bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling Polarization Curves and Impedance Spectra for Simple Electrode Systems
Authors: Bertocci U , Ricker RE
Published: March 2009

A method for modeling the behavior of electrochemical systems based on electrode kinetics instead of equivalent circuits is developed, and examples of the application of this modeling method to three electrochemical systems are presented. It is shown that the behavior of simple, as well as relatively complex, electrochemical systems can be modeled on desktop computers yielding impedance spectra as a function of input quantities that describe steady-state electrode kinetics and the electrode potential. This approach, since it is based on quantities that describe the kinetics of the actual processes that occur at the electrode, has the advantage over other approaches of having a built-in physical interpretation. The impedance plots produced in this way can give a feeling of what to expect experimentally and can be useful in testing hypotheses, in establishing reasonable ranges for quantities not easily accessible to measurement, and in suggesting experimental strategies.
Evaluation of Corrosion Data: A Review
Authors: Anderson DB
Published: March 2009

The needs, objectives, and techniques for evaluation of material property data are reviewed with respect to their applicability to certain types of corrosion data. Examples of approaches that have been taken for data generated from exposures in natural environments and industrial processes are described to illustrate methods used for characterizing the materials, the environment and exposure conditions, the measurement techniques used to describe these components, and the delineation of controlling factors with respect to specific forms of corrosion.
Analyzing Electrochemical Impedance Corrosion Measurements by the Systematic Permutation of Data Points
Authors: Roberge PR
Published: March 2009

The statistical validation of a resistance-capacitance (RC) model from a limited number of data points can be achieved by systematically permuting the three data points that are chosen to extrapolate the centers of semicircular impedance diagrams. An earlier version of the geometric analysis technique, which consisted of finding geometrically the center of an arc formed by the successive data points on a complex impedance diagram, had been successfully applied to the study of erosion corrosion mechanisms of some copper nickel alloys submitted to highly turbulent conditions.

A series of results obtained with a combination of alloy composition, exposure conditions, and environments seems to indicate that the nonadherence to a perfect RC model by electrochemical impedance data provides information concerning the types of corrosion processes occurring on a metallic surface. The analytical method developed to reveal these fundamental characteristics of impedance patterns will be critically detailed with particular emphasis on the parameters controlling its resolution and on its ease of implementation.
A Review of the Development of Computational Corrosion Analysis for Spatial Corrosion Modeling Through Its Maturity in the Mid-1980s
Authors: Munn RS
Published: March 2009

The last decade and a half has seen the development of the discipline of computational corrosion analysis. The joining of electrochemical theory, numerical methods, and computer technology has facilitated rigorous quantitative evaluation of galvanic corrosion systems that now obviates trial-and-error developments, qualitative rules of thumb, and full-scale system experimentation. This paper reviews the development of this capability from its conception in the mid-1970s through its maturation and essentially its completion in the mid-1980s. This review centers on the domain (finite element and finite difference) methods, with a brief review of boundary methods in corrosion analysis.
Computer Modeling of Offshore Cathodic Protection Systems: Method and Experience
Authors: Strømmen RD
Published: March 2009

This paper offers a brief review of methods that are used and presents different applications and experience from computer modeling of offshore cathodic protection systems. This comprises state-of-the-art software based on the Finite Difference Method ( FDM ), Finite Element Method (FEM), and Boundary Element Method (BEM) adapted for the calculation of current and potential distributions on complex, cathodically protected steel structures in seawater.

The numerical discretization procedures referred to above are combined with a data base and procedures for handling the electrochemical boundary conditions. In addition, software modules are included that handle the initialization of the computer models, definition of geometry, the numerical solution of the nonlinear discretized equations, and presentation of results.

In particular, this paper presents the principles and procedures used to handle boundary conditions. The procedures are based on basic corrosion theory and general experience as well as on laboratory and field tests. The author and his company have made use of extensive amounts of data obtained by in situ measurements of current densities and potentials on offshore platforms using proprietary electrical field gradient/current density systems. Thus the modeling results and predictions have been verified by field data.
On the Effect of Some Critical Parameters in Cathodic Protection Systems: A Numerical /Experimental Study
Authors: Carvalho SLD , Telles JCF , de Miranda LRM
Published: March 2009

The potential distribution over the surface of underwater structures depends on a series of environmental parameters in addition to the material properties of the surfaces. Among others, the water velocity, resistivity, temperature, salinity, and dissolved oxygen affect the efficiency of cathodic protection systems. The present work discusses the influence of some of these parameters. Stirring, resistivity of the medium, and geometrical distribution of anodes are particularly considered.

