bluuebunny/crossref_metadata_2025 huggingface dataset:
Interim Results from the Heavy Section Steel Technology (HSST) Shallow-Crack Fracture Toughness Program
Authors: Theiss TJ , Shum DKM , Rolfe ST
Published: March 2009

The Heavy Section Steel Technology Program (HSST) is investigating the influence of flaw depth on the fracture toughness of reactor pressure vessel (RPV) steel. Recently, it has been shown that shallow cracks tend to exhibit an elevated toughness as a result of a loss of constraint at the crack tip. The HSST investigation is a joint analytical/experimental study combining the use of shallow-cracked laboratory specimens with finite element analysis. All tests have been performed on beam specimens loaded in three-point bending using specimens about 100 mm deep. Primarily two crack depths have been considered: a = 50 and 10 mm (a/W = 0.5 and 0.1). Test results indicate a significant increase in the fracture toughness associated with the shallow-flaw specimens in the lower transition region compared to the conventional fracture toughness. Little or no toughness increase is present on the lower shelf where linear elastic behavior takes place. In addition, the test data indicate that specimen thickness had little influence on fracture toughness for either the deep- or shallow-crack specimens.

Posttest analyses were performed for the deep- and shallow-crack specimens to compare the experimental and analytical toughness values and to quantify the constraint in terms of the Q-stress parameter. The Q stress at initiation was found to be about 0 for the deep-crack beam and about -0.7 for the shallow-crack beams. These results indicate no loss of constraint in the deep-crack specimens but a significant constraint loss in the shallow-crack specimens, which is consistent with observed behavior. The posttest analysis has been used to construct a Jc(Q) locus of toughness data.
A Theoretical Framework for Addressing Fracture in the Ductile-Brittle Transition Region
Authors: Anderson TL , Stienstra D , Dodds RH
Published: March 2009

Fracture in the ductile-brittle transition region of ferritic steels is complicated by scatter, produced by local sampling effects, and specimen geometry dependence, which results from relaxation in crack tip constraint. Scatter and constraint are interrelated in that each influences the magnitude of the other. This article summarizes recent research on fracture in the transition region and presents a unified framework for addressing size effects and scatter.

A stress volume model for quantifying constraint effects is described briefly, and a comparison between theory and experiment is presented. This model has been applied only to stationary cracks in plane strain, but methods to account for ductile crack growth and three-dimensional effects are described.

The inadequacies of the weakest link model for cleavage fracture are discussed, and an improved statistical model is introduced. This new model considers the probability of propagation and arrest of cleavage microcracks.

A number of recommendations for analyzing cleavage fracture toughness data are presented. Transition region data for a given material should be viewed as a statistical distribution rather than a single value. However, these data should be corrected for constraint effects and ductile crack growth before applying statistical analysis. One of several statistical distributions may be applied to cleavage data; each of the proposed distribution functions has advantages and disadvantages. One of the unknowns in transition region fracture is the threshold toughness of the material, that is, the absolute lower bound.
Evaluation of Elastic-Plastic Fracture Toughness Testing in the Transition Region through Japanese Interlaboratory Tests
Authors: Iwadate T , Yokobori T
Published: March 2009

International cooperative interlaboratory test programs on elastic-plastic fracture toughness in the transition region have been conducted under the 129th Committee, Japan Society for the Promotion of Science (JSPS), and the Materials Properties Council (MPC). The objective of the tests is to obtain basic information regarding the measurement of lower-bound fracture toughness of steels using small specimens. The test program used ASTM A508 Class 3 steel. The 19 laboratories participated in these programs. Tests were carried out with 25.4-mm (1-in.) thick compact tension (1T-CT) specimens at three temperatures, -100°C (T1), -75°C (T2), and -50°C (T3). In addition to the interlaboratory tests, the effect of strain rate on small-specimen fracture toughness behavior was also investigated.

The Japanese test results provided some information to standardize a method for measuring the lower-bound fracture toughness of steels. Small-specimen fracture toughness KJc values indicated a wide scatter, especially in the higher temperature or in the lower strain rate or both. The causes of the scatter of KJc values typically depend on the stable crack growth, Δa0, the distance from stable crack front to trigger point, X, and the distance from fatigue crack front to trigger point, Δa0 + X. No effect of grain size and material cleanliness and slight effect of sampling location of the specimens and difference of the testing conditions between laboratories were observed. The KJc value at Δa0 = 0, X = 0, and Δa0 + X = 0 was defined as a lower-bound fracture toughness KJci, because additional study using A470 Ni-Cr-Mo-V rotor steel showed that the KJci value coincides well with the lower bound of large-specimen fracture toughness KIc per the ASTM Standard Test Method for Plane-Strain Fracture Toughness of Metallic Materials (E 399). Test results also indicated that the KJci value corresponds to 3% fracture probability toughness of the steel.

