bluuebunny/crossref_metadata_2025 huggingface dataset:
Composite Compressive Strength Prediction Using a Nonhomogeneous Foundation Model
Authors: Xu YL , Reifsnider KL
Published: March 2009

Composite compressive strength prediction using a nonhomogeneous elastic foundation (NEF) model is discussed. Results reported in this paper are some continuing work and development of the solution in Ref. 1 in which fiber microbuckling was studied and composite longitudinal compressive strengths (CLCS) were estimated using a beam-on-elastic-foundation model. In Ref. 1, the stiffness of the foundation was determined through solution of an homogeneous foundation model problem. Realizing that the estimation of the stiffness of the foundation is a crucial part of the approach, an NEF model is employed to reconsider the foundation problem. The elasticity solution of the NEF model problem is obtained, and the nonlinear relation of the stiffness of the foundation, k, with the fiber-buckling wavelength, L, is established using a least square technique. An iteration formula is derived for determination of the critical fiber-buckling wavelength, which yields the minimum fiber-buckling load. It is found that the NEF model predicts a slightly lower CLCS, but very close to the homogeneous model solution.
Dynamic Modulus Measurements and Materials Research
Authors: Berry BS
Published: March 2009

Dynamic modulus measurements are of interest in materials research not only as a source of data on elastic behavior, but also for the insight they provide into structure-property relationships in general. A description is given of a vibrating-reed apparatus which has proved highly adaptable for studies of the elastic and damping behavior of thin-film and other thin-layer electronic materials. Results are reported for amorphous and crystalline ferromagnetic materials, for the high-Tc superconducting oxide Y1Ba2Cu3O7-x, and for thin films of aluminum and silicon monoxide, to illustrate the important role which the dynamic modulus can play as a tool in materials research.
Measurement of the Modulus of Dynamic Elasticity of Extremely Thin (Sub-Wavelength) Specimens
Authors: Kinra VK , Dayal V
Published: March 2009

The current methods of ultrasonic modulus measurement make, implicitly or explicitly, the following key assumption: The front-surface and the back-surface reflections of an incident pulse are separable in the time-domain, i.e., the plate is several wavelengths thick. By combining standard ultrasonic methods with the theory of Fourier Transforms, a new technique has been developed which removes the preceding restriction. The theoretical and the experimental procedures are described in detail. The efficacy of the method is demonstrated for three disparate materials: (1) non-attenuative, non-dispersive; (2) weakly attenuative, non-dispersive; and (3) highly attenuative, highly dispersive.
The Pulsed Ultrasonic Velocity Method for Determining Material Dynamic Elastic Moduli
Authors: Blessing GV
Published: March 2009

Material dynamic elastic moduli can be readily obtained from a knowledge of the material's sound velocity(s) and density. One well-established ultrasonic technique for making the velocity measurements is the pulsed-wave transit-time technique. It is a versatile and potentially very accurate technique that can also assess the material elastic homogeneity and anisotropy. Here the many measurement and material factors affecting the precision of the method are addressed. A specific example of the effect of grain size on measurements in steel is presented in some detail.
Longitudinal and Flexural Resonance Methods for the Determination of the Variation with Temperature of Dynamic Young's Modulus in 4330V Steel
Authors: Cook LS , Wolfenden A , Ludtka GM
Published: March 2009

The variation with temperature of dynamic Young's modulus in 4330V steel has been characterized using a longitudinal resonance method (the piezoelectric ultrasonic composite oscillator technique - PUCOT) and a flexural resonance method (the impulse excitation technique - IET). The PUCOT yielded an ambient temperature dynamic Young's modulus value of 206.3 GN/m2 while values obtained from the IET ranged from 197.5–206.8 GN/m2. Both techniques yielded a dE/dT value of -0.08 GN/(m2 K). In addition, three numerical methods for the calculation of dynamic Young's modulus from flexural resonance frequencies of prismatic specimens have been evaluated. Experimental uncertainty at ambient temperature has been calculated for the PUCOT and the IET.
Monocrystal-Polycrystal Elastic-Constant Models
Authors: Ledbetter H
Published: March 2009

Considering only cubic symmetry (three independent monocrystal elastic-stiffness coefficients, Cij), we review various models for converting the Cij to the effective macroscopic quasiisotropic and homogeneous elastic constants, usually taken as B, the bulk modulus, and G, the shear modulus. To test the models, we consider a typical metal: copper, which possesses a moderate Zener elastic-anisotropy ratio, 3.19, and which was measured by pulse-echo dynamic (MHz) methods. We find that the Hershey-Kröner-Eshelby, and equivalent, models work best. We ignore models that lack a physical basis. Using the H-K-E model, we calculate the effective polycrystalline elastic constants of twenty-five cubic elements.
Acoustic Resonance Methods for Measuring Dynamic Elastic Modulus of Adhesive Bonds
Authors: Sinclair AN , Dickstein PA , Spelt JK , Segal E , Segal Y
Published: March 2009

An investigation is made into acoustic resonance methods for measuring the dynamic elastic modulus of the adhesive layer in a bonded metal-to-metal joint. Empirical studies have indicated that this parameter may be used to infer the cohesive strength of the bond; in theory, an accurate measurement of two or more resonant frequencies should give both the elastic modulus and thickness of the adhesive layer. Verifying the accuracy of the technique was greatly hampered by the strong dependence of elastic properties in the adhesive on the test frequency.