Three electrolytes of distinct conductivities were studied, and for each system analyzed two stirring speeds were used. The systems of cathodic protection were analyzed for three different geometrical configurations between impressed current anodes and cathodes. To assess the influence of the aforementioned parameters, the computer program PROCAT has been used to simulate the experiments. This program is a general application boundary element computer system. It is capable of analyzing three-dimensional, two-dimensional, and axisymmetric corrosion cells, including nonlinear and possibly time-dependent polarization curves. In the present computer simulation, the nonlinear polarization curves were obtained experimentally under different environmental conditions. The experiments were implemented in a rectangular reservoir that was represented as a two-dimensional problem.
Applicability of the Short Rod Fracture Toughness Test to New Microalloyed Bar Steels
Authors: Tschanz TC , Matlock DK , Krauss G
Published: March 2009

The applicability of the short rod fracture toughness test to fracture analyses of new microalloyed bar steels, under consideration as substitutes for quenched and tempered steels, is evaluated. Data on two bainitic steels processed with microstructures of ferrite and austenite in which the austenite transforms to martensite with strain are compared to data on 4140 steel and 1045V steel. The applicability of the short rod fracture toughness test is discussed in conjunction with an analysis of the unique deformation behaviors of the four steels. Alterations to the test criteria for materials with microstructures which change with strain are suggested.
Specimen Size and Orientation Effects in Chevron-Notch Fracture Testing of Aluminum Alloy Plate
Authors: Morrison J , KarisAllen KJ
Published: March 2009

Side grooving of specimens can have a pronounced effect on the fracture behavior of aluminum alloys during plane-strain fracture tests. The first part of this paper describes an investigation of the effect of different amounts of side grooving on KIc determined using compact specimens of varying thicknesses machined from a 6061-T651 plate. The results are also related to KIv measurements made on the same material and are discussed in terms of rising R-curve effects on compact and short-bar fracture specimens.

Chevron-notch fracture tests in accordance with ASTM E 1304-89 were also carried out on nominally 13-mm-thick plates of aluminum alloys 2024-T351, 7075-T651, and 8090-T8771. Various specimen orientations were used, including both in-plane and short-transverse loading. Tension and also, where possible, compact specimen fracture tests have also been carried out on the same plates.

Data are presented showing the variation in load-deflection behavior and measured toughness with alloy type, and also with specimen orientation. Correlations of toughness and strength with plate rolling direction have been made. Problems arising from the E 1304 test method are also highlighted.
Fracture Toughness Evaluation of Ceramic Bonds Using a Chevron-Notch Disk Specimen
Authors: Rosenfield AR , Majumdar BS
Published: March 2009

The chevron-notched diametrally compressed disk specimen has been used to measure the fracture toughness of zirconia/zirconia bonds and zirconia/nodular-cast-iron bonds. The data are reasonably consistent with experience obtained using monolithic ceramics. In particular, the strain energy release rate increases with increasing shear:tension ratio, and the opening-mode fracture toughness measured using the disks is generally within 20% of the value obtained with bend beams. However, the shear toughnesses of the bonds investigated are approximately 2.4 times the opening toughness, a ratio somewhat higher than that for monolithic ceramics. The high ratio can be attributed to rubbing of mutually opposed crack faces, deviation of the fracture plane into higher-toughness zirconia prior to instability for the ceramic/ceramic bonds, and shear of the braze-metal interlayer in the case of the metal/ceramic bonds.
Fracture Toughness of Composite Laminates and Metallic Materials Using a Modified CNSB Specimen
Authors: Lucas JP
Published: March 2009

Mode I fracture toughness was determined for several unidirectional, continuous fiber reinforced polymer matrix composites and a monolithic homogeneous alloy using a modified chevron-notch short bar (CNSB) specimen. The modified short bar specimen consisted of two dissimilar materials and is, consequently, referred to as the hybrid short bar (HSB) specimen. The HSB specimen comprised the host material that contained the chevron notch ligament through which fracture occurred during testing. Bonded to both sides of the host material were metallic adherends. Similar geometric dimensions were maintained between the monolithic (i.e., standard) and the hybrid short bar specimens. Maintaining geometric consistency between the specimens enabled standard short bar fracture toughness analysis techniques to be used in the data reduction of all specimens. Using metal/laminate HSB specimens, Mode I delamination fracture toughness was determined for graphite epoxy and graphite thermoplastic polymer matrix composite laminates. Also, plane strain chevron notch fracture toughness, KIv, was determined for 6061-T651 Al using a metal/metal HSB specimen. The metal/metal HSB specimen consisted of Al 6061-T651 as the host material onto which Ni adherends were bonded via electroplating. Using a low-temperature electroplating process in fabricating the metal/metal HSB specimens provided two significant benefits. First, a strong metallurgical bond was achieved between the dissimilar materials of the metal/metal HSB specimen. Second, during the plating process, modification of the host material microstructure was insignificant. Maintaining consistent microstructures between the metal/metal HSB and the monolithic short bar (SB) specimens permitted direct comparison of experimental fracture toughness test results. After correcting the HSB fracture toughness data to account for effects due to compliance mismatch of dissimilar materials, good agreement was observed between the toughness results obtained using hybrid short bar and monolithic short bar specimens.
Fracture Toughness and Fractography of Corroded Dental Amalgams
Authors: Mueller HJ
Published: March 2009

