bluuebunny/crossref_metadata_2025 huggingface dataset:
In Situ and Laboratory Characterization of Nonlinear Pavement Layer Moduli
Authors: George KP , Uddin W
Published: March 2009

The accuracy of five different backcalculation procedures for in situ characterization of granular/subgrade layers is studied by utilizing deflection data, both Dynaflect and Falling Weight Deflectometer. ELSDEF, BISDEF, MODCOMP2, MODULUS V.4 and FPEDD1/RPEDD1 are the programs evaluated with the authors' data as well as those from the literature. Included in this study is the gyratory resilient moduli of laboratory compacted samples from five sites in Mississippi. Another aspect of backcalculation procedure, lacking total consensus, is how to account for nonlinear response of granular and subgrade materials in a backcalculation algorithm. Patterned after the results of two decades of soil dynamic studies, the authors propose strain-softening models to effect correction of nonlinear behavior. The correction curve, otherwise known as shear strain attenuation curve is implemented in the FPEDD1/RPEDD1 programs. Backcalculated moduli with the FPEDD1 program show satisfactory agreement with laboratory moduli, validating the reasonableness of the strain-softening correction in light load devices. The accuracy of five different backcalculation procedures for in situ characterization of granular/subgrade layers is studied by utilizing deflection data, both Dynaflect and Falling Weight Deflectometer. ELSDEF, BISDEF, MODCOMP2, MODULUS V.4 and FPEDD1/RPEDD1 are the programs evaluated with the authors' data as well as those from the literature. Included in this study is the gyratory resilient moduli of laboratory compacted samples from five sites in Mississippi. Another aspect of backcalculation procedure, lacking total consensus, is how to account for nonlinear response of granular and subgrade materials in a backcalculation algorithm. Patterned after the results of two decades of soil dynamic studies, the authors propose strain-softening models to effect correction of nonlinear behavior. The correction curve, otherwise known as shear strain attenuation curve is implemented in the FPEDD1/RPEDD1 programs. Backcalculated moduli with the FPEDD1 program show satisfactory agreement with laboratory moduli, validating the reasonableness of the strain-softening correction in light load devices.
Stochastic Analysis of Errors in Remaining Life Due to Misestimation of Pavement Parameters in NDT
Authors: Vennalaganti KM , Ferregut C , Nazarian S
Published: March 2009

The recent mechanistic-empirical approaches for predicting the remaining life of flexible pavements are mainly based upon the predicted strains at the interfaces of different layers. To determine these strains, nondestructive testing techniques are utilized. Unfortunately, uncertainties in determining the strains may result in significant errors in the predicted remaining life. A number of major factors that contribute to these inaccuracies include the imprecise knowledge of thickness and Poisson's ratio of each pavement layer and the errors in measuring the loads and the deflections using a NDT device.

A methodology which accounts for these uncertainties in the assumed pavement parameters and measured responses is suggested herein. With this methodology the influence of these parameters on the calculation of the remaining life of the pavement can be quantified. The methodology is based on Monte Carlo simulation techniques and has been used to analyze four pavement sections, representing a wide range of highways from secondary to interstate. The results of the probabilistic analysis show that the variability in pavement parameters increases the probability of failure of the pavement.
Evaluation of Support Conditions Under Jointed Concrete Pavement Slabs
Authors: Crovetti JA , Tirado-Crovetti MR
Published: March 2009

The evaluation of support conditions under jointed concrete pavement slabs is an important input into pavement analyses. Closed-form solutions are available to determine support conditions under the central portion of the slab; however, these solutions assume interior loading (infinite slab) and slab-on-grade conditions.This paper provides corrections necessary to extend these solutions to finite slab sizes.Also provided are closed form solutions for determining foundation support conditions under slab edges and corners using deflection measurements obtained at these locations.
Determination of Voids Under Rigid Pavements Using Impulse Response Method
Authors: Nazarian S , Reddy S , Baker M
Published: March 2009

Presence of voids and loss of support are the major factors contributing to the premature distress of rigid pavements.To detect voids, nondestructive testing techniques are normally utilized.One of the more promising methods in this area is the Impulse Response (IR) method.A careful survey of the literature indicates that the method is employed in a rather subjective manner and is not based upon a solid theoretical background.In this paper, a method for reducing the impulse response data is presented.The outcomes of field and laboratory testing are also reported.From these results, the proposed methodology seems quite simple and has the potential for becoming an effective tool for detecting voids in rigid pavements.
The Quest for a Standard Guide to NDT Backcalculation
Authors: May RW , Von Quintus HL
Published: March 2009

