bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Radiation on Materials: 22nd Symposium
Authors: Allen TR , Lott RG , Busby JT , Kumar AS
Published: April 2008

Description

Thirty-one peer-reviewed papers provide the latest international research on the radiation effects on materials.

Topics cover
Influence of Surface Treatments on Fretting Fatigue of Ti-6242 at Elevated Temperatures
Authors: Chakravarty S , Dyer JP , Conway JC , Segall AE , Patnaik PC
Published: April 2008

Where fretting fatigue of titanium alloy gas turbine engine component is concerned, the effect of temperature on fretting processes can be quite significant. Service exposed third stage compressor blades, operating at 454°C or 850°F, showed severe signs of fretting, wear, CuNiln coating delamination, oxidation and pitting on the dovetail pressure surfaces. Under cyclic loading conditions fretting fatigue cracks, initiated in these damaged areas, can cause dramatic reduction in fatigue life of these components leading to potential catastrophic failure. A study has been carried out to evaluate the influence of various surface treatments, such as ion treatments, coatings and shot peening, on the fretting fatigue life of titanium alloy gas turbine engine components at elevated temperature. Results from high temperature fretting fatigue and pin-on-disk wear tests are discussed in this paper. Significant contrast between the wear and fatigue test results illustrates the potential dangers of using sliding wear tests to rank surface treatments for fretting fatigue amelioration.
Integrating Ground Penetrating Radar and Falling Weight Deflectometer Technologies in Pavement Evaluation
Authors: Scullion T , Saarenketo T
Published: April 2008

The first step in selecting the optimal rehabilitation strategy for any pavement is to identify the cause of the existing defects. In recent years nondestructive technologies such as Falling Weight Deflectometers and Ground Penetrating Radar have been used to evaluate subsurface conditions. However when used independently these technologies are not always adequate for identifying the cause of pavement deterioration. This paper will present the argument for developing an integrated approach to pavement evaluation wherein the high speed GPR survey results can be used to identify homogenous sections, locate potential subsurface defects and estimate layer thicknesses. The GPR then provides critical inputs to both the processing of the FWD data and the interpretation of the results.

In this paper a brief review will be presented on the principles of operation of both air launched and ground coupled GPR systems. Recently developed signal processing techniques for converting the GPR reflected waves into parameters of significance to highway engineers will be described. Five case studies from Texas and Finland will be included which demonstrate how both ground coupled and air launched GPR results can be effectively integrated with the FWD data to make project level decisions.
Nevada's Approach to the Backcalculation Process
Authors: Sebaaly PE , Bemanian S , Lani S
Published: April 2008

This paper documents the procedures and experiences of the Nevada Department of Transportation (NDOT) with the use of falling weight deflectometer (FWD) testing and backcalculation techniques. NDOT has been actively using these technologies for the past several years. As a result of their active involvement NDOT's pavement engineers have established a great amount of knowledge regarding the collection and analysis processes of FWD data. The paper presents standard field testing protocols and data analyses procedures that have been developed by NDOT's engineers to guide the design and analysis processes.

In addition to the traditional use of FWD data, NDOT has experimented with the application of FWD testing and backcalculation technique in other specialized area such as the assessment of fractured portland cement concrete (PCC) pavements and cold in place recycled (CIR) pavements. The NDOT's experience indicated that even though the FWD technology may not be fully successful in directly assessing the in situ properties of such materials, the technology can be successfully used to evaluate the structural coefficient of these layers. The paper presents the process used to establish these coefficients and documents the values currently used by NDOT.
Seasonal Trends and Causes in Pavement Structural Properties
Authors: Ali H , Selezneva O
Published: April 2008

The seasonal monitoring program (SMP) of the long term pavement performance (LTPP) program provides an excellent opportunity to study the seasonal trends in pavement response. In 64 pavement sections in the United States and Canada, FWD testing is performed monthly every other year, subsurface temperature is measured hourly, subsurface moisture and freezing conditions are measured monthly, and climatic factors such as ambient air temperature, solar radiation, wind speed, and precipitation are collected continuously.

In this study, a number of SMP sections were used to establish some general and statistically significant trends. The relationship between the elastic modulus of the AC layer and the temperature gradient within the layer was investigated. The relationship between the frost penetration in unbound layers and their backcalculated modulus was studied. Modeling such variability using linear and nonlinear formulations was attempted, and the practical implications of such effects on the data collection practice are discussed.

