bluuebunny/crossref_metadata_2025_split huggingface dataset:
Estimation of Design Season Modulus for Overlay Design
Authors: Jackson NM , Andrew JW , Drumm EC 
Published: April 2008

Nondestructive evaluation of pavement performance by methods such as the Falling Weight Deflectometer (FWD) are widely used and accepted. Backcalculation and prediction of pavement layer moduli can be effective for both the evaluation of pavement condition and overlay design. However, variations in pavement temperature and subgrade moisture content result in variability in the backcalculated moduli.
In an attempt to evaluate the overall effect of this variability on design, pavement sections in four different regions of the State of Tennessee were instrumented and tested. The in-situ temperature and moisture content of the pavement and subgrade materials were continuously monitored for seasonal changes. Each site was also equipped with a weather station to record precipitation, air temperature, and solar radiation. FWD testing was conducted monthly at each site and the moduli for the pavement and subgrade layers were backcalculated using AASHTO recommended procedures. The seasonal variation in subgrade modulus was compared with measured changes in subgrade temperature and moisture content.
The observed variability in seasonal moduli estimates was used to support a generalized model for estimating seasonal changes in subgrade resilient modulus. A proposed design method that incorporates this generalized model with a relative damage or weighting factor approach is presented. This proposed method will enable the pavement designer to establish a reasonable design subgrade modulus based on limited test data.
The Contributions of George Irwin to Elastic-Plastic Fracture Mechanics Development
Authors: Landes JD 
Published: April 2008

George Irwin, the father of fracture mechanics (FM), is well known for his contributions to linear elastic fracture mechanics, especially the development of the crack-tip field approach and the use of the crack tip stress intensity factor, K. During the early years of FM he was well aware that the limits on the use of K restricted its application to high-strength and low-toughness materials. He encouraged the development of new concepts that would be able to extend the use of FM to the more usual engineering materials, materials that might reach yield stress before fracture toughness on a typical structural component. Concern with that area of FM later led to the development of the technology called elastic-plastic fracture mechanics (EPFM). Besides the encouragement he gave, there are several areas where he contributed technical ideas that helped with the development of the EPFM technology. These ideas include use of crack tip field parameters, the energy and crack tip parameter equivalence, the R-curve approach to fracture toughness evaluation and the concern about constraint effects on fracture behavior.
This paper takes a historical look at these developments in elastic-plastic fracture mechanics and the role that George Irwin played. An important observation that will be made is that the approach originally proposed by Irwin gave the correct direction in each case considered in this paper. The original ideas merely needed further development to become mature technical concepts in the EPFM approach.
Assessments of Low Cycle Fatigue Behavior of Powder Metallurgy Alloy U720
Authors: Gabb TP , Bonacuse PJ , Ghosn LJ , Sweeney JW , Chatterjee A , Green KA 
Published: April 2008

The fatigue lives of modern powder metallurgy disk alloys are influenced by variabilities in alloy microstructure and mechanical properties. These properties can vary as functions of variables the different steps of materials/component processing: powder atomization, consolidation, extrusion, forging, heat treating, and machining [1–4]. It is important to understand the relationship between the statistical variations in life and these variables, as well as the change in life distribution due to changes in fatigue loading conditions. The objective of this study was to investigate these relationships in a nickel-base disk superalloy, U720, produced using powder metallurgy processing. Multiple strain-controlled fatigue tests were performed at 538°C (1000°F) at limited sets of test conditions. Analyses were performed to: (1) assess variations of microstructure, mechanical properties, and LCF failure initiation sites as functions of disk processing and loading conditions; and (2) compare mean and minimum fatigue life predictions using different approaches for modeling the data from assorted test conditions.
Significant variations in life were observed as functions of the disk-processing variables evaluated. However, the lives of all specimens could still be combined and modeled together. The failure initiation sites for tests performed at a strain ratio Rε = εmin/εmax of 0 were different from those in tests at a strain ratio of - 1. An approach could still be applied to account for the differences in mean and maximum stresses and strains. This allowed the data in tests of various conditions to be combined for more robust statistical estimates of mean and minimum lives.
Mitigating the Corrosion of Concrete Pipe and Manholes
Authors: Bell LW , Shook WE , Norris T 
Published: April 2008

