bluuebunny/crossref_metadata_2025_split huggingface dataset:
Three-Dimensional Finite-Element Simulation of Fatigue Crack Growth and Closure
Authors: Chermahini RG , Shivakumar KN , Newman JC 
Published: February 2009

A three-dimensional, elastic-plastic, finite-element analysis of crack growth and closure under cyclic loading was developed and used to study the behavior of a crack in a finite-thickness middle-crack tension specimen. The finite-element model was composed of eight-noded isoparametric, hexahedron elements. The material was assumed to be elastic-perfectly plastic. Two load histories, constant-amplitude loading and a single-spike overload, were considered. The crack front was extended one element length per cycle when the applied stress reached the maximum level. The crack was assumed to grow as a straight-through crack.
Results show that during unloading the crack front closes first on the exterior (free) surface of the specimen and closes last in the interior. Under constant-amplitude loading with a maximum applied stress level Smax of 0.25 times the yield stress of the material, the crack-opening stress levels reached a peak value of 0.34 Smax and 0.6 Smax at the interior and exterior regions of the crack front, respectively. The application of a single-spike overload caused an immediate drop in the opening stress level, but as the crack grew, the opening levels (interior and exterior) rapidly rose to values higher than those calculated under constant-amplitude loading. The calculated crack-opening stresses for the exterior and for the interior of the specimen were in quantitative agreement with previous finite-element calculations under plane-stress and plane-strain conditions, respectively. The crack-opening stresses for the interior were much lower than the exterior values.
Three-Dimensional Aspects of Fatigue Crack Closure in Surface Flaws in Polymethylmethacrylate Material
Authors: Troha WA , Nicholas T , Grandt AF 
Published: February 2009

An experimental investigation using a Newton interference method with a transparent polymethylmethacrylate (PMMA) to measure crack opening displacement and closure on surface flaw crack growth is described. Fatigue crack growth tests are conducted on rectangular plates loaded in bending using optical interferometry measurements to map the crack surface opening displacement profiles and define crack opening loads. Results are presented for an experiment of constant applied stress intensity factor along the crack face free surface. The crack opening displacement patterns and measured closure loads are found to be strongly influenced by the formation of a void internal to the crack surfaces.
Three distinct closure loads are identified and measured for surface flaws of various crack lengths. Upon loading the specimen, the first closure load is defined as the load that initially opens the crack free surface. A second closure load corresponds to the opening of the crack tip in the depth direction along the axis of symmetry. The third closure load corresponds to opening of the crack tip along the entire boundary. The crack closure loads, applied and effective stress intensity factors, and crack growth rates are presented as a function of crack length.
Evaluation of Attempts to Predict Large-Crack-Growth J-R Curves from Small-Specimen Tests
Authors: Marschall CW , Papaspyropoulos V , Landow MP 
Published: February 2009

A combined experimental and analytical study was conducted to assess the ability of J-resistance curves obtained from small fracture toughness specimens to predict large amounts of crack growth in highly ductile nuclear piping materials. Tests were conducted at 288C (550F) on 25.4-mm (1-in.)-thick compact tension specimens of 1T, 3T, and 10T planar dimensions. The materials investigated included Type 304 austenitic stainless steel and ASTM A516, Grade 70 carbon steel. Resistance curves were developed from the data using both deformation J, JD, and modified J, JM, estimation schemes. Some of the tests on austenitic stainless steel also were analyzed by performing elastic-plastic finite-element calculations, and the results were used to evaluate extrapolation procedures.
Extrapolation of small-specimen JD resistance curves to large amounts of crack growth resulted in sizable underestimations of resistance to fracture for the ductile materials studied. The JM-resistance curves, on the other hand, showed much less specimen-size dependence but tended to overestimate fracture resistance when small-specimen data were extrapolated. A tentative empirical method for extrapolating small-specimen data was developed. It was found also that the finite-element far-field J-R curves were very similar to the JM-R curves, and that the far-field finite-element J-R curve for the 10T specimen was virtually an extension of the J-R curves calculated for the 1T and 3T specimens.
An Analytical and Experimental Comparison of Rectangular and Square Crack-Tip Opening Displacement Fracture Specimens of an A36 Steel
Authors: Sorem WA , Dodds RH , Rolfe ST 
Published: February 2009