The results of the analysis showed that the AC layer temperature gradient appears to influence the layer modulus. An exponential model was developed to quantify that effect and adjust the backcalculated modulus to the temperature gradient. Analysis of frost penetration trends showed that surface deflection and the backcalculated subgrade modulus are very sensitive to the existence and extent of a frozen layer within the subgrade. As expected, the thicker the frozen layer, the larger the subgrade modulus, and the further the layer, the lower the subgrade modulus. Exponential models were used to characterize this effect.
The Israeli Experience with the Regular and Extended Dynamic Cone Penetrometer for Pavement and Subsoil-Strength Evaluation
Authors: Livneh M , Livneh NA , Ishai I
Published: April 2008

One of the Israeli modification in the dynamic cone penetrometer (DCP) apparatus is the extension of the length of the standard penetrating rod to a total of about 2.0 meters by screwing on an additional 1.0-meter rod after the original rod has completely penetrated the pavement or subgrade. Such a procedure is required when the strength profile is significant at depths exceeding 1.0 meter or when the total thickness of the pavement layers, including the relevant subgrade layers, exceeds the length of the standard penetrating rod. Through comparative in-situ testing, it was found that a 20% deduction should be applied for this testing procedure to the CBR values calculated from the in-situ DCP results, both for clayey and for granular subsoils, when the standard CBR-DCP equation is used. Similarly, a 10% reduction should be applied to the 1.5-meter penetration rod results. These findings were also qualitatively verified by examining the change in the dynamic efficiency factor for the two penetrating rods. Additionally, a corrective equation is suggested when the penetration is not performed vertically in order to isolate the skin friction that develops along the penetrating rod and that has significant effects on the DCP values. Finally, the standard CBR-DCP relationship is validated again for both CH and CL clays, thus eliminating the need for specific additional relationships for these materials.
Characterization of Transverse Cracks in Jointed Concrete Pavements (JCP's) Using Nondestructive Test (NDT) Methods
Authors: Frabizzio MA , Buch NJ
Published: April 2008

In this study field data was used to demonstrate useful NDT methods and analysis procedures for assessing when and how to repair cracked JCP's. Field data collected from in-service JCP's located throughout southern Michigan was used to accomplish this objective. This paper focuses on descriptions of three NDT methods performed in this study using falling weight deflectometer (FWD) data as well as on the analyses of results obtained from this data. The methods thus considered are: a methodology for determining crack performance parameters; a procedure for backcalculating pavement support and stiffness parameters; and, a technique for assessing void potential near cracks.
Closed-Form and Semi-Closed-Form Algorithms for Backcalculation of Concrete Pavement Parameters
Authors: Fwa TF , Tan KH , Li S
Published: April 2008

This paper presents the development of a family of closed-form and semiclosed-form backcalculation algorithms for nondestructive evaluation of rigid-pavement layer properties. Using measured surface deflections as input, these closed-form algorithms were developed for a rigid pavement slab supported on one of the following foundations: (i) a Winkler (i.e. liquid) foundation, (ii) an elastic solid foundation, and (iii) a two-layer elastic solid foundation. These closed-form algorithms were next employed to develop semi-closed-form algorithms for nondestructive evaluation of rigid pavements with two slab layers. All the algorithms were developed for execution on personal computers. The formulation of the algorithms and the corresponding methods of solution are presented. It is also highlighted that the closed-form algorithms can be used to evaluate the quality of measured deflections and to single out erroneous deflection sensor readings.
Evaluation of Concrete Pavement Conditions and Design Features Using LTPP FWD Deflection Data
Authors: Jiang YJ , Tayabji SD
Published: April 2008

The Long Term Pavement Performance (LTPP) study uses Falling Weight Deflectometers (FWDs) to collect deflection data. As part of a study sponsored by the Federal Highway Administration, load transfer efficiencies (LTEs) were calculated for all the test points of each section of the LTPP GPS 3, 4, and 5 experiments. From statistical analysis, it was found that the doweled joints have significantly higher LTEs than the non-doweled joints. Voids at the slab joints and corners were computed by examining the deflection data of the joint and corner tests at different load levels. The loss of support was then expressed as the percentage of joints or slab corners with voids for each LTPP concrete pavement test section. By examining the ratio of the maximum deflection at the mid-slab test location versus the edge locations, the concrete shoulders were found to provide significantly greater edge support than asphalt shoulders based on a one-tailed Student t-test.
Pavement Characterization Using Ground Penetrating Radar: State of the Art and Current Practice
Authors: Maser KR
Published: April 2008

Over the past 10 years the application of Ground Penetrating Radar (GPR) to pavement layer characterization has undergone significant developments. Current GPR technology is applied using non-contact equipment operating at normal driving speeds for data collection, and automated data processing software. Applications include determination of pavement layer thickness, identifying changes in pavement structure, and detection of pavement deterioration. The paper provides an overview of these applications, including: a synopsis of related research studies and results, expected levels of accuracy, requirements for ground truth, and availability of equipment and software. The paper also presents project case studies illustrating the key features of each current GPR application. Finally, the paper provides an update on current and in-progress specifications and standards for the application of GPR to pavement characterization.
Seismic Pavement Analyzer vs. Falling Weight Deflectometer for Pavement Evaluation: Comparative Study
Authors: Tawfiq K , Armaghani J , Sobanjo J
Published: April 2008

