bluuebunny/crossref_metadata_2025_split huggingface dataset:
An Elastic-Plastic Finite-Element Analysis of the J-Resistance Curve Using a CTOD Criterion
Authors: Newman JC , Booth BC , Shivakumar KN 
Published: February 2009

The tentative test procedure for determining J-R curves (crack-growth resistance curves based on the J-integral) on compact and three-point bend specimens showed a discrepancy between specimen types: the bend specimen gave a higher J-R curve than the compact specimen. The purpose of this paper is to investigate this discrepancy, numerically, by simulating the fracture process on compact and bend specimens using a two-dimensional finite-element analysis and a critical crack-tip opening displacement (CTOD) criterion.
An elastic-plastic (incremental and small strain) finite-element analysis was used with the critical CTOD criterion to model stable crack growth in compact specimens made of HY-130 steel. A combined analysis between plane-stress and plane-strain conditions was found to simulate the fracture process quite well. In the combined analysis, plane-strain conditions were imposed around the crack tip while plane-stress conditions were imposed elsewhere. The same analysis was then used to predict stable crack growth behavior of bend specimens. J-R curves were then calculated from the numerical results for each specimen type using several different methods. In general, the J-R curves obtained from the bend specimens were higher than those obtained from the compact specimens, especially beyond maximum load. Up to maximum load, however, the modified deformation theory of plasticity J*D and the contour-integral JΓ methods gave essentially the same J-R curves for both specimen types.
Evaluation of the KISCC Testing Procedure by Round Robin Tests on Steels
Authors: Yokobori T , Watanabe J , Aoki T , Iwadate T 
Published: February 2009

Round robin test programs of the tentative test procedure for the determination of the threshold stress-intensity factor KISCC were conducted under the auspices of the 129th Committee, Japan Society for the Promotion of Science. The test programs used JIS SNCM 439 (AISI 4340) steels. Thirty-one laboratories participated in these programs. Tests were carried out with both 25.4-mm (1-in.)-thick bolt loaded wedge-opening-loading (WOL) specimens and 25.4 by 25.4-mm cantilever beam (CB) specimens in a 3.5% sodium chloride solution of distilled water.
The results of the round robin test programs showed some informations to standardize the KISCC testing procedure. For valid KISCC values to be obtained, the test must last 7000 h for a WOL specimen and 4000 h for a CB specimen. In the WOL tests, the final crack length and width ratio af/W of a specimen must be smaller than 0.8. An elastic bolt analysis of WOL specimens was recommended to obtain the valid KISCC values and the good relationship between da/dt and KI. In the CB tests, the estimated KISCC value coincided well with that in the WOL tests when at least six CB specimens were used. Slight effect of crack front curvature, test temperature, and pH of the solution on the variance of the KIf values was observed.
With these test results, the KISCC testing procedure was standardized by the Committee and entitled “Standard Test Method for Threshold Stress Intensity Factor KISCC in Stress Corrosion Cracking.”
On the Accuracy of Ductile Failure Assessments
Authors: Hodulak L , Blauel JG 
Published: February 2009

Ductile failure assessments of cracked specimens and components performed on the basis of the J-integral and the limit load concepts are discussed with particular interest in their ability and accuracy to predict actual failure loads. Possible sources of uncertainty in the modeling of material behavior and geometry are treated separately, comparing appropriate calculations with each other and with experimental data.
Especially approximate methods for evaluating Japplied are checked against finite-element calculations and are found accurate in all cases where plane models are relevant. The influence of the stress-strain law on the results of failure predictions is examined in detail, and a procedure is proposed for an appropriate evaluation of the Ramberg-Osgood constants in the Electric Power Research Institute estimation scheme. In addition, the influence of a variation of the material J-R curve and of the crack growth model in failure assessments is demonstrated for several examples.
Computation of the Crack-Tip Energy Release Rate for Cyclic Crack Growth
Authors: Wilkening WW 
Published: February 2009

