Effect of membrane action on the plastic collapse load of circular orthotropic slabs with fixed edges

In the case of reinforced concrete slabs fixed at the boundaries, considerable enhancement in the load carrying capacity takes place due to compressive membrane action. In this paper a method is presented to analyse the effects of membrane action in fixed orthotropic circular slabs, carrying uniformly distributed loads. Depending on the radial moment capacity being greater or less than the circumferential moment capacity, two cases of orthotropy have been considered. Numerical results are worked out for certain assumed physical parameters and for different coefficients of orthotropy. Variations of load and bending moments with the central deflection are presented.

Effect of manganese dioxide on the thermal decomposition of ammonium perchlorate

Thermal decomposition of powdered ammonium perchlorate, catalysed by manganese dioxide (MnO2), has been studied in the low concentration ranges of the catalyst. MnO2 sensitises the thermal decomposition of ammonium perchlorate. The activation energy estimations of catalysed ammonium perchlorate show that the value is about 30 kcal/mol throughout the low and the high temperature regions whereas uncatalysed ammonium perchlorate gives two activation energies, 20 kcal/mol in the low temperature region (280-320°C) and 60 kcal/mol in the higher temperature region (350-390°C). This behaviour has been explained on the basis of an electron transfer process. The effectiveness of MnO2 in the thermal decomposition further increases on pre-heating the sample at 50°C for two weeks; manganese ions enter the ammonium perchlorate lattice during the process of pre-heating.

Effect of Molecular Weight on the Thermal and Impact Sensitivity of Polymers in Propellants

Abstract is not available.

Effect of concentrated force on a Crack in dissimilar media

Efect of concentrated force or edge dislocation with Burger's vector on a line crack in di,aimilar media has been studied in this paper. Crack surfaces may be subjected to surface loads or opuwd by rigid inclusions. Complex variable methods have been employed to study the distribution of stresses and displacements every where and in particnlar at the tips of the crack.

Effect of amplifier imperfections on active networks

The deviation in the performance of active networks due to practical operational amplifiers (OA) is mainly because of the finite gain bandwidth productBand nonzero output resistanceR_0. The effect ofBandR_0on two OA impedances and single and multi-OA filters are discussed. In filters, the effect ofR_0is to add zeros to the transfer function often making it nonminimum phase. A simple method of analysis has been suggested for 3-OA biquad and coupled biquad circuits. A general method of noise minimization of the generalized impedance converter (GIC), while operating OA's within the prescribed voltage and current limits, is also discussed. The 3-OA biquadratic sections analyzed also exhibit noise behavior and signal handling capacity similar to the GIC. The GIC based structures are found to be better than other configurations both in biquadratic sections and direct realizations of higher order transfer functions.

Effect of mechanical cycling on the stress-strain response of a martensitic Nitinol shape memory alloy

An experimental investigation into the ambient temperature, load-controlled tension�tension fatigue behavior of a martensitic Nitinol shape memory alloy (SMA) was conducted. Fatigue life for several stress levels spanning the critical stress for detwinning was determined and compared with that obtained on an alloy similar in composition but in the austenitic state at room temperature. Results show that the fatigue life of the pseudo-plastic alloy is superior to superelastic shape memory alloy. The stress�strain hysteretic response, monitored throughout the fatigue loading, reveals progressive strain accumulation with the cyclic loading. In addition, the area of hysteresis and recoverable and frictional energies were found to decrease with increasing number of fatigue cycles. Post-mortem characterization of the fatigued specimens through calorimetry and fractography was conducted in order to get further insight into the fatigue micromechanisms. These results are discussed in terms of reversible and irreversible microstructural changes that take place during cyclic loading. Aspects associated with self-heating of martensitic alloy undergoing high frequency stress cycling are discussed.

Effect of soil variability on the bearing capacity of clay and in slope stability problems

Site-specific geotechnical data are always random and variable in space. In the present study, a procedure for quantifying the variability in geotechnical characterization and design parameters is discussed using the site-specific cone tip resistance data (qc) obtained from static cone penetration test (SCPT). The parameters for the spatial variability modeling of geotechnical parameters i.e. (i) existing trend function in the in situ qc data; (ii) second moment statistics i.e. analysis of mean, variance, and auto-correlation structure of the soil strength and stiffness parameters; and (iii) inputs from the spatial correlation analysis, are utilized in the numerical modeling procedures using the finite difference numerical code FLAC 5.0. The influence of consideration of spatially variable soil parameters on the reliability-based geotechnical deign is studied for the two cases i.e. (a) bearing capacity analysis of a shallow foundation resting on a clayey soil, and (b) analysis of stability and deformation pattern of a cohesive-frictional soil slope. The study highlights the procedure for conducting a site-specific study using field test data such as SCPT in geotechnical analysis and demonstrates that a few additional computations involving soil variability provide a better insight into the role of variability in designs.

