Adaptive inversion database for electromagnetic nondestructive evaluation

A novel method is proposed for generating an inversion database, by which the defect reconstruction problem of eddy-current testing can be solved. The database realizes a finite approximation of the forward operator that maps defect configurations to output signals. This approximation is achieved by interpolation on an n-dimensional simplex mesh, where n is the number of defect model parameters considered for the inversion. The inversion can be traced back to a nearest point search. The key element of the method is that the mesh supporting the database is optimized to fit the given testing experiment. On one hand, this feature allows the qualification of the inversion results. On the other hand, the mesh structure of the optimized database provides meta-information about the inverse problem, including the capabilities of the testing experiment and the suitability of the applied defect model among others. Some interpolation and meshing issues are discussed as well, and an application example is presented in the paper.     

Cobalt- and copper-substitution effects on thermal stabilities and hydriding properties of amorphous MgNi

Amorphous (a-)Mg(Ni_1−xT_x) with T=Co and Cu were formed by mechanical alloying in the composition range x=0–0.5. The crystallization temperatures increase/decrease by Co/Cu substitution, while the enthalpies of amorphous formation are little changed by substitution. On the other hand, the p–c isotherms indicate that the hydrogen-site energies become partially unstable with substitution. The relation between the enthalpy of amorphous alloy formation and subsequent hydride formation is discussed quantitatively on the basis of thermal analysis and the rule of reversed stability.     

A three-component strain gage dynamometer for grinding and polishing force measurement

The design of a strain gage dynamometer to measure three-dimensional grinding forces during surface finishing of molds and dies is presented in this article. The dynamometer is composed of four measuring blocks to which strain gages are attached. The measuring blocks in this study were designed so that when strain gages are attached at particular places, the blocks deform in such a way that forces in the x, y, and z directions can be separated with little interaction. This behavior was confirmed with finite-element results, and static calibrations performed on the measuring blocks further verified this behavior. In this study, the dynamometer is used to measure grinding forces in a surface-finishing system with a hand grinder mounted on a spindle of a machining center.     

Microstructure and corrosion resistance of molybdenum and aluminum coatings thermally sprayed on 7075-T6 aluminum alloy

Pitting corrosion upon 7075-T6 high strength aluminum alloy, often associated with cathodic intermetallic particles decreases its fatigue life by a factor of about 6 to 8. In order to improve the corrosion resistance of this alloy, arc spray coatings of molybdenum and aluminum are applied. The open circuit potential and potentiodynamic polarization measurements made in 3.5% NaCl naturally aerated solution reveal that the molybdenum coating, which has an excellent hardness, shifts the 7075-T6 corrosion potential (E _corr) to noble values and increases slightly the corrosion current density (i _corr). On the contrary, when the aluminum coating alloy is applied, both E _corr and i _corr are shifted to better values. The increase of i _corr of the alloy when molybdenum coating is applied can be attributed to the high porosity present into the coating. On the other hand, microstructure observations of the aluminum coating reveal a small porosity, which helps the formation of passive oxide film that protects the coating against a further corrosion.     

Physical and Magnetic Properties of Calcium-Substituted Li-Zn Ferrite

The effect of Ca-substitution on the physical and magnetic properties of Li_0.3-0.5x Zn_0.4Ca _x Fe_2.3-0.5x O₄ ferrites (x = 0.0, 0.01, 0.02, 0.03, and 0.05), prepared by the standard ceramic method, has been studied. It is found that the saturation magnetization increases up to x = 0.01 and then it decreases. On the other hand, the initial permeability decreased while the Curie temperature remained almost constant with increasing x. The coercivity and remanence ratio increased with increasing x. A. A. Sattar is on leave from Physics Department, Faculty of Science, Ain Shams University, Cairo, Egypt     

Strength and fracture properties of undermatched joints under dynamic loading study of dynamic deformation and fracture properties of welded joints with strength heterogeneity (Report 2)

Microstructure development in welding material containing Ti and B has been in situ observed by using laser scanning confocal microscopy, with various cooling rates. The samples with different aluminum contents were prepared for the observation. In the sample with low Al/O ratio (0.48–0.73), an acicular ferrite microstructure transforming from intragranular nucleation site was in situ observed. On the other hand, with high Al/O ratio, the bainite microstructure originating from grain boundary of austenite was in situ observed. The transformation temperature decreased with increasing aluminum content. It was clear that the microstructure difference was due to the different inclusion in the matrix. Based on those observations, the chemical composition, cooling rate and microstructure were systematically related and the microstructural developments were summarized as a CCT diagram.     