The elastic-plastic finite-element method, employing the mechanical sublayer theory of plasticity, was used to compute a local crack-tip parameter which shows significant promise for characterization of the cyclic crack growth process. The proposed cyclic crack growth rate characterizing parameter is the crack tip value of the energy release rate. This crack-tip energy release rate (G0), has been shown to be equivalent to the global energy release rate (G), for the case of monotonic loading of a stationary crack. This work extends the proposed definition of the crack tip energy release rate to cyclic loading, including the important effects of crack growth.
Elastic-plastic incremental finite-element analyses of a model which represents the elastically-bounded crack-tip region for the case of small-scale-yielding (SSY) have been performed, for both stationary and growing cracks. The crack-tip energy release rate G0, computed by the simple technique described here, was compared with the magnitude of the remote elastic K-field loading which was applied at the outer boundary of the SSY model, under plane-strain conditions.
The effects of plasticity-induced crack closure upon G0 were investigated by allowing the crack tip to advance into the prior residual plastic zone in several steps, until a steady-state condition was achieved. The occurrence of crack face closure during the unloading portion of each loading cycle and of the subsequent reopening of the crack during the next loading cycle was accurately determined. From these computational results, a modified definition of G0, embodying the effects of plasticity-induced crack closure, was developed. The results of these investigations show, generally, that the crack-tip energy release rate, when appropriately defined and computed in the context of cyclic loading, crack advance and crack face closure, provides a consistent and rational description of the local driving force acting upon the tip of a growing crack. As such, G0 should prove to be a viable cyclic crack growth characterizing parameter.
A New Average-Power Damage Test Facility at LLNL
Authors: Hildum EA , Rainer F , Milam D 
Published: February 2009

We describe a new facility for studying damage induced by 1064-nm, 16-ns, 0.6-J laser pulses at repetition rates up to 120 Hz. This facility is built around four commercial 30-Hz Nd:YAG lasers fired under computer control. The beams from the four lasers are combined using thin-film polarizers and rotating half-wave plates to obtain a single irradiated spot on a test target. We also describe computer controlled beam diagnostics based on a commercial video frame-grabber.
This facility has been used to compile a database of damage thresholds for a variety of materials under average power conditions. Details of this database are presented in a companion paper.
A Sensor for Production Oriented Damage Testing at 1.06μm
Authors: Arenberg JW , Schoen CL , Mordaunt DW 
Published: February 2009

Detection for production laser damage testing at 1.06μm may be accomplished by a single scheme of flash detection. This scheme uses the test wavelength, 1.06/OT, to detect catastrophic damage events and is sufficient to detect the plasma associated with catastrophic damage, the failure morphology typical of production damage testing.
The detection scheme consists of a fiber optic bundle used as a light pipe and a photomultiplier tube as a detector. Uhen introduced into the target area, the collection end of the light pipe is the only element of the detector that need be in proximity to the target area. Since the light pipe has a wide acceptance angle, precise location and orientation of the light pipe end is not required. Therefore, the detector may be moved in and out easily without compromising detector performance. The detector is used in conjunction with electronics that allow the user to define a non-damage level of scatter. When damage occurs and the characteristic plasma plume is formed, a comparator detects the signal exceeding the set threshold and registers a damage event.
The simplicity and low cost aspects of the detection scheme make it a good candidate for all production damage testers at l.06μm. Furthermore, the detection apparatus may be linked electronically to the test laser to shut off the test source upon detection of damage to prevent gratuitous damage to the sample under test. The incorporation of such a binary damage detector is suitable for use in an automated and, therefore, enclosed (Class I) damage tester for use on factory floors.
Laser Damage Studies of Ion Beam Milled Fused Silica
Authors: Wilson SR , Reicher DW , McNeil JR , McNally JJ , Stowell K , Milam D , Gonzales R , Rainer F 
Published: February 2009