Analytical and experimental investigations of both rectangular-cross-section (t by 2t) and square-cross-section (t by t) three-point-bend crack-tip opening displacement (CTOD) fracture specimens were conducted on an A36 steel. This study is part of a long-range investigation aimed at developing criteria to evaluate the susceptibility to fracture in specific structural situations, that is, pressure vessels and structural steels with short cracks (a/W 0.15), where the square CTOD specimen must be used. Generally, the rectangular CTOD specimen is used in laboratory testing, but for weldment testing, where shallow surface cracks may exist, or for other structural applications with crack depth ratios other than a/W = 0.5, the square specimen is often required. The objective of this study is to compare the CTOD fracture toughness results of square specimens with those of rectangular specimens using equivalent crack depth ratios (a/W = 0.5).
Both analytical and experimental studies were conducted on full-size [31.8 by 31.8-mm (1.25 by 1.25-in.)] and sub-size [12.7 by 12.7-mm (0.50 by 0.50-in.)] square specimens. Static CTOD tests were conducted in the lower shelf and lower transition regions where structural steels such as A36 are typically used. Three-dimensional elastic-plastic finite-element analyses were conducted to compare the effect of specimen size and geometry on the specimen stress field.
The results of the square specimens were compared with the results of previously tested rectangular specimens that were tested and analyzed by Wellman et al. following the same procedures. In comparing these four specimen sizes, it was shown that the lower-bound CTOD values obtained experimentally were independent of either specimen size or geometry in the lower shelf and lower transition regions prior to stable crack growth. The near-crack-tip opening mode stresses at the center plane of each specimen were shown to be essentially equal for the four specimen sizes analyzed. This implies that the square and rectangular specimens with a/W = 0.5 may be used interchangeably to characterize the notch toughness prior to stable crack growth. It may also be possible to obtain the same lower-bound results using sub-size specimens which are less than the full thickness of the actual structure.
A Combined Statistical and Constraint Model for the Ductile-Brittle Transition Region
Authors: Anderson TL 
Published: February 2009

A model is presented which uses weakest link statistics to predict the fracture toughness of ferritic steels in the ductile-brittle transition region. This model is different from previous analyses in that it considers large-scale yielding and specimen geometry effects.
The model is used to predict median crack-tip opening displacement (CTOD) transition curves for American Bureau of Shipping (ABS) EH36 steel. The shape of the predicted curves agreed very well with the experimental data, but the absolute position of predicted and experimental curves differed by as much as 20C. The model was also used to predict CTOD distributions at constant temperatures, although direct comparison with experimental data was not possible. Analysis of the predicted toughness distributions indicated that a three-parameter Weibull fit of fracture toughness data may result in a nonconservative estimate of lower-bound toughness. An alternative procedure for estimating lower-bound toughness is described, together with a method for determining an upper-bound transition temperature.
A 300-mm-Diameter Triaxial Cell with a Double Measuring Device
Authors: Dupas J-M , Pecker A , Bozetto P , Fry J-J 
Published: February 2009

A large-diameter triaxial cell (φ 300 mm) is presented. Its uniqueness lies in the double measuring system of all parameters: axial strain, volumetric strain, and pore pressures. Owing to this system, accurate measurements can be taken, enabling the determination of the soil constitutive relationships from very small strains (elastic behavior) to failure strains. The cell can be used either under quasistatic monotonic or cyclic dynamic loadings. The apparatus has been used to evaluate the accuracy of the measurements and the influence of sample size on elastic Young's modulus, Poisson's ratio, and variation of secant modulus with strain.
Preliminary results show that, as opposed to conventional testing, significantly improved results are obtained with the double measuring system.
Environmental Durability of Adhesively Bonded Joints
Authors: Pitrone LR , Brown SR 
Published: February 2009

Effective determination of adhesively bonded joint durability is crucial for reliable component design and realization of advanced performance. In order to model bond endurance in a manner more consistent with severe service environments, a cyclic stress durability apparatus that achieved constant shear stress without loss due to creep relaxation was designed and implemented for accelerated joint durability analysis of two modified epoxy based structural adhesives. Results were compared with those achieved by sustained stress durability.
Thermal analysis of the bulk adhesives, both before and after hygrothermal exposure, was compared with bonded joint mechanical and durability performance to explore the potential utility of thermal analytical methods in describing adhesive joint properties.
Two cure histories for each adhesive were investigated to establish bonded joint performance and environmental resistance for conventional joint fabrication and potential adhesive/adherend co-curing capabilities.
Biomonitoring as an Integral Part of the NPDES Permitting Process: A Case Study
Authors: Marcus JM , Swearingen GR , Scott GI 
Published: February 2009

