Smoldering combustion of "incense" sticks - Experiments and modeling

This paper is concerned with the experimental and modeling studies on the smoldering rates of incense sticks as a function of ambient oxygen fraction in air, the flow velocity and size. The experimental results are obtained both for forward and reverse smolder conditions. The results are explained on the basis of surface combustion due to diffusion of oxygen to the surface by both free and forced convection supporting the heat transfer into the solid by conduction, into the stream by convection and the radiant heat transfer from the surface. The heat release at the surface is controlled by the convective transport of the oxidizer to the surface. To obtain the diffusion rates particularly for the reverse smolder, CFD calculations of fluid flow with along with a passive scalar are needed; these calculations have been made both for forward and reverse smolder. The interesting aspect of the CFD calculations is that while the Nusselt umber for forward smolder shows a clear root( Re-u) dependence ( Re-u = Flow Reynolds Number), the result for reverse smolder shows a peak in the variation with Reynolds number with the values lower than for forward smolder and unsteadiness in the flow beyond a certain flow rate. The results of flow behavior and Nusselt number are used in a simple model for the heat transfer at the smoldering surface to obtain the dependence of the smoldering rate on the diameter of the incense stick, the flow rate of air and the oxygen fraction. The results are presented in terms of a correlation for the non-dimensional smoldering rate with radiant flux from the surface and heat generation rate at the surface. The correlations appear reasonable for both forward and reverse smolder cases.

Children’s Relationship to Plants among Primary School Children in Finland

There is considerable evidence that children in modern society are losing
their contact with nature and, more precisely, with green plants. Is this also the case in Finland, a northern country famous for its forests and wild nature? This study examines the relationship of 9- to 10-year-old Finnish schoolchildren with the green environment and plants. The data were gathered by a questionnaire
comprising structured and open-ended questions. The focus of the research was on two comparisons: first, on the nature and child relationship in rural and urban neighborhoods and, second, among boys and girls. Participants in the study amounted to a total of 76 children, 42 in the Helsinki suburb area and 34 in Paltamo. The results suggested that the children in rural surroundings had closer contact with nature than their urban associates. For example, the children of Paltamo reported to know the trees better, and considered human beings to be part of nature more often (100% vs. 76% of the pupils in Helsinki, P = 0,003). Similarly, the results showed that girls in the study (N = 48) were more interested in plants than boys (N = 28). For the girls, the beauty and joy of plants was important, whereas the boys appreciated plants as the source of life. After the pre-questioning, the children of Helsinki participated in an in-class horticultural intervention and 10 days later, answered a similar questionnaire again. The results of the open-ended questions revealed that equally to children in other Western countries, Finnish children may also be in danger of losing their direct contact with the natural environment. It was common to pass free time in organized sports such as hockey or football (boys), or by just walking and talking with friends (girls). Rural children told that they still built huts, pick berries, and climb trees, whereas urban children played in parks and city groves. The results suggest that it is essential to research
further the children’s own experiences if we are to understand, and subsequently, to enhance, the crucial role of the green environment in their lives. Horticultural interventions can be effective starting points to add to children’s knowledge, affection, and interest toward greenery, but it is highly recommended that they take place outdoors rather than indoors.

Children’s Relationship to Plants among Primary School Children in Finland

There is considerable evidence that children in modern society are losing
their contact with nature and, more precisely, with green plants. Is this also the case in Finland, a northern country famous for its forests and wild nature? This study examines the relationship of 9- to 10-year-old Finnish schoolchildren with the green environment and plants. The data were gathered by a questionnaire
comprising structured and open-ended questions. The focus of the research was on two comparisons: first, on the nature and child relationship in rural and urban neighborhoods and, second, among boys and girls. Participants in the study amounted to a total of 76 children, 42 in the Helsinki suburb area and 34 in Paltamo. The results suggested that the children in rural surroundings had closer contact with nature than their urban associates. For example, the children of Paltamo reported to know the trees better, and considered human beings to be part of nature more often (100% vs. 76% of the pupils in Helsinki, P = 0,003). Similarly, the results showed that girls in the study (N = 48) were more interested in plants than boys (N = 28). For the girls, the beauty and joy of plants was important, whereas the boys appreciated plants as the source of life. After the pre-questioning, the children of Helsinki participated in an in-class horticultural intervention and 10 days later, answered a similar questionnaire again. The results of the open-ended questions revealed that equally to children in other Western countries, Finnish children may also be in danger of losing their direct contact with the natural environment. It was common to pass free time in organized sports such as hockey or football (boys), or by just walking and talking with friends (girls). Rural children told that they still built huts, pick berries, and climb trees, whereas urban children played in parks and city groves. The results suggest that it is essential to research
further the children’s own experiences if we are to understand, and subsequently, to enhance, the crucial role of the green environment in their lives. Horticultural interventions can be effective starting points to add to children’s knowledge, affection, and interest toward greenery, but it is highly recommended that they take place outdoors rather than indoors.

