bluuebunny/crossref_metadata_2025 huggingface dataset:
Creep-Fatigue Interaction in Delamination Crack Propagation of Advanced CFRPs at High Temperatures
Authors: Uematsu Y , Kitamura T , Ohtani R
Published: March 2009

The objective of this study is to elucidate creep-fatigue interaction in Mode I delamination crack propagation of polymers reinforced by carbon fibers at high temperatures. The materials tested are two unidirectionally reinforced laminates, AS4/PEEK (carbon fiber: AS4, matrix: poly-ether-ether-ketone) and T800H/PMR-15 (carbon fiber: T800H, matrix: polyimide). Crack propagation tests are conducted in cyclic loading conditions with and without hold(s) at maximum tension and zero load at 473K for AS4/PEEK laminates and 573K for T800H/PMR-15 laminates, respectively. In fatigue with high frequency, the crack propagation rate per unit cycle da/dN is correlated well with the stress intensity factor range ΔK. However, the crack propagation in AS4/PEEK laminates depends strongly on the load waveform, while that in T800H/PMR-15 laminates is independent of it. The crack propagation in AS4/PEEK laminates is accelerated by the tensile load hold due to the creep deformation of matrix and it is purely time-dependent. In the time-dependent crack propagation, the rate per unit time da/dt is correlated well with the stress intensity factor K at the hold. On the other hand, the time-dependent crack propagation is decelerated by the zero-load-hold because of the creep recovery of matrix.
Characterization of a Graphite/Epoxy Composite Under In-Plane Shear Fatigue Loading
Authors: Shokrieh MM , Eilers OP , Lessard LB
Published: March 2009

To examine the in-plane shear behavior of graphite/epoxy material in fatigue, the three-rail shear test specimen, normally used for static testing, is modified by inserting notches on the edge of the specimen. The performance of the notched specimen shows great improvement in both static and fatigue loading conditions. Therefore, by using the notched specimen, a more reliable experimental data base can be obtained.

The main objective of this research is to fully characterize a graphite/epoxy composite under in-plane shear fatigue loading by using the modified notched specimen. To fully characterize the material under in-plane shear, both static and fatigue tests are performed. Fatigue life, residual strength, and residual stiffness of AS4/3501-6 are measured. Experimental results from both static and fatigue loading show a very clear mode of failure under in-plane shear in the gage area of test specimens. To measure the fatigue life, a cyclic load is applied to the specimen and tests are continued until catastrophic failure is achieved. To measure the residual strength and residual stiffness, the fatigue loading is stopped after a fixed number of cycles (for example, 100, 1000, and so forth) and the residual properties are measured by applying a static load and destroying the specimen. Nonlinear stress-strain behavior of the material under static loading conditions is observed and the effect of fatigue loading on the nonlinearity is studied and discussed. To study the effects of mean stress on the fatigue behavior of the material, fatigue tests are performed under different stress ratios (k = σmin/σmax). The fatigue life, residual strength, and residual stiffness of the material are presented in normalized forms that can be used to predict the fatigue behavior of the composite material, under arbitrary state of stress and stress ratio, based on the presented experimental data base. Thus, the behavior of AS4/3501-6 graphite/epoxy composite under in-plane shear fatigue loading is fully characterized.
Combined Effects of the Low-Earth-Orbit Environment on Polymeric Materials
Authors: Shively J , Miglionico C , Roybal R , King T , Robertson R , Baird J , Davis S , Stein C
Published: March 2009

Understanding the phenomenology of the interaction of the space environment with organic composite spacecraft surfaces is both interesting science and important to the longevity of our space assets. The importance of this understanding has been made even more critical by the desire to use new, organic composite materials whose lower weight and higher stiffness will make it possible to orbit larger payloads. Inconsistencies between ground simulation and space test data clearly indicate that our understanding of the interaction phenomenology is inadequate. Preliminary research carried out by the Phillips Laboratory has demonstrated that the simultaneous interaction of all of the space environmental factors is often required to obtain agreement between ground- and space-test data. This paper describes the test equipment designed by Phillips Laboratory to subject composite materials to a simulated low-earth-orbit environment consisting of simultaneous fluxes of hyperthermal neutral oxygen atoms, energetic electrons, vacuum ultraviolet light, and hypervelocity-particle impacts characteristic of space debris and micrometeorites. Preliminary results of studies of the combined effects of fluxes of atomic oxygen and electrons on polysulfone resins and composites, and an evaluation of impact damage to polysulfone resins and composites from small aluminum particles traveling at velocities up to 6 km/s, are presented. The need for testing standards and methods for measuring space environmental effects is assessed.
Development of TIE Procedures for Complex Mixtures Using Physiological Responses in Fish
Authors: Hewitt LM , Scott IM , Van Der Kraak GJ , Munkittrick KR , Solomon KR , Servos MR
Published: March 2009