The purpose of using nondestructive testing techniques (NDT) for pavement evaluation is to obtain material properties at relatively low strain levels. Backcalculation methods that utilize surface deformation such as falling weight deflectometer (FWD) and Dynaflect assume linear elastic modeling for the pavement layers. Although the same assumption was considered for the seismic pavement analyzer (SPA) method, results obtained from these testing techniques did not conform to each other. To narrow the gap between the obtained pavement moduli values, a total of 22 pavement sites have been tested in Florida using deflection and seismic methods. Using the time-history records as well as the frequency response functions, pavement deformations from deflection and seismic methods were measured and related to the obtained moduli values. Relationships between deformation vs. pavement stiffness are presented. These relationships can be used to extract moduli values at any level of pavement deflection.
Use of Seismic Pavement Analyzer in Forensic Studies in Texas
Authors: McDaniel M , Yuan D , Chen DH , Nazarian S
Published: April 2008

Seismic nondestructive testing technology has been incorporated in two newly developed devices: the seismic pavement analyzer (SPA) and its hand-portable version (PSPA). Shortly after a prototype of the SPA was built and tested under a SHRP contract, the Texas Department of Transportation (TxDOT) acquired a second prototype SPA and several PSPAs. Each of the two devices can rapidly carry out a suite of seismic tests to evaluate pavement condition. A few short-term projects were conducted to learn when and where the use of seismic technology is feasible. The usefulness of the test methods involved in SPA and PSPA has been to some extent evaluated. In their present states, the SPA and PSPA seem to be emerging as valuable tools for forensic studies and the day-to-day operation of TxDOT. The devices have been helpful in understanding some of the complex mechanisms encountered under accelerated pavement testing with the Texas Mobile Load Simulator and have provided useful information to the engineers in a few TxDOT projects. More experience is needed to fully understand the potential and the weaknesses of the devices, and further development of their software is required.
Development of a Laser-Based High Speed Deflectograph
Authors: Hildebrand G , Rasmussen S , Andrés R
Published: April 2008

Today's heavily congested highways provide a difficult setting for bearing capacity measurements using stationary equipment like the FWD resulting in a situation which is dangerous to both drivers and FWD operator. Furthermore, techniques like the FWD method only provide information in discrete points that are often separated several hundred metres apart. To overcome these deficiencies a laser-based high speed deflectograph is being developed which can perform continuous bearing capacity measurements at all driving speeds in the range 20–70 km/h.

The unique concept of the high speed deflectograph utilizes laser Doppler sensors to provide the deflection speed of the pavement surface. By using this technique the deflection speed is determined in one operation as opposed to the more commonly used distance laser sensor method which determines the deflection as the difference between vertical deformation in two different points. The laser Doppler system has been found capable of determining deflection speeds within the desired range of driving speeds with an accuracy of 0.14 mm/sec, which has been shown to correspond to an accuracy of the deflection of 5 μm.

While it is important to measure deflection speeds correctly, it is equally important to continuously register and control the position of the laser sensors using secondary measuring systems like servo systems and inertial units.

The high speed deflectograph consists of a towing truck and a trailer on which the laser sensors are mounted. The trailer is equipped with a system, which allows variations of the applied load.

In parallel with the development of the physical measuring device a study is carried out concerning the interpretation of results from the high speed deflectograph. Results from work carried out to establish a coupling between deflection speeds and absolute deflections, of which the latter can be compared to FWD results, are presented.
Comparative Studies of Backcalculated Results from FWDs with Different Loading Duration
Authors: Matsui K , Kikuta Y , Nishizawa T , Kasahara A
Published: April 2008

The falling weight deflectometer (FWD) test applies an impulsive force on the surface of pavement and measures surface deflections at several locations. Although the test is dynamic, static backcalculation is commonly conducted to estimate pavement layer moduli using peak values of the impulsive force and surface deflections. However, falling weight defiectometers produced by the different manufacturers often differs in loading duration. The difference may affect backcalculation results, because the FWD test is dynamic in nature.

The key issue of this paper is to investigate the effect of the difference on backcalculated layer moduli. First, the difference is numerically studied by conducting static backcalculation on the peak deflection data generated from dynamic analysis with three different loading durations. Secondly, both static and dynamic backcalculations are carried out on the sets of deflections measured by three FWDs with different loading duration. Although the difference between static and dynamic backcalculation results are conspicuous in the case of numerical simulation, but the difference is not significant when actual data are used.
Prediction of Remaining Life of Flexible Pavements with Artificial Neural Networks Models
Authors: Abdallah I , Ferregut C , Nazarian S , Melchor Lucero O
Published: April 2008