This paper deals with the problems of corrosion caused by sulfuric acid generated within sewer systems. The problems are identified and potential economical solutions are presented. There are four major ways to mitigate the corrosion of concrete pipe and manholes, due to sulfuric acid produced in a sewer system: • Utilize Az design to elevate the alkalinity of the concrete. • Coat or line the pipe and structure. • Reduce the microbial induced corrosion (MIC), using computer model designs. • Use acid-resistant cements and antibacterial additives.
The last two methods will be discussed at length because they are the most cost-effective means of extending the life of concrete in a sewer system. By reducing the generation of hydrogen sulfide and at the same time reducing the microbial activity in the system, MIC is effectively reduced. Also, by incorporating acid resistant cements and antibacterial additives, concrete in sewer systems will experience less or no corrosion; thus the life of the sewer system is extended.
Case History of the Installation of a Sanitary Sewer Microtunnel Project
Authors: Meyer JJ , Whitehouse T 
Published: April 2008

This Milwaukee Metropolitan Sewerage District project will require 3200 feet (975m) of 30 inch (750mm) diameter reinforced concrete microtunnel pipe to be installed at depths up to 64 feet (19m).
This specific design of microtunneling pipe was submitted to the owners by the low-bid installer and was accepted as an equal alternate to the original specifications. Microtunneling is a fairly new installation process, the technology of which allows for the trenchless installation of buried conduit while minimizing the need to disturb the street surfaces and/or private properties.
The project is scheduled to start June, 1998 and has an August, 1999 completion date.
The Time-Dependent Deformation of Carbon Fiber-Reinforced Melt-Infiltrated Silicon Carbide Ceramic Matrix Composites: Stress-Rupture and Stress-Relaxation Behavior in Air at 1000°C
Authors: Lara-Curzio E , Singh M 
Published: April 2008

The stress-rupture and stress-relaxation behavior of carbon fiber-reinforced melt-infiltrated silicon carbide composites was investigated in ambient air at 1000°C. It was found that the compliance of the material increases continuously with time when subjected either to a constant composite stress or strain in air at 1000°C. The changes in compliance are explained based on the oxidation of the fiber coating, and on the oxidation, loss of cross-sectional area and rupture of the reinforcing fibers. In the case of stress-rupture, the load previously carried by failed fibers is redistributed to their surviving neighboring fibers inducing further fiber failure. During stress-relaxation, fiber failure is reflected directly on the reduction of the load carried by the composite.
By monitoring the expansion of the specimens during heating, prior to the application of the stress or strain, it was possible to determine the liner coefficients of thermal expansion of the material between 200°C and 1000°C.
A New Technique for High Frequency Multiaxial Thermo-mechanical Fatigue Testing of Materials
Authors: Chieragatti R , Paun F 
Published: April 2008

The proposed thermo-mechanical fatigue test rig is based on a rotating bending machine and employs a high and a low temperature sources. This permits imposing thermal and mechanical loading at relatively high frequencies on a portion of a surface generatrix of a tubular specimen. Using this rig, a series of experiments was carried out on superalloy test specimens.
These tests were conducted at various mechanical loadings with the temperature cycling between 600 and 1050°C in 10 seconds. The temperature distribution on the test specimen was measured under stabilized conditions and the same was calculated using a finite element code. Good correlation was found between the experimental and simulated temperature distributions. The thermal stress field, hence calculated, enables us to identify the critical crack initiation sites of the specimen and to calculate the appliedthermo-mechanical cycle. In this way, an equivalent constant temperature can be defined and fatigue life has been predicted using isothermal fatigue results only.
Quality Control of Earth Fills Using Time Domain Reflectometry (TDR)
Authors: Lin C-P , Siddiqui SI , Feng W , Drnevich VP , Deschamps RJ 
Published: April 2008

