bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Two Jet Engine Lubricating Oils and a Hydraulic Fluid: Their Pyrolytic Breakdown Products and Their Implication on Aircraft Air Quality
Authors: van Netten C
Published: April 2008

Aircraft air quality incidents are often traced to jet engine oil and/or hydraulic fluid leaking into bleed air used to ventilate the cabin. These contaminants can be subjected to temperatures in excess of 500°C. Exposed flight crew members have reported symptoms including dizziness, nausea, disorientation, blurred vision, and tingling in legs and arms.

Pyrolysis experiments of two jet engine oils and one hydraulic fluid at 525°C showed the engine oils to be important sources of carbon monoxide (CO). The same 5 out of the 10 possible tri-cresyl phosphate (TCP) isomers that were found in the bulk oils were found in the atmosphere at ambient temperatures after pyrolysis and were likely associated with smoke particles, illustrating an important potential route of exposure. Tri-orthocresyl phosphate (TOCP) was not found in the oils or fluid tested. The neurotoxin trimethyl propane phosphate (TMPP) was not found.

It was suggested that different symptoms could be expected depending on which fluid was pyrolized.
Proposed ASHRAE Cabin Air Quality Standard (161P)
Authors: Holcomb LC
Published: April 2008

This preliminary material with regard to draft standard for Air Quality on Commercial Aircraft is presented here in hopes that it will aid in defining research needs for the future.

Aircraft are different from buildings. Commercial aircraft fly through an environment that is hostile to human life. Thus, safety features are of greatest importance. In a real-world setting, there will be trade-offs in comfort, safety and health.

The purpose of this standard is to define requirements for air quality in air carrier aircraft and specify methods for measurement and testing in order to establish compliance with the standard.

The scope of the standard covers: • Commercial aircraft carrying 19 or more passengers • Considers chemical, physical and biological contaminants as well as, but not limited to moisture, temperature and pressure • Will not ensure acceptable aircraft cabin air quality for everyone.

The committee has developed a draft standard and an informative appendix. Information on ventilation rates, contaminant standards, relative humidity, temperature, pressure and filtration will be presented.
Rationale for Ventilation Rate Requirements in ASHRAE Standard 62-1999 and in Potential Revisions to the Standard
Authors: Persily AK
Published: April 2008

ASHRAE Standard 62-1999, Ventilation for Acceptable Indoor Air Quality, contains requirements for minimum ventilation rates in buildings. As this standard is being revised, proposals are being discussed to modify these ventilation rates. In reviewing the current rates and proposals to revise them, it is important to understand the scientific research behind these rates and the engineering experience that supports them. Among the relevant research are numerous studies conducted in both chambers and in occupied buildings in which body odor perception was measured as a function of ventilation rate. These studies have shown consistently that 80% of adapted occupants are satisfied in terms of their perception of human body odor at ventilation rates of 2.5 L/s (5 cfm) per person. In addition, about 80% of unadapted visitors are satisfied at 7.5 L/s (15 cfin) per person. Of course, there are other indoor pollutants that impact perception and health besides the bioeffluents associated with body odor. In establishing ventilation rate requirements, a number of key decisions must be made including whether the requirements are established based on adapted occupants or visitors and how non-occupant related pollutants are factored into the required rates.
Prediction of the Distribution of Indoor Air Quality and Comfort in Aircraft Cabins Using Computational Fluid Dynamics (CFD)
Authors: Baker AJ , Taylor MB , Winowich NS , Heller MR
Published: April 2008

Computational fluid dynamics (CFD) analysis has been utilized by the aircraft industry to characterize the distribution of ventilation air in conventionally-configured commercial aircraft passenger cabins. The recent tendency is to increase recirculated air proportion, for operating efficiency. There are also emergent many new cabin interior designs with appurtenances. A principle consideration is assessment of cabin air quality, and comfort, for the aircraft Environmental Control System (ECS) operating in cruise mode at flight altitude, where the efficiency issue is of primary impact. This paper addresses the application potential of CFD to assist in determination, perhaps optimization, of a quality cabin interior environment for broad ranging cabin configuration variations.
Probabilistic Aspects of Life Prediction
Authors: Johnson WS , Hillberry BM
Published: April 2008

Description

Seventeen peer-reviewed papers give you the latest information on probabilistic fatigue life prediction methodology, including how to accurately determine the useful life or inspection intervals for complex structures

Sections cover:

Probabilistic Modeling—life prediction, computational simulations, and service loading spectra

Material Variability—quality, performance, reliability, and uncertainties of various materials, including aluminum, ceramics, and steel, as they relate to fracture toughness and fatigue crack growth

Applications—realistic approaches to and applications of probabilistic fatigue life predictions

STP 1450 is a valuable resource for structural designers, fatigue and fracture engineers, and materials engineers who need to
RAH-66 Comanche Building Block Structural Qualification Program
Authors: Dobyns A , Barr B , Adelmann J
Published: April 2008

The paper discusses the RAH-66 Comanche airframe building block structural qualification program. The components of the building block program included: material selection and qualification tests (lamina properties); coupon level tests (static and fatigue laminate properties, including open hole and filled hole strength, bearing, and sandwich compression after impact strength), and element, subcomponent, and full-scale tests. Element tests included bolted and bonded joint strength tests, beaded shear panel tests, sandwich shear panel tests, crippling tests and bearing-bypass bolted joint tests. Subcomponent testing included fuselage section crush tests, hydraulic ram testing of fuel tanks, and numerous design specific joint tests. The building block program culminated in the full-scale static test of the airframe structure.