A case study of integration of extensive biomonitoring into the National Pollutant Discharge Elimination System (NPDES) permit of a synthetic organic chemical manufacturing firm in South Carolina to meet the objectives of the Clean Water Act is presented. NPDES monitoring requirements for specific chemicals and quarterly toxicity tests (Mysidopsis bahia) failed to predict severe water quality degradation in a small estuarine receiving stream. This severe disturbance was documented through benthic macroinvertebrate assessments and sediment elutriate bioassays. Additionally, chemical testing revealed the presence of a myriad of toxic, carcinogenic, and other organic chemicals in sediments and oyster tissue in the receiving stream and in outlying public shellfishing areas.
Implementation of monthly oyster-larvae bioassays, annual benthic macroinvertebrate community structure assessments, annual oyster recruitment/settlement assessments, and continuation of the mysid shrimp bioassays as NPDES permit requirements resulted in a comprehensive tool for actual determination of effluent toxicity as well as for guiding the in-facility reduction of toxicity. This comprehensive approach of laboratory toxicity testing of effluents and field monitoring of benthic macroinvertebrate communities provides a measure for assessing chronic or cumulative effects of complex effluents on aquatic communities, especially when those effluents are highly variable due to batch manufacturing processes. This case study suggests that biomonitoring is now developed to a level where it can be implemented to ensure directly that complex toxic effluents are regulated for optimum environmental protection.
An Approach for Integration of Toxicological Data
Authors: Shirazi MA , Lowrie LN 
Published: February 2009

The practice of reducing a dose-response test into a single number such as LC50 is convenient but inadequate for distinguishing between dissimilar modes of biological response. When the mean curves of two groups of tests with dissimilar slopes at LC50 cross over at a 50% line, they give rise to equal LC50 cross over at a 50% line, they give rise to equal LC50 numbers for both groups of tests, and if used exclusively to represent the results, the single LC50 will mask this difference. The sensitivity of an organism to an incremental change in the dose is measured by the slope of the dose-response curve at any dose level. The slope for some modes of toxic response can be initially zero at small dose, then increase substantially at higher values, and for other modes it can be infinitely large initially, then level off at higher values of the dose. The management of different chemicals requires different strategies that can be supported with a more comprehensive analysis of existing test data.
Several similar or replicate tests produce slightly different dose-response curves due to uncontrollable experimental and biological test factors. Continued focus on summarizing these tests by averaging their LC50 numbers hinders progress toward discovering a biological response mode from the dose-response points of similar tests.
The paper presents an approach for aggregating a group of similar test data into a single mean dose-response curve with error bounds quantifying the variability of the original data. Groups of similar tests are then classified using generalized exponential dose-response functions whose constants define modes of biological response and facilitate calculation of toxicity and sensitivity. Groups of similar data and classes of different groups of tests are used to demonstrate the application and the utility of the approach.
In Situ, Time-Series Measurements for Long-Term Ground-Water Monitoring
Authors: Benson RC , Turner M , Turner P , Vogelsong W 
Published: February 2009

Because recent legislation has made long-term ground-water monitoring an important issue, the methods by which data at a site are collected are of utmost importance. The traditional method of site assessment, which consists of drilling a number of monitor wells from which water samples can be taken and tested, does not provide enough information on which to base a long-term ground-water monitoring program. In situ, time-series measurements using a variety of geophysical techniques, on the other hand, can provide a wealth of information not available through traditional measurement methods.
Over the past ten years, geophysical measurements made from the surface have been used extensively at waste-disposal sites to assess natural hydrogeologic conditions and map the lateral and vertical distribution of contaminants. In recent years, downhole measurements have been used to produce more-detailed information about vertical contaminant distribution through the use of vertical profiles. Examples illustrating these applications are presented in the text. Made at appropriate intervals over a period of time, surface and downhole measurements can be used to provide highly accurate, three-dimensional maps of contaminant flow in ground water and provide a means of early leak detection at waste-disposal sites.
Because the values measured by geophysical methods are dominated by the specific conductance of pore fluids, they can be related to the specific conductance of ground-water samples, thus correlating geophysics with traditional assessment methods. Correlation between in situ, geophysical measurements and inorganic, ground-water sample analyses have been as good as 0.96 at the 95% confidence level. At one landfill, the correlation with total organic carbon was 0.85 at the 95% confidence level.
Three examples of sites where the spatial extents of contaminant plumes have been mapped using geophysical, time-series measurements are presented in this paper. They consist of a localized spill, a large landfill, and a flowing, abandoned well. Measurements taken over a period of time at each of these sites clearly illustrate how the actual dynamics of a contaminant plume can be assessed as it interacts with natural and man-induced variables.
Verification of Sampling Methods and Selection of Materials for Ground-Water Contamination Studies
Authors: Barcelona MJ , Helfrich JA , Garske EE 
Published: February 2009

