bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Identification of Critical Damage Mechanisms Parameters to Predict the Behavior of Charpy Specimens on the Upper Shelf
Authors: Poussard C , Sainte Catherine C , Forget P , Marini B
Published: April 2008

The use of sub-sized Charpy-V specimens to monitor the mechanical properties of reactor pressure vessel (RPV) steels is receiving increasing attention. It is motivated by the fact that a smaller amount of material can be used to obtain the fracture properties, which can be of great economical interest when dealing with activated materials. Prior to use reduced-size specimens, investigations are still necessary to verify that the properties obtained from sub-sized specimens are comparable to those obtained from standard size specimens. Amongst the approaches that are available, the local approach to failure, which combines a description of the material microstructure (void density, distance between inclusions…) and empirical observations, is a promising way to investigate the transferability of mechanical properties. It has been successfully used to describe the macroscopic behavior of a wide range of cracked or notched specimens and components of various dimensions but restricted so far to quasi-static loading conditions.

The results discussed in the paper are focused on the upper shelf behavior of the French RPV material, equivalent to the American ASTM A508 C1.3 material. Modeling of the material is achieved using the Rousselier coupled damage constitutive equations. This model is implemented in CAST3M, a general-purpose finite element code developed by the French Atomic Energy Agency. Comparisons between the numerical results and the experimental observations are given and the computed local temperature elevations and plastic strain rates discussed to explain the behavior of the specimens.
Interface Strength Evaluation of LSI Devices Using the Weibull Stress
Authors: Minami F , Takahara W , Nakamura T
Published: April 2008

Interface fracture strength is evaluated by the Weibull stress criterion for LSI devices composed of epoxy resin and Fe-Ni alloy sheet. The difference in coefficient of thermal expansion of the epoxy resin and Fe-Ni sheet causes a stress singularity at the corner ends of the device in the cooling process during LSI packaging, which is responsible for the interface fracture of the device. It is shown that the critical Weibull stress, an integrated stress over the stressed body along the interface, at fracture initiation is almost independent of the package geometry, although both the local stresses and the singularity parameters in the LSI device significantly depend on it. Shape design to decrease the Weibull stress values would be effective to improve the LSI devices reliability.
Computational Estimation of Multiaxial Yield Surface Using Microyield Percolation Analysis
Authors: Geltmacher AB , Everett RK , Matic P , Dyka CT
Published: April 2008

Measurements of multiaxial properties of materials, such as yield surfaces, damage surfaces and fracture limit surfaces, are a time and resource intensive problem. For three-dimensional (3D) multiaxial yield of a complex microstructure, hundreds of points are required at different 3D strain states to define a full yield surface to the resolution required for constitutive model implementation. Experimental determination of the effects generated by a specific microstructure on a multiaxial yield surface is hindered by the inability to produce multiple specimens with the exact same microstructure or the inability to subject the same specimen to multiple stress or strain states without changing its response. Full nonlinear analysis of a specific microstructure for such a large set of points is also prohibitive, due to the time constraints of solving large, 3D nonlinear problems. A technique has been developed that uses high resolution 3D tomographic images and finite element simulations to track the development of microplastic connectivity for actual material microstructures in an 1100 aluminum/TiB2 particle composite. This information is then used to estimate the 3D multiaxial yield surface of the material in strain space for the imaged microstructures. The multiaxial yield surface is estimated using linear superposition and load scaling of three orthogonal displacement basis loads. Macroscopic yielding is defined as the percolation of microplastic elements across the model. Interval halving is used to solve for the scaling parameter, iterating to the value at which plastic flow percolation occurs and defining a point on the yield surface. Percolation can occur across one or more of the three directions defined by the model, but it need not occur simultaneously. A small selected set of nonlinear analyses is used as calibration for the estimated yield surface. The aim of this approach is to accelerate the process of building 3D multiaxial yield surfaces from microstructures and to gain insight into the material microstructure performance.
Image-Based Characterization and Finite Element Analysis of Porous SMA Behavior
Authors: Qidwai MA , DeGiorgi VG , Everett RK
Published: April 2008

Porous shape memory alloys (SMAs) are a relatively new group of materials that are of interest because of their potential use in the design of damping and shock mitigation systems. Benefits of the material include reduced weight, high level of energy absorption through phase transformation and possible increased energy absorption through wave scattering due to porosity. Essential to the use of these materials is an understanding of the structural and shock absorbing response of the material. Constitutive models that accurately represent these characteristics are necessary. The emphasis of this research is to develop a computational methodology that will bridge the mesostructural and macrostructural features of porous SMAs. The first step in the process involves the detailed characterization of the relevant mesostructure, i.e., information about pore shape, size, volume fraction and distribution. This representative characterization can be used to produce realistic image-based finite element models. Because the resultant models have large degrees of freedom they cannot be employed to analyze large-scale structural problems. However, simply designed boundary value problems such as the dynamic uniaxial compressive loading of a bar can be used as benchmarks for the verification of phenomenological macro-constitutive models, or models that are derived using averaging methods such as the Mori-Tanaka method or the self-consistent method. In this study, an attempt is made to analyze numerically porous SMA behavior under dynamic conditions based on the representative mesostructural features. Preliminary results are obtained for selected pore volume fractions and distinct trends in material behavior are observed.
Measurement of Crystallinity in Polymers Using Modulated Temperature Differential Scanning Calorimetry
Authors: Reading M , Price DM , Orliac H
Published: April 2008

