Finite element simulation of wedge indentation

A finite element simulation of frictionless wedge indentation of a copper strip has been carried out under plane strain conditions. The problem was first modelled using an one-pass contact algorithm. The difficulties associated with using this method to model wedge indentation problems are explained. An alternative procedure which alleviates some of the problems associated with the one-pass contact algorithm is proposed for modelling frictionless wedge indentation. Also, a re-meshing procedure which has to be carried out when the distortion of the elements around the indenter becomes significant, is discussed. A sample problem involving indentation of a 4 mm copper strip by a rigid wedge indenter has been modelled and the results are compared with experimental and theoretical results.

ICADA: Intelligent computer aided defect analysis for castings

An intelligent computer aided defect analysis (ICADA) system, based on artificial intelligence techniques, has been developed to identify design, process or material parameters which could be responsible for the occurrence of defective castings in a manufacturing campaign. The data on defective castings for a particular time frame, which is an input to the ICADA system, has been analysed. It was observed that a large proportion, i.e. 50-80% of all the defective castings produced in a foundry, have two, three or four types of defects occurring above a threshold proportion, say 10%. Also, a large number of defect types are either not found at all or found in a very small proportion, with a threshold value below 2%. An important feature of the ICADA system is the recognition of this pattern in the analysis. Thirty casting defect types and a large number of causes numbering between 50 and 70 for each, as identified in the AFS analysis of casting defects-the standard reference source for a casting process-constituted the foundation for building the knowledge base. Scientific rationale underlying the formation of a defect during the casting process was identified and 38 metacauses were coded. Process, material and design parameters which contribute to the metacauses were systematically examined and 112 were identified as rootcauses. The interconnections between defects, metacauses and rootcauses were represented as a three tier structured graph and the handling of uncertainty in the occurrence of events such as defects, metacauses and rootcauses was achieved by Bayesian analysis. The hill climbing search technique, associated with forward reasoning, was employed to recognize one or several root causes.

Studies of moisture induced crosslinking in a novel vinyl ether maleic anhydride copolymer

A novel vinyl ether, 2,2-dimethyl-4-vinyioxymethyl-1,3-dioxol (DMVMD), that has a dimethyl ketal protected vicinal diol functionality was synthesizied from readily available starting materials, such as glycerol, acetone and acetylene. Copolymerisation of DMVMD with maleic anhydride (MAH) in various molar ratios was carried out using a free radical initiator. The composition of the copolymer was established by conductometric titration, and was found to be 1:1 irrespective of the monomer feed composition thus establishing its alternating nature. The copolymer formed clear free standing films upon solvent casting which became insoluble upon prolonged exposure to ambeint atmosphere. The insolubility is ascribed to moisture induced crosslinking. A plausible mechanism for the crosslinking involves the hydrolysis of some of the anhydride groups, followed by acid catalysed deketalization, and then by the reaction of the alcoholic groups, thus generated, with the residual anhydride to give ester crosslinks. This hypothesis was confirmed both by model reactions and insitu FT-IR studies.

The effect of preaging on the delayed aging of Al-7Si-0.3Mg

Al-7Si-0.3Mg is a commonly used commercial casting alloy because of its excellent castability combined with good mechanical properties. The post-casting heat treatment is one factor that affects the mechanical properties; during heat treat ment, a delay between solutionizing and artificial aging (delayed aging) leads to a reduction in hardness, ultimate tensile strength, and yield strength in the alloy. The investigation reported here was aimed at understanding the extent to which the harmful effect of delayed aging on hardness/strength can be nullified. The results obtained were explained using Pashley's kinetic model.

Microstructure and properties of squeeze cast Cu-carbon fibre metal matrix composite

There have been reported attempts of producing Cu based MMCs employing solid phase routes. In this work, copper was reinforced with short carbon fibres by pressure infiltration (squeeze casting) of molten metal through dry-separated carbon fibres. The resulting MMC's microstructure revealed uniform distribution of fibres with minimum amount of clustering. Hardness values are considerably higher than that for the unreinforced matrix. Addition of carbon fibres has brought in strain in the crystal lattice of the matrix, resulting in higher microhardness of MMCs and improved wear resistance. Tensile strength values of MMCs at elevated temperatures are considerably higher than that of the unreinforced matrix processed under identical conditions. (C) 1999 Kluwer Academic Publishers.

Icosahedral quasicrystalline and hexagonal approximant phases in the Al-Mn-Be alloy system

We report the formation of a primitive icosahedral quasicrystal with increased stability in Al Mn-Be alloys close to the compound Al15Mn13Be2, by melt spinning and injection casting. The crystal structure of this compound was unknown. We show that in as-cast as well as heat treated condition the intermetallic phase H1 has a hexagonal structure with lattice parameters a = 1.2295 run and c = 2.4634 nm. The space group is P6(3)/mmc In the injection-cast samples, the quasicrystal coexists with another closely related hexagonal phase H2 with a = 1.2295 nm and c = 1.2317 nm with a possible space group of P6/mmm. This phase exhibits specific orientation relationships with the icosahedral quasicrystal given by [0001](hex)//2f(QC) and [01 (1) over bar0](hex)//5f(QC) where 2f(QC) and 5f(QC) represent twofold and fivefold axes respectively. Electron diffraction patterns from both phases exhibit a close resemblance to the quasicrystalline phase. It is shown that the H1 phase is closely related to mu-Al4Mn with the same e parameter while the a parameter is reduced by tau. Following Kreiner and Franzen, it is postulated that both structures (H1 and H2) can be understood by a simple hexagonal packing of I13 clusters.