Based on these test results, the guidelines on the measurement of Δa0, X and Δa0 + X were established, and the tentative test procedure for the determination of the lower-bound fracture toughness using a fractographic data analysis has been developed by the JSPS 129th Committee.
Effect of Strain Rate on Small Specimen Fracture Toughness in the Transition Region
Authors: Iwadate T , Kusuhashi M , Tanaka Y
Published: March 2009

Static and dynamic fracture toughness tests were performed in the transition region for two ASTM A508 Class 3 steels using 25.4-mm (1-in.) thick compact tension (1T-CT) specimens and precracked instrumented Charpy specimens. The strain rate in terms of K ranged from 1.6 to 6.5 × 105 MPa.m1/2/s. The KJc values converted from Jc of small specimens indicated a wide scatter. When the strain rate increases, the dynamic fracture toughness transition curves shift to higher temperature region, and they give the lower-bound fracture toughness of the steels. Increasing the strain rate reduces the scatter of KJc values dramatically, especially in the higher temperature region and decreases the lower-bound fracture toughness. Fractographic examination of the fractured specimen surfaces indicated that the KJc versus stable crack growth. Δa0, distance from stable crack front to trigger point, X, and distance from fatigue crack front to trigger point, Δa0 + X, relationships construct each single curve even in the case of higher strain rate. The scatter of KJc values is caused by the variance in the amount of Δa0, X, and Δa0 + X. With increasing strain rate, the amount of Δa0, X, and Δa0 + X decreases significantly, which leads to the small scatter of KJc values. The KJc values at Δa0 = 0, X = 0, and Δa0 + X = 0 are proposed as the lower-bound fracture toughness of a steel, which are labeled KJci. The shape of KJci versus temperature curve is controlled by the critical stretch zone width, SZWc, which was confirmed by the fact that the KJc values are proportional to the amount of SZWc. The Weibull slope m of fracture toughness KJc values becomes larger with increasing strain rate and decreasing temperature. Higher toughness data with larger stable crack extension than 100 μm violates the linearity of Weibull plots and makes a bilinear relationship. In the statistical approach to determine the lower-bound fracture toughness in the transition region, much more analytical development is needed. The average of KJc values with 3% fracture probability coincide with the KJci value in the lower temperature region even in higher strain rate tests.
An Interpretation of the Scatter in Brittle - Ductile Transition Region As a Statistical Event as a Result of the Two Different Populations
Authors: Yokobori T , Ichikawa M
Published: March 2009

The scatter of fracture toughness in the brittle-ductile transition region may contain cleavage growth-affected (brittle) fracture and ductile growth-affected (ductile) fracture resulting from the fracture of two different types. The mechanism of the fracture of these two types may be considered as different. In this article, the data by the Japan Society for Promotion of Science (JSPS) round robin tests have been analyzed using this concept. The mechanism proposed herein may be related to the results of round robin tests, which show extremely small stable crack growth length in the lower portion and considerable stable crack growth length in the upper portion of the curve plotted using the mean rank.
Resistance Curve Analysis of Surface Cracks
Authors: Ernst HA , Rush PJ , McCabe DE
Published: March 2009

In this work, elastic-plastic fracture mechanics (EPFM) methods are extended to study the behavior of surface cracks. The material used is a tungsten inert gas (TIG) welded 2219-aluminum alloy, welded with 2319 weld wire. Calibration and a crack-growth test were performed. A multiple specimen R-curve technique was used. A group of specimens with the same initial crack geometry was tested to different deformation values. Several different groups were considered. Crack extension as a function of position along the crack front was determined and digitized into data files. A method to estimate values of the J integral as a function of position is presented. Local resistance curves were obtained. A parameter to characterize constraint is proposed. It is only based on the elastic solution for G. It is shown that the slopes of the resistance curves are uniquely related to the constraint parameter for all cases considered.
Simpler JIc Test and Data Analysis Procedures for High-Strength Steels
Authors: Underwood JH , Troiano EJ , Abbott RT
Published: March 2009

Tests of five medium- and high-strength steels were used to investigate some prospective simplifications in JIc test and data analysis procedures. Three-point bend specimens with material strengths of 500 to 1500 MPa and a nominal thickness of 10 mm were tested at room temperature. The investigation included: (1) JIc tests using measured crack-mouth displacement to calculate load-line displacement based on an expression that relates the two displace ments; (2) a simple zero-point adjustment for J versus Δa curves, whereby certain intermediate Δa values are shifted to the blunting line to correct for errors at low values of Δa; (3) a comparison of Δa and JIc results from the load-drop method, which gives a simple measure of crack growth after maximum load, with results from the usual unloading compliance method.