The resonant frequencies of aluminum-to-aluminum adhesive joints were determined by both contact and immersion acoustic resonance techniques; receptance analysis was then used to determine the elastic modulus. Results were consistent with those achieved by time-of-flight measurements on bulk adhesive specimens. Based on these tests, inherent limitations of the Fokker Mark II Bondtester for assessing the cohesive strength of a bond were explored.
An Evaluation of Three Techniques for Determining the Young's Modulus of Mechanically Alloyed Materials
Authors: Smith JS , Wyrick MD , Poole JM
Published: March 2009

Two dynamic and one static technique for determining Young's modulus of mechanically alloyed (MA) materials were evaluated for their suitability for quality control testing and as a tool for development of new MA materials. The dynamic techniques included the commonly used continuously excited free - free beam technique tested in both longitudinal and flexural modes, and the relatively new impulse excitation technique tested in the flexural mode. The dynamic techniques showed a minor difference between the impulse and continuous techniques but still yielded results agreeing within ± 1%. The static technique yielded results differing from -5% to + 7% of the dynamic results. The impulse excitation method is particularly well suited for quality control work, while the continuous method is best for elastic behavior characterization. It is conjectured that the static tensile method accuracy may be adversely affected if the tested material is non-isotropic.
Microstructural Change in Ferritic Steels Under Heavy Ion Irradiation
Authors: Hide K , Sekimura N , Fukuya K , Kusanagi H , Taguchi M , Satake T , Arai Y , Iimuna M , Takaku H , Ishino S
Published: March 2009

Ferritic steel is one of the most promising materials for fuel cladding of fast breeder reactors and fusion first wall. However, not enough data on microstructural evolution under irradiation have been obtained, especially at high doses. In the present study, microstructural changes in several ferritic steels under ion irradiation up to 200 dpa were investigated.

The specimens were irradiated with 200 keV C+ or 3 MeV Ni2+ ions between 698 and 898 K. Post irradiation microstructures were observed with transmission electron microscopes. Few voids were detected in MA957. Dislocation structure and dispersed oxide particles (Y2O3) were found to be stable under irradiation up to 200 dpa. Uniform distributions of fine voids were observed in HT-9, Fe-12Cr-2Mo, and pure Fe-12Cr alloy irradiated with 200 keV C+ ions to 150 dpa. However, 3 MeV Ni2+ irradiation of HT-9 between 748 and 848 K caused heterogeneous nucleation of voids near lath boundaries. As-received metallic compound-strengthened steel consisted of martensitic and ferritic phases. Large voids were formed in limited region in martensitic phase during ion irradiation, whereas few voids were found in the ferritic phase. Radiation-enhanced formation of Laves phase (Fe2Mo) was observed in ferritic phase.
Effects of Thermal Aging on Precipitate Development of Alloy Ht-9
Authors: Chen P-S , Wilcox RC
Published: March 2009

Electron microscopy of carbon extraction replicas was performed to identify and evaluate precipitate evolution in the 12Cr-1Mo ferritic-martensitic alloy HT-9 during long-term aging of two different heats, 84425 and 91354. All samples were heat treated at 1078°C/0.5 h/AC + 760°C/2 h/AC. Thermal aging was conducted in the temperature range of 500 to 800°C and for 30 to 10 000 h. Precipitates were identified using electron microdiffraction patterns and energy dispersive X-ray spectroscopy (EDX) analysis. M23C6, MX. Laves. M3X phases, and aluminum oxide (Al2O3) inclusions were found in various specimens of both heats, while the M2X phase and manganese sulfide (MnS) inclusions were present only in some of the 91354 series specimens. M23C6 was the predominant precipitate in all samples. The MX phase was found in all samples from Heat 91354 but was not found below 700°C in the 84425 series. The Laves phase was present up to 700°C in both heats. M3X was found at 800°C in both series and also after long-term aging at 700 and 750°C in 91354.
Microstructural Development of Titanium-Modified Austenitic Stainless Steel Under Neutron Irradiation in HFIR up to 57 dpa
Authors: Suzuki M , Hamada S , Maziasz PJ , Tanaka MP , Hishinuma A
Published: March 2009

The Japanese prime candidate alloy (JPCA). a titanium-modified austenitic stainless steel, has shown good performance after irradiation in the high flux isotope reactor (HFIR) up to 34 dpa at 300 to 600°C, but considerable void swelling develops in solution annealed (SA) JPCA after irradiation to 57 dpa at 500°C. However, cold worked (CW) or cold worked and aged (CW + A) JPCA still demonstrates good performance after similar irradiation. Swelling resistance appears to depend strongly on the behavior of fine titanium-rich MC precipitates. This paper describes the microstructural evolution process observed in the JPCA steel during HFIR irradiation. The onset of rapid void swelling was related to MC precipitate dissolution, and the instability of the MC was interpreted in terms of a model involving the build and subsequent effects of a solute segregation zone in the matrix surrounding the precipitate particle.
On the Role of Helium in High Temperature Embrittlement of Irradiated Austenitic Steels
Authors: Kesternich W , Nandedkar RV
Published: March 2009