Magnetooptical sensors using in-plane biased garnet films supporting domains

Rare-earth iron garnet films are currently used as magnetooptical indicator films for visualization of magnetic leakage fields in nondestructive testing. For gray scale imaging in-plane magnetized films are used yielding a high spatial resolution. On the other hand, garnet films supporting magnetic domains can be prepared having a very high sensitivity, while their resolution is limited by the size of the domains. This behavior can be improved considerably by applying a bias induction B in the plane of the sensor film. Just above the collapse-induction B_,coll the in-plane magnetized film offers a high spatial resolution with still high sensitivity. Experiments demonstrate a clear improvement of the quality of the magnetooptical imaging. The experimental results are in agreement with calculations.     

The ‘Postmodern Mind’: Hybrid Models of Cognition

In the debate between connectionism and symbolic artificial intelligence (AI) the ‘ecumenical’ stance, which accepts both approaches as valid for modeling cognition, is getting more and more attention. I will characterize here a specific instance of this stance, the postmodern stance, which has its roots in postmodern philosophy. The main principles underlying this stance are: clear differentiation between heterogeneous alternatives, search for transitions between alternatives, and exploitation and study of these transitions in hybrid models. Differentiation between connectionism and symbolic AI reveals the complementary relationship of the two approaches. These complementarities will be used to define transitions between the approaches, which in turn are used to propose possible integrations of the two in hybrid symbolic-connectionist systems. Three such systems will be described and evaluated with respect to their explanatory power as models of cognition. The evaluation shows that hybrid models can better account for transitions between animal and cultural parts of cognition than either connectionist or symbolic approaches do. Hybridity will then also be demonstrated for models on the biological and psychological level. At the end I will speculate that cognitive science in the future might develop towards an ecology of mind offering a more hybrid and multi-perspective view on cognitive phenomena than it does now.     

Morphological development of oxide-sulfide scales on iron and iron-manganese alloys

Pure iron and alloys containing 2, 15, 25, and 50 wt. % manganese have been reacted at 1073 K in controlled gas atmospheres of SO ₂-CO ₂-CO-N ₂.Equilibrium gas compositions were such that (1) FeS was stable but not FeO, or (2) both FeS and FeO were stable, or (3) FeO was stable but not FeS; in all cases, both MnS and MnO were stable. Under all reaction conditions, pure iron corroded to produce both sulfide and oxide. The resultant scale morphologies were consistent with local solid-gas equilibrium for the case in which both oxide and sulfide were stable but in the other cases indicated that equilibrium was not achieved and that direct reaction with SO ₂ (g) was responsible for corrosion. Additions of manganese did not greatly alter the scale morphologies. Under reaction conditions that were oxidizing and sulfidizing, very high levels of manganese were required to reduce the corrosion rate. On the other hand, relatively low levels had a beneficial effect both when FeO but not FeS was thermodynamically stable and similarly when FeS but not FeO was stable.     

超声冲击处理对灰铸铁焊接冷裂纹影响

采用HT150,以焊接冷裂纹三要素中的拘束应力和淬硬组织因素为研究方向,用评定铸铁冷裂纹敏感性的直Y形坡口焊接裂纹试验法,研究了超声冲击处理对焊接冷裂纹的影响.结果表明,焊后通过对焊缝进行全覆盖超声冲击,一方面可以大幅度改善焊接结构的残余应力,经超声冲击处理后的试样焊缝测量点的残余应力R1分别为-53,-57MPa,R2分别为-37,-80MPa;另一方面可以加速焊缝石墨球化过程,消除半熔化区白口组织.因此焊后合理的超声冲击处理能够从拘束应力和淬硬组织两方面抑制焊接结构冷裂纹的产生.     

Microstructure and corrosion resistance of radial friction welded supermartensitic stainless steels

In this work, supermartensitic stainless steel pipes were radial friction (RF) welded and their corrosion behaviours were studied based on potentiodynamic polarisation and double-loop electrochemical potentiokinetic reactivation tests. Measurements were performed on samples taken from the base metal (BM), weld interface and consumable ring (CR) of the RF weldment. The corrosion properties are discussed in terms of their resulting metallurgical microstructure. The precipitation of Cr carbides that takes place during the tempering treatment induces a substantial Cr depletion value (I_r/I_a = 54.22%). On the other hand, CR and weld interface regions, which had their microstructure transformed and their Cr carbide precipitates redissolved by the RF welding thermomechanical cycle, present a low level of Cr depletion (I_r/I_a < 1%). The AC microstructure, which is composed of a mixture of virgin martensite and stable retained austenite, presents an increase in pitting corrosion resistance compared to the tempered structure of the BM region. It was also observed that the δ-ferrite decreases the pitting resistance of the weld interface region.     

