the η-Al₂O₃ nanocrystals have been shown to markedly exceed those on the surface of commercially available γ-Al₂O₃ (A-64). The synthesized nanopowders can thus be used as effective supports of acid catalysts.