Methodology was developed for the isolation and recovery of ompounds from a commercial lampricide formulation associated with hepatic mixed function oxygenase (MFO) enzyme induction in fish. MFO induction in laboratory bioassays was characterized and optimized prior to fractionation experiments. Recovery and isolation of MFO activity directed the chemical fractionations. Fractionation techniques were developed on a preparative scale so that fish exposures could be conducted directly. Formulation impurities associated with MFO induction were separated from the active lampricide using solid phase extraction. Subsequent HPLC fractionations isolated activity in distinct fractions, indicating that multiple formulation impurities are associated with the observed MFO induction. Activity was recovered from each fraction using toluene extraction and the extracts werecharacterized by GC-MS. No activity was associated with several compounds confirmed in the bioactive fractions and other structures are proposed. A preliminary application of these techniques to potential reproductive dysfunctions in fish is discussed.
Chemistry and Toxicity of Sediments from San Diego Bay, Including a Biomarker (P450 RGS) Response
Authors: Anderson JW , Newton FC , Hardin J , Tukey RH , Richter KE
Published: March 2009

Thirty sediment samples were collected from the vicinity of the Naval Docking Facility in San Diego Bay and used to conduct bioassays with amphipods (solid-phase), oyster larvae (elutriate), Microtox, and a new rapid screening test called the cytochrome P450 Reporter Gene System (RGS). This RGS cell line, from a human liver cancer cell, has been engineered to produce luciferase, when the CYP1A1 gene on the chromosome is induced by toxic and carcinogenic organics (dioxin, coplanar PCBs, PAHs). Elutriates were tested with both Microtox and oyster larvae, and organic extracts of sediments were tested with Microtox and the P450 RGS assay. Chemical analyses included total organic carbon (TOC), and acid volatile sulfides (AVS) along with a wide range of metals and organic chemicals. The simultaneously extracted metals (SEM) to AVS ratio was compared to the toxic response of oyster larvae and amphipods. Along each of the piers sampled, contaminant concentrations decreased with distance from shore. A correlation matrix analysis of all biological and chemical data was conducted. The strongest correlation (0.78, r2=0.61) between a chemical measurement and a biological response was that of total PAH versus the P450 RGS response. The use of P450 RGS as a screening tool to assess the relative risk of contaminants on sediments is biologically meaningful, and is a rapid and inexpensive means of determining which samples require complete chemical characterization.
An Argument for the Chicken Embryo as a Model for the Developmental Toxicological Effects of the Polyhalogenated Aromatic Hydrocarbons (Phahs)
Authors: Henshel DS
Published: March 2009

The choice of an animal model is ultimately crucial to toxicological testing. If one does not use the appropriate model for the chemical and endpoint being studied, then the test results may not really provide the appropriate toxicological information. There are three basic types of animal models: sentinel models, screening models, and mechanistic models, Each of these models has specific needs and requirements, some of which overlap, some of which are distinctly different. Therefore, some animal models are more appropriate for evaluating the effects of some chemicals than are other animal models. This article will present the argument that the chicken embryo is especially appropriate as an animal model for studying the mechanism of the developmental toxicological effects of the polyhalogenated aromatic hydrocarbons (PHAHs).

The PHAHs are a group of toxicologically related compounds including, in part, the polychlorinated dibenzodioxins, dibenzofurans and biphenyls. The chicken (Gallus gallus) embryo is relatively sensitive to the toxicological effects of the PHAHs being approximately two orders of magnitude more sensitive than the mature bird. The chicken embryo has been used to demonstrate general toxicological effects (i.e. the LD50), immunotoxicity, cardiovascular toxicity, teratogenicity, hepatotoxicity and neurotoxicity. Many of these effects, or analogous effects, have also been observed in mammals and fish. Thus, most animals appear to respond to the PHAHs with a similar toxicological profile, indicating that many of the biomarkers used for the PHAHs are valid across a number of species, including the chicken. Furthermore, the chicken embryo is relatively inexpensive to use for toxicity testing. In addition, all effects detected are due to direct effects on the embryo and are not complicated by maternal interactions. In short, for sensitivity, ease of use, cost and applicability of results to other animals, the chicken embryo is an excellent animal model for evaluation of the mechanism underlying the developmental toxicological effects of the PHAHs.
Sublethal Exposure to Cadmium Interferes with Cover Seeking Behavior of Juvenile Crayfish, Procambarus Clarkii (Girard)
Authors: Misra R , Antonelli J , Misra K , Steele C , Skinner C
Published: March 2009