Children’s Relationship to Plants among Primary School Children in Finland

There is considerable evidence that children in modern society are losing
their contact with nature and, more precisely, with green plants. Is this also the case in Finland, a northern country famous for its forests and wild nature? This study examines the relationship of 9- to 10-year-old Finnish schoolchildren with the green environment and plants. The data were gathered by a questionnaire
comprising structured and open-ended questions. The focus of the research was on two comparisons: first, on the nature and child relationship in rural and urban neighborhoods and, second, among boys and girls. Participants in the study amounted to a total of 76 children, 42 in the Helsinki suburb area and 34 in Paltamo. The results suggested that the children in rural surroundings had closer contact with nature than their urban associates. For example, the children of Paltamo reported to know the trees better, and considered human beings to be part of nature more often (100% vs. 76% of the pupils in Helsinki, P = 0,003). Similarly, the results showed that girls in the study (N = 48) were more interested in plants than boys (N = 28). For the girls, the beauty and joy of plants was important, whereas the boys appreciated plants as the source of life. After the pre-questioning, the children of Helsinki participated in an in-class horticultural intervention and 10 days later, answered a similar questionnaire again. The results of the open-ended questions revealed that equally to children in other Western countries, Finnish children may also be in danger of losing their direct contact with the natural environment. It was common to pass free time in organized sports such as hockey or football (boys), or by just walking and talking with friends (girls). Rural children told that they still built huts, pick berries, and climb trees, whereas urban children played in parks and city groves. The results suggest that it is essential to research
further the children’s own experiences if we are to understand, and subsequently, to enhance, the crucial role of the green environment in their lives. Horticultural interventions can be effective starting points to add to children’s knowledge, affection, and interest toward greenery, but it is highly recommended that they take place outdoors rather than indoors.

Effect of directionality of unidirectional grinding marks on friction and transfer layer formation of Mg on steel using inclined scratch test

Surface topography has been known to play an important role in the friction and transfer layer formation during sliding. In the present investigation, EN8 steel flats were ground to attain different surface roughness with unidirectional grinding marks. Pure Mg pins were scratched on these surfaces using an Inclined Scratch Tester to study the influence of directionality of surface grinding marks on coefficient of friction and transfer layer formation. Grinding angle (i.e., the angle between direction of scratch and grinding marks) was varied between 0 degrees and 90 degrees during the tests. Experiments were conducted under both dry and lubricated conditions. Scanning electron micrographs of the contact surfaces of pins and flats were used to reveal the surface features that included the morphology of the transfer layer. It was observed that the average coefficient of friction and transfer layer formation depend primarily on the directionality of the grinding marks but were independent of surface roughness on the harder mating surface. In addition, a stick-slip phenomenon was observed, the amplitude of which depended both on the directionality of grinding marks and the surface roughness of the harder mating surface. The grinding angle effect on the coefficient of friction, which consists of adhesion and plowing components, was attributed to the variation of plowing component of friction. (c) 2006 Elsevier B.V. All rights reserved.

