bluuebunny/crossref_metadata_2025 huggingface dataset:
Crack Closure Behavior of Surface Cracks Under Pure Bending
Authors: Foroughi R , Radon JC
Published: February 2009

By the application of a compliance technique the fatigue crack closure behavior of surface cracks in British Standard or Low Alloy Steels, Composition and Properties (BS) 4360-50D structural steel was investigated under pure bending. Crack closure at the vicinity of surface intersection points was monitored by use of an Elber type gage, whereas the overall closure behavior was determined by means of a standard clip gage situated at the notch mouth. Under constant amplitude loading the crack opening load was larger around the surface intersection points than the overall opening load. For the range of ΔK that was considered, Kop increased with Kmax and the variation was dependent on the applied stress ratio. A comparison of the results of this study with those in the literature showed that the closure response of surface cracks under bending was less significant than that observed from the through thickness crack geometries. The closure parameter U showed an increasing trend with ΔK. However, for a low stress ratio the influence of closure was much more pronounced at small ΔK values. Presentation of the crack growth data of the surface intersection points in terms of ΔKeff produced well correlated data without any mean stress effect being observed in the mid-range regime.
Closure Measurements on Short Fatigue Cracks
Authors: Lee J-J , Sharpe WN
Published: February 2009

Single-edged notched specimens, 2.3 mm thick, of 2024-T3 aluminum were cyclicly loaded at R ratios of 0.5, 0.0, −1.0, and −2.0. The notch roots were periodically inspected with an optical microscope and with acetate replicas in order to locate the initiation of very short cracks. The loads were selected to produce fatigue lives of 500 000 cycles or less. The specimens and the load schedules were part of an AGARD-sponsored, round-robin test program designed to study the growth of short cracks.

As an addition to the AGARD program, crack opening displacements were measured at single positions across cracks as short as 0.035 mm and as long as the full thickness of the specimen. Two small reflective indentations were placed across the short crack and illuminated with a 15-mW He-Ne laser. This formed interference fringe patterns that could be monitored to measure the relative displacement between the two indentations. Fringe motion was monitored with a minicomputer-controlled optical scanning system to produce real-time crack opening displacements.

The opening load ratios for the short cracks are somewhat smaller than those for long cracks at positive R ratios but are considerably smaller for negative R ratios. The measured compliances of the very short cracks increase linearly with increasing surface crack length and agree quite well with the predictions of linear elastic fracture mechanics.
Fatigue Crack Closure Outside a Small-Scale Yielding Regime
Authors: Lalor PL , Sehitoglu H
Published: February 2009

An elasto-plastic finite-element model has been developed to simulate fatigue crack growth and to establish crack opening levels in a notched member. Intermediate and high stress levels where small-scale yielding conditions no longer prevail were considered. Variations in crack opening and closure levels with crack length, stress state, R ratio, stress level, and degree of strain hardening were examined. Cracks were allowed to generate their own plastic wake upon advance from the notch surface. Restricting the development of a full plastic wake resulted in lower asymptotic closure levels for certain cases. Complete (R = −1) and partial (R = 0) closure of crack surfaces and the ensuing residual stresses in the crack wake were determined and linked to the crack length effect on closure. Two states of stress (plane strain and plane stress) were considered. Differences in closure levels between the two stress states developed as the crack grew from the notch.
Predictions of Fatigue Crack Growth Behavior Using a Crack Closure Ligament Model
Authors: Keyvanfar F , Nelson DV
Published: February 2009

A ligament model, which performs a simplified, one-dimensional elastic-plastic analysis to predict fatigue crack closure behavior, is described. The model is a modification and extension of a similar one developed by Newman and has the ability to predict the influence of pre-existing residual stress fields on crack closure. Different aspects of the model are examined and, where possible, compared with experimental data and with results from theoretical studies in the literature. For specimens without pre-existing residual stresses, the aspects examined include prediction of plasticity and closure induced residual stresses near the crack tip and prediction of the influence of applied mean stress on crack opening stress. For specimens with pre-existing residual stresses, aspects examined include prediction of residual stress redistribution caused by crack growth and prediction of the influence of such stresses on crack growth behavior, using the closure concept of an effective stress intensity range. Predictions of crack growth are also compared to those based on the superposition approach, for both compressive and tensile residual stresses.
Analysis of Fatigue Crack Closure Caused by Asperities Using the Modified Dugdale Model
Authors: Nakamura H , Kobayashi H
Published: February 2009

Crack closure characteristics in fatigue crack growth were examined using the modified Dugdale model developed by Newman. The model can leave elastic-plastic asperities in the wake of the growing crack tip. The analysis showed the influence of the rigidity E of the asperities, asperity length, asperity thickness, and the distance from the crack tip.

The validity of the unloading compliance technique was examined. The analysis showed a guide of how to determine the crack opening point. When the plasticity induced crack closure prevails, the detected crack opening point gives the correct information regarding the actual one. The crack opening point, rather than the closure point, determined in this way is a useful parameter to describe the crack growth rates.