This paper provides a brief history of the efforts of ASTM Subcommittees D18.10 and D04.39 in working toward a standard guideline for the backcalculation of Nondestructive Testing Deflection data. For nearly six years, this document has been under development and seven drafts have been balloted at the subcommittee level. Currently, this process has been temporarily tabled until after the symposium; because, it is felt by many that this technology is still evolving. The main emphasis of this work is to record the latest version of the draft standard which represents the combined input of the people working on these subcommittees. It is hoped that this paper will elicit comments from the many engineers working in this area so that their constructive criticism can improve upon this guideline and allow it to move forward in the ASTM balloting process.
Results of Round Robin Studies of Light- and Water-Exposure Standard Practices
Authors: Fischer RM
Published: March 2009

Round robin studies of the ASTM standard practices for laboratory accelerated weathering of non-metallic materials have been conducted over the past five years. Test specimens were exposed in commonly specified exposure devices and test conditions. Results from this work show that there is substantial variability between laboratories when comparing the absolute gloss values of exposed polyvinylchoride films for all the standard practices. In contrast, the durability rankings (gloss retention) for a series of materials is highly reproducible between laboratories. By converting the absolute gloss values to relative ranks, the variability in failure rates (test severity) between the individual labs can be ignored.
A Review of the Variability Encountered When Exposing Materials to Glass Filtered Sunlight.
Authors: Crewdson LF , Bahadur-Singh C
Published: March 2009

Test result variability is a common problem related to weathering tests. The addition of a glass cover between the specimens and the sun increases the variability of the test design. The following work measures and reviews the sources of within test run, and test run to test run variability. Five commonly accepted reference materials are exposed and their colour change measured. Within test run variability was shown to be caused by the age and type of glass used. The test run to test run variability was shown to be caused by seasonal variation in the test environment.
Accelerated Weathering of Geosynthetics
Authors: SUITS LD
Published: March 2009

Over the past eight to ten years Committee D35 on Geosynthetics has been struggling with the question of accelerated weathering of geosynthetic products. This paper will attempt to describe the difficulties that have been encountered in developing an appropriate test standard for geosynthetic materials. The difficulties are both in the testing itself, and the use of the results of the testing.

The current test method for geotextiles was adopted in 1984. The method uses the xenon-arc type apparatus. Ever since 1984 the Committee has been performing inter-laboratory test programs aimed at preparing a precision statement for the method. Several factors have prevented this from happening. These include the difficulty in equipment calibration at the site of operation, which equipment manufacturers have indicated needs to be carefully controlled. One other factor which has made the process extremely difficult is the variation in the materials tested.
Irradiance Control in Fluorescent UV Exposure Testers
Authors: Fedor GR , Brennan PJ
Published: March 2009

Variation in ultraviolet (UV) irradiance is one of the prime causes of variability in tests that use UV lamps to simulate sunlight degradation of polymers. Control of irradiance in ASTM G53 fluorescent UV devices previously consisted mainly of periodic replacement and rotation of aging lamps. A newly developed electronic irradiance control system was evaluated for it's effectiveness in controlling UV variation caused by; (1) lamp aging, (2) lot-to-lot variation in lamps, (3) test temperature, and (4) room temperature. In addition, a system of UV baffles and multiple sensors was examined for its effectiveness in reducing variation in UV intensity at different points in the test specimen plane.
Development of Simulated Acid Rain Test Using CCT Method
Authors: Suga S , Suga S
Published: March 2009

At present there are no established test methods for corrosion due to acid rain. The authors carried out experiments to find an adequate simulated acid rain corrosion test method.

Various types of cyclic corrosion tests (CCT) for automotive metallic materials have been widely utilized in Japanese automotive industries and a test method (JASO M 609) was standardized in 1991. This method is based on cyclic procedure in which one cycle comprises 2 hours of salt spray using neutral 5% sodium chloride solution, 4 hours of dry-off and 2 hours of damp heat.

The simulated acid rain test we developed is based on CCT method, except for the test solution which is prepared by adding nitric acid and sulfuric acid to neutral 5% sodium chloride solution. The experiments included tests on four standard bare metals (copper, zinc, aluminium and steel), and metallic and paint coatings on steel.

45 cycles in the Acid rain CCT device correspond to one year of outdoor exposure in the Tokyo area and on Okinawa in reproducing the deterioration of paint coatings as well as metallic coatings.
Comparison of TOX and GC/MS Data for RCRA Groundwater Monitoring Well Samples
Authors: Pruskin SL , Voo L , Mason RM , Lillian D
Published: March 2009

The method for the analysis of total organic halogen (TOX) was developed as a means to trace the products of disinfection in drinking water. It was intended to measure, collectively, compounds such as trihalomethanes and halogenated ethanes. Briefly, the method involves passing a measured amount of sample through a column of activated carbon, followed by pyrolysis of the carbon and analysis of the gases produced for total halogen (as chloride) by microcoulometric titration. It has been shown to produce good recoveries for spiked deionized water and for other simple, fairly clean waters that are free of turbidity. This method is documented as Method 9020 in SW-846 (Test Methods for Evaluating Solid Waste).