Aitosuklaa jäätelöpuikon kuorrutteena

Tutkimuksen kirjallisuuskatsauksessa keskityttiin jäätelöpuikkoihin, erilaisiin suklaakuorrutteisiin ja elintarvikkeiden kuorruttamiseen suklaalla. Lisäksi kirjallisuuskatsauksessa perehdyttiin suklaan koostumukseen, nestemäisen suklaan virtausominaisuuksiin ja koostumuksen ja virtausominaisuuksien välisiin vuorovaikutuksiin. Kokeellisessa osassa tavoitteena oli selvittää, miten maitosuklaakuorrutteen rasvapitoisuuden, emulgointiainepitoisuuden ja kuorrutteen lämpötilanvaihtelut vaikuttavat kuorrutteen viskositeettiin, myötöjännitykseen, jähmettymisaikaan ja jäätelöpuikon päälle jäävän kuorrutteen määrään. Erityisesti pyrittiin selvittämään, miten jäätelöpuikon päälle jäävän kuorrutteen määrää saadaan säädeltyä kuorrutteen rasvapitoisuutta, emulgointiainepitoisuutta ja lämpötilaa muuttamalla. Tutkimuksen koeasetelma tehtiin Box-Behnken-mallilla. Selittäviksi muuttujiksi tutkimukseen valittiin kuorrutteen rasvan määrä, emulgointiaineen määrä ja kuorrutteen lämpötila jäätelöpuikkoja kuorrutettaessa. Vastemuuttujina oli kuorrutteen jähmettymisaika, viskositeetti, myötöjännitys ja jäätelöpuikon päälle jäävän kuorrutteen määrä. Tulokset käsiteltiin regressioanalyysin avulla. Muuttujien välisiä vuorovaikutuksia tutkittiin vastepintamallilla. Vastemuuttujien välisiä korrelaatioita tutkittaessa käytettiin Pearsonin korrelaatiokerrointa. Kuorrutteen rasvan määrän lisääntyminen vähensi tilastollisesti merkitsevästi jäätelöpuikon päälle jäävän kuorrutteen määrää, kuorrutteen jähmettymisaikaa, viskositeettia ja myötöjännitystä. Emulgointiaineen määrän lisääminen kuorrutteessa pienensi kuorrutteen määrää jäätelöpuikon päällä, kuorrutteen jähmettymisaikaa ja kuorrutteen myötöjännitystä. Kuorrutteen lämpötilan lisääminen jäätelöpuikkoja kuorrutettaessa pienensi kuorrutteen määrää ja viskositeettia. Kuorrutteen jähmettymisaika sen sijaan piteni lämpötilaa lisättäessä. Tutkimuksen perusteella voidaan sanoa, että jäätelöpuikkoja kastettaessa suklaakuorrutteen lämpötila, rasvan määrä ja lesitiinin määrä vaikuttivat jäätelöpuikon päälle jäävän kuorrutteen määrään. Vastepintamallinnuksen käyttö soveltui hyvin suklaakuorrutteen määrän tutkimiseen. Sen avulla saatiin selvitettyä, miten jäätelöpuikon päälle jäävän kuorrutteen määrää saadaan säädeltyä muuttamalla kuorrutteen emulgointiainepitoisuutta, rasvapitoisuutta ja lämpötilaa.

Influence of Inclination Angle and Machining Direction on Friction and Transfer Layer Formation

In the present investigation, unidirectional grinding marks were created on a set of steel plates. Sliding experiments were then conducted with the prepared steel plates using Al-Mg alloy pins and an inclined pin-on-plate sliding tester. The goals of the experiments were to ascertain the influence of inclination angle and grinding mark direction on friction and transfer layer formation during sliding contact. The inclination angle of the plate was held at 0.2 deg, 0.6 deg, 1 deg, 1.4 deg, 1.8 deg, 2.2 deg, and 2.6 deg in the tests. The pins were slid both perpendicular and parallel to the grinding marks direction. The experiments were conducted under both dry and lubricated conditions on each plate in an ambient environment. Results showed that the coefficient of friction and the formation of transfer layer depend on the grinding marks direction and inclination angle of the hard surfaces. For a given inclination angle, under both dry and lubricated conditions, the coefficient of friction and transfer layer formation were found to be greater when the pins slid perpendicular to the unidirectional grinding marks than when the pins slid parallel to the grinding marks. In addition, a stick-slip phenomenon was observed under lubricated conditions at the highest inclination angle for sliding perpendicular to the grinding marks direction. This phenomenon could be attributed to the extent of plane strain conditions taking place at the asperity level during sliding. DOI: 10.1115/1.4002604]

