Performance of graphic aluminium particulate composite materials

Friction characteristics of journal bearings made from cast graphic aluminum particulate composite alloy were determined under mixed lubrication and compared with those of the base alloy (without graphite) and leaded phosphor bronze. All three materials ran without seizure while the performance of the particulate composite and leaded phosphor bronze improved with running. Temperature rise in the journal bearing under mixed/boundary lubrication was also measured. It was found that with 0.3D/1000 to 1.5D/1000 clearance and a low lubrication rate (typical value for a bearing of diameter 35 mm × length 35 mm is 80 mm3/min) and at a PV value of 73 × 106 Nm m−2 min−1 graphitic aluminium alloy journal bearings operate satisfactorily without seizure and excessive temperature rise. In comparison, the bronze bearings, with all the other parameters remaining the same, could not run without excessive temperature rise at clearances below D/1000 at lubrication rates lower than 200 mm3/min

Impression creep behaviour of magnesium alloy-based hybrid composites in the transverse direction

The creep behaviour of a creep-resistant AE42 magnesium alloy reinforced with Saffil short fibres and SiC particulates in various combinations has been investigated in the transverse direction, i.e., the plane containing random fibre orientation was perpendicular to the loading direction, in the temperature range of 175-300 degrees C at the stress levels ranging from 60 to 140 MPa using impression creep test technique. Normal creep behaviour, i.e., strain rate decreasing with strain and then reaching a steady state, is observed at 175 degrees C at all the stresses employed, and up to 80 MPa stress at 240 degrees C. A reverse creep behaviour, i.e., strain rate increasing with strain, then reaching a steady state and then decreasing, is observed above 80 MPa stress at 240 degrees C and at all the stress levels at 300 degrees C. This pattern remains the same for all the composites employed. The reverse creep behaviour is found to be associated with fibre breakage. The apparent stress exponent is found to be very high for all the composites. However, after taking the threshold stress into account, the true stress exponent is found to range between 4 and 7, which suggests viscous glide and dislocation climb being the dominant creep mechanisms. The apparent activation energy Q(C) was not calculated due to insufficient data at any stress level either for normal or reverse creep behaviour. The creep resistance of the hybrid composites is found to be comparable to that of the composite reinforced with 20% Saffil short fibres alone at all the temperatures and stress levels investigated. The creep rate of the composites in the transverse direction is found to be higher than the creep rate in the longitudinal direction reported in a previous paper.

Chemical changes during the aging and decomposition of composite solid propellants

During the thermal decomposition of orthorhombic ammonium perchlorate (AP) at 230°C, where the decomposition is only up to 30 wt %, there is an accumulation in the solid of acids, the concentration of which increases up to 15% decomposition, after which it decreases till it reaches the original value. Similar observations have been made in the polystyrene (PS)/AP propellant systems. Aging studies of PS/AP propellants have been carried out earlier [1], where it has been shown that for the aged propellants the thermal decomposition (TD) rate at 230°C and 260°C and ambient pressure burning rate (Image ) both increase and this increase is due to the formation of reactive intermediate “polystyrene peroxide (PSP).” In the present studies it has been observed that during the aging of the propellant at 150°C, the acid is formed and gets accumulated in the propellant, which may also be responsible for the increase in TD rate and perhaps may be more effective than PSP.

The machinability of a cast aluminium alloy-graphite particle composite

The microstructure of a cast Al---Si alloy-graphite particle composite is examined using optical and analytical scanning electron microscopy. Specimens containing different percentages of graphite were machined by orthogonal planning with 25° and 45° rake angle tools at both 6.5 and 13.2 m min−1. The machining forces are reported and the chip-rake-face friction coefficients and shear flow stresses are calculated. It is shown that the reduction in machining forces with increasing graphite content is due mostly to a decrease in the shear flow stress rather than to lower chip-rake-face friction. Both the polished and the machined surfaces of the composite are rougher than those of the simple alloy, apparently owing to the greater porosity, the tearing out of graphite particles, or the opening of cracks at the graphite particles in the wake of the tool.

Iterative modelling for stress analysis of composite laminates

The importance of interlaminar stresses has prompted a fresh look at the theory of laminated plates. An important feature in modelling such laminates is the need to provide for continuity of some strains and stresses, while at the same time allowing for the discontinuities in the others. A new modelling possibility is examined in this paper. The procedure allows for discontinuities in the in-plane stresses and transverse strains and continuity in the in-plane strains and transverse stresses. This theory is in the form of a heirarchy of formulations each representing an iterative step. Application of the theory is illustrated by considering the example of an infinite laminated strip subjected to sinusoidal loading.

Derivation of the decoupling relations for composite models from anomaly constraints and n-independence

It is shown, in the composite fermion models studied by 't Hooft and others, that the requirements of Adler-Bell-Jackiw anomaly matching and n-independence are sufficient to fix the indices of composite representations. The third requirement, namely that of decoupling relations, follows from these two constraints in such models and hence is inessential.