RCRA regulations require the monitoring of TOX as an indicator of groundwater contamination at many hazardous waste management facilities (40 CFR 265.92). Method 9020 is recommended as an economical method for TOX analysis. Another way of measuring TOX is to analyze samples for volatile and semivolatile organics by GC/MS (SW-846 Methods 8240 and 8270) and calculating the sum of the halogen contents (as chloride) of all compounds that are found.

Samples from RCRA groundwater monitoring wells are generally more complex than the drinking water samples that were analyzed when Method 9020 was initially evaluated. In the Region II laboratory we have analyzed many groundwater samples by Method 9020 and by Methods 8240 and 8270. This report is a presentation of a preliminary comparison of the results obtained by these two techniques.
Procedures Used to Measure the Amount of 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (2,3,7,8-TCDD) in the Ambient Air Near a Superfund Site Clean-up Operation
Authors: Fairless BJ , Bates DI , Hudson J , Kleopfer RD , Holloway TT , Morey DA , Babb T
Published: March 2009

Sampling and analytical procedures are described that were successfully used to monitor for 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) in air samples collected near a superfund site clean-up operation. Measured concentrations of 2,3,7,8-TCDD in air samples are related to an action level of 3.0 picograms/cubic meter of air (pg/m3) and to a calculated no observed effect level of 5.5 pg/m3. The study concluded that it is possible to collect reliable data for 2,3,7,8-TCDD in air at concentrations that are below the action level specified by the Centers for Disease Control. Data quality was defined relative to the quality control procedures described in the study. There was no apparent relationship between particulate matter in the air and 2,3,7,8-TCDD in the air.
Review of Studies Concerning Effects of Well Casing Materials on Trace Measurements of Organic Compounds
Authors: Dowd RM
Published: March 2009

This report analyzes the results of laboratory and field studies that allow a direct experimental comparison among commonly used monitoring well casing materials (stainless steel, Teflon, rigid PVC) in terms of their potential effects on measurements of trace organic compounds. Each of the studies analyzed attempts to determine experimentally how much -- if any -- sorption occurs, or what differences result among measured concentrations of a series of organic compounds.

In comparing the measured trace concentrations to determine whether the well casing materials cause significant differences in results, a ratio was formulated to reflect the relative sorption effects of each of the materials; sensibly constant ratios over a reasonable range of trace concentrations would indicate few, or relatively minor, differences between the various materials, while varying ratios would indicate larger differences. Conclusions are drawn about similarities and differences in sorption behavior; additional observations about sample variation, effects of well purging, and limited measurements of non-volatile compounds are noted.
Canister-Based Samplers for Volatile Organics
Authors: McClenny WA , Pleil JD
Published: March 2009

Canister-based samplers for volatile organics are a viable alternative to samplers based on solid sorbent collection. Simple, low-cost units are available that operate for sampling periods of from one minute to several hours without the need for electricity. If electronic flow controllers are used, constant sampling rates can be maintained over 24 hours. Sample integrity of compounds passing through the samplers, and storage stability have been tested. Problems with sample integrity due to contamination in sampler elements upstream of the canisters are common, but have been prevented by proper cleaning procedures. Storage stability over seven days at the 1.0 ppbv concentration level has been established. Reactions among co-collected compounds needs further study. The weatherized versions of these units are suitable for monitoring near hazardous waste landfills.
Direct Determination of Part-per-Billion Levels of Volatile Organics in Water and Soil Samples Using Glow Discharge Mass Spectrometry
Authors: Wise MB , Guerin MR
Published: March 2009

A low pressure glow discharge ion source has been constructed in our laboratory and interfaced with a quadrupole mass spectrometer for the direct monitoring of trace organic vapors in air. Important features of the ion source include a simple design, low cost, low maintenance, and the ability to sample air directly without the need for membranes, splitters, or capillary restrictors. Although the flow rate of air into the source is approximately 2 standard mL /s, the pressure within the ionization region is maintained at 200 mTorr which reduces interferences caused by the formation of water cluster ions. Furthermore, the high flow rate of air into the ion source provides a simple and convenient means of purging volatile organics from water or soil samples directly into the mass spectrometer without additional apparatus or extensive samples directly into the mass spectrometer without additional apparatus or extensive sample preparation. Early studies with this system indicate that low part-per-billion levels of volatile organics such as benzene or trichloroethylene can be quantitatively determined in water and soil samples either by monitoring headspace above a sample or by direct purging. Analysis time of 2–5 min provides a high throughput of 10 or more samples per hour.
Statistical Approaches to Screening Hazardous Waste Sites for Toxicity
Authors: Thomas JM , Athey LA , Skalski JR
Published: March 2009

The kinds of questions bioassays can answer, as well as their advantages, are given. The ability to answer questions, such as “where is the waste?” or “is it toxic?” results from field studies based on twelve procedural steps for conducting remedial action studies. Simple or stratified random, systematic, and judgment sampling are presented as three possible paradigms for field sampling.

