bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies on the Failure Assessment Diagram Using the Estimation Method and J-Controlled Crack Growth Approach
Authors: Shih CF , Kumar V , German MD 
Published: March 2009

The failure assessment diagram procedure for assessing the integrity of flawed structures evolved from the “two criteria” approach due to Dowling and Townley. The present form of the diagram, also referred to as the R-6 diagram, is due to Harrison, Loosemore, and Milne. Chell and Milne generalized the approach to account for thermal and residual stress and for crack growth problems, respectively. The failure assessment curve is obtained by using the Dugdale solution to interpolate between brittle fracture governed by Klc and plastic collapse governed by the limit load Po. This leads to a single failure curve in the R-6 approach. However, it should be noted that the Dugdale solution is intended for a finite crack in a thin infinite sheet subjected to remote tension and also assumes that the material is elastic-perfectly plastic.
Failure assessment diagrams can be determined directly using the estimation method and the J-controlled crack growth approach. The essential elements for constructing the diagrams are the elastic crack solutions (available in several elastic crack handbooks) and the fully plastic crack solutions for the specific crack configurations. It will be shown that the failure assessment equation can be obtained by rearranging the crack growth equilibrium equation associated with the JR-curve approach. The more precise derivations show that the shape and position of the failure assessment curve depend on crack configuration, the relative size of the crack, type of loading, and material deformation properties. Explicit equations for failure curves are derived for elastic-strain hardening material and for elastic-strain hardening material with saturation stress.
Failure curves are constructed for several fracture test specimens and for axially and circumferentially flawed cylinders. The curves are generated for a practical range of deformation properties and crack length-to-width ratios. The usage of these curves is illustrated with several problems. Load-deformation and crack growth behavior of flawed structures can be determined (albeit indirectly!) from the failure curves for the specific structures being evaluated.
On the Unloading Compliance Method of Deriving Single-Specimen R-Curves in Three-Point Bending
Authors: Willoughby AA , Garwood SJ 
Published: March 2009

The application of unloading compliance for deriving single-specimen R-curves in three-point bending has been examined. Various methods, including the use of a double-clip-gage arrangement, are investigated. Finite-element calculations show that the best estimate of crack length is likely to be obtained from the conventional clip gage/load compliance, using a/W ≥ 0.5. The results are compared with those from blunt-notched calibration test specimens and with fatigue-cracked specimens, both with and without side grooves, of two pressure vessel steels. It is found that the initial crack length may be estimated accurately, but that the estimate becomes less precise as tearing occurs. Consequently, predictions of crack extension are rather inaccurate. However, there is considerable scope for improvement in the measurement technique employed, and for the use of correction factors.
The use of two clip gages allows good estimates of load-point displacement, crack-tip opening displacement (CTOD) and J to be made, particularly when plastic displacements become significant. It is suggested that the technique could prove valuable in routine measurements of CTOD and J on bend specimens.
Evaluation of Blunting Line and Elastic-Plastic Fracture Toughness
Authors: Kobayashi H , Nakamura H , Nakazawa H 
Published: March 2009

The Japan Society of Mechanical Engineers (JSME) has made an effort towards standardization of the JIc test method. The recommended procedure includes two multiple-specimen methods [obtained at the intersections of the experimentally determined J-stretched zone width (SZW) blunting line and the R-curve, and of the J-SZW blunting line and the critical stretched zone width (SZWc)] and three single-specimen methods (ultrasonic, electrical potential, and acoustic emission). Concerning the blunting line and the R-curve, many experimental data have been accumulated by the present authors in recent years.
In this paper, the evaluation method of the blunting line and of the R-curve and their application to the JIc test are discussed with special attention to a comparison between two methods recommended by JSME and the American Society for Testing and Materials.
Instability Testing of Compact and Pipe Specimens Utilizing a Test System Made Compliant by Computer Control
Authors: Joyce JA 
Published: March 2009