Ion beam figuring is a promising optical fabrication technique in which substrate material is removed from an optical component by selectively ion beam milling the surface. The effects of ion beam milling on the properties of the optical surface are not completely understood. One area of investigation is the influence of ion beam milling on the laser damage threshold of the substrate. The ion milling process removes part of the damage layer at the surface of the optic formed during fabrication, and this might result in modification of laser damage behavior.
As part of an investigation of the ion beam figuring process, a study was undertaken to determine the effect of ion milling on the laser damage threshold of fused silica. Fused silica substrates were ion milled to depths up to ten microns using a 1500 eV, 40mA Argon ion beam from a Kaufman ion source. The milled substrates were then subjected to laser damage testing using a 1064 nanometer wavelength laser. The tests were performed using one nanosecond pulse width single shot pulses and sixteen nanosecond pulse width thirty Hz pulses. The results indicate that ion beam milling has no significant influence on the damage threshold.
Ion Assisted Deposition of Optical Thin Films at Reduced Substrate Temperature
Authors: Williams FL , McNeil JR , McNally JJ , Exarhos GJ 
Published: February 2009

Ion assisted deposition (IAD) involves bombarding a thin film with low energy ions (Ei &lt;1 keV) while it is being deposited. We have investigated the application of this technique to deposit optical thin films onto substrates at low temperature (T &lt; 150°C). Since conventional deposition methods require heating the substrate to temperatures of −300°C, IAD is important for coating substrate materials that cannot be subjected to elevated temperature.
In this study, we have observed that optical coatings of A12O3, Ta2O5 and TiO2 deposited at low temperature using IAD have higher values of refractive index compared to similar films produced without IAD. In addition, the optical absorption of Al203 and Ta2O5 thin films can be decreased by applying IAD to deposit these materials. We were unable to detect visible absorption of TiO2 thin films produced in this study. We also present results correlating Raman spectra and optical scatter of these films to IAD conditions. Which suggests that IAD TiO2 at low temperature can promote anatase crystallites in the film, with a corresponding increase in optical scatter.
Optical Properties of Low Energy Ion Assisted Deposited TiO2 Films
Authors: Krishna MG , Rao KN , Murthy MA , Mohan S 
Published: February 2009

Absorption in TiO2 films limits their efficiency and stability against high power laser radiation. The optical absorption in single layer TiO2 films is greatly influenced by deposition parameters such as the rate of deposition, oxygen partial pressure, substrate temperature and the starting material. It is also observed that low energy ion assisted deposition enhances the reactivity and results in reduction of absorption.
In this investigation, single layers of TiO2 films have been prepared using ionized oxygen (produced using a Heitmann source) and TiO as the starting material. The optical properties (refractive index n, and extinction coefficient k) and the laser induced damage threshold as a function of deposition parameters has been studied. The discharge currents were varied between 0 and 400 mA with the rate of deposition being 9 and 18 nm/min. The oxygen pressure was maintained at 2×10−4torr. At low deposition rates, in situ optical monitoring of transmission has shown absorption free single layers for moderately low discharge currents (200 mA) whereas at higher deposition rates absorption free films were obtained at higher currents. The damage threshold of these films was found to be directly dependent on the absorption.
Variation in damage threshold values is explained on the basis of film composition, structure and optical properties.
The Discovery of Laser-Induced Intrinsic Optical Damage in Wide-Gap Materials at Visible Wavelength
Authors: Braunlich P , Jones SC , Shen XA , Casper RT , Kelly P 
Published: February 2009

