bluuebunny/crossref_metadata_2025_split huggingface dataset:
Shearing Behavior of Compacted Clay after Saturation
Authors: Lovell CW , Johnson JM 
Published: March 2009

The purpose of this investigation was to ascertain the relationships among the compaction conditions (dry density moisture content and compaction energy) and the shearing behavior after saturation for a kneading compacted, highly plastic clay. The effective stress strength and pore pressure parameters were evaluated for various compaction conditions through the performance of consolidated undrained triaxial tests with pore water pressure measurement (CU¯) at a constant rate of strain. Long-term environmental effects were approximated prior to shear with backpressure saturation followed by consolidation to an isotropic state of stress representing the vertical load applied by succeeding lifts of an embankment.
The results of the testing program showed that the effective stress friction angle is relatively invariate for the range of compaction conditions investigated. The magnitude and range of variation of the measured values of the effective stress strength intercept were small. However, the volumetric strain upon saturation and the values of Skempton's A-parameter at failure were strongly affected by compaction conditions. Accordingly, the undrained strength of the compacted clay was significantly altered by the details of compaction.
Statistical analyses were performed to construct prediction equations based on the compaction variables for percent volume change due to saturation and consolidation. Skempton's A-parameter at failure, and the effective stress strength intercept. The equations obtained for percent volume change due to saturation and consolidation and Skempton's A-parameter at failure indicate that as-compacted dry density, initial degree of saturation, and consolidation pressure are the critical variables influencing behavior. The equation for the effective stress strength intercept indicates that initial void ratio and compaction moisture content are the significant variables. These equations will aid efforts to predict and modify the long-term shear behavior of compacted cohesive soils.
Nonlinear Anisotropic Stress-Strain-Strength Behavior of Soils
Authors: Prevost JH 
Published: March 2009

Soils consist of an assemblage of particles with different sizes and shapes which form a skeleton whose voids are filled with various fluids. The stresses carried by the soil skeleton are conventionally termed “effective stresses” in the soil mechanics literature, and those in the fluid are called the “pore-fluid pressures”. In cases in which some flow of the pore fluid can take place, there is an interaction between the skeleton strains and the pore-fluid flow. The solution of these problems therefore requires that soil behavior be analyzed by incorporating the effects of the flow (transient or steady) of the pore fluid through the voids, and thus requires that a multiphase continuum formulation be available for soils. Such a theory was first developed by Biot (1955) for an elastic porous skeleton. However, it is observed experimentally that the stress-strain behavior of the soil skeleton is strongly nonlinear, anisotropic, elastoplastic, and path-dependent. An extension of Biot's theory into the nonlinear anelastic range is therefore necessary in order to analyze the transient response of soil deposits. Such an extension of Biot's formulation is proposed herein by viewing soil as a multiphase medium consisting of an anelastic porous skeleton and viscous fluids, and by using the modern theories of mixtures developed by Green and Naghdi (1965) and Eringen and Ingram (1965).
In order to relate the changes in effective stresses carried by the soil skeleton to the solid rate of deformation tensor, a general analytical model is used which describes the nonlinear, anisotropic, elastoplastic, stress and strain dependent, stress-strain-strength properties of the soil skeleton when subjected to complicated three-dimensional and, in particular, cyclic loading paths. The theory falls within the general framework of the formalism of classical plasticity theory. It combines properties of isotropic and kinematic plasticity, and allows for the adjustment of the plastic hardening rate to any kind of experimental hardening law by using a collection of nested yield surfaces. It is shown that the model parameters required to characterize the behavior of any given soil can be derived entirely from the results of conventional soil tests. The model's extreme versatility and accuracy is demonstrated by applying it to represent the behavior of both cohesive and cohesionless soils under both drained and undrained, monotonic and cyclic loading conditions.
The use of the proposed formulation for solving boundary value problems of interest in soil mechanics is illustrated.
On the Random Aspect of Shear Strength
Authors: Yong RN , Tabba MM 
Published: March 2009

This paper discusses the random nature of shear strength of soils as opposed to the customary deterministic approach, where shear strength is thought of as a property that attains a specific value. In this approach uncertainty resulting from the intrinsic nature of the soil, as well as from the sampling and testing techniques (STT), is identified and supported by actual data.
Implications of the random character of shear strength are discussed insofar as they affect present concepts of soil plasticity. This paper advances the notion that currently used yield criteria are merely theoretical models which fit available data to some extent and could actually be violated.
An analytical model of mapping and prediction of shear strength is introduced, where one, two, or more sets of measurements corresponding to various STT are analyzed and could be combined to enable prediction of the mean, variance, and covariance of shear strength at desired locations.
The Need for Pore Pressure Information from Shear Tests
Authors: Shields DH , Skermer NA 
Published: March 2009