Helium that is produced by nuclear transmutations can cause severe degradation of the mechanical properties in structural components of fusion and fast fission reactors. For studying the mechanisms of irradiation embrittlement, the helium effects have been simulated by helium implantation from cyclotrons or by making use of (n,α) reactions from thermal neutron fluxes. As is discussed in the present paper, the results from neutron irradiations and helium implantations are contradictory with respect to the helium levels at which helium embrittlement appears. To study the combined effect of helium and neutron irradiation on embrittlement, two titanium stabilized austenitic steels of identical composition, with the exception of their boron content of 40 and 2 ppm, respectively, have been neutron-irradiated at 845 K to thermal neutron fluences of 2.6 × 1025 n/m2. The precipitate and helium bubble microstructure has been quantitatively characterized by transmission electron microscopy (TEM) and has been correlated with the embrittlement behavior, studied in post-irradiation creep experiments at 973 K. Contrary to the expectation the material with the lower helium content was found to exhibit the higher reduction in creep strength after irradiation.

This result and the differences between low-dose neutron and alpha irradiations can only be explained if a new assessment of the role of helium in high temperature irradiation embrittlement is made. Helium embrittlement and a proposal for an additional embrittling mechanism operative under neutron irradiation are discussed.
Helium-Induced Degradation in the Weldability of an Austenitic Stainless Steel
Authors: Lin HT , Goods SH , Grossbeck ML , Chin BA
Published: March 2009

Autogenous gas tungsten arc welding was performed on helium doped Type 316 (UNS 531600) stainless steel. Helium was uniformly implanted in the material, using the tritium trick, to levels of 27 and 105 appm. Severe intergranular cracking occurred in both fusion and heat-affected zones (HAZ). Microstructural observations of the fusion zone indicated that the pore size, degree of porosity, and tendency to form cracks increased with increasing helium concentration. Scanning electron microscopy showed that cracking in helium doped materials was due to the precipitation of helium bubbles on grain boundaries and dendrite interfaces. This study's results demonstrate that using conventional welding techniques to repair materials degraded by exposure to radiation may be difficult if the irradiation results in the generation even of rather small amounts of helium.
Modeling Studies on the Precipitation of Krypton After Implantation into Metals
Authors: Rest J , Birtcher RC , Liu A
Published: March 2009

A rate-theory approach is applied to interpreting observations on the precipitation of krypton injected into nickel at temperatures between 300 and 830 K. At temperatures of 670 K or higher, the implanted krypton precipitates evolve into a bimodal size distribution comprising small solid precipitates and larger, faceted bubbles. The calculations explore the dependence of the observed bimodal distribution on the maximum size of the solid krypton bubbles and the effect of this dependence on bubble mobility. The analyses suggest that during the irradiation, the large bubbles move by surface diffusion control, but the solid krypton precipitates are immobile. The relevance of the krypton-nickel interaction to the maximum size of the solid krypton precipitates is discussed.
Simulation of Solid Inert Gas Bubbles in Metals
Authors: Srinivasan S , Tyagi AK , Krishan K
Published: March 2009

Recent work on the precipitation of inert gases in metals has shown that heavier inert gases such as argon, krypton, and xenon implanted into metals at ambient temperatures can form three-dimensional solid precipitates (referred to as solid bubbles). The formation of solid inert gas bubbles in nickel, aluminum, copper, gold, silver, molybdenum, iron, titanium, and zinc has been reported. We have examined some of these experimental results and found a strong correlation between the solid inert gas lattice parameter and that of the host matrix. In particular, we have carried out an atomistic computer simulation study of solid argon bubbles in nickel. The general features obtained from these results are, however, applicable to other gas-metal systems also.

Three different types of defect configurations in nickel are reported: (1) three-dimensional argon bubbles; (2) argon platelets in (111) planes; and (3) small clusters of argon atoms and vacancies. The relaxation fields of argon and nickel atoms, surface energy at the bubble-matrix interface, and bubble pressure have been computed. The results show that argon atoms can show both inward and outward relaxation with a very strong relaxation field at the surface. The hydrostatic stress shows strong variations at different shells in solid argon although the average bubble pressure is consistent with the experimentally determined pressures. We have also examined the possibility of large relaxation fields in the nickel matrix that could lead to loop punching but do not find any evidence for this.
Microstructural Development in Neutron Irradiated Zircaloy-4
Authors: Yang WJS
Published: March 2009

