Fracture Assessment of Carbon Fibre/Epoxy Reinforcing Rings through a Combination of Full-Scale Testing, Small-Scale Testing and Stress Modeling

Carbon fibre/epoxy rings are used as radial reinforcement for polymer bearing elements with nominal diameter 250 mm functioning under 150 MPa. Full-scale static and dynamic testing revealed no catastrophic failure for loading to 400 MPa, although there was circumferential splitting of carbon fibres at the machined top edge causing counterface wear under sliding. A combined numerical–experimental analysis was applied for design improvement with a representative small-scale qualification test on the real ring geometry, inducing additional stress concentrations compared to ASTM standards. Full-scale modelling revealed high radial–axial shear stresses (33 MPa) in non-hydrostatically loaded zones, while it increased towards 104 MPa under hydrostatic load conditions. The former is the most critical and should be simulated either on a small-scale unidirectional compression test or on a representative short beam shear test, respectively, measuring the radial–axial or radial–tangential shear strength. A relation between both small-scale states of stress was experimentally and numerically studied, experiencing that the composite ring has lower radial–tangential shear stress compared to radial–axial shear stress as a different hydrostatic stress state is observed in the bulk of the composite ring. As a compressive test is however more difficult to perform than a short-beam-shear test, a representative design criterion for shear fracture is determined from failure at 27 kN normal load in a short-beam-shear test. Finally, fracture is avoided by optimising the cross-sectional geometry of the composite reinforcing ring and close control of the processing parameters.     

An Evolutionary Model of Price Competition Among Spatially Distributed Firms

Various studies have shown the emergence of cooperative behavior in evolutionary models with repeated local interaction among spatially distributed agents. We investigate to what extent these findings generalize to evolutionary models of price competition among spatially distributed firms. We consider both one- and two-dimensional models, and we vary the amount of information firms have about competitors in their neighborhood. Our computer simulations show that the emergence of cooperative behavior depends strongly on the amount of information available to firms. Firms tend to behave most cooperatively if they have only a very limited amount of information about their competitors. We provide an intuitive explanation for this phenomenon. Our simulations further indicate that three other factors in our models, namely the accuracy of firms’ information, the probability of experimentation, and the spatial distribution of consumers, have little effect on the emergence of cooperative behavior.     

Solid ? liquid phase transformations in hypereutectic P/M Al-Si-Fe-X alloys

In this study, the metastable and stable solid liquid phase transformations of the hypereutectic alloys Al-20Si-5Fe-2Ni (wt%) and Al-17Si-5Fe-3.5Cu-1.1Mg-0.6Zr in as-atomised powder and in as-hot-forged material have been investigated. Differential Scanning Calorimetry (DSC) measurements at high temperatures have been performed. The resultant products have been thoroughly analysed using Light Optical Microscopy (LOM), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) microanalysis. During solidification large Si, (Al₄FeSi₂), FeNiAl₉, Al₇Cu₂Fe and Q(Cu₂Mg₈Si₆Al₅) are formed. A cooling rate of 5 °C/min and 1 °C/min is too high for the formation of the equilibrium phases (Al₅FeSi) and Al₇Cu₂Fe. The understanding of the sequence of transformations is useful in order to define appropriate processing parameters for these alloys produced by powder metallurgy. The temperature at which the first liquid phase appears during heating at 5 °C/min is 559 °C for the Al-Si-Fe-Ni powder and 506 °C for the Al-Si-Fe-Cu-Mg-Zr powder.     

The wetting of solids by molten metals and its relation to the preparation of metal-matrix composites composites

This review aims at making a bridge between the fundamentals of the wetting of solids by liquid metals and the practice of the preparation of metal-matrix composites. One recalls first the significance of concepts such as surface tension, work of adhesion, adsorption and the relation between these concepts, the phenomenon of wetting and the process of liquid metal infiltration. Thereafter, the wetting of various types of solids is considered: metals, oxides, carbon and carbides. !n the !light of this body of science, one proposes finally a critical evaluation of the literature concerning the preparation of metal-matrix composites by liquid metal infiltration techniques. Particular emphasis is devoted to reinforcements made of graphite, alumina or silicon carbide multifilament fibres; the use of coatings and the addition of alloying elements to the metal are successively discussed.     

Genetic Variation in Jasmonic Acid- and Spider Mite-Induced Plant Volatile Emission of Cucumber Accessions and Attraction of the Predator <Emphasis Type="Italic">Phytoseiulus persimilis</Emphasis>

Cucumber plants (Cucumis sativus L.) respond to spider–mite (Tetranychus urticae) damage with the release of specific volatiles that are exploited by predatory mites, the natural enemies of the spider mites, to locate their prey. The production of volatiles also can be induced by exposing plants to the plant hormone jasmonic acid. We analyzed volatile emissions from 15 cucumber accessions upon herbivory by spider mites and upon exposure to jasmonic acid using gas chromatography—mass spectrometry. Upon induction, cucumber plants emitted over 24 different compounds, and the blend of induced volatiles consisted predominantly of terpenoids. The total amount of volatiles was higher in plants treated with jasmonic acid than in those infested with spider mites, with (E)-4,8-dimethyl-1,3,7-nonatriene, (E,E)-α-farnesene, and (E)-β-ocimene as the most abundant compounds in all accessions in both treatments. Significant variation among the accessions was found for the 24 major volatile compounds. The accessions differed strongly in total amount of volatiles emitted, and displayed very different odor profiles. Principal component analysis performed on the relative quantities of particular compounds within the blend revealed clusters of highly correlated volatiles, which is suggestive of common metabolic pathways. A number of cucumber accessions also were tested for their attractiveness to Phytoseiulus persimilis, a specialist predator of spider mites. Differences in the attraction of predatory mites by the various accessions correlated to differences in the individual chemical profiles of these accessions. The presence of genetic variation in induced plant volatile emission in cucumber shows that it is possible to breed for cucumber varieties that are more attractive to predatory mites and other biological control agents.     

