Soot measurements in a chlorinated counterflow diffusion flame using a laser scattering and extinction technique

The effects of the presence of chlorinated species on soot formation have been studied in laminar diffusion flames burning chlorinated hydrocarbons. Measurements have been made of the structure of a chlorinated laminar, diffusion flame that is stabilized in a stagnation point flow around a porous cylinder. Comparisons have been made between a pure methane flame and a flame of 50% methane and 50% methyl chloride. Temperature profiles were obtained with a thermocouple. Laser Doppler velocimetry was used to measure the velocity of the gas along the streamline. Laser extinction and scattering techniques were employed to characterize the soot aerosol. It was found that the addition of the methyl chloride to methane caused soot production, as measured by the soot volume fraction, to increase by at least an order of magnitude.     

Strain-rate and inertia effects in the collapse of two types of energy-absorbing structure

The dynamic plastic collapse of energy-absorbing structures is more difficult to understand than the corresponding quasi-static collapse, on account of two effects which may be described as the “strain-rate factor” and the “inertia factor” respectively. The first of these is a material property whereby the yield stress is raised, while the second can affect the collapse mode, etc. It has recently been discovered [6,7]that structures whose load-deflection curve falls sharply after an initial “peak” are much more “velocity sensitive” than structures whose load-deflection curve is “flat-topped” (Fig. 1a); that is, when a given amount of energy is delivered by a moving mass, the final deflection depends more strongly on the impact velocity. In this paper we investigate strain-rate and inertia effects in these two types of structure by means of some simple experiments performed in a “drop hammer” testing machine, together with some simple analysis which enables us to give a satisfactory account of the experimental observations. The work is motivated partly by difficulties which occur in small-scale model testing of energy-absorbing structures, on account of the fact that the “strain-rate” and “inertia” factors not only scale differently in general, but also affect the two distinct types of structure differently.     

Analysis of cross and vertical buckling in sheet metal rolling

In sheet metal rolling, shape defects called “cross buckling” or “vertical buckling” sometimes appear, which are wrinkles like washboards. The direction of the crest line of the cross buckling inclines at a certain degree against the rolling direction, while that of the vertical buckling is parallel to the rolling direction. In this study, analysis of the cross and vertical buckling is performed using the elementary theory of buckling. First, we calculate the stress distribution in three-dimensional sheet metal rolling near the exit cross section inside the roll gap. Next, we calculate the residual stress distribution near the exit cross section outside the roll gap. Furthermore, sheet metal buckling is analysed using the residual stress distribution. Type of buckling, distance between neighboring wrinkles, inclination of the crest line of the wrinkles against the width direction and the region where the wrinkles appear are obtained. We compare analytical results with published experimental results, and find that the former agree well with the latter. Hence, we conclude that this method of analysis is valid, and that the cause of the cross and vertical buckling is the residual stress distribution near the exit cross section outside the roll gap.     

Stress and failure probability analysis for a transversely isotropic, brittle, elastic cylinder subjected to internal pressure and axisymmetric thermal loading

Procedures are developed for the determination of the stresses in and thence the probability of failure of a transversely isotropic cylinder made of a brittle material and loaded by an internal pressure and an axisymmetric radial temperature gradient. As examples of the application of the procedures a cylinder is analysed first with isotropic material properties, then with various degrees of anisotropy including both the “fibrous” and “laminar” types. The treatment is non-dimensional; results are presented graphically in the form of failure probability “contours”. For the dimensions and materials considered it is shown that the probability of failure is affected only slightly by the fibrous form of anisotropy but markedly by the laminar form when the thermal loading predominates.     

Analysing the vibrating conveyor

Several possible vibrating conveyor designs—the “sealskin” conveyor, the “jerk” conveyor, the conveyor with inclined motion and the conveyor with out-of-phase motion—are first discussed and their relative performances are compared. The most promising (and most widely employed) design, namely the conveyor with inclined motion, is then analysed in detail. The analysis is in all cases limited to conveyors with a horizontal track and with vertical track accelerations not exceeding g, the gravitational constant. Since the analytical performance prediction of the conveyor with sinusoidal motion is very difficult, an alternative type of motion having a triangular velocity profile is introduced. This allows analytical expressions for conveyor performance by simple methods to be derived. The results of this analysis are compared with the theoretical predictions for sinusoidal motion obtained by means of a simulation on the analogue computer. To simplify the presentation of the performance results, the design variables are reduced to two non-dimensional parameters, one for vertical acceleration and the other for horizontal sliding. The performance, too, is described by a non-dimensional parameter, so that the completely general performance maps presented for triangular and sinusoidal track velocity profiles need contain only three parameters.     