The various results and comparisons are discussed in relation to their usefulness as a general JIc test procedure for a variety of materials or a limited use test for certain materials. Two specific test and data analysis procedures are proposed for general use in JIc testing, as follows: 1. A new expression is described that calculates load-line displacement for the bend specimen from measured crack-mouth displacement, for a range of a/W values and strain-hardening exponents. The expression makes possible a single-displacement unloading compliance JIc test for the bend specimen, using a single, standard, crack-mouth clip gage. 2. A simple zero-shift procedure is proposed for general use with JIc tests and for addition to ASTM Test Method for JIc, a Measure of Fracture Toughness (E 813). The procedure adjusts the zero point of Δa so that on average the Δa values lie on the blunting line over the J range of 20 to 60% of the provisional fracture toughness, JQ. The adjustment calculations can be done with a calculator or a few lines of computer code.
R-Curve, Energy Dissipation Rate, and Crack Opening Angle Models for Large Amounts of Ductile Crack Growth in Bending
Authors: Turner CE
Published: March 2009

Stable crack growth taken to large growths in the fully plastic state is characterized through the true energy dissipation rate, D, for real elastic-plastic (rep) material. The term is shown to be very closely related to the crack-opening angle (COA) model. A J-type R curve, Jdis, can be formed that degenerates exactly to G for linear-elastic fracture mechanics (LEFM). Unlike conventional J-based models for growth, it satisfies conservation of energy for the rep case and is not a function of crack growth rate in the rigid plastic limit. The dissipation rate, D, can be split into areal and volumetric components. These components, and also the COA, are geometry-dependent thereby offering an explanation for the size-dependent trends seen for R curves in the literature. The specific intensities of these rates of energy dissipation (SIRED) are also likely to be functions of constraint, but the known data are too sparse to allow a definite conclusion. Nevertheless, the use of areal and volumetric components of energy dissipation offers a new route for the conditional transference of estimates of R-curve data from one configuration to another.
Dislocation Emission and Dynamics Under the Stress Singularity at the Crack Tip and Its Application to the Dynamic Loading Effect on Fracture Toughness
Authors: Yokobori AT , Iwadate T , Isogai T
Published: March 2009

In previous work, computer simulation of dislocation emission and motion was carried out considering the stress singularity near the crack tip. It was found that there is a region in which no dislocation exists along the slip plane near the stressed source, namely, a dislocation free zone (DFZ), and that there is an inverse pileup of dislocations against the tip of this DFZ. A formula was obtained correlating the maximum dislocation density with the DFZ length.

Based on those results, an evaluation has now been attempted for fracture toughness within the brittle-ductile transition range of steel. The effect of dynamic loading on the fracture toughness and trigger point observed in the experimental results reported in the literature is explained.
Fracture Criteria for Surface Cracks in Brittle Materials
Authors: Reuter WG , Newman JC , Macdonald BD , Powell SR
Published: March 2009

If a structural material behaves in a linearly elastic manner, it is generally assumed that plane-strain fracture toughness (KIc) and a proven equation for calculating an applied stress-intensity factor can be used to predict conditions for catastrophic fracture. The adequacy of this approach has been verified for some specific applications, generally through-cracks in plate material. Recent fracture test results and analyses of surface cracks in brittle materials have raised a concern about the validity of using KIc and the maximum value of the calculated stress-intensity factors to predict fracture conditions. This paper presents test data and results obtained from different procedures, all based on KIc, for predicting failure for three-dimensional surface cracks.
The Crack Tip Opening Displacement and J Integral Under Strain Control and Fully Plastic Conditions Estimated by the Engineering Treatment Model for Plane Stress Tension
Authors: Schwalbe K-H
Published: March 2009

The Engineering Treatment Model (ETM) relates the crack tip opening displacement (CTOD) and the J integral with the applied load or applied strain using a geometry independent, master-curve-type, equation. In the present paper, CTOD and J were examined as a function of the applied strain by means of comparing ETM predictions with earlier experimental and numerical results. A comparison was also made with a theoretical solution by Shih and Hutchinson. It was concluded that the ETM provides useful engineering approximations.
Fracture Capacity of High Flux Isotope Reactor (HFIR) Vessel with Random Crack Size and Toughness
Authors: Chang S-J
Published: March 2009

The probability of fracture versus a range of applied hoop stresses along the high flux isotope reactor (HFIR) vessel is obtained as an estimate of its fracture capacity. Both the crack size and the fracture toughness are assumed to be random variables and subject to assumed distribution functions. Possible hoop stress is based on the numerical solution of the vessel response by applying a point pressure-pulse at the center of the fluid volume within the vessel. Both the fluid-structure interaction and radiation embrittlement are taken into consideration. Elastic fracture mechanics is used throughout the analysis. The probability function of fracture for a single crack due to either a variable crack depth or a variable toughness is derived. Both the variable crack size and the variable toughness are assumed to follow known distributions. The probability of vessel fracture with a multiple number of cracks is then obtained as a function of the applied hoop stress. The probability of fracture function is, then, extended to include different levels of confidence and variability. It, therefore, enables one to estimate the high confidence and low probability fracture capacity of the reactor vessel under a range of accident loading conditions.
Simulation of Fatigue Crack Growth of an Inclined Elliptically Shaped Subsurface Crack in Residual Stress Fields
Authors: Mayrhofer K , Fischer FD , Parteder E
Published: March 2009