The behavioral effects of heavy metals on crayfishes may significantly affect their survival in the environment. Changes in their ability to remain under cover could substantially decrease their survivorship due to increased predation. The effect of sublethal cadmium exposure on the ability of juvenile crayfish to remain in cover was evaluated. Four different treatment groups were used (N=11 juveniles each): a control group (not exposed to cadmium), and three experimental groups exposed to 1, 2, or 3 mg Cd/L for 7 d. Crayfish were placed, individually, into glass aquaria containing 3 L of laboratory water pre-treated to detoxify all heavy metals, with continuous aeration. Each crayfish was provided with a dark, thigmotactic shelter. Cadmium was introduced into the aquaria on days 1 and 4 to maintain the nominal concentrations. Beginning on day 5 and continuing through day 7, observations were taken on each crayfish five times per day, with a minimum of 30 minutes between observations. Crayfish position was recorded as in cover or in the open area of an aquarium. Juveniles in the control groups were in cover 78.3% of the observations. Over the 3 d of observations, juveniles in the 1 mg Cd/L exposure groups used cover 72.1%. Those in the 2 and 3 mg Cd/L groups used cover 53.9% and 60.0%, respectively, indicating hyperactivity induced by cadmium exposure. Examining the daily results, however, those juveniles in the 1 mg Cd/L group were in cover only 60.0% of the time by day 7, indicating a latency to produce hyperactivity at this concentration. Those in the 2 mg Cd/L group were using the covers similarly to the controls by day 7 of exposure, indicating habituation to the cadmium or “exhaustion” of the animals by hyperactivity. Those in the 3 mg Cd/L group behaved similarly to controls on day 5, but beginning on day 2 and continuing into day 3 of the observations spent progressively fewer of the observations in cover, suggesting that initial hyperactivity occurred prior to the beginning of observations, and “exhausted” the animals, or that they were severely traumatized by the exposure to 3 mg Cd/L and required time to recover before exhibiting hyperactive behavior.
Quality Assurance Guidance for Laboratories Performing Aquatic Toxicity Tests
Authors: Harrass MC , Klemm DJ
Published: March 2009

Satisfactory laboratory performance is critical to the use of aquatic toxicity tests in regulatory, industrial and research applications. Quality Assurance and Quality Control (QA/QC) practices are fundamental to demonstrating satisfactory performance. Laboratory aquatic toxicity test procedural and performance criteria can help a potential client decide that an aquatic toxicity laboratory will meet a need, as well as help an outside reviewer determine that test results are valid. Laboratory practices to assure and control quality include training staff, using standard procedures, and keeping valid records, but also include evaluating and improving performance. These components echo several widely used quality management principles. The costs of poor quality (lost time, lost production and lost image) touch both the laboratory and the laboratory's customers. While the level of quality should reflect the use of the study, higher quality work provides for better control, better data and better service, benefits ultimately shared by both the suppliers and users of aquatic toxicity data.
Development of a Mathematical Model for Design of Multiple-Well Soil Vapor Extraction Systems
Authors: Hsu H-T , Yeung AT
Published: March 2009

Soil vapor extraction (SVE) is a proven tecnnology that can remove volatile organic compounds (VOCs) from the subsurface effectively if the conditions are favorable. However, most systems are designed by empirical methods or engineering judgement based on results of pilot tests. An attempt is made to develop a mathematical model for the technology so that optimal operating parameters can be obtained. The pressure distributions induced by multiple-well extractions are obtained by superimposing an existing analytical solution. Concentrations of VOCs as a function of time and space are obtained by numerical simulation of the migration and fate of VOC. The effectiveness of SVE systems using different operating parameters is evaluated on the basis of the quantity of contaminant removed. The developed mathematical model provides the necessary engineering design tools to evaluate different operation scenarios.
Incorporating Consumer Feedback into Package Description and Presentation: Multi-Media Approach Techniques
Authors: Moskowitz H , Krieger B , Tomber N
Published: March 2009

This paper presents a new approach to identify the important aspects of packaging. The approach uses experimentally designed concepts dealing with packages, their uses, and their benefits. The concepts comprise “elements,” which are short words, pictures, and video clips (short videos lasting 3 to 5 s), combined by an experimental design and presented to the consumer on a computer screen. The consumer rates each combination on acceptance and expected performance. The computer acquires the ratings just after presenting the concept stimulus. The resulting database, comprising concept elements and consumer responses, is analyzed by dummy variable regression analysis to reveal which specific elements drive each consumer-rated attribute, respectively. The results of the analysis yield a model that allows the developer to “optimize” the package concept in order to maximize acceptance and/or to communicate different end benefits while so doing. The paper illustrates the method by an experiment with “baby wipes” (premoistened towelettes).
Perceiving What Package Designs Express: A Multisensory Exploratory Study Using Creative Writing Measurement Techniques
Authors: Durgee JF , O'Connor GC
Published: March 2009

The purpose of this research is to assess consumers' ability to correctly interpret messages that designers incorporate into new package designs. Packages today are designed to communicate many different messages—status, femininity, environmentally conscious, security (tamper-proof), etc. The goal of this project was to explore how consumers perceive and interpret these messages, and how consumers' interpretations of designers' messages relate to liking the package.

Results suggest that in cases where consumers correctly interpret designer messages: 1. Messages are clear and unambiguous. 2. Messages deal more with positive image associations than practical or functional benefits. 3. Designers and receivers might be communicating on subconscious levels. 4. Designs that communicate well are liked more than designs which communicate poorly.
High-Temperature Internal Friction and Intergranular Fracture in Ni-Cr Alloys
Authors: Cao B , Benoit W , Schaller R
Published: March 2009

Internal friction measurements have been performed on various compositions of polycrystalline alloys (Ni-8.6, 20 and 31.4 at.%Cr) and single crystals (Ni-20 and 33.6 at.%Cr), as well as in industrial alloys of Ni-22 at.%Cr containing respectively 0, 20, 66, and 180 at. ppm cerium.

