Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences最新文献_第2页

High strain-rate shear response of polycarbonate and polymethyl methacrylate 聚碳酸酯和聚甲基丙烯酸甲酯的高应变速率剪切响应

Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences Pub Date : 1990-06-08 DOI: 10.1098/rspa.1990.0069

N. Fleck, W. Stronge, J. Liu

{"title":"High strain-rate shear response of polycarbonate and polymethyl methacrylate","authors":"N. Fleck, W. Stronge, J. Liu","doi":"10.1098/rspa.1990.0069","DOIUrl":"https://doi.org/10.1098/rspa.1990.0069","url":null,"abstract":"The high strain rate response of polycarbonate (PC) and polymethyl methacrylate (PMMA) are measured using a split Hopkinson torsion bar for shear strain rates Ẏ from 500 s-1 to 2200 s-1, and temperatures in the range —100°C to 200°C. The yield and fracture behaviours are compared with previous data and existing theories for Ẏ < I s-1. We find that PC yields in accordance with the Eyring theory of viscous flow, for temperatures between the beta transition temperature Tβ ≈ — 100°C and the glass transition temperature Tg = 147°C. At lower temperatures, T < Tβ , backbone chain motion becomes frozen and the shear yield stress is greater than the Eyring prediction. Strain softening is an essential feature of yield of PC at all strain rates employed. Poly methyl methacrylate fractures before yield in the high strain rate tests for T < 80°C, which is close to the glass transition temperature Tg120°C. It is found that the fracture stress for both materials obeys a thermal activation rate theory of Eyring type. Fracture is thought to be nucleation controlled, and is due to the initiation and break down of a craze at the fracture stress τf. Examination of the fracture surfaces reveals that failure is by the nucleation and propagation of inclined mode I microcracks which link to form a stepped fracture surface. This reveals that failure is by tensile cracking and not by a thermal instability in the material. The process of shear localization is fundamentally different from that shown by steel and titanium alloys.","PeriodicalId":20605,"journal":{"name":"Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1990-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73248214","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 99

Convective-diffusive-reactive Taylor dispersion processes in particulate multiphase systems 颗粒多相体系中的对流-扩散-反应泰勒分散过程

Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences Pub Date : 1990-06-08 DOI: 10.1098/rspa.1990.0077

S. Dungan, M. Shapiro, H. Brenner

{"title":"Convective-diffusive-reactive Taylor dispersion processes in particulate multiphase systems","authors":"S. Dungan, M. Shapiro, H. Brenner","doi":"10.1098/rspa.1990.0077","DOIUrl":"https://doi.org/10.1098/rspa.1990.0077","url":null,"abstract":"Convective-diffusive transport of a chemically reactive solute is studied analytically for a general model of a multiphase system composed of ordered or disordered particles of arbitrary shapes and sizes. Use of spatially periodic boundary conditions permits analysis of particulate multiphase systems of effectively infinite size. Solute transport occurs in both the continuous and discontinuous bulk phases, as well as within and across the interfacial phase boundaries separating them. Additionally, the solute is allowed to undergo generally inhomogeneous first-order irreversible chemical reactions occurring in both the continuous and discontinuous volumetric phases, as well as within the interfacial surface phase. Our object is that of globally describing the solute transport and reaction processes at a macro- or Darcy-scale level, wherein the resulting, coarse-grained particulate system is viewed as a continuum possessing homogeneous material transport and reactive properties. At this level the asymptotic long-time solute macrotransport process is shown to be governed by three Darcy-scale phenomenological coefficients: the mean solute velocity vector ͞U*, dispersivity dyadic ͞D*, and apparent volumetric reactivity coefficient ͞K*. A variant of a Taylor-Aris method-of-moments scheme (Brenner & Adler 1982), modified to include solute disappearance via chemical reactions, is used to express these three macroscale phenomenological coefficients in terms of the given microscale phenomenological data and geometry. The general solution technique, illustrated here for a simple, ordered geometrical realization of a two-phase system, reveals the competitive influences of the respective volumetric/surface-excess transport and reaction processes, as well as the solute adsorptivity, upon the three macroscale transport coefficients.","PeriodicalId":20605,"journal":{"name":"Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1990-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85875249","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 19

Natural convection effects on thermal ignition in a porous medium. I. Semenov model 多孔介质中自然对流对热点火的影响。1 . Semenov模型

Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences Pub Date : 1990-06-08 DOI: 10.1098/rspa.1990.0072

V. Balakotaiah, P. Pourtalet

{"title":"Natural convection effects on thermal ignition in a porous medium. I. Semenov model","authors":"V. Balakotaiah, P. Pourtalet","doi":"10.1098/rspa.1990.0072","DOIUrl":"https://doi.org/10.1098/rspa.1990.0072","url":null,"abstract":"A one-dimensional diffusion-convection-reaction model is formulated to account for natural convection effects on thermal ignition in an open system consisting of a porous medium. Various limiting cases of the model are considered. A detailed analysis of the Semenov (lumped) model is presented. Explicit relations are derived for the dependence of the critical Semenov number (ψc) on the Rayleigh number (R*). It is shown that for R* → 0, ψc approaches the classical (conduction) limit e-1, while for R* ≫ 1, the ignition locus is given by the convection asymptote ψc/R* = 4 e-2. Inclusion of reactant consumption shows that the conduction asymptote disappears at B = 4 while the convection asymptote ceases to exist for B Ls < 3 + 2√2, where Ls is a modified Lewis number and B is the heat of reaction parameter. It is shown that the Semenov model has five different types of bifurcation diagrams of temperature against Rayleigh number (particle size), (single-valued, inverse S, isola, inverse S + isola and mushroom). This behaviour is found to be qualitatively identical to that of the forced convection problem investigated by Zeldovich & Zysin.","PeriodicalId":20605,"journal":{"name":"Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1990-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91365201","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 7

