Experimental and analytical studies on the prediction of forming limit diagrams

Metal forming processes are widely used in industrial productions, automobile bodies, food industries, oil refineries, and liquid and gas transmission systems. Analyzing these processes is very important to reduce wastes and optimize the processes. Study of some main factors such as physical and mechanical properties of material and its formability, die geometry, die material, lubrication and pressing speed has been the topic of many research projects. In this paper, forming limit diagrams (FLDs) for LC and ULC steels and the effect of different parameters like the work-hardening exponent, n, and the plastic strain ratio, r, on these diagrams have been evaluated and simulated using ABAQUS/Standard. In this case, Hill’s quadratic anisotropy function is assumed to be the yield function and the Atkins criterion is used as the failure criterion.     

An experimental and theoretical study on the prediction of forming limit diagrams using new BBC yield criteria and M–K analysis

In the present paper, a comprehensive study on the prediction of forming limit diagrams (FLDs) for an AA3003-O aluminium alloy is developed theoretically and experimentally. For obtaining the experimental FLDs, an out-of-plane formability test was performed based on the technique proposed by Ozturk and Lee [F. Ozturk, D. Lee, J. Mater. Process. Technol. 170 (2005) 247–253]. The classical Marciniak–Kuczynski (M–K) model and some new yield criteria are utilized to simulate the necking phenomenon and calculate the limit strains theoretically. The employed yield functions are: the BBC2000, BBC2002, and BBC2003 yield criteria proposed by Banabic et al. [D. Banabic, S.D. Comsa, T. Balan, in: Proceedings of the Cold Metal Forming 2000 Conference, Cluj-Napoca, 2000, p. 217; D. Banabic, T. Kuwabara, T. Balan, D.S. Comsa, D. Julean, Int. J. Mech. Sci. 45 (2003) 797–811; D. Banabic, H. Aretz, D.S. Comsa, L. Paraianu, Int. J. Plast. 21 (2005) 493–512]. To calibrate and determine each particular coefficients of performed yield functions an appropriate error-function is defined and minimized by a Newton algorithm. To compare the calculated yield stresses and r-values with experimental data a relative root mean square deviation method presented by Leacock [Alan G. Leacock, J. Mech. Phys. Solids 54 (2006) 425–444] is used. Work-hardening effects on the FLD are analyzed by using Swift and Voce hardening laws. The effect of yield surface on the prediction of numerical FLDs and the number of experimental anisotropy parameters on the accuracy of yield functions are also studied.     

Thermoplastic composite from innovative flat knitted 3D multi-layer spacer fabric using hybrid yarn and the study of 2D mechanical properties

Due to their improved mechanical properties, 3D multi-layer spacer fabrics could be used for lightweight applications such as textile-based sandwich preforms. Modern flat knitting machines using high performance yarns are able to knit complex 3D multi-layer spacer fabrics consisting of individual surface and connecting layers. This paper reports on the development of 3D flat knitted spacer fabric for 3D thermoplastic composites using hybrid yarns made of glass (GF) and polypropylene (PP) filaments. Moreover, mechanical properties of reinforcement yarns, 2D knit fabrics and 2D composites manufactured using various integration methods of reinforcement yarns were also studied. The integration of reinforcement yarns as biaxial inlays (warp and weft yarns) is found to be the best solution for knitting, whereas the tuck stitches show optimal results.     

A comparative study of the atomic and electronic structure of F centers in ferroelectric KNbO3: Ab initio and semi-empirical calculations

The linear muffin-tin-orbital method combined with density functional theory (in a local density approximation) and the semi-empirical method of the intermediate neglect of the differential overlap (INDO) based on the Hartree-Fock formalism are used for the supercell study of the F centers (O vacancy with two electrons) in cubic and orthorhombic ferroelectric KNbO₃ crystals. The two electrons are found to be considerably delocalized even in the ground state of the defect. Their wave functions extend over the two Nb atoms closest to the O vacancy and over other nearby atoms. Thus, the F center in KNbO₃ resembles much more electron defects in the partly covalent SiO₂ crystal (the so-called E₁′ center) rather than usual F centers in ionic crystals like MgO and alkali halides. This covalency is confirmed by the analysis of the electronic density distribution. The absorption energies were calculated by means of the INDO method using the ΔSCF scheme after a relaxation of atoms surrounding the F center. For the orthorhombic phase three absoprtion bands are predicted, the first one is close to that observed experimentally under electron irradiaton.     