The plane strain short-rod fracture toughness of six dental amalgams after having been aged in air or exposed to 0.1% sodium chloride for 2 years was investigated. Amalgams were also corroded by polarization. Their fractured chevron surfaces were characterized by scanning electron microscopy. Results revealed an effect from sample diameter. The 6.35 mm diameter high-copper amalgams had a fracture toughness 20-37% higher than that for 11.28 mm diameter size. Only one amalgam, one with indium revealed significantly higher toughness, this being 16% after immersion, whereas the other amalgams showed no significant differences between air and solution conditioning. Increases in toughness were also obtained by polarization-induced corrosion, which after excessive charge transfer, decreased toughness. Chlorine was detected within regions of the fractured chevron planes indicating diffusion to a depth of 300 μm and more. It was thought that chlorides were deposited along Ag-Hg matrix phase grain boundaries inhibiting their decohesive rupturing thereby enhancing toughness.
Using Chevron-Notch, Short-Bar Specimens for Measuring the Fracture Toughness of a Martensitic Stainless Steel at High Hardness
Authors: Marschall CW , Held PR , Dolan FJ
Published: March 2009

Fracture toughness tests were conducted at room temperature and at – 196°C on a martensitic stainless steel that had been quenched and tempered to a hardness of Rockwell C 61-63. The fracture toughness specimens were chevron-notch, short-bar specimens for which B was 12.7 mm and W was 25.4 mm. Tests were conducted in accordance with ASTM Test Method for Plane-Strain (Chevron Notch) Fracture Toughness of Metallic Materials (E 1304-89).

Five tests were conducted at each temperature, and each test produced a valid KIv result. Test results were unusually reproducible for plane-strain fracture toughness tests; the standard deviation for room temperature tests was approximately ±5% and for -196°C tests was approximately ±2% of the mean value of KIv.

For comparison with the chevron-notch test results, three standard KIc tests were conducted on fatigue-precracked compact (tension) specimens at room temperature. The tests were conducted in accordance with ASTM Test Method for Plane-Strain Fracture Toughness of Metallic Materials (E 399). As was the case for the KIv tests, the KIc tests produced very reproducible results: the standard deviation for three tests was approximately ±2% of the mean value. However, it was found that the mean KIv values for this high-hardness steel were approximately 18% greater than the mean KIc values. That result confirms the warning included in ASTM E 1304 that KIc values may be larger than KIc values in some materials.
Rock Fracture Toughness Determination with Chevron-Notched and Straight-Through-Notched Three-Point Bend Round Bar Specimens
Authors: Qizhi W , Xuefu X
Published: March 2009

Chevron-notched and straight-through-notched three-point bend round bar specimens were used to test fracture toughness of a Chongqing limestone. Comparable values were obtained from these two kinds of specimens, but the chevron-notched specimens had the merits of easiness for deducing and detecting overloading, less the possibility for deviation of crack growth from notch plane, and a included nonlinear correction factor in fracture toughness calculation. However, there was some size effect for chevron-notched specimens; the test values increased with increment in crack length and diameter.
Failure Analysis of Notched Unidirectional Graphite/Epoxy Tubes Under Combined Loading
Authors: Hirschfeld DA , Herakovich CT
Published: March 2009

Crack growth from notched unidirectional graphite/epoxy tubes subjected to axial, torsional, and combined loading conditions was studied experimentally and theoretically. Tubes with fiber orientations of 2.5, 15, 45, and 87.5° were notched with slots 0.5 cm long, parallel to the tube axis.

The stress state at the notch of the thin tubes was determined using an elasticity analysis of an infinite plate with an elliptical hole. The normal stress ratio theory was used to predict the far-field stresses and the direction of crack growth at crack initiation. The slots in the tubes were modeled as an ellipse having the same notch tip radius as the slot, an ellipse having the same length and width, or as a circular hole depending on the loading regime. The normal stress ratio theory correctly predicted the direction of crack growth parallel to the fibers, but did not provide good correlation with the experimental far-field stress for crack initiation in all cases. It is believed that this lack of correlation for the critical stresses is due to the different notch geometries in the theoretical model and actual tubes.

The fracture surfaces of the failed tubes were examined using a scanning electron microscope. It was found that failure occurred primarily with the cracks growing from the notch either fully within the matrix or along the fiber/matrix interface depending upon the far-field loading.
Damage Prediction in Cross-Plied Curved Composite Laminates
Authors: Martin RH , Jackson WC
Published: March 2009

This paper details the analytical and experimental work required to predict delamination onset and growth in a curved cross-plied composite laminate subjected to static and fatigue loads. The composite used was AS4/3501-6, graphite/epoxy. Analytically, a closed-form stress analysis and 2-D and 3-D finite element analyses were conducted to determine the stress distribution in an undamaged curved laminate. The finite element analysis was also used to determine values of strain energy release rate at a delamination emanating from a matrix crack in a 90° ply. Experimentally, transverse tensile strength and fatigue life were determined from flat 90° coupons. The interlaminar tensile strength and fatigue life were determined from unidirectional curved laminates. Also, Mode I fatigue and fracture toughness data were determined from double cantilever beam specimens. Crossplied curved laminates were tested statically and in fatigue to give a comparison to the analytical predictions. A comparison of the fracture mechanics life prediction technique and the strength-based prediction technique is given. Generally, both prediction techniques gave good comparisons with the experimental results.
The Change in Thermal Expansion Coefficient as a Damage Parameter During Thermal Cycling of Crossply Laminates
Authors: Boniface L , Ogin SL , Smith PA
Published: March 2009

