bluuebunny/crossref_metadata_2025 huggingface dataset:
Fretting Fatigue Behavior of Ti-6Al-4V against Ti-6Al-4V under Flat-on-Flat Contact with Blending Radii
Authors: Hutson AL , Nicholas T
Published: April 2008

A study was conducted to evaluate fretting fatigue damage of Ti-6Al-4V under flat-on-flat contact at room temperature. Results were obtained to establish the fatigue limit of the material. Axial stresses necessary to fail specimens at 107 cycles for different contact radii, applied normal stresses, and stress ratios were evaluated to determine the baseline fretting fatigue behavior. Then, the effect of fretting fatigue on specimen life was quantified by conducting interrupted fretting tests for various load ratios and normal stresses followed by residual strength uniaxial fatigue tests. Fractography was used to characterize the nature of fretting damage. Results indicate that no degradation in fatigue limit is observed when the material is subjected to up to 10 percent of fretting fatigue life.
Evaluation of Fretting Stresses Through Full-Field Temperature Measurements
Authors: Harish G , Szolwinski MP , Farris TN , Sakagami T
Published: April 2008

The near-surface stress field in fretting has long escaped experimental characterization due in large part to the fact that the friction coefficient in the slip zones associated with the partial slip contacts cannot be evaluated from measured forces. Attempts at circumventing this through measurements of microslip or extent of the slip zones have been inconclusive. However, newly available infrared detector technology is capable of resolving finely, both spatially and temporally, subsurface temperatures near the fretting contact. These temperature changes are induced by both frictional heating at the surface due to microslip as well as the coupled thermoelastic effect arising from the strains in the material. A finite element model has been developed for fretting that includes the heat generation due to sliding and partial slip; and the coupled thermoelastic effect. The model also incorporates heat conduction, thermal deformation, and contact. The correlation between the temperature changes measured by the infrared camera and those predicted by the finite elements is remarkable. During gross sliding, a patch of heating throughout the contact length, attributed to frictional heating, is observed. As the friction coefficient rises and the contact transitions to a partial slip regime, the temperature changes are more clearly associated with strain through the coupled thermoelastic effect. The excellent agreement of the finite element results with the experiments demonstrates the ability of the model to provide validated values for fretting-induced stresses and microslip.
Fracture Mechanics Approach to the Fretting Fatigue Strength of Axle Assemblies
Authors: Makino T , Yamamoto M , Hirakawa K
Published: April 2008

The objective of the present paper is to evaluate the fatigue crack growth behavior in press-fitted axles using a fracture mechanics approach and to predict the fatigue strength regarding crack propagation (σw2). The relationship between nominal bending stress (σn) and non-propagating crack length in press-fitted axles is also discussed. Rotating bending fatigue tests were conducted on the induction hardened and quench-tempered axles of 38 and 40 mm in diameter. The equation for ΔK was formulated from the result of FEM analyses in which the micro-profile at the contact edge was taken into consideration. The threshold stress intensity factor range ΔKth for small cracks was estimated from the crack size measured after the fatigue tests by using a modified stress ratio effect at fully compressed stress reversals due to high compression residual stress. σw2 and the relationship between σn and non-propagating crack length were predicted by using the above mentioned ΔK and ΔKth. The predicted σw2 and non-propagating crack length were in good agreement with the experimental values.
Pavement Testing and Backcalculation Technologies—Challenges for the 21st Century
Authors: Mahoney JP
Published: April 2008

The background information presented in this paper was collected for the opening presentation at the Third International Symposium on Nondestructive Testing of Pavements and Backcalculation of Moduli. The paper will be used to address three questions or topics which are: • Where are we? • Where are we going? • Thoughts about the future.
Variations in Backcalculated Pavement Layer Moduli in LTPP Seasonal Monitoring Sites
Authors: Briggs RC , Lukanen EO
Published: April 2008

Seasonal variations in structural parameters were calculated from Falling Weight Deflectometer data on 25 LTPP flexible seasonal monitoring sections. In all, 23,976 deflection basins were analyzed. The deflection basins were collected monthly between the fall of 1993 and the spring of 1995. The test locations were distributed around North America from Saskatchewan to South Texas and from Idaho to Maine. The sections all consisted of asphalt surfacing and granular bases (and some granular subbases) over subgrades. Asphalt thicknesses ranged from 46 to 277#mm. Seasonal variations observed on selected sections in this database and documented in this paper include variations in asphaltic materials with temperature, variations in moduli of the unbound materials with precipitation, and variations in moduli of unbound materials due to freeze/thaw. For moderately thick to thick asphalt sections (>125 mm) the temperature dependency can clearly be seen in the deflection basins. As expected, this variation in deflections, and AC modulus is sinusoidal over the year. The amplitude of the sinusoidal variations were found to be heavily influenced by the thickness of the AC layer. Thicker AC sections exhibited higher sinusoidal variations. Base and subgrade values tended to be influenced by temperature but remained more consistent throughout the year except in cases where freeze̸thaw effects were seen. During freeze conditions, the moduli of the unbound (base and subgrade) layers drastically increased.
Seasonal Variations in Backcalculated Pavement Layer Moduli in Minnesota
Authors: Ovik JM , Birgisson B , Newcomb DE
Published: April 2008

