bluuebunny/crossref_metadata_2025 huggingface dataset:
A Comparison of the NRT Displacement Model and Primary Damage Formation Observed in Molecular Dynamics Cascade Simulations
Authors: Stoller RE , Greenwood LR
Published: April 2008

The method of molecular dynamics (MD) has been used to simulate atomic displacement cascades in iron with energies up to 50 keV. Since this corresponds to the damage energy of the average iron recoil from an elastic collision with a 2.3 MeV neutron, these simulations have reached well into the regime relevant to fast neutron irradiation. The final cascade damage state is that present when the PKA energy has been dissipated and atomic motion returns to a level characteristic of the irradiation temperature; this typically requires a simulation time of 10 to 20 ps. This state has been characterized in terms of several parameters: the total number of surviving point defects, the fraction of the surviving point defects contained in clusters, and the size distribution of the point defect clusters formed during the cooling of the cascade. The energy dependence of the MD primary damage parameters has been compared with values predicted by the industry-standard NRT secondary displacement model and spectrum-averaged values have been obtained for several relevant neutron energy spectra. The effect of neutron energy spectrum on total point defect survival is relatively weak, supporting the use of NRT dpa as a damage correlation parameter. However, a potentially significant spectrum dependence is observed in the point defect cluster size distributions.
Measurement of Eigenvalue Separation in Coupled-Core Systems using Optical Fiber with Scintillator
Authors: Unesaki H , Shiroya S , Hashimoto K , Horiguchi T , Takeda T , Yamamoto T , Kitada T , Aizawa O , Yamamoto J
Published: April 2008

The first-harmonic eigenvalue separation of loosely coupled cores constructed at the light-water moderated/reflected core in the Kyoto University Critical Assembly (KUCA) have been measured using optical fiber with scintillator. The method is based on the measurement of flux tilt introduced by the asymmetric insertion of control rod in the two coupled core halves. The use of the optical fiber detector enabled the rapid flux tilt measurement compared to the conventional activation wire method. The measured eigenvalue separation showed excellent agreement with the results of the rod drop and Feynman-α measurements. The flux tilt method gave the smallest experimental error, and is applicable to a less loosely coupled system with a larger eigenvalue separation, where the conventional Feynman-α method is hardly applicable.
Characterization and Representation of the HPGE Detector Efficiency
Authors: Sparks MH , Griffin PJ , Flanders TM , Sallee WW , Vehar DW
Published: April 2008

The feasibility and utility of calculating efficiency curves for HPGe detectors using the MCNP 4B transport code are explored. The calculated curves are compared to experimental data obtained from a 137Cs source counted on a HPGe detector. Efficiency data for the four centimeter reference location are reported in this work. The detector, shield, and counting fixtures are included in the model.

This work also involved extensive sensitivity analyses. Sensitivity studies focused on seven parameters involving the active area of the germanium crystal. Three of the seven variables were found to be significant.
Use of Reaction 93Nb(n, n')93mNb to Determine Neutron Spectra at Outer PV Surface of WWER-1000 Reactor
Authors: Gritzay OO , Rusinko PM , Vasylyeva OG
Published: April 2008

Among threshold reactions that are used to determine neutron field characteristics on the pressure vessel surface of the WWER-1000 reactor, the 93Nb(n,n')93mM) reaction has the greatest importance. Analysis shows that the set of experimentally obtained specific activities and the set of activities calculated using the IRDF-90 cross sections are not self-consistent. Comparative analysis of data for the 93Nb(n,n')93mNb reaction cross section, which is contained in the IRDF-90 library, and this cross section estimation on the basis of ENDF/B-VI, BROND-2 and ENSDF libraries have been performed.
Real-Time Dosimetry Method Using an Imaging Plate
Authors: Sakasai K , Katagiri M , Kishimoto M , Fujii Y
Published: April 2008

The real-time dosimetry method using an imaging plate has been studied. A small, remote radiation sensor using commercially available imaging plates has been developed for the purpose. The sensor adopts wavelength shift fibers for signal transmission and side-glow fibers for illumination of laser on the imaging plates. The developed sensor will be useful for various purposes such as local dose monitoring in reactors and beam loss monitoring in accelerator facilities.
Fatigue Crack Growth Thresholds, Endurance Limits, and Design
Authors: Newman JC , Piascik RS
Published: April 2008

Description

Leading experts provide 24 papers addressing four areas pertinent to fatigue crack growth thresholds: mechanisms, test procedures, analysis, and applications.

Mechanisms: Three mechanisms that influence thresholds are discussed including: crack-tip closure, environment, and Kmax effects. A simplistic four-parameter model that describes FCG threshold behavior of elastic-plastic materials is also presented.

Test Procedures: Eight papers focus on loading and specimen-type effects with research showing that the resistance-curve (R-curve) method to determine the threshold for fatigue-crack growth should allow more reliable application of ΔKth values to engineering problems.