The interaction of the building block program testing with the Comanche detail design is described including specific examples where results from compression after impact, tub crush, and hydraulic ram testing caused changes in the structural configuration of the aircraft. This paper discusses only the Sikorsky Aircraft portion of the RAH-66 building block program. Boeing-Philadelphia also performed a related program to substantiate the design of their portion of the aircraft.
Influence of Ply Waviness on Fatigue Life of Tapered Composite Flexbeam Laminates
Authors: Murri GB
Published: April 2008

Nonlinear tapered flexbeam laminates, with significant ply waviness, were cut from a full-size composite rotor hub flexbeam. The specimens were tested under combined axial tension and cyclic bending loads. All of the specimens had wavy plies through the center and near the surfaces (termed marcelled areas), although for some of the specimens the surface marcels were very obvious, and for others they were much smaller. The specimens failed by first developing cracks through the marcels at the surfaces, and then delaminations grew from those cracks, in both directions. Delamination failure occurred in these specimens at significantly shorter fatigue lives than similar specimens without waviness, tested in Ref 2.

A 2-D finite-element model was developed which closely approximated the flexbeam geometry, boundary conditions, and loading. In addition, the FE model duplicated the waviness observed in one of the test specimens. The model was analyzed using a geometrically nonlinear FE code. Modifications were made to the original model to reduce the amplitude of the marcels near the surfaces. The analysis was repeated for each modification. Comparisons of the interlaminar normal stresses, σn, in the various models showed that under combined axial-tension and cyclicbending loading, for marcels of the same aspect ratio, σn, stresses increased as the distance along the taper, from thick to thin end, increased. for marcels of the same aspect ratio and at the same X-location along the taper, σn, stresses decreased as the distance from the surface into the flexbeam interior increased. A technique was presented for determining the smallest acceptable marcel aspect ratio at various locations in the flexbeam.
Open Hole Compression Strength and Failure Characterization in Carbon/Epoxy Tape Laminates
Authors: Bau H , Hoyt DM , Rousseau CQ
Published: April 2008

Open hole compression (OHC) design criteria often size the thicknesses of composite aircraft skin structures. Therefore, there can be a significant payoff in improving OHC allowables through better characterization of OHC strength and behavior. This study, using progressive damage analysis and empirical methods, provides new insight into OHC strength and failure behavior.

OHC failure behavior was modeled using PDHOLEC, a progressive damage, 2-D finite-element code. Ultimate strength predictions were combined into carpet plots over a wide range of layups in three graphite composite material systems. A detailed evaluation of PDHOLEC progressive failure output resulted in the identification of several distinct predicted failure mechanisms. Predicted failure mechanisms and ultimate strengths are compared with OHC test data.

Two distinct failure mechanisms for OHC configurations were identified based on the PDHOLEC ailure study and strength trend studies of test data: a 0° ply kinking/buckling failure mechanism and a matrix cracking mechanism. The PDHOLEC predictions and test data were grouped by the identified failure mechanisms. Then curve fit equations were generated to characterize the ultimate strength behavior for each failure mechanism.
The Influence of Fastener Clearance Upon the Failure of Compression-Loaded Composite Bolted Joints
Authors: Sawicki AJ , Minguet PJ
Published: April 2008

The effects of fastener hole-filling and hole clearance upon the compressive strength of IM6/3501-6 tape composite bolted joints were investigated experimentally and analytically. Tests were conducted using coupon specimens loaded at several bearing-bypass loading ratios, with defined hole clearances spanning the range permitted in Class 1 structural holes (nominal bolt diameter +0.076/-0.000 mm). Bearing-bypass loads were applied using a dual actuator servo-hydraulic load frame augmented with bearing reaction supports. Three primary failure modes (net section compression, offset net section compression, and bearing) were observed. A linear relationship between bearing stress and bypass strain at failure was observed for specimens failing in the offset net section compression mode. Mean joint strengths were found to vary at most 7% due to variances in initial hole clearance. A semi-empirical strength prediction methodology, which uses 2-D finite-element analysis and ply-level quadratic failure theory, was used to interpret test results. Reasonable agreement between experimental data and predicted trends was demonstrated for IM6/3501-6 tape laminates. Incorporation of bolt elasticity effects and improved failure criteria within the methodology is necessary to improve the accuracy of strength predictions.
Finite Element Analysis of Delamination Growth in a Multidirectional Composite ENF Specimen
Authors: König M , Krüger R , Rinderknecht S
Published: April 2008