The aim of this paper is to demonstrate that a computer-controlled test machine can replace a test machine made compliant by a mechanical spring for tearing instability testing of simple compact and cracked pipe geometries. For both geometries tested herein, close agreement was demonstrated between the “computer compliant” and “spring compliant” test systems. The results show that though the computerized system utilized here is slower than the spring machine, this is not a serious drawback for structural materials with low to moderate rate dependence. The “inertia free” response of the computerized system is in fact a positive feature for studying tearing instability arrest and promises to be very useful to further studies in that area.
Experimental results obtained in this study on the circumferentially cracked pipe geometry show that J-R curves from the pipe geometry lie well above J-R curves obtained from subscale compact specimens removed from the pipe wall. Tearing instability occurs in the pipes at crack extension values well in excess of what was obtained from compact specimens of the scale utilized, and a prediction of pipe instability based on the compact J-R curve alone would give very conservative results.
An Analysis of Elastic-Plastic Fracture Toughness Behavior for JIc Measurement in the Transition Region
Authors: Iwadate T , Tanaka Y , Ono S , Watanabe J 
Published: March 2009

Fracture toughness tests were performed in the transition region for ASTM A508 Class 3 and A470 nickel-chromium-molybdenum-vanadium steels using about 300 specimens of 0.5T, 1T, 2T, and 4T compact tension (CT) specimens. The KJ-values which are converted from Jc of the smaller specimens indicated a wide scatter ranging from below the KIc-value to much higher toughness. The fracture behavior was investigated with a scanning electron microscope in detail and the sources of scatter of the toughness in small specimens were studied. The fast brittle fracture behavior in the transition regime can be divided into two regions: (1) the region where fracture occurs on a blunting line (Region I) and (2) the region where fracture occurs on an R-curve (Region II). The scatter of the KJ-values in each region is caused by the amount of crack extension contained in the specimens.
Methods to obtain the fracture toughness equivalent to the KIc from the KJ-values are presented. In Region I the lowest bound of KJmin-values obtained using specimens that meet the requirement NB ⩾ 3000 Jcmin/σY is recommended, and this method may also be used in Region II. In Region II a modified R-curve method is proposed.
A Method of Application of Elastic-Plastic Fracture Mechanics to Nuclear Vessel Analysis
Authors: Paris PC , Johnson RE 
Published: March 2009

The primary purpose of this work was to develop analytical relationships which could be used to assess the safety of irradiated nuclear reactor pressure vessels against unstable fracture. The need for such a calculation occurs when the Charpy uppershelf energy of the vessel steel is predicted to fall below the required 50 ft ∙ lb (67.8 J) level from accumulated neutron radiation damage. The method used was based on “tearing instability” concepts under “J-controlled growth” conditions for the crack stability criterion. The aforementioned purpose was served by developing fracture mechanics methods of wider applicability than previously available and applying them in analyses at uppershelf conditions (above the transition temperature). Elastic-plastic fracture mechanics concepts were used to extend recognized linear elastic fracture mechanics flaw analysis equations for through-the-thickness flaws and surface flaws into the plastic range. The approach also made use of J-R curve characterization of the material fracture resistance.
A crack stability diagram in the form of J as a function of Tplot was shown to be useful in demonstrating safe levels of loading (applied J) by comparison with the material J-R curve, reduced onto the same diagram. Consequently, a safe level of applied load, J50 [for J/T = 50 in. ∙ lb/in.2 (8.756 kJ/m2)], was suggested and the possibility of its correlation with upper-shelf Charpy energy values discussed.
Experimental Validation of Resistance Curve Analysis
Authors: Milne I 
Published: March 2009