An experimental and theoretical study of the effect of 90° ply cracking on the thermal expansion coefficients of crossply laminates has been carried out. It has been found experimentally that reductions in the coefficient of thermal expansion of up to 50% are caused by 90° ply cracks induced mechanically, although considerable care is needed in the experimentation. This behavior was modeled using a simple shear-lag analysis, and the resulting analytical expressions are compared with other approaches available in the literature. The growth of matrix cracks in a model GFRP system under severe thermal cycling (77 to 373 K) is investigated. The changes in expansion coefficient are affected by the growth of 0° ply cracks in addition to the 90° ply cracks. The crack growth rate/cyclic strain energy release rate range data are compared with those reported previously for mechanical fatigue cycling of similar material. The two data sets are consistent if plotted in terms of a fracture mechanics parameter which aims to account for the temperature dependence of material properties.
Tensile Deformation of SiC/Ti-15-3 Laminates
Authors: Lerch BA , Saltsman JF
Published: March 2009

The damage mechanisms of a laminated, continuous SiC fiber-reinforced Ti-15-3 composite were investigated. Specimens consisting of unidirectional as well as cross-ply laminates were pulled in tension to failure at room temperature and 427°C and subsequently examined metallographically. Selected specimens were interrupted at various strain increments and examined to document the development of damage. When possible, a micromechanical stress analysis was performed to aid in the explanation of the observed damage. The analyses provided average constituent microstresses and laminate stresses and strains. The damage states were found to be highly influenced by the fiber architecture.
Assessment of Interlayer Shear Slip Theory for Delamination Modeling
Authors: Lu X , Liu D
Published: March 2009

This paper studied the effects of delamination on composite structure behavior. Composite beams made of glass/epoxy and pure glass were examined. Experimental results were compared with analytical solutions which were based on a previously developed theory, namely the interlayer shear slip theory (ISST). The ISST accounted for both interlaminar shearstress continuity and displacement discontinuity conditions on the delamination interface. A finite element program was developed for delamination simulation. It was found from the studies that central deflections and fundamental vibration frequencies were not significantly affected by the changes of delamination length and location except when delamination extended to beam ends. In addition, the changes of deflection and vibration were not sensitive to the delamination position in the beam thickness direction except at midplane. Since both beam ends and midplane had maximum transverse shear stresses, it is concluded from these results that the modeling of delamination should consider the transverse shear effect.
Effect of Initial Delamination on Mode I and Mode II Interlaminar Fracture Toughness and Fatigue Fracture Threshold
Authors: Murri GB , Martin RH
Published: March 2009

Static and fatigue double-cantilever beam (DCB) and end-notch flexure (ENF) tests were conducted to determine the effect of the simulated initial delamination on interlaminar fracture toughness, Gc, and fatigue fracture threshold, Gth. Unidirectional, 24-ply specimens of S2/SP250 glass/epoxy were tested with Kapton inserts at the midplane at one end to simulate an initial delamination. Four insert thicknesses were used: 13, 25, 75, and 130 μm. Some specimens were also tested with either tension or shear precracks as the initial delamination. To determine Gth, fatigue tests were conducted by cyclically loading specimens until delamination growth was detected. The fatigue fracture threshold was defined to be the maximum cyclic strain energy release rate, Gmax, below which no delamination growth would occur in less than 1 × 106 cycles.

For the DCB specimens, consistent values of Mode I fracture toughness, GIc, were measured for specimens with inserts of thickness 75 μm or thinner, or with shear precracks. The fatigue DCB tests gave similar values of GIth for the 13, 25, and 75-μm specimens. Results for the shear precracked specimens were significantly lower than for specimens without precracks.

Results for both the static and fatigue ENF tests showed that measured GIIc and GIIth values decreased with decreasing insert thickness, so that no limiting thickness could be determined. Results for specimens with inserts of 75 μm or thicker were significantly higher than the results for precracked specimens or specimens with the 13 or 25-μm inserts.
Damage and Failure Mechanisms in Scaled Angle-Ply Laminates
Authors: Kellas S , Morton J , Jackson KE
Published: March 2009

The effect of specimen size upon the response and strength of ± 45° angle-ply laminates has been investigated for two graphite fiber-reinforced plastic systems and several stacking sequences. The first material system was an epoxy-based system, AS4 fibers in 3502 epoxy, and the second was a thermoplastic-based system, AS4 fibers in PEEK matrix. For the epoxy-based system, two generic ±45° layups were studied; ( + 45°n/-45°n)2s (blocked plies), and ( + 45°/-45°)2nS (distributed plies), where n = 1, 2, 3, and 4. In the case of the thermoplastic system, only the layup with distributed plies was investigated, ( + 45°/-45°)2nS, for n = 1 and 2. The in-plane dimensions of the specimens were varied such that the width/length relationship was 12.7 × n/127 × n mm, for n = 1, 2, 3, or 4.