Some time ago a proposal was made [1] for an approach to calculating the initial crystallinity for polymers using MTDSC, i.e., the crystallinity of the sample before the start of the experiment. The essence of the technique is that it attempts to estimate the contribution from the vibrational heat capacity to the total enthalpy absorbed by the sample over the temperature range where crystallization, rearrangement and melting occur. This estimate is made from the reversing signal by using interpolation to subtract any contributions to this signal from crystallisation rearrangement or melting processes. The difference between the total enthalpy and the estimate of the vibrational heat capacity contribution must then be a measure of the enthalpy of melting of any initial crystallinity. The thermodynamic basis of this approach is presented in this article together with examples of its application to both simple and complex systems. There are alternatives to this procedure and the advantages and disadvantages of the various possible approaches are discussed.
Crystallization of Polymers and the Rigid Amorphous Fraction Studied by the Temperature-Modulated Techniques TMDSC and TMDMA
Authors: Schick C , Wurm A , Merzliakov M
Published: April 2008

Quasi-isothermal temperature-modulated DSC and DMA measurements (TMDSC and TMDMA, respectively) were performed to determine heat capacity and shear modulus as a function of time during crystallization. Non-reversible and reversible phenomena in the crystallisation region of polymers can be observed. The combination of TMDSC and TMDMA yields new information about local processes at the surface of polymer crystals, like reversible melting. Until now we have found only one semicrystalline polymer showing no excess heat capacity during crystallization, namelyBisphenol-A Polycarbonate (PC). This allows study of vitrification and devitrification of the rigid amorphous fraction in PC. For other polymers the fraction of material involved in reversible melting, which is established during main crystallization, keeps constant during secondary crystallization. Simply speaking, polymer crystals are “living crystals.”.
Glass Transformation Studies of Vitreous As2Se3 by Temperature-Modulated DSC
Authors: Kasap SO , Tonchev D
Published: April 2008

We have carried out temperature-modulated differential scanning calorimetry (TMDSC) measurements on a typical chalcogenide glass system, As2Se3, which has been well-characterized previously in the literature by conventional DSC. We have studied the behavior of the total and reversing heat flows as the glass is cooled from a temperature above the glass transition temperature, that is, from a liquid-like state. The glass transition temperature Tg was operationally defined as the temperature where the reversing heat flow evinces an inflection point in changing from liquid-like to solid-like behavior. We have studied (a) the dependence of Tg on the cooling rate q under conventional DSC conditions and (b) the dependence of Tg on the modulation period P under TMDSC conditions. These two studies were carried out towards characterizing the glass relaxation kinetics. We have also examined whether Tg shows any dependence on the modulation amplitude A at a given cooling rate.
Comparison Between Modulated Differential Scanning Calorimetry (MDSC) and Dynamic Differential Scanning Calorimetry (DDSC)
Authors: Fuller LC , Judovits L
Published: April 2008

Both modulated differential scanning calorimetry (MDSC) and dynamic differential scanning calorimetry (DDSC) are registered tradenames for instrumental techniques which are part of the temperature-modulated differential scanning calorimetry (TMDSC) family. Both oscillate their input ramps differently in that the MDSC uses a sine wave while DDSC generates a sawtooth wave. Although we have found similarities between both techniques we do note some differences. These differences primarily occur in the melting reversing signal for the same conditions and as one changes period and amplitude. These differences may be ascribed to the different time response as noted between a heat flux and power compensation DSC.
Obtaining Kinetic Parameters Using Modulated Temperature
Authors: Blaine RL
Published: April 2008

Flynn and Dickens demonstrated in 1976 that continuous kinetic information may be derived from thermogravimetry profiles using a periodic temperature square wave signal. Blaine extended this approach to the sine wave. Extension of the sine wave approach to differential scanning calorimetry, however, requires consideration of the effects of the heat capacity heat flow, not present in thermogravimetry. The heat capacity term is always present and is theoretically 90° out of phase with the kinetic heat flow. Sine wave signals of the same period, however, add together to produce a sine wave of intermediate phase. To understand the effects of these mixed signals, a partial series of models is proposed for modeling pure crystalline and polymer melts on the way to a more complete understanding and measurement of kinetic parameters.
Analysis of Curing Using Simultaneous Dynamic Mechanical and Dielectric Measurements
Authors: Suwardie JH
Published: April 2008

Previously, curing reaction of a thermosetting system, with one of the components being a volatile material, was studied using Simultaneous Thermal Analyzer (STA). The actual heat of curing can be determined by subtracting the heat of volatilization from the heat of the curing process.