Zircaloy-4, a zirconium base alloy used extensively as cladding and core structural material in water cooled nuclear reactors, was examined by transmission electron microscopy after neutron irradiation and postirradiation annealing. Phase instabilities found during irradiation include the amorphous transformation and the dissolution of intermetallic precipitate Zr(Fe,Cr)2 in the α-recrystallized matrix and the dissolution of the metastable precipitate Zr4(Fe,Cr) in the β-quenched matrix. The alloy is driven toward a single phase solid solution during the irradiation. The presence of fast diffusion iron species in the matrix due to the precipitate dissolution may have caused the irradiation growth breakaway phenomenon. The microstructural evolution during irradiation consists of ¯c dislocation development and grain boundary migration. The presence of ¯c dislocations indicates permanent strain in the matrix. The postirradiation annealing at 833 K does not anneal out the ¯c dislocations. The ¯c dislocation is postulated to have developed due to the intergranular constraints under the continuous growth in the breakaway region.
The Influence of Microstructure and Solutes on Void Formation and Void Growth in Irradiated Materials
Authors: Stoller RE , Mansur LK
Published: March 2009

In the present work, the reaction rate theory of radiation effects has been used to compare the relative significance of several microstructure-dependent mechanisms that influence void formation and growth. Some of these mechanisms reduce the time required for a gas-stabilized bubble to reach the critical size for void formation by either increasing the gas accumulation rate or by reducing the critical number of gas atoms required for void formation. Void growth can be increased by mechanisms that lead to more efficient partitioning of vacancies to the voids. Several of these mechanisms involve the presence of precipitates; they are: helium collection at matrix-precipitate interfaces, point-defect collection at matrix-precipitate interfaces, the interface energy credit due to the coupled growth of a cavity-precipitate pair and possible local bias effects due to matrix-precipitate interface strains. The influence of the total precipitate sink strength on the evolution of matrix cavities has also been examined. Other mechanisms included in this comparison are helium collection at network dislocations and solute trapping. The results of the comparison indicate that a “favorable” microstructure can lead to large reductions in the void formation time and increases in the void growth rate. The influence of precipitates shown in this work is consistent with the experimental observation that the largest voids in irradiated alloys are frequently associated with these particles. Helium and point-defect collection are shown to be the most significant precipitate effects. The former influences primarily the incubation time and the latter, both the nucleation time and the swelling rate. Helium trapping at dislocations can also accelerate void formation to a great degree when some fraction of the trapped helium is distributed to bubbles.
The Development of Periodical Spatial Structures in Crystals under Irradiation
Authors: Sugakov VI
Published: March 2009

Due to the elastic interaction of point defects created by external irradiation, the homogeneous distribution of defects is shown to become unstable at defect concentration larger than certain threshold value and the superlattice of defect density appears in the crystal. The parameters of the superlattice are determined by kinetic characteristics of the system (diffusion coefficient, lifetime of defects, and so on). The created superlattice is an example of the dissipative structure that exists far from equilibrium. The condition of development, the stability, the main parameters of superlattice are analyzed for three cases when a crystal contains (1) vacancies, (2) vacancies and interstitials, and (3) vacancies, interstitials and traps for defects. The calculations show that for realistic parameters of crystals and realistic conditions of irradiation the most preferable conditions for the creation of superlattice occur in the third case.
Surface effect on Dislocation Loop Formation
Authors: Hashimoto T
Published: March 2009

The nucleation of interstitial loops, in the presence of a defect flow toward the surface, is investigated using a rate theory based model. A di-interstitial is assumed to be the nucleus of a dislocation loop, and both homogeneous and heterogeneous nucleations are considered. One-dimensional diffusion of point defects toward the surface is included in the formulation. Two stages appear in the loop nucleation due to the difference in mobility of interstitials and vacancies. In the first stage, loop nucleation occurs under the condition in which only interstitials migrate toward the surface and are lost. The loop concentration initially increases linearly with time, and then nucleation slows down. The second stage begins when vacancies migrate to the surface, and the loop concentration increases, again linearly with time. The defect-production rate dependence of loop concentration, when compared at a constant time, varies from square to linear as irradiation proceeds. The activation energy of loop nucleation is equal to the migration energy of the interstitial in the first stage, and is equal to the migration energy difference between the interstitial and the vacancy in the second stage. Because the increase of loop nucleation in the second stage occurs earlier near the surface, the depth of the layer devoid of dislocation loops decreases as irradiation is continued.
The Slowing Down of Dislocation Climb by Voids at Later Stages of Material Irradiation
Authors: Borodin VA , Ryazanov AI
Published: March 2009

One of the most interesting recent results in the realm of irradiation creep studies is the experimental demonstration of creep cessation in stainless steel 316 at high neutron exposures. Different mechanisms have been proposed to explain this phenomenon. Here we discuss in some detail one such mechanism that is related to the diffusional interaction of climbing dislocations with voids. It is shown that the pipe diffusion of point defects along dislocations can result in “capturing” of dislocations by voids. On the other hand, the kinetics of growth of dislocation-associated voids differ from that of voids in the material volume.
Void Ensemble Response to Periodical Variations of Irradiation Conditions
Authors: Koptelov EA , Korolev VV
Published: March 2009