Recent advances in flexible pavement design have prompted agencies to move toward the development and use of mechanistic-empirical (M-E) design procedures. The purpose of this paper is to analyze seasonal trends in flexible pavement layer moduli in order to calibrate a mechanistic-empirical design procedure specific to Minnesota. The relationships investigated were between climate factors, surface and subsurface conditions, and pavement material properties. The results presented focus on the base and subgrade layers and show that the layer moduli vary with the state of moisture in the pavement. The data used to develop this approach were collected from four flexible pavement Long Term Pavement Performance Seasonal Monitoring Program sites (LTPP SMP) and the Minnesota Road Research Project (Mn/ROAD). Temperature data are used in this study to characterize the severity of a winter and to approximate the onset of freezing and thawing cycles. Finally, seasonal trends in pavement layer moduli were quantified for use in an M-E design of flexible pavements.
Dynamic Backcalculation and Overlay Design Based on FWD Data
Authors: Maina JW , Yokota H
Published: April 2008

A study on dynamic backcalculation and overlay design based on falling weight deflectometer (FWD) data is presented. Dynamic slab-ground theory (DSGT) was used for dynamic backcalculation of a pavement structure. A computer program based on DSGT generated theoretical dynamic deflections of the pavement. For the backcalculation of equivalent full-depth asphalt concrete (AC) thickness and subgrade modulus, these deflections were matched with FWD deflections from major roads in Miyazaki Prefecture, Japan. Temperature influence on Young's modulus of AC was also considered. Results were then compared with those from DSGT's static analysis version (SSGT) and also from a Japanese representative method, NIPPO, which is a static elastic multilayer method. Characteristics of dynamic backcalculation analysis are discussed. The range of pavement variables showing necessity for dynamic analysis was also considered by comparison of theoretical deflections using DSGT and SSGT. Furthermore, overlay thickness design using Kentucky Transportation Center's procedure was carried out.
Computer Aided Nondestructive Evaluation Method of Welding Residual Stresses by Removing Reinforcement of Weld (Proposal of a New Concept and Its Verification)
Authors: Kumagai K , Nakamura H , Kobayashi H
Published: April 2008

A new method (the bead flush method) is proposed to estimate welding residual stresses non-destructively. First, the reinforcement of the weld is removed. Then from released strains on the surface due to removal, eigenstrain distributions are estimated by an inverse analysis. Finally, residual stresses are determined by the finite element method (FEM) using estimated eigenstrains as boundary conditions.

Numerical simulations were conducted to develop a sophisticated procedure. It is shown by numerical simulations that the proposed method gives reasonably good predictions of residual stress. Also, the validity of the proposed method was evaluated experimentally for a butt-welded plate joint. Based on this work, future problems to overcome are discussed.
Application of the Weibull Methodology to a Shallow-Flaw Cruciform Bend Specimen Tested Under Biaxial Loading Conditions
Authors: Williams PT , Bass BR , McAfee WJ
Published: April 2008

This paper describes the application of the Weibull methodology to the analysis of a shallow-flaw cruciform bend specimen tested under biaxial loading conditions. The cruciform bend fracture mechanics specimen was developed at Oak Ridge National Laboratory (ORNL) to introduce a far-field, out-of-plane biaxial bending stress component in the test section that approximates the nonlinear stresses resulting from pressurized-thermal-shock or pressure-temperature loading of a nuclear reactor pressure vessel (RPV). Tests with the cruciform specimen demonstrated that biaxial loading can have a pronounced effect on shallow-flaw fracture toughness in the lower transition temperature region for an RPV material. High-constraint deep-flaw compact tension C(T) and low-constraint shallow-flaw cruciform fracture toughness data were used to assess the ability of the Weibull methodology to predict the observed effects of biaxial loading on shallow-flaw fracture toughness. A new hydrostatic stress criterion along with five equivalent-stress criteria from the literature were selected to serve as candidate kernels in the integral formulation of the Weibull stress. Among these candidates, the hydrostatic stress criterion, derived from the first invariant of the Cauchy stress tensor, was determined to have the required sensitivity to multiaxial-loading states. In addition, a new calibration technique developed by researchers at the University of Illinois for determining the necessary Weibull parameters is applied to the C(T) and cruciform data. A three-parameter Weibull model based on the hydrostatic stress criterion is shown to predict the experimentally observed biaxial effect on cleavage fracture toughness by providing a scaling mechanism between uniaxial and biaxial loading states. In summary, the conclusions that can be drawn from this study are as follows: (1) With respect to its effect on fracture toughness, the biaxial effect is a constraint effect. (2) A Weibull statistical fracture model has been successfully calibrated with uniaxial toughness data obtained from a conventional high-constraint C(T) specimen and a uniaxially loaded shallow-flaw cruciform that is effectively equivalent to a conventional shallow-flaw SE(B) specimen. (3) The calibrated fracture model was able to successfully predict the intermediate constraint-loss effects associated with two levels of biaxial loading. (4) These preliminary results at a single test temperature offer encouragement that complex multiaxial loading effects on transition region fracture toughness can be predicted with statistical fracture models developed using data obtained from conventional specimens. (5) Future work is required to investigate these effects at other temperatures within the transition region.
Prediction of Time-Dependent Crack Growth with Retardation Effects in Nickel Base Alloys
Authors: Van Stone RH , Slavik DC
Published: April 2008