The high-temperature internal friction spectra obtained in these alloys are characterized by the presence of two relaxation peaks (P1 and P2) and a large thermal hysteresis between the curves measured during heating and cooling. The P1 peak appears at about 950 K both in polycrystalline specimens and in single crystals. The P2 peak, appearing at about 1100 K, and the large thermal hysteresis occur only in the polycrystalline specimens. It is shown that the origin of P1 peak lies in the interior of the grains and that the P2 peak and the hysteresis are due to the grain boundaries. The PI peak could be interpreted as a Zener peak due to local stress-induced ordering. The P2 peak is certainly due to grain boundary sliding, more precisely to grain boundary dislocation motion. These dislocations interact with chromium carbide precipitates located in the grain boundary. The hysteresis is then interpreted as due to the dissolution during heating and the reprecipitation upon cooling of these discrete carbides in the grain boundaries.

The three anelastic phenomena, the P1 and P2 peaks and the hysteresis, appear in the same temperature range where intergranular embrittlement was observed during tension tests. This embrittlement, as well as the P2 peak, is associated with grain boundary sliding and is enhanced by carbide dissolution. On the contrary, pinning of the grain boundaries by carbides leads to the disappearance of P2, and plastic deformation is then intragranular. It is shown that cerium additions stabilize the carbides at the grain boundaries. The penetration of oxygen along the grain boundaries, on the contrary, destabilizes the carbide precipitates and enhances grain boundary sliding.
Composite Rotorcraft Flexbeams with Viscoelastic Damping Layers for Aeromechanical Stability Augmentation
Authors: Smith CB , Wereley NM
Published: March 2009

The objective is to experimentally determine the damping levels that can be achieved by cocuring constrained viscoelastic damping layers in a composite beam. Beams were clamped in a cantilever condition and excited using piezo actuators. Natural frequencies were identified using frequency response data. Transient response data were collected using strain gages and analyzed using logarithmic decrement, Hubert transform-based, and moving block damping identification algorithms. Two sets of experiments were performed. First, benchtop tests of four fully constrained layer rectangular-cross-section laminated composite beams were conducted. The cocured beam consisted of a six-ply graphite/epoxy (Gr/Ep) composite host structure, a damping layer of viscoelastic material (VEM) that varied in thickness from 0 to 15 mils in 5 mil increments, and a 2-ply Gr/Ep constraining layer. The natural frequency exhibited a gradual increase with VEM thickness, and damping increased from 0.75% in the beam with no VEM to 5.40% in the beam with a 26.2% volume fraction (15 mil layer) of VEM. The second set of experiments involved two I-cross-section laminated composite beams in rotation. Each I-beam flange had a layup identical to that of the beams used in the benchtop experiments, with damping layer thicknesses of 10 or 15 mils, and the web layup was the same as the flange, minus the VEM layer. These beams were tested at rotational speeds from 0 to 750 rpm in a vacuum chamber, and transient response data were analyzed. The natural frequency increased quadratically as rotational speed increased. Further, as the viscoelastic layer thickened from 10 to 15 mils, the increase in damping remained nearly constant even as the rotational speed increased. At 0 rpm this increase was 33.8%, while at 750 rpm the increase was 33.3%. Structural damping decreased as a function of rpm, due to centrifugal stiffening.
Modeling Dislocation Breakaway Damping and Harmonic Generation
Authors: Beshers DN
Published: March 2009

Amplitude-dependent damping, being nonlinear, has associated with it an acoustic harmonic spectrum. Sufficient data have now accumulated to make desirable an effort to understand the complicated results. We have recently suggested that a sharp dip as a function of amplitude of the third harmonic in iron can be explained as a phase cancellation effect. A simple model, a discontinuous jump in amplitude of a sine wave, indicated that the phase of the emitted acoustic radiation depended on the phase of the jump. Supposing a distribution of breakaway stresses for dislocation segments, one expects that some segments will be emitting with a phase sufficiently different from others to give significant cancellation effects. In this paper, using a more physical representation of the breakaway event, we confirm the results on the tendency of the phases and observe qualitatively that they may be adequate to explain the data for brass as well as iron. Detailed modeling now seems worthwhile.
Comparison of Elastic and Anelastic Properties of SiC and MoSi2/Ti5Si3 as a Function of Temperature
Authors: Wolfenden A , Bauer KJ , Kury PB , Oliver KA , Rynn PJ , Petrovic JJ , Singh M
Published: March 2009