Renewable surface electrodes based on dopamine functionalized exfoliated graphite: NADH oxidation and ethanol biosensing

Exfoliated graphite (EG) was modified by covalently attaching dopamine (DA) (3,4-dihydroxyphenethylamine) through amide linkages, using -COOH groups introduced on the EG surface. The modified material was characterized by FT-IR spectroscopy, Xray photoelectron spectroscopy and electrochemical techniques. Composites of DA modified EG dispersed in organically modified silicates were prepared by a sol-get process. Electrodes were fabricated by casting the composites in glass tubes. The sol-gel based electrodes were found to be active for the electrocatalytic oxidation of NADH and biosensing of ethanol in presence of NAD(+) and alcohol dehydrogenase enzyme. The modified composite electrodes were found to be stable for several months. The surface of the electrode could be renewed just by mechanically polishing the electrode using emery sheets. The modified EG was also pressed and restacked in the form of a pellet and the use of this material as a binderless bulk-modified electrode was also demonstrated. The performance of sol-gel derived composite EG electrodes with binderless bulk-modified EG electrodes was compared. (C) 2002 Elsevier Science B.V. All rights reserved.

Solid propellant binders

Solid, propellants are widely used in modern rockets and missiles. Although the history of solid rockets could be traced to the discovery of gunpowder over a thousand years ago, the technology could be perfected only by the later half of the 20(th) century. The failure of gunpowder rockets was largely due to the unknown consolidating technique of the powder composition. The emergence of large solid propellant motors had, to await the dawn of polymer. science and technology(S&T). Specific syntheses of functionally terminated polymers having cross-linking capability led to the emergence of casting technology of solid composite propellants. This review describes the various polymeric fuel/binder systems used or considered for use in solid,propellants. It includes a brief background, advantages, and shortcomings of the various systems, an account of the currently used binders and a critical survey of the advanced polymers envisaged for future usage. Special emphasis has been laid on recently synthesized polymers having N-N bonds in their structures, and-on the feasibility of developing smokeless propellants based on ammonium nitrate.

Grain Floatation During Equiaxed Solidification of an Al-Cu Alloy in a Side-Cooled Cavity: Part I-Experimental Studies

Experimental studies were performed to investigate the role and influence of grain movement on macrosegregation and microstructure evolution during equiaxed solidification. Casting experiments were performed with a grain-refined Al-Cu alloy in a rectangular sand mold. For the aluminum alloy studied, the equiaxed grains are lighter than the bulk melt and thus float up. Experiments were designed to investigate floatation phenomena of equiaxed grains in the presence of thermosolutal convection. Cooling curves were recorded at key locations in both the casting and the chill. Quantitative image analysis and spatial chemical analysis were performed on the solidified casting to observe the chemical and microstructural inhomogeneity created by the melt convection and solid floatation. Several notable features that can be attributed to grain movement were observed in temperature histories, macrosegregation patterns, and microstructures. In our experiments, the floatation of grains influences the thermal conditions and the overall flow direction in the casting cavity. In some cases, the induced flow resulting from the grain movement caused a flow reversal. This in turn influences the solidification direction, microstructure evolution, and the overall macrosegregation behavior.

Polymerization of pyrrole and processing of the resulting polypyrrole as blends with plasticised PVC

Polypyrrole was synthesized by chemical oxidation of pyrrole in water containing various sulphonic acids like toluene sulphonic acid (TSA), sulphosalicylic acid (SSA), and camphor sulphonic acid (CSA), as well as a combination of each sulphonic acid with sodium dodecyl benzene sulphonate (NaDBS) to investigate the effect of doping on conductivity, yield, and processability of the conducting polymer. Free-standing blend films of polypyrrole and plasticized polyvinyl chloride (PVC) were obtained by casting an homogeneous suspension of the two polymers in tetrahydrofuran. The maximum conductivity of the blend film is similar to 0.3 S/cm, corresponding to a weight fraction of 0.16 w/w polypyrrole. The blend film is semiconducting in the range 300-10 K. A TG-DTA scan indicates the blend film to be amorphous with a stepwise decomposition process similar to pristine PVC. The choice of a dual dopant system during synthesis and the plasticised polymer during subsequent processing were keys to obtaining homogeneous high-quality films. (C) 2001 John Wiley & Sons, Inc.