Analysis: Three papers analyze the behavior of fatigue cracks in the threshold regime using several different analysis methods. These methods were the elastic-plastic finite-element method (FEM), the Dugdale-type mode, the BCS (Bilby, Cottrell and Swinden) model, and a discrete-dislocation model.

Applications: Nine papers address applications of threshold concepts and endurance limits to aerospace and structural materials. The impact of a number of testing variables on the measurement of fatigue-crack-growth thresholds, in particular ASTM E 647, Test Method for Measurement of Fatigue Crack Growth Rates is also discussed.
Pendulum Impact Testing: A Century of Progress
Authors: Siewert TA , Manahan MP
Published: April 2008

Description

This unique volume examines 23 peer-reviewed papers that represent the latest worldwide technology in pendulum impact testing. Written by 50 U.S. and international experts in their field, these papers are organized into 4 sections:

• Background of Impact Testing

• Reference Energies, Machine Stability, and Calibration

• Impact Test Procedures

• Fracture Toughness Assessment from Impact Test Data

STP 1380 marks the 100 year anniversary of the invention of the pendulum impact test by S. Bent Russell, and the research and standardization efforts of G. Charpy during the early part of the 20th century. As an added bonus, reprints of two landmark papers written by Russell and Charpy are included in this volume, describing the development of the test equipment and procedures.
Marine Corrosion in Tropical Environments
Authors: Dean SW , Delgadillo GH-D , Bushman JB
Published: April 2008

Description

This unique, new ASTM publication details the latest worldwide research on atmospheric corrosion, seawater corrosion, deterioration of concrete, and underground corrosion issues pertaining to tropical environments.

21 peer-reviewed papers cover:

• Mechanisms of corrosion processes.

• Performance of various remedial measures to prevent corrosion damage to steel in concrete.

• Proposal for revision of the ISO atmospheric corrosivity classification.

• New approach to cathodic protection of rebar and concrete.

• Evaluation of stainless steel for rebar in concrete as a long-term solution.

• Protection of underground structures in tropical marine environments.

• Difficulties of coating stainless steels for use in seawater.
Impact of Hydrogen on Plasticity and Creep of Unirradiated Zircaloy-4 Cladding Tubes
Authors: Bouffioux P , Rupa N
Published: April 2008

This paper deals with the impact of hydrogen on plasticity and creep of unirradiated CWSR Zircaloy-4 cladding tubes. Specimens with low tin content (≈1.3%) were charged with hydrogen between 100 and 1100 ppm using gaseous technique. Uniaxial and biaxial mechanical tests (tension and creep) were conducted on as-received and hydrided material at room and elevated temperatures (350 and 400°C). Analysis of the results showed that both precipitated hydrides and hydrogen in solid solution play a role in the viscoplastic behavior of the Zircaloy-4 cladding. With respect to plasticity, hydrogen affects the hardening kinetics by decreasing the yield stress, increasing the linear hardening coefficient, and enhancing the dynamic recovery kinetics, especially in the hoop direction. It has no effect on the strain anisotropy. Hydrogen increases the creep resistance. The creep rate of the hydrided material decreases by a factor of 2 to 4 depending on the temperature, the hydrogen concentration, and the stress biaxiality. Potential mechanisms such as localized plasticity in the vicinity of hydrides are discussed, as well as the composite effect induced by hydrides acting like inclusions within the ductile metal matrix, and the respective role of hydrogen in solid solution and of hydrides on the dislocation mobility and recovery. Even if no firm conclusions regarding those mechanisms have been reached, the results of this study are already useful in predicting the mechanical behavior of hydrided Zircaloy-4 cladding under handling and long-term interim dry storage conditions.
Effect of Dilute Alloy Additions of Molybdenum, Niobium, and Vanadium on Zirconium Corrosion
Authors: Sabol GP , Comstock RJ , Nayak UP
Published: April 2008

An alloy development effort was undertaken to improve the corrosion performance of zirconium-based alloys for high-burnup applications. As part of that effort, three binary alloys were studied to establish the relationship between alloy chemistry, processing, microstructure, and corrosion behavior. the binary additions included molybdenum, niobium, or vanadium at concentrations ranging from 0.1 to 2.5 weight percent. Process variables included cooling rate from the beta phase, aging temperature from 500 to 700°C, and aging times up to 1000 h. The corrosion behavior of these alloys was then studied by testing in 360°C water and 427°C steam and compared to Zircaloy-4.

The effect of alloy content and processing was monitored by characterizing the microstructure of the material. In general, quenching from the beta phase formed martensite for all three alloys with essentially all alloy additions remaining in solution. Subsequent working and aging treatments resulted in precipitation and precipitate growth. These changes in the microstructure were correlated to changes in the corrosion behavior. Typically, corrosion performance initially improved with aging followed by gradual degradation with continued aging. While this trend was observed for all three alloys, the optimum aging treatment was dependent upon alloy chemistry and composition. The results showed that the corrosion behavior was dependent upon the amount of alloying element present in the alpha zirconium matrix, provided the precipitates remained less than a critical size. This critical size was alloy dependent. The vanadium alloy was observed to be more sensitive to heat treatment than the molybdenum and niobium alloys. For all three alloys, corrosion performance superior to Zircaloy-4 could be achieved by an optimum aging treatment.

