bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Simple Method for Measuring Tearing Energy of Nicked Rubber Strips
Authors: Oh HL 
Published: March 2009

A convenient test configuration for measuring critical tearing energy of rubber is to pull thin nicked strips of the rubber in extension. In the past, methods of measurements employed for this configuration are based on concepts which obtain “tearing energy” through differentiation with respect to the crack length. As a consequence, measurements have to be made on several identical specimens having different crack lengths. This paper describes a simple method based on the J-integral which requires no differentiation and calculates the tearing energy from measurements made on one specimen only. This allows an efficient use of test material and reduces the complexity of critical tearing energy measurement.
Implementation of the J-integral method is illustrated on the uniaxial stretching of a nicked rubber strip. The accuracy of results obtained is found to be comparable to that obtained by existing methods.
A Fracture Mechanics Approach to Creep Crack Growth
Authors: Landes JD , Begley JA 
Published: March 2009

A fracture mechanics approach was used to study high-temperature creep crack propagation. Crack growth rates were correlated with the C*-parameter which is an energy rate line integral. For materials conforming to a nonlinear stress and strain rate relationship in the steady-state creep range, specifically, those which can be properly idealized as purely viscous (negligible elastic and transient creep effects), C* characterizes the crack tip stress and strain rate fields.
Crack growth rate tests were conducted in the creep range on a discaloy superalloy at 1200°F (920 K). Two specimen geometries were tested, a center cracked panel and a compact geometry, to establish the geometry independence of this approach. The results showed that crack growth rate correlated with the C*-integral, while other parameters (K and nominal stress) failed to adequately characterize crack growth rate.
What R-Curves Can Tell Us About Specimen Size Effects in the KIc Test
Authors: Lake RL 
Published: March 2009

Size effects in the KIc test were investigated by testing duplicate compact specimens in ten different combinations of five thicknesses and five widths. Curves of crack resistance as a function of crack extension were calculated in terms of strain energy release rate, G, rather than stress intensity factor, K. It was found that the entire set of data could be represented by a single linear equation of the form, R = Ro + ρΔa. The coefficient, ρ, was found to be an inverse function of specimen thickness.
When this family of R-curves is compared with the driving force, G, curves for the various specimen sizes, it can be seen that the ratio of maximum load to the measuring point load (Pmax/PQ) in the record of a plane strain toughness test, depends primarily on the width/thickness ratio of the specimen. This ratio appears to bear no relation to the contribution of crack tip plasticity to the apparent crack extension at the measuring point. Accordingly, inclusion of a maximum value of this ratio in the validity requirements of ASTM Method E 399 for the purpose of restricting such a contribution is questioned.
Residual Life Estimates for Structures with Partial Thickness Cracks
Authors: Besuner PM 
Published: March 2009

This paper presents a practical approach for estimating residual fatigue life of structures with partial thickness cracks under arbitrary Mode I cyclic elastic stress fields. Residual life is defined herein as the number of cycles required to grow the crack from specified initial dimensions to some final configuration that results in static failure. A powerful influence function theory is modified for application to three-dimensional stress analysis of planar crack problems with arbitrary crack front shapes. The resulting procedure allows stress intensity factor solutions and residual fatigue life estimates for any Mode I stress field applied to the crack geometry.
Exact stress intensity factor solutions are presented for the buried ellipse under arbitrary Mode I stress fields. A procedure is outlined to build useful, accurate stress intensity factor algorithms for complex surface crack geometries from a few three-dimensional numerical stress analyses.
Establishing Steady-State Thermal Conditions in Flat Slab Specimens
Authors: Shirtliffe CJ 
Published: March 2009

The thermal response of flat slab specimens subjected to four sets of thermal boundary conditions is examined. The conditions are typical of thermophysical test apparatus, and the four sets of conditions are similar. Initial temperatures are uniform and the cold face temperature is stepped to the required value. There are four different hot face conditions: (1) constant temperature, (2) constant heat flow, (3) zero heat flow followed by constant temperature, and (4) zero heat flow followed by constant heat flow.
Solutions are given for the heat transfer problems, and the equations are truncated, then inverted, to yield simple, approximate expressions for response time. The precision of the approximate equations is shown to be adequate for prediction purposes; the four sets of conditions are ranked in order of increasing response time; and the occurrence of optimum situations is noted.
Radiative Contribution to the Thermal Conductivity of Fibrous Insulations
Authors: Linford RMF , Schmitt RJ , Hughes TA 
Published: March 2009