A note on surface water waves for finite depth in the presence of an ice-cover

A class of I boundary value problems involving propagation of two-dimensional surface water waves, associated with water of uniform finite depth, against a plane vertical wave maker is investigated under the assumption that the surface is covered by a thin sheet of ice. It is assumed that the ice-cover behaves like a thin isotropic elastic plate. Then the problems under consideration lead to those of solving the two-dimensional Laplace equation in a semi-infinite strip, under Neumann boundary conditions on the vertical boundary as well as on one of the horizontal boundaries, representing the bottom of the fluid region, and a condition involving upto fifth order derivatives of the unknown function on the top horizontal ice-covered boundary, along with the two appropriate edge-conditions, at the ice-covered corner, ensuring the uniqueness of the solutions. The mixed boundary value problems are solved completely, by exploiting the regularity property of the Fourier cosine transform.

An Improved Compact Compliant Mechanism for an External Pipe-Crawler

An external pipe-crawling device presented in this paper aids the inspection of pipes in hazardous environments and areas inaccessible to humans. The principal component of our design, which uses inchworm type motion, is a compliant ring mechanism actuated using shape memory alloy (SMA) wire. It was fabricated and tested and was reported in our earlier work. But this device had a drawback of low crawling speed (about 1 mm/min) owing to the delay in heating and cooling of the SMA strips in the linear actuation. Additionally, that design also had the difficulties of mounting on pipes with closed ends, large radial span, and the need for housing for electrical insulation and guiding of the SMA wire. In this paper we present a compact design that overcomes the difficulties of the earlier design. In particular, we present a compact compliant mechanism with two halves so as to enable mounting and un-mounting on any closed or open pipe. Another feature is the presence of insulation and guiding of the SMA wire without housing. This design results in a reduction of the radial span of the ring from 22 mm to 12 mm, and the stiffness of the mechanism and the SMA wire are matched. An SMA helical spring is to used in the place of an SMA strip to increase the crawling speed of the device. A microcontroller-based circuitry is also fitted to cyclically.activate the SMA wires and springs.

Microstructural evolution in liquid metal processed Al-alloy/SiCp composites

Al-Zn-Mg/SiCP composites processed by a liquid metal processing (stir casting) technique have been microstructurally characterised in the as-cast and extruded conditions. Uniform distribution of SiCP is observed with few defects, such as particle clusters, which are due to partial wetting and associated gas porosity. The constituent particles are associated with SiCP although their composition remains unaffected compared with the control alloy. Hot extrusion of the composite using a shear type die showed banding of particles in the extruded direction with 9 vol.% composite. Such defects however, are not predominant in 18% SiCP extruded composites. The presence Of Mg2Si is detected at the particle matrix interface as well as in the matrix.

Determination of solid fraction evolution during solidification of aluminum alloy in presence of linear electromagnetic stirring

In many industrial casting processes, knowledge of the solid fraction evolution during the solidification process is a key factor in determining the process parameters such as cooling rate, stirring intensity and in estimating the total solidification time. In the present work, a new method of estimating solid fraction is presented, which is based on calorimetric principles. In this method, the cooling curve data at each point in the melt, along with the thermal boundary conditions, are used to perform energy balance in the mould, from which solid fraction generation during any time interval can be estimated. This method is applied to the case of a rheocasting process, in which Al-Si alloy (A356 alloy) is solidified by stirring in a cylindrical mould placed in the annulus of a linear electromagnetic stirrer. The metal in the mould is simultaneously cooled and stirred to produce a cylindrical billet with non-dendritic globular microstructure. Temperature is measured at key locations in the mould to assess the various heat exchange processes prevalent in the mould and to monitor the solidification rate. The results obtained by energy balance method are compared with those by the conventional procedure of calculating solid fraction using the Schiel equation.

Coupled electro-mechanical response of an electroactive polymer cantilever structure and its application in energy harvesting

Ionic polymer-metal composites (IPMC), piezoelectric polymer composites and nematic elastomer composites are materials, which exhibit characteristics of both sensors and actuators. Large deformation and curvature are observed in these systems when electric potential is applied. Effects of geometric non-linearity due to the chargeinduced motion in these materials are poorly understood. In this paper, a coupled model for understanding the behavior of an ionic polymer beam undergoing large deformation and large curvature is presented. Maxwell's equations and charge transport equations are considered which couple the distribution of the ion concentration and the pressure gradient along length of a cantilever beam with interdigital electrodes. A nonlinear constitutive model is derived accounting for the visco-elasto-plastic behavior of these polymers and based on the hypothesis that the presence of electrical charge stretches/contracts bonds, which give rise to electrical field dependent softening/hardening. Polymer chain orientation in statistical sense plays a role on such softening or hardening. Elementary beam kinematics with large curvature is considered. A model for understanding the deformation due to electrostatic repulsion between asymmetrical charge distributions across the cross-sections is presented. Experimental evidence that Silver(Ag) nanoparticle coated IPMCs can be used for energy harvesting is reported. An IPMC strip is vibrated in different environments and the electric power against a resistive load is measured. The electrical power generated was observed to vary with the environment with maximum power being generated when the strip is in wet state. IPMC based energy harvesting systems have potential applications in tidal wave energy harvesting, residual environmental energy harvesting to power MEMS and NEMS devices.