bluuebunny/crossref_metadata_2025 huggingface dataset:
American Football in the Courtroom—Legal Liability Associated with the Game
Authors: Davis PM
Published: March 2009

This paper reviews the development of the game of football, and its accompanying risk of injury and the various rule changes over time brought about to reduce injuries. The development of litigation related to football injuries is detailed including the potential liability of all associated with the game.
Effect of Swell Pressure on GCL Cover Stability
Authors: Stark TD
Published: March 2009

This paper describes the importance of bentonite swell pressure on the stability of cover systems that incorporate a geosynthetic clay liner (GCL). The results of a one-dimensional swell test indicate that the field swell pressure of a needle-punched GCL ranges from 35 to 40 kPa. An effective normal stress at or near this swell pressure may be required to maximize the contact area between the GCL and geomembrane and increase the static and seismic stability of a GCL cover. Since an effective normal stress of 35 to 40 kPa is probably not practical and a soil cover is usually not immediately placed, it is recommended that free swell conditions be assumed for GCL shear testing and the slope be designed using the resulting shear strength parameters. Suggestions for modifying existing products to increase GCL cover stability are also presented.
Influence of Initial Hydration Conditions on GCL Leachate Permeability
Authors: Didier G , Comeaga L
Published: March 2009

Modern landfill liners typically contain several geosynthetics and natural omponents integrated into a system whose primary function is the containment of waste and leachate. One of these hydraulic barrier components is represented by Geosynthetic Clay Liners (GCL). The GCLs are factory manufactured hydraulic barriers consisting of bentonite clay supported by geotextiles or geomembranes. Since the waterproofing function is assured by the bentonite clay it is therefore advisable to verify its chemical compatibility with the leachate and its effect upon the hydraulic conductivity value. According to the climatic situations occurring between the GCLs and waste installation, the leachate exposure moment can correspond to various GCLs hydration degrees. In this context, this paper aims at analyzing the total or partially hydrated GCL's behavior after a long time exposure to leachate. The permeability tests carried out for two needle-punched GCLs in three situations (saturated with water, water partially hydrated and saturated with leachate) show an important variation of the permeability with the hydration degree.
Manufacturing Quality Control and Specification Criteria for Geosynthetic Clay Liners
Authors: von Maubeuge KP
Published: March 2009

Geosynthetic clay liner (GCLs) combine geological materials with synthetic fabrics and require a new approach to conformance and quality control testing. GCLs have been used in various sealing applications over the last 10 years and have found an increased use in landfill applications. Therefore during the June 1993 ASTM meetings, a GCL subcommittee, D 35.04 was created with Mr. Larry Well of CH2M Hill, Portland, OR. serving as subcommittee chairman. The subcommittee comprises 6 task groups: • Physical properties • Manufacturing quality control and assurance (MQC/MQA), • Logistics, • Endurance, • Hydraulic properties, and • Mechanical properties.

As an example, the Manufacturing QC/QA task group has currently developed a standard of practice for manufacturing quality control of GCLs, and methods for determining a swell index value for clay and the fluid loss of the clays. A standard for manufacturing quality assurance is currently in development.

In the past quality control and quality assurance programs were developed by various manufacturers resulting in QC/QA programs which benefit the manufacturers products and not necessarily the project requirements. Another problem is the fact that the construction quality control and quality assurance (CQC/CQA) plan is often written in isolation by different people from those writing the MQC plan [1]. This paper will discuss the state-of-the-art of quality control and quality assurance for GCL testing to help to maximize GCL performance.
Subcritical Crack Growth in Ceramic Composites at High Temperature Measured Using Digital Image Correlation
Authors: Mumm DR , Morris WL , Dadkhah MS , Cox BN
Published: March 2009

An in situ experimental technique is described that allows high resolution, high sensitivity determination of displacements and full-field strains during high temperature mechanical testing. The technique is used to investigate elevated temperature crack growth in SiC/Nicalon composites. At 1150°C, the reinforcing fibers have a higher creep susceptibility than the matrix. Fiber creep leads to relaxation of crack bridging tractions, resulting in subcritical crack growth. Differential image analysis is used to measure the crack opening displacement profile u(x) of an advancing, bridged crack. With appropriate modeling, such data can be used to determine the traction law, from which the mechanics of cracking and failure may be determined.
Fatigue Life Modeling of Hybrid Ceramic Matrix Composites
Authors: Newaz GM , Bonora N
Published: March 2009

An investigation was undertaken to examine the fatigue characteristics of unidirectional dual fiber ceramic matrix composites made from Nicalon and SCS-6 fibers in UTRC-200 lithium aluminosilicate (LAS) glass matrix. Damage evolution was monitored as a function of fatigue cycles and stress levels via longitudinal stiffness loss. The damage consisted of matrix cracks, fiber-matrix disbonds, and broken fibers. Magnitude of damage was found to be strictly dependent on applied strain level. The consequence of damage development is manifested as stiffness loss for the composite. The stiffness degradation was monitored carefully, and a trend was observed. Based on the observed trend, a stiffness reduction model as a function of fatigue life was proposed that accounted for applied maximum strain and initial damage based on the first cycle maximum strain. The model was shown to be quite effective in predicting the damage evolution and thus fatigue life of dual fiber ceramic matrix composites (CMCs). The proposed fatigue life model is a generic one and can be applied to other CMCs exhibiting stiffness reduction as a result of multiple complex damage modes.
Evaluation of the Lubrication Properties of Biodegradable Fluids and Their Potential to Replace Mineral Oil in Heavily Loaded Hydrostatic Transmissions
Authors: Feldmann DG , Hinrichs J
Published: March 2009