Bioassay results from two previously reported field studies illustrate how maps of toxicity can be prepared based on systematic sampling and show how cleanup decisions can be made using bioassay results based on few samples.

In the first study, logarithmically spaced soil samples (0–15 and 15–30 cm depths) were obtained along four parallel transects (90 m long and 15 m apart) at the Rocky Mountain Arsenal. A total of 72 soil samples (36 at each of two depths) were subjected to phytoassay using lettuce seeds; most samples were also subjected to Daphnia, Microtox, algal, earthworm, and lettuce root elongation bioassays. These latter bioassay results (exception earthworms) were inconclusive regarding toxicity, but allowed us to ignore several classes of compounds (i.e., water-soluble heavy metals, herbicides, and insecticides) single prior results [1] using pure chemicals showed depressed algal growth in the presence of these contaminants.

In order to depict the spatial pattern of observed seed mortality at each depth, we used kriging (a statistical technique developed for use in the mining industry) to produce contour maps. The results clearly showed that lettuce seed mortality was higher in the 15–30 cm fraction, that waste-trench soil was highly phytotoxic, and that toxicity decreased as a function of distance from the trench. In addition, we found that mortality contours produced by kriging could be useful in site cleanup decisions.

The second study used a series of water and sediment samples collected from a narrow stream adjacent to a wood treatment plant in Canton, Mississippi. Both creosote and pentachlorophenol were used for wood treatment. Sediment samples (15 cm) were collected every 20 m in the visibly contaminated zones. Based on sample linear interpolation of bioassay results, we found that different bioassays led to different conclusions regarding the toxicity of different areas, suggesting that contaminants other than creosote may have caused the observed toxicity. Moreover, chemical analysis was an inaccurate predictor of toxicity.
Evaluation of SW-846 Cold-Vapor Mercury Methods 7470 and 7471
Authors: Beckert WF , Messman JD , Churchwell ME , Livingston RL , Sgontz DL , Wallace GF
Published: March 2009

The protocols for Methods 7470 and 7471 in the SW-846 methods manual are designed for the cold-vapor atomic absorption spectrometric (CV-AAS) determination of total mercury in aqueous (extracts, wastewater, ground water, etc.) and solid (soils, sediments, sludges, etc.) materials, respectively. Aqueous samples are digested with a combination of nitric and sulfuric acid plus permanganate and persulfate solutions at elevated temperature; solid samples are heated either on a steam bath with aqua regia and permanganate, or in an autoclave with sulfuric acid, nitric acid and permanganate. The mercuric ions in the digests are then reduced with hydroxylamine, and the elemental mercury is aerated into the AAS cell, either in a closed (recirculating) or an open system, where the absorption at 253.7 nm is determined.

The topics of this presentation are the results of a performance evaluation study of these methods conducted, without and with changes, by the Battelle Columbus Division Laboratory. The methods were evaluated using aqueous and solid environmental samples of homogeneous and known compositions in order to assess the accuracy and precision of the methods without introducing uncertainties due to sample inhomogeneities. The methods, as originally written, were satisfactory for the analyses of samples containing relatively high concentrations of mercury. However, the method quantification limits for the closed and open systems were inadequate for the determination of mercury in environmental samples such as ground-water samples, when low concentrations were encountered. Spectral interferences which are caused by nonspecific absorption of the analytical radiation degraded the accuracy of the recirculating CV-AAS method.

The protocols in Methods 7470 and 7471 were modified to improve mercury detectability and to minimize the additive effect of nonspecific background absorption. The use of an amalgamation CV-AAS system operated in an open configuration resulted in an improvement of one order of magnitude in instrumental detection limit for mercury over the recirculating method. The results of the analyses of four reference sediment materials and a simulated aqueous waste sample by the amalgamation CV-AAS method indicated acceptable accuracy and precision for most of the environmental samples tested. As expected, the amalgamation CV-AAS method revealed no spectral interferences resulting from nonspecific absorption of the analytical radiation by organic vapors.

The modified protocols are at present the subject of a multilaboratory evaluation with the Battelle Columbus Division Laboratory as the coordinating laboratory. Seven laboratories are participating in this study.
Determination of Extractable Organic Halides in Soils and Oily Wastes by Pyrolysis/Microcoulometric Titration
Authors: Lieu VT , Woo VH
Published: March 2009

Two pyrolysis/microcoulometric titration methods for the determination of extractable organic halides in soils and oily waste are described. The first method involves the washing of soil sample in a column packed with granular activated carbon with a dilute nitrate solution to remove interfering inorganic halides. The organic halides are subsequently determined by pyrolysis/microcoulometric titration of the sample soil-activated carbon mixture. The second method involves the extraction of soil or oily waste samples with a mixture of octanol and 1 M sulfuric acid. The organic halides are extracted into the octanol phase and then analyzed by pyrolysis/microcoulometry. The inorganic halides are removed by extraction into the aqueous phase. The second method has the advantage of extending the technique to the analysis of a broader spectrum of organic halides including polar compounds such as chloroacetic acid
Evaluation of Microwave Techniques to Prepare Solid and Hazardous Waste for Elemental Analysis
Authors: Binstock DA , Grohse PM , Swift PL , Gaskill A , Copeland TR , Friedman PH
Published: March 2009