Accurate crack growth prediction methods are playing an increasing role in the design and evaluation of rotating gas turbine engine components. Fracture mechanics methods used to predict the cyclic lives (without time-dependent effects) are well established. As mission times and temperature increase, nickel base superalloys experience time-dependent crack growth where the crack growth response is a function of time under load (hold time) as well as overpeaks that occur prior to hold times. Linear elastic fracture mechanics methods havebeen developed that accurately predict the acceleration associated with hold times at elevated temperatures using a linear superposition of cyclic and static crack growth rates. The beneficial effects of retardation induced by overpeaks can be predicted using a modified Willenborg retardation model. Results of subcomponent validation tests for a variety of conditions and materials used to validate these methods are reported. Applicability of these model to predict complex missions and combinations of complex missions is also discussed.
Damage Repair Simulation of a Tension Panel and Pressurized Cylindrical Shell Using Adhesively Bonded Patches
Authors: Curtin TJ , Adey RA
Published: April 2008

The bonded patch repair performance of a cracked tension panel, and a pressurized cylindrical shell with longitudinal through-crack, is simulated using a commercially available boundary element code. Three-dimensional, quadrilateral-shaped, reduced-quadratic order, boundary elements are used to model the panel, cylindrical shell, and repair patch. The adhesive layer is modeled using a continuously distributed system of linear springs. A special boundary element is used to model the crack. The tension panel analysis is based on a single-sided repair configuration. The relationship between crack length and stress intensity factor (SIF) for both the unrepaired and repaired panel is presented. The reduction in SIF and change in stress field, for the repaired panel compared to the unrepaired panel, determined from the present analysis, are compared with FME and analytical results. The occurrence of out-of-plane bending and its impact on the through-thickness SIF variation in the panel is discussed. Crack growth simulation results show the crack front becoming curvilinear as the crack advances below the patch. The reduction in SIF for a pressurized cylindrical shell with a double-sided elliptical patch repair is presented as a special case.
Comparison of AASHTO Standard and LRFD Code Provisions for Buried Concrete Box Culverts
Authors: Rund RE , McGrath TJ
Published: April 2008

AASHTO developed the LRFD Bridge Design Specification, with the intent of replacing the Standard Specifications for Highway Bridges with a reliability based code that provides more uniform safety for all elements of bridges. Although many provisions in these two codes are the same, there are important differences that can have a significant effect on the amount of reinforcement required for buried precast reinforced concrete box culverts under some conditions.

AASHTO LRFD Code provisions that differ from the Standard Specifications include load factors, load modifiers, load combinations that produce the maximum force effect, multiple presence factors, design vehicle loads, distribution of live load to slabs and through earth fill, dynamic load allowance, live load surcharge, and reinforced concrete design methodology for fatigue, shear strength, and control of cracking. These provisions are compared with the equivalent provisions from the AASHTO Standard code, and discussed in detail.

Several combinations of culvert sizes and fill heights are evaluated using provisions from both the Standard and LRFD Specifications. A comparison of results show that in general, LRFD provisions result in increased design loads and reinforcement areas.
Test Procedures for Determining the Delamination Toughness of Ceramic Matrix Composites as a Function of Mode Ratio, Temperature, and Layup
Authors: Polaha JJ , Davidson BD
Published: April 2008

A study was conducted to improve upon currently used test procedures for determining the Mode I, Mode II and mixed-mode delamination toughness of ceramic matrix composite materials. Test methods and specimen geometries were chosen that may be used to test unidirectional or multidirectional layups. The test methods consisted of the Mode I double cantilever beam test, the Mode II end-notched flexure test and the mixed-mode single leg bending test. Procedures for these tests were developed that could be used at room or elevated temperature and for which a compliance calibration method of data reduction could be employed. These procedures were then used to perform a study on a Nicalon/MAS-5 fiber-reinforced ceramic to determine the effects of mode ratio, temperature and layup on delamination toughness. It was concluded that the three test methods combined can be used to provide sufficient information on the variation of toughness with mode mix for most design purposes.
Effect of Loading Mode on High-Temperature Tensile Deformation of a SiC/SiC Composite
Authors: Ünal Ü
Published: April 2008