Increasing public interest in the environmental impact of technical machinery has led to the development of new hydraulic fluids. In case of leakage these fluids pose less of an environmental threat than mineral oil, because they degrade faster and are less toxic or non-toxic.

The following paper describes method and results of laboratory tests with these new, so called biodegradable fluids, in a hydrostatic transmission on a flywheel restrig under high load conditions.
Tribological Properties of Fire-Resistant, Nonflammable, and Petroleum-Based Hydraulic Fluids
Authors: Lacey PI , Naegeli DW , Wright BR
Published: March 2009

Petroleum-based hydraulic fluids qualified under MIL-H-6083 are highly flammable. As a result, a fire-resistant polyalphaolefin (PAO)-based fluid, qualified under MIL-H-46170 and developed in the 1970s, and more recently, a nonflammable chlorotrifluoroethylene (CTFE) hydraulic fluid, were developed as potential replacements. However, the chemical and physical properties of both fluids are significantly different from those of conventional fluids. This paper outlines a laboratory study to define the interrelated parameters of degradation and wear of contacts lubricated with various hydraulic fluids, with particular reference to CTFE. The results rank the likely wear, corrosiveness, and oxidation properties of CTFE in comparison to currently used silicone-, PAO-, and petroleum-based fluids. In general, the antiwear characteristics of the CTFE hydraulic fluid were found to be similar to those of petroleum-based fluids but marginally inferior to those of PAO-based fluids. However, CTFE produced severe corrosion of brass at temperatures above approximately 135°C. As a result, it is believed that operation at very high temperatures is likely to cause unacceptable material removal from copper-based metals. Several surface treatment processes were identified to minimize potential side effects, evident under more severe operating conditions with CTFE.
Correlating Fluid Lubrication Characteristics to Pump Wear Using a Bench Top Surface Contact Test Method
Authors: Eleftherakis JG , Webb RP
Published: March 2009

One measure of a good test procedure ultimately answers the question, “How well does the procedure duplicate field observed results?” This is especially true with test methods for hydraulic components such as pumps due to the unique wear processes at play in today's high performance hydraulic systems.

This paper discusses the development of a benchtop, surface contact pin and journal wear test method and the research conducted to determine its usefulness in predicting the wear characteristics of fluid system components. Discussed are the limitations discovered in the various other machines and methods used for assessing the antiwear characteristics of fluids (i.e., lack of fluid circulation system, lack of contamination control and lack of variable speed control of the wearing surfaces). These limitations are emphasized when applied to hydraulic system related testing.

Further discussed in the paper are two surface wear studies--one on the lubrication characteristics of hydraulic fluids and the other a wear assessment of fuel pumps. Both studies are shown to correlate well with actual field experience.

These studies are the basis to justify further efforts to correlate results from the bench test proposed with hydraulic pump testing. Such correlation would minimize the need to conduct the more expensive and time consuming pump testing.
Youth Baseball Deaths And Injuries
Authors: Kyle SB , Adler PW
Published: March 2009

There are an average of 3 to 4 deaths per year to children under age 15 in association with baseball (including softball and tee-ball). In 1994, there were an estimated 181,000 baseball-related injuries to this age group. Consumer Product Safety Commission (CPSC) data indicate that the rate of injury was higher among 10 to 14 year olds than among 5 to 9 year olds. In 1994, most injuries to 5 to 9 year olds occurred in the head/neck region; injuries to the face accounted for the highest percent. For the 10 to 14 year olds, head/neck and upper limb injuries each contributed approximately 30 to 40 percent of the injuries; injuries to the face and fingers predominated. A CPSC special survey on how these injuries occur is planned.
Baseball Eye Protection: The Effect of Impact by Major League and Reduced Injury Factor Baseball on Currently Available Eye Protectors
Authors: Vinger PF
Published: March 2009

Currently used eye protectors were tested with major league (ML) and reduced injury factor (RIF 1) baseballs at normal speeds of play. Catchers’ face masks and protectors which passed ASTM F910 gave satisfactory protection. The helmet mounted C flap and most other protectors were not satisfactory. Eye protectors which pass the standard for women’s lacrosse come the closest to giving adequate, but incomplete protection for baseball. Three-mm center thick polycarbonate spectacle lenses have satisfactory impact resistance, but none of the tested frames could retain the lens and prevent eye contact. The data is insufficient to comment on the influence of ball hardness on the effectiveness on eye protectors in baseball.
Deceleration Distance Estimation using a Kinematic Model and Elapsed Time Measurements: An Application to Baseball
Authors: Koenig K , Davis N , Wilson T , Randle R , Slavings R
Published: March 2009

