bluuebunny/crossref_metadata_2025_split huggingface dataset:
Prediction of Failure Loads of Adhesive Joints Using the Singular Intensity Factor
Authors: Groth HL 
Published: February 2009

A method to predict failure of adhesive joints is described. The fracture criterion is based on material-induced singularities that appear at the terminus of the joint. The criterion can be interpreted physically in terms of the elastic strain energy density. The criterion is formulated in terms of a singular intensity factor Q that is analogous to the stress intensity factor for the case when cracks are present. The strengths of the singularities are dependent on the elastic properties of the adhesive and the adherends and on the geometry of the bond terminus, but are postulated to be independent of loading and global geometry.
For the case of an adhesive joint, the different materials inducing the singularities may be the adherend and the adhesive. The criterion assumes that no cracks are present in the vicinity of the material-induced singularity and that fracture will occur as a cohesive fracture in the adhesive layer. It has been shown earlier that the criterion predicts with good accuracy the fracture load of test specimens loaded in combined tension and shear. The fracture load of the single-lap joint is predicted and compared with experimentally obtained values.
The presented method of predicting fracture in adhesive joints may be applicable to general joint geometries.
Single-Specimen Test Measurement of Ji and J-Δa with a Pulsed D-C Potential-Drop Technique
Authors: Thaulow C , Hauge M , Gunleiksrud Å , Paauw AJ 
Published: February 2009

Fracture mechanics testing [KIc, J-integral, and crack-tip opening displacement (CTOD)] of a QT-steel (AISI 4137 H) has been carried out in order to compare the testing methods. The tests were performed at room temperature, and the material toughness was varied by applying annealing temperatures from 300 to 650°C.
The J-initiation values were successfully determined with a specially developed d-c potential-drop (PD) method. The technique is based upon pulsed current and reference electrodes. Only the potential-drop difference caused by a current difference is measured; this eliminates the thermo-electric effect and offset voltage associated with PD equipment.
On the basis of the PD measurements both the J-initiation value and the R-curve (J-Δa) could be determined from a single-specimen test.
The R-curves could be fitted to a third-order polynomials, but even if the initiation values were nearly constant for replicate specimens, the slope of the R-curve would vary significantly. The mechanisms of crack initiation and growth are different, and the observed results indicate that the crack growth properties, as characterized with the R-curve, of the present steel quality vary from one specimen to the next.
The J-initiation values determined with the multispecimen technique recommended in ASTM E 813 showed considerably more scatter in comparison with the present PD technique. The results suggest that the J-initiation value should be determined on each specimen and not calculated with extrapolation techniques.
Determination of the Fracture Toughness of Irradiated Reactor Pressure Tubes Using Curved Compact Specimens
Authors: (Peter) Chow CK , Simpson LA 
Published: February 2009

This paper describes a case in which nonstandard test configurations had to be used to assess fracture toughness, and an experimental, analytical program to support the validity of the results.
Zirconium alloy pressure tubes (103 mm inside diameter, 5 mm thick) contain the primary coolant in CANDU™ reactors. Because irradiated materials lacks ductility, the pressure tube cannot be flattened to produce flat specimens to determine fracture toughness. Therefore, a method was devised for spark eroding 17-mm compact specimens from sections of pressure tubing. These specimens retained the normal in-plane dimensions of the standard compact specimens, but possessed the curvature of the tube. By comparing results from flat and curved specimens, this paper shows experimentally that flat-plate equations can be applied to both specimen types to calculate the fracture toughness parameters with little error. A simple analytical calculation estimates that the maximum curvature-induced stress should be less than 10% of the in-plane tensile stress at the crack tip.
Developments in the Application of the CTOD Approach to Fracture Assessment of Welded Construction
Authors: Harrison JD , Anderson TL 
Published: February 2009

The crack-tip opening displacement (CTOD) approach to the assessment of the risk of fracture, which has been incorporated into the British Standard's Published Document PD 6493, has served the United Kingdom welding fabrication industry well for the past 15 years. However, application of the approach and further research have drawn attention to several aspects which need improvement. For example, the PD 6493 document gives no guidance on the derivation of the critical CTOD value to be used in the analysis. Also, the fracture assessment method in PD 6493 suffers from a number of limitations.
This paper describes proposed improvements to the CTOD test and CTOD-based design approaches. A recently drafted appendix for weldment testing, which is proposed to be incorporated into the British CTOD test standard, is discussed briefly. Also, proposals for dealing with stable tearing, pop-in, and scatter in CTOD data are described. Finally, a three-tier fracture assessment procedure is proposed which allows flaws to be assessed at various levels of complexity, depending on the application. The three levels of assessment, in increasing order of complexity and accuracy, are 1. Modified version of the present PD 6493 method. 2. Strip yield model. 3. Reference stress approach.
All three levels utilize CTOD as the fracture toughness input. Some guidelines for choosing the appropriate assessment level are given.
Unloading-Compliance and Load-Drop Analysis of JIc Tests of Irradiated 348 Stainless Steel
Authors: Underwood JH , Haggag FM , Reuter WG 
Published: February 2009