Tensile deformation of a silicon carbide (SiC) matrix/Nicalon SiC fiber composite was studied under static and cyclic loads at 1300°C in nitrogen environment. Monotonic tensile tests were carried out to determine the stress levels to be applied during the ensuing tests. It was shown that under comparable stresses, higher strain accumulates under the static loads than the cyclic loads. Yet, the failure took place much more readily under the cyclic loads because of the damages induced on the load carrying O°-fibers. When the applied cyclic loads were small, the total strain and the rate of strain accumulation were similar under both types of loading, indicating similar deformation mechanisms in this range. At higher loads, however, under the cyclic loading, the matrix and fiber cracking controlled the deformation; under the static loading, the fiber creep dominated the deformation.
Damage Accumulation in 2-D Woven SiC/SiC Ceramic Matrix Composites
Authors: Morscher GN , Gyekenyesi JZ , Bhatt RT
Published: April 2008

Ceramic matrix composites are envisioned for use at elevated temperatures (1000 to 1400°C) in oxidizing environments. For non-oxide composites, the time-dependent failure stress is dependent on the severity of reactions between the environment and the load-bearing fibers and interphase. One of the most severe pitfalls for these types of materials occurs at intermediate temperatures, 600 to 1000°C. Environmental access to load-bearing fibers occurs through matrix cracks that are bridged by load-bearing fibers. The rate at which these composites lose the ability to carry load is partially controlled by the extent of cracking in the matrix. In this study, the damage accumulation of woven SiC/SiC composites tested in tension was quantified using unload/reload hysteresis tests and modal acoustic emission. The behavior of composites reinforced with ceramic-grade Nicalon™, Hi-Nicalon™, and Sylramic® fibers, with carbon or boron nitride interphases and chemically vapor-infiltrated or melt-infiltrated SiC matrices was investigated. The most significant finding of this study is that the formation of matrix cracks that bridge the load-bearing fibers (0° cracks) occurs at approximately the same strain for all of the woven SiC/SiC composites tested. All of these systems have at least a CVI SiC matrix layer adjacent to the interphase. In addition, the onset stress-strain condition for 0° cracks corresponds to the tensile stress-strain condition above which intermediate temperature embrittlement occurs for BN interphase SiC/SiC composites. For carbon interphase SiC/SiC composites, the critical stress-strain condition for the onset of intermediate temperature embrittlement corresponds to the first cracks in the matrix which can occur at stresses half the 0° crack onset stress.
Development of an Injury Surveillance System: Results from a Longitudinal Study of High School Athletes
Authors: Rice SG
Published: April 2008

An injury surveillance study among all 18 high school sports in the Puget Sound area of Washington State was conducted for approximately fifteen years, tracing 60,000 athletes who participated in more than 2.5 million days of athletic activity. This technique of injury surveillance, using a Daily Injury Report (DIR) form, was able to follow all sports simultaneously over many years, permitting a large database to be assembled. The data collection instrument (DIR) has been modified to meet the needs of hockey teams. Injury rates are expressed as injuries/100 athletes/season and as injuries/1000 athletic exposures. Injury severity is delineated through significant injuries (“one week” or longer), major injuries (“three weeks” or longer) and out-for-season injuries. Fall sports had more injuries than spring sports. Girls had more injuries than boys did in identical sports. Cross country running and soccer, for both boys and girls, ranked in the first tier of injuries along with football, wrestling and gymnastics. The data produced results that would not have been predicted by the conventional wisdom of the times.
Is the Face Mask Good for Ice Hockey?
Authors: Vinger PF
Published: April 2008

The ice hockey face protector is an extremely effective sport's protective device. At this time over one million participants wear face protection certified by the Hockey Equipment Certification Council (HECC). Ice hockey face protectors prevent over 70,000 eye and face injuries a year with a savings to society of over $10 million each year in the United States. No blinding eye injuries have been reported in any player who was wearing a HECC or CSA approved full-face protector while playing ice hockey. The success of the hockey face mask stems from the studied, deliberate process involved in the evaluation of the mechanisms of hockey injury and their means of prevention.
A Comparison of the Epoxy Alloy and Magnesium Alloy Headforms
Authors: Bishop PJ
Published: April 2008

Headform durability is a problem for standards bodies evaluating hockey helmets. Presently the Canadian Standards Association (CSA) uses a skull form fashioned from an epoxy-metal alloy, but because this headform is susceptible to cracks and because it is difficult to obtain replacements from suppliers, the CSA is considering a change to the use of a machined magnesium headform. Before doing so, a comparative study of the performance capabilities of the magnesium and epoxy headforms was undertaken at two separate laboratories. The headforms were evaluated on a uniaxial monorail system at velocities that produced energy levels of 10, 20 and 30 joules. Each headform was tested against a modular elastomer programmer (MEP) pad which covered the impact pedestal. Five impacts to each of 6 locations (Front, Front Boss, Side, Rear, Rear Boss and Crown) on both headforms were conducted. Peak headform acceleration was the impact criterion measure. Overall the peak headform acceleration was 165g for the magnesium headform and 151g for the epoxy headform, a difference of 9%. As expected, the magnitude of peak acceleration varied according to location with the side and rear boss showing the largest difference between headforms. When the results of all tests were combined the correlation in peak acceleration between the two headforms was, 92. Based on a linear regression model, a 275g acceleration criterion for the epoxy headform would be equivalent to 272g for the magnesium headform. These results suggest that the magnesium headform performs in a manner similar to that of the epoxy headform.
A Psychosocial Perspective of Aggression in Ice Hockey
Authors: Smith AM , Stuart MJ , Colbenson CML , Kronebusch SP
Published: April 2008