Motivated by safety concerns in baseball and softball, a study has been conducted of the distance required by people to stop from running. The deceleration following the sprint from home plate to first base is used to represent stopping actions which occur in baseball and softball. Measurements of home-to-first sprint and stop times from actual games and staged experiments are combined with an analytical model to estimate stopping distances.. Comparisons with other analyses and sports events indicate the validity of the present model. Data from high school (male) baseball and the corresponding analysis are presented. The results suggest that baseball and softball players require on the order of 40 feet (12.2 meters) to stop after the home-to-first sprint and that this distance may be a useful value to first consider for safety zones.
Spectator Safety Management in Baseball/Softball
Authors: Lucenko LK
Published: March 2009

A major area of concern when planning, constructing and managing a baseball/softball facility should be the provision of an adequate spectator protection system. The administrators of such a facility must consider the concepts of risk management to insure that the spectators will be provided a safe environment when attending a baseball/softball game.

This paper examines spectator safety considerations which should be implemented at all stadia that are designed to attract spectators. The paper also undertakes an analysis and comparison of three representative baseball/softball facilities; a professional baseball field in Salt Lake City, Derk’s Field; the Board of Education/Recreation Department Softball Complex in Wappinger’s Falls, New York and the Municipal Recreation Field, in Purchase, New York. In addition to a comparison of the exemplary fields, recommendations are made regarding the reduction of spectator injuries and subsequent litigation.
Constructing and Maintaining Safe Playing Surfaces
Authors: Waddington DV , McNitt AS , Landschoot PJ
Published: March 2009

A primary goal when constructing or maintaining baseball and softball fields should be to provide a playing surface that enhances both player safety and player performance. Field-related player injury on baseball and softball fields may be due to factors such as field hardness, traction, ball bounce and speed, and sliding surface properties. Various methods are available for objective assessment of hardness, traction, and ball responses, and they should be used to assess a range of turfed and skinned areas. The quality of the playing surface is greatly affected by soil properties, turfgrass characteristics, wear, and interactions among these factors. Appropriate construction and maintenance procedures should be utilized to provide uniform, safe, and playable surfaces. Guidelines for construction and maintenance are of value to those planning, constructing, and maintaining fields, and several standard guides are being prepared within the framework of ASTM.
A Coupled/Uncoupled Computational Scheme for Deformation and Fatigue Damage Analysis of Unidirectional Metal-Matrix Composites
Authors: Wilt TE , Arnold SM , Saleeb AF
Published: March 2009

A fatigue damage computational algorithm utilizing a multiaxial, isothermal, continuum-based fatigue damage model for unidirectional metal-matrix composites has been implemented into the commercial finite element code MARC using MARC user subroutines. Damage is introduced into the finite element solution through the concept of effective stress that fully couples the fatigue damage calculations with the finite element deformation solution. Two applications using the fatigue damage algorithm are presented. First, an axisymmetric stress analysis of a circumferentially reinforced ring, wherein both the matrix cladding and the composite core were assumed to behave elastic-perfectly plastic. Second, a micromechanics analysis of a fiber/matrix unit cell using both the finite element method and the generalized method of cells (GMC). Results are presented in the form of S-N curves and damage distribution plots.
Short Fatigue Crack Characterization and Detection Using Confocal Scanning Laser Microscopy (CSLM)
Authors: Varvani-Farahani A , Topper TH
Published: March 2009

This paper presents a new technique for studying the growth and morphology of fatigue cracks. The technique allows short fatigue crack growth, crack depth, aspect ratio (crack depth/half crack length), and crack front configuration to be measured using a Confocal Scanning Laser Microscope (CSLM). CSLM measurements of the initial stage of crack growth in Al 2024-T351 revealed that microstructurally short fatigue cracks grew initially along a plane inclined to the applied stress. The angle of the inclined plane (Stage I crack growth) was found to be about 45 degrees to the axis of the applied tensile load. Aspect ratio and the angle of maximum shear plane (Mode II), obtained using the CSLM technique, showed a good agreement with those obtained using a Surface Removal (SR) technique. The aspect ratios obtained using the CSLM technique were found to remain constant with increasing crack length in Al 2024-T351 and SAE 1045 Steel at 0.83 and 0.80, respectively.

Optical sectioning along the length of a crack revealed that the crack front in the interior of the materials has a semi-elliptical shape. These results are in good agreement with results obtained using the SR technique.

The CSLM technique was employed to characterize the fracture surface of fatigue cracks in an SAE 1045 Steel. CSLM image processing of the fracture surface near the crack tip constructed a three dimensional profile of fracture surface asperities. The heights of asperities were obtained from this profile.