A detailed study of Li-DNA fibres at various salt concentrations reveals a non-helical B-DNA and a possible similarity of solution and solid state structures

A thorough investigation of salt concentration dependence of lithium DNA fibres is made using X-ray diffraction. While for low salt the C-form pattern is obtained, crystalline B-type diffraction patterns result on increasing the salt concentration. The salt content in the gel (from which fibres are drawn) is estimated by equilibrium dialysis using the Donnan equilibrium principle. The salt range giving the best crystalline B pattern is determined. It is found that in this range meridional reflections occur on the fourth and sixth layer lines. In addition, the tenth layer meridian is absent at a particular salt concentration. These results strongly suggest the presence of non-helical features in the DNA molecule. Preliminary analysis of the diffraction patterns indicates a structural variability within the B-form itself. Further, the possibility of the structural parameters of DNA being similar in solid state and in solution is discussed.

Anionic clay-Pt metal nanoparticle composite through intercalation of hexachloroplatinate in nickel zinc hydroxysalt

Nickel zinc hydroxysalt–Pt metal nanoparticle composite was prepared by intercalation of the anionic platinum complex, [PtCl6]2− in nickel zinc hydroxysalt through ion exchange reaction and subsequent reduction of the platinum complex by ethanol. Powder X-ray diffraction and microscopy studies indicate that the process of reduction of the platinum complex in the interlayer region of the anionic clay takes place topotactically without destroying the layers.

Wear characteristics and bearing performance of aluminium-mica particulate composite material

Some tribological properties of a mica-dispersed Al-4%Cu-1.5%Mg alloy cast by a conventional foundry technique are reported. The effect of mica dispersion on the wear rate and journal bearing performance of the matrix alloy was studied under different pressures and under different interface friction conditions. The dispersion of mica was found (a) to increase the wear rate of the base alloy, (b) to decrease the temperature rise during wear and (c) to improve the ability of the alloy to resist seizure.

Performance of an Al-Si-graphite particle composite piston in a diesel engine

Al-Si-graphite particle composite alloy pistons containing different percentages of about 80 μm uncoated graphite particles were successfully cast by foundry techniques. Tests with a 5 hp single-cylinder diesel engine show that Al-Si-graphite particle composite pistons can withstand an endurance test of 500 h without any apparent deterioration and do not seize during the running-in period. The use of the Al-Si-3% graphite particle composite piston also results in (a) up to 3% reduction in the specific fuel consumption, (b) considerable reduction in the wear of all four piston rings, (c) a reduction in piston wear, (d) a 9% reduction in the frictional horsepower losses of the engine as determined by the motoring test and (e) a slight increase in the exhaust gas temperature. These reductions (a)–(d) appear to be due to increased lubrication from the graphite particles which are smeared on the bearing surface, the higher damping capacity of the composite pistons and the reduced coefficient of thermal expansion of the composite pistons. Preliminary results indicate that aluminum-graphite particle composite alloy is a promising material for automotive pistons.

Application of the method of initial functions for the analysis of composite laminated plates

The method of initial functions has been applied for deriving higher order theories for cross-ply laminated composite thick rectangular plates. The equations of three-dimensional elasticity have been used. No a priori assumptions regarding the distribution of stresses or displacements are needed. Numerical solutions of the governing equations have been presented for simply supported edges and the results are compared with available ones.

Calorimetric values of composite solid propellants

The calorimetric values of composite solid propellant based on polystyrene, polyphenolformaldehyde, poly(vinyl chloride) and carboxy-terminated polybutadiene were determined using combustion calorimetry in order to assess the uncertainities in their measurements. The dependence of the calorimetric values on various propellant composition was obtained. The stoichiometry of oxidizer and fuel in the propellant for complete combustion obtained experimentally were compared with the theoretical stoichiometry calculated based on the oxidizer decomposition.

Thermal studies on melting and crystallization of polyamide fibres

Effect of heating rate on melting and crystallization of polyamide fibres has been examined using differential scanning calorimetric (DSC) technique. Peak temperature for melting (T m) and crystallization (T k) get suppressed with the increase in the heating rate which has been explained on the basis of chain orientation. Heat of melting (DeltaH m) and crystallization (DeltaH k) have been measured.DeltaH m vs. T m shows a nonlinear dependence which has been explained on the basis of entropy change. Quantitative difference inDeltaH m andDeltaH k values has been explained on the basis of orientation and degradation of the polymer.

Some studies on free vibration of composite laminates

Free vibration analysis is carried out to study the vibration characteristics of composite laminates using the modified shear deformation, layered, composite plate theory and employing the Rayleigh-Ritz energy approach. The analysis is presented in a unified form so as to incorporate all different combinations of laminate boundary conditions and with full coverage with regard to the various design parameters of a laminated plate. A parametric study is made using a beam characteristic function as the admissible function for the numerical calculations. The numerical results presented here are for an example case of fully clamped boundary conditions and are compared with previously published results. The effect of parameters, such as the aspect ratio of plates, ply-angle, number of layers and also the thickness ratios of plies in laminates on the frequencies of the laminate, is systematically studied. It is found that for anti-symmetric angle-ply or cross-ply laminates unique numerical values of the thickness ratios exist which improve the vibration characteristics of such laminates. Numerical values of the non-dimensional frequencies and nodal patterns, using the thickness ratio distribution of the plies, are then obtained for clamped laminates, fabricated out of various commonly used composite materials, and are presented in the form of the design curves.