The use of microwave energy to facilitate sample decomposition prior to elemental analysis is now receiving considerable attention. Both wet and dry digestions are achievable. When microwave energy is used in combination with acid mixtures in closed vessels, the combined pressure and rapid heating can reduce digestion times to a few minutes from hours or days that may be required for open beaker digestions. This savings in time and labor is significant and has prompted the Office of Solid Waste to evaluate this technology as a preparation tool for solid wastes. Of particular interest are used oils and other fuels slated for incineration, incinerator ash, and particulates from these processes. This study reports on the evaluation of a commercially available microwave oven sample preparation system for this application. The effect of sample preparation conditions, including the acid matrix, heating time, and pressure, were evaluated for fifteen toxic or hazardous elements in particulates, ashes oils, and oil fuels. Analyses were carried out by inductively coupled plasma emission spectroscopy.
Determination of Formaldehyde in Samples of Environmental Origin
Authors: Bicking MKL , Cooke WM , Kawahara FK , Longbottom JE
Published: March 2009

An analytical method was developed for the determination of formaldehyde in liquid samples and leachates of solid samples. After a review of the current literature, five candidate methods involving chemical derivatization were chosen for evaluation. Methods involving both liquid and gas Chromatographic procedures were considered. The derivatization method which satisfied all performance criteria was reaction with 2,4-dinitrophyenylhydrazine (DNRH) at pH 5, followed by quantification using liquid chromatography with absorbance detection. Mildly acidic derivatization conditions were employed to avoid unwanted generation of formaldehyde from ubiquitous precursors. Optimized experimental procedures include a 30 minute reaction time, followed by extraction using methylene chloride or a solid sorbent method. The derivatization of formaldehyde proceeded in high yield with excellent reproducibility. Laboratory blank levels were in the 10–15 ug/L range. The method satisfied performance criteria over the range of 15–1400 ug/L. Several authentic sample matrices were used to evaluate the method. The method was subjected to a single laboratory validation protocol.
Comparison of Capillary and Packed Column Analysis for Volatile Organics by GCMS
Authors: Clark RR , Zalikowski JA
Published: March 2009

Capillary column analysis of volatile organics has been approved be the EPA for use in several methods. Currently the EPA has several different method for the analysis of volatile organics, including packed and capillary methods. This paper presents a comparison betveen the methods and between packed and capillary columns.
A Comparison Between Thermospray and Particle Beam LC/MS for Environmental Applications
Authors: Apffel A , Goodley PC
Published: March 2009

A study is described comparing thermospray LC/MS and Particle Beam LC/MS techniques. The two systems are examined on the basis of applicability, quantitative and qualitative performance. On the basis of this study, the conclusions are drawn that the two techniques are roughly equivalent in both applicability, and quantitative performance, but generate different types of spectral information.
Automation of Regional Data Validation
Authors: Shumann CR , Olivero RA , Homsher MT , Petty JD
Published: March 2009

A computerized system has been developed to assist in U.S. Environmental Protection Agency data validation studies of organic analytical data collected for hazardous waste site assessments. The Regional Automated Data Auditing System (RADAS) is a data evaluation and management computer program that provides data entry, file maintenance, data qualifying, and report generation for results from gas chromatography and gas chromatography/mass spectrometry analyses. The RADAS system determines the validity of individual analyte concentrations reported by the laboratory. This determination is based on instrument calibration, sample holding time, blank contamination, and contract required detection limit. Delivery-ready reports are produced, including data tables, sample and calibration listings, and a documented summary of data validation. The system developed has been found to perform appropriately and its use represents a significant improvement in terms of turn-around time, completeness, and consistency of data validation studies.
Application of the Method of Caustics to J-Testing with Standard Specimen Geometries
Authors: Sanford RJ , Judy RW
Published: March 2009

The optical caustic technique offers unique opportunities for experimental measurement of fracture parameters under conditions where conventional instrumentation either can not be used or is not available. The apparent simplicity of the method has attracted the interest of metallurgists and materials scientists. However, there are subtle problems with the method which complicate the interpretation of results. Some of the problems have not been fully explored and others need clarification before the method can be routinely applied. Of particular concern is the fact that existing theories for caustic behavior apply only in special cases which are rarely, if ever, attained in test specimens of practical dimensions for fracture testing. Nonetheless, the potential promise of the method justifies a systematic study of the influence of various parameters, both physical and optical, on the observed behavior of the caustic.