The details of the relationship between heat-treatment, microstructure, and corrosion response are presented and discussed.
Impact of Second Phase Particles on BWR Zr-2 Corrosion and Hydriding Performance
Authors: Rudling P , Wikmark G , Lehtinen B , Pettersson H
Published: April 2008

BWR fuel cladding corrosion and hydriding performance may limit the fuel residence time. Historically, out-of-pile high-temperature steam tests have been used to predict the BWR corrosion performance of Zircaloy materials. However, results indicate that no correlation exists in many cases between in-pile and out-of-pile Zircaloy corrosion performance. Concerning BWR hydriding performance there appears to be no reliable out-of-pile test that predicts the BWR Zircaloy hydriding performance.

The Zircaloy corrosion and hydriding performance is a function of: 1. The environment such as the temperature, fast neutron flux, water chemistry. 2. The Zircaloy microstructure, such as texture, dislocation density, matrix chemical composition, and second phase particle SPP characteristics.

One way to solve the problem with the lack of reliable out-of-pile tests is to correlate the BWR Zircaloy corrosion and hydriding performance to the initial microstructure. Such a correlation will of course not predict the impact of temperature, fast flux, and water chemistry on Zircaloy corrosion and hydriding performance.

This paper describes the correlation between the BWR Zircaloy corrosion and hydriding performance and the Zircaloy SPP microstructure. Six Zr-2 fuel cladding rods irradiated in three different reactors to a fuel rod average burnup of >40 MWd/kgU were included in the study. The fuel claddings had varying chemical compositions and were manufactured by three different process routes, resulting in large differences in SPP characteristics. Hot cell examinations including oxide thickness and hydrogen content determinations were performed. Also SPP SEM analyses were done to assess the size distributions of the irradiated materials. In addition, SEM and TEM analyses were performed on non-irradiated achive samples from the same manufacturing lots as the irradiated materials. We further describe how the initial SPP size distribution alters with irradiation and how the BWR Zr-2 corrosion and hydriding performance correlates with the initial SPP size distribution and SPP chemistry.
Interpretations of Tensile Properties of Polyamide 6 and PET Based Thermoplastics Using ASTM and ISO Procedures
Authors: Jia N , Kagan VA
Published: April 2008

As more and more U.S. companies are looking to convert from ASTM to ISO standards for materials development, testing, and analysis in order to gain greater opportunities and compete more effectively in the global market, it has become increasingly important to deal with the concerns raised during the conversion process, so that the differences can be reconciled and harmonies can be brought into the two sets of standards.

This article presents our investigation on several technical issues in the ASTM and ISO standards on the tensile properties of plastics. Using polyamide (PA) 6 and polyethyleneterephthalate (PET) based thermoplastics as examples, our analysis revealed a range of similarities and differences in these two testing procedures. With either procedure — ASTM or ISO — similar results were obtained for material parameters such as tensile strength, tensile strain, and modulus of elasticity, in nonreinforced and short glass fiber reinforced plastics.

The investigation also focused on the role of the system compliance on the tensile strain and modulus measurements, and the effect of grips (wedge- and side-action grips) and gripping on the tensile behavior of the materials. Among the two types of grips, the wedge-action grip was found to cause greater measurement variability, especially in Young's modulus. The analysis of system compliance, on the other hand, reinforced the statements in both testing standards that an accurate strain and modulus measurement would require the use of extensometer. The results in this article went further to indicate how to improve the accuracy in the Young's modulus using the system compliance when the extensometer was not applied during testing. Recommendations were made on the effective use of the testing procedures in product development and design.
A Study of Bond Strength Testing for Solvent Cement Joints in PVC Piping Systems
Authors: Paschal JR
Published: April 2008

To evaluate the strength of the bond area formed by solvent-cementing of thermoplastic pipe and fittings, tests are conducted at 2 hours, 16 hours and 72 hours. Because the data is statistical in nature, more than a single specimen must be tested to provide a representative strength at each cure time. Considering that 3 tests are run, each consisting of multiple specimens, a method was developed for testing joined plaques rather than pipe and fittings. This method, known in the industry as “lap-shear” is much less time intensive than actual pipe joint preparation, and in theory, provides a good approximation of the anticipated strength of a pipe/fitting joint. A study of this test method was conducted to investigate variables in preparation technique and their effect on strength. The results indicate an extreme sensitivity to minor variations in preparation. The interpretation of this data with respect to joint strength is also discussed. An explanation of these significant deviations encountered due to the changes in preparation is provided, based on thermodynamic considerations of the mixing/dissolution process and work input to sample/solvent system. This paper presents an analysis of the sample preparation technique, in both a theoretical and qualitative context of solution thermodynamics and an evaluation of the minor changes in methodology that can cause major differences in test results. Notable results of the study include changes in shear strength on the order of 12–100% based solely on sample handling within the first 30 seconds, and a lack of sensitivity to the composition of the cement within normal ranges. The solution thermodynamics analysis provides some insight as to the relative significance of the variables in the preparation method.
Instrumented Pendulum Impact Testing of Plastics
Authors: Manahan MP , Cruz CA , Yohn HE
Published: April 2008