The development of proven sampling methods which incorporate the use of noncontaminating materials has progressed steadily in the past five years. Once the hydrogeologic conditions and potential contaminant source characteristics have been identified at a particular study site, the selection of drilling methods, suitable sampling mechanisms, and appropriate materials must be made for the chemical constituents of interest. The results of laboratory and field testing of sampling mechanisms, tubing and well casing materials, and sampling procedures have identified elements of sampling protocols which are effective in reducing sampling bias and imprecision. The proper selection of these elements bears on the accuracy and precision of all subsequent measurements, since field blanks, sample splits, replicate samples, and standards can only account for errors which occur after sample collection.
The limited laboratory and field studies of sampling error strongly suggest that poor borehole seals and improper well purging techniques are serious sources of bias for chemical constituent determinations. Sampling mechanisms and materials are also potential sources of bias, particularly for pH and gas-sensitive parameters and volatile organic compounds. Quality assurance must begin with the decisions made in establishing a sampling point (that is, well or dedicated installation) and collecting samples.
Adsorption and Degradation of Enhanced Oil Recovery Chemicals
Authors: Crocker ME , Marchin LM 
Published: February 2009

The possible contamination of ground waters by injection of chemicals used for enhanced oil recovery was evaluated at the National Institute for Petroleum and Energy Research. The objective of the study was to delineate the nature of the reservoir rock/injected chemical interactions and the potential for ground-water contamination.
As a preliminary step in the investigation, a method for determining the cation exchange behavior of consolidated sandstone specimens at in situ flow-through conditions as compared to a crushed specimen method at ambient conditions was developed. The flow-through method was tested in the laboratory on small core specimens (0.038 by 0.102 m) and was used as an indicator of the potential of chemicals to interact with the rock matrix.
Results obtained provided individual concentration profiles for major and minor amounts of cations removed from the core after exchanging with lanthanum. The information obtained is valuable in assessing the potential compatibility of injected fluids with a reservoir formation. Upon comparing the cation exchange capacity (CEC) for specimen C071 (Parkman formation, sandstone) the values were 13.9 meq/kg for the crushed method versus 6.11 meq/kg for the flow-through method. This was a consistent finding for all the specimens tested; CECs determined on the crushed core specimens were higher than those determined by the lanthanum flood on the whole core. These displacement tests could also indicate prior chemical contamination by observation of the cations displaced by the flow-through method. This option is not available using the crushed core method.
The whole core flow-through method was adapted to a larger (0.155 by 0.762 m) closed core system to evaluate the stability/degradability of enhanced oil recovery (EOR) chemicals: three surfactants, a co-surfactant, and a polymer. Seven separate tests were conducted with test periods ranging from 17 to 135 days. The tests were conducted at simulated reservoir conditions of temperature, pressure, and fluid flow rate. Specimens were taken periodically and analyzed using gas chromatography, liquid chromatography, ultraviolet spectroscopy, or colorimetric techniques of both. The chemicals were found to be stable for the conditions studied during the testing periods with no detectable amounts of degradation products. These tests indicate the stability of these EOR chemicals over extended time periods at in situ conditions and the potential of the chemicals to contaminate ground-water sources over a long time period.
Monitoring Ground-Water and Soil Contamination by Remote Fiber Spectroscopy
Authors: Klainer SM , Koutsandreas JD , Eccles L 
Published: February 2009

Fiber optics, lasers, chemistry, fiber optic chemical sensors (FOCS), optics, and spectroscopy have been integrated to form the new technology of remote fiber spectroscopy (RFS). This method permits the development of ductile probes to detect and monitor ground-water contaminants. The key to this concept is the FOCS, a fiber termination with preselected chemical and physical properties. This is attached to the distal end of the fiber so that specific, sensitive analyses of ground-water constituents can be made. A single fiber is used for both excitation and for collection of the return signal, thus keeping the sensor small and optically simple.
The first FOCS being developed is to be used for both “early warning” and long-term monitoring of organic chloride. The chemical basis for this FOCS is a modified Fujiwara reaction. The FOCS, in conjunction with a field fluorimeter, have been used to make in situ measurements in a chloroform-contaminated well. Preliminary data indicate good agreement between the FOCS data and independent gas chromatography analysis of collected samples.