A software program has been developed to predict the remaining life of flexible pavements using artificial neural network (ANN) technology. The remaining life due to either rutting or fatigue cracking can be predicted. The inputs to the software are the best estimate of the thickness of the layers, the deflection basin measured with a falling weight deflectometer (FWD), and optionally, the extent of damage at the time of the FWD test. The outputs are the best estimate of the remaining life and the pavement performance curve. If uncertainty in the thicknesses, FWD measurements and traffic exists, a probabilistic description of the remaining life is also provided. The main benefit of the proposed approach is that the backcalculation process for determining moduli is not necessary. The remaining lives or alternatively the critical stresses needed to calculate them are directly estimated. As such, the results seem to be more robust. In this paper, the overall procedure and the details of the methodology followed in developing the software are described. A case study is included to demonstrate the application of the methodology.
Estimation of Design Season Modulus for Overlay Design
Authors: Jackson NM , Andrew JW , Drumm EC
Published: April 2008

Nondestructive evaluation of pavement performance by methods such as the Falling Weight Deflectometer (FWD) are widely used and accepted. Backcalculation and prediction of pavement layer moduli can be effective for both the evaluation of pavement condition and overlay design. However, variations in pavement temperature and subgrade moisture content result in variability in the backcalculated moduli.

In an attempt to evaluate the overall effect of this variability on design, pavement sections in four different regions of the State of Tennessee were instrumented and tested. The in-situ temperature and moisture content of the pavement and subgrade materials were continuously monitored for seasonal changes. Each site was also equipped with a weather station to record precipitation, air temperature, and solar radiation. FWD testing was conducted monthly at each site and the moduli for the pavement and subgrade layers were backcalculated using AASHTO recommended procedures. The seasonal variation in subgrade modulus was compared with measured changes in subgrade temperature and moisture content.

The observed variability in seasonal moduli estimates was used to support a generalized model for estimating seasonal changes in subgrade resilient modulus. A proposed design method that incorporates this generalized model with a relative damage or weighting factor approach is presented. This proposed method will enable the pavement designer to establish a reasonable design subgrade modulus based on limited test data.
The Contributions of George Irwin to Elastic-Plastic Fracture Mechanics Development
Authors: Landes JD
Published: April 2008

George Irwin, the father of fracture mechanics (FM), is well known for his contributions to linear elastic fracture mechanics, especially the development of the crack-tip field approach and the use of the crack tip stress intensity factor, K. During the early years of FM he was well aware that the limits on the use of K restricted its application to high-strength and low-toughness materials. He encouraged the development of new concepts that would be able to extend the use of FM to the more usual engineering materials, materials that might reach yield stress before fracture toughness on a typical structural component. Concern with that area of FM later led to the development of the technology called elastic-plastic fracture mechanics (EPFM). Besides the encouragement he gave, there are several areas where he contributed technical ideas that helped with the development of the EPFM technology. These ideas include use of crack tip field parameters, the energy and crack tip parameter equivalence, the R-curve approach to fracture toughness evaluation and the concern about constraint effects on fracture behavior.

This paper takes a historical look at these developments in elastic-plastic fracture mechanics and the role that George Irwin played. An important observation that will be made is that the approach originally proposed by Irwin gave the correct direction in each case considered in this paper. The original ideas merely needed further development to become mature technical concepts in the EPFM approach.
A New Incremental Fatigue Method
Authors: Chu C-C
Published: April 2008

By analyzing the material's strain-life data differentially, this paper brings to light the generally overlooked incremental damage concept which underlies the conventional uniaxial rainflow counting algorithm and the strain-based fatigue method. This incremental damage concept not only allows the uniaxial rainflow program to be logically extended to multiaxial problems, it also forms the basis for a new incremental fatigue damage accumulation method. Several simple examples, including a multiaxial rainflow algorithm, are given to illustrate how the new approach can be applied to general multiaxial problems and how it can be formulated so that any chosen uniaxial model using the traditional parametric approach can be closely reproduced.
Assessments of Low Cycle Fatigue Behavior of Powder Metallurgy Alloy U720
Authors: Gabb TP , Bonacuse PJ , Ghosn LJ , Sweeney JW , Chatterjee A , Green KA
Published: April 2008

The fatigue lives of modern powder metallurgy disk alloys are influenced by variabilities in alloy microstructure and mechanical properties. These properties can vary as functions of variables the different steps of materials/component processing: powder atomization, consolidation, extrusion, forging, heat treating, and machining [1–4]. It is important to understand the relationship between the statistical variations in life and these variables, as well as the change in life distribution due to changes in fatigue loading conditions. The objective of this study was to investigate these relationships in a nickel-base disk superalloy, U720, produced using powder metallurgy processing. Multiple strain-controlled fatigue tests were performed at 538°C (1000°F) at limited sets of test conditions. Analyses were performed to: (1) assess variations of microstructure, mechanical properties, and LCF failure initiation sites as functions of disk processing and loading conditions; and (2) compare mean and minimum fatigue life predictions using different approaches for modeling the data from assorted test conditions.