Static and dynamic behaviour of soils : a rational approach to quantitative solutions. I. Fully saturated problems 土壤的静态和动态行为:定量解决方案的合理方法。1、完全饱和问题

Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences Pub Date : 1990-06-08 DOI: 10.1098/rspa.1990.0061

O. Zienkiewicz, A. Chan, M. Pastor, D. K. Paul, T. Shiomi

引用次数: 367

Droplet combustion near a cold surface 靠近冷表面的液滴燃烧

Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences Pub Date : 1990-06-08 DOI: 10.1098/rspa.1990.0070

S. Chandra, C. Avedisian

{"title":"Droplet combustion near a cold surface","authors":"S. Chandra, C. Avedisian","doi":"10.1098/rspa.1990.0070","DOIUrl":"https://doi.org/10.1098/rspa.1990.0070","url":null,"abstract":"The combustion of a liquid droplet adjacent to a cold surface was studied experimentally. To isolate the effect of the proximity of the droplet to the surface, the ambient pressure (0.101 MPa), liquid composition (n-heptane), initial liquid volume (7 x 10-4 ml), surface material (quartz) and ambient temperature (20 ± 2°C) were held constant. A range of distances L from the surface were studied (1 mm < L < ∞). Both horizontal and vertical surface orientations were examined. A more limited set of experiments were carried out in a low gravity (i. e. low buoyancy) environment to provide a basis of comparison with relevant theoretical analyses. The flame shape, soot formation, fuel condensation, and droplet burning rate were all found to be strongly affected by the proximity of the droplet to the surface. For sufficiently large L the flame was observed to be closed around the droplet throughout burning. As L decreased, the flame was truncated. The droplet burning rate decreased as the droplet was brought progressively closer to the surface (in qualitative agreement with a relevant closed form potential flow solution to the analogous problem of a droplet burning adjacent to an adiabatic surface) and the burning rate of a droplet adjacent to a vertical surface was larger than for a horizontal surface. Surface orientation effects were observed to be absent for burning at low gravity. The extent of sooting as revealed by the flame colour was decreased, and fuel vapours condensed in a lens-like shape on the surface, as L was sufficiently reduced.","PeriodicalId":20605,"journal":{"name":"Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1990-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86001743","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 4

Receptivity of boundary layers: asymptotic theory and experiment 边界层的可接受性:渐近理论与实验

Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences Pub Date : 1990-06-08 DOI: 10.1098/rspa.1990.0064

V. Kozlov, O. Ryzhov

引用次数: 41

On the evolution of plane detonations 关于飞机爆炸的演变

Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences Pub Date : 1990-06-08 DOI: 10.1098/rspa.1990.0060

J. F. Clarke, D. Kassoy, N. E. Meharzi, N. Riley, R. Vasantha

引用次数: 40

Examination of electrocatalysis in the anodic O2 evolution reaction at Pt through evaluation of the adsorption behaviour of kinetically involved intermediate states 通过评价动力学参与中间态的吸附行为来考察Pt阳极析氧反应中的电催化作用

Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences Pub Date : 1990-06-08 DOI: 10.1098/rspa.1990.0065

B. Conway, T. Liu

{"title":"Examination of electrocatalysis in the anodic O2 evolution reaction at Pt through evaluation of the adsorption behaviour of kinetically involved intermediate states","authors":"B. Conway, T. Liu","doi":"10.1098/rspa.1990.0065","DOIUrl":"https://doi.org/10.1098/rspa.1990.0065","url":null,"abstract":"In regular heterogeneous catalytic reactions, evaluation of the adsorption behaviour of the ephemeral intermediates that participate kinetically in the main reaction pathway is often inaccessible experimentally. In electrocatalysis, on the other hand, electrochemical transient methods can provide such information. In the present paper, potential-relaxation transients are used to derive information on the electroactive, kinetically significant adsorbed intermediate states that are involved in the anodic O2 evolution reaction (OER) at Pt electrodes. By means of such transients, digitally recorded over 5–6 decades of time from microseconds to seconds, the adsorption capacitance of the intermediate states in the reaction is evaluated as a function of potential over a range corresponding to appreciable current densities for O2 evolution. Anodic O2 evolution takes place at Pt, as at all other metal anodes, on an oxide film. A well-defined state of such a film must be established by a pre-conditioning programme to make meaningful and reproducible kinetic studies on the OER. The state of the oxide film is conveniently characterized by means of cyclic-voltammetry. The intermediate surface states in the reaction can be two or more oxidation states of Pt atoms in the oxide and OH or O species at the oxide’s surface. Two distinct types of adsorption behaviour are distinguished for potentials above and below ca. 1.85 V against the reversible H2 electrode (RHE), and are related to the observed kinetics of the OER.","PeriodicalId":20605,"journal":{"name":"Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1990-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87272944","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 7

11B NMR spectra and structure of boric oxide and alkali borate glasses 氧化硼和碱硼酸玻璃的11B核磁共振光谱和结构

Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences Pub Date : 1990-05-08 DOI: 10.1098/rspa.1990.0048

S. Prabakar, K. Rao, C. Rao

引用次数: 29

Histories of adiabatic quantum transitions 绝热量子跃迁的历史

Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences Pub Date : 1990-05-08 DOI: 10.1098/rspa.1990.0051

M. Berry

引用次数: 148