Effect of surface radiation on conjugate natural convection in a horizontal annulus driven by inner heat generating solid cylinder

This paper reports a numerical study of the laminar conjugate natural convection heat transfer with and without the interaction of the surface radiation in a horizontal cylindrical annulus formed between an inner heat generating solid circular cylinder and an outer isothermal circular boundary. Numerical solutions are obtained by solving the governing equations with a pressure correction method on a collocated (non-staggered) mesh. Steady-state results are presented for the flow and temperature distributions and Nusselt numbers for the heat generation based Grashof number ranging from 10(7) to 10(10), solid-to-fluid thermal conductivity ratios of 1, 5, 10, 50 and 100, radius ratios of 0.226 and 0.452 and surface emissivities of 0-0.8 with air as the working medium. It is observed that surface radiation reduces the convective heat transfer in the annulus compared to the pure natural convection case and enhances the overall Nusselt number.

Effect of reinforcement form on the bearing capacity of square footings on sand

This paper presents the results of laboratory model loading tests and numerical studies carried out on square footings supported on geosynthetic reinforced sand beds. The relative performance of different forms of geosynthetic reinforcement (i.e. geocell, planar layers and randomly distributed mesh elements) in foundation beds is compared; using same quantity of reinforcement in each test. A biaxial geogrid and a geonet are used for reinforcing the sand beds. Geonet is used in two forms of reinforcement, viz. Planar layers and geocell, while the biaxial geogrid was used in three forms of reinforcement, viz. planar layers, geocell and randomly distributed mesh elements. Laboratory load tests on unreinforced and reinforced footings are simulated in a numerical model and the results are analyzed to understand the distribution of displacements and stresses below the footing better. Both the experimental and numerical studies demonstrated that the geocell is the most advantageous form of soil reinforcement technique of those investigated, provided there is no rupture of the material during loading. Geogrid used in the form of randomly distributed mesh elements is found to be inferior to the other two forms. Some significant observations on the difference in reinforcement mechanism for different forms of reinforcement are presented in this paper.

The effect of horizontal resolution on simulation of very extreme US precipitation events in a global atmosphere model

We investigate the ability of a global atmospheric general circulation model (AGCM) to reproduce observed 20 year return values of the annual maximum daily precipitation totals over the continental United States as a function of horizontal resolution. We find that at the high resolutions enabled by contemporary supercomputers, the AGCM can produce values of comparable magnitude to high quality observations. However, at the resolutions typical of the coupled general circulation models used in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, the precipitation return values are severely underestimated.

A numerical study of the effect of loading conditions on tubular hydroforming

In this work, the mechanics of tubular hydroforming under various types of loading conditions is investigated. The main objective is to contrast the effects of prescribing fluid pressure or volume flow rate, in conjunction with axial displacement, on the stress and strain histories experienced by the tube and the process of bulging. To this end, axisymmetric finite element simulations of free hydroforming (without external die contact) of aluminium alloy tubes are carried out. Hill’s normally anisotropic yield theory along with material properties determined in a previous experimental study [A. Kulkarni, P. Biswas, R. Narasimhan, A. Luo, T. Stoughton, R. Mishra, A.K. Sachdev, An experimental and numerical study of necking initiation in aluminium alloy tubes during hydroforming, Int. J. Mech. Sci. 46 (2004) 1727–1746] are employed in the computations. It is found that while prescribed fluid pressure leads to highly non-proportional strain paths, specified fluid volume flow rate may result in almost proportional ones for the predominant portion of loading. The peak pressure increases with axial compression for the former, while the reverse trend applies under the latter. The implication of these results on failure by localized necking of the tube wall is addressed in a subsequent investigation.

Effect of Al substitution on the magnetic properties of amorphous Fe73.5Cu1Mo3Si13.5-xAlxB9 alloy

We have synthesized FINEMET type amorphous Fe73.5Cu1Mo3Si13.5-xAlxB9 alloy by the single wheel melt spinning technique. The effect of Al substitution on the magnetic properties has been studied using a vibrating sample magnetometer, SQUID and Mossbauer spectroscopy. Magnetization and Curie temperature of the amorphous phase of the alloys were found to decrease with A] concentration. The results are attributed to the dilution effect of At on the magnetic moment of Fe and to the increase in Fe-Fe interaction distance resulting in the weakening of exchange interaction. (C) 2007 Elsevier B.V. All rights reserved.