Conventional impact tests (without instrumentation) are performed to measure the energy required to break a notched specimen under dynamic loading. Instrumented impact tests not only measure the notched specimen breaking energy but also quantify the energy required to form a crack at the root of the notch and the energy required to propagate the crack through the material. Instrumented test systems use strikers which have strain gages so that the load-deflection curve during the impact event can be derived. These data provide load, deflection, and energy data which can be correlated with engineering parameters such as fracture toughness, ductility, and fracture resistance.

This paper compares instrumented impact results obtained using both the Charpy and Izod test procedures. Several possible limitations of the instrumented test procedure have been identified and test procedures to overcome these limitations have been proposed. In addition, an important potential limitation of the Izod test, specimen clamping pressure, has been studied.
The History and Importance of Impact Testing
Authors: Siewert TA , Manahan MP , McCowan CN , Holt JM , Marsh FJ , Ruth EA
Published: April 2008

Charpy impact testing is a low-cost and reliable test method which is commonly required by the construction codes for fracture-critical structures such as bridges and pressure vessels. Yet, it took from about 1900 to 1960 for impact-test technology and procedures to reach levels of accuracy and reproducibility such that the procedures could be broadly applied as standard test methods. This paper recounts the early history of the impact test and reports some of the improvements in the procedures (standard specimen shape, introduction of a notch, correlation to structural performance in service, and introduction of shrouds) that led to this broad acceptance.
Post-Remediation Monitoring for Soil, Sediment and Water Contamination by Lead from a Controlled Superfund Site in Mississippi
Authors: Tchounwou PB , Siddig AA , Marian ML
Published: April 2008

The United States Congress enacted the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), commonly known as the Superfund, in 1980, with the purpose of dealing effectively with the dangers posed by the nation's hazardous waste sites (HWS). In this research, we evaluated lead levels in soil, sediment, and surface water collected from selected locations near a HWS in Mississippi, and estimated the potential ecological health risk associated with the presence of lead in these environmental matrices. Monthly samples were collected for a period of 12 months, at four different stations selected with respect to the HWS, and analyzed for their lead content by AA or UWVisible spectrometry following a sample preparation by microwave -assisted acid digestion, or by mild digestion on hot plate. Other physical and chemical parameters including BOD, COD, conductivity, DO, nitrate, pH, sulfate, temperature, TDS, TSS, and turbidity were also assessed. Levels of lead in soil, sediment, and water collected from the sampling site (Site 1) closest to the controlled HWS were significantly higher (p < 0.05) than the other three sampling sites. While lead levels in soil and sediment were found to fall below the screening level (500 mg/kg), its concentrations in water samples exceeded the required criterion (3.2 ug/L) set by EPA for protection of aquatic life from chronic toxicity. No significant difference was found in the values of nitrate, pH and temperature at the 4 sampling sites; however, there were significantly (p < 0.05) lower levels of DO, and higher levels of BOD, COD, conductivity, sulfate, TDS, TSS, and turbidity, at Site 1 compared with Sites 2, 3, and 4.
Design of a Relative Risk Model Regional-Scale Risk Assessment with Confirmational Sampling for the Willamette and McKenzie Rivers, Oregon
Authors: Landis WG , Luxon M , Bodensteiner LR
Published: April 2008

The estimation of regional risks due to multiple Stressors is a frontier in environmental toxicology and risk assessment. We are conducting a regional scale ecological risk assessment of multiple Stressors in the Willamette Valley, Oregon. The Willamette River drains an extensive agricultural area and forests of both the Coastal and Cascades mountains. The river also receives effluents from paper mills and urban wastewater treatment facilities. A major tributary of the Willamette is the McKenzie River. The McKenzie watershed, which extends into the Cascade Mountains, is extensively forested. Stressors in this watershed include alterations in the landscape due to the harvest of trees, the infrastructure required for the logging, modification of the river or stream banks, and inputs due to contamination by localized urban and non-point sources. We are using the relative risk model (RRM) for ecological risk assessment developed by Wiegers, Landis, and colleagues to combine multiple Stressors and receptors in a regional context. The first step in the RRM process is the establishment of assessment endpoints for the particular area and the placement of the endpoints in the landscape. Next, the method involves the development of risk matrices that combine diverse Stressors and habitats within the region with numerical ranks. We have broken the McKenzie and Willamette watershed study areas into 13 risk regions and have mapped the locations of the point sources and are incorporating land use data. Using a variety of documents we have established the assessment space and are developing criteria for ranking Stressors and habitats. We have also initiated a 3-year field research activity to confirm the risk predictions within the main channel. The sampling sites correspond to the risk regions of the RRM. The sampling program will characterize the population density and structure of the fish assemblage and measuring the health of the individual fish.
General Assessment Endpoints for Ecological Risk Assessment at Los Alamos National Laboratory
Authors: Reagan DP , Kelly EJ , Hooten MM , Michael DI
Published: April 2008