The influence of a residual stress field on the fatigue crack growth was investigated by a numerical simulation for an inclined elliptically shaped subsurface crack in a half space. The necessary opening mode stress intensity factors Kl caused by the resulting stress field were calculated by means of the singular integral equation method. The crack growth analyses were conducted by the application of linear elastic fracture mechanics using the Paris law relationship between Kl and da/dN.
Surface Crack Growth in Inconel 718 During Large Unload-Reload Cycles
Authors: McClung RC , Hudak SJ
Published: March 2009

Thin Inconel 718 plates with deep (a/t = 0.6 to 0.9) semicircular surface flaws were subjected to different numbers of large load-unload-reload cycles with various minimum and maximum loads and crack mouth displacements. Elastic compliance measurements and marker bands were used to estimate crack lengths at each cycle of interest. Crack growth was analyzed from the perspective of low-cycle fatigue crack propagation using ΔJeff as the correlating parameter. Calculations of ΔJeff were based on a modified version of the reference stress estimate that takes crack closure into account. Results from these tests were correlated consistently with both resistance curve data and baseline small-scale yielding fatigue crack growth data. The development of the crack shape during both single-cycle ductile tearing and multiple-cycle fatigue crack growth was characterized.
Effects of Cyclic Loading on the Deformation and Elastic-Plastic Fracture Behavior of a Cast Stainless Steel
Authors: Joyce JA , Hackett EM , Roe C
Published: March 2009

The objective of this program was to develop the appropriate material properties to characterize the cyclic tensile deformation, cyclic elastic-plastic crack growth, and the ductile tearing resistance of a pipe elbow made from a cast stainless steel equivalent to ASME SA-351CF8M. This material was used for large-scale tests in the high level vibration test program, which applied intense cyclic loadings to reactor piping system components and revealed that fatigue crack growth could be a serious problem in these components. The tests conducted included monotonic and cyclic tension tests, monotonic J-R curve tests, and cyclic elastic and elastic-plastic fatigue crack growth rate tests. The cyclic elastic-plastic fracture behavior of the stainless steel was of primary concern and was evaluated using a cyclic J-integral approach.

It was found that the cast stainless steel was very resistant to ductile crack extension. J-resistance curves essentially followed a blunting behavior to very high J levels. High cycle fatigue crack growth rate data obtained on this stainless steel was typical of that reported in standard textbooks. Low cycle fatigue crack growth rate data obtained on this material using the cyclic J-integral approach was consistent with the high cycle fatigue crack growth rate and with a standard textbook correlation equation typical for this type of material. Evaluation of crack closure effects was essential to determine accurately the crack driving force for cyclic elastic-plastic crack growth in this material.
General Purpose Software for Fatigue Testing
Authors: Dharmavasan S , Peers SMC
Published: March 2009

Recently, most manufacturers of servohydraulic materials test equipment have developed digital control systems. Digital systems have several advantages over the more mature analog controllers, in particular, the availability of features that allow more realistic tests to be carried out. Also, the ability to interface and communicate with computers easily makes it possible to perform not only realistic but also very complex control and data acquisition tasks. However, the software required to define these complex tasks and communicate with digital controllers is demanding.

The development of digital controllers has been made possible by the tremendous advances in microprocessor technology. These developments have also given rise to computers with everincreasing capabilities at lower costs. The software architectures controlling these computers have also given rise to sophisticated developments in order to make the computers easier to use. Most computers now have some form of graphical user interface (GUI). The downside of most GUIs is that the development of application software is much more complex. In addition, most of these operating systems are not ideally suited for real-time control that is absolutely vital for automated fatigue testing.

The difficulties associated with developing software for specific fatigue tests may be somewhat alleviated by the development of suitable tools within an integrated architecture that allow the scientist/engineer to define the required test in the form of functional blocks. This type of general-purpose software can then take the test definition provided by the scientist and convert it into a form suitable for the digital controller.

A suitable test description paradigm is proposed in terms of general requirements; a test-description language with elements such as objects, functional blocks, time, events, and data presentation; and some specific requirements for a software development environment. From this, general-purpose software for automated fatigue testing can be developed and used at a high level of abstraction. In addition, the paper reviews the development of an integrated general-purpose program for automated fatigue testing that implements the functional blocks required but without the full test description language. The paper also uses the example of testing offshore structural components using realistic sea-state sequences, such as WASH, to illustrate the problems that must be solved.