Significant variations in life were observed as functions of the disk-processing variables evaluated. However, the lives of all specimens could still be combined and modeled together. The failure initiation sites for tests performed at a strain ratio Rε = εmin/εmax of 0 were different from those in tests at a strain ratio of - 1. An approach could still be applied to account for the differences in mean and maximum stresses and strains. This allowed the data in tests of various conditions to be combined for more robust statistical estimates of mean and minimum lives.
Bulk Property Evaluation of a Thick Thermal Barrier Coating
Authors: Rejda EF , Socie DF , Nuel BP
Published: April 2008

Thick thermal barrier coatings (TTBCs) for diesel engine applications are being developed to improve engine performance through increased operating temperatures and lower emissions. To more completely assess the bulk properties of coating materials, a miniature test stand for the mechanical testing of coating materials independent of the substrate was developed. Using a piezoelectric translator as an actuator and a miniature load cell, it was possible to conduct uniaxial testing in both compression and tension of very small samples. In this study, room temperature deformation experiments were conducted on an air plasma-sprayed 24% CeO2-ZrO2 coating material. Mechanical properties in both the in-plane and transverse coating directions were evaluated in both compression and tension. From simple monotonic tests, the anisotropy of the material could be quantified. A key finding was that both the loading modulus and tensile strength were about two to three times higher in the in-plane direction. This anisotropy is believed to be due to the directionality of microcracking in the material. Cyclic loading experiments showed that the coating material also exhibits considerable irreversible strain behavior in both the transverse and in-plane directions. A model describing the irreversible strain behavior based on the combined sliding and closing of pre-existing microcracks is proposed and compared with experimental results. It is shown that the model describes the qualitative and quantitative aspects of the material behavior quite well, especially in compression.
Application of the Two-Parameter J-A2 Description to Ductile Crack Growth
Authors: Chao YJ , Zhu XK , Lam P-S , Louthan MR , Iyer NC
Published: April 2008

Typical ASTM fracture testing determines the J-integral resistance (J-R) curve or fracture toughness (JIC) based on specimens with high-constraint geometry such as those specified in ASTM E 1737-96. A three-term asymptotic solution with two parameters, J and A2 (a constraint parameter), has been developed for characterizing the constraint effect of various geometries. The present paper extends the J-A2 characterization of a stationary crack tip to the regime of stable crack growth. Similar to the concept of J-controlled crack growth, theJ-A2 description can be approximately used to characterize ductile crack growth under certain amount of crack extension. The region ofJ-A2controlled crack growth is much larger than that controlled by theJ-integral alone. From the relationships between A2 and the test data, JIC, and tearing modulus, TR, the coefficients used to define a J-R curve can be determined. for non-standard specimens or actual structures, once the constraint parameter A2 is determined, the J-R curves appropriate for these geometries can then be obtained. A procedure of transferring J-R curves determined from the standard ASTM procedure to non-standard specimens or flawed structures is outlined in the paper.
The Technical Basis for ASTM E 1820-98 Deformation Limits on JC
Authors: Kirk MT , Lott RG
Published: April 2008

ASTM Standard Test Method E 1820-96, “Measurement of Fracture Toughness,” was recently revised (E 1820-98). This revision includes a relaxation of the deformation limits/size requirements that must be satisfied to report a valid value of fracture toughness at instability prior to significant stable crack extension (JC). E 1820-96 required that valid JC values satisfy the following inequality (with an M value of 200). Bb0≥MJcσflow E 1820-98 relaxes this requirement to M = 100 for all metals and to M = 50 for ferritic steels. In this paper we present results from both finite element analysis and from fracture toughness testing that supports these changes. This evidence demonstrates that JC values meeting the deformation limits of E 1820-98 are specimen-size invariant. Consequently, these values can be applied with confidence in fracture integrity assessments of much larger structures.
A Strip-Yield Model for Part-Through Surface Flaws Under Monotonic Loading
Authors: Daniewicz SR , Aveline CR
Published: April 2008

A slice synthesis methodology was developed and used to construct a weight function based strip-yield model for a semi-elliptical part-through surface flaw in an elastic-perfectly plastic material under monotonie loading. The model enables rapid approximate computation of crack surface displacements and the crack front plastic zone size. A mathematical description of the model is presented. A model verification is discussed in which results from the strip-yield model were compared with results from finite element analyses. Crack surface displacements and crack mouth opening displacements from the model are shown to compare well with results from detailed three-dimensional elastic-plastic finite element analyses. Plastic zone sizes from the model were found to be significantly larger than those determined fromthe finite element model.
Local Approach to Dynamic Fracture Toughness Evaluation
Authors: Minami F , Ochiai T , Hashida T , Arimochi K , Konda N
Published: April 2008