Optical sectioning from a post-image-processed crack provided crack depth and crack mouth width at every point along the crack length for each load level. The crack opening stress was taken as the stress level at which the crack depth stopped increasing with increases in applied stress.
Ultrasonic Longitudinal and Surface Wave Methods for in situ Monitoring of Damage in Metal Matrix and Ceramic Matrix Composites
Authors: Buchanan DJ , John R , Stubbs DA , Benson DM , Karpur P
Published: March 2009

This paper discusses the development of a unique set of integrated Nondestructive Evaluation (NDE)/Mechanical test techniques for characterization of ceramic matrix composites (CMC) and metal matrix composites (MMC). These techniques are sensitive to the initiation and accumulation of damage in CMC and MMC. These techniques use longitudinal (bulk) wave and surface wave ultrasonic energy to interrogate the composite specimens, in situ, during mechanical testing. Changes in surface and longitudinal wave characteristics are compared with stiffness changes for extensometer measurements during tension, creep and fatigue testing of SiC/BMAS (barium-magnesium alumino-silicate) CMC. Surface waves were used to identify the onset of surface and near-surface cracks in CMC. Changes in the surface wave characteristics provide a better indicator of impending failure during fatigue testing of Sigma/Ti-6242 MMC than extensometer data. Longitudinal wave propagation was successfully used to monitor the changes in the stiffness of the composite during fatigue loading conditions of CMC and MMC. The changes in the peak-to-peak amplitude of the transmitted wave signal appears to be an equal or better indicator of impending failure of the composite than the extensometer data.
Using Ultrasonic Measurements and a Two-Phase Composite Model to Assess Radiation Damage in Reactor Pressure Vessel Steels
Authors: Wang JA
Published: March 2009

Ultrasonic methods used in the study of radiation damage and recovery in single crystals appear to also be useful for similar studies on polycrystalline alloys. Ultrasonic methods have demonstrated a sensitivity to radiation damage as affected by neutron fluence, irradiation temperature, large changes in composition, and possibly, as well, by neutron energy spectrum. On the microstructure defect evolution, only the residual defects created through the radiation event will contribute to the final macroscopic material property change. From a microstructure point, it is generally accepted that radiation hardening and embrittlement in metals are caused by clusters of vacancies, interstitial, and solute atoms that impede the motion of slip dislocations. Although vacancy-type defects are a major contributor to the material hardening, they also indicate the presence of other interstitial defects. Thus the total volume change of vacancy-type defects before and after irradiation can serve as a direct index to the final material property changes. The volume change of the vacancy-type defects can be determined by utilizing the two-phase composite model (matrix and void-type inclusion) to interpret wave velocities of baseline and irradiated specimens that are obtained from the ultrasonic wave experiment. This is a relatively economic and straightforward procedure. The correlation of the volume change of the vacancy-type defects with the existing destructive mechanical test results may play an important role in the future for the prediction of the radiation embrittlement and remaining plant life, especially for the older plants on the verge of exhausting all the available mechanical test specimens loaded in the surveillance capsules. The above hypothesis was supported by the limited irradiated data analyzed and presented in this paper. The proposed ultrasonic methodology also has a potential application to assess creep damage in fossil power plants.
Orientation Softening as a Mechanism of Ultra-High Molecular Weight Polyethylene (UHMWPE) Wear in Artificial Hip and Knee Joints
Authors: Wang A , Edwards B , Yau S-S , Polineni VK , Essner A , Klein R , Sun DC , Stark C , Dumbleton JH
Published: March 2009

The wear of ultra-high molecular weight polyethylene is one of the most important factors in the longevity of total joint replacement prostheses. This paper investigates the morphological changes in UHMWPE induced by plastic deformation and wear. A plasma etching technique was used to reveal the lamellar structure and its crystalline orientation in UHMWPE. Specimens under examination included unconsolidated UHMWPE powder, freeze fractured surfaces, microtomed slices, surfaces of tensile stretched specimens, shear fracture surfaces, and worn surfaces of acetabular and tibial components that had been tested on hip and knee joint simulators. For the unconsolidated powder and the freeze fracture surfaces, the orientation of the lamellae on the surface was random. For the surfaces of microtomed slices and tension specimens, the orientation of the lamellae was perpendicular to the direction of microtoming and tensile deformation. X-ray diffraction of the tension specimen indicated preferential orientation of the c-axis of the orthorhombic structure in the stretching direction. A similar orientation phenomenon was observed on the worn surfaces of acetabular and tibial components. A sequential biaxial tension test was conducted to study the effect of molecular orientation on the longitudinal and transverse strength of UHMWPE. An orientation-induced softening phenomenon was observed when the UHMWPE was stretched in a direction perpendicular to the molecular chains. Based on these observations, an orientation softening wear model was proposed. The model states that molecular orientation induced by plastic deformation during joint articulation is undesirable for the wear resistance of UHMWPE acetabular and tibial components.
Effect of Gamma-Radiation Induced Oxidation and Crosslinking on the Wear Performance of Ultra-High Molecular Weight Polyethylene (UHMWPE) Acetabular Cups
Authors: Polineni VK , Wang A , Essner A , Sun DC , Stark C , Dumbleton JH
Published: March 2009