It is shown that the stress/strain response and the ultimate strength of these angle-ply laminates depends on the laminate thickness and the type of generic layup used. The ultimate strength of the epoxy matrix material was found to be much more sensitive to specimen size when compared to the thermoplastic matrix system. Scaling effects defined with respect to the first ply failure, strain at ultimate failure, and ultimate strength are isolated and discussed. Furthermore, it is shown that first ply failure occurs in the surface plies as a result of normal rather than shear stresses. The implications of the experimental findings upon the validity of the ±45° tension test, which is used to determine the in-plane shear response of unidirectional composites, are discussed.
The Influence of Interleaf Deformation Behavior and Film-Resin Adhesion on the Fracture Toughness of Interleaved Composites
Authors: Armstrong-Carroll E , Iskandarani B , Kamel I , Donnellan TM
Published: March 2009

Two-dimensional laminated composite materials are susceptible to damage by interlaminar crack growth. Delaminations severely degrade composite load-carrying capability. Interleaved composites are fabricated with thin films inserted between composite prepreg plies. Previous work has shown that interleaved composites have significantly higher delamination and impact resistance than composites without interleaves.

This paper examines interleaving as a technique for the improvement of delamination resistance in composites. In particular, the influence of the deformation behavior of the interleaf film and film adhesion on composite fracture toughness is studied. Teflon and Kapton interleaf film materials are compared. Kapton displays predominantly brittle deformation behavior. Teflon exhibits substantial deformation before failure. Both films are plasma treated to vary film-resin bond strengths. The fracture toughness of composites interleaved with these films is determined. Plasma treatments are shown to increase film-resin adhesion and fracture toughness. The effectiveness of Teflon as an interleaf material may be limited by the toughness of this film. Fracture toughness specimens are found to fail at the film-plasma grafted polymer interface. Additional optimization of the film-grafted polymer bond is necessary for improved performance.
Interlaminar Fracture Analysis of Unsymmetrical Laminates
Authors: Armanios EA , Li J
Published: March 2009

A simple analytical model is developed to predict the interlaminar stresses and the total strain energy release rate for delaminated unsymmetrical laminates. The method is based on a shear deformation theory and a sublaminate approach. The solution is obtained in closed form, and the controlling parameters are isolated. Results for a class of laminates with [-θ, (90-θ)2, -θ, θ, (θ-90)2, θ]T layup exhibiting extension-twist coupling are provided. Potential delamination sites are predicted by applying the analysis to laminates with successive delaminated interfaces. Critical interfaces are determined based on the peel stress distribution and the total strain energy release rate.
Some Observations on the Analysis of In-Plane Matrix Failures in Fibrous Composite Laminates
Authors: Hart-Smith LJ
Published: March 2009

The prediction of matrix failures of fibrous composite laminates under in-plane loading is discussed. It is shown that a complete micromechanical analysis is needed to analyze such failures, even when attention is focused on significant structural damage as opposed to discontinuous microcracking. It is shown that matrix-dominated composite structures could not be certified even if they could be analyzed reliably. All that is needed is an ability to distinguish between those laminates which fail in the matrix and those which fail in the fibers since structurally significant matrix failures preceding the breaking of the fibers automatically signify inferior laminates. This permits the reliable use of failure theories very much simpler than conventional micromechanics to predict fiber-dominated strengths with no loss of accuracy. There is actually no need to calculate matrix-dominated strengths. Indeed, since fewer material properties are needed and are easier to measure than the much larger number needed for a full micromechanical assessment, physically realistic analyses confining attention to failures of only the fibers are actually more accurate than any micromechanical prediction of laminate strength under in-plane loads.
Meso-lndentation Testing of Composite Materials as a Tool for Measuring Interfacial Quality
Authors: Lesko JJ , Carman GP , Dillard DA , Reifsnider KL
Published: March 2009

A unique application of indentation testing to composite materials is presented. The primary goal is to evaluate the sensitivity of conventional penetration techniques to fiber-matrix bond strength in laminated composites. The Vickers fixed-load hardness test and the continuous ball indentation test (CBIT) are employed for the penetration of continuous fiber-reinforced epoxy systems. These indentations are performed in the axial (fiber) direction of laminated unidirectional composites. Both techniques demonstrate significant sensitivity to fiber-matrix adhesion in graphite/epoxy systems which possess a systematic variation to their interfacial characteristics. The CBIT displayed the best opportunity for making quantitative measurements of interfacial strength. An innovative micromechanics model of the composite contact by a spherical indenter predicts trends and failure phenomena observed in the tests. Experimental and analytical results suggest that the ball penetration test is sensitive to the shearing characteristics of the composite. Preliminary results also reveal interrelationships between composite strength properties and hardness values.
Local Delamination in Laminates with Angle Ply Matrix Cracks, Part II: Delamlnation Fracture Analysis and Fatigue Characterization
Authors: O'Brien TK
Published: March 2009

Constant amplitude tension-tension fatigue tests were conducted on AS4/3501-6 graphite epoxy (02/θ2/-θ2)s laminates, where θ was 15, 20, 25, or 30°. Fatigue tests were conducted at a frequency of 5 Hz and an R-ratio of 0.1. Dye penetrant-enhanced X-radiography was used to document the onset of matrix cracking in the central - θ° plies and the subsequent onset of local delaminations in the θ/-θ interface at the intersection of the matrix cracks and the free edge.