Two different finite element models have been applied to the analysis of delamination growth in a multidirectional graphite/epoxy ENF specimen, which has previously been investigated experimentally. For a more accurate computation of energy release rates along the delamination front, and particularly the individual mode contributions, a layered 3-D shell finite element has been used. A 2-D finite element, based on Reissner-Mindlin plate theory, has been employed for simulation of the delamination growth. This element incorporates a process layer in which the delamination can grow. The virtual crack closure method is employed in both models to compute the energy release rates along the delamination front. It is postulated that these energy release rates control the development of the shape of the delamination front, as well as the final unstable growth of the delamination, as observed in the experiment.

By a comparison between simulation and experiment it is found that in the present case of pure shear mode (combination of Modes II and III) the Griffith criterion predicts correctly the global delamination growth.
Curved Laminated Beams Subjected to Shear Loads, Moments, and Temperature Changes
Authors: Peck SO
Published: April 2008

Closed-form 2-D solutions for the displacements, strains, and stresses in curved, laminated orthotropic beams subjected to shear loads, moments, and temperature changes are developed. The solutions are exact and therefore equally applicable to sandwich structures as well as to ordinary laminates. The displacement solutions include rigid-body terms that are used to predict the contribution to spring-in of curved composite laminates due to differential thermal expansion in the radial and circumferential directions. Sample calculations for graphite/epoxy face-skinned aluminum honeycomb curved beams clearly predict anticipated failure modes.
Damage, Stiffness Loss, and Failure in Composite Structures
Authors: Chatterjee SN
Published: April 2008

Laminated plate theory is widely used for elastic analysis and design of fiber composite structures. Use of the results for prediction of failure and for design of structures to avoid failure (with a margin of safety) is a more complex issue. Use of failure theories in terms of stresses or strains at a point can sometimes yield a very conservative estimate of the failure load. It is recognized that such theories, in conjunction with laminate analysis, yield an estimate of the point of damage onset (often in the matrix), but final failure usually requires progressive fiber breaks and significant load redistribution. Methods have been suggested to perform stress analyses beyond damage initiation, but they are very rarely used in practice (as compared to the use of plasticity theory for metal structures). Many progressive damage models make use of ad hoc assumptions for stiffness knockdowns. The objective of this paper is to demonstrate that damage mechanics (using a single or multiple damage parameters) can yield a set of constitutive laws, which are based on sound physical principles. It is shown that the dissipated energy density in a ply can be used as a damage parameter. Two structural problems are considered for demonstration. Results for the case of a pressure vessel are compared with those from netting analysis, a valid and widely accepted method for such designs. The second case is the problem of the “hole size effect,” which is currently handled in practice by the use of semi-empirical methods and a series of tests.
The Effects of Initial Imperfections on the Buckling of Composite Cylindrical Shells
Authors: Starnes JH , Hilburger MW , Nemeth MP
Published: April 2008

The results of an experimental and analytical study of the effects of initial imperfections on the buckling response of thin unstiffened graphite-epoxy cylindrical shells with and without a cutout, and with three different shell-wall laminates, are presented. Results that identify the individual and combined effects of traditional initial geometric shell-wall imperfections, and nontraditional shell-wall thickness variations, shell-end geometric imperfections, and variations in loads applied to the ends of the shells on the shell buckling and nonlinear responses, are included. The shells have been analyzed with a robust nonlinear finite-element analysis code for shells that accurately accounts for these effects on the buckling and nonlinear responses of the shells. The analysis results generally correlate well with the experimental results. The nonlinear analysis results are also compared with the results from a traditional linear bifurcation buckling analysis that is commonly used for shell design. The results suggest that the nonlinear analysis procedure can be used for determining accurate, high-fidelity, design knockdown factors for shell buckling and collapse. A discussion of how this high-fidelity nonlinear analysis procedure can be used to form the basis for a shell analysis and design approach that addresses some of the critical shell-buckling design criteria and design considerations for composite shell structures is included.
Interaction of High-Cycle and Low-Cycle Fatigue on Fretting Behavior of Ti-6-4
Authors: Cortez R , Mall S , Calcaterra JR
Published: April 2008

The fretting behavior of Ti-6Al-4V when subjected to combined high-cycle fatigue/low-cycle fatigue (HCF/LCF) was investigated. Constant amplitude fretting fatigue tests were first conducted at room temperature at both 1 Hz and 200 Hz frequencies. The fretting fatigue life was smaller for the higher frequency condition than for the lower one. Then, fretting tests combining the interaction of both high-frequency and low-frequency waveforms were conducted which yielded similar lives to the constant amplitude fretting fatigue tests. Tests consisting of HCF/LCF blocks of 50:1, 500:1, and 5000:1 were examined where the ratio represented the number of HCF cycles to LCF cycles. Overall, Miner's linear damage summation rule provided a reasonable estimate of combined HCF/LCF fretting lives for the HCF/LCF tests considered.
Fretting Fatigue of Some Nickel-Based Alloys in Steam Environment at 265°C
Authors: Attia MH
Published: April 2008