Some implications of this approach in future fatigue testing applications are also discussed in the paper.
An Automated Image Processing System for the Measurement of Short Fatigue Cracks at Room and Elevated Temperatures
Authors: Yi L , Smith RA , Grabowski L
Published: March 2009

An automated short crack monitoring and testing system has been developed that is fully controlled by purpose-written software. This is capable of testing and monitoring the growth of short surface breaking cracks as small as 10 μm in notched and plain specimens subject to fatigue cycling up to temperatures of 700°C. Using this new system, short fatigue crack growth data have been obtained in Waspaloy at room and elevated temperatures in a faster and more easy manner compared to the conventional methods involving surface replication techniques.
Automated Data Acquisition and Data Bank Storage of Mechanical Test Data: An Integrated Approach
Authors: Bracke G , Bressers J , Steen M , Over HH
Published: March 2009

The Mechanical Performance Laboratory of the Institute for Advanced Materials/Joint Research Centre (IAM/JRC) in Petten houses a range of universal and bend testing machines, used to generate tensile, creep, fatigue, and crack growth data on structural materials. A decentralized concept of data automation is implemented, in which each testing machine or group of testing machines is equipped with a dedicated PC for control and data acquisition purposes. All PCs are linked in a network, allowing data analysis and editing from any computer in the network and enabling the transfer of files to other users, for example, the High Temperature Materials Data Bank. The major criteria for selecting the chosen concept are user friendliness and flexibility. The potential of the automation system is illustrated with the help of examples relating to the computer-assisted alignment of a test specimen in a testing machine, to thermomechanical fatigue testing, and to a computer vision system for the in situ tracking of microcracks during thermomechanical fatigue testing.
The Significance of Variable Amplitude Fatigue Testing
Authors: Schütz D , Heuler P
Published: March 2009

Experimental fatigue and durability assessment plays a prominent role in light-weight design. There is broad evidence, however, that the fatigue strength of materials and structures determined under constant amplitude loading may be not relevant—quantitatively or even qualitatively—for variable amplitude or spectrum loading. Various phenomena both on a microstructural and a macrostructural level contribute to this finding as discussed in the paper including consideration of the fatigue limit, the role of crack growth mechanisms and fracture surface topography, residual stresses, scatter, relative proportions of crack initiation and crack propagation phases, detection of fatigue-critical locations, and ranking of materials and design details. Some general aspects regarding the application of variable amplitude testing for design and clearance purposes such as the required experimental efforts are also considered.
Automated Fatigue Test System for Spectrum Loading Simulation of Railroad Rail Cracks
Authors: Jablonski DA
Published: March 2009

A digital servohydraulic test system has been utilized to apply stress spectra, which represented the railhead stress cycles caused by passage of a train, on laboratory compact tension specimens. The system was designed so that tasks that required immediate action were built into the machine controller firmware. Tasks that did not require immediate action were generally performed in the control software on a personal computer. This system was utilized to measure fatigue life of railroad rails under real-life stress spectra that represented the reconstructed railhead stresses for various types of trains. A stress intensity mapping procedure was utilized to simulate the railhead “detail fracture” in laboratory compact tension specimens.

This test system was used to measure fatigue crack growth rate under five different stress spectra. Two of the stress spectra were ordered according to decreasing maximum stress (DMS). The fatigue crack growth rate and crack closure behavior were different for the real sequence ordered (RSO) and decreasing maximum stress ordered (DMS) spectra. Constant amplitude fatigue crack growth rate was measured at three different stress ratios to develop a fatigue crack growth rate model for the material. The fatigue crack growth rate could be modeled with either a modified Walker equation that accounted for stress ratio effects or with an effective ΔK model that accounted for crack closure effects. The constant amplitude test data were used to predict the spectrum load crack growth rates using a modified Palmgren-Miner's rule. The predictions based upon the modified Walker equation were nonconservative. Predictions based upon constant amplitude test data, when corrected for crack closure effects, compared well with the experimental results.
Crack Closure Measurements and Analysis of Fatigue Crack Propagation Under Variable Amplitude Loading
Authors: Amzallag C , Le Duff J-A , Robin C , Mottet G
Published: March 2009

An experimental program has been conducted on a Type 316L stainless steel to analyze the behavior of surface and embedded metallurgical defects in components.

Crack closure measurements have been performed under plane stress and plane strain conditions, under constant amplitude loading, and after overloads.

The crack opening load was measured by four different methods including surface, center, and bulk measurements.

Fatigue crack growth rates were determined, at different R ratios, under constant amplitude and under random loading conditions, using a stationary Gaussian sequence (I = 99%). Numerical analysis of the crack closure phenomenon has been carried out.