Two strain energy release rate (G) solutions for local delamination from angle ply matrix cracks were derived: one for a uniform delamination front across the laminate width, and one for a triangular-shaped delamination area that extended only partially into the laminate width from the free edge. Plots of maximum cyclic G versus the number of cycles to local delamination onset (Gmax versus N) were generated to assess the accuracy of these G solutions. The influence of residual thermal and moisture stresses on G were also quantified.
Effects of Stress Ratio on Edge Delamination Characteristics in Laminated Composites
Authors: Scrivner GC , Chan WS
Published: March 2009

The effects of stress ratio on delamination onset behavior under cyclic loading was investigated in AS4/3502 [+/-252/90]s graphite/epoxy laminates. For the purpose of this study, delamination onset was defined as a delamination 5% of the laminate width. The resulting data showed definite changes in delamination behavior between stress ratios (R ratio) of 0.1 and 0.5.

For maximum amplitude stresses below about 80% of the static delamination stress, delamination onset occurred later at R = 0.5 than for R = 0.1. Also for the corresponding Gmax, delamination growth rates at delamination onset were slower for R = 0.5 than for R = 0.1. This was reflected in changes of power law exponent from 10.2 for R = 0.1 to 31.6 for R = 0.5 and the constant from 1.10 × 10-2 for R = 0.1 to 254 for R = 0.5.

Fractographic analysis suggested that the failure mode, which appeared to be predominantly Mode I, remained unchanged; however, the density of shallow hackles was greater for R = 0.1 than for R = 0.5. This presumably was due to a more rapid coalescence of microcracks which was consistent with the larger crack opening displacements for R = 0.1.
Effect of Interleaves on the Damage Mechanisms and Residual Strength of Notched Composite Laminates Subjected to Axial Fatigue Loading
Authors: Swain RE , Bakis CE , Reifsnider KL
Published: March 2009

The effect of interleaving on the fatigue damage mechanisms and residual tensile strength of two graphite/epoxy material systems subjected to cyclic axial loads is investigated. The two materials, AS4/985 and AS4/1808, have stacking sequences of [0/45/90/-45]s2 and [0/-45/90/45]s4, respectively. All specimens have centrally located through-holes. The 16-ply specimens are subjected to tensile fatigue loads, while the 32-ply specimens are subjected to fully reversed fatigue loads. Interleaving these laminates at every interface with a thin (on the order of 10% of the ply thickness), tough, thermoplastic film results in an expected increase in mass and decrease in laminate stiffness, but also in higher virgin tensile strengths, lower normalized residual tensile strengths, and slightly altered damage patterns and rates of damage growth in both laminate types. The presence of the interleaves alters the baseline virgin tensile load-to-failure and damage patterns to a greater extent in the 1808 material than in the 985 material.
Monitoring Fatigue Damage Development in Ceramic Matrix Composite Tubular Specimens by a Thermoelastic Technique
Authors: Liao K , Dunyak TJ , Stinchcomb WW , Reifsnider KL
Published: March 2009

Tubular specimens made of borosilicate glass reinforced by chopped carbon fibers for high-temperature applications were designed and fabricated by an injection molding process. Specimens were cyclically loaded in tension-tension at maximum stresses of 60, 70, and 85% (R = 0.1) of the ultimate tensile strength at room temperature to one million cycles and then loaded to failure in quasistatic tension. A thermoelastic technique known as SPATE (stress pattern analysis by thermal emission) was used to characterize fatigue damage development in these tubular specimens. Qualitative SPATE results were shown to be related to surface crack initiation and growth in the specimens, circumferentially and radially. Damage initiation sites and subsequent growth of cracks as well as residual strengths were found to be primarily influenced by the local manufacturing related microstructure of individual specimens and secondarily influenced by fatigue damage.
High-Cycle Fatigue Crack Growth Properties of Aramid-Reinforced Aluminum Laminates
Authors: Stanzl-Tschegg SE , Papakyriacou M , Mayer HR , Schijve J , Tschegg EK
Published: March 2009

The fatigue crack growth properties of the laminated fiber-reinforced composite material Arall (Arall® 1 and Arall® 2) have been studied at low cyclic stress amplitudes and high numbers of cycles. For the experiments, a high-frequency (21 kHz) ultrasound resonance fatigue machine has been used (R = -1).

In order to determine the threshold stress intensity (for Arall 1), tests were performed by increasing the stress amplitude stepwise. The resulting threshold stress intensity increases with increasing crack length. In addition, tests with constant cyclic stress amplitude were carried out (for Arall 1 and Arall 2). For these, the fatigue crack propagation rates decrease with increasing crack length and become zero at a defined crack length if the applied constant stress amplitude is lower than a defined “critical” stress amplitude. Fiber bridging, causing extensive crack closure, is the reason for this effect. At cyclic stresses higher than this “critical” stress, cracks continue to grow, though with reduced speed.