In previous work, the authors demonstrated that there is a correlation between the measured caustic diameter and the value of the J-integral parameter obtained from mechanical measurements for planar 1T compact tension specimens in various steels, subject to some restrictions. As might be expected, this correlation did not agree with existing theoretical relations since the theories are all based on plane stress assumptions. In the present paper, these correlations are studied further and the influence of imaging distance and specimen thickness examined in detail. In addition, the characterization of caustic behavior in standard bend specimens is investigated.

For these studies, a new four-lens caustic camera was used which permits the simultaneous determination of four caustics with varying image distances at each increment of applied load. With the aid of this camera, sufficient data were obtained to determine empirical relations for the calculation of the J-integral values from optical measurement of the caustic.
Impact Fracture of a Tough Ductile Steel
Authors: Douglas AS , Suh MS
Published: March 2009

The impact fracture of a tough ductile material is examined by comparing the results of static and dynamic viscoplastic finite element computations with experimental observations of the crack tip opening displacement (CTOD) during static and dynamic (impact) fracture. Experiments measured the relative displacement of two small indents 100 μm behind a fatigue crack tip in a three-point bend specimen to determine the CTOD as a function of load (in static tests) or as a function of time (in dynamic tests).

Static computations show that a two-dimensional simulation can capture both the overall structural response, as measured by boundary quantities (such as the applied load and the crack mouth opening displacement), and the near-tip CTOD when crack closure is accounted for. Dynamic finite element simulations also use a two-dimensional model of the three-point bend specimen, but must include the projectile and loading tup to account for the complex stress wave interactions generated during impact loading in order to simulate the CTOD versus time response. Since the finite element model correlates with the observed CTOD history, it can be used to determine relevant field quantities, such as the J-integral, as well as stresses and strains of interest.

The finite element model shows that it is essential to include the effects of viscoplasticity in order to capture the correct CTOD response in the dynamic experiments. These calculations show that the rate of change of the stress intensity factor is K ∼ 5 × 106 MPa √m/s in the impact fracture tests. The fracture initiation time has not been unambiguously determined; therefore a unique fracture toughness has not been established.
Dynamic Key-Curves for Brittle Fracture Impact Tests and Establishment of a Transition Time
Authors: Böhme W
Published: March 2009

Impact tests with precracked bend specimens were performed, and the crack tip loading was measured utilizing the shadow optical method of caustics and high-speed photography. Some results are presented in comparison to a quasi-static solution for the crack loading history, which is based on a simple mass-spring model. The deviations obtained are a quantitative measure of dynamic effects acting at the crack tip and they define dynamic correction functions kdyn. In a normalized form these time-dependent functions are very general curves for impact tests; therefore they can be considered as dynamic key-curves. They allow the prediction of the dynamic crack tip loading history for arbitrary impact test conditons so far as the usual restrictions of the linear elastic fracture mechanics are fulfilled.

The dynamic key-curves show clearly the decrease of dynamic effects with increasing time, allowing us to define transition times tdyn. For times larger than tdyn the crack loading history can be described sufficiently accurately by the quasi-static solution. The established transition time tdyn is compared with transition times defined by Ireland and by Nakamura, Shih, and Freund.
Explosive Testing of Full Thickness Precracked Weldments
Authors: Gifford LN , Carlberg JR , Wiggs AJ , Sickles JB
Published: March 2009

We describe an explosive test which uses small charges to induce plastic strain up to a few percent in a cracked structural element with thickness on the order of 50 mm (2 in.). The boundary conditions of the test section, its nominal strain versus time history, and peak strain as a function of charge weight are all determined experimentally. Finite element models capable of reproducing this behavior are also described; their purpose is to allow computation of possible fracture-governing parameters and to correlate response of the element to full-scale structural behavior. Some early fracture test results for shallow cracks in HY-80 GMA welds are presented and discussed. We find that these tests, which reflect severe but realistic service conditions, are well beyond the limits of current ASTM elastic-plastic fracture tests such as E 813-87, Test Method for JIc.
Analysis of Fracture Toughness Data for Modified SA508 Cl2 in the Ductile-to-Brittle Transition Region
Authors: Miglin MT , Wade CS , Van Der Sluys WA
Published: March 2009

Fracture toughness testing of steels in the ductile-to-brittle transition region is complicated by a large amount of data scatter. There are many available methods of analyzing transition region toughness data with the objective of reducing the data scatter and arriving at a representative value for the lower bound toughness. Ten 1T and five 4T compact specimens of SA508 C12 pressure vessel steel given a special heat treatment were tested in the transition region, and the data were analyzed according to six of the available methods. Of three purely statistical methods, one based on a large collection of pressure vessel and rotor steel data is preferred. Of three analytical methods, one which subtracts the contributions of plasticity and crack growth from measured toughness is preferred.
Effects of Warm Pre-Stressing on the Transition Toughness Behavior of an A533 Grade B Class 1 Pressure Vessel Steel
Authors: Lidbury D , Birkett P
Published: March 2009

It is now well recognized that pre-loading a ferritic steel structure at a temperature above its ductile-brittle transition range may result in an effective increase in toughness on loading at a lower temperature where fracture occurs by cleavage. Of particular significance is the fact that cleavage failure has never been reported in a cracked structure at a low temperature, following pre-loading at a higher temperature, for cases where the applied crack driving force was constant or decreasing with time. This is the basis of the so-called “conservative” warm pre-stressing (WPS) principle. Although this principle is of considerable practical importance, much work is still needed to further understand all aspects of WPS phenomena in order that analysts be better able to assess their effects quantitatively in safety cases.