In comparison with plane fatigue, fretting damage may lead to a substantial decrease in the fatigue strength of the material due to the addition of alternating frictional stresses, and the continuous destruction of the surface oxide. Fretting fatigue and plain fatigue tests have been conducted to establish the effect of fretting on the fatigue strength of two nickel-based alloys, Inconel 600 and Incoloy 800 against carbon steel and 410S stainless steel, respectively. The tests were conducted in steam environment at 265°C. The main test variables were the contact pressure 0 < pc < 138 MPa and the mean stress 0 < σm < 138 MPa. The results of the S-N curves for plain and fretting fatigue tests indicated that the reduction factor in the fatigue strength of Inconel I-600 alloy due to fretting is in the range of 2.2 to 3.5, depending on the loading conditions. The results also showed that Incoloy I-800 is more susceptible to fretting fatigue than I-600 by approximately a factor of 1.5.
Analysis of Fretting Damage Using Confocal Microscope
Authors: Chandrasekaran V , Yoon YI , Hoeppner DW
Published: April 2008

Fretting fatigue experiments were conducted on 7075-T6 and 2024-T3 Aluminum alloy specimens. The primary objective of this study was to quantitatively characterize fretting damage that resulted on the fatigue specimens. Fretting fatigue experiments were performed in laboratory air at various maximum fatigue stress levels at a constant normal pressure. The hypothesis of this study was that the intensity and the nature of fretting damage would vary depending upon the applied maximum fatigue stress and the three dimensional nature of the damage that would result from fretting could be quantified. Fretting fatigue experiments were interrupted at a predetermined number of cycles to analyze the damage on the fatigue specimens. Confocal microscopy was used to analyze and quantify fretting damage. Digitized images of fretting damage were obtained from the confocal microscope, using a pixel counting software package which also allowed length measurement of fretting induced cracks on the faying surface of the fatigue specimen. In addition, fretting damage was quantified in terms of material removal by characterizing the depth as well as the geometry of fretting-generated pits on the faying surface of the specimen. Pit size in terms of pit depth (Pd), pit area (PA), and pit dimension perpendicular (PDy) as well as parallel (PDx) to the applied load also were quantified. From the confocal microscopy analysis of fretting damage, it was observed that fretting-generated multiple cracks on the faying surface could be responsible for the fracture of 7075-T6 aluminum alloy specimens whereas the fracture of 2024-T3 aluminum alloy specimen could be attributed to fretting-generated multiple pits on the faying surface. From the results, it is proposed that fretting nucleates damage of different nature depending on the material microstructure as well as its composition and the methods to alleviate fretting should consider issues pertaining to a specific material.
Stage II Crack Propagation Direction Determination Under Fretting Fatigue Loading: a New Approach in Accordance with Experimental Observations
Authors: Dubourg MC , Lamacq V
Published: April 2008

Cracking is a dangerous degradation mode under fretting loading and the understanding of crack initiation and propagation is thus a necessity. A double experimental and theoretical approach has been undertaken to deal with crack initiation during Stage I [1,2], Stage I/Stage II transition and Stage II propagation. The work presented here is related to the latter point and aims at determining the direction and the propagation mode of cracks. A new approach is proposed here to account for non-proportional mixed mode conditions such as those encountered under fretting conditions at crack tips. Propagation directions during Stage II are derived from Δσθθ*max, the maximum effective amplitude of the tangential stress perpendicular to the crack trajectory. They correlate well with experimental data. The stress field analysis shows that the trajectory of cracks borders the tensile-compressive and the tensile zones existing around the crack tip over a loading cycle.
Fretting Fatigue Behavior of TiN-Coated Steel
Authors: Okane M , Shiozawa K , Ishikura T
Published: April 2008

Fretting fatigue tests of carbon steel coated with titanium nitride (TiN) by the PVD method were carried out to determine the effects of ceramic coating on fretting fatigue behavior. The fretting fatigue strength of the present carbon steel was significantly increased by TiN coating onto the specimen. The fretting fatigue fracture process in TiN-coated steel was as follows: Fretting cracks initiate at a certain stage of fatigue life from the flaws or worn region in TiN film initiated by fretting action, and propagate until final unstable fracture occurs. The improvement of fretting fatigue strength by TiN coating resulted mainly from the retardation of fretting fatigue crack initiation due to the existence of hard TiN film on the contact surface of the specimen.
Fretting in Aerospace Structures and Materials
Authors: Farris TN , Szolwinski MP , Harish G
Published: April 2008