Under some closure mechanisms, however, it is pointed out that this technique may not be useful. Especially, when asperities are attached near the initial notch tip like under corrosive environment, the crack opening point becomes an overestimate of the actual level. On the other hand, when they are attached near the crack tip like near the threshold region in an air environment, it becomes an underestimate.

An analytical procedure was developed to determine the crack opening stress intensity Kop from the contact stress at minimum stress intensity. By using this parameter, the crack tip opening displacement or the crack growth rate is described uniquely.
The Influence of Crack Closure on Fatigue Crack Growth Thresholds in 2024-T3 Aluminum Alloy
Authors: Phillips EP
Published: February 2009

Crack opening loads were determined in load-shedding fatigue crack growth threshold tests on 2024-T3 aluminum alloy at stress ratios R of −2, −1, 0, 0.33, 0.5, and 0.7. The effects of load-shedding procedure and rate were investigated. Values of threshold ΔK were found to vary significantly with R, whereas values of threshold effective ΔK did not. That is, the variation of threshold ΔK with R was almost completely explained by accounting for the measured variation in crack opening load behavior with R. The load-shedding guidelines of ASTM Test Method for Measurement of Fatigue Crack Growth (E 647) produced a threshold ΔK value for R = 0.7 that was in agreement with the value determined using a procedure that should minimize closure effects (constant-Kmax, increasing-Kmin test). At both R = 0 and R = 0.7, high load-shedding rates produced high values of threshold ΔK caused by large closure effects.
Using Acoustic Waves for the Characterization of Closed Fatigue Cracks
Authors: Buck O , Thompson RB , Rehbein DK
Published: February 2009

Partial contact of two rough fatigue crack surfaces leads to transmission, reflection, diffraction, and mode conversion of an acoustic signal at those contacts (asperities). This paper reviews recent experimental and theoretical efforts to understand such interactions and uses them to quantify in greater detail the contact between actual fatigue crack surfaces under plane strain conditions. It is shown that the size and density of individual contacts, or asperities, can be estimated from acoustic measurements. Furthermore, it is shown that this information is needed to calculate the static stress across a partially closed crack as well as the “effective” stress intensity range, which activates fatigue crack propagation.
Influence of Fatigue Crack Wake Length and State of Stress on Crack Closure
Authors: Telesman J , Fisher DM
Published: February 2009

The location of crack closure with respect to crack wake and specimen thickness under different loading conditions was determined. The rate of increase of KCL in the crack wake was found to be significantly higher for plasticity induced closure in comparison to roughness induced closure. Roughness induced closure was uniform throughout the thickness of the specimen while plasticity induced closure levels were 50% higher in the near surface region than in the mid-thickness. The influence of state of stress on low-high load interaction effects was also examined. Load interaction effects differed depending upon the state of stress and were explained in terms of ΔKeff.
Effects of Closure on the Fatigue Crack Growth of Small Surface Cracks in a High-Strength Titanium Alloy
Authors: Jira JR , Weerasooriya T , Nicholas T , Larsen JM
Published: February 2009

Fatigue crack growth experiments were conducted on surface flaws in a high-strength titanium alloy. Surface crack lengths in the range 50-μm to 8 mm were investigated under both increasing and decreasing ΔK conditions. Crack length and closure loads were determined from load-displacement data obtained with the aid of a laser interferometric displacement gage, which has resolution capability at 0.01 μm. Stress ratios of 0.1, 0.5, and −1.0 and net-section stress levels from 0.2 to 0.9 of yield stress were utilized. The applied stress intensity factor range, ΔK, correlated crack-growth-rate data for R = 0.1 and R = −1, but all R = 0.5 data fell along a separate band. The effective stress intensity factor range ΔKeff determined from closure data, consolidated most of the data into a single band, but some small-crack data fell outside the band. Fracture surface roughness and plasticity were concluded to be the primary features contributing to crack closure.
Preconstruction Brick Veneer Evaluation Testing
Authors: Raths DC
Published: February 2009

This paper discusses and presents a preconstruction testing program for a brick veneer cavity wall. It presents the testing program and the application of ASTM and industry standards to the evaluation testing of the brick masonry materials. It provides findings on brick and mortar characteristics, steps taken to improve the performance of the selected brick wall materials, and engineering procedures for determining material compatibility and performance.
Problems and Solutions to Masonry Buildings
Authors: Gensert RM , Bretnall WC
Published: February 2009

The authors have been actively investigating masonry buildings for over 25 years and have documented problems associated with differential movement within masonry systems and between systems and their supporting structures. While they have found many buildings and components which perform well, it has been their experience that masonry buildings with problems have often been brought to the attention of the public without full and in-depth understanding of the source of the trouble.