Damaging effects like delamination owing to failure of the resin in addition influence the fatigue crack growth behavior of Arall at high cyclic stress amplitudes.
Utilization of Reactor Pressure Vessel Surveillance Data in Support of Aging Management
Authors: Mager TR
Published: March 2009

The majority of pressurized water reactors (PWR) operating in the United States have a “design basis life” of 30 to 40 years. These design basis life estimations were not based on technical studies of material degradation in general but rather on fatigue usage factors for the most part. Recognizing this fact, the subject of operating an existing nuclear steam supply system (NSSS) for longer periods than originally intended has become an important issue worldwide. Radiation embrittlement of the reactor vessel beltline region (the area surrounding the height of the reactor core) is the main concern in extending the operation of the NSSS. Radiation damage, if any, to the reactor pressure vessel material is monitored by a material radiation surveillance program. If the data from the reactor vessel materials surveillance program indicate that the reactor pressure vessel will not meet the rules of the Code of Federal Register (CFR) and various regulatory guides (RG), there are a number of options a utility may take to ensure reactor pressure vessel design life attainment or extension. This paper describes the results from 12 surveillance capsule programs, which encompass four reactor vessel materials and five reactor vessel manufacturers.
Study by Positron Annihilation of Neutron Damage in a Pressurized Water Reactor (PWR) Pressure Vessel Steel After a 13-Year Irradiation in the CHOOZ A Reactor Surveillance Program
Authors: Van Duysen JC , Bourgoin J , Moser P , Janot C
Published: March 2009

The microstructural evolution of a pressure vessel steel (C shell base metal) was studied after a long-term irradiation (13 years) in the surveillance program of a CHOOZ A reactor. The positron lifetime technique was used to determine if the neutron-induced damage is partially composed of voids. Analysis of spectra measured on irradiated samples (fluence = 14 × 1019 n∙cm-2, E > 1 MeV) reveals that the neutron irradiation has not induced the formation of voids containing more than about 50 vacancies (that is, voids with a radius higher than about 0.5 nm). On the other hand, some results suggest the presence after irradiation of a low density of very small voids (less than 10 vacancies) probably located in precipitates.
Analysis of the Results from the Surveillance Specimen Program for Reactor Pressure Vessels of Nuclear Power Plant W-2 in Jaslovské Bohunice
Authors: Kupča Ĺ , Beňo P
Published: March 2009

This paper presents the results of the first three stages of the surveillance specimen programs (one, two, and three years of irradiation) for the reactor pressure vessels (RPV) of W-213 type operated in Units 3 and 4 of nuclear power plant (NPP) Jaslovské Bohunice (EBO 3, EBO 4). The results of the tension and Charpy test specimens in both power reactors are analyzed. The changes of the mechanical parameters after irradiation are compared with the unirradiated condition of 15Ch2MFA steel for three material types: base material (BM), heat affected zone (HAZ), and weld metal (WM). Trends are presented for the shift of the transition temperature of both RPVs through end of operation. Some results from other WWER-440 units and aspects of the surveillance specimen program philosophy used in the WWER-440 reactor type are also presented. The data obtained from this program are used for the development of a database on irradiation degradation of all W-213 reactor vessels operated in the Czech and Slovak Federative Republic.
Fracture Properties of Irradiated A533B,Cl.1, A508,Cl.3, and 15Ch2NMFAA Reactor Pressure Vessel Steel
Authors: Havel R , Vacek M , Brumovský M
Published: March 2009

Within the framework of the International Atomic Energy Agency (IAEA) Coordinated Research Program (CRP) phase III, radiation embrittlement studies were performed on A533,C1.1 and A508,C1.3 reactor pressure vessel steels. Obtained results are compared with radiation embrittlement of 15Ch2NMFAA commercially produced steel, used for WWER-1000 reactor pressure vessel production, in terms of Charpy impact energies and fracture toughness, measured as a function of temperature.
Radiation Embrittlement and Annealing Recovery of CrNiMoV Pressure Vessel Steels with Different Copper and Phosphorus Content
Authors: Vacek M , Novosad P , Havel R
Published: March 2009

The influence of copper and phosphorus content on Charpy-V-notch impact energy, on dynamic fracture toughness, and on radiation hardening recovery of tensile and hardness properties by postirradiation annealing at different temperatures was explored for one commercial heat and six laboratory melts of CrNiMoV pressure vessel steels irradiated to 0.9 to 1.3 × 1023 n/m2 (E > 1 MeV) at 280°C.

Practically linear proportionality between Charpy-V impact energy and dynamic fracture toughness transition curve shifts for all melts was found.

The effect of phosphorus content on radiation embrittlement of laboratory melts considered in this study was very weak in comparison to the significant effect of copper. However, percentage of recovery of radiation-affected hardness was in all laboratory melts permanently slightly lower for melts with higher content of phosphorus with the same copper content.

Copper content had no significant effect on percentage recovery of all laboratory melts as measured by hardness after annealing of irradiated specimens.