The scratch hardness and friction of a soft rigid-plastic solid

The paper describes an experimental and analytical study of the normal and scratch hardnesses of a model soft rigid-plastic solid. The material known as ‘Plasticine’, a mixture of dry particles and a mineral oil, has been deformed with a range of rigid conical indentors with included angles of between 30° and 170°. The sliding velocity dependence of the computed scratch hardness and friction has been examined in the velocity range 0.19 mm/s to 7.3 m/s. Data are also described for the time dependence of the normal hardness and also the estimated rate dependence of the intrinsic flow stress. The latter values were estimated from data obtained during the upsetting of right cylinders. Three major conclusions are drawn from these data and the associated analysis. (1) A first-order account of the scratching force may be provided by adopting a model which sums the computed plastic deformation and interfacial sliding contributions to the total sliding work. This is tantamount to the adoption of the two-term non-interacting model of friction. (2) For this system during sliding, at high sliding velocities at least, the interface shear stress which defines the boundary condition is not directly related to the bulk shear stress. The interface rheological characteristics indicate an appreciable dependence on the imposed strain or strain rate. In particular, the relative contributions of the slip and stick boundary conditions appear to be a function of the imposed sliding velocity. (3) The computed normal and scratch hardness values are not simply interrelated primarily because of the evolving boundary conditions which appear to exist in the scratching experiments.

Molecular-dynamics studies of systems of confined dumbbell molecules

We present the results of molecular-dynamics simulations of systems of dumbbell molecules confined by parallel molecular walls. We have carried out systematic studies of three cases: freezing, steady flows, and stick-slip friction. We find that the molecular orientational degrees of freedom cause the surface layers to deviate from a planar configuration. Nevertheless, steady flows, in a channel as narrow as 15 molecular sizes, display continuum behavior. A range of mechanisms in the dynamics of the freezing of a confined fluid is found, as a function of the wall-fluid interactions and the bond length of the dumbbell molecules. The simple order-disorder transition associated with stick-slip motion in the presence of a layer of monoatomic lubricant molecules is supplanted by more complex behavior due to rotational degrees of freedom of the diatomic molecules.

Hidden order in serrated flow of metallic glasses

We report results of statistical and dynamic analysis of the serrated stress-time curves obtained from compressive constant strain-rate tests on two metallic glass samples with different ductility levels in an effort to extract hidden information in the seemingly irregular serrations. Two distinct types of dynamics are detected in these two alloy samples. The stress-strain curve corresponding to the less ductile Zr65Cu15Ni10Al10 alloy is shown to exhibit a finite correlation dimension and a positive Lyapunov exponent, suggesting that the underlying dynamics is chaotic. In contrast, for the more ductile Cu47.5Zr47.5Al5 alloy, the distributions of stress drop magnitudes and their time durations obey a power-law scaling reminiscent of a self-organized critical state. The exponents also satisfy the scaling relation compatible with self-organized criticality. Possible physical mechanisms contributing to the two distinct dynamic regimes are discussed by drawing on the analogy with the serrated yielding of crystalline samples. The analysis, together with some physical reasoning, suggests that plasticity in the less ductile sample can be attributed to stick-slip of a single shear band, while that of the more ductile sample could be attributed to the simultaneous nucleation of a large number of shear bands and their mutual interactions. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Response of Materials during sliding on various surface textures

In the present investigation, basic studies were conducted using Inclined pin-on-plate sliding Tester to understand the role of surface texture of hard material against soft materials during sliding. Soft materials such as Al-Mg alloy, pure Al and pure Mg were used as pins and 080 M40 steel was used as plate in the tests. Two surface parameters of steel plates — roughness and texture — were varied in tests. It was observed that the transfer layer formation and the coefficient of friction which has two components, namely adhesion and plowing component, are controlled by the surface texture of harder material. For the case of Al-Mg alloy, stick-slip phenomenon was absent under both dry and lubricated conditions. However, for the case of Al, it was observed only under lubricated conditions while for the case of Mg, it was observed under both dry and lubricated conditions. Further, it was observed that the amplitude of stick-slip motion primarily depends on plowing component of friction. The plowing component of friction was highest for the surface that promotes plane strain conditions near the surface and was lowest for the surface that promotes plane stress conditions near the surface.

Response of Materials During Sliding on Various Surface Textures

In the present investigation, soft materials, such as Al-4Mg alloy, high-purity Al and pure Mg pins were slid against hard steel plates of various surface textures to study the response of materials during sliding. The experiments were conducted using an inclined pin-on-plate sliding apparatus under both dry and lubricated conditions in an ambient environment. Two kinds of frictional response, namely steady-state and stick-slip, were observed during sliding. In general, the response was dependent on material pair, normal load, lubrication, and surface texture of the harder material. More specifically, for the case of Al-4Mg alloy, the stick-slip response was absent under both dry and lubricated conditions. For Al, stick-slip was observed only under lubricated conditions. For the case of Mg, the stick-slip response was seen under both dry and lubricated conditions. Further, it was observed that the amplitude of stick-slip motion primarily depends on the plowing component of friction. The plowing component of friction was the highest for the surfaces that promoted plane strain conditions and was the lowest for the surfaces that promoted plane stress conditions near the surface.