A critical component of any ecological risk assessment is the specification of the assessment endpoints. However, selecting assessment endpoints for risk assessment is often a formidable task, particularly for sites with extensive and diverse ecological resources, such as those found at Los Alamos National Laboratory. The General Assessment Endpoint (GAE) process provides a comprehensive, systematic and defensible basis for reaching consensus with regulators and other stakeholders on the assessment endpoints for ecological risk assessments. This paper provides an overview of the GAE process and reports on a pilot project to implement the process for the Pajarito Plateau ecosystem, the ecosystem potentially affected by the Laboratory's legacy hazardous waste.
Commentary on Cultural Considerations in Risk Assessment: An Ethical Responsibility
Authors: Young AL , Hocking EK , McGinn CW
Published: April 2008

The United States Department of Energy's (DOE) Center for Risk Excellence has been charged with developing the “Risk Plan” for the Hanford Nuclear Reservation's (Richland, WA) Groundwater/Vadose Zone Integration Project. The goal of the Integration Project is to assure the protection of water resources, the Columbia River environment, river-dependent life, and users of the Columbia River resources. Credible data and predictive analytical tools are needed to assess impacts associated with the remedial options proposed by DOE as the Department engages with regulators, Tribal Nations, and stakeholders in making cleanup decisions. Cultural risk impact assessment can be defined as part of a quality of life assessment--an assessment of the quality of our human health and environmental health. Cultural risk assessments should gauge how human health and environmental risks impact the cultures we live in and that give our lives meaning. We are making strides in the human health and ecological risk assessments that are standard to the current remediation process, but we are less clear on how to assess cultural impacts. However, to comprehensively evaluate and address the risks resulting from past and future DOE operations, we must consider the effects to cultural endpoints. To do less could be an unethical exercise of our responsibilities to assess and manage risk.
Multiple Stressor Effects in Relation to Declining Amphibian Populations
Authors: Linder G , Krest S , Sparling D , Little E
Published: April 2008

Description

Original research discusses the protocols and approaches to studying the effects of multiple environmental stressors on amphibian populations and gives new perspectives on this complicated subject. This new publication integrates a variety of stressors that can act in concert and may ultimately cause a decline in amphibian populations.

Sixteen peer-reviewed papers cover:

Toxicity Assessment examines methods, which range from long-established laboratory approaches for evaluating adverse chemical effects to amphibians, to methods that link chemicals in surface waters, sediments, and soils with adverse effects observed among amphibians in the field.

Field and Laboratory Studies illustrates studies in the evaluation of multiple stressor effects that may lead to declining amphibian populations. A range of laboratory and field studies of chemicals, such as herbicides, insecticides, chlorinated organic compounds, metals, and complex mixtures are also included.

Causal Analysis demonstrates the range of tools currently available for evaluating "cause-effect" relationships between environmental stressors and declining amphibian populations.

Audience: This new publication is a must-have for scientists and resource management professionals from diverse fields, including ecotoxicology, chemistry, ecology, field biology, conservation biology, and natural resource management.
The Relation between Low-Temperature Rheology of Lubricating Mineral Oils and Gelatin Index
Authors: Webber RM , George HF , Covitch MJ
Published: April 2008

The association of the predominantly n-paraffinic components of mineral oils into wax nuclei that grow and interact to form macroscopic crystalline structures leads to highly non-Newtonian rheology that is strongly dependent on both temperature and stress history. Upon cooling to temperatures lower than the onset temperature for wax crystallization (Tc), the viscosityrtemperature curve shows a high activation energy region that persists over a narrow temperature range (∼3–5 °C). In this temperature range, the oil transitions from a homogenous solution to a two-phase wax crystallite dispersion. By applying controlled stress rheometric techniques, we show that the high activation region is related to gelation index described in ASTM D 5133, and that the gelation index temperature corresponds to Tc. The high activation energy region is associated with the relief of supersaturation accrued within the oil upon cooling to temperatures below that of the saturation temperatures of the paraffin molecules in solution. Therefore, the gelation index characterizes the onset of nucleation rather than the formation of macroscopic wax crystal structures that would be associated with a yield stress and gelation. The activation energy and rheology at T < Tc depend on temperature and stress history, the paraffin molecular weight distribution in the oil, and the concentration of pour-point depressant. We show that the gelation index parameter is non-unique, coupled to both the effects of stress history on viscosity and the dependence of nucleation on the n-paraffin mplecular weight distribution. It is not surprising then that no correlation between gelatipn index and MRV TP-1 yield stress (ASTM D 4684) is observed.
Aircraft Cabin Air Quality: A Critical Review of Past Monitoring Studies
Authors: Nagda NL , Rector HE , Li Z , Space DR
Published: April 2008

