Finite element analysis of moving contact in mechanically fastened joints

The Finite Element Method (FEM) has made a number of otherwise intractable problems solvable. An important aspect for achieving an economical and accurate solution through FEM is matching the formulation and the computational organisation to the problem. This was realised forcefully in the present case of the solution of a class of moving contact boundary value problems of fastener joints. This paper deals with the problem of changing contact at the pin-hole interface of a fastener joint. Due to moving contact, the stresses and displacements are nonlinear with load. This would, in general, need an interactive-incremental approach for solution. However, by posing the problem in an inverse way, a solution is sought for obtaining loads to suit given contact configuration. Numerical results are given for typical isotropic and composite plates with rigid pins. Two cases of loading are considered: (i) load applied only at the edges of the plate and (ii) load applied at the pin and reacted at a part of the edge of the plate. Load-contact relationships, compliance and stress-patterns are investigated. This paper clearly demonstrates the simplification achieved by a suitable formulation of the problem. The results are of significance to the design and analysis of fastener joints.

A new kinetic model for bulk polymerization of vinyl chloride based on two-phase hypothesis

A kinetic model has been developed for the bulk polymerization of vinyl chloride using Talamini's hypothesis of two-phase polymerization and a new concept of kinetic solubility which assumes that rapidly growing polymer chains have considerably greater solubility than the thermodynamic solubility of preformed polymer molecules of the same size and so can remain in solution even under thermodynamically unfavourable conditions. It is further assumed that this kinetic solubility is a function of chain length. The model yields a rate expression consistent with the experimental data for vinyl chloride bulk polymerization and moreover is able to explain several characteristic kinetic features of this system. Application of the model rate expression to the available rate data has yielded 2.36 × 108l mol−1 sec−1 for the termination rate constant in the polymer-rich phase; as expected, this value is smaller than that reported for homogenous polymerization by a factor of 10–30.

Interdiffusion and activation energy in Ti3Au phase with A15 crystal structure

The knowledge of diffusion parameters, such as integrated diffusion coefficient and the activation energy for diffusion is important to understand the growth rate of the product phase and the atomic mechanism of diffusion. These parameters are determined in Ti3Au phase with A15 crystal structure. The calculated diffusion parameters will help in validating the theoretical analysis on defect structure of the phase.

Finite element analysis of moving contact in mechanically fastened joints

The Finite Element Method (FEM) has made a number of otherwise intractable problems solvable. An important aspect for achieving an economical and accurate solution through FEM is matching the formulation and the computational organisation to the problem. This was realised forcefully in the present case of the solution of a class of moving contact boundary value problems of fastener joints. This paper deals with the problem of changing contact at the pin-hole interface of a fastener joint. Due to moving contact, the stresses and displacements are nonlinear with load. This would, in general, need an interactive-incremental approach for solution. However, by posing the problem in an inverse way, a solution is sought for obtaining loads to suit given contact configuration. Numerical results are given for typical isotropic and composite plates with rigid pins. Two cases of loading are considered: (i) load applied only at the edges of the plate and (ii) load applied at the pin and reacted at a part of the edge of the plate. Load-contact relationships, compliance and stress-patterns are investigated. This paper clearly demonstrates the simplification achieved by a suitable formulation of the problem. The results are of significance to the design and analysis of fastener joints.

ac susceptibility and electrical resistivity in Fe80-xNixCr20 (21 \leq x \leq 30) alloys

ac susceptibility and electrical resistivity studies on polycrystalline Fe80-xNixCr20 (21 \leq x \leq 30) alloys, with x=21, 23, 26, and 30, between 4.2 and 80 K, are reported. A previous dc magnetization study indicated the presence of ferro-spin-glass mixed-phase behavior in x=23 and 26 alloys while the alloys with x=21 and 30 were found to be spin-glass and ferromagnetic, respectively. The present ac susceptibility results support the above picture. In the electrical resistivity study, a low-temperature minimum in the resistivity-temperature curve is observed in all the alloys except the ferromagnetic one.

Origin of the activation barrier in the process of hydrogen abstraction: the perturbation treatment

The perturbation treatment previously given is extended to explain the process of hydrogen abstraction from the various hydrogen donor molecules by the triplet nπ* state of ketones or the ground state of the alkyl or alkoxy radical. The results suggest that, as the ionization energy of the donor bonds is decreased, the reaction is accelerated and it is not influenced by the bond strength of the donor bonds. The activation barrier in such reactions arises from a weakening of the charge resonance term as the ionization energy of the donor bond increases.