On the basis of the rate theory approach to void swelling we consider analytically the response of the radiation-induced defects to harmonic oscillations of irradiation parameters. The small deviations δx of the squared radius from its value in the stationary regime are shown to obey, in a linear approximation, the equation of a forced oscillator with damping. The term corresponding to an external force accounts for periodical variations of the damage rate or the irradiation temperature or both. The damping decrement σ considerably exceeds the intrinsic frequency of the system Ω, which means that in real irradiation conditions no resonance phenomena can exist. Thus, the deviations δx could be significant only for frequencies ω of irradiation parameters oscillations that are not too large compared to ωeff = Ω2/2σ. The average void growth rate, however, remains practically unaffected by irradiation parameters pulsing almost in the whole temperature range of swelling except in the zone adjacent to the high temperature limit of swelling. Numerical data for meson physics facility irradiation with a typical frequency of 100 Hz and duty factor of 10-2 are presented.
An HVEM Study of Displacement Cascade Damage in Nb3Sn at 13 K
Authors: Kirk MA , Baker MC , Kestel BJ , Weber HW , Kampwirth RT
Published: March 2009

We have begun a series of experiments to study the defect structure produced by ion irradiation in A15 superconductors. Low temperature irradiations and microscopy are performed in the high voltage electron microscope (HVEM) accelerator facility at Argonne National Laboratory, Argonne, IL. The first transmission electron microscope (TEM) images of the martensitic structure in niobium three tin (Nb3Sn) were recorded at various temperatures between 12 and 30 K. The transition to the superconducting state was observed by a slight deflection of the electron beam due to a perturbation of the magnetic field of the objective lens at the sample. The primary interest is in irradiation effects due to fast neutrons from a fusion reactor, and therefore, ion irradiation conditions that are somewhat comparable to this were selected. These consisted of 50 keV Xe+ irradiations to simulate neutron produced cascades in a near surface region (<20nm) and 1.5 MeV Kr+ to produce cascade damage through a greater sample thickness (0.5μm). Defect images were obtained as a function of ion dose at 13 K using both fundamental and superlattice dark field reflections in two-beam conditions.

For 50 keV Xe+ irradiations at 13 K, the defect yields, which are black-white contrast features in fundamental reflections or black dot contrast features in superlattice reflections, were quite low at low ion doses (2 × 1011 cm-2), where individual defect cascades are well separated. At higher ion doses (3 × 1012 cm-2), when significant cascade overlap is present, defect density and contrast became greater than expected. Annealing to room temperature produced a large increase in visible defect density. Irradiation by 1.5 MeV Kr+ at 15 K removed the martensitic structure by an ion dose of 5 × 1012 cm-2, Further irradiation to 3.5 × 1013 cm-2 produced evidence for the initial stage of amorphization.
Phase Dissolution Caused by Reimplantation Studied by Mössbauer Effect
Authors: Asundi VK
Published: March 2009

Some effects of high dose implantation, performed at room temperature to implant iron ions in aluminum, have been examined by Mössbauer spectroscopy (MS). The changes brought about by post-implantation heat treatments and subsequent reimplantation have also been studied, with special reference to the formation and dissolution of intermetallic phases. The values of the quadropole split with ΔE and the quadrupole doublet shift δsq have been used for phase identification. The Mössbauer observations have been interpreted, keeping in view the results of earlier investigations based on Rutherford backscattering spectrometry (RBS) and X-ray diffraction (XRD) on aluminum specimens subjected to implantation and thermal treatments somewhat similar to those used in the present work.
Atomistic Computer Simulation of Alloy Corrosion
Authors: Newman RC , Song Q , Cottis RA , Sieradzki K
Published: March 2009

Atomistic computer simulation is concerned with the modeling of the behavior of an alloy by modeling the dissolution of individual atoms from a section of a simulated crystal. Monte Carlo techniques are used for the construction of a random array of atoms in the crystal lattice and to decide on the behavior of individual atoms. The technique has previously proved valuable in understanding several aspects of dealloying; this paper is concerned with the extension of this work to cover the active-passive transition in binary alloys such as Fe-Cr. It is found that a very simple set of rules for estimating the dissolution probability for an individual atom can give a realistic representation of the active-passive transition. These rules are based on the concept that fully developed passivity due to the chromium content of the alloy depends on the existence of continuous chains of -Cr-O-Cr- linkages at the metal surface.
Modeling of Electrode Processes and Surface Chemistry in Carbon Dioxide Containing Solutions
Authors: Turgoose S , Cottis RA , Lawson K
Published: March 2009

Corrosion processes and the rates of the individual electrode reactions in carbon dioxide containing solutions are well known to be affected by solution composition and hydrodynamics. There are many different mechanistic explanations for the observed, from rotating-disk studies, cathodic current-potential-rotation speed relationships, most of which obtain the observed currents by the simple addition of two or more currents due to processes (for example, chemical reactions and diffusion) that are considered to act independently. The validity of this is not clear, since many of the species contributing interact in the boundary layer.