Fracture toughness properties of structural steels of 490-MPa strength class and weld metals under dynamic loading are studied in the light of the near crack tip stress fields. The loading rate in toughness tests range from 0.1 to 500 mm/s. The near-tip stress fields are analyzed by 3D-FEM considering the strain rate effect on the flow properties of materials. Temperature rise caused by high-speed plastic deformation is also included in the FE analysis. The critical CTOD at brittle fracture initiation decreases when increasing the loading rate. This is due to the elevation of a local stress near the crack tip. The local approach is applied to the dynamic fracture toughness evaluation. It is shown that the brittle fracture resistance evaluated in terms of the Weibull stress, an integrated stress over a highly stressed region near the crack tip, is a material property independent of the loading rate. Based on the Weibull stress fracture criterion, the dynamic fracture toughness can be predicted from static toughness results. An engineering procedure to estimate the loading rate effect on the fracture toughness is also presented.
Fatigue Strength of Weld Repair Specimens Under Simulated Program Loading of an Overhead Traveling Crane
Authors: Kitsunai Y , Maeda Y , Yoshihisa E , Honda T , Sundara Raman SG
Published: April 2008

Service stresses acting on an overhead traveling crane were monitored and analyzed by the rain flow method. To assess the effectiveness of various repair schemes for components of aged overhead traveling cranes, weld-repaired gusset specimens, several kinds of plate specimens with cracks repaired by welding, and cover plate specimens were fabricated,and the fatigue strength of the weld-repaired specimens was evaluated under a program loading determined from the monitored service stresses. The fatigue strength of weld-repaired gusset plate specimens was approximately the same as that of uncracked gusset plate specimens, because the fatigue crack always initiated from the weld toe of the as-welded side in both specimens. The fatigue strength of one-surface repaired specimens decreased with an increase in the initial crack length. In case of one-surface repaired specimens with the initial crack length beyond half of the specimen width and one-surface cover plate specimens, the fatigue strength did not satisfy the design requirement. On the other hand, the specimens with cracks repaired completely by welding on both surfaces displayed sufficient fatigue strength to satisfy the requirement. The fatigue crack growth rate of the weld-repaired gusset specimens under the program loading was correlated with an effective stress intensity factor range, which considered the effect of residual stresses.
Effect of Moisture on Fracture Toughness of Composite/Wood Bonded Interfaces
Authors: Qiao P , Davalos JF , Trimble BS
Published: April 2008

Current research on wood reinforcement has focused on the use of fiber-reinforced plastic (FRP) strips or fabrics bonded to wood members. Although significant increases in stiffness and strength have been achieved by this reinforcing technique, there is a concern about the reliable performance of the wood-FRP interface bond, which can be susceptible to delamination. The objective of this study is to present a combined analytical/experimental study to evaluate the effect of moisture on fracture toughness of composite/wood bonded interfaces under Mode I loading. A contoured double cantilever beam (CDCB) specimen is used to characterize the fracture toughness of both wood-wood and wood-FRP samples. The specimens are designed by the Rayleigh Ritz method to achieve a linear rate of compliance with respect to crack length and are calibrated experimentally and also analytically by the finite element method. Both wood-wood and wood-FRP samples are tested under dry and wet conditions, and bonded interface fracture toughness data under Mode I loading are obtained. The guidelines and procedures for the modeling and design of CDCB specimens for hybrid or dissimilar adherends using a Rayleigh-Ritz model are presented briefly, and a modified Rayleigh-Ritz method is further developed. The effect of moisture on fracture toughness is evaluated, and increases in interface fracture toughness are observed due to moisture absorption for wet wood-wood and wood-FRP samples; the toughening of the interface under moisture is due mainly to a much more plastic fracture failure mode of the interface.
Mitigating the Corrosion of Concrete Pipe and Manholes
Authors: Bell LW , Shook WE , Norris T
Published: April 2008

This paper deals with the problems of corrosion caused by sulfuric acid generated within sewer systems. The problems are identified and potential economical solutions are presented. There are four major ways to mitigate the corrosion of concrete pipe and manholes, due to sulfuric acid produced in a sewer system: • Utilize Az design to elevate the alkalinity of the concrete. • Coat or line the pipe and structure. • Reduce the microbial induced corrosion (MIC), using computer model designs. • Use acid-resistant cements and antibacterial additives.

The last two methods will be discussed at length because they are the most cost-effective means of extending the life of concrete in a sewer system. By reducing the generation of hydrogen sulfide and at the same time reducing the microbial activity in the system, MIC is effectively reduced. Also, by incorporating acid resistant cements and antibacterial additives, concrete in sewer systems will experience less or no corrosion; thus the life of the sewer system is extended.
Case History of the Installation of a Sanitary Sewer Microtunnel Project
Authors: Meyer JJ , Whitehouse T
Published: April 2008

This Milwaukee Metropolitan Sewerage District project will require 3200 feet (975m) of 30 inch (750mm) diameter reinforced concrete microtunnel pipe to be installed at depths up to 64 feet (19m).

This specific design of microtunneling pipe was submitted to the owners by the low-bid installer and was accepted as an equal alternate to the original specifications. Microtunneling is a fairly new installation process, the technology of which allows for the trenchless installation of buried conduit while minimizing the need to disturb the street surfaces and/or private properties.