Procedures for determining J-integral fracture toughness were applied to load versus load-line displacement data from a series of three-point bend specimens of irradiated 348 stainless steel tested at 23 and 427°C. The ASTM Test Method for JIc, a Measure of Fracture Toughness (E 813-81) was emphasized, using both unloading-compliance and load-drop measures of crack growth.
An effective modulus procedure was included in the unloading—compliance method using recently published load-line displacement results. Two procedures were used for calculating JIc from the J versus unloading-compliance crack growth plots: the linear fit procedure from ASTM Method E 813 and a power-law fit with a 0.2-mm offset value of JIc.
Based on the results of these various procedures, conclusions were reached regarding the most consistent measures of fracture toughness from these data. Suggestions were given regarding the use of effective modulus with unloading-compliance measurement of crack growth and the limitations of the load-drop method for measuring crack growth.
A Comparison of J-Integral and CTOD as Fracture Toughness Parameters
Authors: Anderson TL 
Published: February 2009

The J-integral and the crack-tip opening displacement (CTOD) are widely used throughout the world to measure the fracture toughness of structural materials. There are many similarities between these two parameters, as well as a number of important differences. Because of these differences, the CTOD parameter tends to be more conservative when applied to structures.
The J-integral and CTOD were compared qualitatively and analytically. This work differs from previous comparisons in that the present study compared engineering estimates of J and CTOD, which are not necessarily equal to the true values of J and CTOD. However, the fracture toughness of a material is nearly always characterized in terms of the engineering approximations of J or CTOD.
The main difference between J and CTOD as measures of toughness is that J is directly proportional to the area under the load-displacement curve whereas CTOD is proportional to the clip gage displacement. This means that the relationship between the two parameters depends on strain hardening and constraint.
The Influence of Cracks on the Buckling Capacity of Axially Compressed Columns
Authors: Evensen JD , Gradin PA , Lereim J 
Published: February 2009

When using slender beams as compression load-carrying members, one has to consider the risk of buckling failure. Apart from cross-sectional properties, length of the beam, and elastic properties, the initial lateral deflection and the boundary conditions will be important in determining the critical load, or buckling capacity. The presence of cracks may release the end constraints and drastically change the boundary conditions.
A growing fatigue crack may then lead to a gradual change from a rigid joint to a more flexible one with its lower extreme as moment-free. Thus it may be expected that the buckling strength will decrease with increasing fatigue crack size and therefore be time-dependent. Such a behavior would be of great concern in dynamically loaded structural elements containing growing fatigue cracks. This situation is highly realistic for a variety of offshore structures which are constructed as complex welded frames where high local stress levels in the nodal points in combination with dynamic loads due to current, wind, and waves may cause fatigue cracks to grow.
In order to provide some further insight into this problem, experiments and corresponding numerical analyses were performed with a Euler-III column of rectangular cross section and with surface cracks of varying length at the clamped end. The numerical results were combined with possible crack length versus load cycle relations to show the time dependence of the buckling load.
From the experiments it was concluded that the calculated elastic buckling load versus crack length relation (based on linear material behavior) represents an upper bound for the buckling load in the crack length interval considered.
A Crack-Tip Opening Displacement Method for the Analysis of Ductile Materials
Authors: Garwood SJ 
Published: February 2009