A new study of a similar thermosetting system using simultaneous dynamic mechanical and dielectric measurements will compare the onset and completion of the curing reaction between the two measurements. In addition, the new study will also compare between rheological properties such as dynamic loss modulus, G”, and dynamic viscosity, ETA*, and dielectric property such as dynamic loss parameter, ε”.
Characterization of Organic Surfactants and Dispersants by Frequency-Dependent Dielectric Thermal Analysis and Electrochemistry
Authors: Lvovich V , Cahoon J , Riga A
Published: April 2008

Multi frequency electrochemical impedance spectroscopy (EIS), dielectric thermal analysis (DETA), and cyclic voltammetry (CV) were employed as a basis for evaluating organic detergents and dispersants in a hydrocarbon based lubricating oil. These dielectric and electrochemical techniques appear to be a powerful tool capable of detection and monitoring of oil additives, surfactants and dispersants, and investigation of general mechanisms of oil degradation in an operating engine. These techniques were applied to the identification and detection of various types of chemical additives.

Measurement of electrochemical impedance spectroscopy over a sufficiently wide range of frequencies, electrochemical potentials, and temperatures yielded detailed qualitative and quantitative information. EIS ceded the dynamics of charge transport and reduction or oxidation reactions of ionic species and individual chemical components across the bulk lubricant and at the electrode-lubricant interface. Highly selective studies of spatial distribution of charge-transfer processes taking place in bulk solution and at the interface were achieved. A combination of EIS and CV based electrochemical methods provided a complete chemical analysis of lubricant conditions. These included detection, quantification and differentiation of adsorption and lubricant film formation on an electrode surface, and investigating kinetics of reduction or oxidation reactions of major oil components (detergents, dispersants, etc.). DETA polarization plots clearly ranked the surface-active detergents and the less active dispersants. Frequency dependent EIS, and DETA, as well as CV can be easily used for characterizing chemical additives for engine oils.
Development of Bismaleimide/Cyanate Ester Copolymers
Authors: Sisk BC , Chuang K , Pan W-P
Published: April 2008

Since the beginning of the space age, the goal of materials development in the aerospace industry has been to replace metal alloys with much lighter polymer resins, while maintaining the strength over a wide temperature range characteristic of metals. Polymers such as polyimides and epoxies have been used to satisfy many needs, but strength, temperature resistance, and ease of processing are difficult to incorporate into a single polymer.

Because of this gap, bismaleimides and cyanate esters, and possibly combinations of the two, are seen as having potential in applications where ease of processing characteristic of epoxies is desired, but for which temperature resilience better than that of epoxies is desired. In this paper, bismaleimide and cyanate ester compositions based on commercially available monomers are created and evaluated to determine what monomers are favorable.
The Influence of Inorganic Cations on Glyphosate Activity-Review and Perspectives
Authors: de Ruiter H , Downer RA , Uffing AJM , Ebert TA , Pikaar PJJ , Hall FR
Published: April 2008

The influence of calcium, iron, magnesium, other cations, and mixtures of cations on the activity of glyphosate and the interaction with pH is reviewed, discussed, and demonstrated with laboratory data. The strategy to overcome antagonistic effects of the cations via use of adjuvants is discussed and illustrated with data.

The influence of calcium concentration on glyphosate efficacy was investigated on black nightshade (Solanum nigrum L.) by monitoring glyphosate activity via fluorescence technology and inhibition of growth. Giant foxtail (Setaria faberi Herrm) was also used for biological evaluation. Calcium concentrations equal to the glyphosate concentrations were most antagonistic; higher concentrations of calcium were less antagonistic.

Different adjuvants were tested to overcome the antagonistic effect of calcium. Results are discussed in relation to the physical chemical properties of the adjuvants. With a more appropriate scientific base, remedial measures may protect field performance of glyphosate and reduce farm costs.
Dynamic Surface Tension of Selected Nonionic Agricultural Surfactants at Surface Ages Relevant to Component Processes in Spray Application
Authors: Cooper JA , Fox RD , Dexter RD , Bukovac MJ
Published: April 2008

Dynamic surface tension data for selected nonionic surfactants, pesticides and other miscellaneous liquids are presented. Surface tension was measured using the oscillating jet technique at surface ages ranging from 0.5 to 7 ms. These early measurements are particularly important since new surfaces are being rapidly created, and they represent the time frame of spray droplet formation and impaction processes.
Recent Trends in Pesticide Formulation in Japan
Authors: Tsuji K
Published: April 2008

Recently in the pesticide industry in Japan, it has become considerably more desirable to develop products that are safer both for workers and the environment. Moreover, number of farm workers of advanced age and women have gradually increased. Therefore, it is also desirable to develop more efficient and more labor-saving formulations and application technologies in order to make agricultural work lighter. for these purposes, various promising formulations have been developed such as flowable formulations for direct application, water dispersible granules, microcapsules, jumbo herbicides, 1 kg granules, water surface spreading formulations, seedling box treatment, fertilizers containing pesticides, and physical controlling methods. These formulations are reviewed, and their advantages and trends are discussed.
Strategies for Agricultural Formulations: A Statistical Design Approach
Authors: Ashrawi SS , Elsik CM , Stridde HM , Smith GA
Published: April 2008

The traditional approach used by formulators of agricultural and pesticide formulations relies heavily on experience, and has been quite valuable in generating acceptable formulations that may or may not be at a global optimum. However, it can be time consuming, and it generally lacks the ability to provide a global view of the contributions of the different components to the performance of the whole. Additionally, the approach does not permit the use of the collected information to investigate or predict the behavior of formulations within the composition space without carrying out further experimentation.