Reorientation of Water Inside Carbon Nanorings by Large Angular Jumps

Molecular dynamics simulations of the orientational dynamics of water molecules confined inside narrow carbon nanorings reveal that reorientational relaxation is mediated by large amplitude angular jumps. The distribution of waiting time between jumps peaks at about 60 fs, and has a slowly decaying exponential tail with a timescale of about 440 fs. These time scales are much faster than the mean waiting time between jumps of the water molecules in bulk.

Ultrafast Switching Time and Third Order Nonlinear Coefficients of Microwave Treated Single Walled Carbon Nanotube Suspensions

Microwave treated water soluble and amide functionalized single walled carbon nanotubes have been investigated using femtosecond degenerate pump-probe and nonlinear transmission experiments. The time resolved differential transmission using 75 femtosecond pulse with the central wavelength of 790 nm shows a bi-exponential ultrafast photo-bleaching with time constants of 160 fs (130 fs) and 920 fs (300 fs) for water soluble (amide functionalized) nanotubes. Open and closed aperture z-scans show saturation absorption and positive (negative) nonlinear refraction for water soluble (amide functionalized) nanotubes. Two photon absorption coefficient, beta(0) similar to 250 cm/GW (650 cm/GW) and nonlinear index, gamma similar to 15 cm(2)/pW (-30 cm(2)/pW) are obtained from the theoretical fit in the saturation limit to the data for two types of nanotubes.

Dilute Solution Properties of Methyl Methacrylate/Acrylonitrile Random Copolymers, 2a)

The Stockmayer-Fixman relation was used to evaluate the short range and long range interaction parameters for methyl methacrylate/acrylonitrile copolymers of 0,566 and 0,657 mole fraction of monomeric units of acrylonitrile in the solvents acetonitrile, 2-butanone, dimethyl formamide, and y-butyrolactone, at different temperatures (30, 45, and 60 “C). The values of KO were found to be lower than those of the parent homopolymers, and their values depend on both solvent and temperature. Even negative Ko-values were obtained, in cases in which the Mark Houwink exponent a is nearly unity. The values of the polymer-solvent interaction parameter, x, , are high and close to 0,5, indicating that these solvents are not good. The values of the excess interaction parameter, xAB, are negative and are not affected by temperature. The large extension of these copolymer chains, as exhibited by a and a;-values, can be understood in terms of unusual short range interactions only. Similar results were obtained for some cellulose derivatives.

Optimization of gasket thickness in a Bridgman anvil system

The effect of gasket thickness on the pressure in the Bridgman anvil system has been studied experimentally. The existence of the optimum thickness from the experimental data has been interpreted in a theoretical model of stress distribution in an anvil system. Review of Scientific Instruments is copyrighted by The American Institute of Physics.

Intermolecular interactions in the formation of aromatic hydrocarbon dimers

Both short-range and long-range intermolecular interaction energies between two aromatic hydrocarbon molecules, both in their ground state, separated by a range of interplanar distances of 3 ∼ 4 Aring, are estimated using the standard perturbation theory. The results show that aromatic hydrocarbons can form weak sandwich dimers with larger separation between them than is normally believed in their excimers. The non-sandwich form of dimer in which the long in-plane axes of the monomers are parallel and their short in-plane axes inclined, represents an unstable orientation because this form can pass to the perfect sandwich form without an energy barrier.

Viscoelastic Properties of Nanocrystalline Films of Semiconducting Chalcogenides at Liquid/Liquid Interface

The interfacial shear rheological properties of a continuous single-crystalline film of CuS and a 3D particulate gel of CdS nanoparticles (3−5 nm in diameter) formed at toluene−water interfaces have been studied. The ultrathin films (50 nm in thickness) are formed in situ in the shear cell through a reaction at the toluene−water interface between a metal−organic compound in the organic layer and an appropriate reagent for sulfidation in the aqueous layer. Linear viscoelastic spectra of the nanofilms reveal solid-like rheological behavior with the storage modulus higher than the loss modulus over the range of angular frequencies probed. Large strain amplitude sweep measurements on the CdS nanofilms formed at different reactant concentrations suggest that they form a weakly flocculated gel. Under steady shear, the films exhibit a yield stress, followed by a steady shear thinning at high shear rates. The viscoelastic and flow behavior of these films that are in common with those of many 3D “soft” materials like gels, foams, and concentrated colloidal suspensions can be described by the “soft” glassy rheology model.