After two decades of research, the question “What is the nature of intrinsic breakdown of wide-gap optical materials exposed to short laser pulses at visible wavelength?” has recently been answered unambiguously for two cases: 532 nm, picosecond pulses tightly focused in NaCl and KBr. This remarkable achievement warrants some reflection on its impact on the field of high laser power optical materials.
Clearly, the problem of extrinsic damage to coatings and surfaces remains unsolved and formidable, and the quest for higher damage thresholds will continue without any realistic hope to achieve intrinsic behavior in the foreseeable future. However, such pessimistic realism is no longer justified for bulk breakdown, because the possibility of fabricating intrinsic high-power optical materials—not just alkali halides, but also technologically important alkaline earth halides and metal oxides—must now be taken seriously.
In light of this new development we will re-examine the results of some classic damage experiments and the conclusions on the laser damage mechanisms that were based on erroneous assumptions of intrinsic material behavior. Extrinsic damage, presumed to be intrinsic for the purpose of data interpretation, will always appear to be avalanche formation via electron impact ionization if only damage thresholds are measured.
With this in mind, we will look again at self-focusing and defocusing effects, the traditional exclusive reliance on subjectively defined damage criteria and, thus, uncertain thresholds, and the role of primary laser-generated photo-chemical defects in the historical “workhorse” materials, the alkali halides.
Reverse Thermal Wave Approximation for Temperature Transients in Optical Thin Fitms and Substrates Reflective Optics for High Power Continuous Wave Lasers
Authors: Palmer JR 
Published: February 2009

It is the intent for the purpose of this paper to continue with the application of the Reverse Thermal Wave Model to problems associated with the damage thresholds and temperature gradients for optical components which are provided with optical thin films. This problem is particularly acute for those optical components which are part of a high power Continuous Wave laser system.
In this paper are descriptions of how the approximations provide techniques for evaluating the maximum threshold for optical thin films deposited on components with very thick and very thin optical faceplates. The Reverse Thermal Wave Model provides some rather dramatic results for those optical systems that are used for imaging in the infrared portion of the spectrum, in as much as these optical elements are generally very thin faceplates and may be subject to damage from very high power lasers.
Both mathematical descriptions and figures are provided to show the damage thresholds predicted by the model and correlated to one dimensional semi-infinite plate experimental data For the most part, authors have treated with infinite and semi-infinite walls. The attention for this article is to treat with those conditions that do not meet the boundary requirements for the semi-infinite plate. Given this boundary, the use of what we describe as the Reverse Thermal Wave Approximations will be implemented to allow the calculation of the transient temperature rise in thin optical faceplates. Equations are described and the regimes of their application are outlined Additionally, curves are generated to provide the reader examples of how to implement the equations.
Viscoplasticity Based on Overstress Applied to Creep-Fatigue Interaction
Authors: Krempl E , Lu H , Satoh M , Yao D 
Published: February 2009

The uniaxial version of the viscoplasticity theory based on overstress is applied to the deformation behavior of Type 304 stainless steel at 650°C. The effects of strain rate, waveform, and position of hold-time are computed for a cyclic steady-state as well as the ratchetting behavior under zero-to-tension load control.
The computations of deformation behavior are used in correlating and predicting the low-cycle fatigue life at 593°C using the strainrange partitioning method as well as an incremental damage accumulation law developed previously. The results of the computations exhibit the appropriate trends, but can show deviations from actual life exceeding a factor of two. Considering all the uncertainties, the results are deemed acceptable and promising.
The incremental damage accumulation law permits application to arbitrary stress or strain histories. The effect of position of hold-time on the hysteresis loop is computed and shown to exhibit the appropriate trend.
Application of Small Specimen Crack Growth Data to Engineering Components at High Temperature: A Review
Authors: Skelton RP 
Published: February 2009

This review considers the standard low-cycle fatigue (LCF) specimen, the area of the component it represents, the empirical crack growth relations measured on that specimen, and their ranges of validity. It also presents some recent observations on the effects of crack shape, strain rate, weld material, notches, and aging upon cyclic propagation rates at high temperature.
In applying LCF growth results to estimate crack behavior in service, size effects must be considered. From crack growth tests at constant plastic strain on LCF specimens of differing width, it is shown in both cases that the cracks accelerated, then decelerated after a critical depth which occurred sooner in the smaller specimens. Accompanying variations in the shape of the hysteresis loop and crack closure effects (all of which have implications for service loading) are also reported.
Beyond a certain depth in the specimen, crack growth is no longer describable by the bulk plastic strain, so other parameters (cyclic J integral and equivalent stress intensity) are compared and their ranges of validity discussed.
The survey next considers a constant-load test where, despite equal tension and compression ranges, ratchetting of the specimen occurred, leading to quite different conditions for crack closure. The crack growth data nevertheless agree with LCF data when the correct stress range is taken into account.
Finally, a high temperature lifetime assessment route is briefly described, where the user is permitted to enter a permissible defect path which utilizes many of the experimental short crack data mentioned in this review.
Life of Crack Initiation, Propagation, and Final Fracture under High-Temperature Creep, Fatigue, and Creep-Fatigue Multiplication Conditions
Authors: Yokobori AT , Yokobori T , Kuriyama T 
Published: February 2009