In the statistical design approach, one begins with the definition of objectives and constraints, then sets up the experiment with the appropriate response factor measurements. After data collection, a best-fit mathematical model is generated to describe the results and can be displayed graphically in various ways for various purposes. Among other things, model analysis typically reveals how each component contributes to the properties being measured. The model is used to locate optimum performance regions that balance the properties of the different components and satisfy any other constraints that are imposed. Scenario analysis can then be used to predict the performance as component levels are changed. In this work, we will discuss the conceptual framework of the statistical design approach, and exemplify its usefulness with an emulsifiable concentrate formulation.
Formulating Options for Aerosol Insecticides
Authors: Stocky L , Cantalupi D , Lucas J , Kowalik R
Published: April 2008

With ever tightening VOC regulations for consumer insecticides, formulators are being pushed to use more water and/or more LVP (low vapor pressure) fluids that are not reportable as VOCs in their products. The particular choice of LVP fluid and its concentration may also affect the biological performance of insecticide formulations. To demonstrate these effects, a variety of hydrocarbon LVP carrier fluids were combined with the insecticides S-bioallethrin and deltamethrin in both solvent and water-based insecticide formulations. Experiments were conducted to evaluate knockdown and residual activity against German cockroaches.

Data indicated that use of hydrocarbon LVP carrier fluids with higher levels of normal paraffins resulted in faster knockdown of the cockroaches under a variety of test conditions. Higher concentrations of hydrocarbon LVP carrier fluids in water-based formulations also enhanced their knockdown performance. The residual activities of water-based formulations, inferred from the lengths of time the formulations remained efficacious after they were applied to ceramic tile and painted plywood, were adversely affected by higher concentrations of normal paraffins or LVP hydrocarbons.

The results suggest that normal paraffins and higher concentrations of LVP hydrocarbon fluids may increase the penetration of the formulations into insect and household surfaces. With the insects this leads to faster intake of insecticide. With the household surfaces this reduces insecticide availability. One can use this information to select active ingredients, LVP fluids, and their concentrations, along with other formulants, to optimize formulation performance for specific application requirements and meet VOC regulations. Of the LVP hydrocarbon fluids tested, a mixed aliphatic fluid with a moderate concentration (20% w/w) of normal paraffins appeared to offer the best balance of properties for use in crawling insect killers.
Design and Performance of Crop Oil Concentrate Emulsifiers
Authors: Stern AJ , Hazen JL
Published: April 2008

Experimental design was used to study the interactions of selected low cost emulsifier components and thus identify a crop oil concentrate emulsifier blend having optimum performance and low cost. For this study, the mixture variables included: nonylphenol + 6 EO, nonylphenol +10 EO, tall oil fatty aid (TOFA), and paraffinic petroleum oil. Water, although not an independent variable, was included as a coupling agent. The responses measured were number of phases, emulsion stability in soft water, emulsion stability in hard water, and emulsion stability in 2.5% ammonium sulfate solution, all at ambient temperature.

Using experimental design software, it is possible to visualize the interrelationships of the four components for each test condition, making it possible to predict the performance of any composition within the design space. After analyzing the response surface contour maps of the four-dimensional design space, we find that it is possible to formulate a crop oil concentrate that is single phase, offers very good emulsion performance in soft and hard water, and performs moderately well when tank mixed with ammonium sulfate solution. Coupling the performance data with a simple cost calculation, the formulator can select a composition that maximizes performance while at the same time minimizing cost.
Novel Polymeric Dispersants for Water Dispersible Granules
Authors: Herbert R
Published: April 2008

High concentration extruded water dispersible granules (WG) can be processed using styrene acrylic and modified styrene acrylic dispersants at formulation concentrations usually found in wettable powder formulations: 3–7 % (w/w). These dispersants have found application with a wide range of active ingredients at concentrations ranging from 75% to >90% (w/w) of technical grade active ingredient. Extruded granule formulations containing these dispersants demonstrate excellent granule disintegration and physical suspension upon dilution both initially and upon extended storage at elevated temperatures. Experimental design techniques have also been identified which dramatically shorten the product development time frame.
Alkoxylated Glyceride Emulsifiers in Agricultural Applications
Authors: Anderson TH , Mainx H-G
Published: April 2008

Ethoxylated glycerides have long been known as effective and safe nonionic emulsifiers. They have been used in applications as diverse as food processing, textile applications, fiber finishes, leather processing, metal working, cosmetics, Pharmaceuticals, and of course, as agricultural other ingredients. In addition to their excellent emulsifying properties for oils, fats and solvents, ethoxylated triglycerides are widely recognized for their favorable human and ecotoxicological profiles. They are a preferred choice whenever sensitive environments must be protected and in cosmetic applications where they are known to mitigate the irritation potential of more aggressive surfactants.