Scientific and methodological foundations for determining the angular motion of a rocket using a four-lined gyrostabilized platform

The present article considers models of four-lined gyrostabilized platforms (GSP) and alternative positions of the measuring elements that make it possible to create inertial reference systems on gyrostabilized platforms and construct relationships between the coordinate systems of the platform. The models also make it possible to calculate the angular relocation of a rocket in inertial space with the use of readings of the turning angle sensors of the GSP gimbals. __________ Translated from Izmeritel’naya Tekhnika, No. 12, pp. 21–25, December, 2007.     

Controlled interactions between silanol groups at the surface of sepiolite and an acrylate matrix: Consequences on the thermal and mechanical properties

Elastomer filled with fibrous clay (sepiolite) was manufactured using a hydrophilic elastomer matrix, poly 2-hydroxyethylacrylate (PHEA). The surface silanol groups located onto the channel sides of the sepiolite were functionalized with both octyltrimethoxysilane (OTMS) and 3-methacryloxypropyltrimethoxysilane (MPTMS), which form covalent bonds with the mineral surface and modify their properties. After the grafting of OTMS, PHEA is in contact with a non-polar chain, which prevents matrix–filler interactions. After the grafting of MPTMS, covalent bonds are formed between the acrylate groups of PHEA and MPTMS, which increase the matrix–filler interactions. After functionalization, there is no change in the structural and zeolitic water of the sepiolite which conserves its hydrophilic character. So, an equivalent distribution of the pristine and modified sepiolite is detected in the elastomeric matrices on transmission electron microscopy views of ultramicrotome cuts. The elastomeric macroscopic behavior is therefore related to the PHEA–sepiolite interactions. We show that the stronger the host–matrix interactions, the more important is the reinforcement effect. A direct relation between the interaction strength and the improvement of the mechanical properties was established. The control of the nature, quantity, and localization of the molecules grafted on the sepiolite surface allows us to manage the mechanical properties.     

The degradation of 1,2,4-trichlorobenzene using synthesized Co3O4 and the hypothesized mechanism

Co₃O₄ was synthesized with cabbage-like, plate-like and sphere-like morphologies. The effect of different morphologies on the degradation of 1,2,4-trichlorobenzene (1,2,4-TrCB) was evaluated, and the cabbage-like Co₃O₄ exhibited the highest reactivity. The degradation of 1,2,4-TrCB on the cabbage-like Co₃O₄ is hypothesized to act competitively via hydrodechlorination and oxygen-attacking pathways. By the hydrodechlorination pathway, 1,2,4-TrCB is successively dechlorinated into the three dichlorobenzenes (DCBs) and then monochlorobenzene (MCB). The yield of the DCBs was in the order of p-DCB > m-DCB > o-DCB, which can be explained by the calculated C-Cl bond dissociation energies in 1,2,4-TrCB and DCBs. Derivatization and electron spin resonance experiments identified that lattice oxygen and superoxide anions may take part in the oxidation pathway. The lattice oxygen initiated a partial oxidation of 1,2,4-TrCB, leading to the formation of chlorinated phenols. The superoxide anions caused ring-cracking oxidation of 1,2,4-TrCB, possibly producing some low-molecular-weight products, thus explaining a mass imbalance in the chlorine atoms and total organic carbon.     

Thermal diffusivity and conductivity of Li2ZrO3 using the modulated electron beam technique

Thermal diffusivity and thermal conductivity of three Li₂ZrO₃ specimens with two different density values, 82.6 and 87% theoretical density, have been measured between 350 and 900°C. The modulated electron beam thermal diffusivity method was used. Heating the specimens above some 850°C but below 900°C results in a reversible increase in both the diffusivity and the conductivity. When heating to higher temperatures generally still higher increases are noticed but measurements become rapidly unstable and irreversible.     