Studies were carried out on the crack initiation and propagation laws under high-temperature creep, fatigue, and creep-fatigue multiplication conditions for notched specimens of SUS 304 stainless steel.
For crack initiation life, it was found that relative notch opening displacement (RNOD) can be used. Furthermore, the remaining part of crack initiation life can be predicted by RNOD criterion; that is, by recording RNOD with respect to the suitable time within the service term and extrapolating the data with a straight line until the line intersects the critical value of RNOD.
The crack propagation life was expressed by a thermally activated type equation in explicit terms of independent parameters such as applied stress and temperature. The equation was approximately expressed in terms of the time-temperature equivalent parameter T(ℓn tp + C), where T = absolute temperature, tp = crack propagation life, and C = a nearly constant numerical factor. The experimental data are well expressed by this parameter.
Creep and Creep-Fatigue Intergranular Damage in Austenitic Stainless Steels: Discussion of the Creep-Dominated Regime
Authors: Levaillant C , Grattier J , Mottot M , Pineau A 
Published: February 2009

Creep and strain controlled low-cycle fatigue tests with an imposed hold time at maximum tensile strain were carried out, mainly at 600°C, on two heats of 316L stainless steel. Very long times to failure (≃ 104 h) corresponding to low applied strain and long dwell period (24 h) were investigated. Both fatigue and creep damage were measured by quantitative metallography.
Creep intergranular surface cracking shortens the initiation stage of fatigue cracks, while creep intergranular bulk cracking accelerates the average fatigue crack growth rate. These observations are the basis for a creep-fatigue interaction model previously proposed using intergranular damage as a life correlating parameter. The applicability of this model is tested with results of 104 h creep-fatigue tests showing a saturation effect. The saturation in creep-fatigue life observed for long dwell periods is explained by an improvement in creep ductility.
This intergranular damage approach is discussed in the light of the creep dominated regime concept. It is shown that pure creep failure data cannot provide reliable prediction of creep fatigue life. The need to use a model that takes into account the effect of creep intergranular damage on fatigue crack propagation is emphasized.
Elevated Temperature Fatigue-Creep Behavior of Nickel-Base Superalloy IN 625
Authors: Bui-Quoc T , Gomuc R , Biron A , Nguyen HL , Masounave J 
Published: February 2009

A research program has been carried out to establish the low-cycle fatigue and creep-fatigue behaviors of Inconel 625 at elevated temperatures (650 and 815°C). The main observations were related to the effect of temperature and of hold times. Under continuous cycling, a temperature increase from 650 to 815°C caused a reduction in the fatigue life by a factor of 2 at a high strain and by a factor of 3 at a low strain.
Tension hold times had little detrimental effect on cyclic life at 650°C concerning the life reduction with respect to continuous cycling; at 815°C, on the other hand, this became more significant. Compressive hold times also had a damaging effect on fatigue life, and this was larger than that associated with tensile hold times; in particular, it was very pronounced for low strain levels at 815°C.
An analysis of data using a life prediction method previously suggested for creep-fatigue combination loadings has also been carried out. The method takes into account the damaging effect due to a compression hold time separately from that due to a tensile hold time in interspersed creep-fatigue loadings. The overall correlation between theoretical calculations and experimental results is reasonably good, for strain levels ranging from 1.2 to 0.4%.