Geotechnical engineers are familiar with the role that time plays in the stability of the sides of an excavation. The sides of trenches dug through silts and fine sands are often observed to stand vertically for perhaps 10 or 15 min, then start to fail; railroad cuts through London clay started to fail after 60 years. The time to failure is a function of both the permeability and the volume change characteristics of the soil or rock which is involved.
In open pit mining, the time to failure is of utmost importance, yet it is only now that theoretical tools are available which enable the engineer to design slopes for both economy and safety. This recent theoretical work points out the need for the pore pressure response of the soil or rock to be measured during strength testing. The need and the test requirements are the subject of this article.
Fatigue Crack Growth Rates as a Function of Temperature
Authors: Marci G 
Published: March 2009

The equation dadN=C[(KlG−Klmin)+ΔKT][(Klmax−KIG)−ΔKT]2 had been proposed by the author to predict fatigue crack growth rates. By adopting this functional relation and setting KIG = 0.5 KImax (KIG ∼ KIopen under constant-amplitude cyclic loading), there are the two parameters, C and ΔKI, left to be determined from experimental data.
The parameters C and ΔKT for several structural alloys as a function of temperature between room temperature and 811 K had been analyzed. It was found that the “fatigue tolerance range” ΔKT decreased linearly with increasing temperature. Initially, the parameter C increases nearly linearly with increasing temperature and then increases steeply at higher temperatures. In the present work, this temperature dependence is shown to be found between 4 and 911 K by analyzing low-temperature as well as additional high-temperature data for Inconel 718 and Inconel X-750. By assuming the observed qualitative temperature dependence of C and ΔKT as being correct, available fatigue crack growth rates for Type 304 stainless steel obtained at temperatures ranging from 4 to 922 K were analyzed with respect to C and ΔKT.
Anomaly of Toughness Behavior with Notch-Root Radius
Authors: Datta KP , Wood WE 
Published: March 2009

The present investigation has studied the effects of notch-root radii on the Charpy apparent toughness of as-quenched and tempered 4340 steel as a function of (1) test temperature (liquid nitrogen and room temperature), (2) strain rate (high and slow strain rates corresponding to Charpy and plane-strain fracture toughness testing rates), and (3) grain size (25 and 250 μm). The toughness was evaluated by instrumented and slow-bend Charpy tests. Fracture surfaces were examined by scanning electron microscopy.
The results showed that initially the toughness increased as the notch-root radius increased, but that after a critical notch-root radius was reached, the toughness dropped. The loss in toughness was coincident with a change to an intergranular fracture mode initiation. Also, the critical root radius at which the drop in toughness occurred was temperature and strain-rate dependent. These results are not in agreement with other published results, which always show increasing toughness with increasing notch root radius beyond a limiting root radius. These results and the limitation of the current theories are presented and discussed in this paper. A physical process for the intergranular fracture mode initiation is also discussed.
Fracture Mechanics Technology Applied to Individual Aircraft Tracking
Authors: Denyer AG 
Published: March 2009

The paper presents a crack growth analysis approach to individual aircraft tracking that will meet the intents and objectives of the U.S. Air Force requirements. The structural life definitions are discussed in terms of definitive crack sizes for both the durability and damage tolerance of the structure.
Instituting a tracking program for a specific aircraft fleet requires a background of data relating to baseline spectra, critical structural locations, and expected airplane usage. The sources of such data are outlined. The body of the paper presents a cost-effective crack growth integration technique which makes tracking for durability feasible even if the life is as much as 100 000 h. Closely linked with the crack growth analysis technique is the method of collecting the flight data. The presentation considers two distinct approaches, a pilot form system and a structural loads measuring system. The methodology is being incorporated into the overall tracking system for the USAF T-39 Utility Trainer which will be the first to use the crack growth principle for both durability and damage tolerance tracking. Some T-39 data are presented for explanatory and demonstration purposes.
An R-Curve for a Surface Crack in Titanium
Authors: Lewis JC , Sines G 
Published: March 2009

R-curves for surface cracks in Ti-6A1-4V titanium alloy were generated for the purpose of studying the resistance of the alloy to their subcritical growth under a monotonically increasing load typical of a proof test. Another purpose was to evaluate Ehret's compliance calibration for measuring the instantaneous size of a surface crack using the unloading slope of a load-versus-clip-gage-opening curve. Another purpose was to study “leak-before-burst” during sustained load and during subcritical crack growth under rising load.
Clips were mechanically attached to either side of the surface crack on the face of the specimen. A clip-gage extensometer was used to plot load-versus-clip-gage opening. Slopes were taken periodically by unloading about 10 percent so that subcritical crack growth could be distinguished from crack-tip plastic deformation. The tests were run in accordance with the ASTM Recommended Practice for R-Curve Determination (E 561-78T) as much as possible.
Stress-Intensity Factor for a Corner Crack at the Edge of a Hole in a Plate
Authors: Palusamy SS , Raymund M 
Published: March 2009

