bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ion Exchange Strengthening of Nd Doped Phosphate Laser Glass
Authors: Cerqua KA , Jacobs S , McIntyre BL , Zhong W 
Published: February 2009

Recent advancements in high repetition rate and high average power laser systems have put increasing demands on the development of solid state laser materials with high thermal loading capabilities.
We have investigated strengthening of commercially available Nd doped phosphate glass via an ion-exchange process. Introduction of a compressive layer to the glass' exterior surfaces through this exchange, results in dramatically improved (approximately 4–5x) thermal shock resistance for specific sample geometries. This resulting increase in strength was directly measured through thermal shock resistance tests.
Our thermal shock test data showed extremely small (approximately ± 5%) standard deviations compared with data acquired through conventional mechanical fracture techniques. Additional topics investigated were strengthened layer thickness and effectiveness as a function of treatment time and the relationship of strengthening to the overall optical quality of the strengthened sample's surface.
Laser Induced Damage and Ion Emission of GaAs at 1.06 μm
Authors: Huang AL , Becker MF , Walser RM 
Published: February 2009

The experiments in this study were focused on the N-on-1 laser damage and sub-damage threshold ion emission of gallium arsenide. The initial goals were (1) to determine the N dependent damage threshold due to N-on-1 laser irradiance and (2) to correlate ion emission with surface damage events. A Q-switched Nd:YAG laser (1.064 μm, 45 nsec pulse, 580 μm spot diameter) was used to irradiate the ⟨100⟩ single crystal gallium arsenide samples.
Using values of N from 1 to 100, we obtained accumulation curves based on 50% damage probability. Corresponding damage threshold fluences were 0.4 – 0.8 J/cm2 for N&gt;1 and approximately 1.5 J/cm2 for N=1. We observed large site-to-site fluctuations in ion emission, and emission occurred before surface damage was initiated. We found the onset of ion emission at a fluence of 0.2 J/cm2 for all cases, whereas the damage threshold fluence was two to five times larger and dependent on N. Experimental measurements of linear and nonlinear absorption coefficients were made to check for anomalous absorption. The measured values were in agreement with those previously reported. Once surface damage occurred, ion emission was greatly increased. This type of behavior seems to support a surface cleaning model for ion emission which precedes surface damage.
N-on-1 Damage Testing of Single Crystal Metal Surfaces at 1.06 μm
Authors: Jee Y , Becker MF , Walser RM 
Published: February 2009

We examined the accumulation dependence of laser damage on single crystal metal surfaces under Q-switched Nd:YAG laser irradiation (1.064μm, 20 nsec pulses with a 200μm spot diameter). The samples were chemically polished, electropolished, and single point diamond machined Al, Cu and Ni single crystal surfaces of several crystallographic orientations. The single point diamond machined samples did not have single crystal surfaces as detected by electron channeling patterns, whereas the other samples had good single crystal surfaces.
Damage probability curves and accumulation curves were plotted to investigate N-on-1 damage behavior. The slope of the damage probability curve increased with the number of pulses required for damage. Accumulation curves, derived from 50% damage fluences, often had two regions showing different slopes. We interpret these measurements to indicate two different damage mechanisms, a defect related local melting at low pulse numbers and plastic deformation damage at high pulse numbers. These observations correlate with typical damage morphologies obtained by a Nomarski optical microscope and by SEM.
Ion Beam Deposited Oxide Coatings
Authors: Raj T , Price JS , Carniglia CK 
Published: February 2009

Single-layer coatings of SiO2, Al2O3 and ZrO2 were deposited by ion beam deposition (IBD). IBD is carried out by directing an ion source at a target made of the desired coating material. The material sputtered from the target is directed toward the substrate being coated. The targets chosen for this work were commercially available hot-pressed oxides. To further modify the coating properties, a secondary ion gun was directed toward the substrate to assist the deposition. Thus, ion assisted deposition (IAD) can be combined with IBD. The following coating deposition parameters were varied: composition of the sputter deposition gas mixture, composition of the ion assist gas mixture, and beam voltage and beam current for the ion assist beam. No external heat was applied to the substrates.
Single-layer ZrO2 coatings were also deposited from a Zr metal target by bombarding this target with an O2:Ar ion beam (Reactive Ion Beam Deposition [RIBD]). These depositions were performed with ion assistance (RIBD/IAD) and without. However, filament life of the ion guns was found to be a problem with these coatings because of the presence of oxygen in the ion beam.
The refractive indices for all the coatings were determined by ellipsometry at 633 nm. Representative coatings were analyzed by Auger Electron Spectroscopy (AES) to determine stoichiometry and to provide information on the nature and level of impurities. The RMS surface roughness was determined by TIS (Total Integrated Scatter) measurements. In addition, absorption was determined for a few selected coatings from spectral transmission measurements. The influences of ion beam deposition parameters and ion assist-beam parameters on thin film properties of SiO2, Al2O3 and ZrO2 coatings are discussed.
High reflector coatings at 351 nm were deposited on super-polished substrates utilizing the optimum deposition parameters obtained from the single-layer studies. The reflectors were made from ZrO2 and SiO2 targets. A peak reflectance greater than 99% was achieved.
Time of Damage and the Effect of the Pulse Repetition Frequency on the Laser Induced Damage Threshold
Authors: Wood RM , Sharma SK , Waite P , Gorton EK , Lewis K 
Published: February 2009