The project is scheduled to start June, 1998 and has an August, 1999 completion date.
Flexural and Tensile Properties of a Two-Dimensional Nicalon™ -Reinforced Sylramic™ S-200 Ceramic Matrix Composite
Authors: Gonczy ST , Jenkins MG
Published: April 2008

A round robin study of mechanical test methods provided an opportunity for direct comparison of flexural and tensile test methods and results for one hundred ninety test specimens (one hundred flexure and ninety tension) of a commercial ceramic fiberreinforced ceramic matrix composite (Sylramic™ S-200) consisting of eight plies of ceramic grade (CG)-Nicalon™ eight harness satin weave (8HSW) fabric in a silicon-carbonitride matrix (Sylramic™) with a boron-nitride-containing interphase coating. Flexural test specimens (110 × 9 × 3 mm) were tested in four-point quarter-point loading per ASTM Test Method for Flexural Properties of Continuous Fiber-Reinforced Advanced Ceramic Composites (C 1341). Grand means for the ultimate “flexural strength,” flexural strain at ultimate “flexural strength,” and elastic modulus in flexure for the ten laboratories, were 339 MPa, 4640 μm/m and 93 GPa, respectively. The dog-bone tensile test specimens (150 × 12 × 3 mm) were tested per ASTM Test Method for Monotonic Tensile Strength Testing of Continuous Fiber-Reinforced Advanced Ceramics with Solid Rectangular Cross-section Specimens at Ambient Temperatures (C 1275). Grand means for ultimate tensile strength, strain at ultimate tensile strength, and elastic modulus for the nine laboratories were 251 MPa, 4310 μm/m and 93 GPa, respectively. A key finding was that the ultimate flexural strength values calculated from the conventional beam bending equations are not representative of the measured ultimate tensile strength. The key material variable was the tensile strength of the coated ceramic fibers, rather than fiber volume fraction, bulk density, or open porosity. Dimensional measurements was a key experimental variable.
Fiber Test Development for Ceramic Composite Thermomechanical Properties
Authors: DiCarlo JA , Yun HM
Published: April 2008

Many of the key thermomechanical tensile properties of continuous-fiber ceramic composites (CFCC), such as ultimate fast-fracture strength and long-term rupture strength, are controlled by the deformation and fracture properties of the reinforcing fibers. For this reason, research efforts are ongoing at NASA to develop fiber test procedures and composite property models that will allow use of the fiber data to accurately predict these CFCC strength properties for a variety of potential application conditions. Because of the current interest in two-dimensional woven composites, emphasis is being placed on the testing of single small-diameter fibers and single-ply fabrics. The primary objective of this paper is to review the status of these efforts. It is shown that the fabric tests and procedures need further development in order to use bundle strength theory to predict the fast-fracture strength of as-fabricated CFCC. On the other hand, the single-fiber tests using simple composite rupture models yield predictions in good agreement with available data for CFCC rupture strength at high temperatures.
Effect of Fiber Waviness on the Tensile Response of 2D C(f)/SiC Ceramic Matrix Composites
Authors: Steen M
Published: April 2008

The mastercurve approach was employed to analyze the response of a satin weave and a plain weave reinforced C(f)/SiC ceramic matrix composite under tensile loading at both room and elevated temperatures. For each test specimen, the mastercurve was used to determine the magnitude of the axial residual stresses and to derive the “actual” values of the constituent properties, namely the first additional matrix cracking stress and the fiber fracture stress. It is shown that the waviness of the fiber reinforcement affects the matrix cracking stress but that the type of weave does not influence the in-situ fiber strength properties.
The Time-Dependent Deformation of Carbon Fiber-Reinforced Melt-Infiltrated Silicon Carbide Ceramic Matrix Composites: Stress-Rupture and Stress-Relaxation Behavior in Air at 1000°C
Authors: Lara-Curzio E , Singh M
Published: April 2008

The stress-rupture and stress-relaxation behavior of carbon fiber-reinforced melt-infiltrated silicon carbide composites was investigated in ambient air at 1000°C. It was found that the compliance of the material increases continuously with time when subjected either to a constant composite stress or strain in air at 1000°C. The changes in compliance are explained based on the oxidation of the fiber coating, and on the oxidation, loss of cross-sectional area and rupture of the reinforcing fibers. In the case of stress-rupture, the load previously carried by failed fibers is redistributed to their surviving neighboring fibers inducing further fiber failure. During stress-relaxation, fiber failure is reflected directly on the reduction of the load carried by the composite.