In the present work, WPS experiments have been carried out using 20-mm-thick, plain-sided compact specimens sectioned from 150-mm-thick A533 Grade B Class 1 pressure vessel steel. The effects of load-unload-cool-fracture (LUCF) and load-cool-fracture (LCF) pre-loading cycles (KWPS ≈ 100 to 350 MPa √ m; TWPS = 25 or 290°C) on cleavage fracture resistance have been investigated over a range of temperatures spanning the ductile-brittle transition range.

A particular objective of the work was to investigate the combined effects of WPS and strain ageing on transition toughness behavior; therefore, in addition to WPS experiments, tests were carried out on “virgin” specimens to obtain base-line data and on specimens sectioned from material which had been uniformly pre-strained by 2% at ambient temperature and then aged for 1.25 h at 290°C to obtain control data.

The main results were as follows. The validity of the conservative WPS principle was confirmed: In every test performed, an increase in loading was required to cause cleavage fracture at low temperature following a severe pre-load at a higher temperature. Moreover, in the case of pre-loading carried out at 25°C, conferred WPS margins were observed even for those tests where pre-loading had resulted in ductile tearing (0 ⩽ Δa ⩽ 1.0 mm) under conditions of ligament yielding; and the Case 1 and Case 2 solutions of Chell's Q1 -integral theory of WPS yielded reasonably accurate predictions of final fracture. A deleterious effect of pre-loading at 290°C on effective transition toughness below a level of ≈ 200 MPa√m was demonstrated by a combination of control and LUCF and LCF WPS data, and found to be consistent with the expected embrittling effect of strain ageing. However, all toughness data generated by the study were bounded by the ASME KIc versus temperature curve indexed to the value of RTNDT (=-30°C) appropriate to the material in the non-strain-aged condition.
Unique Elastic-Plastic R-Curves: Fact or Fiction?
Authors: Etemad MR , Turner CE
Published: March 2009

A simple model is presented for the effect of size and geometry on fracture toughness when represented as J-R curves in the fully plastic region. The model, which is little more than dimensional analysis, refers to growth beyond anyJ-controlled regime. It suggests that the abscissa of a J-based R-curve should be Δa/c, where c may be thickness, ligament, or material toughness (expressed as a plastic zone size) according to circumstance. The analysis is consistent with the well known picture in the LEFM regime where thickness is the only geometric term that affects toughness.

Comparison is made with many published results, in most cases satisfactorily. The agreement is best for tests of various ligament widths with constant thickness. The reason for this is the limited understanding of how the shear lips develop before a steady-state pattern of growth is reached and the likelihood that the controlling factor may change when thickness is a variable. Since for the fully plastic state the increment of work from which toughness is derived involves only the limit load and dq/da, the relation between an increment of displacement and the corresponding crack growth, the latter seems to be the factor that contributes most to the differing trends of fully plastic J-R curves as initial geometry is varied. The near total lack of published data for dq/da needs urgent remedy if these geometric effects are to be understood.
Simulation of Crack Growth and Crack Closure under Large Cyclic Plasticity
Authors: Kim KS , Van Stone RH , Laflen JH , Orange TW
Published: March 2009

The propagation of a crack during cyclic loading with large plasticity was simulated using a finite element method. The numerical procedure included the determination of crack closing and opening by examining the contact condition of the crack surfaces in the plasticity iteration. The method was applied to the growth of cracks in Alloy 718 single edge notch specimens at 538°C subject to Rϵ = -1 strain cycling under both nominally elastic and elastic-plastic conditions. Experimentally measured remote displacements were used to establish the boundary conditions for the finite element analysis. The measured load and crack mouth opening displacement were used to verify the results. The results show, among other things, that the crack closure and opening stresses become more compressive as the loading becomes more plastic, and that, under a given control condition, the closure and opening stresses become less compressive as the crack propagates.
Comparison of Elastic-Plastic Fracture Mechanics Techniques
Authors: Brust FW , Nakagaki M , Gilles P
Published: March 2009

The first part of this paper reviews the adequacy of simple estimation procedures for predicting the crack growth and failure behavior of cracked structures. These simple methods include: J-estimation schemes (where five different schemes are presented including two new methods), the R6 approach, and the VR-curve technique. The second part of the paper discusses methods for predicting elastic-plastic fracture under conditions where the simple schemes are not applicable. This includes a discussion of integral parameters, mainly focusing on the T*-integral, and the local (or damage) based approaches. These two approaches are required where the degradation near a crack tip depends on the history of damage accumulation.
Finite Element Meshing Criteria for Crack Problems
Authors: Gerstle WH , Abdalla JE
Published: March 2009

Rules for the meshing of finite element problems with elastic cracks have never been established. Therefore finite element results for crack problems presented in the literature are of uncertain accuracy. This paper establishes the finite element meshing criteria, based upon a “least dimension” concept, necessary to calculate mixed-mode stress-intensity factors in linear elastic crack problems to a pre-specified accuracy.