A corner-cracked hole in a plate, subjected to remote tension loading, is one of the three benchmark problems identified for the validation of three-dimensional techniques at the workshop held in Battelle Columbus Laboratories. Stress-intensity factor results for the case of circular corner crack obtained by the macroelement technique is presented in this paper. Results for the remote tension loading are compared with those obtained by the boundary-integral equation (BIE) method and three-dimensional finite-element technique based on singular elements.
Since this investigation was carried out as a part of an overall program aimed at developing stress-intensity factor values for cracks in reactor vessel nozzles, results for six other crack surface loadings were obtained and compared with the results obtained by BIE method.
For the case of remote tension loading, the results of the macroelement technique in the regions removed from the free surface agree within 2.5 percent of those obtained by BIE and the singularity finite-element method. For the case of crack surface loadings, the results of the macroelement technique are shown to be in good agreement with the BIE method throughout the crack front. Comparisons with the limited results available in the literature which take into account constraint variation at the free surface show that the macroelement results for the free surface will be too conservative for thermal shock applications. However, it is concluded that the macroelement technique will give reasonably accurate results for nozzle corner crack problems except in the regions of free surface.
Relationship Between Critical Stretch Zone Width, Crack-Tip Opening Displacement, and Fracture-Energy Criterion: Application to SA-516-70 Steel Plates
Authors: Nguyen-Duy P 
Published: March 2009

Relationships are developed between the crack-tip opening displacement (CTOD), fracture-energy criterion (JIc), and critical stretch zone width (WSZc) using a simple geometrical model of the crack tip. Stretch zone width is directly measured from micrographs of fracture surfaces.
For three-point-bend specimens of SA-516-70 steel, JIc evaluated from measured values of WSZc is equal to 0.173 MJ-m−2 compared with 0.200 MJ-m−2 determined from the single-specimen method in which the crack onset point is detected by the electrical potential method.
Single-Specimen Tests for JIc Determination—Revisited
Authors: Clarke GA 
Published: March 2009

Since the development of the unloading compliance method, numerous improvements to this JIc and J-R curve testing procedure have occurred over the past five years. This paper presents a description of many of these test technique improvements along with the results of the improvements.
Improvements in both mechanical and electrical systems are shown to greatly improve the reproducibility of the unloading compliance data. Computerization of the data reduction has led to a better understanding of the requirements necessary for an accurate J-versus-Δa R-curve.
Small-Specimen Brittle-Fracture Toughness Testing
Authors: Andrews WR , Kumar V , Little MM 
Published: March 2009

Accurate estimates of valid plane-strain fracture toughness, KIc, for low-alloy steels in the ductile-to-brittle transition temperature range may be made by using JIc-valid specimens and accounting for a size effect evident for cleavage fracture. The size effect is explained using a “weakest link” theory that predicts variance in test results using constant-size specimens and decreasing average results when the specimen size is increased. Cleavage fracture occurs when the maximum tensile stress near the crack tip equals or exceeds the cleavage stress, σf*, over a microstructurally significant distance, the process-zone diameter. Variation in specimen toughness arises due to variations in the microstructure within the process zone; the weakest feature in the process zone causes catastrophic cleavage fracture of the specimen.
Our work indicates that the size effect on JIc is represented by J1∕J2=(B2∕B1)1∕m where m is the Weibull modulus, Bi is the specimen thickness for specimen i, and Ji is the mean JIc for several specimens. Experimental evidence supporting the theory is shown.
Analysis and Modeling of the Leaching Process
Authors: Paule RC 
Published: March 2009

A statistical analysis has been made on data obtained in the study of the leaching process for the American Society for Testing and Materials special fly ash specimen using distilled water as the extractant. Two laboratories made extractions under a variety of conditions, and after acid stabilization, the leachates were analyzed by a third laboratory using inductively-coupled plasma analysis. Fifteen elements were studied. Three types of experimental variables were examined: (1) the extractor (60 and 180 cpm shaker tables, and the National Bureau of Standards (NBS) mixer); (2) the liquid/solid ratio (4/1, 10/1, and 20/1); and (3) the time (24 and 48 h).
The 60 cpm shaker table at the 4/1 liquid/solid ratio and at 24 h showed the greatest variability of results; the NBS mixer showed the smallest variability. The NBS mixer and the 180 cpm shaker table exhibited very similar extraction efficiencies and were, for a number of elements, noticeably different from that of the 60 cpm shaker table.
The data were examined in terms of three plausible extraction models. Many of the elements studied fit the model that practically all of the elemental material capable of being extracted is extracted under the test conditions, and that for the higher liquid/solid ratios this material is simply diluted. This results in the concentration being inversely proportional to the liquid/solid ratio. Data for the remaining elements appear to be in better accordance with a leaching model based on interrelated chemical equilibria. We observe, for example, that when the aluminum concentration decreases, the silicon concentration increases. This effect appears to be so pronounced that for the cases of the NBS mixer and the 180 cpm extractor, the silicon concentration actually goes up for the higher liquid/solid dilution ratios. A third plausible leaching model which is based on the concept of a constant elemental saturation under all experimental conditions generally was not found to be supported by the data.
Evaluation of the Extraction Procedure Testing of Hazardous Industrial Wastes
Authors: Larson RJ , Malone PG , Myers TE , Shafer RA 
Published: March 2009