This paper reviews measurement studies of aircraft cabin air quality conducted between 1985 and 1998. Study results are evaluated in terms of monitoring objectives, sampling design, measurement parameters, data characteristics, quality assurance, level of review, and findings. Monitoring designs ranged from modest efforts involving a handful of flights to extensive efforts involving about 100 flights. Most of the studies reported measurement data for bioaerosols, carbon monoxide (CO), carbon dioxide (CO2) and particulate matter. Formaldehyde, ozone (O3), and volatile organic compounds (VOCs) were measured in fewer studies. Semivolatile organic compounds (SVOCs) were not measured in any of the studies reported in this paper. Average concentrations of bioaerosols and CO were lower than or similar to those encountered in ground-level environments. Average levels of CO2 routinely exceeded the 1000-ppm level, which is often used for judging acceptability of air quality in buildings but may be inappropriate for the cabin environment. Measurement methods used for bioaerosols, CO, and CO2 were found to be reliable. Although concentrations of particulate matter appeared to be low, this finding was not shared by all studies; this is most likely due to variation in the robustness for selected measurement methods, rather than actual differences in concentrations. The paucity of data or inadequacies in methods and instrumentation used for measuring formaldehyde, O3 and VOCs precludes definitive conclusions.
USAF Experience in the Qualification of Composite Structures
Authors: Lincoln JW
Published: April 2008

The prospect of significant reduction in aircraft structural mass has motivated the United States Air Force (USAF) and the aerospace industry to incorporate composite structures in their aircraft designs. The USAF found threats to structural integrity such as moisture, temperature, delaminations, and impact damage that made them take a cautious approach for the acquisition of aircraft with composite materials. Each of these threats acted as an inhibitor to using these materials in the design of operational aircraft. However, the USAF has successfully incorporated composites on several aircraft, including the B-2, C-17, and F-22. The challenge is to find new approaches for the qualification of composite structures that will make them more economically viable for future procurements. It is the purpose of this paper to discuss the background for the current qualification program for composites and suggest some possibilities for improvement of the certification process.
A Review of Some Key Developments in the Analysis of the Effects of Impact Upon Composite Structures
Authors: Olsson R , Asp LE , Nilsson S , Sjögren A
Published: April 2008

This paper reviews work at the Aeronautical Research Institute of Sweden, and addresses major issues of importance in evaluating the effect of impact on composite structures. Some more extensive reviews of work by other researchers are referenced. The paper addresses impact response and damage formation, damage characterization, and residual strength and stability by combination of experiments and analysis. Studies showing that impact response type depends on impactor-plate mass ratio are presented. Small mass impact is generally more critical at a given configuration and energy. Analytical models for small mass impact and for damage initiation and growth during large mass impact are discussed. Rate dependency of matrix-dominated properties is briefly discussed. Geometric and constitutive characterization of impact damage zones is presented and the influence of degraded properties demonstrated. The use of an FE-based plate model to simulate delamination growth due to sublaminate buckling and panel skin buckling in stiffened panels after impact is described. Skin buckling causes a steep increase in delamination strain energy release rate and should be prevented.
Certification Cost Reduction Using Compression-After-Impact Testing
Authors: Anderson TC
Published: April 2008

An approach to reduce certification development cost can be accomplished by testing the important strength allowables that make up the primary design drivers. Through a process referred to as a “modified building block approach,” these primary design drivers are weighted and selected based on criticality. This approach was used to minimize the development cost of a prototype composite tailboom being considered for a light model helicopter (similar in size to a Bell Model 407). The material system of choice (AS4/APC-2 thermoplastic) and the tailboom's susceptibility to impact damage drove the need to understand impact damage and its effect on strength. Compression after impact (CAI) at barely visible impact damage (BVID) was therefore selected as the critical design parameter. The cost benefit is realized by focusing on the critical design parameters; thus the number of coupon tests necessary to support full aircraft development can be significantly reduced because only limited design aspects have to be considered. The critical design drivers selected would not necessarily be applicable to the fuselage or rotor blades, but they do provide a means to optimize the tailboom design while minimizing the development cost. Certification would still be verified by full-scale testing.
Mechanisms and Modeling of Delamination Growth and Failure of Carbon-Fiber Reinforced Skin-Stringer Panels
Authors: Greenhalgh E , Singh S , Nilsson K-F
Published: April 2008

The main objective of this work was to investigate and predict the behavior of damaged structural elements (skin-stringer panels). The study combined characterization through testing with fractographic analysis, and analysis of delamination using the finite-element method. The experimental studies entailed investigation of damage growth from embedded skin defects in panels under compressive load, and the subsequent structural failure. Parameters such as defect size, location with respect to substructure and through-thickness position were studied. Local delamination and global panel buckling were modeled, and the resulting delamination growth was simulated using a moving mesh technique. The results illustrated the importance of the location of the 90° plies to the damage evolution, and the criticality of global buckling and stringer detachment in the structural failure. The understanding gained from both the experimental investigations and numerical simulations has led to guidelines for realistic modeling and rules for designing damage tolerant structures.
The Effects of Marcel Defects on Composite Structural Properties
Authors: Caiazzo A , Orlet M , McShane H , Strait L , Rachau C
Published: April 2008