One cannot analyze a building's problems by a quick visual inspection and a first reading of the drawings and specifications. It is necessary to document all signs of distress as an overlay upon the structural frame. Materials must be sampled and tested for quality and compatibility. Walls must be probed with fiber optic instruments to determine the quality of assemblages and their attachments to the structure. Architectural details, such as drainage, flashing, movement joints, bonding, etc., are important to the well-being of masonry walls and must be examined. Structural support of masonry and its interaction with the supporting structural component and with the structural frame as a whole is also critical in terms of differential movements. The authors have documented this experience by means of photography computer graphics instrumentation, and this paper will share with you the knowledge gained by this work effort.
Influence of Tie Flexibility, Relative Length, and End-Boundary Condition on Brick Veneer-Metal Stud Flexural Bond Stress
Authors: Chin IR , Krogstad NV , Monk CB
Published: February 2009

Based on insights from the Clemson test report on the wall system under discussion, the authors analytically examined the issue of the relative stiffness between the brick veneer and the metal stud.

Much controversy has surrounded the contention that the inherent stiffness of the brick veneer will result in critical flexural bond stresses in the veneer when laterally supported on metal studs. Using ordinary conventional relative stiffness methods of analysis, the brick veneer can attract 85% or more of the wind load, whereas the metal studs attract 15% or less. Even if the studs are designed to take full wind load at a span-deflection ratio of 360 to 600, ordinary analysis may still indicate that critical flexure bond stresses will occur in the veneer prior to full participation of the stud.

This paper shows that if the inherent tie flexibility, normal shorter metal stud length, and usually free top boundary wall condition are taken into account, critical flexural bond stresses do not exist in the brick veneer on typical brick veneer/metal stud walls. Recommendations on the utilization of inherent boundary conditions to minimize the development of critical flexural bond stresses in the veneer are presented.
Analysis and Test of a Torsional Sensitive C-Shaped Prefabricated Brick Spandrel Panel
Authors: Arnold RC , Dondanville LJ , Krogstad NV , Monk CB
Published: February 2009

Recognizing the inherent torsional flexibility of an open C-section, the authors analyzed in detail the dead and live load behavior of the section under review. The section consisted of a sloping sill, a vertical spandrel, and a horizontal soffit configuration fabricated as a continuous bent plate. The three planes when joined together form an open C-section. To explore the stress patterns in this shaped plate, the authors modeled the analysis for a hand solution. This was then compared to a more rigorous solution using a finite-element computer approach.

The hand approach determined the principal axes of inertia, the shear centers, and the principal states of stress by Mohr's circle. Comparison is shown with graphic plots of principal stresses from the finite-element analysis. The latter technique makes a detailed investigation possible, including plots of both principal tensile and shearing stresses. The modeling of the complex metal embedments at each reaction location was also possible by the finite-element solution.

Full-scale testing of the panel was made utilizing dead weight from brick loading platforms that exerted gravity and wind loading on the spandrel panel through a series of compound lever frames. Contrary to results of brittle torsional failure expected from the analytical work, the experimental behavior demonstrated a capacity to a load factor of five without cracking or collapse.
Test of Model Masonry Single Pier Under Dynamic Shaking and Quasistatic Cyclic Loading
Authors: Chen H-L , Shah SP
Published: February 2009

In order to improve seismic design of masonry structures, research is needed in the area of masonry response to seismic loading. One of the purposes of this program is to investigate the difference of the structural response of masonry single pier when in-plane shear force is applied dynamically and slowly. In addition, modeling techniques for brick masonry were studied.

The experimental results are reported for the structural behavior of two brick masonry piers under dynamic shaking and slowly applied cyclic loading. Each specimen was an unreinforced model pier having a height-to-width ratio of 1 with fixed-end conditions. The model was constructed of one fourth scale brick and mortar composed of fine sand, lime, and cement. Compressive tests of model mortar cubes, prisms, and one square panel were done to understand the modeling techniques of brick masonry. It was found that the piers under dynamic shaking are characterized by localized failure and abrupt stiffness degradation. However, the peak strength was lower under dynamic shaking. This tentative, preliminary conclusion should be verified with further tests.
Statistical Primer for Brick Masonry
Authors: Grimm CT
Published: February 2009

Methods of sampling and statistical data reduction applicable to brick masonry are reviewed. Techniques for plotting histograms and probability density functions for normal and log normal distributions are discussed. Criteria for establishing sample size and specification requirements are enumerated. Binary operations with variables are illustrated. The concept of structural reliability is introduced. Seventeen log-normal graphs of various brick masonry properties are included.
In-Situ Evaluation of Compressive Stresses
Authors: Manmohan D , Schwein RL , Wyllie LA
Published: February 2009

The use of terra cotta as a cladding material emerged in the 1880s and began to decline in the late 1930s. During this period, high-rise buildings employing terra cotta cladding included no provisions for differential movement between the cladding and structural framing. Numerous terra cotta clad buildings are showing signs of distress due to weathering and induced stresses from frame shortening under load. Determination of residual compressive stresses within the terra cotta cladding is often necessary for evaluation and repair of the distressed material.