The time of damage has been measured as a function of pulse input energy for a range of i-r windows and mirrors.
More data and understanding of the mechanisms involved has been gained of the effect of laser pulse repetition frequency on the laser induced damage thresholds of infra-red transmitting window materials. Results on Ge, Si, GaAs, ZnS, ZnSe, NaCl and KCl are presented together with comments on the mechanisms which lower the damage threshold from the single shot damage level.
Unified Treatment of Deep and Shallow Notches in Rotating Bending Fatigue
Authors: Nisitani H , Endo M 
Published: February 2009

As a concept useful for evaluating the strength of notched members, “linear notch mechanics” is proposed. It is explained by this concept that the elastic-plastic behavior near the root of a notch under the condition of small-scale yielding is controlled by the maximum elastic stress σmax and the notch root radius ρ alone, independently of the other notch geometries. In order to confirm the effectiveness of “linear notch mechanics” in fatigue problems, rotating bending fatigue tests are carried out on notched steel specimens having widely varying notch geometries. Moreover, the fatigue notch effects of extremely shallow notches, whose depths are of the order of the grain size, are also discussed.
Summarizing the present studies, a unifying treatment of fatigue notch effects is presented.
Critical Behavior of Nonpropagating Crack in Steel
Authors: Kunio T , Yamada K , Kim MG 
Published: February 2009

A study has been made on the critical condition for the nonpropagation of a crack in Stage II growth at the endurance limit of pearlitic steel with special emphasis on the closure behavior of the crack.
It is found from fatigue experiments and measurements of crack opening displacement that a tip of the nonpropagating crack (NPC) is closed at the stress level of the endurance limit. It is also found that the tip of the NPC opens again under the original endurance limit when the NPC is vacuum-annealed. Therefore, it turns out that the crack which has propagated in Stage II growth stops its propagation by the closure effect resulting mainly from the local residual compressive stress at the crack tip.
Further experimental evidence implies that not only the crack closure due to residual compressive stress (plasticity induced), but also the closure associated with the oxidation during the reduced crack propagation, is responsible for the existence of NPC at the endurance limit.
High-Temperature Crack-Arrest Toughness Measurements Using Compact Specimens
Authors: Rosenfield AR , Mincer PN , Marschall CW 
Published: February 2009

The ASTM Crack-Arrest Test, which is under development, is generally limited to providing data up to 20 to 40°C above the ductile-to-brittle transition temperature (expressed as RTNDT in the ASME Boiler and Pressure Vessel Code). For this test, the geometry is a wedgeloaded compact specimen containing a brittle weld starting notch, which appears incapable of reliably generating a rapid crack above the stated temperature range.
Two alternatives have been used for obtaining data at higher temperatures: very large specimens combined with soft loading systems and modified compact specimens. This paper describes compact-specimen modifications which have extended the successful temperature range to the onset of the Charpy upper shelf, the highest relative temperature reached being RTNDT + 100°C.
Specific modifications utilized are: a high-strength steel crack-starter section (duplex specimen), a low-friction loading arrangement (inverted split pins), and contoured side grooves. The high-temperature data generated using these modifications compare favorably with largespecimen results.
The Failure of Aluminum Compact Shear Specimens Under Mixed-Mode Loading
Authors: Riddle RA , Streit RD , Finnie I 
Published: February 2009