This paper describes a method for predicting key structural properties of carbon fiber reinforced composite materials containing ply waviness several times the nominal ply thickness. These socalled marcelled regions have been observed in a number of highly loaded thick structural components. The origins of these defects are not fully understood, although several contributing factors have been identified. The goal of this work is to develop an analysis based disposition criterion for components where fabrication process changes cannot be readily implemented to eliminate marcel defects. Work to date has focused on developing a micro-mechanics-based procedure for modeling the strength and stiffness properties of a marcelled region given basic properties of the material and simple geometric parameters of the marcel that can be measured nondestructively. The result is a general constitutive model that can be used in global structural analysis packages to assess the effects marcel defects have on component performance. Analyses of test coupons containing marcelled regions have been carried out to illustrate the method and establish the validity of the modeling approach. Results indicate that the degree to which marcel defects affect structural properties depends not only on the maximum fiber misalignment angle, but also on the location and size of the marcelled region and nominal applied strain field.
Three-Dimensional Stress Analysis and Failure Prediction in Filled Hole Laminates
Authors: Iarve EV , Mollenhauer DH
Published: April 2008

An observed stacking sequence effect [1] on pin bearing strength was examined by three-dimensional modeling. A displacement spline approximation method was used to perform the stress analysis. The laminate and the fastener were assumed to be linear elastic. Processing residual stresses were included in the analysis. The contact region and stress were unknown a priori and resulted from the solution. A nonuniform contact region through the thickness was allowed. Undamaged thermoelastic moduli were employed in the model. A stacking sequence effect on bearing strength was investigated by comparing stress distributions in two quasi-isotropic laminates of [02/902/452/-452]s and [02/452/902/-452]s stacking sequence. Stress magnitudes were displayed relative to ply strength properties. It was observed that all stress components, including the in-plane stresses, were affected by the stacking sequence. In the vicinity of the bearing plane, very high transverse shear stresses were found. A qualitative agreement between predicted stress distributions and experimental damage investigation, performed in Ref 1, was demonstrated. Using a point stress failure criterion, a prediction of failure on-set was performed. The predicted failure initiation load for the [02/902/452/-452]s stacking sequence was approximately 40% higher than the predicted failure initiation load for the [02/452/902/-452]s stacking sequence.
New Experiments Suggest that All Shear and Some Tensile Failure Processes are Inappropriate Subjects for ASTM Standards
Authors: Piggott MR , Liu K , Wang J
Published: April 2008

There are four ASTM standards which involve apparent shear failure of composites. These include the Iosipescu (D 5379), tube torsion (D 5448), the short beam test (D 2344), and two-rail and three-rail shear (D 4255). However, careful experiments in which polymers have been sheared show that failure is normally restricted to tensile failure with breaking of polymer chains and cross links. Moreover, it is already known that shear hackle is produced by a tensile process. In view of this, these standards should be reexamined to determine whether strengths should be reported at all. The same argument applies to the new standard being developed for mixed Mode I-Mode II interlaminar fracture toughness. Mode I is the only failure mode which is consistent with experimental observations.

In addition, the D 3039 standard for tensile strength has been revised to include balanced and symmetric laminates. Experiments have shown that, with angle ply laminates, much greater strengths can be obtained just by making the specimen wider and shorter. These latter tests agree very well with tests on pressurized filament wound tubes, with structures equivalent to the angle ply structures. This strongly indicates that the ASTM test can severely underestimate the strength. The ASTM standard also seriously underestimates the stiffness. There appears to be an “edge softening” effect, so that apparent properties are very dependent on the aspect ratio of the test sample. Thus, true material properties are not measured.

It is proposed that all ASTM D 30 mechanical tests be reexamined to determine (a) what purpose is served by having the test at all, and (b) whether it is measuring a true materials property.
Accelerated Tests of Environmental Degradation in Composite Materials
Authors: Reynolds TG , McManus HL
Published: April 2008

Combined moisture cycling and thermal cycling environments are known to create damage, such as cracking of material near exposed surfaces and edges, in many new materials intended for high-temperature service. Material models suggest the damage mechanisms; these models are used to design tests to (1) isolate the effects of different damage mechanisms, and (2) accelerate them. Tests are carried out in the combined environment and in its individual components: time at moisture, moisture cycling, time at temperature, and thermal cycling. Accelerated moisture cycling and thermal cycling tests are also designed and carried out. Results are presented which suggest that, for the IM7/PETI-5 and IM7/PIXA-M materials tested, time at moisture is the most important cause of microcracking damage, with thermal cycling playing some role. Moisture cycling plays a role in the distribution of damage. The models are used to reduce laminate-specific microcracking data to general design data in the form of fracture toughness versus cycle (GIc(N)) curves.
Advances in Adhesives, Adhesion Science, and Testing
Authors: Damico D
Published: April 2008