The experimental evidence which supports the existence of stable ductile crack extension in metallic specimens and structures is reviewed and compared with modern failure assessment procedures. The evidence includes data from the following: 1. Materials—aluminium alloys, mild steel, two nickel-chromium-molybdenum-vanadium forging steels, A533B and A508 pressure vessel steels, a quenched-and-tempered steel, austenitic steels, and HY-130. 2. Geometries—3-point bend specimens of various sizes, compact tension specimens plane and side-grooved, single-edge-notched tension specimens, double-edge-notched tension specimens, center-cracked tension panels, wide plate specimens, pressurized pipe geometries, and pressurized nozzle geometries with the crack located in the crotch corner, 3. Section sizes—thicknesses ranged from 2 to 700 mm in specimen geometries with crack sizes between 0.1 and 0.9 of the section.
It is concluded that for materials with a low to moderate capacity for strain hardening, an adequate engineering assessment can be obtained using a simple form of assessment such as the Central Electricity Generating Board's procedures, R6. However, for materials with a high capacity for strain hardening, total elastic plastic behavior can be predicted only by a procedure which allows for this strain hardening capacity explicitly. Nevertheless, the load capacity of such materials appears to be satisfactorily predicted using a flow stress criterion.
Pulsed CO2 Damage Threshold Measurements of Rb:KCl and NaCl
Authors: Detrio JA , Dempsey DA 
Published: March 2009

The l-on-N damage threshold of specimens of forged NaCl, Rb:KCl and antireflection coated KCl were measured at 10.6 μm with a pulse duration of 10 μ sec. An acid etch significantly improved the survivability of the NaCl specimens which normally received surface damage while the response of KCl was not influenced by the etch treatment. The coated KCl survived about as well as the uncoated specimens. The measured damage thresholds were: etched NaCl, 24.2 J/cm2; NaCl, 12.0 J/cm2; etched KCl, unetched KCl, and coated KCl, 10 J/cm2.
The damage morphology included entrance and exit surface damage on all types of specimens and bulk damage in the KCl specimens. The surface damage observed in some cases was an artifact produced by a plasma which formed at the specimen entrance face.
Multiple-Shot Laser Damage Thresholds of Ultraviolet Reflectors at 248 and 308 Nanometers
Authors: Foltyn SR , Newnam BE 
Published: March 2009

Multiple-shot damage thresholds of dielectric reflectors have been measured at 248 and 308 nm. Standard irradiation conditions were a 10-ns pulsewidth, 0.6-mm spot diameter and 35-Hz pulse repetition frequency. The reflectors, from various sources, were composed of oxide and fluoride films.
Although damage was generally initiated at visible film defects, there was no correlation between damage susceptibility and the appearance of these defects. At levels near threshold, damage was most often observed as an increase in white-light scatter of a site with no growth upon continued irradiation; at higher levels, the damage site grew with successive shots.
Test sites were subjected to at least 103 shots and some sites received as many as 2.5 × 104 shots; however, with only one exception damage was found to occur within the first few shots or not at all.
Reflectors at 248 nm typically had damage thresholds in the 1.0–1.8 J/cm2 range with two samples exhibiting unexpectedly high thresholds of 2.8 and 3.0 J/cm2. In some cases, a subthreshold pre-irradiation treatment resulted in a 20–25% enhancement in damage resistance.
A Novel Technique for Investigating Impurity Initiated Short Pulse Laser Damage in Thin Films
Authors: Wiggins TA , Walker TW , Guenther AH 
Published: March 2009

A preliminary study has been conducted to investigate the effects of spot size on the laser induced damage threshold in thin films. Damage was produced by the interference fringes of two beams from a frequency-doubled Nd-YAG laser with a nearly Gaussian spatial profile. Fringes of spacing from 5 to 125μm were used on ZnS, ZrO2 and ThF4/ZnS films. The damage threshold and morphology were observed and are reported.
Microscopic examination indicated that the appearance within a damaged region, which is as narrow as 1μm, is not different from that produced by a single beam whose half-intensity diameter is a hundred times larger. Interesting results concerning the relative importance of scratches and other defects were revealed by Nomarski microscopic observation of the damage morphology.
It has been reported that laser damage to thin films is initiated primarily by small-size dielectric impurities and the dependence of the damage threshold on pulse length, film thickness, wavelength, and material investigated. In the present study it was observed that the damage threshold increased with decreasing film thickness in agreement with previous observations. However, there was no significant increase or decrease in threshold for the two-beam case over that for a single beam when the increased energy density due to interference effects is considered. In concert with previous observations it is concluded from the damage morphology and the absence of a spot size dependence that the source of damage initiation is impurities smaller than 1μm for these 5 ns pulse lengths.
The Use of Ion-Beam Deposited Diamond-Like Carbon for Improved Optical Elements for High Powered Lasers
Authors: Aisenberg S , Stein M 
Published: March 2009