The principal results obtained are: 1. Immediately after overload, crack blunting occurs, and there is no crack closure: this fact is observed using both the different experimental measurement techniques and the calculations. 2. Under plane stress conditions, calculations have shown that crack closure decreases after overload over a distance of ∼1 mm, then increases; good agreement was found between experiments and calculations. 3. Under plane strain conditions, calculations have shown that crack closure rapidly increases after overload, the initial value is reached after ∼1 mm propagation; this was not detected experimentally because a pure plane strain state did not exist in the tested specimens. 4. The fatigue crack growth rates, da/dN, under random loading were expressed in terms of ΔKrms and ΔKeq. A better correlation of fatigue crack growth rates under constant amplitude loading and random loading was found using ΔKeq compared to ΔKrms.

The equivalent load approach is appropriate for describing the crack growth under this narrow band sequence that does not present a strong interaction between cycles. It may not be applicable to other load spectra.
A Fatigue Crack Propagation Model Under Variable Loading
Authors: Gerald J , Menegazzi A
Published: March 2009

In order to understand the behavior of metallic structures in service it is necessary to be careful in both the experimental analysis and the analytical modeling of the fatigue crack propagation under variable loading.

A relatively general model to simulate crack propagation under variable loadings is proposed. It describes the cycle-by-cycle progression of the crack. The propagation law formulation is actually a Paris law type model, transient effects are introduced through a concept of an effective SIF range, as did Elber, whose approach it generalizes.

This model offers some advantages: it remains simple, it generalizes well-know models, and the transient effect predictions are encouraging as shown in some proposed applications.
Sensitivity of Equivalent Load Crack Propagation Life Assessment to Cycle-Counting Technique
Authors: Le Pautremat E , Olagnon M , Bignonnet A
Published: March 2009

The purpose of the present study is to assess a simple prediction method for the fatigue life of structures subjected to variable amplitude loading, and to validate it in the whole range of possible irregularity factors.

This method based on an equivalent load concept (reducing the load history to constant amplitude cycles) leads to a fair prediction of fatigue life with few parameters.

Five cycle-counting methods were compared as to the determination of the equivalent load amplitude. The tests were carried out with several histories chosen either for their specific irregularity factors or to be relevant to offshore structures (WASH(W) sequence).
Fatigue Test Methods and Damage Models Used by the SNCF for Railway Vehicle Structures
Authors: Leluan A
Published: March 2009

This paper outlines the use of railway equipment structures, specifically with reference to bogie frames, and describes (1) the way of determining the spectra of stresses applied in service, (2) the tools for determining damage accumulated in structures, and (3) experimental verification of the method applied.
Using Maximum Likelihood Techniques in Evaluating Fatigue Crack Growth Curves
Authors: Cunningham SE , Annis CG
Published: March 2009

Maximum likelihood is used to develop a quantitative means for defining confidence bounds on single crack growth curves and for comparing more than one crack growth curve. The concept of likelihood is discussed, the technique is applied to the Paris crack growth law, and statistical tests appropriate for pertinent comparative situations are reviewed. Examples of each test are examined, contrasted, and compared, and a practice for engineering comparisons of crack growth rate curves is suggested. Examples using data generated in the Fracture Mechanics Lab at Pratt & Whitney are presented and discussed. These discussions will lead to a final point regarding the role of statistical methods in augmenting engineering judgment and experience.
Advances in Hysteresis Loop Analysis and Interpretation by Low-Cycle Fatigue Test Computerization
Authors: Degallaix G , Hottebart P , Seddouki A , Degallaix S
Published: March 2009

Low-cycle fatigue test computerization offers new perspectives in the analysis and interpretation of test results. Test control and data acquisition with a microcomputer allow for increased versatility and accuracy in the evaluation of pertinent characteristic parameters. A specific software package, AICYFAP, has been developed. It provides from the acquired data files 43 parameters on each hysteresis stress-strain loop, including conventional parameters, elasticity and work-hardening parameters, and loop shape parameters. The software package has been used in low-cycle fatigue studies for two kinds of materials: AISI 316L-316LN austenitic stainless steels (energy approach) and a duplex stainless steel (continuous damage mechanics approach). The AICYFAP software package appears to be a complementary tool for a better understanding of low-cycle fatigue behaviors.
Material Data Banks: Design and Use, an Example in the Automotive Industry
Authors: Diboine A
Published: March 2009

Today's engineering requires fast and easy access to various types of information, including economical, process, technical, and material data. A large number of databases that cover these fields have been launched recently. However, where the mechanical behavior material data are concerned, engineers often deal with those materials specific to their industry. Such is the case in the automotive industry. Therefore, data for these materials are often not available from large national or international databases. This is one of the reasons for developing an inhouse PC-based materials database.

This paper describes the process of designing, testing, and implementing this database. The design of the database proved to be quite difficult according to the needs for calculation, material selection, and component fatigue life assessment.

The selection and acquisition of the data to be stored is a critical problem. This project has clearly shown the importance of testing standards to guarantee the homogeneity and the reliability of the data.