Fretting, the deleterious and synergistic combination of wear, corrosion, and fatigue phenomena driven by the partial slip of nominally clamped surfaces, has been linked to severe reductions in service lifetimes of a myriad of contacting components, including bearings, turbine blades and mechanically fastened joints-both structural and biological. This paper serves to frame the aggregate of economic, operational, and technical developments responsible for engendering renewed interest in fretting fatigue of critical structural elements of both commercial and military aerospace systems, including riveted primary structure and the blade/disk pair in jet propulsion plants. A collection of both empirical evidence of fretting-induced componential degradation and an overview of results from recent investigations conducted by the authors serves to motivate the need for design-oriented metrics that can be used to ensure the structural integrity and safe operation of both current and future aerospace systems.
On a New Methodology for Quantitative Modeling of Fretting Fatigue
Authors: Dang Van K , Maitournam MH
Published: April 2008

A new intrinsic methodology for the prediction of fretting fatigue failure of a structure is presented. It is based, first, on the evaluation of local relevant thermomechanical parameters by new thermoelastoplastic computational methods (direct cyclic method) and, second, on the systematic use of the Dang Van multiaxial high-cycle fatigue criterion. For the validation of this proposal, numerical simulations of fretting fatigue tests on a particular experimental setup considered as a structure are performed. The resulting prediction of the experimental fretting fatigue map in relation to plastic and fatigue material properties is good.
Pendulum Impact Machines: Procedures and Specimens
Authors: Siewert T , McCowan C , Manahan M
Published: April 2008

Description

Ten peer-reviewed papers cover the latest information on pendulum impact machines. STP 1476 represents the work of impact test researchers from around the world and provides input for further improvements in test methods, especially those used in construction codes and standards.

These papers are organized into four major areas:

Historical Developments in Impact Testing—covers the history and procedure development for Impact Testing

Impact Test Procedures and Machine Effects—discusses the effects on absorbed energy of removing and replacing an 8 mm Charpy striker

Reference Specimens—address certification of Charpy reference specimens at IRMM, uncertainty analyses on reference values of Charpy Impact Test Specimens, analysis of Charpy Impact verification data, and much more.

Issues with Instrumented Strikers—provides different approaches for the verification of force values measured with instrumented Charpy strikers
Evaluation of Laboratory Determined and Nondestructive Test Based Resilient Modulus Values from WesTrack Experiment
Authors: Seeds S , Alavi S , Ott W , Mikhail M , Mactutis J
Published: April 2008

Resilient modulus is an important material property required for characterization of pavement layers for use in modern mechanistic pavement design. The resilient modulus can be determined in the laboratory using various types of tests, which measure a material's response under simulated field loading conditions. It can also be estimated from nondestructively measured pavement surface deflections and the so-called backcalculation procedures. Unfortunately, studies have shown that the resilient modulus determined from laboratory testing can differ significantly from that determined from nondestructive test (NDT) based backcalculation procedures.

This paper further addresses the issue by presenting the results of a site-specific comparison of the resilient modulus determined through laboratory testing and NDT-based backcalculation analysis. Unlike some of the earlier studies that focused more on developing a correlation between the two, this study explores some of the flaws and weaknesses of the two processes that are likely to result in the observed differences. It is also important to point out that the results of this study are based on an intensive amount of both laboratory and NDT data gathered from a pavement constructed to exceptional standards of construction quality, i.e., the WesTrack full-scale accelerated load test facility in northern Nevada.

The emphasis of the paper is on the unbound layers (i.e., base and recompacted subgrade soil layers) below the pavement surface. Although laboratory testing of the hot-mix asphalt (HMA) surface layer was completed, the data were not yet to a level of quality acceptance to produce a meaningful comparison with the NDT-based backcalculation results of the surface layer.
Prediction of Pavement Deterioration Based on FWD Results
Authors: Maina JW , Yokota H , Mfinanga DA , Masuda S
Published: April 2008

Prediction models for pavement deterioration of major roads in Miyazaki Pre-fecture, Japan, using falling weight deflectometer (FWD) data are presented. The models would be incorporated in a pavement management system (PMS), for the prefecture, which is under development. At first, a relation between Japanese maintenance control index (MCI) and cumulative equivalent single axle loads (CESAL) was established. MCI was computed using variables that were automatically measured by a vehicle mounted with laser beam, cameras and profilometers. AASHO performance equation provided the basis for the development of these new models. Strength (deflection) factor was introduced into the coefficient that controls the slope of the performance curve through multiple regression analysis. Given FWD deflection and CESAL, these models could predict the trend of future pavement deterioration. This method increases the range of applicability of FWD data and may complement pavement condition rating systems that provide a measure of current pavement conditions only.
Comparison of Backcalculated and Laboratory Measured Moduli on AC and Granular Base Layer Materials
Authors: Zhou H
Published: April 2008