Effects of pressure and carbon dioxide,hydrogen and nitrogen concentration on laminar burning velocities and NO formation of methane-air mixtures

We studied the effects of increasing pressure and adding carbon dioxide, hydrogen and nitrogen to Methane-air mixture on premixed laminar burning velocity and NO formation in experimentally and numerically methods. Equivalence ratio was considered within 0.7 to 1.3 for initial pressure between 0.1 to 0.5 MPa and initial temperature was separately considered 298 K. Mole fractions of carbon dioxide, hydrogen and nitrogen were regarded in mixture from 0 to 0.2. Heat flux method was used for measurement of burning velocities of Methane-air mixtures diluted with CO₂ and N₂. Experimental results were compared to the calculations using a detailed chemical kinetic scheme (GRI-MECH 3.0). The results in atmosphere pressure for Methane-air mixture were calculated and compared with the results of literature. Results were in good agreement with published data in the literature. Then, by adding carbon dioxide and nitrogen to Methaneair mixture, we witnessed that laminar burning velocity was decreased, whereas by increasing hydrogen, the laminar burning velocity was increased. Finally, the results showed that by increasing the pressure, the premixed laminar burning velocity decreased for all mixtures, and NO formation indicates considerable increase, whereas the laminar flame thickness decreases.     

Simplified Modeling of Deflagration in Vessels

A simplified method that models the deflagration process occurring in closed or vented vessels is described. When combustion occurs within the spherical or cylindrical vessels, the flame moves spherically or segmentally to the vessel periphery. The volume and area of each element along the propagating flame front are calculated by using simple geometrical rules. For instabilities and turbulence resulting in enhanced burning rates, a simple analysis results in reasonable agreement with the experimental pressure transients when two burning rates (a laminar burning rate prior to the onset of instability and an enhanced burning rate) were used. Pressure reduction caused by a vent opening at predetermined pressure was modeled. Parameters examined in the modeling include ignition location, mixture concentration, vented area, and vent opening pressure. It was found that venting was effective in reducing the peak pressure experienced in vessels. The model can be expected to estimate reasonable peak pressures and flame front distances by modeling the enhanced burning rates, that is, turbulent enhancement factor.     

Pressure between elastic bodies having a slender area of contact and arbitrary profiles

A numerical method is presented for calculating the pressure distribution and contact area shape between two elastic bodies of arbitrary profile which make contact over a slender contact area, i.e. where the relative curvature of the two profiles is much smaller in the longitudinal direction than in the transverse. The pressure distribution is assumed to be piecewise-linear in the longitudinal direction and semi-elliptical in the transverse. No a priori relationship is assumed between the shape of the contact area and the longitudinal variation in pressure; they are found simultaneously from dual integral equations for the compatibility of (a) the normal displacement and (b) the transverse curvature along the longitudinal axis of the contact zone.In cases where the profiles of the contacting bodies are smooth and continuous up to, and beyond, the ends of the contact area, the method gives a very reliable measure of the contact pressure distribution. Where discontinuities in profile are present, at roller ends for example, stress singularities are to be expected and like any numerical method, only approximate values of the stress concentration can be found. In the cases studied, the concentration of pressure associated with a “sharp” edge of contact is found to be very local.The method has been applied to both cylindrical and variously “crowned” rollers, also to a ball “over-riding” the edge of a closely conforming groove.     