The use of thin films of ion-beam deposited diamond-like carbon (DLC) appears to provide a number of properties that could result in improved optical elements (windows, mirrors) for high powered lasers. Many of these properties have already been described.
Of particular importance for high powered lasers is the ultra-smooth nature of the ion-beam deposited DLC plus its transparency, chemical intertness, and barrier properties. Several mechanisms predict and explain why DLC films are observed to be smoother than the substrate, and can result in improved transmission and reflection coefficients. The problem of high power surface breadkown associated with microscopic irregularities in the substrate can be reduced as a result of the ion-beam deposition energy and the smoothing effects of a film of ion-beam diamond-like carbon. The relationship of DLC to high power breakdown at surface defects, as well as plasma breakdown will be discussed to show how the ion-beam diamond-like carbon coating can improve performance.
An Elastic-Plastic Fracture Mechanics Prediction of Stress-Corrosion Cracking in a Girth-Welded Pipe
Authors: Abou-Sayed IS , Ahmad J , Brust FW , Kanninen MF 
Published: March 2009

Despite the fact that weld-induced residual stresses arise as a result of thermoplastic material deformation, current analyses of crack growth in welds assume that linear elastic fracture mechanics (LEFM) conditions are valid. In particular, the stress-intensity factor K, the LEFM-based measure of the crack driving force, is calculated using the linear superposition techniques that strictly hold for linear clastic material behavior. Another common idealization is that only the normal component of the residual stress field that acts on the crack plane is significant.
To assess the importance of these assumptions, a heuristic elastic-plastic fracture mechanics analysis procedure is developed in this paper and applied to determine the rate of stress-corrosion crack growth in an axially-loaded 102-mm (4-in.)-diameter girth-welded Type 304 stainless steel pipe. It is found that the more rigorous elastic-plastic analysis predicts higher crack growth rates than do the currently used LEFM-based calculations. It is concluded that more rigorous prediction methods may be needed for safety assessments of welded structures than those now in use.
Transparent Polymers as a New Class of Optical Materials for Lasers
Authors: Dyumaev KM , Manenkov AA , Maslyukov AP , Matyushin GA , Nechitailo VS , Prokhorov AM 
Published: March 2009

Possibilities of using transparent polymer materials for production of different optical elements (active elements with lasing dyes, bleachable O-switching filters, etc.) for high-power lasers are discussed. Laser damage resistance of various polymers is particularly investigated. The dependences of laser-induced damage threshold on the initial monomer purity, chemical composition and temperature of polymers, frequency and duration of laser pulses, on the focal spot, as well as statistics and morphology of damages, the accumulation effect in damage in a multiple irradiation regime, light nonlinear scattering and subthreshold UV-glow have been investigated to elucidate the mechanisms of laser-induced damage in polymers.
Absorbing defects of different kinds have been established to play an initiating role in the damage process. Purification of the initial monomers was found to result in high values of laser damage thresholds of polymers comparable with those for crystals and glasses, although considerable differences are revealed in the polymer damage characteristics compared to other optical materials.
Analysis of these peculiarities is presented and it is concluded that the molecular characteristics of plasticating agents are decisive in the mechanism of microdamage appearance initiated by absorbing defects, and that visco-elastic properties of polymers have a considerable effect on the growth of damages from micro- to macrodimensions.
A theoretical model of laser damage, as well as practical, effective ways of increasing laser damage resistance of polymer materials are discussed.
Studies of Laser-Produced Damage to Transparent Optical Material in the UV Region and in Crossed UV-IR Beams
Authors: Gorshkov BG , Epifanov AS , Manenkov AA , Panov AA 
Published: March 2009