The level of stresses induced in the cladding of a high-rise building in San Francisco was measured by performing strain relief tests. Uniaxial strain gauges were adhered vertically to the face of the terra cotta blocks and initial balance readings were obtained. The mortar bed joints were sawn along the terra cotta units and the strains monitored during and after the cutting. Samples of the terra cotta block were cut, instrumented, and tested in compression to determine elastic properties and ultimate compressive strength.

Having obtained the physical properties of the terra cotta, compressive stresses due to frame shortening in the structure were determined. Strain data obtained indicated stress levels which were low enough to eliminate the need for stress relief. Optimum saw cutting locations were determined had stress levels been high enough to require stress relief.
Restoration of the John J. Glessner House
Authors: Sourlis T
Published: February 2009

Glessner House in Chicago was designed in 1886 by H. H. Richardson contemporaneously with the first skyscrapers. The Chicago Architecture Foundation, the present owner of Glessner House, commissioned tuck-pointing and cleaning of exterior granite facades for the building's centennial year. Sourlis Masonry Restoration, Inc. was awarded the contract and proceeded with the project in seven phases: (1) rigging and protection of the building; (2) grinding of mortar joints; (3) preliminary tuck-pointing of mortar joints to prevent penetration of caustic cleaning chemicals; (4) cleaning of the granite; (5) repair of the chimneys; (6) pink beading of the mortar joints; and (7) breakdown of scaffolding and landscaping repairs.
Masonry Cracks: A Review of the Literature
Authors: Grimm CT
Published: February 2009

Masonry surface cracks are objectionable because they are the primary source of water permeance and may be aesthetically displeasing or indicative of structural distress. Cracks are the most frequent cause for masonry's failure to perform as intended. The types, locations, patterns, sizes, and causes of cracks are discussed. Methods are described for their prevention and repair.
Numerical Comparison of Global and Local Fracture Criteria in Compact Tension and Center-Crack Panel Specimens
Authors: Mudry F , di Rienzo F , Pineau A
Published: February 2009

Numerical computation of the stress-strain fields ahead of the crack tip of compact tension (CT) and center-crack panel (CCP) specimens were performed. Various crack length to width ratio and strain hardening exponents were investigated. The results of these calculations were used to simulate numerically either brittle fracture or ductile rupture. For this purpose, the comparison between global fracture criteria, such as JIc or the critical crack-tip opening displacement [(CTOD)c], and local fracture criteria is made. It is shown that both types of criteria provide similar results when the specimens are loaded under small-scale yielding. On the other hand, under large-scale yielding significant differences are found. Local fracture criteria are used to specify the validity range for the global parameter, JIc. It is shown that this validity range depends both on the specimen shape and on fracture micromechanisms.
Comparison Between Experimental and Analytical (Including Empirical) Results of Crack Growth Initiation Studies on Surface Cracks
Authors: Reuter WG
Published: February 2009

Surface-cracked specimens are used to simulate the behavior of structures containing defects. For these ferritic steel specimens, the test temperatures of 255 and 297 K corresponded to the lower shelf and the lower region of the ductile-brittle transition curve, respectively. Therefore, the conditions tested ranged from elastic to elastic-plastic to fully plastic with only small changes in tensile properties but substantial changes in fracture toughness. This paper compares experimental results based on crack initiation for the surface-cracked specimens with predictions of JIc and on an empirical correlation using the flow stress.
Plasticity Near a Blunt Flaw Under Remote Tension
Authors: Tracey DM , Freese CE
Published: February 2009

Elastic-plastic analyses of a group of blunt-tipped crack-like flaws were performed. Elliptical, semicircular, and circular tip geometries were considered. Results show very minor excursions of the plastic zone along the crack faces in contained plasticity, even after the characteristic butterfly shaped crack-tip zone has developed. As a result of this yielding behavior, it was found that stress triaxiality predictions following from slipline theory significantly overestimate the elastic-plastic results. J-integral computations show that there is significant path dependency near the tip, which can be associated with the nonproportional stress histories and partial crack face unloading that was detected. The results should be important in applications of critical stress and J-integral concepts to fracture from crack-like imperfections.
Fracture Mechanics Tests on Welded Joints
Authors: Dawes MG , Pisarski HG , Squirrell SJ
Published: February 2009

This paper gives recommendations and reasons for modifying existing plain material test methods for application to welded joints. The test methods are based upon those described in the ASTM and British Standards (including drafts) for plane-strain fracture toughness, KIc, crack-tip opening displacement (CTOD), and J contour integral tests, but with appropriate modifications to suit the testing of weldments.