This paper presents a comparison of pavement layer moduli determined from backcalculation with those measured in the laboratory on asphalt concrete (AC) and granular base materials. Deflection data and pavement materials obtained from two conventional flexible pavement structures were used. Pavement surface deflections were measured with a Falling Weight Deflectometer and were used in backcalculation analysis to determine pavement layer moduli. AC cores and granular materials from the base layer were taken for testing in the laboratory to determine resilient modulus in accordance with established ASTM testing procedures. The comparison of backcalculated and laboratory measured moduli for two pavement structures showed that for the AC surface layer the backcalculated moduli were generally lower than the laboratory measured at the same temperature; the difference was in a range of 20 to 30 percent. The backcalculated moduli also seemed to be less susceptible to temperature variation. For the base aggregate materials, the backcalculated moduli exhibited tendency of stress dependency similar to those measured in the laboratory. In the range where actual pavement stresses generally fall, a favorable comparison was observed, indicating that the modulus-stress relationship determined from backcalculation could be used in the analysis of nonlinear property of granular base materials.
Use of Instrumented Dynamic Cone Penetrometer in Pavement Characterization
Authors: Nazarian S , Tandon V , Crain K , Yuan D
Published: April 2008

The dynamic cone penetrometer data had been conventionally used for estimating the base and subgrade California bearing ratio. In recent years, a need for developing mechanistic pavement design procedures has been emphasized. However to develop mechanistic pavement design procedures, measuring engineering properties of pavement layers is essential. Two modifications to the existing dynamic cone penetrometer have been proposed in this paper for obtaining engineering properties of pavement layers.

First, an ordinary dynamic cone penetrometer was instrumented with a load cell and an accelerometer to determine the energy imparted to the ground, the resistance to the penetration, and the penetration of the device into the base and subgrade. A second device consisting of a three-dimensional accelerometer embedded in a DCP-like rod was developed to measure modulus and Poisson's ratio of the base and subgrade layers. This device can be placed in the same hole drilled for the first device, thus, requiring minimum coring. Although both devices are proven to be feasible, further analysis is needed for reliably extracting information from these measurements.
LTPP Rigid Pavement FWD Deflection Analysis and Backcalculation Procedure
Authors: Khazanovich L , McPeak TJ , Tayabji SD
Published: April 2008

This paper presents the results of a falling weight deflectometer (FWD) deflection analysis study performed as a part of data analysis study under the Long-Term Pavement Performance (LTPP) program. The paper presents backcalculation procedures for rigid pavements adapted in this study and discusses the results of backcalculation. Backcalculation was performed using dense liquid (DL) and elastic solid (ES) subgrade models. Although backcalculated parameters determined in this study were found to be realistic for the majority of the LTPP rigid pavement sections, this study also uncovered some limitations of the current backcalculation procedures for rigid pavements. It was noted that backcalculated values may vary significantly due to factors such as temperature at the time of testing, slab curling conditions, time of day, and time of year. Current rigid pavement backcalculation technology is inappropriate to adequately address all of these matters; however, the LTPP database provides an excellent opportunity to conduct an in-depth study.
A New Backcalculation Procedure Based on Dispersion Analysis of FWD Time-History Deflections and Surface Wave Measurements Using Artificial Neural Networks
Authors: Kim YR , Xu B , Kim Y
Published: April 2008

A new layer moduli backcalculation procedure using transient measurements from both a falling weight deflectometer (FWD) test and a surface wave test is presented in this paper. This algorithm employs numerical solutions of a multi-layered half-space based on Hankel transforms as a forward model and Artificial Neural Networks (ANNs) for the inversion process. Two ANNs are used in series; a depth to a stiff layer is predicted first and used as input for the second ANN to be used for the prediction of layer moduli.

Falling weight deflectometer (FWD) and surface wave tests were performed on experimental pavement sections in North Carolina with different asphalt mixture types and surface conditions. Dispersion analysis was performed on FWD transient deflections and surface wave test measurements using the Short Kernel Method. Conventional backcalculation was also performed on FWD deflections using the MODULUS 5.0 program. It was concluded that the dispersion-based backcalculation method is sensitive to changes in upper layer condition and results in less variable sub-surface layer moduli and more accurate prediction of depth to a stiff layer than the conventional backcalculation does using FWD peak deflections.
Effect of Frequency-dependent Asphalt Concrete Layer Moduli on Pavement Response
Authors: Chatti K , Kim TK
Published: April 2008

The viscoelastic nature of asphalt concrete (AC) renders its properties to be frequency-dependent. Static backcalculation of layer moduli from Falling Weight Deflectometer (FWD) testing does not take into account this frequency-dependence. This paper shows the effect of frequency-dependent AC properties on the horizontal strain and vertical deflection using the computer program SAPSI-M and field results. The analysis shows that the decrease in horizontal strain with increasing truck speed can be duplicated only by using frequency-dependent properties for the asphalt concrete layer. However, using a constant backcalculated AC surface layer modulus and static analysis seems to be sufficient for giving a prediction that is reasonably close to the actual tensile strain under moving loads. This is so because the backcalculated modulus value for the AC surface layer is generally higher than the creep modulus, and the horizontal tensile strain is not affected by speed when using a constant AC layer modulus.
Use of Multifrequency Backcalculation for Determining Moduli of a Pavement Structure
Authors: Kang YV
Published: April 2008