Description

Eleven peer-reviewed papers focus on new adhesives, particularly from the perspective of the newer test methods emerging to better determine adhesive reliability. Subjects cover:

• Test methods and specification that improve the ability to determine long-term bond durability

• Bonding and debonding of wood products

• Test methods that generate more meaningful material information on adhesive reliability

• Method of measuring viscoelastic behavior of adhesives

• Accurate method of measuring yield strength of adhesives and other materials

• Characterizing fracture properties of adhesive joints under impact loading conditions

• Fracture mechanics applied to adhesive joints

• Coating adhesion testing

• Diffusion of fluids in pressure sensitive adhesives

STP 1463 is a valuable resource for design engineers and those with interest in advanced test methods for adhesive validation.
Titanium, Niobium, Zirconium, and Tantalum for Medical and Surgical Applications
Authors: Zardiackas LD , Freese HL , Kraay MJ
Published: April 2008

Description

Reactive metals and their alloys are used in a variety of biomedical applications from pace makers to hips implants. This new ASTM publication provides the latest developments on these alloys, their processing techniques for medical applications, characterization of fundamental materials properties critical to their use for biomedical applications, and evaluation of biological and clinical performance.

Eighteen peer-reviewed papers cover:

Alloy Processing—includes information on the formulation and processing of five important, new implantable metallic biomaterials

Alloy Properties—focuses on the bulk and surface properties, especially stress corrosion cracking and fatigue, of a number of different titanium alloys, which may be used for implants. Additional information is provided on the fracture mechanisms of several of these alloys.

Biological and Clinical Evaluation—deals with the biological and clinical evaluation of titanium, niobium, zirconium and tantalum used in the medical and surgical setting, including a new method of grit-blasting for implant surfaces, clinical evaluation of 14 retrieved modular body (SROM) total hip stems removed at the time of revision surgery, and a practical methodology to generate titanium and stainless steel wear debris particles for use in further study of the process of osteolysis and its treatment.
A New Approach to the Prediction of the Fretting Fatigue Life that Considers the Shifting of the Contact Edge by Wear
Authors: Hattori T , Nakamura M , Watanabe T
Published: April 2008

In fretting fatigue the contact edge will shift inward due to wear. The effect of this shifting on crack propagation behavior is considered here for accurate prediction of fretting fatigue life. The stress intensity factor(KI) for cracking due to fretting fatigue was calculated by using contact pressure and frictional stress distributions, which were analyzed by the finite element method. The S-N curves for fretting fatigue were predicted by using the relationship between the calculated stress intensity factor range (ΔKI) and the crack propagation rate (da/dN) obtained using CT specimens. Fretting fatigue tests were performed on Ni-Mo-V steel specimens. The S-N curves of experimental results were in good agreement with the analytical results obtained by considering the shifting of the contact edge.
On the Standardization of Fretting Fatigue Test Method—Modeling Issues Related to the Thermal Constriction Phenomenon and Prediction of Contact Temperature
Authors: Attia MH
Published: April 2008

The temperature field in the contact zone has a significant effect on the material microstructure, its properties, the oxidation process, and the thermal contact stresses. To standardize fretting fatigue tests, one has to be able to predict and control the contact temperature. Since direct temperature measurement is practically impossible, analytical models are required to estimate the friction-induced temperatures rise under fretting conditions. The main objective of the present work is to model the thermal constriction phenomenon in fretting fatigue and wear processes, considering the roughness and waviness of contacting surfaces. These asperity-scale models can be combined with large scale analyses, e.g. finite element method, to account for the thermal characteristics of the whole tribo-system, its boundary conditions, as well as the spatial variation in the slip amplitude and coefficient of friction over the interface. The debatable question on whether the contact temperature in fretting fatigue is significant is addressed, considering a wide range of materials and applied loads. The analysis showed that the randomness of the contact size may substantially increase the micro-constriction impedance of the fretting interface. The paper is concluded with recommendations for future work to experimentally validate these models, and to examine the effect of the spatial maldistribution of the micro-contacts, and the effect of surface oxide on the contact temperature prediction.
Length Scale Considerations in Fretting Fatigue
Authors: Nowell D , Hills DA , Moobola R
Published: April 2008

The presence of fretting can be shown to decrease the fatigue life of a component by accelerating crack initiation and subsequent propagation. Behavior in the “long crack” regime may be adequately explained using linear-elastic fracture mechanics. In contrast crack initiation is complex and much more difficult to understand. A size effect has been recorded in which the fretting fatigue life for contacts loaded to the same magnitude of stress varies with contact size. This phenomenon is used to explore the various length scales present in the crack initiation problem. It is shown that it is important to consider the relative magnitudes of these dimensions when attempting to analyse any particular initiation problem.