Measurement of soil density and water content in compacted fills is the principal means of quality control to assure adequate performance. Current testing methods have various limitations, including the use of hazardous materials, limitations in accuracy, the need for extensive calibration, or the test duration. A new technique using time domain reflectometry (TDR) to measure the water content and density of soil is introduced. The purpose of this paper is to present a historical and theoretical background of this new approach. Prototype equipment was developed for routine use in the quality control testing of compacted soils. The method was evaluated with theoretical study and laboratory experiments. The results of the TDR method are compared with results from conventional methods on actual construction sites. The advantages and limitations of this new method are also discussed.
A TDR device is used to transmit an electromagnetic wave into the soil and receive a reflected waveform. The dielectric constant of the soil can be calculated from the travel time of the waveform. Water content and density are the basis used to assess the quality of a compacted earth fill. These are the same factors that affect the dielectric properties of soil; so a relationship between them can be established. A procedure to measure soil density in-situ using TDR was developed. This procedure obtains results comparable in accuracy to existing methods such as the nuclear density gage and the sand-cone test. The test duration is approximately 15 minutes. A new approach is under development to interpret the reflected waveform and extract additional information regarding the electromagnetic soil properties. This approach appears to be very promising and has the potential to provide even more rapid and accurate test results for assessing the water content and density of compacted soils.
Implementation of Constitutive Model in FEA for Nonlinear Behavior of Plastics
Authors: Skrypnyk ID , Spoormaker JL , Smit W 
Published: April 2008

The main elements of implementation into a finite-element analysis (FEA) package of the earlier developed model for nonlinear viscoelastic behavior of plastics are described.
The Henriksen scheme of discretization of the hereditary integral has been chosen for implementation. This scheme enables development of a fast procedure for modeling of viscoelastic behavior. As a result, the time necessary for calculation of problems of viscoelasticity is not much larger than the calculation time required for simulation of elasto-plastic behavior.
Several discretization schemes have been analyzed, implemented in FEA software MARC and verified. The numerical algorithm, which is chosen as a result of comparison, allows us to reach a total deviation of less than 8% to 10% for the modeling of creep and recovery of PMMA and HDPE for the broad range of loading levels.
The case study of a thick plate under distributed transversal loading is examined to compare the results achieved using the Schapery model with the newly proposed approach.
Study of Nb and Fe Precipitation in α-Phase Temperature Range (400 to 550°C) in Zr-Nb-(Fe-Sn) Alloys
Authors: Toffolon-Masclet C , Barberis P , Brachet J-C , Mardon J-P , Legras L 
Published: April 2008

This work is aimed at improving our knowledge of the Nb and Fe precipitation in the low α-temperature range as a function of Fe and Sn contents in ZrNb based alloys. Several experimental variants, with Nb contents ranging from 0.3–0.8 wt%, Fe from 0.01–0.5 wt% (and also Sn additions), have been studied, with special attention paid to the residual Nb content in the matrix, and to the SPP crystallographic nature and chemical composition as a function of the nominal alloy composition, annealing time/temperature, and initial metallurgical condition.
For ZrNb alloys, recent studies have pointed out the necessity of performing long term annealing treatments in order to avoid the persistence of metastable phases, and to reach a thermodynamic equilibrium state of precipitation. For that purpose, experimental alloys were annealed for up to 2 years at 400, 470, and 550°C. The evolution of SPP chemical compositions with temperature and annealing time was first quantified. For the longer annealing times, i.e., for conditions close to thermodynamic equilibrium, the results suggest an existence of a composition range for the SPP phases under equilibrium conditions. This specific point is currently taken into account to improve the thermodynamic description of the ZrNbFe phase diagram.
Also, the influence of preliminary cold work on the precipitation kinetics of equilibrium βNb phase has been investigated. This study was conducted on two Zr-1%Nb alloys containing initially metastable βZr precipitates. It was observed that cold work significantly accelerates the precipitation of equilibrium βNb phase, mainly for annealing treatments too short to allow significant recovery of the dislocation network, i.e., between 1 and 100 h of annealing.
Finally, all of these experimental results are discussed with regard to their consequences on the thermodynamic modeling of the equilibrium phase diagram and precipitation kinetics.
Microstructural Stability of M5™ Alloy Irradiated up to High Neutron Fluences
Authors: Doriot S , Gilbon D , Béchade J-L , Mathon M-H , Legras L , Mardon J-P 
Published: April 2008