Method of movable lattice particles

A new simulation technique for modeling elastoplastic deformation and friction processes based on the dynamics of a system of “lattice particles” is proposed. In usual simulation methods like molecular dynamics, only interactions compatible to the symmetries of space (invariant with respect to translations and rotations) are used. In the proposed method, the interaction potentials depend both on the relative position of particles and the orientation of their relative radius vector with respect to prescribed “lattice directions”. We show that in spite of this relation with the “external space”, the system behaves, in linear approximation, as an isotropic elastic medium invariant to both the translations and rotations of the medium as a whole. The coupling with the external space occurs to be a surface effect, which either does not play an important role (if the motions of the boundaries are prescribed) or can be handled properly by introducing fictive compensating surface forces. Introduction of forces depending on the orientation of the local surroundings of a particle makes it possible to describe elastic media with arbitrary elastic properties by using only interactions between the next neighbours. The system of lattice particles shows better stability properties and allows one to describe large plastic deformations, avoiding problems of “packaging” typical for many particle methods.     

High precision lapping for polygonal holes

Lapping has been used as a finishing method to improve the roundness of shafts and holes. This paper introduces two methods for the finishing of polygonal holes whose shapes are ellipsoidal, three-lobed, four-lobed, and so on. One method is the “regular polygonal lap” in which the amplitude of the desired Fourier component of the out-of-roundness is kept constant and the other components are decreased. The other is the “tripod lap,” which can increase the amplitude of any Fourier component using special types of lapping tools produced by applying the “tripod roundness measuring method.” Based on a theoretical analysis, this study shows that any component of the out-of-roundness can be increased by using the new tripod lap method.     

The free vibrations of a thin circular finite rotating cylinder

The natural frequencies of a finite circular thin cylinder are obtained by employing an exponential matrix expansion of the so-called “fundamental matrix”. It is shown that the method is general enough and able to handle any system of linear differential equations of constant coefficients together with arbitrary boundary conditions. Results are given for rotating cylinders with clamped and free edges. The vibration frequencies of a stationary finite cylinder, previously obtained by other methods of solution, are used as a check on the present method with the special case of zero spinning velocity.     

Influence of end-conditions during tube hydroforming of aluminum extrusions

Tube hydroforming experiments were conducted to develop the forming limit diagram of AA6082-T4 by utilizing three types of end-conditions: (i) “free-end”, (ii) “pinched-end” or “fixed-end” and (iii) “forced-end”. It was found that “free-end” hydroforming gives the lowest forming limits followed by “pinched-end” and “forced-end” hydroforming. It was noticed that the tube failure occurs within 5° to the extrusion weld in the “free-end” experiments, within 7° in the “pinched-end” condition and extended up to 10° in the “forced-end” hydroforming experiments. Finite element simulations were carried out to capture the effects of the weld geometry, weld mechanical properties and the end-conditions of the extruded tube on the maximum induced stress and location of the maximum von Mises stress. It was found that the anisotropy of the weld material and the end-condition used during hydroforming experiments have the largest influence on the failure location with respect to the weld center.     

Fractal modeling method for 3D structure of vitrified-bonded wheel

Our goal is the development of the morphological model faithfully representing the structure of a real vitrified-bonded wheel in order to determine the wheel structure to meet a required wheel grade and derive the wheel composition to form such a wheel structure. This paper describes the two and new morphological model for a vitrified-bonded wheel using fractal modeling techniques. One model is the “agglomerate model of a plastic mixture” representing a plastic mixture before the burning process of a wheel on the basis of the diffusion-limited aggregation algorithm and another is the “morphological model of a burnt wheel” representing the structure of the burnt wheel on the basis of the sandpile algorithm. Both models bear resemblances to the real productions in structure. In particular, the morphological model of a burnt wheel bears resemblances not only in morphology but also in bulk density to real wheel structure, and it provides the structural characteristics such as average grain spacing and number of bond bridges per grain that relate to the tensile strength of wheels. Therefore, our models play an important role in the development of new wheels.     