The use of multifrequency backcalculation can overcome the limitation on the maximum allowable number of layers in most static backcalculation programs. However, its convergence may break down when using high-frequency deflections with static estimation. Based on the dispersive characteristics of the surface waves, a newly developed procedure for estimating the seed moduli was implemented. The proposed method was then applied to three typical profiles. The numerical results show that surface wave estimation improves significantly the convergence of the backcalculation process even for pavement systems with high modulus contrast. It also overcomes the frequency limitation found in the static estimation.
Continuous Profiling of Flexible and Rigid Highway and Airport Pavements with the Rolling Dynamic Deflectometer
Authors: Bay JA , Stokoe KH
Published: April 2008

The Rolling Dynamic Deflectometer (RDD) is a relatively new tool for assessing the condition of pavements. The RDD measures continuous deflection profiles rather than deflections at discrete points. This paper discusses the operating parameters for RDD testing and presents the results of RDD testing on rigid and flexible pavements. Additionally, measurement of deflection basins “on the fly” and measurement of frequency-response spectra at discrete locations with the RDD are discussed and illustrated.
Irwin's Stress Intensity Factor—A Historical Perspective
Authors: Newman JC
Published: April 2008

This paper is written to honor Dr. George R. Irwin and reviews several key developments in fracture mechanics based on his “stress-intensity factor” concept. The early development of two fundamental crack solutions, (1) an edge crack in a semi-infinite body and (2) the surface crack, are highlighted. Applications of Irwin's early concepts by other researchers to characterize fatigue-crack growth and brittle fracture of metallic materials are presented. The stress-intensity factor is the cornerstone of the damage-tolerance and durability design concepts used by the aerospace community around the world. The stress-intensity factor concept, crack-closure mechanics, and the observation that “fatigue is crack propagation” in many engineering materials has led to a merger of fatigue and fracture mechanics analysis methodologies. Irwin's recognition of the importance of the normal stress parallel to the crack (now referred to as the T-stress) in fracture led many to propose a two-parameter characterization for fracture. The importance of constraint on crack-tip yielding has been further advanced by the use of high-powered computers to calculate a normal-stress constraint parameter following his ideas. The father of fracture mechanics has left a legacy that will endure and provide safer and more reliable structures in the future.
Biaxial Fatigue of Stainless Steel 304 under Irregular Loading
Authors: Kim KS , Lee BL , Park JC
Published: April 2008

Fatigue tests are performed on tubular specimens of stainless steel 304 under variable amplitude, irregular axial-torsional loading. Three parameters are chosen for correlating fatigue life: the Smith-Watson-Topper (SWT) parameter for normal fracture, Fatemi-Socie (FS), and Kandil-Brown-Miller parameters (KBM) for shear fracture. A life computation procedure is employed in which rainflow cycle counting on normal (SWT) or shear (FS, KBM) strain history and the Miner-Palmgren rule are used. It is found that, while the life calculation procedure appears to be viable and each parameter yields acceptable results for most loading conditions, there are cases for which correlation is poor. The SWT parameter performed well except for torsion-dominated cycles, where it overpredicted lives. The FS and KBM parameters did better than the SWT parameter in torsion, but showed poor performance in some other loading conditions.
Fatigue Life Estimation Under Cumulative Cyclic Loading Conditions
Authors: Kalluri S , McGaw MA , Halford GR
Published: April 2008

The cumulative fatigue behavior of a cobalt-base superalloy, Haynes 188, was investigated at 760°C in air. Initially, strain-controlled tests were conducted on solid cylindrical gage section specimens of Haynes 188 under fully reversed, tensile and compressive mean strain-controlled fatigue tests. Fatigue data from these tests were used to establish the baseline fatigue behavior of the alloy with (1) a total strain range type fatigue life relation and (2) the Smith-Watson-Topper (SWT) parameter. Subsequently, two load-level multi-block fatigue tests were conducted on similar specimens of Haynes 188 at the same temperature. Fatigue lives of the multi-block tests were estimated with (1) the linear damage rule (LDR) and (2) the non-linear damage curve approach (DCA) both with and without the consideration of mean stresses generated during the cumulative fatigue tests. Fatigue life predictions by the nonlinear DCA were much closer to the experimentally observed lives than those obtained by the LDR. In the presence of mean stresses, the SWT parameter estimated the fatigue lives more accurately under tensile conditions than under compressive conditions.
Variations of Constraint and Plastic Zone Size in Surface-Cracked Plates Under Tension or Bending Loads
Authors: Aveline CR , Daniewicz SR
Published: April 2008

Elastic-plastic finite element analyses of surface-cracked plates are performed using the commercial finite element code ANSYS. Various crack geometries are analyzed under tension and bending loads. A constraint factor dependent on the location along the perimeter of the surface crack, similar to the global constraint factor defined by Newman, is presented. This newly defined constraint factor is the averaged normal stress to flow stress ratio acting on a line originating on and perpendicular to the crack front at a prescribed location and terminating at the perimeter of the plastic zone on the crack plane.