On Combining Artificial Neural Nets

This paper reviews research on combining artificial neural nets, and provides an overview of, and an introduction to, the papers contained in this special issue, and its companion (Connection Science, 9, 1). Two main approaches, ensemble-based, and modular, are identified and considered. An ensemble, or committee, is made up of a set of nets, each of which is a general function approximator. The members of the ensemble are combined in order to obtain better generalization performance than would be achieved by any of the individual nets. The main issues considered here under the heading of ensemble-based approaches are a how to combine the outputs of the ensemble members, b how to create candidate ensemble members and c which methods lead to the most effective ensembles? Under the heading of modular approaches, we begin by considering a divide-and-conquer approach by which a function is automatically decomposed into a number of subfunctions which are treated by specialist modules. Other modular approaches are also identified and considered, for while the divide-and-conquer approach is designed to improve performance, the term modularity can be given a wider interpretation. The broadly defined topic of modularity includes the explicit decomposition of a task based on the designer's understanding, and the exploitation of specialist modules in order to accomplish tasks which could not be performed by a monolithic net.     

To Journal of Phase Equilibria and Diffusion Phase Relationship of the BaO-ZrO<Subscript>2</Subscript>-YO<Subscript>1.5</Subscript> System at 1500 and 1600 °C

Phase relationship of a BaO-ZrO₂-YO_1.5 system at 1500 and 1600 °C was examined in order to determine whether a phase separation at the composition of 15% yttrium-doped barium zirconate exists. According to a pseudoternary phase diagram of the BaO-ZrO₂-YO_1.5 system established by this work, the solubility of yttria into cubic barium zirconate at 1600 °C is 0.25 in a mole fraction of yttria (X_\textYO1.5 ) (X_{{{\text{YO}}_{1.5} }} ) . Thus, we confirmed that there is no phase separation at the composition of 15% yttrium-doped barium zirconate at 1600 °C. On the other hand, at 1500 °C, there might be a phase separation at the composition of 15% yttrium-doped barium zirconate into yttrium-doped barium zirconate where quite small amount of yttrium is doped and a new phase whose composition is close to reported BZ(II) phase.     

Control of graphite formation in solidification of white cast iron

Abstract

Graphite formation should be strictly suppressed for the most abrasion resistant white cast irons, since austenite (γ)+graphite eutectic structure shows lower hardness and selectively wears thus deteriorates the abrasion resistance even though the austenite transform to hard phase such as martensite. On the other hand, a small amount of fine graphite is desired to distribute in rolls for hot steel mills to suppress the scoring. However, strong carbide formers such as Cr, V, Nb have been increasingly added to rolls, in order to crystallise more harder carbides. As γ+carbide eutectic grows, the residual liquid among eutectic cells becomes poor in carbide formers and rich in elements which promote graphite formation. Therefore an appropriate alloy design is essential for the hot steel milling rolls. In this study, the graphite formation mechanisms are discussed for chromium cast iron, high speed steel type cast iron and Ni hard type cast iron.     

Digital terrain modelling and industrial surface metrology — converging crafts

Quantitative characterisation of surface form, increasingly from digital 3-D height data, is cross-disciplinary and can be applied at any scale. Thus, separation of industrial-surface metrology from its Earth-science counterpart, (digital) terrain modelling, is artificial. Their growing convergence presents an opportunity to develop in surface morphometry a unified approach to surface representation. This paper introduces terrain modelling and compares it with metrology, noting their differences and similarities. Examples of potential redundancy among parameters illustrate one of the many issues common to both disciplines.     

Effect of fine dispersoids and anisotropic nature of β-Sn on thermal fatigue properties of flip chips connected by Sn–xAg–0·5Cu (x: 1, 3 and 4 mass-%) lead free solders

Abstract

A significance of two factors, fine dispersoids in a solder and the anisotropic nature of β-Sn, on thermal fatigue endurance is discussed using flip chips connected by Sn–xAg–0·5Cu (x: 1, 3 and 4 mass-%) lead free solders, together with Sn and Sn–1·2Ag–0·5Cu–0·05Ni, for comparison. Both 3Ag and 4Ag showed better thermal fatigue properties than Sn and 1Ag, and a thermal fatigue life of 1·2Ag with Ni was close to that of 3Ag despite of its low silver content. Microstructures of the solders before thermal fatigue tests can be classified into a single crystal-like and a fine grain type. However, this classification, which affects the amount of thermal strain by the anisotropic nature of β-Sn, cannot accurately describe thermal fatigue lives observed. On the other hand, Vickers microhardness of the solders, which was resulted from fine dispersoids, showed good relationship with observed thermal fatigue endurance.     