The piezoelectric ultrasonic composite oscillator technique (PUCOT) was used at frequencies near 120 kHz to measure the elastic and anelastic properties of two kinds of advanced ceramics as a function of temperature (T) up to about 1300 K and of strain amplitude in the range 10-7 to 10-4. The specimens consisted of commercially available silicon carbide (SiC) from Norton Co., reaction-formed SiC (RFSC) [with and without molybdenum disilicide (MoSi2) additions] made at NASA Lewis Research Center, and MoSi2/Ti5Si3 [With Ti5Si3 (pentatitanium trisilicide) concentrations in the range 10 to 50%] made at Los Alamos National Laboratory. The measured values of dynamic Young's modulus, E, damping, Q-1 and strain amplitude were analyzed. The main findings are: The Values of (1/E(0))(dE/dT), where E(0) is the value of E at room temperature, fall near -3 X 10-4 K-1; the damping in the materials is small and independent of strain amplitude for most of the specimens and temperatures used; and limited data for the silicides with 30 and 40% Ti5Si3 indicate a breakaway of the strain amplitude dependence of damping. The similarities and differences in the behavior of the mechanical properties are discussed for the two types of material.
Snoek Relaxation in Fe-Cr Alloys (O to 100%Cr)
Authors: Golovin IS , Blanter MS , Mourisco A , Schaller R
Published: March 2009

Internal friction (IF) spectra of α-Fe-FexCry-Cr ferritic alloys have been investigated with the help of forced and free decayed pendula in the frequency range 0.01 to 10 Hz. he Snoek-type relaxation has been found in all the investigated ternary alloys, iron-chromiumcarbon (Fe-Cr-C), starting with pure iron and finishing with pure chromium. The temperature of the Snoek peak (Tmax) in α-Fe is found to be 315 K (1 Hz), the activation energy deduced from the “T-f' shift is 78 kJ/mol, and the Tmax in Cr is 433 K with an activation energy 107 kj/mol. The Snoek-type peaks in Fe-Cr alloys are much wider than those in pure Fe and Cr. This is connected with the redistribution of atoms between octavoids with different numbers of Fe and Cr atoms in neighboring sites around octavoids and therefore different relaxation times. The “temperature location versus chromium content” curve passes through a maximum in the vicinity of 35 wt.%Cr, where Tmax is 573 ÷ 578 K,f = 1.2 Hz, and the activation energy is about 140 kJ/mol.

The new approach, based on interaction of carbon-carbon (C-C) and carbon-substitutional C-s) atoms, is suggested for the explanation of the influence of composition on Snoek-peak location. The long-range strain-induced interactions supplemented by the “chemical” interaction in the two nearest atomic shells around a fixed substitutional atom have been used for the modeling of C-s interaction. It is suggested that the interatomic interaction affects IF by changing the carbon atom arrangement (the short-range order was simulated by the Monte Carlo method) and the energy of C atoms in octahedral interstices, that is, the activation energy of IF. The carbon atoms contribution to IF has been calculated by the Debye equation with the use of energies of C-C and C-s interaction. The Tmax shift due to the iron alloying by Cr is much stronger than that due to chromium alloying by Fe and is explained from the point of view of the above-mentioned interactions.
Factors Affecting the Damping Capacity of TiC Particle Reinforced Zinc-22 Aluminum Composites
Authors: Lu J , Van Aken DC
Published: March 2009

Damping behavior of eutectoid zinc-aluminum composites was studied in the 25 to 33O°C temperature range using a low-frequency torsion pendulum. In this study the internal friction was affected by changes in microstructure and by the amount of cold work prior to testing. The highest damping was obtained for a composite with 15% titanium carbide (TiC) particles, a fine lamellar microstructure, and after being cold worked 20%. A high-temperature (HT) internal friction peak at a temperature just below the eutectoid transformation temperature was observed in the composite materials, and in the annealed base alloys cold worked prior to testing. The authors believe this HT peak is associated with recrystallization of the matrix prior to the eutectoid transformation.
Damping Behavior of 6061 Al/SiC/Gr Spray-Deposited Composites
Authors: Zhang J , Perez RJ , Lavernia EJ
Published: March 2009

Spray deposition processed 6061Al/SiC/Gr hybrid metal matrix composites (MMCs), in their as-extruded condition, have been demonstrated to exhibit both relatively high damping and high elastic modulus, but a reduced strength in comparison with that of unreinforced 6061-T6A1 alloy. In order to explore the possibility of obtaining optimal mechanical properties for potential structural applications, the present work reports on the effect of T6 heat treatment on the damping capacity, elastic modulus, yield, and ultimate strengths of the hybrid MMCs. Both damping capacity and dynamic modulus were measured using a dynamic mechanical thermal analyzer at frequencies of 0.1, 1, and 10 Hz over a 30 to 250°C temperature range. Tension tests were conducted at room temperature on an Instron testing machine. Experimental results revealed that the 6061 Al/SiC/Gr MMCs, following T6 heat treatment, exhibit an optimum combination of room temperature mechanical properties along with an improved damping capacity in the intermediate testing temperature range. The operative damping mechanisms are discussed on the basis of microstructural analyses.
Modeling the Damping Mechanism in Electrorheological Fluid Based Dampers
Authors: Kamath GM , Wereley NM
Published: March 2009