Finite element convergence studies, using meshes which consist of eight-noded quadrilateral elements and corresponding six-noded quarter-point singularity elements, are presented for several benchmark problems with known stress-intensity factor solutions. It is assumed that the stress-intensity factors are extracted from the analysis using the displacement correlation method, a common practice in the analysis of mixed-mode problems.

The convergence studies give the analyst valuable information about meshing requirements for arbitrary crack problems. In performing a convergence study for such analyses, three key meshing parameters associated with a given crack tip must be considered: size of the crack tip elements, number of crack tip elements surrounding the crack tip, and size of regular elements near the crack tip. Recommendations for each of these three parameters to achieve an efficient mesh and a prespecified accuracy are presented.
Method and Models for R-Curve Instability Calculations
Authors: Orange TW
Published: March 2009

This paper presents a simple method for performing elastic R-curve instability calculations. For a single material-structure combination, the calculations can be done on some pocket calculators. On microcomputers and larger, it enables the development of a comprehensive program having libraries of driving-force equations for different configurations and R-curve model equations for different materials. The paper also presents several model equations for fitting to experimental R-curve data, both linear elastic and elasto-plastic. The models are fit to data from the literature to demonstrate their viability.
Chemical Resistance Evaluation of Geosynthetics Used in Waste Management Applications
Authors: Landreth RE
Published: March 2009

Geosynthetics, including membranes, geonets, geotextiles, geogrids and plastic pipes are finding increased use in waste management facilities. Their use has been prompted by design requirements for improved drainage, separation and barrier performance and economics to provide additional free air space. An important consideration in their use is their ability to withstand the potential chemical attack from the waste and leachate. This paper identifies an immersion procedure for exposing the materials and tests for evaluating the materials after exposure for those materials other than membranes. The paper also discusses fingerprinting.
An Evaluation of Chemical Compatibility Test Results of High Density Polyethylene Geomembrane Exposed to Industrial Waste Leachate
Authors: Dudzik BE , Tisinger LG
Published: March 2009

HOPE geomembrane was exposed to leachate generated from an existing hazardous waste landfill for up to one year both in the laboratory (EPA Method 9090) and in a leachate collection sump at the site. Various mechanical, physical, and microstructural properties were monitored after 30, 60, 90, 120, and 365 days of exposure in the laboratory and after 120 and 365 days in the sump. Comparison of the tensile property results among the laboratory and sump-exposed samples showed considerable similarity. Variability in the geomembranes tested was evident. Test results are presented, along with a discussion on measuring the apparent variability of the geomembrane.
The Effects of Seaming on the Durability of Adjacent Polyethylene Geomembranes
Authors: Peggs ID , Carlson DS
Published: March 2009

Several stress cracking failures in the liners of fluid waste impoundments have been observed in and adjacent to all types of seams in polyethylene geomembranes. The majority of these cracks occur at the outer edge of extruded fillet and lap seams and the inside edge of hot wedge seams. Stress cracking is the predominant mechanism that presently compromises the long-term durability of polyethylene geomembrane and that, in cold weather, may initiate spectacular, rapid crack propagation failures. Each type of polyethylene resin has its own fundamental stress cracking characteristics, which can be modified by the time/temperature history during manufacture of the geomembrane and, subsequently, during seaming. This paper reports the results of a preliminary series of constant tensile load tests using single edge notched specimens to determine the effects on stress crack growth rates of different types of seams in different polyethylene geomembranes. The influence of microstructure on stress cracking is also assessed.
Performance Test Methods for Geomembranes and Geocomposites Used in the Design of Waste Containment Facilities
Authors: Sprague RT , Frobel RK
Published: March 2009

During the design process for today's generation of waste containment facilities, the design engineer must consider the use of geosynthetics, whether required by regulatory guidelines or sound engineering judgement. Just as with other civil engineering materials, geosynthetics are tested and evaluated using a variety of test methods.

This paper describes three performance test methods, two of which are draft test methods which are currently being used to evaluate performance properties of geomembranes and selected geocomposites: 엯 Wide strip tensile test; 엯 Direct shear test; and 엯 Large scale hydrostatic pressure test.

The paper will attempt to correlate performance test methodswith actual field performance based upon case histories of success and failure in geomembrane systems.