The effect of gamma-radiation sterilization on the mechanical and physical properties of ultra-high molecular weight polyethylene (UHMWPE) has been studied in depth, but the effect on tribological properties remains a matter of considerable debate and contention. Most of the conclusions about the tribological properties are either hypothetical or based on wear testing that does not simulate the in vivo wear conditions adequately. In this paper, extensive hip simulator data are presented regarding the wear behavior of UHMWPE acetabular cups. The following sterilization treatments are considered: no sterilization, gamma-radiation in air, gamma-radiation in an inert atmosphere and stabilization, and ethylene oxide (EtO) sterilization. Hip simulator testing was conducted in both the anatomical and the inverted anatomical configurations. In the anatomical configuration, the stabilized UHMWPE acetabular cups demonstrated a reduction in wear of about 65% over EtO sterilized acetabular cups and 20% over air-irradiated cups. The unirradiated UHMWPE cups demonstrated the same wear behavior as EtO sterilized cups. In the inverted anatomical configuration, stabilized cups showed a 54% reduction in wear over the EtO sterilized cups. Oxidation studies further showed that air-irradiated UHMWPE had a propensity for increased oxidation levels over time with a peak in the subsurface while stabilized acetabular cups showed consistently lower oxidation levels with accelerated aging. Gel content analysis showed an increase in the insoluble constituents with gamma radiation, indicating an increase in crosslinks. Based on this study, it was concluded that gamma sterilization in an inert environment followed by thermal activation to accelerate free radical decay improves the tribological properties of UHMWPE while controlling any increase in oxidation levels even after accelerated aging.
Investigation of Free Radicals in Ultra-High Molecular Weight Polyethylene (UHMWPE) Materials Following Irradiation and Aging
Authors: Trieu HH , Thomas DE , Jahan MS , Haggard WO , Conta RL , Parr JE
Published: March 2009

The ultra-high molecular weight polyethylene (UHMWPE) used in total joint arthroplasty has been sterilized commonly by gamma radiation. Irradiation and subsequent aging in air reportedly cause extensive oxidation in this material. The original properties of UHMWPE, including wear resistance, can be altered significantly as a result of oxidation. In this study, long-lived free radicals in gamma-sterilized and subsequently shelf-aged UHMWPE tibial components were investigated. UHMWPE bar stock, resin powder, and fibers that had been irradiated with electron beam and then stored in air for three years were also characterized for long-lived free radicals. Significant concentrations of free radicals were found in all irradiated UHMWPE materials. Peroxy radicals are predominant in the UHMWPE materials that are highly accessible to oxygen, while more primary radicals remain in the UHMWPE materials that are isolated from oxygen. Based on this study, it is expected that irradiation of UHMWPE in an inert environment would result in long-lived primary radicals, which could be a potential cause of long-term oxidation.
Marking of Ceramic Femoral Heads
Authors: Calès BJ
Published: March 2009

In order to guarantee long term traceability for hip joint heads, permanent marking must be used. Two marking techniques are currently used today for ceramic femoral heads: mechanical machining and laser beam engraving. The objective of this paper was to analyze the risks and advantages of each technique and to evaluate the influence of marking on the mechanical performance of ceramic heads. It has been noted that: -i) the flaws due to mechanical marking are two orders of magnitude larger than for laser engraving, -ii)the stress concentration at the bottom of the head, where machined marking is preferably made, could be significantly higher than at the top of the bore, where laser engraving is currently performed. It is therefore argued that laser engraving is a more suitable marking procedure to guarantee long term reliability.
Test Method for the Assessment of Fretting at the Femoral Head and Neck Taper Interface
Authors: McLean TW , Lambert RD
Published: March 2009

Today in the United States, 95% of all total hip implants contain at least one modular junction. The most common of these junctions connects the femoral head and neck taper. Because this connection utilizes a Morse taper, various materials and design variables can influence fretting and corrosion behavior at the mating surfaces, and ultimately the longevity of the device.

In order to isolate and study the behavior of the femoral head/neck taper connection, a simplified model of a neck taper was designed. Test specimens were manufactured of Ti-6Al-4V and Co-Cr, and were designed to accept a Co-Cr femoral head. These constructs provided control in the experiment by focusing on the femoral head/neck taper interface, and by facilitating debris collection. Each construct was encapsulated with Ringer's solution and subjected to a fatigue load of 490 N to 4900 N at a rate of 10 hertz for ten million cycles. Using direct current plasma-optical emission spectroscopy (DCP-OES), the Ringer's solution was analyzed for titanium and cobalt ions after the fatigue test. The titanium level measured for the Ti-6Al-4V/Co-Cr constructs was less than 0.05 mg/L. For the Ti-6Al-4V/Co-Cr and Co-Cr/Co-Cr constructs, the cobalt levels were 0.95 – 0.23 mg/L and 1.16 – 0.57 mg/L, respectively.