A model is described that derives cathodic current densities and surface solution chemistries for the rotating-disk electrode over the range of conditions of practical relevance. The model allows for the slow homogeneous chemical step of carbon dioxide hydration, diffusion, convection, charge transfer processes, and the rapid acid-base equilibria. It is shown that the experimental data are adequately modeled without the need to consider a heterogeneous surface hydration of carbon dioxide, and that the electrochemical response under conditions not previously studied is predicted. Further, the increase in cathodic limiting current at pH > 6 is shown to be a consequence of the solution chemical equilibria and the direct reduction of bicarbonate is not necessary to explain the experimental data. None of the mechanisms previously proposed is valid over the entire pH range of interest.

The concentration profiles in the near surface region throw light on the rate determining steps in the cathodic process and can be used to predict the possibility of surface film formation.
Computation of Corrosion Macrocell Current Distribution and Electrochemical Impedance of Reinforcing Steel in Concrete
Authors: Kranc SC , Sagues AA
Published: March 2009

The case of a reinforcing steel bar experiencing localized corrosion in a concrete cylinder has been modeled numerically to obtain the d-c macrocell current distribution and the associated electrochemical impedance response. The bar contains a small anodic and a large cathodic region. Cylindrical symmetry has been assumed. The d-c polarization problem was solved using finite-difference equations applied to a two-dimensional grid. The boundary conditions included polarization at the cathode, accounting for both activation and diffusional effects. The a-c impedance calculation was made for cylindrical counter electrodes. The computation used a two-dimensional equivalent circuit resistive grid representing the electrolyte and calculated for cylindrical geometry. The a-c polarization conditions at the bar surface were represented by discrete impedance elements, computed from the current densities obtained in the d-c calculation. Both activation and diffusional impedance components were considered as well as interfacial capacitance. The model was used to investigate macrocell current distribution and the applicability of electrochemical impedance to the measurement of corrosion currents in reinforced concrete structures with large cathode-to-anode area ratios. Predicted impedance spectra for concrete resistivity of 10 000 Ω-cm, with an effective oxygen diffusion coefficient of 10-5 cm2/s, and for various cathode/anode area ratios are presented. The results show that the distribution of the alternating current excitation emphasizes the impedance contribution of the cathodic reaction to the overall impedance spectrum.
Software for Quantitative Analysis of Polarization Curves
Authors: Shih H , Mansfeld F
Published: March 2009

A computer program (POLFIT) has been developed for the analysis of polarization curves that provides full graphics functions and has both simulation and fitting procedures. Electrochemical parameters such as anodic and cathodic Tafel slopes, polarization resistance, corrosion current density, and corrosion potential, the errors for each of these parameters, and the results of the statistical analysis are displayed in tabular form. The experimental and fitted polarization data are plotted on the computer screen and can be obtained as hard copies. A unique feature is the possibility of eliminating the uncompensated ohmic resistance (Ru) in the data analysis. Inspection of the current deviation between the experimental and fitted data points at each potential allows elimination of data points with excessive scatter and detection of systematic errors such as those arising from the neglect of Ru in the data analysis. The performance V of the program has been evaluated for theoretical data with various random normal noise levels and for experimental data (Cu/artificial seawater).
Software for Simulation and Analysis of Electrochemical Impedance Spectroscopy (EIS) Data
Authors: Mansfeld F , Tsai CH , Shih H
Published: March 2009

The software program BASICS can be used for the simulation and analysis of simple corrosion systems which are under charge transfer or mass transport control. Data for systems under charge transfer control ( one-time-constant model ) can be analyzed with the Bodefit method using Bode-plots, the Cirflt method using complex plane plots, and the Intfit method using plots of —Z″ versus log f. Data for systems under mass transport control can be analyzed with the Warfit method using complex plane or Randles-plots. Systems for which an inductive loop is observed can be analyzed with the Indflt method. Examples are given for the simulation and analysis of impedance data for the three different systems.
Computer Modeling of Corrosion Using the Boundary Element Method
Authors: Adey RA , Niku SM
Published: March 2009

The development of computational systems for the simulation of galvanic corrosion is discussed. Techniques are described for the representation of the physics and chemistry of corrosion in mathematical form and their computational implementation. Applications of the system to marine and offshore engineering problems are described.
Analysis of Some Compliance Calibration Data for Chevron-Notch Bar and Rod Specimens
Authors: Orange TW , Bubsey RT , Pierce WS , Shannon JL
Published: March 2009

This paper presents a set of equations describing certain fracture mechanics parameters for chevron-notch bar and rod specimens. They are developed by fitting earlier compliance calibration data. Numerical differentiation must be used to determine the minimum stress intensity factor and the critical crack length, and the problem this presents for these specimens is discussed.
Aluminum-Lithium Alloys: Evaluation of Fracture Toughness by Two Test Standards, ASTM Method E 813 and E 1304
Authors: Purtscher PT , McColskey JD , Drexler ES
Published: March 2009

Fracture toughness of three aluminum-lithium alloys and Alloy 2219 (a total of nine different plates) was measured with two different types of specimens and methods: (1) compact specimens using ASTM E 813 and (2) chevron-notched short-bar specimens using ASTM E 1304. The properties were measured in two orientations (T-L and L-T) and at three temperatures (295,76, and 4 K). In general, the short-bar specimens exhibited a higher fracture toughness than the compact specimens. The difference between the two procedures was relatively constant, independent of test orientation and strength. However, when the specimens exhibited extensive delaminations on the fracture surface, the compact specimens had a higher fracture toughness than the short bar specimens. The difference in fracture toughness measured by the two procedures is explained in terms of the alloys' crack growth behavior.
Use of the Chevron-Notched Short Bar Test to Guarantee Fracture Toughness for Lot Release in Aluminum Alloys
Authors: Bray JW
Published: March 2009

Chevron-notched short bar fracture toughness (KIvM per ASTM E 1304) has been correlated with plane strain fracture toughness (KIc or KQ per ASTM E 399 or ASTM B 645) for commercial 2124-T851, 7050-T7451, 7050-T7651, and 7475-T7351 plate.