Design studies on the reuseable surface insulation (RSI) systems for the Space Shuttle require accurate data on the thermal conductivity of ceramic-fiber insulations. Well-established laboratory techniques, such as the guarded hot plate experiment, are available for such measurements; however, caution must be exercised in applying laboratory data to widely different re-entry thermal environments. The heat-transfer associated with infrared radiation transmitted through the fibrous materials must be considered. Various analytical models have been developed to account for this radiant heat transfer, but their verification has often been incomplete. A new approach has now been applied in which infrared transmission measurements were made with an optical system that collected all the scattered radiation transmitted through the back surface of fibrous samples. Experimental data were analyzed using a “two-flux” model for the radiation scattered and absorbed in the materials and excellent correlation was obtained between theory and experiment. To account for the wavelength dependence of the scattering cross-sections of many materials, a “four-flux” model was developed. This model was used to compute the contribution of the radiation transmission to the total thermal conductivity of samples measured on the guarded hot plate equipment. The contribution was shown to be as high as 75 percent of the total conductivity at temperatures above 1000 K.
The significance of this result is that data obtained from such instruments should not be used in heat-transfer design computations without regard to the radiation transmission. Such regard will be particularly important in the thermostructural analyses of RSI for the Space Shuttle and other re-entry vehicles.
Analysis and Measurement of the Heat Transmission of Multi-Component Insulation Panels for Thermal Protection of Cryogenic Liquid Storage Vessels
Authors: Bourne JG , Tye RP 
Published: March 2009

A new concept involving the use of easily fabricated and assembled panels consisting of balsa wood, rigid plastic foams, and wood facings has been proposed for the external thermal protection of large liquid natural gas storage vessels.
Heat transmission determinations in scale models of the proposed panels up to 90-mm thick have been undertaken with the use of a 600-mm square guarded hot plate apparatus for the proposed use temperature conditions. In addition, thermal conductance measurements on the basic components have been made at regular temperature intervals over the approximate range 100 to 300 K.
An analytical model has been derived to predict the variation in test results with geometry. This model can be used to select the optimum full scale configuration considering both thermal and structural performance and to predict tank heat leakage.
Uniaxial Failure of Composite Laminates Containing Stress Concentrations
Authors: Nuismer RJ , Whitney JM 
Published: March 2009

Two previously developed failure criteria for predicting the uniaxial tensile strength of a laminated composite containing through-the-thickness material discontinuities (notches) are subjected to further experimental scrutinization. In particular, the two-parameter (unnotched tensile strength of the laminate and a characteristic length) models, which are capable of predicting observed discontinuity size effects without resorting to the concepts of linear elastic fracture mechanics, are based on limited experimental verification.
In the present paper, and experimental program is presented which examines the effect of changes in the material system, the laminate fiber orientations, and the notch shape and size (stress gradient), on the model predictions. This is accomplished by obtaining experimental data on two material systems, glass/epoxy and graphite/epoxy, in conjunction with two orientations of fiber-dominated laminates containing through-the-thickness circular holes and sharp tipped cracks of several sizes.
In addition to the test results, two observations based on the models are presented. First, the statistical failure distribution for a composite containing a circular hole is predicted using the models and shown to agree well with experimental observations. Second, an Irwin type correction factor applied to the stress intensity factor is shown to result in nearly constant values of the critical stress intensity factor for all values of crack length. The correction factor is shown to be related to the characteristic length of the present models.
Fracture Mechanics Correlation of Boron/Aluminum Coupons Containing Stress Risers
Authors: Adsit NR , Waszczak JP 
Published: March 2009

The mechanical behavior of boron/aluminum near stress risers has been studied and reported. This effort was directed toward defining the tensile behavior of both unidirectional and (0/ ±45) boron/aluminum using linear elastic fracture mechanics (LEFM). The material used was 5.6-mil boron in 6061 aluminum, consolidated using conventional diffusion bonding techniques.
Mechanical properties are reported for both unidirectional and (0/ ±45) boron/aluminum, which serve as control data for the fracture mechanics predictions. Three different flawed specimen types were studied. Tension coupons containing circular centerholes, double edge notches, and center notches as well as control specimens were tested. The circular hole and double edge notched specimens were tested with various flaw sizes. In each case the series of specimens remained geometrically similar to eliminate variations in finite size correction factors. The center notched specimens were used to obtain conditions more in line with conventional plane-strain fracture testing.
The fracture data from these tests were reduced using two techniques. They both used conventional LEFM methods, but the existence of a characteristic flaw was assumed in one case and not the other. Both the data and the physical behavior of the specimens support the characteristic flaw hypothesis. Cracks were observed growing slowly in the (0/ ±45) laminates, until a critical crack length was reached at which time catastropic failure occurred.
Measurement of the Viscosity of Multigrade Oils in a Running Engine
Authors: Lane G , Roberts DC , Tims JM 
Published: March 2009