The present paper is focused on the microstructural stability of the Framatome-ANP M5™ (Zr-1%NbO) alloy. Thin foils were cut from M5 cladding tubes irradiated from 1 to 6 annual cycles in EDF PWRs, and examined by analytical transmission electron microscopy (TEM). The results show that within the wide range of irradiation conditions investigated, the initial β-Nb particles undergo no amorphisation and only minor evolutions in size distribution, number density, and composition. Finally, very few ⟨c⟩ component basal loops were detected, so that no sign of accelerated growth regime has to be feared for the fuel burn-ups currently considered (∼70 GWd/t) for PWRs.
In the second part of this paper, other industrial or experimental alloys (Zy-4, M4, Zr-2.5%Nb, ZrNbSnFe) are considered to improve our knowledge about the irradiation-induced evolution of β-Nb and other minor SPP. Thin foils were cut from specimens irradiated in PWRs or MTRs (OSIRIS, SILOE) and also examined by transmission electron microscopy. In addition, Small Angle Neutron Scattering (SANS) was used to provide quantitative and statistical information on the radiation-enhanced precipitation of β-Nb needles and possible other defects or solute clusters. All these results allow a general discussion of evolution of SPP with regard to their initial structure and composition, and of the noteworthy irradiation stability of the M5™ up to high neutron fluence with respect to other alloys.
Microstructure and Growth Mechanism of Oxide Layers Formed on Zr Alloys Studied with Micro-Beam Synchrotron Radiation
Authors: Motta AT , Yilmazbayhan A , Comstock RJ , Partezana J , Sabol GP , Lai B , Cai Z 
Published: April 2008

The structures of oxides formed in water and lithiated water on three Zr-based alloys with varied corrosion behavior were studied with micro-beam synchrotron radiation and optical microscopy. Micro-beam synchrotron radiation (0.2 μm spot) has a unique combination of high elemental sensitivity (ppm level) and fine spatial resolution that allowed the determination of various oxide characteristics such as phase content, texture, grain size, and composition as a function of distance from the oxide-metal interface.
Micro-beam X-ray fluorescence shows that the oxides formed in lithiated water have increased levels of Fe absorbed from the autoclave environment indicating greater oxide porosity in these oxides. The phase content, texture, and grain size of oxides were studied in detail using synchrotron radiation micro-beam diffraction for samples corroded in water and lithiated water. A remarkable periodicity was observed in the oxide structures using various techniques including X-ray peak intensities for both monoclinic and tetragonal zirconia, texture, and optical microscopy. The periods were similar to the transition period and were less visible in the oxides that behaved worse in lithiated water. These results are discussed in terms of models of oxide growth and of the differences between alloys.
Role of Iron for Hydrogen Absorption Mechanism in Zirconium Alloys
Authors: Kakiuchi K , Itagaki N , Furuya T , Miyazaki A , Ishii Y , Suzuki S , Terai T , Yamawaki M 
Published: April 2008