It was found that the chevron-notched and KIc(KQ) test methods correlated regardless of alloy, orientation, or temper. However, larger scatter in the higher toughness materials resulted in expected retest rate advantages (% of time the correlative test would fail and the referee test would pass lot release) when separating the results into “low” and “high” toughness databases. An A value minimum approach, via computation of derived properties (as defined in paragraphs 9.2.10 and 9.2.11 of Military Handbook 5E), was used to calculate the lot release correlations between KIvM and KIc(KQ). In addition, statistical correlations were performed on the entire database in order to utilize the chevron-notched short bar test more effectively for research and development programs.
Chevron-Notched, Flexure Tests for Measuring the Elevated-Temperature Fracture Resistance of Structural Ceramics
Authors: Jenkins MG , Ferber MK , Ghosh A , Peussa JT , Salem JA
Published: March 2009

Chevron-notched, three-point flexure specimens were used to study the quasistatic fracture behaviour of a variety of structural ceramics at temperatures to 1400°C. Types of materials tested included monolithic ceramics (SiC., Si3N4, MgAl2O4), self-reinforced monoliths (acicular-grained Si3N4, acicular-grained mullite), and ceramic matrix composites (SiC whisker/Al2O3 matrix, TiB2 particulate/SiC matrix, SiC fibre/CVI SiC matrix, Al2O3 fibre/CVI SiC matrix).

Fracture resistance behavior of the materials was quantified as three distinct regimes of the fracture histories. At the initial part of the crack propagation, the apparent fracture toughness was evaluated as the critical stress intensity factor for the chevron notch, KIvM. During stable crack propagation, the crack growth resistance was characterized by the instantaneous strain energy release rate, GR, using a compliance method assuming linear-elastic unloading to calculate the effective crack lengths. At final fracture, the complete fracture process was quantified using the work-of-fracture, γWOF, which can be equated to the fracture surface energy for linear-elastic materials.

Results indicate that the chevron-notched, three-point flexure specimen facilitates the study of fracture behaviour in a wide range of brittle and quasi-brittle materials at elevated temperatures. The unique features of the chevron geometry, which are automatic crack initiation and inherent stable crack growth, are crucial to the successful evaluation of the fracture tests.
Failure of Graphite/Epoxy Panels with Stiffening Strips
Authors: Sawicki AJ , Graves MJ , Lagace PA
Published: March 2009

Nine graphite/epoxy panels were tested in uniaxial tension to examine the ability of stiffening strips to redirect propagating damage. The materials used were Hercules A370-5H/3501-6 prepreg fabric and AS4/3501-6 prepreg unidirectional tape. The layup of the unstiffened regions of the panels was four plies of fabric with the quasi-isotropic layup [0f/45s]f. Three different four-ply unidirectional tape stiffener layups parallel to the applied load were tested. The specimen width was 203 mm with stiffener widths of either 48 or 64 mm. Slits of three lengths, 51, 71, and 102 mm (1.0 mm wide), were precut into the panels perpendicular to the direction of loading. The panels were tested under load control. Stress-strain and photoelastic data were taken. The finite element code ADINA was used to examine the two-dimensional response of the panels. The three slit lengths were modeled to gain an understanding of the local stress and strain response ahead of the slit in the stiffened region. Contour plots of maximum strain and the orientation of these maximum values with respect to the load direction near slits and stiffened regions were generated. These analytical models showed higher strains in the stiffened regions ahead of the slit compared to the strains in the unstiffened regions. The local orientation of the maximum tensile strains in the stiffened regions ahead of the slit remained perpendicular to the slit and parallel to the applied load. At failure, propagating damage progressed directly across the stiffener either perpendicular to the applied load or at 45° with respect to the applied load. It is concluded that the maximum tensile strain and its orientation ahead of the slit, as derived from the analysis, plays a key role in the prediction of subsequent damage propagation in these laminates. It is also concluded that the structural and material couplings, due to the unsymmetric layups in the stiffener regions, have little, if any, affect on the ability of the stiffener to redirect damage propagation, since in all cases damage progressed through the stiffeners.
Failure Initiation and Ultimate Strength of Composite Laminates Containing a Center Hole
Authors: Chu GD , Sun CT
Published: March 2009