By monitoring the expansion of the specimens during heating, prior to the application of the stress or strain, it was possible to determine the liner coefficients of thermal expansion of the material between 200°C and 1000°C.
The Relationship between Interphase Oxidation and Time-Dependent Failure in SiCf/ SiCm Composites
Authors: Lewinsohn CA , Henager CH , Simonen EP , Windisch CF , Jones RH
Published: April 2008

Flaw-tolerant ceramic matrix composites typically possess an interphase between the reinforcing fibers and the matrix that allows debonding for desirable mechanical properties. However, commonly used interphase materials, such as carbon and boron nitride, are susceptible to oxidation at elevated temperatures. In general, oxidation of interphase materials produces gases and voids between the fibers and the matrix leading to an increase in the compliance of bridging fibers and a subsequent decrease in the toughening increment due to fiber bridging. On the other hand, silicon carbide fibers and matrices oxidize to form solid reaction products (oxides), leading to increased bonding between fibers and the matrix. A competition between interphase oxidation and the formation of solid oxide phases determines the composite failure mechanism under a given set of environmental conditions. The mechanisms by which oxidation degrade the mechanical properties of SiCf/SiCm will be discussed. Techniques for identifying failure mechanisms and approaches to modeling component lifetimes will be presented.
Characterization of Damage Accumulation in a Carbon Fiber-Reinforced Silicon Carbide Ceramic Matrix Composite (C/SiC) Subjected to Mechanical Loadings at Intermediate Temperature
Authors: Verrilli M , Kantzos P , Telesman J
Published: April 2008

Creep-rupture and fatigue tests were conducted to identify the failure modes and degradation mechanisms of a [0/90] carbon fiber reinforced silicon carbide (C/SiC) composite at 550 and 650°C. When compared on a maximum stress versus time to failure basis at a given temperature, fatigue testing yielded longer lives than creep-rupture testing. Tests conducted at 550°C had longer lives than 650°C tests. The rate of modulus degradation was similar for both temperatures and loading modes. Examination of tested specimens revealed that oxidation of the carbon fibers was the dominant damage mechanism for C/SiC at these temperatures and test conditions. The oxidation damage occurred globally within the surface of the specimen gage section, and locally in the interior of the composite, around pre-existing matrix cracks and pores. The results of this study indicate that, under the test conditions employed here, specimen life is governed by a combination of time at temperature and time-averaged stress and is not cycle dependent.
Sports Injury Surveillance: Foundations of Data Collection
Authors: Powell JW
Published: April 2008

Research programs aimed at reducing the injury potential for young athletes are based on the quality of the data available for analysis. In developing a protocol for studying risk patterns for sports, the first priority is to have a thorough knowledge of the baseline injury pattern. Whatever safety interventions are designed and implemented, there must be a mechanism for evaluating the intervention and its impact on existing injury pattern. The quality of the available data and its utility in decision-making is based on the breadth and depth of the data collection process. Today's technology has made available to the researcher a new cadre of approaches to routine injury data collection. This paper discusses some of the important procedural areas that must be addressed in the design of an injury data collection system. It examines administrative issues, data collection and management approaches, and data analysis models.
Comparison of International Safety Standards for Ice Hockey Helmets
Authors: Pearsall DJ , Wall RE , Hoshizaki BT
Published: April 2008

The purpose of this study was to determine the similarities of international certification standards for ice hockey helmets. The American Society for Testing and Materials (ASTM), Committee European de Normalization (CEN), Canadian Standards Association (CSA) and International Organization for Standardization (ISO) protocols were compared. Only the impact testing methods at ambient temperatures were examined. Four helmet models, currently available to consumers, were used for testing. No significant differences (p<0.05) were found between the standards in a rank order comparison. Further analysis of differences, with peak accelerations separated by impact locations showed significant differences (p<0.05) between all standards, at four of the six defined impact sites, with no differences being found between standards at the side and front sites. Post-hoc pairwise multiple comparisons also showed significant performance differences (p<0.05) between helmet models.
The Single Strap Helmet Fixation System in Intercollegiate Ice Hockey: A Source of Variable Face Protection
Authors: LaPrade RF , Broxterman RJ
Published: April 2008

Mandatory use of face masks in intercollegiate ice hockey has resulted in a decrease in the incidence of facial lacerations (1). However, it has been noted that a single helmet strap does not securely fix helmets with this type of fixation system well on the head, which results on the helmet moving during the course of a collision which may contribute to the existing frequency of facial lacerations. The purpose of this prospective study is to report on the types of injuries seen with the single strap helmet fixation system in intercollegiate ice hockey. Over the course of three varsity intercollegiate ice hockey seasons, the occurrence, location, and mechanism of facial lacerations were recorded at the University of Minnesota. The total number of facial lacerations was 26. Of these 26 lacerations; 16 occurred due to the face mask colliding with the face as it tilted back on the head during a collision; 5 were the result of anterior tipping of the face mask where the nose was in turn lacerated. It is proposed that further studies be performed to evaluate the role of alternative helmet fixation systems in reducing the incidence of facial lacerations.
Care and Transport of Injured Participants with Potential Spine Injuries from Ice Rinks
Authors: LaPrade RF , Broxterman RJ , Bahr M , Wentorf FA , Feist RJ , Cardinal KJ , Freed J
Published: April 2008

In this paper the safety issues involving the proper immobilization of the cervical spine and the transfer mechanisms necessary to secure an injured athlete prior to moving them off the ice are reviewed. It is recommended that the helmet be left on during this process to provide stability to the cervical spine. All medical teams which care for ice hockey athletes should follow and rehearse this technique.