Modelling of 3D response pulse at the bottom of asphalt layer using a novel function and artificial neural network

Fatigue life of asphalt mixes in laboratory tests is commonly determined by applying a haversine or sinusoidal load with a specific frequency. However, the frequency (time duration) and shape of horizontal tensile stress and strain pulses at the bottom the asphalt layer depend on pavement design (thickness and stiffness of layers) and loading specifications (speed and contact radius). The first objective of this paper is to introduce a novel function for a more realistic representation of 3D response (stress and strain pulses in longitudinal, transverse and vertical directions) at the bottom of the asphalt layer. The second objective is to establish a framework for determination of magnitude and shape of 3D response pulse at the bottom of the asphalt layer using artificial neural network. This framework enables designers to predict the shape and magnitude of stress and strain pulses in three directions based on some parameters related to pavement structure and loading specifications.     

Synthesis and characterization of β type solid solution in the binary system of Bi2O3-Eu2O3

We have investigated Bi₂O₃-Eu₂O₃ binary system by doping with Eu₂O₃ in the composition range from 1 to 10 mole% via solid state reactions and succeeded to stabilize β-Bi₂O₃ phase which is metastable when pure. Stability of β-Bi₂O₃ polymorph was influenced by heat treatment temperature. Tetragonal type solid solution was obtained in 3–6 mole% addition range when annealed at 750°C and the range was 2–7 mole% when annealed at 800°C. We have also carried out investigations on lattice parameters, microstructural properties and elemental compositions of this β type solid solution for each doping ratio. Lattice parameters increased with amount of Eu₂O₃ addition. Our experimental observations strongly suggested that oxygen deficiency type non-stoichiometry is present in doped β type solid solutions.     

Spatial regression analysis of NOx and O3 concentrations in Madrid urban area using Radial Basis Function networks

This paper discusses the performance of Radial Basis Function networks (RBF) in a problem of spatial regression of pollutants in Madrid. Specifically, the spatial regression of NO_x and O₃ is considered, in such a way that, starting from a set of measuring points provided by the air quality monitoring network of Madrid, the complete surface of the pollutants in the city is obtained. This pollutant surface can be used as an initial step for modeling intra-urban pollution using land-use regression techniques for example. Also, different works has used a pollutant surface to study the patterns of pollution in different cities in the world and also to establish their air monitoring networks under mathematical criteria. The paper is focussed in analyzing the performance of RBF networks to obtain this first pollutant surface, so different RBF training algorithms are tested in this paper. Specifically, evolutionary-based RBF training algorithms are described, and compared with classical training algorithms for RBF networks with Gaussian kernels. The inclusion of meteorological variables in the RBF networks are also discussed in the paper. The experimental part of the article studies real results of the application of RBF networks to obtain a first pollutant surface of NO_x and O₃, using the data of the air pollution monitoring network of Madrid and the meteorological network of the city.     

Influence of benzene on the Ni3Fe nanocrystalline compound formation by wet mechanical alloying: An investigation combining DSC,X-ray diffraction,mass and IR spectrometries

Nanocrystalline Ni₃Fe powders were obtained via wet mechanical alloying using benzene as surfactant. The differential scanning calorimetry (DSC) measurements showed the presence of an exothermic peak which does not correspond to any phase transformation or phase formation as was proved by X-ray diffraction measurements. The exothermic peak was observed neither for the dry milled samples nor for the wet milled and subsequently annealed powders at 350 °C for 4 h. The infra-red (IR) spectra registered for the wet milled samples showed a series of vibration bands corresponding to C₆H₆ and also to a series of fragments resulting from benzene decomposition. The results obtained by IR investigation were confirmed by thermogravimetry and mass spectrometry (TG + MS) investigations. The main fragments resulting from the benzene decomposition on the surface of the nanocrystalline Ni₃Fe powders are: CO₂, CO and C. The evolution of the particle size distribution versus the milling time has been determined for the wet mechanical milling process of nanocrystalline Ni₃Fe powders. The DSC analysis reveals a displacement of the exothermic peak onset towards lower temperatures and an increase of the surface of this peak attributed to the changes in the particles specific surface and to the quantity of benzene added in the milling experiments.     

Calculation of J-integrals using experimental and numerical data: Influences of ratio (a/W) and the 3D structure

Contrary to J-integral values calculated from the 2D numerical model, calculated J-integrals [1] from 3D specimen in the numerical and experimental cases are not very close with J-integral used in the literature and two distinct points are present. The first one is according to (a/W) and can be reduced, when this ratio is inferior to 0.2. The second is a structure problem and can be explain by local three-dimensional effects surrounding the crack tip. Two applications using polymer materials for large and minor deformations are experimented. A grid method is used to experimentally determine the in-plane displacement fields around a crack tip in a Single-Edge-Notch (SEN) tensile polyurethane and PMMA specimens. This indirect method composed of experimental in-plane displacement fields and of two theoretical formulations, allows the experimental J-integral to be determined and the results obtained by the numerical simulations to be confirmed.     