Current United States Environmental Protection Agency regulations restrict the choices available to agricultural formulators to a single triglyceride, castor oil, with between 5 and 54 moles of ethoxylation on growing crops, raw agricultural commodities and animals. No other ethoxylated or alkoxylated glycerides are specifically approved or located on the “List of 2500”, although some companies may have letters in their files allowing specific usage. Unfortunately the agricultural formulator choosing a castor-based surfactant is exposed to cyclical price swings. This would be lessened greatly if alternatives based on soybean or canola oil were found to be satisfactory.

The present work examines the emulsification properties of several alkoxylated glycerides derived from canola oil. Comparisons are drawn with examples of castor oil and castor wax ethoxylates. The systems studied included a selection of solvent-based Emulsifiable Concentrate (EC) formulations as well as a commonly used methyl ester.
A New Adjuvant Blend for Glyphosate Herbicides
Authors: Burow RF , Penner D , Roggenbuck FC , Wallick DE
Published: April 2008

With the advent of glyphosate-resistant crop seed, glyphosate has become the herbicide of choice for controlling weeds in a wide range of field crops. Many manufacturers of agricultural chemicals are adding glyphosate herbicides to their herbicide product lines to serve this market need. An adjuvant blend has been developed specifically to enhance the performance of these glyphosate products.

Organosilicone (OS) surfactants are effective adjuvants to boost the performance of a number of foliar-applied herbicides. They are effective adjuvants when used with glyphosate herbicides against a number of weed species, but are weak or antagonistic on certain weeds, particularly lambsquarters and certain perennial grasses. Alkyl diphenyl oxide disulfonate (ADODS) surfactants, on the other hand, are effective on many of the weeds that are not enhanced by the organosilicone surfactants. It has been found that combinations of the organosilicone and ADODS surfactants are effective across a broad range of weed species.

In greenhouse studies using a low rate of glyphosate, the use of a combination of a mixture of OS and ADODS surfactants provided control of a broad range of weed species and provided rainfastness as well.
An Analysis of the Sliding Properties of Worker's Footwear and Clothing on Roof Surfaces
Authors: Nagata H
Published: April 2008

To obtain information needed to prevent falls from the pitched roofs of wooden houses, the slide characteristics of roofing materials were evaluated using a clothed dummy and various footwear on an experimental, adjustable pitched roof. To determine sliding properties of worker's clothing and footwear, five roofing materials, viz., sheet metal, ceramic tile, slate shingle, bitumen felt, and plywood were tested. Slide characteristics of three types of footwear: sneakers, safety shoes and Japanese construction worker's footwear were tested. The most slippery roofing was sheet metal in wet conditions. Sheet metal and plywood roofing surfaces showed remarkably large reductions in the sliding-friction coefficient when they became wet. Thus, should it rain while working on a roof, the unexpected reduction of friction can trigger roof-fall accidents, especially on sheet-metal and plywood surfaces. The frictional properties of clothing on sheet metal and plywood in dry conditions are much lower than that of footwear. That implies that there is a great possibility of sliding down even a gently-pitched roof in dry conditions if a worker's body weight cannot be supported at the shoe soles, typically because of a loss of balance.
Examination of Sticktion in Wet-Walkway Slip-Resistance Testing
Authors: Smith RH
Published: April 2008

Under certain circumstances, the measured slip resistance of wet walkways has been found to be greater than readings obtained from the same surfaces when dry, a seemingly anomalous result. This phenomenon, sometimes termed sticktion, is most often seen when using a leather test foot. Sticktion has been ascribed to surface-tension adhesion. Surface-tension adhesion is examined with a focus on its production in wet-walkway slip-resistance testing. Past research has indicated that surface hardness is a determinant of frictional resistance. A hypothesis is proposed that, when using leather test feet on wet surfaces, a large portion of the increase in readings over dry values is attributable to water-absorption softening of the leather, and constitutes real slip resistance. Reinterpretation of wet-leather test results as an indication of the presence of sticktion is suggested. Water must physicochemically ‘wet’ both the test foot and test surface for surface-tension adhesion to develop. Tests reveal that such wetting takes place on a number of test-foot and shoe-sole materials of interest. However, for surface-tension adhesion to be of significant magnitude in tribometry, a number of critical conditions must be present. The likelihood of significant surface-tension adhesion occurring when measuring slip resistance is assessed.
Observations and Analysis of Relative Slip in Fretting Fatigue
Authors: Nishida T , Kondoh K , Xu J-Q , Mutoh Y
Published: April 2008