The annealing recovery behavior of radiation-affected yield stress (Rp0.2IA) was expressed by an experimental relationship that includes yield stress after irradiation (Rp0.2I), temperature of irradiation (TI), and temperature of annealing (TA).
Investigation on the Impact Strength and Toughness of A533 Grade B Composition Weld Metal Using Small Specimens
Authors: Varga T , Liu QC
Published: March 2009

An investigation was carried out to determine the impact strength and the fracture toughness of the multipass submerged arc (SA) weld metal of A533 grade B (20MnMoNi55) composition using Charpy V-notch and precracked Charpy-type specimens. The experimental results show that there is no large difference between the micro-hardness measured in the primary and secondary zones of the SA weld metal. The Charpy V-notch impact and fracture mechanics tests yield similar results in the primary and secondary zones. Nearly all specimens investigated exhibit the phenomenon of crack jump (“pop-in” of the load), that is, sudden cleavage or quasicleavage often followed by arrest of the crack.
Influence of Specimen Orientation on the Upper Shelf Energy and Transition Temperature Shift of Reactor Pressure Vessel Steel Base Metal
Authors: Leitz C , Klausnitzer EN , Hofmann G
Published: March 2009

In surveillance programs for some older nuclear power plants, the orientation of specimens is longitudinal to the main working direction. According to presently valid codes and standards, the specimen orientation should be transverse. The material toughness is lower in the transverse direction. However, according to former test results, there was common acceptance that the shift as a result of irradiation is independent of orientation. The results of more recent research on trepan material taken from a decommissioned power plant seemed to give reason for doubt in this respect.

Siemens/KWU has simultaneously irradiated Charpy-V specimens made of steel 22 NiMoCr 3 7 (similar to ASTM A 508 cl. 2) with both orientations. Furthermore, transverse specimens were made out of the broken specimen halves from irradiation experiments with only longitudinal specimens using electron beam welding techniques.

The available results of this research and an ample number of relevant data from literature were evaluated. From this it is concluded that independent of a wide variation of parameters the 41-J transition temperature of transverse specimens is on average about 11°C higher than that of longitudinal specimens and the irradiation-induced shift ΔT41 is independent of specimen orientation. The upper shelf energy (USE) shows a wider scatter. As a lower bound, the proposal of the U.S. Nuclear Regulatory Commission (NRC) standard review plan to substitute 65% of longitudinal USE for unavailable transverse values is confirmed by 90% of all data for unirradiated and irradiated material. The deviations, especially of the Gundremmingen trepan results, obviously depend on fabrication inhomogeneity rather than on irradiation effects.
Mechanical and Nondestructive Testing of Irradiated Half Charpy Specimens
Authors: Gillemot F , Oszwald F , Pozsgay G
Published: March 2009

After the five scheduled surveillance testings of WWER-440-type reactor pressure vessels, 5 × 36 half Charpy and 5 × 36 Charpy size crack-opening displacement (COD) specimen pieces remain. These can be used for further testing to obtain more information on aging or annealing.

Two methods using these specimen remnants are described. The Barkhausen noise measurement is a promising way to get more information on aging by nondestructive testing. On the subsize tensile bars cut from these remnant pieces, tensile properties and absorbed specific energy of fracture (ASFE) can be measured. By comparison of smooth and sharply notched specimens, true toughness value can probably be predicted, and the effect of thermal annealing can be studied.
Radiation Embrittlement of Soviet 1000-MW Pressurized Water Reactor Vessel Steel 15KH2NMFAA
Authors: Vishkarev OM , Zvezdin YuI , Shamardin VK , Tulyakov GA
Published: March 2009

In the design of the Soviet 1000-MW pressurized water reactor (PWR), developed to replace the former Soviet 440-MW PWR, the irradiation condition is much less severe. This condition permits the use of a new pressure vessel steel (PVS) 15KH2NMFAA containing nickel (Ni) rather than the previously used PVS 15KH2MFAA, thereby achieving better weldability, higher strength (σy350 > 450 MPa at 350°C), and a lower initial transition temperature (Tk = -30°C). PVS 15KH2NMFAA is manufactured from natural, clean, raw materials to increase its radiation stability. Statistical analysis shows that the transition temperature shift after irradiation (ΔTf) at irradiation temperature (Tir) 290°C and fluence (F) of 6 × 1023 n/m23, E > 0.5 MeV is defined by copper (Cu) and phosphorus (P) content: ΔTf=230[(Cu+10P)+20]±25°C

Values under typical practice are: Cu + 10P = 0.10 to 0.15%∙ΔTf. Values calculated using both this equation and the U.S. Nuclear Regulatory Commission (NRC) Regulatory Guide 1.99 (Rev. 2) gave similar results. On the basis of this equation, demands for the permitted impurity level of PVS 15KH2MFAA have been developed as follows: Cu < 0.1 and P < 0.01%.

The well-known Soviet equation ΔTf = Af(F × 10-22)-1/3 for PVS 15KH2NMFAA irradiated at a Tir of 290°C is correct only at F < 1 × 1024 n/m2∙ Af = 23°C (n/m2)-1/3 at the permitted impurity level.

The radiation embrittlement quasi-steady-state model that is presented here provides a sufficient interpretation of the combined effect of both Tir under temperatures ranging from 100 to 350°C and F up to 4 × 1024 n/m2 (E > 0.5 MeV) on the reference PVS 15KH2NMFAA (Cu + 10P = 0.13%). 1ΔTf=1508+22.41Fexp(-5900RT)

The influence of nickel (Ni) on the PVS 15KH2NMFAA RE is decreased by increasing Tir and lowering F.