Novels patterns of hydration and new compounds in the ternary system of CaO-Al2O3-P2O5

 The patterns of hydrating and solidifying with the compositional variation of phosphorus-rich, phosphorus-calcium-rich and aluminum-calcium rich regions in ternary system CaO-Al₂O₃-P₂O₅ has been studied in detail, and two new ternary compounds L and H have been synthesized here. The results indicate that the region of 48–56% P₂O₅ doesn’t present cementitiousness, which contains mainly crystal phases of β-C₂P(2CaO·P₂O₅), α-C₃P(3CaO·P₂O₅) and AlPO₄; the phosphorus-calcium-rich region of 21–35% P₂O₅ exhibits substantial cementitiousness, which contains mainly crystal phase of α-C₃P and certain amount of CA(CaO·Al₂O₃) and new phases L/H; and the aluminum-calcium-rich region of 8–18% P₂O₅ is full of promise for cementitiousness. It contains mainly new crystal phase L and certain amount of α-C₃P and CA. The hydration and solidification mechanisms have been preliminarily analyzed by means of XRD, XPS and DTA. It appears that crystal phase CA might hydrate directly to the stable phase of C₃A·6H₂O in the phosphorus-rich case of 21–35% P₂O₅; new phase H has the behavior of rapid setting; and L, being a dominant phase, can prevent cement pastes from significant strength loss in long curing cycles. Received: 12 March 1998 / Accepted: 29 July 1998     

V2O5-B2O3-TeO2体系低熔点玻璃形成规律及特性

较详细地研究了V2O5-B2O3-TeO2三元体系的熔化温度、冷却熔体的相组成及玻璃形成规律;并测试分析了V2O5-B2O3-TeO2三元体系玻璃的热性能和特征温度。结果表明,V2O5-B2O3-TeO2三元体系具有较低的熔化温度,存在3个不同的结晶区域和一个较广阔的玻璃形成区,其玻璃形成区域为:V2O50%～70%、B2O30%～30%、TeO230%～100%(均为摩尔分数);V2O5-B2O3-TeO2系玻璃具有较低的熔化温度和封接温度,是无铅低温封接玻璃的理想体系之一。     

Li_(1+x)Ti_(2-x)Cr_xP_3O_(12)系统的相关系与电性

研究了 Li_(1+x)Ti_(2-x)Cr_xP_3O_(12)系统的相组成与电性的关系。结果表明,Cr~(3+)能取代 LiTi_2P_3O_(12)中的Ti~(4+)生成固溶体,直至 x=0.8。在固溶体范围内,电导率随 x 的增加不断升高,至 x=0.8时达到极大。此时在室温和300℃的电导率分别为2.4×10~(-4)和4.8×10~(-2)S/cm,电子迁移数在10~(-4)数量级,分解电压为1.8V。对所得结果从结晶化学角度进行了讨论。     

The influence of the molar ratio of Al2O3 to Y2O3 on sintering behavior and the mechanical properties of a SiC–Al2O3–Y2O3 ceramic composite

The influence of the molar ratio of Al₂O₃ to Y₂O₃ (i.e. M_Al2O3/M_Y2O3) on sintering densification, microstructure and the mechanical properties of a SiC–Al₂O₃–Y₂O₃ ceramic composite were studied. It was shown that the optimal value of M_Al2O3/M_Y2O3 was 3/2, not 5/3, which is customarily considered the optimal molar ratio for the formation of YAG (Y₃Al₅O₁₂) phase. When M_Al2O3/M_Y2O3 is 5/3, materials existed in two phases of YAG and very little YAM phases. The sintering mechanism of the solid phase occurred at 1850 °C. When M_Al2O3/M_Y2O3 was 3/2, materials existed in the two phases YAG (Y₃Al₅O₁₂) and YAM (Y₄Al₂O₉). The formation of the low melting point eutectic liquid phase (YAG + YAM) increased sintering densification. Flexure strength, hardness and relative density were all higher.