Electrorheological (ER) material behavior exhibits a transition from viscoelastic properties in the pre-yield region to viscous properties in the post-yield region. A nonlinear dynamic model based on linear shear flow mechanisms is proposed to describe ER fluid behavior. The nonlinear model combines a 3-parameter fluid element and a viscous (dashpot) element using sigmoidal weighting functions. The weighting functions are dependent on the strain rate and serve to enforce the transition between the viscoelastic and the viscous characteristics. The model is then extended to characterize a damper based on ER fluids. A single-degree-of-freedom system incorporating an ER fluid damper is considered and its dynamics studied via numerical simulations. The results of the simulations show that, as the applied electric field is increased, a significant attenuation in the amplitude can be achieved, while the response changes significantly. A system identification methodology is suggested to determine the model parameters from simple vibration experiments. An important issue of the amplitude dependence of the material behavior is addressed and modifications to the model suggested so as to incorporate these effects.
Probabilistic Technique Related to Amplitude-Dependent Damping Under Combined Stresses
Authors: Cupschalk SG
Published: March 2009

The pioneering efforts of Koehler and of Granato and Lücke established, theoretically, the role of dislocations with respect to damping in metals and, in the latter case, provided a mechanism for amplitude-dependent damping. The original Granato and Lücke model, based on the bowing of dislocation segments and their eventual unpinning from solvent atoms situated along their lengths, was assumed to result solely from the applied stress. This approach has subsequently been extended to include thermal contributions to unpinning.

This study is concerned with refinements to the original treatment. Although dislocation bowing, etc., on slip planes was assumed to occur under the action of the resolved shear stress, no attempt was made to calculate that stress as a function of differing grain orientations in polycrystalline materials or of crystal structure. In the present case, the maximum shear stress cumulative probability, that is, the fraction of all possible slip plane orientations on which the shear stress exceeds some arbitrary value, is first determined from a 3-D Mohr's circle analysis. It is valid for all crystal structures and for all states of stress in randomly oriented polycrystalline materials. The resolved shear stress distribution function, which depends specifically on crystal structure, is next derived from the above cumulative probability. These functions are then introduced into the original Granato and Lücke treatment for the cases of simple tension and shear. The procedure outlined above may readily be generalized to include the effect of preferred orientation.
Computer Model of Zener Relaxation
Authors: Blanter MS , Kolesnikov EV
Published: March 2009

The model takes into account the fact that the displacements of atoms around each substitutional atom are governed by other substitutionals and their arrangement, that is, by short-range order. In general the symmetry of these displacements is lower than that ofcrystal lattice. Such a substitutional atom can be treated as an elastic dipole, the energy of which is dependent on the direction of the applied stress. It will diffuse under alternating stress and contribute to internal friction. The relaxation strength of each atom is taken as a strength of such elastic dipole. It was suggested that the activation energy of reorientation of the elastic dipole by jump of a substitutional atom is equal to the sum of the activation energy of tracer self-diffusion of one of the components of an alloy and the shift of energy of this atom in the force field of other substitutionals. The short-range order is simulated by the Monte Carlo method using pair interaction energies. The internal friction is calculated by summing up contributions of all substitutional atoms in accordance with the Debye equation. This model is equally good for both low and high concentrations. The model was used for analysis of internal friction and interaction energies for copper-zinc and silver-gold alloys. It gives the concentration dependence of relaxation strength like that found in the experiment. The interaction energies obtained by comparison of calculated peak temperatures with experimental ones are in a good agreement with the values obtained from diffuse scattering of X-rays and neutrons. This fact means that the difference between activation energies of diffusion and Zener relaxation can be attributed to substitutional interaction.
Barriers to Injury Prevention in Youth Football
Authors: Glassman R
Published: March 2009

The National Youth Sports Safety Foundation (NYSSF), formerly the National Youth Sports Foundation for the Prevention of Athletic Injuries, a nonprofit, 501 (C) (3) educational research organization dedicated to reducing the number and severity of injuries youth sustain in sports activities, has been involved in injury prevention efforts in youth football since 1989. During that time the Foundation has traveled an eye-opening journey encountering many different barriers to injury prevention at all levels. These barriers include: (1) misinformation, (2) attitude, (3) dissemination of information, (4) lack of coaching education, and (5) surveillance.