Finally, the significance of the distribution and follow-up of the database is discussed.
Further Studies of Cure and Durability of Building Sealants
Authors: Beech J , Beasley J
Published: March 2009

Some results from the second phase of a two year experimental study are reported and discussed. A range of well cured commercial sealants products was exposed to natural weather and to various laboratory simulations of the factors in weather which cause degradation or changes in properties, for up to 12 months. These include heat (70°C), with and without UV(B) radiation, and artificial weathering including UV(B) radiation and moisture condensation (QUV apparatus).

The cure properties of polyurethane, silicone and poly sulphide sealants over a two year period are described. For these materials, the majority of which were well cured in the second year of the study, the effects of heat and of UV(B) radiation are discussed. Polyurethane sealants showed significant correlations between changes in modulus and in extensibility, after exposure to UV and to artificial weather. The effect of heat was more significant for polysulphides and for some silicone sealants.

As in the earlier phase of this work it was possible to demonstrate significant correlations between modulus changes in the full range of sealants after exposure to weather for twelve months and to artificial weathering for eight weeks. In addition, heat aging caused changes in extensibility that correlated highly with the effects of natural weather.
Expansion Joints in Deck Waterproofing Systems
Authors: Rutila DA , Ruggiero SS
Published: March 2009

Structural expansion joints that interrupt plaza and traffic bearing waterproofing membranes are often a source of leakage. Most joint seals in plaza type waterproofing systems are “buried,” making them difficult and expensive to maintain. Exposed joint seals in traffic bearing waterproofing systems are subject to severe loading conditions, such as vehicular traffic, but are generally accessible.

This paper presents design concepts for waterproofing expansion joints in building decks. We review assemblies commonly used to waterproof expansion joints and we examine several design concepts. Membrane/waterproofing continuity across joints and joint maintenance are of particular concern. An estimate of the joint movement is necessary to select a joint seal. Adequate drainage away from the joints remains the most important design consideration
Test Method for Evaluating Pavement Sealants Under Simultaneous Cyclic Shear and Normal Deflections
Authors: Al-Qadi IL , Abo-Qudais SA
Published: March 2009

A new method to evaluate the performance of sealants, used in rigid pavement joints, was developed. A special fixture was designed to transfer cyclic in-line deflection, applied by a testing machine, to simultaneous cyclic normal and shear deflections, at a specific ratio, on a sealant sandwiched between two-51 mm portland cement mortar cubes. The developed fixture was used to evaluate the performance of three commercially available one-component sealant types (A, B, and C): A is a low modulus silicone, B is a self leveling silicone, while C is a polyurethane used with primer.

The sealants were evaluated under both cyclic compression/shear and tension/shear tests at 25 Hz. Each sealant was evaluated at two joint widths, 6.5 mm and 19 mm. Analysis of test results indicated that sealant C performed the best with no failure after 500,000 cycles in all tests, while the performance of sealant B was the worst with cohesive failure in most cases. Sealant A, on the other hand, failed adhesively at a joint width of 6.5 mm. All sealants, not surprisingly, performed better in cyclic compression/shear than in cyclic tension/shear.
Selecting Rehabilitation and Replacement Bridge Projects
Authors: Weissmann J , Harrison R , Burns NH , Hudson WR
Published: March 2009

Evaluating the cost-effectiveness of new techniques, materials, and systems to extend bridge life frequently requires some form of life cycle analysis at the project level. Where networks are concerned, life cycle analysis can be useful in determining budgetary levels and the scheduling of activities which will ensure that maximum bridge life is obtained. As part of this latter process, a procedure developed for the state of Texas is reported, which allocates a budget for bridge replacement and rehabilitation projects using multi-attribute criteria and user-friendly computer programs. The system is a two-level closed loop procedure based on standard bridge inventory data and addresses the concerns of both state and district levels within the state. One state level program determines those bridge projects meeting FHWA financing criteria while a second program takes this subset and applies specific state criteria for project ranking and prioritization. The user of this module can rank the candidate projects using a multi-attribute technique and can complement this with an automatic qualification process based on user-defined threshold values. The multi-attribute approach uses statistical techniques applied to the entire state bridge population. Therefore, as this data set is regularly updated in accordance with FHWA requirements, it captures information on both recent deterioration and improvements to structures. A district reporting program incorporates regional knowledge of structures and their condition into the decision-making process.

The system methodology can be useful to any state officials engaged in ranking bridge projects since it incorporates managerial experience and uses statistics derived from current national bridge survey data. It also fits into the latest research findings on the development of a comprehensive bridge management system.
Retrofit of Cracked Welded Steel Bridge Girders
Authors: Pullaro JJ
Published: March 2009

A welded plate girder bridge on a main interstate highway in service for over 25 years suddenly develops a through crack in the web and flange of a fascia girder. An in-depth inspection and metallographic examination reveal the crack started in the vicinity of a welded diaphragm. The crack propagated quickly and was characteristic of a brittle fracture. Further analysis, including strain gauging and Charpy V-notch (CVN) tests, does not conclusively identify the cause for the propagation of the crack.