The incidence of aggression in ice hockey and the consequences of violent on-ice behavior is of major concern to those interested in the safety of the sport. The purpose of this paper is to examine the history of aggression in hockey, how it is measured and why it happens. A hypothetical integrated model of antecedents of aggression in hockey is presented which may guide future research investigations. Officiating in ice hockey, penalty statistics at specific levels of participation, and the categorization of penalties are discussed. An assessment was done to determine whether there has been a change in player's perceptions of the attitudes of significant others toward aggression. The results were compared to previous research [1], which examined reinforcers of aggressive behavior in hockey players. A case study of an injured hockey player is presented which depicts the physical and psychosocial consequences of a penalized aggressive on-ice incident. Steps that can be taken to reduce aggression and identify barriers that are likely to impede attempts to reduce aggression in the game will be discussed. Suggestions for future research are presented.
Psychological, Physiological, and Performance Variables in Goalies During Hockey Games
Authors: Smith AM , Stuart MJ , Fish KN
Published: April 2008

Prompted by an intrigue with the challenges of goaltending, questionnaires were given to 67 youth hockey goalies. Seventy-six percent responded that the psychological aspects of the position caused the greatest difficulties. A subsequent study examined the relationship between psychological, situational, and physiological variables and on-ice performance. Goalies completed psychometric instruments before going on the ice and their electrocardiograms were monitored during on-ice stations. Subjects were videotaped at the Puck Shooting Machine (PSM) station. Mean heart rate (HR) was 163 beats per minute (bpm) at the PSM and 175 bpm at other stressful stations (e.g., breakaway and slap shot). Goalies with 100% saves (N=7) were older, more experienced, less anxious, and had faster HR's than those who performed poorly. Because elevated arousal levels were detected at the goalie camp, a subsequent study of different Bantam, High School, and Junior A goalies (N=13) were studied during 31 games. Rapid HR's were sustained during games, even when goalies were standing still.
Tracking the Relative Age Effect Across Minor Amateur and Professional Ice Hockey Leagues
Authors: Montelpare WJ , Scott D , Pelino M
Published: April 2008

The purpose of this study was to examine the relative age effect across age divisions in various minor amateur and professional ice hockey leagues. The term relative age effect refers to the difference in biological and chronological age between children in the same age grouping that results from different birth dates within the same birth year. Differences in the rate of change in maturation across an age cohort are expected to accentuate any relative age effects. The present study tested the null hypothesis that the distribution of month of birth for ice hockey players in elite or representative leagues was similar to players in recreational leagues. The results are based on the month of births collected for minor amateur, university, junior, and professional leagues. The results showed that a relative age effect exists within the elite or representative levels of each league, but not within the recreational or “house” leagues.
Crashing into Court: Liability Facing the In-Line Skating Industry
Authors: Sawin RA , Gross BD
Published: April 2008

During the 1990's, in-line skating has become the fastest growing participation sport in the United States. Participation in the sport has grown more than 640% during that time. Along with the tremendous increase in participation, there has also been an increase in the number of injuries associated with the sport. With this increase in injuries comes a greater likelihood that injured participants will bring suit against the manufacturers, or the owner of the property on which they were skating. Many of the suits brought against in-line skate manufacturers will likely be based on an alleged lack of warning about the dangers associated with in-line skating and the need to wear protective gear. To avoid exposure to liability, manufacturers should provide warnings that apprise skaters of the dangers associated with in-line skating, and the measures they should take to avoid or minimize those dangers.
Modelling Thermo-mechanical Fatigue Hysteresis Loops from Isothermal Cyclic Data
Authors: Skelton RP , Webster GA , de Mestral B , Wang C-Y
Published: April 2008

A simple TMF facility is described which is capable of ‘in-phase’, ‘out of phase’ and ‘diamond’ type strain-temperature cycling. Typical TMF loops are presented for the ‘diamond’ type cycle for the nickel-base alloys IN100, Nimonic 90, IN738 and directionally solidified CM247LC-DS over the temperature range 400 °C-1000 °C. Alongside these results, isothermal cyclic stress-strain data are provided for ascending and descending strain amplitudes at discrete temperatures encompassing the strain and temperature range of the TMF tests. Testing on any individual specimen was terminated after a fixed energy consumption.