A recursive field-normalized bibliometric performance indicator: an application to the field of library and information science

Two commonly used ideas in the development of citation-based research performance indicators are the idea of normalizing citation counts based on a field classification scheme and the idea of recursive citation weighing (like in PageRank-inspired indicators). We combine these two ideas in a single indicator, referred to as the recursive mean normalized citation score indicator, and we study the validity of this indicator. Our empirical analysis shows that the proposed indicator is highly sensitive to the field classification scheme that is used. The indicator also has a strong tendency to reinforce biases caused by the classification scheme. Based on these observations, we advise against the use of indicators in which the idea of normalization based on a field classification scheme and the idea of recursive citation weighing are combined.     

THE ANTI-STRIPPINC PROPERTIES OF BASIC NITROGEN IN HYDROCRACKED RESIDS

The hydrocracked residues were found to be considerably enriched both in total nitrogen and in basic nitrogen relative to total nitrogen with respect to the feed asphalt. The matrix in which these basic nitrogen components are most likely to be found consisted of compact aromatic structures containing relatively few naphthenic and paraffinic moieties

Upon hydrocracking, the basicity of the remaining basic nitrogen increased with the level of conversion. It is this increased nitrogen basicity which most probably accounted for the enhanced anti-stripping properties of the hydrocracked residues.

Hot storage, such as could be expected during the transportation of the paving asphalt, resulted in the apparent loss of approximately 10%, on average, of basic nitrogen without a commensurate decrease in the anti-stripping effectiveness of the additive. Possible explanations lie in the chemical reactivity of the asphaltic binder

Attempts at isolation of a basic nitrogen concentrate have met with a modicum of success. Indications are that the nitrogen compounds extracted depend largely on the method of extraction     

直接拉伸试验及Superpave规范系统研究蜡对沥青低温性能的影响

用两种不同分子量的石蜡及一种微晶蜡掺和在沥青中,来研究蜡的性能(如分子量分布、平均分子量等)对沥青低温性能的影响.用Superpave沥青胶结料性能规范系统的BBR、DTT、临界龟裂温度(Tcritical)及玻璃转换温度(Tg)来研究掺有3%或6%蜡的沥青低温性能,低分子量及分子量分布窄的石蜡降低了沥青的DTT破坏应力,同时增加了正割模量(Secant Modulus)及BBR的热应力.微晶蜡对沥青的DTT破坏应力的影响比较少,并且不影响正割模量,但增加了BBR的热应力;但当将不同蜡的沥青混合,即将蜡的分子量分布扩大,则DTT破坏应力略为降低,正割模量不变,而BBR的热应力则减少.换言之,如果将含不同蜡的沥青混合,则蜡对沥青低温性能的影响降低,这会改善含蜡沥青的低温性能,原因可能是蜡的凝结受其分子量所影响,较宽的分子量分布会导致蜡在较宽的温度范围内慢慢凝结,缓和了蜡突然结晶对沥青低温性能的有害反应.     

Acoustic emission during fatigue crack propagation in SiC particle reinforced Al matrix composites

The acoustic emission (AE) behavior during fatigue propagation in aluminum 6061 and aluminum 6061 matrix composites containing 5, 10, and 20 wt pct SiC particle reinforcement was investigated under tension-tension fatigue loading. The purpose of this investigation was to monitor fatigue crack propagation by the AE technique and to identify the source(s) of AE. Most of the AEs detected were observed at the top of the load cycles. The cumulative number of AE events was found to correspond closely to the fatigue crack growth and to increase with increasing SiC content. Fractographic studies revealed an increasing number of fractured particles and to a lesser extent decohered particles on the fatigue fracture surface as the crack propagation rate(e.g., †K) or the SiC content was increased. This article is based on a presentation made in the symposium entitled “Creep and Fatigue in Metal Matrix Composites” at the 1994 TMS/ASM Spring meeting, held February 28–March 3, 1994, in San Francisco, California, under the auspices of the Joint TMS-SMD/ ASM-MSD Composite Materials Committee.     

Validation of a supervisory control system for energy savings in membrane bioreactors

The application of fixed operational protocols and settings for membrane bioreactors (MBR) often leads to suboptimal filtration conditions due to the dynamic nature of mixed liquor characteristics. With regard to process optimization and energy savings, the potential benefits of a dynamic control system, enabling to adapt fouling control actions (ACS outputs) in an automated way to the actual mixed liquor fouling propensity, are thus obvious. In this paper, the pilot-scale validation of such an advanced control system (ACS) is elaborated. A specific on-line fouling measurement method, the MBR-VFM (VITO Fouling Measurement), was used for the evaluation of the mixed liquor’s reversible fouling propensity, which was used as a primary ACS input parameter. A first series of tests with a gradual increase in complexity of the selected input and output parameters indicated the functionality of the ACS and demonstrated a substantial reduction of aeration, however sometimes at the expense of a higher fouling rate. The ACS was further fine-tuned and subsequently tested for a longer period under more dynamic operating conditions. A significant correlation was found between the reversible fouling potential measured by the MBR-VFM and the on-line permeability, indicating that the MBR-VFM is a suitable ACS input. Furthermore, an average 22% reduction in aeration flow to the membranes could be achieved without any obvious negative effect on filtration performance. This indicates that this approach is promising to optimize energy consumption in MBRs.