A distinction is made between tests for general assessments of welded joint fracture toughness and those for specific assessments of the toughness associated with known or postulated cracks in welded structures, that is, tests that can be used as part of a specific fracture mechanics based fitness-for-purpose design or assessment. These applications are considered in relation to the choice of specimen geometry and notch location within the weld heat-affected zones and weld metals of single and multipass welds.

The special techniques that need to be employed in preparing welded specimens for testing are described. Details are given of how the results from the tests may be interpreted, together with a recommendation for metallurgical examination of the specimens after testing.

This paper is intended to provide a framework for standard fracture mechanics tests on welded joints.
Elastic-Plastic Fracture Mechanics Evaluations of Stainless Steel Tungsten/Inert-Gas Welds
Authors: M Nakagaki , CW Marschall , FW Brust
Published: February 2009

A combined experimental and analytical study of ductile crack growth in a high-toughness austenitic stainless steel weld was performed. The substantially greater yield strength of the weld metal relative to the base metal favored plastic deformation in the base metal adjacent to the weld. Accordingly, the analytical studies focused on the stress/strain interaction between the crack tip and the weld/base-metal interface.

Experimental work included development of J-resistance curves from both compact (tension) specimen tests and pipe bend tests. To provide several ratios of weld size to specimen size, the compact specimens were of three planform sizes (0.5T, 1.5T, and 3T) machined from a tungsten/inert-gas (TIG) weldment, also known as a gas/tungsten-arc (GTA) weldment, in Type 304 stainless steel plate. A TIG-welded pipe test conducted by the David Taylor Naval Ship Research and Development Center was also analyzed.

A clear dependence of the crack initiation toughness on the weld size relative to the specimen size was found.

Elastic-plastic finite-element methods were used to model the tests. Because of stress/strain nonproportionality associated with local unloading due to crack growth, attention was focused on crack-tip integral parameters, such as Tp* and , that remain path independent under these conditions. However, an engineering J-estimation scheme also was employed in attempting to predict the load-carrying capacity of the welded pipe with a circumferential through-wall crack under bending.
Effect of Prestrain on the J-Resistance Curve of HY-100 Steel
Authors: I Bar-On , FR Tuler , WM Howerton
Published: February 2009

Metal forming and welding operations can introduce residual stresses into structural components. In this study the effect of prestrain on the J-resistance (J-R) curve of subthickness specimens of HY-100 steel was investigated. Prior to testing, the specimen blanks were subjected to four levels of tensile strain up to 10% prestrain. J-resistance curves were determined for unstrained material using multiple-specimen and single-specimen techniques and for the prestrain material using the single-specimen technique. In all cases a half-thickness, full-width, three-point bend specimen geometry was used. Irregularities in the J-resistance curves were correlated with distinct features on the fracture surfaces. In particular, discontinuities in the J-R curve were correlated with the location of ridges along the crack front. The J-R curves obtained after considering the effect of these discontinuities showed a definite influence of the prestraining: the fracture toughness JIc and tearing modulus T decrease with increasing levels of prestrain, with T being more sensitive to the prestrain level than JIc.
A Viewpoint on the Failure Assessment Diagram
Authors: DE McCabe
Published: February 2009

This paper presents the results of a study to evaluate certain features of interest in the failure assessment diagram (FAD). The concept of one universal calibration curve of interpolation between the two extremes of linear elastic and plastic collapse behavior is examined. One universal curve is implicit in the Dugdale strip yield elastic-plastic model, and this is examined in the light of trends that other elastic-plastic models suggest. Material work hardening, variable constraint, and geometry were identified as variables to consider by the other models. However, in some cases the universal calibration curve concept is not appreciably affected by these additional variables.

A major problem area is the consistency of load normalization by limit-load equations. These generally are imprecise estimates of the collapse load which impart a detrimental influence on the calibration curve shape and introduce the weakest link into a universal curve based FAD methodology. Three examples are given on the use of key curves to develop FAD calibration curve Kr values (elastic KI/elastic-plastic KR). A good fundamental relationship was shown to exist which, in effect, showed that FAD calibration curves represent another form of dimensional analysis. The key curve could also be used to study ways to reduce the deleterious effects associated with plastic collapse load determination problems.

A procedure was shown on a way to apply FAD calibration curves to develop K-applied curves for conventional R-curve analysis.
Stable Crack Growth and Fracture Instability Predictions for Type 304 Stainless Steel Pipes with Girth Weld Cracks
Authors: Cardinal JW , Kanninen MF
Published: February 2009