Many injuries can be prevented through educational programs but there has to be a perceived need for these programs. There should be effective dissemination, follow-up, and evaluation systems in place.
Head Injuries In Sports: Concussion Management in Football
Authors: Kelly JP
Published: March 2009

Surveys have found that 10% of college football players [1] and 20% of high school football players [2] experience concussions in a given football season. That translates to more than 250 000 concussions per year in football alone. The Sports Medicine Committee of the Colorado Medical Society drafted the “Guidelines for the Management of Concussion in Sports” that have subsequently been endorsed by several national physician organizations and widely distributed for the use of coaches, trainers, and allied health personnel as well as physicians. These guidelines are consistent with available evidence in clinical and research literature as well as consensus formed by medical experts.
A Proposed Method for Evaluating Neck Protection Equipment
Authors: Otis JC , Burstein AH
Published: March 2009

The catastrophic nature of cervical spine injuries in football, although the incidence of these injuries is infrequent, has led to recent attempts to develop new methods of neck protection. Currently, no performance standards or test standards exist for neck protection equipment to assure the user that there would be a reduction in the risk of catastrophic neck injury. Additionally, no performance standards or test standards exist to assure that there would not be an increased risk of injury to other portions of the user's body or to the opponent's, and to assure that the equipment would perform adequately from a structural standpoint. Thus, a need arises to develop a standardized method for evaluating neck protection equipment. A proposed method for evaluating such equipment consisting of an analytical screening protocol and a physical test is presented.
The Process of Certification of Protective Equipment For Sports
Authors: Morehouse CA
Published: March 2009

The details of the three essential phases for the certification of protective equipment for sports in the United States are described in this paper. The initial phase includes the necessary prerequisites for the development of written objective, scientific standards based on physical tests consistent with current engineering technology. The recommended features of a certification council including the employment of a third party validator for the adherence of products to available standards are outlined in the second phase. The third and final phase consists of the communication and cooperation of rules-making organizations necessary for proper compliance and the ultimate safety of the sports participants. The model used for illustrating the entire process of certification is the Hockey Equipment Certification Council (HECC), a volunteer organization established in 1976 for the certification of ice hockey equipment. The fact that mandated use of certified eye and face protection has reduced the eye and facial injuries in organized ice hockey by over 99% since the program was initiated in 1978 is evidence that certification can be very effective in the reduction of injuries if properly organized and administered.
The Football Coach and Football Safety
Authors: Borkowski RP
Published: March 2009

The game of football and especially those that play it, have benefitted from the extensive improvements that lower the potential for injuries. Equipment, facilities, and the general body of sports medicine knowledge have all helped to lower the chances of minor and major injuries.

The most important factor for safety in American football, however, has been and continues to be the attitude and skill of the coach.

This paper addresses those attitudes and skills that a coach must possess to offer a worthwhile and safe experience to those in his charge. This paper addresses the human factor in football safety. It further offers a list of situations to avoid within the football atmosphere that are based on this author's personal litigation experience. This paper makes several proposals to improve the safety quotient in football.
Football Injuries, Safety Standards, and Insurance Underwriting
Authors: Clarke KS
Published: March 2009

American football produces injuries, which produce costs, which produce expectations for two types of insurance: accident/medical and liability. Underwriters for insuring carriers rely on “experience” and the interpretation of that experience to determine the “whether” and “how much” of coverage. For accidents and the direct costs experienced, this is a more objective process than for liability. For the latter, the standards against which a defendant would be judged can be objective if available from a standard-promulgating source, or they must be derived from the opinion of an array of experts. ASTM provides a process for capturing expert consensus when it exists.
Perspectives on Geosynthetic Clay Liners
Authors: Koerner RM
Published: March 2009

This overview paper addresses a number of topics and issues pertaining to geosynthetic clay liners, or as they are usually referenced, GCLs. GCLs are factory manufactured products consisting of a layer of bentonite contained between two geotextiles by using adhesives, stitch bonding or needle punching, or by adhesively bonding the bentonite to a geomembrane. A number of commercially available products are available on a worldwide basis. The various products are reviewed along with some of the basic elements of their manufacturing process. The primary areas of acceptance and utilization are also presented.

Relevant physical, hydraulic, mechanical and endurance properties and their associated test methods are presented from the perspective of manufacturing quality control (MQC) tests versus design oriented (or performance) tests. Research and development testing is also addressed as contrasted to MQC and design testing. Lastly, current activity and recommendations are suggested for these relatively new and unique barrier materials.

It is hoped that the paper sets the proper tone for subsequent papers in this symposium which will add to the growing body ofV information and knowledge. Indeed, GCL's (acting individually or as composite materials) are changing the very essence of liquid barriers and their associated containment systems.
Effect of Normal Stress during Hydration and Shear on the Shear Strength of GCL / Textured Geomembrane Interfaces
Authors: Hewitt RD , Soydemir C , Stulgis RP , Coombs MT
Published: March 2009

A laboratory testing program was performed to evaluate the interface shear strength of a geosynthetic clay liner (GCL) / textured geomembrane interface utilizing two pre-shear inundation methods designed to simulate field conditions. Two commercially-available products were tested, a needlepunched and a stitch-bonded GCL. Oedometer swell tests provided swell data for the two products which were used to design the interface shear testing program. Interface shear tests were performed for 1) GCL samples inundated under a low normal stress for a short time and sheared under a higher normal stress, and 2) GCL samples inundated for a longer period under the design normal stress. The results for the two different GCL materials and the two preshear inundation conditions are compared.
Short-Term and Creep Shear Characteristics of a Needlepunched Thermally Locked Geosynthetic Clay Liner
Authors: Siebken JR , Swan RH , Yuan Z
Published: March 2009