A failure analysis method that includes the free edge effect was proposed for failure prediction in composite laminates containing a center hole. The location of onset of failure in the hole was determined by comparing the strengths of off-axis coupon specimens with the hoop stress around the hole. The subsequent failure progression was performed by the ply-by-ply classical laminate failure analysis. Experiments on [0/90/±45]s and [0/90]s laminates and their off-axis specimens were performed to verify the present method.
Matrix Cracking-Induced Delamination Propagation in Graphite/Epoxy Laminated Composites Due to a Transverse Concentrated Load
Authors: Liu S , Kutlu Z , Chang F-K
Published: March 2009

An investigation was performed to study the delamination propagation induced by matrix cracking in graphite/epoxy laminated composite beams subjected to transverse concentrated loading. The major focus of the study was to fundamentally understand the interaction between matrix cracking and delamination propagation in laminated composites resulting from transverse loadings. A nonlinear finite element analysis combined with a failure criterion and fracture mechanics was developed for modeling the damage initiation and propagation in composite beams subjected to a concentrated line load. A contact analysis based on the Lagrange multiplier technique was also adopted for modeling the contactslip condition of delamination and matrix crack surfaces during loading. Results of the calculations based on the analysis were compared favorably with the existing data and the data generated during the investigation.
Evaluation of Impact Damage in Composite Materials Using Acoustic Emission
Authors: Bolduc M , Roy C
Published: March 2009

The Defence Research Establishment, Valcatier (DREV) has been studying the application of composite materials for use in a lightweight anti-tank recoilless gun. Since thermoset resins are very sensitive to impact, it is important to determine the severity of damage using a nondestructive technique in order to establish the serviceability of the tube.

Acoustic emission (AE) was identified as a very promising method to measure the level of damage accumulation due to low-velocity impact, and a study was undertaken. The experimental program consisted of impacting 28 of 36 tubes with energies varying from 3 to 18 J. These tubes, fabricated by a wet winding process using carbon fiber/epoxy resin, were 25.4 cm long, and had a 9-cm internal diameter and a 3.6-mm wall thickness. The winding angle was ±71°. The AE was measured while pressurizing these tubes to rupture. Results indicate the potential of acoustic emission as a means of estimating the serviceability of a composite tube.
Modeling Ply Crack Growth in Laminates Under Combined Stress States
Authors: Chatterjee SN , Wung ECJ , Yen CF
Published: March 2009

First ply failure in brittle matrix composites usually indicates generation of transverse cracks in a ply. In a laminate, these cracks cannot cause failure since they are constrained by fibers in adjoining laminae. Many investigators are studying stiffness loss due to such cracks under transverse tensile stresses. In this work, use is first made of a phenomenological approach that models the response of homogeneous materials that have a large number of possible microcrack planes with different orientations in space. Densities of cracks of similar orientation can be treated as internal variables in the strain (or complementary) energy, which is also a function of the average strains (or stresses) over a representative volume element. The energy formulation is employed to model the response of a lamina under combined stresses containing cracks parallel to fibers. Estimates of the change in complementary energy due to the dilute concentration of cracks in a ply as obtained from simple solutions and results reported in literature are utilized to calculate the increase in compliance. Crack initiation and growth are predicted by the use of criteria which are similar to those used for homogeneous media. Results are compared with test data for ( ± θ)ns layups for small and moderate crack densities. A relationship is established between the phenomenological and fracture mechanics-based approaches for the particular case of cross ply layups with large crack densities. Results are compared with test data. Advantages and limitations of both approaches are discussed.
Thickness Effect of Double Cantilever Beam Specimen on Interlaminar Fracture Toughness of AS4/PEEK and T800/Epoxy Laminates
Authors: Hojo M , Aoki T
Published: March 2009

The influence of specimen thickness on Mode I interlaminar fracture behavior was investigated with laminates made from ICI APC-2 prepregs (AS4/PEEK) and from Toray P2212 prepregs (T800/epoxy). The mechanisms of the influence of the thickness effect were discussed on the basis of the direct measurement of the fiber bridging. Double cantilever beam (DCB) specimens 3, 4, 5, and 8 mm thick were prepared from the same unidirectional laminate of 8 mm in thickness in order to avoid molding effects. Fracture toughness, GIC, at the initiation of crack growth was carefully measured in order to clarify the increment of GIC from the initiation values with crack propagation. The initiation values of GIC were independent of the specimen thickness both for AS4/PEEK and T800/3631 laminates. The GIC values for AS4/PEEK laminates increased quickly from the initiation values and leveled off. The thicker specimen indicated slightly higher propagation values of GIC. The thickness effect obtained here was much smaller than that obtained from specimens of originally different thickness. For the case of T800/epoxy laminates, two series of tests from different panels indicated different propagation values of GIC. For one panel, the values of GIC increased continuously with crack length, whereas for the other panel, the GIC values were almost constant, and agreed with the initial values. The influence of different panels and the scatter of data was much larger than the influence of specimen thickness. This suggests that the propagation values of GIC can be used as an indication of fiber alignment of laminates which cannot be detected by the initiation values of GIC. Fiber-bridged zone length was measured in order to discuss the mechanism of the R-curve behavior. A weak correlation between the fiber-bridged zone length and the increase of GIC from the initiation value was observed.