Conventional laboratory viscometric methods are not adequate to characterise the behaviour of multigrade oils in service, in that they take no account of the high shear rates occurring in running engines. A technique has been developed which permits the measurement of apparent viscosity in the crankshaft bearings of engines running under road conditions. The technique is to isolate a single bearing, provide it with its own oil feed and calibrate flow-rates through it under normal running conditions using single grade oils. Flow rates obtained with multigrade oils can then be converted to apparent viscosities, seen by the bearing under operating conditions.
Results show that temporary viscosity loss due to shear is important even at moderate speeds (3000 rpm) in normal production engines. Shear breakdown characteristics of a range of different chemical types of VI Improvers have been compared. The technique has also been modified to permit determination of the minimum viscosity acceptable to the engine by relating this parameter to temperature increases in the bearings.
Time Dependance of Polymer Oils Shear Thinning Theoretical and Practical Consequences
Authors: du Parquet JPR 
Published: March 2009

Theoretical analysis supported by specially designed experiments show that the viscosity loss of polymer thickened oils is basically a time dependant phenomenon. Depending on the value of the residence time of the oil in the contact and on the critical degradation time corresponding to the shear severity, it is possible to describe the case of EHD contacts such as gears and HD contacts such as plain bearings.
The results have theoretical and practical consequences. In particular the viscosity in EHD contacts could be much lower than usually supposed. A better understanding of mechanical shear is expected from the proposed approach.
Current Concepts of Indicator Bacteria
Authors: Yehuda K 
Published: March 2009

Pathogenic bacteria excreted in human feces are found in low counts in wastewater and are known to be more sensitive to environmental conditions than Escherichia coli. The latter, excreted both by humans and warm-blooded animals, are used as an indicator of fecal wastes which may contain the pathogen, but the validity of this practice is often questioned. In wells recharged with chlorinated lake water, regrowth of coliform bacteria reached 105/100 ml when the water was re-pumped 7 to 28 days later. Very often, the more sensitive E. coli die away and are replaced by other coliforms, so that counts do not in themselves indicate a change in water quality.
Recently, low numbers of Samonella have been detected with the aid of large sampling procedures. On the other hand, there has been little additional data on the efficiency of wastewater treatment plants. Survival varied from 0.003 up to 29 percent in a recent study. S. typhimurium survived in a sand column up to 44 days, while S. typhi did not last more than seven days. Shigella flexneri, introduced into an experimental oxidation pond, were recovered from the effluent but were killed by application of 8 mg/1 chlorine after a short contact time.
The possibility of using coliphage as a means for identifying E. coli has been considered in an additional investigation. Coliphage are found in wastewater effluents in counts ranging from 104 to 105/100 ml. They are quite durable under adverse conditions and have been found to be highly resistant to chlorination. Enterovirus densities in wastewater vary between 100 and 2000/100 ml. Comparative studies have indicated that coliphage are found whenever enteroviruses are, and their ratio may vary from 1000 to one to as low as ten to one. It is believed that this recent technique employing indicator microorganisms will permit more rapid and precise evaluations of water quality and potential health hazards.
Microbiological Monitoring—A New Test for Fecal Contamination
Authors: Leclerc H , Mossel DA , Trinel PA , Gavini F 
Published: March 2009

Bacteriological monitoring of drinking water has not changed essentially during the last decennium. Escherichia coli and fecal coliforms are still traditionally used as index organisms, although methods are slightly different in various countries.
Investigations carried out by the authors have demonstrated that conventional methods can still be criticized in two respects. The spontaneous dying off of the Salmonella in water often occurs at a considerably lower rate than that of E. coli, which can lead to falsely negative results. In addition, investigations on human enteric flora composition, using newer methodology, have demonstrated that coli-aerogenes bacteria other than E. coli occur in relatively high concentrations. Two approaches will allow the elimination of these deficiencies of conventional monitoring of drinking water. They are using the entire group of Enterobacteriaceae as index organisms or considerably increasing the sensitivity of testing for E. coli.
For the latter purpose, an instrumental, continuous method has been developed. Water samples are first passed through a hollow fiber ultrafiltration device. Thereupon enrichment is carried out by culturing in lactose broth at 41°C. After stripping off the carbon dioxide (CO2) formed by fermentation, the liquid is mixed with a glutamate solution buffered at pH 3.9, the CO2 formed set is freed by acidification, and then absorbed in a phenolphtalein buffer which is ultimately examined colorometrically. The sensitivity of this method is 1 colony forming unit (cfu) of E. coli/100 ml or better. It has the additional advantage of allowing much more representative sampling of a water supply than customarily carried out.
Potential Health Hazards Associated With Pseudomonas aeruginosa in Water
Authors: Hoadley AW 
Published: March 2009