In-situ observation of the relative slip along the contact surface was conducted on a servo-hydraulic fatigue machine with scanning electron microscope. It was found that the relative slip observed by this method was much smaller than that obtained by a conventional small extensometer. It was also found that the relative slip depended on the rigidity of the contact pad. The higher the rigidity of the pad was, the larger the relative slip became. Numerical analysis with the use of the finite element method (FEM) program ABAQUS was also carried out. The relative slip estimated by the FEM agreed well with the observed one. Therefore, it was proved that the in-situ observation method introduced in this study was effective enough for measuring relative slip at the contact edge.
Observations and Analysis of Fretting Fatigue Crack Initiation and Propagation
Authors: Mutoh Y , Xu J-Q , Kondoh K
Published: April 2008

Many factors, such as the amplitude of the cyclic load, the relative rigidity of components and the frictional condition, play important roles in the fretting fatigue process. This study has focused on the local singular stress field at the fatigue crack tip or at the contact edge where the initial crack occurs, based on the numerical analysis results with the use of finite element method (FEM) program ABAQUS. It is proposed that all the effect of test conditions can be contained by the local stress field, which would dominate the fatigue crack initiation and propagation. By comparing with the experimental results, it was found that the initial fatigue crack should occur at the point of maximum shear stress range near the contact edge, and would propagate in the direction of maximum tangential stress range. An analytical simulation of fretting fatigue crack propagation has been carried out. It was found that a fatigue crack was always under the mixed mode conditions, the fracture path could be estimated by the maximum tangential stress theory (Δσθmax), and the propagation curve could be characterized by the stress intensity factor range in this direction ( ΔKσθmax ).
Application of Multiaxial Fatigue Parameters to Fretting Contacts with High Stress Gradients
Authors: Nowell D , Araújo JA
Published: April 2008

Many practical fretting contacts give rise to high stress concentrations or singularities that cause high stress gradients. Straightforward application of initiation-based life prediction methods can result in conservative life predictions as the high stress levels are not sustained over a critical volume. This paper uses experimental results that show a size effect with the Hertzian contact geometry to investigate the application of Smith, Watson, Topper, and Fatemi-Socie multiaxial initiation parameters to fretting fatigue. It is concluded that, for cases where a high stress gradient exists, an averaging procedure is required in order to produce an acceptable prediction of initiation life. This approach is compared to an alternative procedure based on short crack arrest and the similarities and differences are discussed.
Improvement of Fretting Fatigue Strength by Using Stress-Release Slits
Authors: Hattori T , Nakamura M , Watanabe T
Published: April 2008

A new estimation method for fatigue crack initiation criteria using plain fatigue limit, threshold stress intensity factor range, and specific depth is proposed. Using this, new design method for improving fretting fatigue strength have been developed by using stress-release slits on the pads near the contact edges. This design has analyzed on the basis of stress singularity parameters at the contact edges, and the analysis results were used to optimize the slit shapes, such as slit depth and slit position.This optimization takes into account the fretting fatigue crack initiation strength at the contact edge and the fatigue strength at the slit root. We confirmed that the fretting fatigue crack initiation strength of the optimized design is about twice that of a conventional (i.e., slitless) design.
High-Frequency Fretting Fatigue Experiments
Authors: Matlik JF , Farris TN
Published: April 2008

The fretting problem is of particular interest to the damage tolerant design of turbine blades in today's gas turbine engines. The exotic environment, high-frequency, and variable amplitude load history associated with the dovetail blade/disk connection create a critical location for fretting induced crack nucleation. With little work having been done on investigating fretting contact behavior at high-frequencies and variable amplitude load spectra, sufficient impetus has been generated to better characterize these two currently ambiguous fretting factors. The threat of early crack nucleation and propagation due to these fretting conditions has led to several major research efforts aimed at explicating the high cycle fatigue (HCF) and low cycle fatigue (LCF) interaction and behavior of advanced materials used in modern aircraft turbomachinery. As a part of this effort, a well-characterized experimental setup has been constructed to aid the observation and analysis of the aforementioned frequency and loading factors in fretting. A detailed description of the designed high-frequency fretting rig is presented. Significant vibration and bending results observed during high frequency operation suggest further design modification for improved specimen and pad alignment. Preliminary experimental observations illustrate crack nucleation and failure in specimens subjected to operational frequencies between 100 and 350 Hz. A stress invariant equivalent stress life model is employed for comparison of predicted and observed experimental crack nucleations. The paper concludes with suggested future work aimed at experimentally explicating the frequency and variable amplitude factor effects in fretting fatigue.
An Investigation of Fretting Fatigue Crack Nucleation Life of Ti-6Al-4V under Flat-on-Flat Contact
Authors: Hutson AL , Ashbaugh NE , Nicholas T
Published: April 2008