Elastic-plastic finite-element fracture mechanics analyses were conducted on 102-mm (4-in.) and 406-mm (16-in.)-nominal-diameter Type 304 stainless steel pipes containing circumferential through-wall cracks located in girth welds. The 406-mm (16-in.) pipe was analyzed for a fixed axial load combined with a monotonically increasing bending moment. The 102-mm (4-in.)-diameter pipe analysis was performed under a four-point bending load. Material J-resistance curves appropriate for each problem were used to initiate and grow the initial crack. Calculations were performed to analyze the 406-mm (16-in.) welded pipe treated as (1) a monolithic pipe entirely composed of base metal and (2) a composite of base metal and weldment. The 102-mm (4-in.) welded pipe analysis modeled the material as a composite of base metal and weldment and utilized a material J-resistance curve generated from an elastic-plastic analysis of a welded compact tension specimen. The results of the 406-mm (16-in.)-diameter pipe analysis demonstrated that the predictions of the extent of stable crack growth and the applied load at fracture instability depend on whether or not the pipe is modeled monolithically or as a composite of base metal and weldment. The 102-mm (4-in.) pipe fracture analysis, using a normalized interpretation of the material J-resistance curve, produced good agreement with corresponding experimental crack growth and deflection data.
A Methodology for Ductile Fracture Analysis Based on Damage Mechanics: An Illustration of a Local Approach of Fracture
Authors: Rousselier G , Devaux J-C , Mottet G , Devesa G
Published: February 2009

Major solutions needed in fracture analysis are (a) simple and accurate material characterization and (b) easy transferring of material data to cracked structures. In the proposed methodology, constitutive relationships, including cavity growth and coalescence, are used. Material characterization is based on the simple notched tension test. Several structural steels have been characterized, especially A508 steel, and the direct transferring of material data has been demonstrated with tests on circumferentially cracked tension specimens.

In addition, the extrapolation of material data to different inclusion contents and temperatures was attempted, with favorable results for the first factor through a specific parameter of the model. The temperature dependence of A508 steel ductility is related to an inverse strain rate effect on the flow curve; the modeling of this effect gives encouraging results, but it must be refined to produce an effective prediction.
Crack Growth Instability in Piping Systems with Complex Loading
Authors: Nestell JE , Coward RN
Published: February 2009

The ability of high-energy piping systems in nuclear power plants to tolerate large flaws without unstable crack growth during earthquake conditions is the basis for the leak-before-break concept being used for the safety analyses of new and existing plants. In this work, a stability criterion for a crack in a piping system is developed from simple considerations of the moment-carrying capability of the elastic-plastic cracked pipe cross section without regard to the nature or distribution of applied loads. In particular, the constant load-point displacement assumption used for the development of existing applied tearing modulus stability theories is not required. Although the resulting expression appears to be functionally similar to the traditional applied tearing modulus stability criterion, the physical picture of the crack hinge behavior is more general. As a result, this new view of crack stability is more easily justified for application to piping systems subject to multiple-point or distributed loads. The effects of simplifying assumptions regarding purely plastic or perfectly plastic crack hinge behavior on the conservatism of the stability analysis are investigated. In addition, practical considerations for the evaluation of the stability of real piping systems are discussed.
Critical Depth of an Internal or External Flaw in an Internally Pressurized Tube
Authors: Leitch BW
Published: February 2009

Using a combination of theoretical and experimental techniques, the critical depth of a long, internal or external surface flaw in an internally pressurized cylinder can be found. The theoretical study is performed using nonlinear finite-element methods. Assuming an infinitely long, axially oriented, surface crack in the wall of a pressure tube, a quarter of the tube cross section was modeled in plane strain. Three different crack penetrations were examined by specifying crack depth to wall thickness ratios (a/t) equal to 0.25, 0.5, and 0.75. The crack-tip stress-strain field was simulated using collapsed isoparametric elements containing a 1/r singularity.

The J-integral, and thus the stress-intensity factor, was found using the virtual crack extension method. Initially, elastic values were calculated, but, as the tube is manufactured from a zirconium alloy having a work-hardening material behavior, the analyses were extended into the elastic-plastic regime. Choosing the J-integral as the crack-driving force parameter, elastic and elastic-plastic theoretical crack-driving force curves were produced for internal and external surface flaws.

Experimental J-resistance curves have previously been determined using small-specimen test pieces. In the experimental tests, various property states of the zirconium alloy, such as unirradiated versus irradiated conditions and different levels of hydrogen concentrations, have been examined. Using the theoretically derived crack-driving force curve for an internal or external surface flaw, and the appropriate experimental J-resistance curve, an estimate of the critical depth can be obtained. The depth values obtained using this method compare very favorably with the result of a recent experimental burst test of a pressure tube containing a long external surface flaw.
Use of a Ductile Tearing Instability Procedure in Establishing Pressure-Temperature Limit Curves
Authors: Yoon KK , Bloom JM , Van Der Sluys WA
Published: February 2009

Fracture mechanics analysis procedures have been used in the nuclear power industry for almost 15 years to establish allowable pressure-temperature limit curves. In this procedure, a reference flaw is assumed to exist, and the pressure-temperature limits that will allow safe operation of the plant are determined. As a plant ages, the analysis must be updated periodically to take into account any possible degradation of the pressure vessel material due to irradiation.