The U.S. Environmental Protection Agency (EPA) Extraction Procedure (EP) is designed to simulate the leaching action of rain and groundwater in the acidic environment present in mixed landfills or open dumps. The objective of the present project is to compare concentrations of selected constituents obtained in the extraction testing with the concentrations of the same materials in leachate obtained from a large-scale industrial/municipal waste co-disposal test, that simulates conditions in an actual landfill.
The EPA Extraction Procedure was run on specimens of three industrial wastes: a sludge from an electroplating operation, a chlorine production sludge, and a glass etching (calcium fluoride) sludge. These same sludges were also tested by adding approximately one metric ton (dry weight) of industrial wastes to two metric tons (dry weight) of municipal wastes and leaching the combined wastes. Both extractant and leachate were analyzed for arsenic, cadmium, total chromium, copper, mercury, nickel, lead, selenium, and zinc. There was a remarkable lack of correspondence between the concentrations appearing in the extractants and in the leachates. In most cases, the concentrations observed in the leachates were higher than the concentrations observed in the extractant. However, for some metals where redox and the availability of sulfide ion strongly affect oxidation states and solubility, the concentrations in the aerobic extractant were much higher than in the anaerobic leachate.
If the goal of extraction testing is to simulate the effects of a landfill environment on a hazardous waste, additional test development may be required. Present test procedures did not always accurately predict the loss of constituents measured in this study.
A Comparison of Groundwater Quality at Selected Landfills to Leaching Test Results
Authors: Rinaldo-Lee MB , Kunes TP , Nichols DG 
Published: March 2009

This paper compares the results of groundwater investigations of five industrial waste sites with leaching test data from the wastes produced by these manufacturing facilities. Since leaching test data are used by some regulatory agencies to classify wastes and predict their actual environmental impact, this study was initiated to examine the correlation between leaching test and groundwater quality data. The sites examined represent three different industries, and are located in different parts of the United States. The quality of groundwater directly in contact with the waste, or immediately downgradient, is compared with leaching test results.
Except for barium, the concentrations of metals in groundwater are less than those released by the leaching tests, although apparently anomalously high concentrations of iron and manganese are found in groundwater immediately downgradient of several waste facilities. These high concentrations may be due to release of iron and manganese by the soils. Generally, concentrations of inorganic nonmetallic parameters released by leaching tests from these wastes are less than concentrations in groundwater. Although laboratory leaching tests are important in estimating leaching potential of wastes, these results indicate leaching tests cannot be used alone to predict the actual environmental impact of waste disposal.
Surrogate Screening for Volatile Organics in Contaminated Media
Authors: Pojasek RB , Scott MF 
Published: March 2009

Waste and spill site investigations often involve the need for a significant number of expensive analyses. The most mobile chemical species involved in most of these studies are volatile organic solvents. Often the cost for this portion of the investigation may approach anywhere from 30 to 50 percent of the total project cost. There is a clear need to develop surrogate testing protocols for these sites.
The philosophy behind the surrogate testing approach is simple. If one could reliably screen the site rapidly, taking 30 to 100 discrete analyses in a day, it would be possible to determine locations where specimen testing should be conducted. This approach also can be used to rank order randomly selected specimens so that the more meaningful specimens can be analyzed first. While the philosophy is simple, conducting a surrogate testing program needs very careful attention. Maximum specimen throughput must be carefully balanced by attaining the minimum chance for operator error.
Surrogate screening for volatile organics in soil and residues is described. A relatively inexpensive test was developed to allow screening of a large number of specimens for volatile organic solvents to determine locations where more detailed analyses, for example, gas chromatography/mass spectrometry (GC/MS) purge and trap techniques, could be used. Preserved specimens are ultrasonically homogenized with organic-free water in a screw-cap vial. A portion is withdrawn and placed in a second vial, where the septum is sealed with mercury, and equilibrated at 70°C (158°F) in an inverted position. A head space specimen is obtained from the vial, and injected onto a gas chromatograph (GC) column run on a fast elute isothermal or temperature program basis. The resulting plot is integrated for total peak areas and compared to standards.