A study was conducted to investigate fretting fatigue damage of Ti-6Al-4V against Ti-6Al-4V under flat-on-flat contact with blending radii at room temperature. Both the location of and the time required to nucleate fretting fatigue cracks were investigated for two static clamping stress values representative of those estimated for turbine engine blade attachments. Fatigue limit stresses for a 107 cycle fatigue life were evaluated for the selected conditions. Fretting fatigue nucleated cracks were identified in situ using shear wave ultrasonic NDI. The effect of fretting fatigue on uniaxial fatigue life was quantified by interrupting fretting fatigue tests at 10% of life, and conducting uniaxial residual fatigue life tests. Metallography, scanning electron microscopy and spectral analysis were used to characterize the fretting damage.
Evaluating Fatigue Life of Compressor Dovetails by Using Stress Singularity Parameters at the Contact Edge
Authors: Yoshimura T , Machida T , Hattori T
Published: April 2008

Fretting fatigue life of compressor dovetail for gas turbine was investigated using stress singularity theory. It is found that the crack initiation of fretting fatigue between blade dovetail and wheel dovetail occurs at the contact edge of blade dovetail. The parameters of stress singularity obtained from maximum principal stress distribution are capable to evaluate the fretting fatigue strength with the cyclic load having a constant angle against the contact surface under a variable contact pressure. The ratio of between the intensity range of stress singularity and the critical intensity range of stress singularity, Δ Hl/Δ Hc, is an effective parameter to predict the fretting fatigue life of compressor dovetail.
Evaluation of Aggregate Contributions to Rutting Susceptibility of Asphalt Mixtures
Authors: Mohammad LN , Huang B , Tan ZZ
Published: April 2008

This paper presents the research results of a laboratory study that evaluated the influence of mixture types and aggregate types to the rut-susceptibility of asphalt mixtures. Three types of mixtures were considered. These three mixtures were: 1) stone mastic asphalt (SMA), 2) coarse matrix high binder (CMHB) and, 3) dense-graded wearing course mixture. For the SMA mixtures, three types of aggregates, siliceous limestone, sandstone and novaculite were evaluated. For the other two mix types, crushed limestone was used. An SB polymer modified asphalt cement meeting Louisiana specification for PG 70-22M was used for all the mixtures. A total of five mixtures were evaluated in the laboratory through a series of fundamental engineering property tests.

A comprehensive comparison suggested that SMA mixture with sandstone exhibited best performance in rut-resistance among all five mixes. For mixtures containing limestone aggregate, dense-graded mixture and the coarse matrix high binder had higher rut-resistant indices than the SMA mixtures. For the SMA mixtures with different aggregate types, mixture with sandstone exhibited the best rut-resistant indices while the one with novaculite showed better indices than the one with limestone.
Evaluation of the Sensitivity of Repeated Simple Shear Test at Constant Height Based on Laboratory Rutting Characteristics of WesTrack Fine Mixes
Authors: Natu G , Guada I , Tayebali AA
Published: April 2008

This study evaluated sensitivity of the repeated simple shear test at constant height (RSST-CH) based on laboratory rutting (permanent deformation) characteristics of fine mixes used in WesTrack full scale testing in Nevada.

Mix variables in this study included three aggregate gradations, three asphalt contents, and three air void contents. For each mix, three replicate specimens were tested for a total of eighty-one specimens. The RSST-CH tests were performed according to AASHTO TP7 Procedure F. These tests were conducted at 50°C temperature for 10000 cycles or 5% plastic shear strain, whichever occurred first. The loading cycle consisted of 69-kPa haversine load with 0.1 second loading time followed by 0.6-second rest period.

The test results — permanent shear strain, and dynamic shear modulus evaluated using the RSST-CH test — were found to be sensitive to the mix parameters: aggregate gradation, asphalt content, and air void content. A statistical analysis of test results confirmed the above finding that the differences between permanent shear strain and dynamic shear modulus for various mixes were due to different gradation, asphalt content, and air void content and not due to RSST-CH test variability.
Effects of Fine Aggregate Angularity on VMA and Rutting of Kansas HMA Mixtures
Authors: Cross SA , Purcell EM
Published: April 2008

With the recent introduction of Superpave, mix designers in Kansas have had difficulty meeting the voids in the mineral aggregate (VMA) requirements. To meet VMA, designers have been importing chat, a flaky fine aggregate of nearly pure chert produced as a by-product from lead and zinc mining, to boost VMA.

The objectives of this research were to evaluate the effect of fine aggregate angularity (FAA) on VMA and rutting. Two 12.5-mm Superpave gradations, one coarse and one fine, were developed using 100% crushed limestone. To change the FAA of the mix, the fine aggregate was replaced with natural sand and chat, a byproduct from lead and zinc mining. The resultant VMA and FAA of each blend was compared and samples were tested for rutting.

The results indicate that increased FAA results in greater VMA, after exceeding a minimum, and decreased rutting. Chat was shown to be effective at increasing VMA but reduced stability. Meeting Superpave mix requirements did not insure a stable mix.
Fine Aggregate Angularity: Conventional and Unconventional Approach
Authors: Chowdhury A , Button JW
Published: April 2008

Superpave adopted ASTM Test Methods for Uncompacted Void Content of Fine Aggregate (C1252 Method A) to determine fine aggregate angularity (FAA). This is an indirect method for estimating fine aggregate angularity and texture. The FAA test is based on the assumption that more fractured faces will result in higher void content in the loosely compacted sample; however, this is not always true. The paving and aggregate industries have found that cubical shaped particles, even with 100 percent fractured faces, may not meet the FAA requirement for high-volume traffic. State agencies are concerned that local materials previously considered acceptable and which have provided good field performance, now cannot meet the Superpave requirements.