The plastic zone shape and size around the three-dimensional crack front determined from the finite element analyses are also presented. The analyses indicate that the maximum plastic zone size occurs beneath the free surface (2° < ϕ < 5°). Geometry and applied loading parameters are considered in equations relating them to constraint along the crack front.
Transition Fracture Toughness Testing with Notched Round Bars (NRB)
Authors: Wilson CD , Landes JD
Published: April 2008

The notched round bar (NRB) geometry was assessed for use with ASTM E 1921-97 Standard for Test Method for the Determination of Reference Temperature, T0, for Ferritic Steels in the Transition Range. Instead of precracking the NRB specimens, apparent fracture toughness using three different notch root radii was extrapolated to a zero radius to infer sharp crack fracture toughness. The reference temperature using A302B NRB specimens was determined to be -89°C, while A302B C(T) specimens yield T0 of -87.3°C. In applying ASTM E 1921 to the NRB geometry, a simple scheme to remove notch root radius bias from apparent fracture toughness was developed. In addition, a size correction for converting NRB results to comparable 1T-C(T) results was investigated.
Dislocation Mechanics Basis and Stress State Dependency of the Master Curve
Authors: Natishan ME , Wagenhofer M , Kirk MT
Published: April 2008

The Master Curve approach to characterizing fracture toughness transition behavior of pressure vessel steels is based on statistical analysis of empirical data and not on a physics-based understanding of the fracture behavior of these steels. While there is an over-abundance of empirical data that supports the idea of a single curve shape for all pressure vessel steels, this cannot replace the need for solid physical modeling. The lack of fracture toughness data for a considerable proportion of the nuclear fleet suggests that a purely empirical argument cannot validate the Master Curve for all conditions of interest. In order to validate the Master Curve approach research has been undertaken to provide a physical understanding of the fracture behavior of pressure vessel steels. This will provide the basis for defining the limits of the Master Curve as well as for enabling extrapolation of the Master Curve model to other material conditions with only limited testing. A previous paper [1] detailed a dislocation mechanics-based constitutive model approach to describe the link between microstructure and temperature dependence of flow and fracture toughness behavior. In this paper, the strain to fracture under the appropriate stress state will be discussed in terms of the dislocation mechanics-based constitutive models and the effect on the shape of the Master Curve.
Investigation of a New Analytical Method for Treating Kinked Cracks in a Plate
Authors: TerMaath SC , Phoenix SL
Published: April 2008

A new analytical method for treating kinked and branched cracks is investigated to understand its subtleties and their effects on accuracy and efficiency. Based on a weighted superposition approach, this method uses analytical functions built from opening displacement profiles to determine full stress and displacement fields in a linearly elastic two-dimensional infinite plate containing interacting kinked and branched cracks under far field loading. In addition, results include stress intensity factors at tip and kink locations. Rapid convergence is achieved for few degrees of freedom yielding crack face tractions consistent with those prescribed. Moreover, this method involves no numerical integration, eliminating unnecessary computational errors. The features of this method are demonstrated by the solution of a V-shaped crack. The method yields stress intensity factor results that are in agreement with a particular case found in a well-known handbook.
Calculation of Stress Intensity Factors for Cracks of Complex Geometry and Subjected to Arbitrary Nonlinear Stress Fields
Authors: Glinka G , Reinhardt W
Published: April 2008

Fatigue cracks in shot-peened and case-hardened notched machine components are subjected to stress fields induced by the external load and residual stresses resulting from the surface treatment. Both stress fields are characterized by nonuniform distributions, and handbook stress intensity factor solutions are in such cases unavailable, especially in the case of planar nonelliptical cracks. The method presented here is based on the generalized weight function technique enabling the stress intensity factors to be calculated for any Mode I loading applied to arbitrary planar convex and embedded crack. The stress intensity factor can be determined at any point on the crack contour by using one general weight function discussed in the paper. The weight function, mA, can be sufficiently well described by two quantities, i.e., the distance, ρ, from the load point, P(x, y), on the crack surface to the point, A, on the crack front where the stress intensity is to be calculated and the length, Γc, of the inverted crack contour. The stress intensity factors are calculated by integrating the product of the stress field and the weight function over the entire crack area.

The general weight function and calculated stress intensity factors are validated against arious numerical and analytical data. The numerical procedure for calculating stress intensity factors for arbitrary nonlinear stress distributions is briefly discussed as well. Several examples of typical input data and stress intensity factor results are presented including embedded and edge cracks subjected to two-dimensional stress fields. The method is particularly suitable for modeling fatigue crack growth in the presence of complex stress fields.