Fatigue analysis reveals it is very unlikely the crack could have been initiated by fatigue within the 25-year life span of the structure. The problem is traced to a 3-mm (1/8-in.) porosity defect at the root of a weld at the diaphragm connection. Propagation is attributed to out-of-plane bending in the web of the girder, high residual stresses, low toughness of steel, and cold weather.

A method for retrofitting the structure via “softening the connections” and repairing the cracked girders is selected as the course of action.
Neoprene in Bridge Bearing Pads—The Proven Performance
Authors: Burpulis JS , Seay JR , Graff RS
Published: March 2009

Elastomeric bearings have a long and successful record of performance supporting bridges, railroads, buildings, and heavy machinery. Bearings based on neoprene synthetic rubber have been in use in the United States since 1957. Today, millions of bearings based on neoprene support highway and railroad bridges throughout the world.

Elastomeric bearings are economical, effective, and require no maintenance. They are simple solid pads with no moving parts. The pad deflects in shear to accommodate expansion, contraction, and end rotation of the bridge structure. There is no need for lubrication, no need for cleaning, and no opportunity for the bearings to seize.

Sound bearing design principles have been developed based on experience accumulated over the years. This paper will highlight installations using neoprene bridge pads with 17 to 32 years service to describe the technology necessary to document their performance. Physical property data on these aged neoprene pads will be presented.
Designing Bridge Decks to Match Bridge Life Expectancy
Authors: Bettigole NH
Published: March 2009

The easiest purchasing policy to enforce is least first cost. Under TQM (total quality management), the new mandate is to obtain least life cycle cost.

Experience with highway bridge construction in the United States is that the usable life of the bridge deck is only one half of the useful life of the bridge. The average age of bridges when replaced is 68 years, and the average length of service of bridge decks before replacement is 35 years.

Bridge deck replacement during the service life of the bridge is much more costly than a new deck on a new bridge, due primarily to the requirements of traffic maintenance during the construction phase of bridge rehabilitation projects.

Estimation of the cost of construction of design options for life cycle and serviceability, although extremely difficult to document objectively, must now be accomplished. New public policy has enunciated the importance of determining relative life cycle costs.

Estimated bridge costs in the 1950s were $20 to $40 per square foot. Estimates of bridge rehabilitation cost in the 1990s will be $70 to $200 per square foot.

This paper reviews various bridge deck construction methods and the theoretical and historical comparisons which may be observed. A discussion of how design, construction, and service considerations impact life cycle cost and serviceability is included for several types of bridge deck.

In his conclusions and recommendations, the author proposes guidelines for comparing available bridge deck types. The discussion includes checklists of specific project needs, whether new or rehabilitation designs, to meet the objective of matching bridge and deck useful life.
Elastomeric Concrete: Observations and Recommendations Based on a Decade of Installation History in the United States
Authors: Watson RJ
Published: March 2009

Expansion joint systems play an important role in extending the life of bridges. Elastomeric concrete's use as an end dam or transition area material for casting expansion joints into bridge decks dates back to 1979 in the United States. While the concept has been widely successful, problems have surfaced with increased usage. Particular attention must be paid to blockout preparation, mixing of components, placement, and quality control for an elastomeric concrete installation to be successful. Recommendations for materials properties have been made which will hopefully serve as a basis for the development of an ASTM standard specification.
Fourteen Years' Service with Deep Impregnation of a Reinforced Concrete Bridge Deck
Authors: Weyers RE , Cady PD , Feeney MA , How Lum SF
Published: March 2009

A test installation of deep impregnation was applied to a heavily traveled bridge deck in Bethlehem, Pennsylvania, in 1975. The deep impregnation process involves drying the concrete, impregnating with a monomer to a depth of 3 to 4 in., and polymerizing the monomer in situ. At the time of the impregnation, the bridge deck was eight years old and the chloride contents were above the corrosion threshold level. The test area, 3.7 m2, is centered on the right wheel path of the traffic lane.

During the 14-year period, spalling and delaminations have occurred, on 20% of the deck with no evidence of spalling or delamination in the impregnated area. The deep impregnation has reduced the surface wear in the wheel path by 65%. Chloride contents have increased in both areas but at a slower rate in the impregnated area. The percent active corrosion potentials have remained the same in the nonimpregnated area but increased to 50% in the impregnated area. However, the corrosion current in the impregnated area is a factor of six less than in the nonimpregnated area. The concrete resistivity is a factor of six higher in the impregnated area and of sufficient magnitude to significantly reduce the rate of corrosion. Microscopical examination of cores showed that preexisting corrosion cells were arrested by the impregnation process.