The values of the damage thresholds of some alkali halide crystals, sapphire and fused quartz at λ = 0.266 μm are presented.
The role of electron avalanche in the damage of real wide-gap dielectrics in the UV region is discussed.
Some peculiarities of the interaction of intense UV radiation with dielectrics (nonlinear absorption, photoionization of impurities, self-focusing and others) are considered.
Experiments on laser damage induced by two synchronous, crossed laser beams with different frequencies (λ1 = 1.06 μm and λ2 = 0.266 μm) are described. This method makes it possible to establish the influence of “seeding” electrons on the development of laser-produced damage, as well as to determine if the damage mechanisms are similar at different frequencies.
In order to record directly and estimate concentrations of the free carriers excited by UV laser radiation, d.c. photoconductivity experiments have been carried out.
Accumulation and Laser Damage in Optical Glasses
Authors: Maldutis EK , Balickas SK , Kraujalis RK 
Published: March 2009

Bulk damage of the optical glasses by single and multiple periodic laser pulses of nanosecond duration has been investigated. In the case of multiple irradiation, damage is shown to occur with the energies considerably lower than the damage threshold by a single pulse.
The dependence of the accumulating damage threshold on the number and frequency of the irradiation pulses, the wavelength of laser radiation and the conditions of its focussing into the volume of the sample has been observed.
The bulk damage of glass K-8 induced by a single pulse of radiation with 1.06 μm and 0.53 μm wavelength is shown to be determined by different mechanisms. By employing absorptive-spectral analysis, the degradation of the medium under laser irradiation with intensity ten times lower than damage threshold was observed. The mechanisms of the accumulation and bulk damage are also discussed.
Damage Thresholds to Metal Mirrors by Short-Pulse CO2 Laser Radiation
Authors: Figueira JF , Thomas SJ , Harrison RF 
Published: March 2009

Measurements of damage to metal surfaces induced by intense nanosecond pulses of ir radiation are reported. Single-shot damage thresholds of Cu, stainless steel, molybdenum and aluminum surfaces have been measured for various angles of incidence and the predicted increase in damage thresholds for grazing incidence optical components have been experimentally verified for the first time at 10-μm.
Multiple-shot damage tests have also been performed and practical lifetime curves for Cu mirrors have been established. Scanning electron micrographs of the mirror show the damage mechanism to be the development of a fine scale (1 μm) microstructure on the copper surface.
Thermo-Elastic Action of the Powerful High Pepetition Rate Laser Radiations on the Solid State Surface
Authors: Apollonov VV , Chyotkin SA , Khomich VY , Prokhorov AM 
Published: March 2009

The phenomena of the thermoelastic behavior of materials under powerful, high-repetition-rate laser radiation are discussed. An analysis is based on the Duamel integrals for the thermo-stress characteristics which correspond to CW and high-repetition-rate laser irradiations.
Relationships for the upper-level laser intensities which are connected with admissible elastic surface distortion, plastic flow of the material, fatigue distributions, and melting of the surface layer are calculated.
Optical Properties of Hydrogenated Amorphous Carbon (a-C:H) - a Hard Coating for IR-Optical Elements
Authors: Bubenzer A , Dischler B , Nyaiesh A 
Published: March 2009

Hydrogenated amorphous carbon films a-C:H were deposited on glass and germanium substrates. The films are transparent in the IR and are extremely hard (Mohs's hardness of about 8). The a-C:H coatings were prepared according to the method of Holland in an RF excited discharge sustained by various hydrocarbon gases.
Thickness, density, refractive index (at 0.3 μm and 2 – 10 μm) and relative hydrogen content were determined. Variations in IR-refractive index and relative hydrogen content could be correlated with deposition conditions. With a refractive index of approximately 2 a-C:H is an ideal AR-coating for germanium (n = 4). Laser calorimetric measurements of optical absorption at 10.6 μm give a loss as low as 4% for a 1.3 μm thick coating on germanium (λ/4 for n = 2 at 10.6 μm). Preliminary damage tests with a CO2 laser (600 W, cw) were performed.