By superimposing the symmetrical isothermal loops about a common origin, the isothermal data are then used to predict the observed (asymmetrical) TMF behaviour. The method works well for materials which show history independence such as IN100. However, for some of the materials, slight modification to the procedure is required. The sensitivity of the method to the form of isothermal data is demonstrated.
Response of 60Sn-40Pb Under Thermal and Mechanical Cycling
Authors: Woodmansee MW , Neu RW
Published: April 2008

An understanding of the internal mechanisms responsible for the enhanced deformation and degradation under combined thermal and mechanical fatigue in solder alloys is sought. Inelastic deformation can accumulate simply during unconstrained thermal cycling, -55°C to 125°C, in solder alloys due to the heterogeneous microstructure, the variation in properties, primarily the coefficient of thermal expansion, among the different phase and crystallographic grains, the low flow strength, and microstructural instability. To separate the effects driven by thermal cycling versus those driven by mechanical cycling, the local deformation and microstructural changes are tracked using independent interrupted thermal cycling and isothermal fatigue experiments. The deformation is measured by tracking surface roughness using a confocal scanning laser microscope. The accumulated deformation in 60Sn-40Pb under a -55°C to 125°C thermal cycle is significant. The accumulated deformation observed in two Sn-Ag base solder alloys as well as polycrystalline Sn under the same thermal cycle is notably smaller.
Thermo-mechanical Fatigue Investigation of Single Crystal Nickel Base Superalloy SRR99
Authors: Engler-Pinto CC , Rézaï-Aria F
Published: April 2008

This paper deals with the comparison between thermal fatigue (TF) and thermomechanical fatigue (TMF) testing for SRR99 superalloy. First, a measured TF mechanical strain-temperature (εm-T) profile between 200°C and 1100°C has been reproduced on a TMF specimen to allow for an estimation of the stresses and inelastic strains which occur during TF. Thermal-fatigue-based (TFB) εm-T profiles were determined based on the measured TF profiles. These TFB cycles, together with the well-known out-of-phase profile, were employed for all of TMF tests. The comparison of the results reveals that the TF and TMF out-phase tests are more damaging in terms both of the applied stress and strain range, while the TMF out-of-phase test is more severe if the comparison is made in terms of the inelastic strain range. Finally, it is shown that the results can be rationalized quite well by plotting the fatigue lives as a function of the maximum stabilized stress (σmax).
Realization of Complex Thermal-mechanical Fatigue by a Two-specimen Testing System
Authors: Angarita L , Pitz G , Lang K-H , Löhe D
Published: April 2008

Many components are exposed to high thermal and mechanical loadings. For example, the blades of gas turbines are subjected to thermally and mechanically induced strains and stresses at varying temperatures. The former arise from inhomogeneous temperature fields, which are due to start-stop cycles, resulting in thermal fatigue. The latter arise from centrifugal forces, which arise from the rotation of the turbine, resulting in mechanical low cycle fatigue and creep during service.

The combination of thermally induced loading and mechanically induced loading can neither be investigated in a conventional (strain controlled) thermal-mechanical fatigue (TMF) test nor in a conventional (stress controlled) creep test. Also the interaction between different volume elements within a component can not be investigated in a single specimen experiment. To simulate such “complex ” thermal-mechanical fatigue loading, a twospecimen testing system was build up. At this testing system the thermal-mechanical loading of the specimens, each of them representing a distinct volume element of a component, is generated just by varying the temperature-time history of the two specimens and the coupling conditions between them. Furthermore, it is possible to superimpose an external force, e.g. representing the centrifugal force. The distribution of this force on the two specimens and the resulting deformation behaviour are the result of the interaction of the two specimens. The testing and interpretation methods as well as the results of first experiments with a 12% chromium steel and a 316 type stainless steel are presented.
Compactive Effort Applied by Hand-Operated Compactors
Authors: Filz GM , Duncan JM , Brandon TL
Published: April 2008

The rate of energy transfer between compactor and compacted soil is directly related to compaction effectiveness. In this study, a vibrating plate compactor and a rammer compactor were instrumented to determine contact forces and energy transfer rates. The compactor energy measurements and the corresponding unit weight measurements of the compacted soil were in good agreement with the results of conventional laboratory compaction tests. Consequently, it is possible to determine the amount of operating time required for these compactors to impart a particular compactive effort to a lift of soil of known volume. It was found that a Wacker BPU2440A vibrating plate compactor imparts the standard Proctor (ASTM D 698) compactive effort to one cubic meter of soil in about 18 minutes and a Wacker BS60Y rammer compactor imparts the standard Proctor compactive effort to one cubic meter of soil in about 12 1/2 minutes. Such knowledge may be useful in contractors' estimates of construction costs and, as an adjunct to unit weight measurements, in quality control and quality assurance programs.
Equation for Complete Compaction Curve of Fine-grained Soils and Its Applications
Authors: Li H , Sego DC
Published: April 2008