This test method was designed to determine the debris generated at the femoral head/neck taper interface by controlling for specific design/fixation variables. It can be used to predict how such factors as material, taper diameter, taper angle, taper engagement, and tolerances affect the generation of wear debris during fatigue. Although the results do not predict the debris generation of an actual hip prosthesis, they may indicate performance characteristics which can be generalized to in-vivo behavior of the device.
Assessing Morse Taper Function: The Relationship between Impaction Force, Disassembly Force, and Design Variables
Authors: Schmidt AH , Loch DA , Bechtold JE , Kyle RF
Published: March 2009

Increasing experience with modular total hip implants has revealed problems with the Morse taper, including disassembly, corrosion, and wear debris. There are no standards for taper dimensions, manufacturing tolerances, or surface finish, and it is not known how these variables affect the function of the tapered connection. In this study, the relationship between the pull-off strength of a Morse taper and the force of impaction was determined for several commercial hip implants. The purpose of this study is to introduce this method of assessing Morse taper function, and to relate differences in taper performance to different design variables among the manufacturers. The results showed that taper distraction strength varies more than two-fold among the devices tested. Because of the many design differences noted among the different implants, the relative importance of each cannot be determined. Further work is warranted to refine these findings, and to identify the clinical significance of differences in taper distraction strength.
Fretting Corrosion Fatigue Study of Modular Joints in Total Hip Replacements by Accelerated In Vitro Testing
Authors: Bhambri SK , Gilbertson LN
Published: March 2009

The performance of modular head/taper joints in total hip replacements now in use for nearly two decades can be easily termed as a clinical success. However, associated with concerns of metal particulates found in retrieved tissues, a critical review of modularity in hip joints has recently emerged. Evaluation of retrieved modular joints has shown some surface morphological changes and debris generated at the mating surfaces which has not been demonstrated equally by any in vitro laboratory testing.

In this investigation, an experimental setup was developed to conduct fretting corrosion tests of modular head/taper assemblies in an aggressive environment to accelerate the in vivo phenomena. The fretting corrosion tests were conducted in a low pH Ringer's solution at 50°C. A maximum cyclic load of 5.34 kN was applied at 5 Hz on simulated modular head/taper assemblies mounted in a 15° valgus anatomic orientation. Ti-6Al-4V and Co-Cr- Mo alloy tapers and Co-Cr-Mo alloy (cast or wrought) and zirconia ceramic femoral heads in various combinations were evaluated. The morphology evaluation of taper and head bore surfaces after 10 million cycles revealed features such as etching of structure, preferential leaching and fretting in congruence to those reported for retrieved modular hip joints. Nitrogen diffusion surface hardening of Ti-6Al-4V alloy tapers resulted in an increase in resistance to fretting corrosion-induced changes, and a reduction in generated debris. A zirconia ceramic femoral head tested on either a Ti-6Al-4V or a Co-Cr-Mo alloy taper showed an enhanced resistance to both mechanical and chemical phenomena.
Fretting Corrosion Mechanisms at Modular Implant Interfaces
Authors: Jani SC , Sauer WL , McLean TW , Lambert RD , Kovacs P
Published: March 2009

Modular connections have been commonly and successfully utilized in orthopaedic implant systems for the last 15 or so years, particularly at the head/neck junction in total hip arthroplasty (THA). However, recent retrieval studies have shown that some of the tapered junctions between femoral heads and stems in total hip arthoplasty can be prone to fretting corrosion, and may be a cause for concern in the longevity of implants. Fretting corrosion, which may release metallic products (particulate debris and ions) into the joint space, is a complex phenomenon in which the interplay between mechanically induced interfacial micromotion (fretting) and electrochemical corrosive activity play an important role, along with materials selection and processes. This suggests that interfacial fretting corrosion at modular implant interfaces can be significantly affected by the design variables of the modular junction. The working hypothesis of this study was that different designs of the modular head/stem combination of femoral hip prostheses exhibit different release of fretting corrosion metal products during fatigue testing used to simulate ten years of in vivo service. Three designs of femoral head (Co-Cr-Mo alloy) and stem (Ti-6Al-4V alloy) combinations were investigated in this study. The study included detailed taper metrology followed by environmental fatigue testing of the tapered junctions. The results of this study showed that important taper design differences do exist in the three constructs tested, and these differences manifested in different fretting corrosion behavior.
Femoral Stem Fatigue Characteristics of Modular Hip Designs
Authors: Heim CS , Postak PD , Greenwald AS
Published: March 2009

Modularity in total hip arthroplasty design has received increased citation in the literature. Clinical concerns in the application of these systems include structural compromise at metal-metal interconnections due to cyclic microdisplacements. A laboratory fatigue test method, incorporating proximal support was developed and utilized to determine performance characteristics for these systems. Structural fatigue curves for four modular systems currently in clinical use were obtained and compared to anticipated in vivo service loading conditions for the normal hip. The structural fatigue strength of these designs was at least 1.3 times the anticipated service load. The results demonstrate that the in vivo structural integrity of these systems should not be compromised by the presence of metal-metal interconnections.
Factors Affecting the Reproducibility of Upward Propagation Pressure Thresholds of Metals in Gaseous Oxygen
Authors: Key CF , Lowery FS , Darby SP , Libb RS
Published: March 2009