Confined fluids in a Janus pore: influence of surface asymmetry on structure and solvation forces

Density distribution, fluid structure and solvation forces for fluids confined in Janus slit-shaped pores are investigated using grand canonical Monte Carlo simulations. By varying the degree of asymmetry between the two smooth surfaces that make up the slit pores, a wide variety of adsorption situations are observed. The presence of one moderately attractive surface in the asymmetric pore is sufficient to disrupt the formation of frozen phases observed in the symmetric case. In the extreme case of asymmetry in which one wall is repulsive, the pore fluid can consist of a frozen contact layer at the attractive surface for smaller surface separations (H) or a frozen contact layer with liquid-like and gas-like regions as the pore width is increased. The superposition approximation, wherein the solvation pressure and number density in the asymmetric pores can be obtained from the results on symmetric pores, is found to be accurate for H > 4 sigma(ff), where sigma(ff) is the Lennard-Jones fluid diameter and within 10% accuracy for smaller surface separations. Our study has implications in controlling stick slip and overcoming static friction `stiction' in micro and nanofluidic devices.

Geometry of static balancing during posture transition

The interaction between the digital human model (DHM) and environment typically occurs in two distinct modes; one, when the DHM maintains contacts with the environment using its self weight, wherein associated reaction forces at the interface due to gravity are unidirectional; two, when the DHM applies both tension and compression on the environment through anchoring. For static balancing in first mode of interaction, it is sufficient to maintain the projection of the centre of mass (COM) inside the convex region induced by the weight supporting segments of the body on a horizontal plane. In DHM, static balancing is required while performing specified tasks such as reach, manipulation and locomotion; otherwise the simulations would not be realistic. This paper establishes the geometric relationships that must be satisfied for maintaining static balance while altering the support configurations for a given posture and altering the posture for a given support condition. For a given location of the COM for a system supported by multiple point contacts, the conditions for simultaneous withdrawal of a specified set of contacts have been determined in terms of the convex hulls of the subsets of the points of contact. When the projection of COM must move beyond the existing support for performing some task, new supports must be enabled for maintaining static balance. This support seeking behavior could also manifest while planning for reduction of support stresses. Feasibility of such a support depends upon the availability of necessary features in the environment. Geometric conditions necessary for selection of new support on horizontal,inclined and vertical surfaces within the workspace of the DHM for such dynamic scenario have been derived. The concepts developed are demonstrated using the cases of sit-to-stand posture transition for manipulation of COM within the convex supporting polygon, and statically stable walking gaits for support seeking within the kinematic capabilities of the DHM. The theory developed helps in making the DHM realize appropriate behaviors in diverse scenarios autonomously.

Elastic-plastic contact conditions for frictionally constrained bodies under cyclic tangential loading

A Frictionally constrained condition implies dependence of friction force on tangential displacement amplitude. The condition may occur due to chemical, physical, and/or mechanical interaction between the contacting surfaces. The condition, sometimes also referred to as the presliding condition or partial slip condition, is characterized under fretting. Under such conditions, various experimental studies indicate the existence of two distinguishable regions, that is, stick region and slip region. In the present study, frictionally constrained conditions are identified and the evolutions of stick-slip regions are investigated in detail. Investigations have been performed on self-mated stainless steel and chromium carbide coated surfaces mated against stainless steel, under both vacuum and ambient conditions. Contact conditions prevailing at the contact interface were identified based on the mechanical responses and were correlated with the surface damage observed. Surface degradation has been observed in the form of microcracks and material transfer. Detailed numerical analysis has also been performed in order to understand the energy dissipation and the damage mode involved in the surface or subsurface damage. It has been observed that under frictionally constrained conditions, the occurrence of annular slip features are mainly due to the junction growth, resulting from elastic-plastic deformation at the contact interface. Ratcheting has been observed as the governing damage mode under cyclic tangential loading condition.