A complete compaction curve for fine-grained soil and its characteristics are discussed. The formulation of the relationship to model the curve is introduced. The equation is versatile in its ability to quantify the shape, size and position of compaction curves. It is capable of describing the compaction curve from the dry to very wet condition and can be used to predict a family of compaction curves for a given soil for different input of compaction energies. All parameters in the equation have specific physical definitions. Simple procedures to obtain all parameters directly from a standard compaction curve are developed and described in detail. The examples show that the proposed equation is good at representing the soil compaction curve and demonstrates excellent agreement between laboratory test data and the predicted curves. The family of curves predicted by the equation would improve the practice of the one-point method in the field.
Evaluation of Procedures Presented in TR-26 and TR-27 for Design and Construction of Earth Fills Using Soil Containing Oversize Rock Particles
Authors: Talbot JR
Published: April 2008

In the early 1960's, the Soil Conservation Service (now Natural Resources Conservation Service) established some procedures for agency use in making laboratory and field tests for control of density and water content of compacted soil containing variable amounts of rock particles. The procedures included guidance for when the rock particles would undergo some breakdown during the compaction process. This paper summarizes the procedures, providing an awareness of them to interested parties, and compares them to those established by others. Although the procedures in TR-26 and TR-27 are less than definitive in some instances, the guidance regarding evaluation of breakdown and testing methods for these soils helps to satisfy the need for evaluating these soils. Further studies using the procedures in TR-26 and TR-27 may be useful in providing more usable techniques for design and construction testing of soils containing rock that is subject to particle breakdown during the compaction process.
Proposed Compaction Specifications to Minimize Hydrocompression-Induced Settlements in Fills Supporting Residential Structures
Authors: McMahon DJ , Kropp AL
Published: April 2008

Laboratory compaction tests, field compaction tests, response-to-wetting tests nd case history data are examined in terms of percent saturation in order to help design engineers reduce hydrocompression-induced settlements in fills caused by post-construction wetting. Over 900 laboratory compaction tests (ASTM D1557) are examined to show that the maximum dry density is, on average, achieved at about 85% saturation, and that the line of optimums derived from compaction tests with lower compactive effort is roughly parallel to the 85% saturation line. Laboratory response-to-wetting tests and controlled wetting tests are used to show that the largest portion of hydrocompression-induced settlements occur below about 85% saturation. Case history data is used to illustrate that the percent saturation typically achieved during construction of residential fills is as low as 50%, and averages about 60%. Post-construction wetting is shown to commonly increase this value to as high as 95%, with an average of about 80%. This wetting can result in potentially damaging hydrocompression-induced settlement within the fills. Based upon this understanding of the importance of percent saturation, a new type of compaction specification is proposed to reduce hydrocompression-induced settlements in fills by specifying a zone of acceptable dry density/water content combinations based on achieving a minimum percent saturation. This new specification is also shown to have the advantage of providing a wider range of acceptable density and water contents (compared to increasing the minimum density or increasing the water content). The proposed specifications based on percent saturation are shown to make construction more practical than specifications based solely on density and water content. These specifications can be easily implemented by field technicians, greatly reducing the potential for damaging hydrocompression.
Variability of Initial Subgrade Modulus at Ohio SHRP Test Road
Authors: Sargand SM , Masada T , Wasniak DL
Published: April 2008

Premature deterioration of highway pavements is often attributed to the base and subgrade. In highway construction projects, construction quality control during the subgrade preparation involves nuclear moisture-density testing at specified depths at equally spaced stations along the entire project length. However, the authors' field study at the Ohio-SHRP Test Road revealed that this conventional approach was not effective for minimizing the variability of the subgrade stiffness. First of all, it was not possible to achieve a uniform moisture-density (or dry density) condition throughout the entire project. Secondly, even when the nuclear test data indicated that a fairly uniform relative compaction was established within an area, the subgrade stiffness could still vary significantly. The reasons for this were that the conventional approach could provide only very localized data on the state of the soil compaction and that the relative compaction alone could not be a reliable indicator to describe the soil stiffness. An alternative approach is to employ a rapid, nondestructive stiffness test method, such as Falling Weight Deflectometer (FWD), Dynaflect, and soil stiffness gage (SSG), in the field to monitor the stiffness of the entire thickness directly during the subgrade preparation.
Mechanical Evaluation of 70:30 Poly (L/DL-Lactide) Bone Screws After In Vitro Degradation
Authors: Disegi JA , Dwyer JW , Fairer RE
Published: April 2008

Controlled in vitro degradation testing is typically used to complement animal trials in order to understand the material, design, and fabrication factors that affect in vivo resorption rates of bioabsorbable implants. Resorbable 1.5 mm craniofacial bone screws were injection molded from amorphous 70:30 poly (L/DL-lactide) granules. The screws were vacuum dried, bulk packed, and gamma sterilized. Some of the screws were fully immersed in 7.4 pH phosphate buffer solution. The solutions were maintained at 37°C during short term exposure periods that extended to 8 weeks. Non-exposed control samples were stored in sterilized packages until the testing commenced. Stability testing was performed with rigid polyurethane foam to evaluate whether this test material was satisfactory for use in phosphate buffer solution.