Influence of activated carbon on crevice corrosion in adsorption tower of advanced liquid processing system

ABSTRACT

The adsorption tower made of type 316L stainless steel (SS) in Multi-nuclide Removal Equipment (Advanced Liquid Processing System) which uses Ag-impregnated activated carbon (Ag AC) as an adsorbent experienced crevice corrosion. The influence of Ag AC on the crevice corrosion susceptibility and E_sp of 316L SS was investigated by performing electrochemical experiments. Crevice corrosion was observed in the specimen in contact with the Ag AC. On the other hand, there was no crevice corrosion without the Ag AC in both pH 7.4 and pH 12 solutions. Clear ennoblement of spontaneous potential (E_sp) by in contact with activated carbon was observed and that was clearly higher than the repassivation potential for crevice corrosion (E_R,CREV). Thus, the presence of the AC notably increased E_sp of 316L SS and this resulted in increased crevice corrosion susceptibility by the galvanic effect.

This paper is part of a supplementary issue from the 17th Asia-Pacific Corrosion Control Conference (APCCC-17).     

Optimising the AWJ cutting process of ductile materials using nozzle oscillation technique

Striations and roughness on workpiece surfaces produced by abrasive waterjet (AWJ) have been the most persistent problems that stand in the way of wider applications of the technology in industry. This paper presents the experimental investigation on the impact of using nozzle oscillation cutting technique in minimising or reducing these AWJ cut surface irregularities. The technique was used for cutting ductile materials, i.e. mild steel and aluminium, at various traverse speeds, oscillation angles and frequencies of oscillation. The results show that by oscillating the nozzle during cutting, the improvement in surface finish as measured by centre-line average R_a can be obtained by as much as 30%.     

Improving the accuracy of calculating the conditions of mechanized surfacing

For some years now, the light engineering sector has been in search of welding and/or joining technologies allowing high-speed processing at low temperatures. This way, damage to galvanized coating, for example in the case of steels, could be avoided or significantly reduced.

Damage to the galvanized coating represents an outwardly visible phenomenon that can have a negative impact on the component's corrosion resistance.

On the other hand, from the metallurgical viewpoint, controlling heat input represents an important way to solve the problems associated with heat joining of metals with incomplete solid-state solubility. The formation of fragile intermetallic phases during cooling, for example, occurs with aluminium/steel or aluminium/titanium. The process and the correct choice of filler materials are key points for the success of the joining method. In the case of the combination of aluminium and steel, zinc represents a suitable filler material, for example for brazing. The melting temperature is around 420°C and the wettability, with regard to galvanized steel, is favoured by the zinc layer, while on the aluminium part, it is possible to avoid the use of flux, thanks to the activating action of the voltaic arc. However, the low melting and vaporization temperatures of zinc make even ‘short arc’ processing rather difficult.

Only new developments in electrical sources for welding, and in particular new processes, offer the possibility of reducing the heat input by modifying the ‘short arc’ process. The difficulties described are also valid for the combination of titanium and aluminium, and are associated with the formation of phases such as Ti _x A1 _y . Again in this case, this paper will present a strategy for joining sheets less than 2 mm thick.

In the past years, an increasing number of strategies to join zinc-coated steels can be observed. Brazing represents a profitable way to join zinc-coated steels at low temperatures, reducing or avoiding zinc evaporation.

In order to completely avoid damaging zinc coating, the set of ZnAl-fìllers was already investigated for laser brazing of zinc-coated steels as well as for joining steel with aluminium.

Furthermore, thanks to new developments in arc wire technology, ZnAl-electrodes can be used for MIG-brazing as well. In this case, the conventional short arc, which normally does not allow brazing with zinc wires as eruption-like evaporation occurs, is modified and controlled. The drop formation on the wire tip, the metal transfer, and the heat input can be controlled and modified very precisely, so that processing of filler material can be performed easily for thin sheets (till 0.8–1.5 mm) and at low-processing speed, below 0.3–0.4 m/min. The control of the heat input occurs due to abruptly reducing the current after short arc.

The disadvantages connected with a lower heat input in the base material are a restricted wetting behaviour of the zinc pool on the base material and the low-brazing speed due to a very high cooling rate. The focus of the presented investigation is the development of strategies, in order to enhance process conditions for brazing sheets of zinc-coated steels and aluminium.     

Feasibility of magneto-optic flaw visualization using thin garnet films

We investigate the feasibility of using rare-earth iron garnet films grown on (111)-oriented substrates as magneto-optic indicator films for the visualization of magnetic leakage fields in non-destructive evaluation. In most cases the leakage field of the defect has a strong component in the film plane. The influence of this in-plane dc magnetic field on the image formation is investigated. It is shown that the presence of a strong in-plane magnetic field allows one to extend the dynamic range of the out-of-plane field imposed by the uniaxial anisotropy field H_A. On the other hand, an in-plane field reduces the sensitivity. The guidelines for selecting parameters of magneto-optic indicator films are given.