The results of an investigation into the reproducibility of promoted combustion test data for various metallic materials are presented. Tests were conducted in the promoted combustion test fixtures at NASA's Marshall Space Flight Center, in gaseous oxygen at pressures from 0.7 MPa to 68.9 MPa. The tests were conducted using circular and square crosssection samples. The effects of sample size on pressure threshold reproducibility are discussed also.
Influence of Alloying Additions on the Flammability of Nickel-based Alloys in an Oxygen Environment
Authors: Tayal M , Wilson DB , Stoltzfus JM
Published: March 2009

The need for burn resistant materials has been long realized by the aerospace industry for applications such as oxygen-rich preburners and turbopumps. It has been found that some nickel-based superalloys show excellent burn resistance which can be attributed to the type and quantity of the alloying elements. Currently, there is no known thorough study that explains the influence of individual alloying elements on the flammability of nickel-based alloys in an oxygen environment. In this study, a series of binary nickel-based alloys was prepared and tested for flammability in an oxygen environment. The influence of alloying elements on varying the flammability of nickel binary alloys was analyzed and compared with relevant binary phase diagrams. A correlation between the binary phase diagram and flammability of alloys in an oxygen environment is postulated.
Analysis of Metals Combustion Through Powder Production
Authors: Wilson DB , Sircar S , Hornung S , Stoltzfus JM
Published: March 2009

The usual catastrophic results of metal-oxygen fires lends impetus to the search for the fundamental mechanisms of metals combustion. A variety of experimental techniques and their subsequent analysis needs to be pursued. This paper analyzes the powder produced during NASA standard flammability experiments of zinc, vanadium, molybdenum, tungsten and silicon at pressures ranging from 3.44 MPa to 68.9 MPa. Each product powder has a distinctive shape and size distribution. These distributions are described and detailed. The effect of variation of oxygen pressure on these shapes and size distributions is reported. In addition, a qualitative description of the combustion mechanism and powder growth is suggested for each metal. In these experiments, the metals burned in heterogeneous reactions.
Fuel Cell Elastomeric Materials Oxygen Compatibility Testing: Effect of 450 and 6200 kPa Oxygen
Authors: Waller JM , Hornung SD , Beeson HD
Published: March 2009

The oxygen compatibility of five O-ring formulations used in the Space Shuttle oxygen/hydrogen (O2/H2) fuel cell was evaluated following exposure to 450 and 6200 kPa (65 and 900 psi) oxygen at 121 °C (250 °F) for 48 h. The elastomers tested were Neoprene compound C873-70, and four fluoroelastomers: Aflas® 7182D, Kalrez® 1045, Fluorel® 2180, and compound V884-75. Post-aging changes in mass, dimension, tensile strength, elongation at break, durometer hardness, and compression set were determined for each elastomer. Aging results were compared to ignition and combustion data, namely the autogenous ignition temperature (AIT) and heat of combustion (ΔHc). Finally, the possibility of heterogeneous oxidation is discussed.
Eliminating Bypass Valves in Selected Oxygen Systems
Authors: Castillo DG , Werley BL
Published: March 2009

CGA Pamphlet G-4.4 recommends the use of bypass valves around isolation valves “where required to minimize adiabatic compression or particle impingement.” Bypass valves add cost and can be vulnerable components. Strategies for eliminating the need to provide bypass valves are reviewed based upon an interpretation of the intent of bypass valves and the thesis that an isolation valve should be operated either without differential pressure or with minimal differential pressure.
Effect of Crumb Rubber Particle Size and Concentration on Performance Grading of Rubber Modified Asphalt Binders
Authors: Tayebali AA , Vyas BB , Malpass GA
Published: March 2009

This study evaluates two aspects of the performance related Superpave™ binder specification methodology: 1) the applicability of the dynamic shear rheometer (DSR) to crumb rubber modified binders, and 2) the effect of crumb rubber particle size and concentration on the higher temperature performance grading of rubber modified asphalt binders.

Results indicate that the Superpave™ DSR test protocol is applicable to the modified binders used in this study. The average coefficient of variation for the different specimen thickness and replicate testing based on the measured property G*/sinδ obtained was 6.2% and 6.5%, respectively. In general, the crumb rubber particle size did not affect the performance grading of the modified binders. A 7% crumb rubber modification increased the high temperature performance grading by one grade; whereas, the 14% crumb rubber modification increased the performance grading by two grades. For high temperature range, the unmodified and modified binders with the same performance grade appear to show similar characteristics.
SHRP PG Classification and Evaluation of In-Service Asphalts after Eight Years
Authors: Galal KA , White TD
Published: March 2009