The failure behavior of 7075-T6 aluminum under mixed-mode loading was investigated using the compact shear specimen. This specimen is capable of providing a range of Mode I and Mode II loading conditions at the crack tip, depending upon the boundary conditions provided by the loading fixtures.
Finite-element analyses of the specimen were made which included the effects of loading fixture constraints and the material's elastic-plastic properties. The symmetric and antisymmetric components of the stress and deformation fields were used to calculate the applied J-integral values, JI and JII, corresponding to the Mode I and Mode II loading at the crack tip. Methods to obtain the critical values of the J-integral at crack initiation from the load displacement curves of the specimen are discussed.
The failure behavior of the material varied greatly depending upon the relative amounts of Mode I and Mode II loading at the crack tip. For near Mode I loading, the specimen behavior at failure loads was nearly elastic, and the failure processes appeared to be typical of those for Mode I plane-strain fracture toughness testing. A fairly significant amount of shear loading seemed to have little effect on the failure load. For near Mode II loading, the amount of plastic deformation is much more significant, with the ligament ahead of the crack tip nearly fully plastic at the failure load. The failure processes in the material, as evidenced by the fracture surface morphology, are different as compared to Mode I type failure. There is evidence of slow stable crack growth occurring at loads near the departure from linearity of the specimen load-displacement curve.
For a mixed-mode case in which Mode II dominates with a smaller amount of positive Mode I loading, the critical J-integral value is substantially larger than the value of the critical J value for Mode I loading. When it is transformed into the corresponding critical stress intensity factor values, KIIc and KIc, it is found that KIIc is approximately twice KIc. However, there is some question as to whether the specimen failure is controlled by a critical stress intensity value or by the applied shear stress.
The use of the J-integral as a failure criterion and as a means to predict the angle of crack growth for elastic-plastic failure is discussed.
Investigation of Ductile Fracture Properties of Welded Type 304 Stainless Steel Pipe and Large Plan Compact Specimens
Authors: Hays RA , Vassilaros MG , Gudas JP 
Published: February 2009

An experimental investigation was performed to evaluate the J-integral resistance curve behavior of 10-cm (4-in.) nominal pipe size Schedule 80 welded Type 304 stainless steel pipe. Tests were performed in four-point bending at 288°C (550°F) on 1219-mm (48-in.)-long pipe specimens with machined flaws contained in circumferential welds. Two flaw geometries were investigated. The first was a through-wall crack growing circumferentially (simple) and the second was a 360-deg part-through radial crack superimposed on a through-wall circumferential crack (complex). During the tests load, load line displacement, crack mouth opening displacement, and electrical potential drop across the crack mouth were monitored. Elastic compliance and direct current potential-drop (DCPD) techniques were used simultaneously to estimate crack extension during the tests. Pipes containing simple cracks had an average J-initiation of 1120 kJ/m2 (6400 in. · lb/in.2). The presence of the complex crack reduced the J-initiation level by approximately a factor of four and also reduced the apparent tearing modulus significantly as compared to pipes containing simple cracks.
A second part of this investigation concerned the use of laboratory-sized specimens of the same thickness as the wall of the pipe to model the J-R curve behavior of the simple through-wall cracked pipe. Large plan compact specimens were cut from a welded plate and tested at 288°C (550°F) using both elastic compliance and DCPD crack length estimation techniques. J-initiation values from the two types of specimens appear comparable, but the small amount of crack extension from the compact specimens limited comparison of the far-field J-R curve.
Determination of Mixed Mode Stress-Intensity Factors Using Explicit Weight Functions
Authors: Sha GT , Yang C-T 
Published: February 2009

An efficient finite-element methodology for evaluating the stress-intensity factors (KI, KII) and the weight functions (hI, hII) of a self-similar propagating mixed-mode crack has been established with a single colinear virtual crack extension. This is accomplished through the use of a symmetric mesh in the crack-tip neighborhood that provides the decoupling characteristics for the field parameters of stresses, strains, displacements, tractions, and strain energy release rates into Mode I and Mode II components within the symmetric mesh zone. The application of this newly established technique to the three-point bend specimen has been studied with the mixed fracture mode introduced by deviations from normal test conditions of either loading or support eccentricity. These eccentricity effects on KI and KII values for three-point bend specimens are detailed in this paper.
The angular dependence of the strain energy release rate, G(θ), as a function of eccentricity, is also provided herein to account for the testing irregularities associated with three-point bend tests, which have span-to-width ratio s/W = 4 and different crack lengths 0.1 ≤ a/W ≤ 0.8. By assuming the crack propagation taking place at the angle (θcr), with maximum strain energy release rate (Gmax), the predictions are also provided for expressing θcr angles as a function of both loading and support eccentricities. It is found that the load eccentricity has a more severe effect than that of the support eccentricity as indicated in our numerical results for three-point bend specimen with s/W = 4.
Also presented explicitly are the characteristics of the Mode I and Mode II weight functions for three-point bend specimens (equivalent to edge crack geometry) with s/W = 4 and 0.1 ≤ a/W ≤ 0.8 at the crack faces and other key traction application surfaces. The explicit weight function information at these key traction application boundaries is very useful to the fracture mechanics practitioner and designer for guiding traction application locations and directions that produce the least stress-intensity factor.
For a given crack geometry, the explicit weight functions depend on the constraint conditions. The method of obtaining the required stress-intensity factors of an asymmetric crack geometry under the constraint conditions, which are different from the available weight function for the same asymmetric crack geometry, is also made available here. This is accomplished by combining the predetermined explicit weight functions with self-equilibrium forces, which include both the applied surface tractions and the reaction forces induced by constraints.
The Significance of CTOD in Transversely Loaded Weldments with Weld Metal Overmatching in Strength
Authors: Denys RM 
Published: February 2009