Until recently, this procedure was based on linear elastic fracture mechanics and was applicable only over a limited portion of the operating temperature range. This paper describes a proposed new approach to this analysis procedure which makes use of both elastic fracture mechanics techniques and a new ductile tearing instability analysis to establish allowable pressure-temperature limit curves over the entire operating temperature range.

The ductile tearing instability analysis is based on the deformation plasticity failure assessment diagram. The paper describes in detail how this procedure will be applied. Safety factors and acceptance criteria are proposed.

A discussion of the materials properties needed to perform the analysis is presented. The properties used in the analysis include the KIR curve from the American Society of Mechanical Engineers Boiler and Pressure Vessel Code, J-R curves, and stress-strain properties of the vessel material. An example problem showing the application of the overall approach is included in the paper.
A Study of the Initiation and Growth of Complex Cracks in Nuclear Piping Under Pure Bending
Authors: Kramer GS , Papaspyropoulos V
Published: February 2009

In this study the validity of various analyses in the prediction of crack initiation, maximum load, and the corresponding displacements for 168-mm (6.625-in.)-diameter circumferentially complex-cracked pipe under pure bending was assessed. The results of six pipe fracture experiments on three materials (SA-376 TP304 stainless steel, Inconel 600, and A106 Grade B carbon steel) were used to verify the accuracy of these analytical predictions. All experiments were conducted at 288C (550F).

Two different sets of analyses were conducted using J-R curves and J-estimation schemes. J-resistance (J-R) curves were calculated from each pipe experiment using the -factor method. These results revealed that the J-R curves from the complex-cracked pipe experiments were significantly lower than J-R curves from 0.5T compact tension specimens. Furthermore, the pipe J-R curves decreased systematically with increasing ratios of surface crack depth to pipe wall thickness.

Predictions of loads and displacements in each experiment were made using four different J-estimation schemes. Good agreement was obtained between the predictions and the experimental data up to maximum load. Once past maximum load, however, the J-estimation schemes overpredicted loads and displacements.
Metallurgical Aspects of Plastic Fracture and Crack Arrest in Two High-Strength Steels
Authors: JP Gudas , RB Pond , GR Irwin
Published: February 2009

Elastic-plastic fracture toughness tests were carried out with HY-80 and ASTM A710 Grade A Class 3 steels, and crack arrest tests were carried out with the HY-80 steel. Metallurgical analyses were conducted to describe the local plastic fracture processes which contribute to ductile crack initiation and cleavage crack arrest. The fracture toughness, JIc, of the ASTM A710 steel was over two times that of the HY-80 steel. Large manganese sulfide (MnS) inclusions in the HY-80 steel controlled fracture by reducing local crack-tip constraint and promoting fast shear fracture in regions of high local strain. Fracture in ASTM A710 steel occurred by full void coalescence because of reduced inclusion content, a higher strain hardening capacity than that seen in HY-80, and discontinuous carbide distribution, which retarded local shear instabilities. A stress-modified critical strain model was observed to explain the relative fracture toughness of the two steels adequately, and this suggested a higher critical distance parameter for ASTM A710 steel, which was qualitatively verified. The micromechanisms of crack arrest in HY-80 include shear fracture of ligaments behind the crack-tip connecting noncoplanar regions of cleavage and, for the case of near upper shelf arrest, large deformations associated with the lateral spreading of cleavage.
Kinetics of Fracture in Fe-3Si Steel Under Model I Loading
Authors: Bessendorf MH
Published: February 2009

This paper deals with experimental studies of fatigue crack propagation (FCP) in Fe-3Si steel. The FCP experiments were performed on single-edge crack specimens. Results show that an extensive damage zone consisting of slip bands surrounds and precedes the propagating crack. The system of the crack and the damage zone constitutes the crack layer (CL). The results demonstrate that fracture propagates by the translation, expansion, and distortion of the part of CL called the active zone. The contours of the damage distribution show that different loading stresses may cause significantly different shapes of damage. Application of the stability criteria is demonstrated. It was shown that the critical energy release rate depends on the history of loading.
Separation of Energies in Elastic-Plastic Fracture
Authors: Mecklenburg MF , Joyce JA , Albrecht P
Published: February 2009

The area under load versus the load-line displacement record represents the sum of the stored potential energy, the released elastic energy, and the dissipated plastic energy necessary to grow a crack through a test specimen. When partitioned as presented in this paper, these energy components can be evaluated in terms of current elastic-plastic fracture parameters. The authors show that the elastic energy release rate, G, as calculated by measuring the appropriate component from the test record, is identical to G calculated from Kq. The plastic energy dissipated, as measured directly from the load-displacement record, represents a much higher value than would be indicated by current J-type calculations.