The latest PIE results of Zry-2 and HiFi alloy (0.4 %Fe-Zry2) showed that iron addition reduces the hydrogen pick-up ratio. In order to clarify this lower hydrogen absorption mechanism, three types of experiments were carried out for both alloys: (1) Measurements of the hydrogen pick-up ratio in the pre-transition region using an autoclave. (2) CPD (Contact Potential Difference) and FBP (Flat-band Potential) measurements of oxide film using a High Temperature Kelvin system and Photocurrent system. (3) Investigation of hydrogen absorption properties by Sieverts system and corrosion properties by autoclave for intermetallic compounds simulating SPP's Fe/Cr and Fe/Ni ratio in Zry-2 and HiFi.
Autoclave tests showed that the corrosion behaviors of both alloys were similar. However, the hydrogen pick-up ratio depended on not only iron addition but also surface treatment (with and without pickling). Iron addition and non-pickling (as-received) reduced the hydrogen pick-up ratio.
ΔCPD and FBP shifted to the positive side as the result of iron addition, and FBP changed with and without pickling. This difference in surface potential might be caused by the existence of anion vacancy concentration in the oxide film and furthermore may affect the electrochemical potential gradient over the oxide film. This potential gradient might control the proton diffusion in the oxide film.
In the results of the hydrogen absorption tests on intermetallic compounds, Zr(Fe,Cr)2 with a higher Fe/Cr ratio showed lower hydrogen absorption, and Zr2(Fe,Ni) showed higher hydrogen absorption than Zr(Fe,Cr)2. In the results of corrosion tests on intermetallic compounds, Zr2(Fe,Ni) showed a much larger corrosion rate than Zr(Fe,Cr)2. It is considered that Zr2(Fe,Ni)-type precipitate might be oxidized easily in the oxide film, thus it might not contribute to the window for hydrogen absorption, and Zr(Fe,Cr)2 with a higher Fe/Cr ratio would reduce the amount of hydrogen penetrating through SPP at the oxide/metal interface.
Based on these results, a tentative hydrogen absorption mechanism is proposed, explaining both roles of the electrochemical potential gradient over oxide film and the SPP window for the hydrogen absorption.
Ductility of Zircaloy-4 Fuel Cladding and Guide Tubes at High Fluences
Authors: Yagnik SK , Hermann A , Kuo R-C 
Published: April 2008

Zircaloy fuel cladding suffers progressive degradation of ductility as its neutron exposure and hydrogen uptake increase with burnup. The loss of ductility appears to be the key property governing the cladding integrity in service. We report ductility data of Zircaloy-4 fabricated in stress-relief annealed (SRA) and recrystallized (RXA) conditions, covering a range of fluence, hydrogen content, and irradiation and test temperature.
The testing was performed on unirradiated and irradiated Zircaloy-4 cladding and guide tubes in SRA and RXA conditions, respectively, in the temperature range 25–350°C. These materials had been exposed to an estimated neutron fluence of ̃ 8 to 10 × 1025 n/m2 (E &gt; 1 MeV) over four cycles of PWR operation. Due to its RXA fabrication condition, the guide tube material was also believed to represent BWR cladding. The hydrogen contents in the irradiated cladding was in the range of ̃ 200–600 ppm, exhibiting typical radial distribution of circumferential hydrides. By comparison, the hydrogen content in the irradiated guide tube material was in the range of ̃ 250–1800 ppm, exhibiting fairly uniform through-wall distribution of circumferential hydrides. Tensile tests and hydraulic burst tests were conducted on 130–150 mm long tubular specimens. In addition, smaller specimens machined in the form of 55 mm long curvilinear dog-bone and 10 mm slotted semicircular arc were tested in plane stress and plane strain configurations. Corresponding unirradiated archive materials in as-received condition and with uniform hydrogen charging up to 1200 ppm were also tested by identical methods. In all tests the fracture mode was examined by SEM fractography.
The investigations revealed a decrease in ductility of Zircaloy-4, mainly caused by irradiation and only partly by increasing hydrogen content. Unlike the elongation data, the strength data remained nearly constant with increasing hydrogen content in both materials at all test temperatures. The irradiated RXA material showed better ductility than irradiated SRA material at equivalent hydrogen levels, and exhibited a clearer correlation of ductility with hydrogen content, mainly due to its uniform hydrogen distribution. The paper will provide these and other quantitative data, e.g., those correlating ductility with the local (near fracture surface) hydrogen content. The paper synthesizes the experimental results and discusses their possible application to the criteria for hydrogen concentration and ductility limits in high burnup fuel.