Dynamic properties of outwardly propagating spherical hydrogen-air flames at high temperatures and pressures

Computational experiments on fundamental unstretched laminar burning velocities and flame response to stretch (represented by the Markstein number) of hydrogen-air flames at high temperatures and pressures were conducted in order to understand the dynamics of the flames including hydrogen as an attractive energy carrier in conditions encountered in practical applications such as internal combustion engines. Outwardly propagating spherical premixed flames were considered for a fuel-equivalence ratio of 0.6, pressures of 5 to 50 atm, and temperatures of 298 to 1000 K. For these conditions, ratios of unstretched-to-stretched laminar burning velocities varied linearly with flame stretch (represented by the Karlovitz number), similar to the flames at normal temperature and normal to moderately elevated pressures, implying that the “local conditions” hypothesis can be extended to the practical conditions. Increasing temperatures tended to reduce tendencies toward preferential-diffusion instability behavior (increasing the Markstein number) whereas increasing pressures tended to increase tendencies toward preferential-diffusion instability behavior (decreasing the Markstein number).     

Local couple transfer to a torsionless grillage

The paper exploits a special form of discontinuity in the moment field (previously used for concentrated force) to develop a possible field of moment in rectangular regions of torsionless grillage with a concentrated local couple applied at the centre. These equilibrium fields for force and moment, for which simple equations emerge, are intended for use in design of reinforced concrete slabs on column supports by the “Hillerborg strip” statical method. Patterns of moment derived for finite-size columns using the discontinuity are compared with patterns obtained using interwoven strips of finite width.     

Inelastic buckling of columns : The effect of imperfections

In the design of columns of mild steel (idealized as an elastic-perfectly plastic material) it is usual to take account of the effect of possible initial crookedness by means of a “Perry” formula. In contrast, the design of columns of aluminium alloys (and other materials which cannot reasonably be idealized as perfectly plastic) is usually made by means of the “tangent modulus” formula, which is strictly relevant only to initially perfect columns. The paper proposes a way of supplementing this formula for initially imperfect columns, and a simple graphical procedure is devised to generate a family of “column curves” for different degrees of imperfection.It turns out that although the “column curve” based on the tangent-modulus formula is sensitive to the precise shape of the rising stress-strain curve, the curves for the imperfect columns are insensitive to this shape, except for stocky columns. This suggests, paradoxically, a possible design approach using a Perry formula for columns made of aluminium alloys.     

Coating thickness effects on initial wear of nitrogen-doped amorphous carbon in nano-scale sliding contact: Part I—in situ examination

This paper, the first of a two-part series, presents the empirical data obtained from in situ examination on the generation of wear particles on carbon nitride coatings by a spherical diamond counter-face during repeated sliding contacts. In particular, the effect of coating thickness, varying from 1 to 500 nm, on the generation of wear particles was examined.Based on the in situ examination, the shape transition maps for generated wear particles were obtained for carbon nitride coatings of various thickness. The results show that the critical number of friction cycles, Nc, for the transition from “no observable wear particles” to “wear particle generation” generally increased with increasing coating thickness. It was noted that up to 20 friction cycles, the maximum Hertzian contact pressure, P_max, for “no observable wear particles” regime can be increased from 1.39Y to 1.53Y if silicon was coated with carbon nitride coating thicker than 10 nm, where Y is defined as the yield strength of silicon.     

Wear volume determination during running-in for PEHL contacts

The relation of wear volume and the change of average surface roughness under the “zero-wear” condition was derived, with the assumption that the original profiles of the surface below the wear plane remain exactly the same as before, i.e. no plastic deformation. The flattening of asperities on an engineering rough surface was simulated with numerical techniques. The variation in wear volume and average surface roughness with the depth of wear was studied. The pattern and the correlation length of rough surface were checked and found to have no effect on the relation of wear volume and change of average roughness. The simulated results show that the variation of wear volume and the change of average roughness can be described by a second order polynomial. The model was also validated with experimental results obtained by using a two-disc wear machine.     

Erosion of α-Fe by spherical glass particles

Polycrystalline α-Fe has been eroded at 30° and 90° with glass spheres of average diameters 70 μm and 200 μm in the velocity range 61–122 m s⁻¹. Detailed studies of the influence of the impact variables on the erosion rate as well as scanning electron microscopy studies of the eroded surfaces have been performed. It was observed that “breaking” waves developed on erosion at 30° and hills and valleys at 90°. Several different material loss processes that operate at various positions within waves, hills and valleys have been identified. It was clear that most material loss processes involved extensive localized shear and required the surface to become “conditioned” by a specific number of impacts before material loss began.