A study was undertaken to evaluate the ability of current Superpave FAA method to measure fine aggregate angularity, to determine if it can distinguish between good performing and poor performing aggregates, and compare FAA test results with other measures of particle angularity. Fine aggregates from different regions of USA were collected along with their performance history. Those aggregates were tested with ASTM C 1252, Method A, ASTM Test Method for Direct Shear Test of Soils Under Consolidated Drained Conditions (D 3080), Compacted Aggregate Resistance (CAR) test, visual inspection, and surface area analysis. SHRP-LTPP database was also used to find any correlation between FAA and field rutting.
Differential GPS Update
Authors: Lange AF , Buick R
Published: April 2008

In May 2000 the U. S. Department of Defense eliminated the purposeful degradation of accuracy of the Global Positioning System (GPS) called Selective Availability (SA). This action resulted in the accuracy of GPS improving from around 50 m to better than 10 m. With this improvement in accuracy civilians are enjoying very good performance from low-cost handheld GPS receivers, although GPS is still not accurate enough for many professional uses. The limitation of accuracy of GPS is caused by a number of system errors. Some system-wide correctable errors of GPS are reduced through the use of differential GPS techniques. The elimination of SA will allow the optimization of Wide Area DGPS networks because of the change in characteristics of the remaining error sources.
Modeling the Spatial and Temporal Distribution of Soil Moisture at Watershed Scales Using Remote Sensing and GIS
Authors: Starks PJ , Ross JD , Heathman GC
Published: April 2008

Soil water content (2v) is of fundamental importance in meteorology, agriculture, and hydrology, among other scientific disciplines. In hydrology, 2v partitions rainfall into runoff and infiltration, thus impacting surface and groundwater recharge, flood forecasting, and flow routing modeling. Measurement of 2v at a point is straightforward, but point measurements are inadequate for watershed hydrology due to variability of soil properties, land cover, and meteorological inputs over space. Passive microwave remote sensing systems have been successfully used to provide regional estimates of surface 2v (0–5 cm surface layer) at the spatial resolution of the sensor. To extend these data to other depths and scales, a two-layer soil water budget model was used to combine remotely sensed estimates of 2v and spatial information on land cover, soil type and meteorological inputs to predict root zone 2v over a 611 km2 watershed. A GIS was used to pre-process and geo-register spatial data sets for input into the soil water budget model, and analyze the results.
Spatial Scale Analysis in Geophysics — Integrating Surface and Borehole Geophysics in Groundwater Studies
Authors: Paillet FL
Published: April 2008

Integration of geophysical data obtained at various scales can bridge the gap between localized data from boreholes and site-wide data from regional survey profiles. Specific approaches to such analysis include: 1) comparing geophysical measurements in boreholes with the same measurement made from the surface; 2) regressing geophysical data obtained in boreholes with water-sample data from screened intervals; 3) using multiple, physically independent measurements in boreholes to develop multivariate response models for surface geophysical surveys; 4) defining subsurface cell geometry for most effective survey inversion methods; and 5) making geophysical measurements in boreholes to serve as independent verification of geophysical interpretations. Integrated analysis of surface electromagnetic surveys and borehole geophysical logs at a study site in south Florida indicates that salinity of water in the surficial aquifers is controlled by a simple wedge of seawater intrusion along the coast and by a complex pattern of upward brine seepage from deeper aquifers throughout the study area. This interpretation was verified by drilling three additional test boreholes in carefully selected locations.
Application of GPS for Expansion of the Vertical Datum in California
Authors: Ikehara ME
Published: April 2008

Global Positioning System (GPS) surveying is helping to expand the sparse coverage of geodetic stations referenced to the North American Vertical Datum of 1988 (NAVD 88) in California. Accurate and precise vertical control is an important aspect of solutions to various hydrologic problems such as floodplain mapping and aqueduct gradient determinations. The National Geodetic Survey (NGS) has developed guidelines for GPS procedures that will result in local accuracies for ellipsoid heights of 2 cm at 95% confidence. The NAVD 88 datum in California is being expanded in segments of GPS networks that are observed by multiple-agency partnerships. Networks between San Francisco and Sacramento have been completed, and expansion in the Central Valley is being pursued. Determination and maintenance of accurate vertical heights in the Central Valley is particularly difficult because of large historical and unknown current effects of land subsidence resulting from massive quantities of groundwater withdrawal for several decades prior to the 1980's. Other NGS goals are to establish more geodetic and tidal datum connections, and to provide real-time water level information to harbor pilots for safer and more efficient vessel loading and navigation.