Screw pull-out strength was measured in accordance with ASTM F 1691. Shear strength before and after in vitro degradation was analyzed by determining the maximum applied force required to shear the screw shaft when mounted in a specialized test fixture.
Evaluation of Adhesive and Absorption Properties for Absorbable Tissue Adhesives
Authors: Allan JM , Flagle JA , Kline JD , Dooley RL , Shalaby SW
Published: April 2008

Absorbable tissue adhesives for wound repair have gained interest in recent years compared with traditional devices for wound closure such as sutures and staples. while the demand for tissue adhesives continues to increase, in vitro methods for their evaluation remain scarce. The lack of a widely accepted method for evaluation of tissue adhesives and the availability of a family of novel absorbable tissue adhesive systems provided an incentive to develop a test method for assessing the two key parameters of candidate adhesives, namely adhesive strength and absorption. This report describes a new method for determining the absorption characteristics and adhesive strength of methoxypropyl cyanoacrylate-oxalate formulations.
Bacterial Polyesters for Biomedical Applications: In vitro and in vivo Assessments of Sterilization, Degradation Rate and Biocompatibility of Poly (β-hydroxyoctanoate) (PHO)
Authors: Marois Y , Zhang Z , Vert M , Deng X , Lenz RW , Guidoin R
Published: April 2008

Poly (β-hydroxyalkanoates) (PHAs) are bacterial polyesters with chemical and physical properties that make them suitable for medical applications. They are obtained by fermentation techniques, are biodegradable and may be metabolized into normal constituents of the body. A PHA produced by Pseudomonas oleovorans has generated a random copolymer called poly (β-hydroxyoctanoate) (PHO) having elastomeric properties and displaying lower crystallinity and less rigidity than poly (β-hydroxybutyrate) (PHB). As part of an extensive study, we compared the effects of two methods of sterilization on the physical and structural characteristics of PHO, studied the mechanism and degradation rate of PHO in vitro over a 24-month period in physiological media and finally, investigated the biocompatibility and degradation rate of PHO in vivo as a new sealant for the polyester arterial prosthesis. Results have shown that the physical and structural properties of PHO were well-preserved after ethylene oxide sterilization, whereas gamma radiation caused random chain scission and physical cross-linking. In vitro incubation studies demonstrated that the degradation rate of PHO films in water or isoosmotic PBS is a very slow hydrolytic process exceeding two years. In vivo, PHO showed good biocompatibility in terms of tissue enzymatic activity and cellular reactions. Degradation was slow and exhibited similar rate as that observed in vitro. As a sealant in a polyester arterial prosthesis, PHO contributed to the impermeabilization of the graft wall and to the development of an internal collagenous capsule with a confluent endothelium secreting prostacyclin.
The Clinical Evaluation of a Bioresorbable Minipin
Authors: Hutmacher DW , Kirsch A , Ackermann KL , Liedtke H , Hürzeler MB
Published: April 2008

The gradual shift from nonresorbable membranes to biodegradable and bioresorbable membranes represents one of the most significant trends in guided tissue regeneration (GTR) and guided bone regeneration (GBR) research. The clinical benefits of biodegradable and bioresorbable membranes that have the capacity to integrate with surrounding soft and hard tissues are a result of a more mechanically stable and therefore predictable wound healing environment. This biomechanical stability can be further enhanced by the stabilization of the physical barrier construct using additional fixation devices. Therefore, bioresorbable minipins have been desigened and fabricated. The minipins are made of poly (L-lactid-co-D, L-lactid) in a 7:3 ratio. The average molecular weight was measured at Mw 140 000, Mn 36 900, and Mw/Mn 3.7 respectively, with the intrinsic viscosity of 1.3 dl/g. The degradation and resorption kinetics as well as the biocompatibility of injection molded devices made of poly (L-lactid-co-D, L-lactid) 70/30 has already been evaluated in several in vitro and in vivo studies. Experimental as well as clinical evaluation of the bioresorbable minipin was performed. Mass loss of the minipin was initiated after 6 months and it was completely metabolized by the body after 9 to 12 months without a clinically detectable foreign body reaction.
Preventing Positive Pore Water Pressures with a Geocomposite Capillary Barrier Drain
Authors: Stormont JC , Stockton TB
Published: April 2008

The Geocomposite Capillary Barrier Drain (GCBD) has been developed and tested to prevent positive pore water pressures from developing by laterally draining water while it is still in tension. The GCBD consists of two key layers that function as long as the water pressures in the system remain negative: (l) a transport layer that laterally drains water and (2) a capillary barrier layer that prevents water from moving downward. Prototype GCBD systems have been tested in a 3 m long lateral drainage test apparatus. For most test conditions, the GCBD systems drained water under negative pressures at a rate sufficient to prevent any positive water pressures from developing in the overlying soil. Further, the drain system served as a barrier as it prevented downward flowing water from moving into the underlying soil.