Pseudomonas aeruginosa is an opportunistic pathogen of man and animals which may be spread by water. The major source of P. aeruginosa in waters appears to be fecal wastes of man and animals associated with man, although growth may occur under certain conditions. The demonstration of the species in surface waters suggests the influence of man, and its numbers reflect the degree of pollution. However, they survive only for short periods, and there frequently appears to be little relation between populations of P. aeruginosa and those of other pathogens or fecal indicators.
The value of P. aeruginosa as an indicator of potential health hazards associated with water must be judged on the basis of its own role as a waterborne pathogen. In this paper, the role of P. aeruginosa as a waterborne pathogen, its sources, and its behavior in aquatic environments are reviewed. Its isolation from drinking waters, farm water supplies, swimming pool waters, whirlpool waters, and surface recreational waters should be regarded with concern. However, while authorities have recommended limitations on P. aeruginosa in waters used for various purposes, few epidemiologic studies have been undertaken upon which to base standards, and few standards have been established.
Bifidobacteria as Water Quality Indicators
Authors: Levin MA 
Published: March 2009

The potential value of bifidobacteria as indicators of fecal pollution in water has not been fully explored. Nevertheless, a number of workers have suggested that bifidobacteria may be useful as indicator Organisms because (a) they do not multiply in nature, (b) they exhibit survival characteristics which compare favorably to Escherichia coli, and (c) they may be useful as specific indicator organisms to differentiate animal from human fecal pollution.
An identification scheme for the most common species and which may be applicable in determining the type of pollution has been developed, and current techniques of speciation and quantitation are discussed.
Klebsiella
Authors: Vlassoff LT 
Published: March 2009

Klebsiella pneumoniae is well distributed in the environment and found to be associated primarily with wastes high in organic matter and human activity.
K. pneumoniae is a serious opportunistic pathogen of increasing concern in hospitals, where precolonization seems to be a prerequisite to infection. Epidemiological data are lacking to link infection with high K. pneumoniae concentrations in the environment. Presently, it cannot be enumerated reliably by primary plating methods.
The presence of K. pneumoniae in water indicates degraded quality, and it is probably as significant as finding Escherichia coli and a good indicator of pollution from certain organic wastes.
Effect of Moisture on Epoxy Resins and Composites
Authors: Delasi R , Whiteside JB 
Published: March 2009

The effect of absorbed moisture on the properties of six neat epoxy resins (3501-5, 3501-6, 3502, 5208, 934, and NMD 2373) and three epoxy composites (AS/3501-5, B/5505, and hybrid B/5505-AS/3501-5) is explored. Excellent agreement among the diffusion coefficients, activation energy, and activation entropy is observed for all resins with the exception of NMD 2373. Good correlation exists between neat resins and corresponding composites. The effect of a weekly thermal cycle on the diffusivity and equilibrium moisture content of two resins and three composites is presented. Correlations are developed between preconditioning temperature and relative humidity on the magnitude of the anomalous moisture absorption.
In addition, the effect of absorbed water on the glass transition temperature of six neat epoxy resins and two composites using thermomechanical analysis is considered. The water generally behaves as a classical plasticizer of the epoxy resin, lowering the glass transition temperature as predicted from theory. Comparison between neat 3501-5 resin and AS/3501-5 reveals generally good correlation in Tg at comparable resin moisture levels, but plasticized hybrid boron-graphite/epoxy laminate exhibits a somewhat lower Tg than predicted from theory.
Effect of an External Stress on Moisture Diffusion and Degradation in a Graphite-Reinforced Epoxy Laminate
Authors: Gillat O , Broutman LJ 
Published: March 2009

The effect of external stress on moisture diffusion and mechanical properties degradation of a graphite/epoxy composite, Scotchply SP-313, has been investigated. Moisture gain as a function of time is determined for the composite subjected to four tensile stress levels in the range of 0 to 65 percent of its ultimate tensile strength (UTS).
Experimental techniques to determine moisture gain in a composite subjected to external stress have been developed and discussed. In addition, the residual (after drying) and the current (wet) short-beam shear strength and the flexural strength as a function of moisture content and external stress level have been determined for the composite.
The formation of environmental damage by the combined stress and humid environment conditions as well as the mode of failure in the short-beam test was investigated by scanning electron microscope (SEM) studies. Results indicated that the moisture absorption process into the graphite/epoxy composite subjected to external stress, at the levels used in this study, can be predicted effectively by Fick's second law of diffusion. Increasing the external stress level produces higher effective diffusivities, and higher initial absorption rates. A significant increase was observed in laminates subjected to more than 45 percent of their UTS and containing more than 1 percent moisture. This was attributed to early formation of cracks within the 90-deg plies caused by moisture degradation of the matrix or interface strength.
The current and residual short-beam shear strength was reduced with increase in moisture content. By enhancing the moisture penetration into the composite, the external stress accelerates the mechanical degradation process.
The flexural strength, which is a fiber-dominated property, showed a very low sensitivity to application of external stress for the levels used in the present study.