A series of constant-rate direct shear tests were conducted on a needlepunched thermally locked geosynthetic clay liner (GCL) in accordance with ASTM Test Method for Determining the Coefficient of Soil and Geosynthetic or Geosynthetic and Geosynthetic Friction by the Direct Shear Method (D 5321). The test results demonstrate that the needlepunched thermally locked reinforcing fibers provide substantial short-term shear strength to a GCL. However, there is a growing concern that the long-term shear strength of this type of GCL can be affected due to the potential of creep within the reinforcing fibers under sustained constant loads which occur in the field. An attempt was made to address this concern through an incrementally-loaded creep shear test conducted in a newly developed constant-load (creep) shear testing device. The results of the creep shear test to date show that the GCL has undergone relatively small shear displacements with incremental shear rates decreasing with time within each loading phase.
Long-Term Shear Strength Behavior of a Needlepunched Geosynthetic Clay Liner
Authors: Trauger RJ , Swan RH , Yuan Z
Published: March 2009

This paper describes two large-scale constant-load (creep) shear testing devices that were developed to evaluate the long-term shearing behavior of geosynthetic clay liners (GCLs) and interfaces between GCLs and other geosynthetics or soils. One device was designed to simulate loading conditions that typically occur on a GCL deployed in a landfill cover system. The other device was designed to simulate loading conditions that typically occur on a GCL deployed in a landfill lining system. A needlepunched GCL was selected for evaluation of its long-term shearing behavior under these two types of loading conditions and the test results are presented in terms of time-displacement curves and shear rate-displacement curves. The results to date show that the GCL has undergone relatively small shear displacements and that the shear displacement rates within the GCL and/or at the test interface have been continuously decreasing with time. For the conditions used in this testing program, it is believed that the GCL's behavior can be considered stable. Further testing is planned to moreaccurately define the time-dependent internal and interface shear behavior of the GCL.
Shear Strength Testing for Geosynthetic Clay Liners
Authors: Gilbert RB , Scranton HB , Daniel DE
Published: March 2009

This paper provides guidelines for measuring the internal and interface shear strengths of geosynthetic clay liners (GCLs) in a direct shear test. Currently, there is significant variability between laboratories in shear testing procedures for GCLs; the major differences are related to specimen hydration and shear rate. The guidelines presented in this paper are intended to provide for consistent test results that can be interpreted without ambiguity. They are also intended to provide measured strengths that are representative of typical field conditions.
Laboratory Hydraulic Conductivity Testing of GCLs in Flexible-Wall Permeameters
Authors: Daniel DE , Bowders JJ , Gilbert RB
Published: March 2009

One of the important properties of geosynthetic clay liners (GCLs) is hydraulic conductivity. In the laboratory, hydraulic conductivity of GCLs is typically measured in flexible-wall permeameters. The most important variables in hydraulic conductivity testing of GCLs are addressed, including (i) trimming the GCL specimen; (ii) determining the thickness of the specimen; (iii) selecting the effective stress; (iv) selecting the hydraulic gradient; and (v) selecting the first wetting liquid and permeant liquid. A round-robin testing program was conducted in which 18 laboratories independently measured the hydraulic conductivity of a GCL that was permeated with water. The test specimens all came from the same GCL sample. The coefficient of variation, accounting for all sources of variability, was 42%. For experienced laboratories, this value reduced to 35%, which was identical to the variation in quality control tests performed over a 7-month period by the manufacturer on a variety of GCL samples. The round-robin test results are encouraging; there was less variability than might be expected, considering the difficulty in accurately measuring the hydraulic conductivity of relatively impermeable materials such as GCLs.
A study of the CBR Bearing Capacity Test for Hydrated Geosynthetic Clay Liners
Authors: Fox PJ , De Battista DJ , Chen S-H
Published: March 2009

A modified version of the California Bearing Ratio (CBR) penetration test was used to investigate the bearing capacity of hydrated geosynthetic clay liners (GCLs). The bearing capacity of GCLs is a concern because, once hydrated, the soft bentonite may squeeze laterally under concentrated loads. A series of bearing capacity tests were performed to study the influence of GCL product type, surcharge pressure, displacement rate, mold diameter, and termination criterion on lateral bentonite squeezing. Test results show that adhesive-bonded GCLs have a somewhat greater tendency for bentonite squeezing than reinforced GCLs. The magnitude of surcharge pressure during hydration is an important variable for GCL bearing capacity testing. The rate of piston displacement has little influence on the bearing capacity of hydrated GCLs. Confining molds having a diameter ⩾ 235 mm are satisfactory for the measurement of GCL bearing capacity. A standard CBR mold with a diameter of 152 mm is not recommended. Termination criteria based on a specified force or a peak in the force-displacement relationship may be unreliable for some tests. A specified displacement termination criterion of 20 mm was found to be more appropriate for the GCL bearing capacity tests conducted in this investigation.