In all cases examined, it is further shown that energy released or dissipated is strongly dependent on the size of the test specimen and the size of the initial crack length. Further, while the rolling orientation and prestraining of the steels investigated affect the plastic energy dissipation rate, there seems to be little effect on the elastic energy release rate.
A Computer Controlled Hydraulic Triaxial Testing System
Authors: Menzies BK
Published: February 2009

A computer controlled hydraulic triaxial testing system is introduced. A desktop computer is linked to a hydraulic triaxial cell via three microprocessor controlled hydraulic actuators and two subsystems, one for the measurement of axial deformation and the other for the measurement of pore pressure. The separate system elements and subsystems are described in detail. The operation of the system is described, and control algorithms are explained with particular reference to K0 consolidation and swelling and automatic testing rate by controlled hydraulic gradient. System performance is illustrated by reference to published data describing K0, stress path, cyclic loading, and triaxial extension tests. The advantages of the system are summarized.
Microcomputer-Based Data Acquisition Systems for Triaxial Testing of Soft Yielding Rocks
Authors: Reeves M
Published: February 2009

The structure and design of a generic, device-independent, set of software data acquisition and control routines for long-term rock mechanics monitoring are described. The routines are designed for an Intel 8086/8088-microprocessor-based microcomputer running under the MS-DOSR (Microsoft Disk Operating System). It is assumed that the rock will undergo long-term, slow deformation rather than rapid elastic rupture, and the routines are designed primarily for low strain rate and creep/consolidation testing.

The main features of the package include instrumental drift compensation, inputs from multiple interfaces, on-line configuration changes, complex control functions based on multiple sensor values, automatic elimination of erratic sensors, background acquisition and control, and on-line real-time graphics.
A Stress- and Strain-Controlled Monotonic and Cyclic Loading System
Authors: Vaid YP , Negussey D , Zergoun M
Published: February 2009

A combination hydraulic-pneumatic loading system for triaxial testing of soils under a variety of loading modes is described. The system permits both monotonic and cyclic loading under stress or strain control. Anisotropic consolidation and stress path control during monotonic or cyclic shear are important features of the system. A combination stress- and strain-controlled loading on the same specimen can also be carried out. Typical test results are presented in support of the capabilities of the loading system.
Simultaneous Hydraulic/Physical Parameter Measurement on Rock Specimens Subjected to Triaxial Conditions
Authors: Donath FA , Holder JT , Fruth LS
Published: February 2009

The apparatus described provides for laboratory studies of stress-coupled parameters, with simultaneous measurement of mechanical deformation, permeability, electrical resistivity, and compressional wave velocity in 10- by 20-cm (4- by 8-in.) cylindrical test specimens with pore fluid pressure and subjected to triaxial test conditions. The compact collar-coupled design facilitates specimen installation and apparatus mobility. Axial and volumetric strains are determined using external linear displacement transducers, and differential axial stress is determined by a load cell which is an integral part of the loading column. Hydrostatic pressures in the confining fluid and in the pore fluid reservoirs up- and downstream from the test specimen are measured with pressure transducers. Data acquisition and servocontrol of the confining pressure and axial loading are performed by a microcomputer system, and test results are cross-correlated with the applied differential axial stress. Transient pulse techniques are used to determine the permeability of specimens in the range of 10−20 to 10−16 m2 (10 nanodarcies to 100 microdarcies). The electrical resistivity measurements incorporate phase-sensitive detection with a four-terminal configuration. Transducers in the specimen end caps generate and detect mechanical pulses for wave velocity measurements. The apparatus is designed to operate with corrosive pore fluids such as brine. System performance is illustrated by representative results from tests on a specimen of domal salt during equilibration, and during and after deformation.
State-of-the-Art Paper: A Reevaluation of Conventional Triaxial Test Methods
Authors: Baldi G , Hight DW , Thomas GE
Published: February 2009

A practical reevaluation of some aspects of conventional triaxial test methods is made, based on Bishop and Henkel's book The Measurement of Soil Properties in the Triaxial Test (2nd ed., Edward Arnold, London, 1962). Some advances in measurement techniques, methods of preparing, installing and saturating specimens, and the measurement of the initial effective stress are discussed, with particular emphasis on potential sources of disturbance and methods to reduce this. The use of unconsolidated undrained tests and various stress paths in relation to current needs is represented.
Consolidated Drained Triaxial Testing of Piedmont Residual Soil
Authors: Lambe PC , Heartz WT
Published: February 2009

The paper describes problems encountered in performing consolidated drained triaxial tests on Piedmont residual soil specimens trimmed from both Shelby tube samples and block samples. The micaceous silty soil has steeply dipping layers, planes of weakness, and granular seams. These characteristics complicate trimming and cause specimens to bend during consolidation and shearing. Because some specimens failed at strains of 14% to 20%, the nonuniformities influence the estimation of peak shear strength. To cope with variability, a multistage test on one specimen was compared to behavior measured on three single-stage tests performed on three specimens; all four specimens were trimmed from the same block. Comparative results were inconclusive.