A study has been conducted on the changes to in-service asphalts. This study represents ongoing extensive research efforts at Purdue University to investigate the changes to in-service asphalts and to evaluate the recently developed SUPERPAVE asphalt binder specifications. During the 1985 construction season, samples from the original asphalt binders and the truck mix samples (original mixtures) were retained from a number of paving projects in Indiana. In 1992/1993, after 7 to 8 years in-service, cores from these pavements were taken. During the same period of time, distress surveys were conducted. In a later stage, six projects were selected for detailed analysis using the SUPERPAVE binder test equipment and procedures. A major interest of this research was to characterize the changes in the asphalt binders in-service and to correlate these changes with the pavement distresses, mainly: permanent deformation (rutting), fatigue cracking, and low temperature cracking. Consequently, the performance grade (PG) binder specifications could be evaluated. The SUPERPAVE binder tests and associated criteria were used to determine the high, intermediate, and low temperature characteristics (stiffness, (Pa)) of the asphalt binders tested. The results compare the relation between the conditioned (aged) asphalt binders from the Rolling Thin Film Oven (RTFO) test and the asphalt binders extracted from the original mixtures and the relation between the asphalt binders conditioned in the Pressure Aging Vessel (PAV) to the asphalt binders extracted from the in-service (field) cores. The results indicate that the current SUPERPAVE RTFO conditioning does not simulate short term aging. Similarly, the results show that the PAV aging procedure does not correspond to the aging encountered after eight years in-service.
Critical Evaluation of the Superpave Performance Prediction Model for Permanent Deformation and Supporting Theory
Authors: Zhang X , Kriech AJ , Huber GA
Published: March 2009

Superpave performance prediction models for permanent deformation were evaluated. Experimental design contained three unmodified asphalt binders, one Superpave level 1 mix design, and two aging procedures. Results of this study indicate that temperature, asphalt binder grade, and aging significantly affect mixture stiffness. The parameter m of the creep compliance equation which is used in the Superpave models as the slope of the permanent deformation equation is not reliable and should not be used to predict rutting. Pattern search method used to determine the Vermeer plastic properties failed to reach a solution in all cases. The parameter m and pattern search failure in the Vermeer model are, in part, responsible for unreasonable predictions.
Rainscreen Computer Program
Authors: Rousseau J , Quirouette RL
Published: March 2009

Pressure equalized rainscreen walls control rain penetration by eliminating the forces which drive or draw water into a wall. A rainscreen wall incorporates two layers or wythes separated by an air space; the outer layer is vented to the outside. The performance of a pressure equalized rainscreen wall will be dependant on the leakage area of the air barrier system, the area of vent openings, the volume of the cavity, the stiffness of the air barrier and of the cladding and the leakage area of the compartment seals. The design of rainscreen is not intuitive, the RAIN computer program is a tool developed to assist practitioners in their design.
In Situ Assessment of Moisture Levels in Exterior Walls of Single-Family Residences Clad with Exterior Insulation and Finish Systems (EIFS)
Authors: Williams MF , Williams BL , Hamilton LJ
Published: March 2009

This paper discusses comparative test results obtained using different kinds of moisture meters on mockup walls clad in an exterior insulation and finish system (EIFS). The accuracy and efficacy of intrusive and non-intrusive meters as moisturescreening tools was evaluated. Specifically, a mockup of the most commonly used EIFS wall assembly was constructed and a known quantity of water was introduced into the various layers of the assembly. Moisture meters were then used to determine their effectiveness in locating moisture within the mockup wall. Comparison of the moisture meter data found that non-intrusive meters appear to be a practical, effective, and accurate means of moisture detection when supplemented with intrusive meter use. This finding is important since the need to screen EIFS-clad residences for moisture has increased due to recent findings of moisture behind EIFS claddings installed on some houses.
Quantification of Large Inclusions in Bearing Steels
Authors: Lund TB , Törresvoll K
Published: March 2009

With the advances made in clean steel technology in recent times, most current techniques to quantify inclusion contents fail to provide relevant feed-back to process engineering. This is a particular dilemma in that the larger a defect, the more dangerous it is, and the harder it is to find as inclusion size distributions are log-normal. By employing a destructive, laboratory ultrasonic test procedure valuable insights into the frequency, the size distribution and the composition of large deoxidation products can be gained. In this context, large inclusions are in the intermediate size range normally not detected by microscopic or macroscopic methods. This ultrasonic technique also can be used to map and measure other defects as porosities at the billet stage with a precision previously not attainable. Additionally, a development of conventional step-down testing can be used to enhance the understanding of exogenous large inclusion sources and frequency.
From White Etching Areas Formed Around Inclusions to Crack Nucleation in Bearing Steels Under Rolling Contact Fatigue
Authors: Vincent A , Lormand G , Lamagnère P , Gosset L , Girodin D , Dudragne G , Fougères R
Published: March 2009

A method of calculating fatigue life of bearing steels, which accounts for the material fatigue process in relation with its microstructure, is required for optimizing these materials. Such a new approach is presented for bearing steels submitted to rolling contact fatigue, for which inclusions are well known to play a fundamental role on steel fatigue strength. A characterization of the steel is carried out by means of nano-indentation tests for determining the elastoplastic properties of the inclusions, and compression tests for determining the microyield stress and cyclic plasticity behavior of the steel matrix. Furthermore the number of cycles to crack nucleation is determined by high frequency ultrasonic echography. A model is developed to estimate movement and accumulation of dislocations around high modulus inclusions. This model enables us to calculate shape and size of white etching areas formed around inclusions as well as the number of cycles to crack nucleation.