Stress Intensity Factor using Finite Element Analysis in Rectangular Orthotropic Composite Annular Disk

The quadratic isoparametric elements which embody the inverse squareroot singularity were used to determine the stress intensity factor in an annular disk made of Boron-Epoxy composite material. The displacements and stresses were determined in a rectangular orthotropic composite annular disk using isoparametric finite elements. The singularity in the strain field was provided by means of 8-noded isoparametric elements (4-nodes at the four corners and four mid-side nodes each at l/4th distance from the edge). The results were obtained for various material properties and fibre orientation. The geometry of the annular disk was reported when subjected to a boundary radial and tangential. The r singularity was provided at the boundary of the circular hole and the rest of the annular disk was modelled with ordinary isoparametric elements. The apparent stress intensity factor (K/sub I/=) was computed from the stress data near the circular hole, when it was subjected to uniform tension. A curve was drawn for apparent stress intensity factor versus the distance from the crack edge and was extrapolated to r = 0, the actual stress intensity factor was found on the y-axis

Ultra fine chromite concentration using spiral concentrator

The conventional chromite beneficiation circuit utilises spiral concentrator for recovering chromite fines and as its efficiency decreases with respect to the decrease in particle size. Pilot scale studies have been performed to understand the effect of different process parameters which influence the separation of ultra fine chromite fines from a typical plant tailing. The process parameters of spiral concentrator such as feed rate (m3/hr), feed pulp density (% solids by weight) and splitter position (cm) are considered for the study. Splitter position has major influence on both grade and recovery of the concentrate fraction of spiral concentrator. Maximum grade of 48.54% Cr2O3 can be achieved in the concentrate fraction of spiral concentrator with 20.41% Cr2O3 recovery. Performance of spiral concentrator at different combination of process parameters was analysed with 3D surface plots

Studies on photochemically produced metal complexes with coordinated free radicals

In cobalt(III) amine complexes containing amino acids, photolysis in the chargetransfer bands leads to the formation of alkyl cobalt(III) complexes. Steady and flash photolysis of complexes [Co(LL)2X]2+ and [Co(LL)2Y2]+ (LL = ethylene diamine, polypyridyl or propylenediamine, X = amino acid and Y = nitro ligand) were carried out. Steady irradiation of [Co(bpy)2(gly)]2+ ion (bpy = bipyridine, gly = glycine) in aqueous medium (pH 1-7) produces the six-coordinated complex [Co(bpy)2(CH2NH2)]2+. Flash photolysis of the complex under identical conditions gives an alkyl complex. The alkyl complex formed in the case of [Co(bpy)2(gly)]2+ ion is stable and could be isolated; the corresponding alkyl complex formed from [Co(bpy)(en)(gly)]2+ ion leads to the labilisation of the ethylenediamine ligand in acidic solutions. Photolysis of the nitro complexes of the type [Co(en)2(NO2)2]+ ion in acetonitrile, methanol and ethanol produces ap-bonded transient nitro complex which reacts with molecular oxygen to give the mononuclear superoxo, dinuclear superoxo and dinuclear peroxo complexes in sequence. The formation of these products from the free radical coordinated cobalt(II) complex has been followed by the flash photolysis method and the rate constants have been determined. The details of the mechanisms are discussed

Effect of compliance and backlash on the output speed of a transmission system

Backlash is one of the most commonly encountered nonlinearities in drive systems employing gears or ball-screws and indicates the play between adjacent movable parts. Presence of backlash causes delays and oscillations and consequently gives rise to inaccuracies in the position and velocity of the machine. Coupled with this, if the drive system consists of compliant members, torsional oscillations may also occur. Though the presence of backlash may not be of utmost significance in the case of a general speed controlled drive system, web handling systems stand as a unique exception to this observation; any small change in the web speed causes large changes in the controlled tension and hence tight control of speed is an essential requirement in web handling systems. Also, it is of interest to know an estimate of the accuracy of speed achievable in a given closed-loop control system. This paper addresses the effects of compliance and backlash on the output speed of the transmission system.A model to include the effects of compliance and backlash is proposed under the assumption that the collisions due to backlash are sufficiently plastic to avoid bouncing. The proposed model considers the compliance (which may be either due to the elasticity of the shafts or belt in a belt-pulley transmission system) and backlash appearing in series in a drive system. In contrast to the classical backlash model which considers both input and output to the backlash as displacements, the proposed model considers (torque) force as input to the backlash and (angular velocity) velocity of the driven member as the output of the backlash. Thus, the proposed model does not assume that the load is stationary when contact is lost due to backlash width, i.e., momentum of the load is taken into account in the proposed model.From the proposed model, a bound on the speed error due to the presence of backlash is derived. To derive the bound on speed error due to backlash, two situations are considered: (i) closed-loop speed control system with a given backlash, and (ii) the same closed-loop system with no backlash. The difference between the outputs of these two systems indicates the error caused by the backlash and represents the achievable accuracy of the closed-loop system. Closed-loop experiments were conducted on a rectilinear system to obtain the error caused by different backlash widths. The bound obtained from the experimental results agrees with the theoretically computed bound.Mechanical and Aerospace Engineerin

Proton coupled electron transfer reaction of phenols with excited state ruthenium(II) - polypyridyl complexes

The reaction of phenols with the excited state, *[Ru(bpy)3]2+ (E0 = 0.76V) and *[Ru(H2dcbpy)3]2+, (dcbpy = 4,4'-dicarboxy-2,2'-bipyridine) (E0 = 1.55 V vs. SCE) complexes in CH3CN has been studied by luminescence quenching technique and the quenching is dynamic. The formation of phenoxyl radical as a transient is confirmed by its characteristic absorption at 400 nm. The kq value is highly sensitive to the change of pH of the medium and ΔG0 of the reaction. Based on the treatment of kq data in terms of energetics of the reaction and pH of the medium, proton coupled electron transfer (PCET) mechanism has been proposed for the reaction