The purpose of this paper is to review the effects of weld metal overmatching on weld joint behavior. The notch toughness parameters crack-tip opening displacement (CTOD) and crack opening displacement (COD) are used to evaluate the degree of weld metal overmatching on weld joint performance. Exploratory experimental work on wide-plate specimens loaded in tension is presented to support the theoretical observations.
It is concluded that weld metal overmatching has a beneficial effect on the overall performance of transversely loaded welded joints loaded in tension. The results also indicate that the CTOD bend test gives mainly an idea about the local notch tip ductility and that, if a “fitness for purpose” evaluation is to be based upon the small-scale CTOD test, the benefits which accrue from the use of overmatching weld metal on tolerable defect size cannot be described adequately by the design curve approach.
Specimen Thickness Effects for Elastic-Plastic CTOD Toughness of an A36 Steel
Authors: Wellman GW , Sorem WA , Dodds RH , Rolfe ST 
Published: February 2009

This paper describes the results of an experimental and analytical study of the effect of specimen size on the fracture toughness behavior of A36 steel, primarily in the lower-transition region. This region is beyond the limits of plane strain as defined by ASTM Method E 399, but in the region where failure occurs prior to any macroscopic fibrous tearing. Experimental results were obtained using crack-tip opening displacement (CTOD) three-point bend specimens, and analytical results were obtained using a 3-D elastic-plastic finite-element analysis. Two specimen sizes, full thickness [31.8 mm (1.25 in.)] and reduced thickness [12.7 mm (0.50 in.)], were investigated using the preferred t × 2t × 8t specimen size.
Testing was conducted according to the procedure outlined in BS 5762:1979, Methods for Crack Opening Displacement Testing. CTOD-temperature transition curves were developed for both specimen sizes. A sufficient number of specimens were tested at two temperatures in the lower-transition region to allow statistical characterization of the CTOD results. Both normal and Weibull distributions were used for that characterization.
Three-dimensional elastic-plastic finite-element analyses were conducted to determine the effect of specimen size on the near-crack-tip opening stresses through the specimen thickness. The near-crack-tip stress fields were compared at various CTOD levels well into the elastic-plastic regime, but prior to any stable crack growth. At each of the applied CTOD levels, the maximum near-crack-tip opening stress occurred at the specimen centerplane and was found to be essentially independent of specimen size.
The results of this study showed that the lower bound of the elastic-plastic CTOD toughness values of A36 steel for small specimens is essentially equal to those of larger specimens in the lower-transition region prior to any stable crack growth. Thus it may be possible to characterize the notch toughness of low-strength structural steels, such as A36 steel in the lower-transition region, using small specimens provided that a sufficient number of specimens are tested. However, additional study is required before any recommendations can be made.
A Study of Crack Initiation in the Ductile-to-Brittle Transition Region of a Weld
Authors: Ebrahimi F 
Published: February 2009

The ductile-to-brittle transition behavior of a shielded metal-arc weld was characterized for various specimen geometries by the crack opening displacement (COD) testing method. The transition curve shifted to higher temperatures with increasing the specimen thickness and the crack length to width ratio (a/W).
Emphasis was placed on mechanisms of crack initiation as characterized by detailed fractography. A ductile shear zone, next to the fatigue precrack, preceding the unstable fracture, was revealed on the fracture surface of all specimens tested, except for specimens that broke under small-scale-yielding conditions. It is shown that brittle or ductile microcracks, depending on the test temperature, initially form at a distance ahead of the tip of a blunted crack. Subsequently, the ligament between these microcracks and the crack tip fails by a shearing mechanism. On the basis of this observation it is proposed that the statistical nature of fracture in the ductile-to-brittle transition regime is related to the probability of propagation of an unstable crack from the brittle or ductile microcracks.
JR-Curve Testing of Three-Point Bend Specimens by the Unloading Compliance Method
Authors: Steenkamp PAJM 
Published: February 2009

The unloading compliance technique for JR-curve testing is not well established for single-edge notched specimens loaded in three-point bending (SENB) to date. This paper investigates various effects hampering the successful application of the method of SENB specimens. It is shown that the specimen's compliance is significantly affected by rotation of the specimen halves during deformation and stable crack extension. By contrast, the effects of roller indentation, outer roller movements and friction, and of crack front curvature are relatively minor. Based on these findings, a general procedure is proposed for correcting the experimentally measured compliance of SENB specimens for the above effects.
Crack extensions predicted for three steels from SENB unloading compliance experiments incorporating the proposed corrections are seen to correlate within ±10% with dye penetrant beachmarks made at several points during the tests.