Although crack-tip opening displacement (CTOD) analysis procedures are well established for the prediction of tolerable crack sizes in ferritic steels, no specific procedures exist which incorporate a resistance (R) curve to facilitate estimation of the ductile instability conditions for a fully ductile material.
This paper discusses a modification to the CTOD procedure, based on the strip yield model, to enable the prediction of maximum nominal stress and the extent of stable ductile crack growth, using a CTOD R-curve as input.
The effectiveness of this procedure is assessed by predicting the behavior of wide plate tension tests and burst tests in API 5LX56 and A533B Class I ferritic parent steels and of wide plates in stainless steel plate and weldments. The predictions are then compared with physical data obtained from the tests.
Reasonable predictions of maximum applied stress are achieved. However, the accuracy is very dependent on the plastic collapse estimations. This is particularly true for the high work-hardening stainless steel plate where, to avoid an overestimate of collapse, the effective flow stress must be taken to be the stress at 3% strain in a uniaxial tension test.
Predictions of the test results are also made using maximum load toughness values, measured using CTOD test specimens complying with BS 5762, with either the CTOD design curve or the modified strip yield model approach. Predictions give safe estimates of nominal stress.
It is concluded that maximum load values provide the most practical general approach when detailed resistance curve information is not available.
Production and Properties of Perrhenate-Doped Alkali Halide Crystals
Authors: Nestor OH , Figueira JF 
Published: February 2009

The growth and selected properties of single crystals of KCl doped with ReO4- is described. The crystals have been used as saturable absorbers to modulate and control CO2 laser radiation. ReO4- ion concentrations in excess of 1017 cm-3 were achieved in KCl with good optical quality. The room temperature absorption of the ReO4- ion in KCl was centered at 936.8 cm-1 with 1.5 cm-1 linewidth and with absorption cross-section determined to be (0.46 + 0.02) × 10-16 cm2. The addition of Li+ as a second dopant resulted in a splitting of the ReO4- resonance into two components at 957.5 cm-1 and 900.7 cm-1.
The characteristically sharp resonance of ReO4- was not detected in NaCl grown with NaReO4 additions to the melt. Only with addition of Ca++ as a co-dopant was the ReO4- resonance observed. The absorption, detected as a very weak resonance through a 92 mm path length, was centered at 946.0 cm-1with linewidth of 6 cm-1, over-lapping the P(20) transition in the 10 micron CO2 band.
Radiation-Induced Absorption in Fused Silica
Authors: Miley GH , Chapman R , Nadler J , Williams W 
Published: February 2009

The transient radiation-induced absorption in fused silica due to neutron and γ-ray irradiation has been investigated. Transient absorption coefficients at 325 nm have been measured during and after pulsed reactor (TRIGA) irradiation. Radiation-induced absorption results from the generation of color centers.
Most of the previous efforts have been concerned with the permanent effects due to low dose rate steady-state irradiations. This study focuses on the transient effects due to pulsed irradiations and their dependence on dose rate and total dose. The transient absorption coefficient increases very rapidly to a maximum value during the pulse, then decreases over a time period &gt;1000 seconds to a permanent value after the pulse. In general, the absorption coefficient is found to increase with increasing dose rate and total dose.
Large Scale Damage Testing in a Production Environment
Authors: Weinzapfel CL , Greiner GJ , Walmer CD , Kimmons JF , Wallerstein EP , Marchi FT , Campbell JH , Hayden JS , Komiya K , Kitayama T 
Published: February 2009

We are using laser damage test systems on a production scale to scan large castings of laser glass for the presence of damage-causing platinum inclusions. These systems support glass melting production lines at two plants; one is in the U.S. (Schott Glass Technologies, Inc.) and the other is in Japan (Hoya Corporation).
The damage test systems are designed to scan an entire glass casting using the pulsed output from a commercial Nd:YAG laser. The system is fully automated and operates unattended. Following testing, the glass casting is removed from the system and visually inspected for the presence of Pt-damage sites. We routinely test polygonally-shaped castings that are about 0.5 meter in size, weigh approximately 30 kg and contain about 7 liters of glass. It takes roughly 6 to 8 hours to test a piece of this size. To date the systems have been in use about 12 hours-per-day, up to 5 days-a-week for a period of about 15 months. Of the approximately 300 disks that have passed the damage test so far, sixty-two percent of the disks have no platinum inclusions at all and ninety-two percent have an inclusion density of less than 0.2 per liter.
Mapping of Surface Defects of Optical Components by a High Speed Surface Analysis System
Authors: Lalezari R , Knollenberg R 
Published: February 2009

A scanning darkfield laser scatterometer is used to produce maps of surface defects on optical component surfaces. This instrument was originally developed for the examination of silicon wafers. The short depth of filed, high resolution darkfield imaging design of the scattering measurement head, enables the instrument to examine the cleanliness and surface condition of transparent as well as opaque optical surfaces, including coated surfaces.
The measurement system consists of a laser illuminated darkfield optical head mounted on a linear translation stage, a spinning chuck, and a data acquisition and display system. The instrument is capable of resolving the ac scattered light component to two parts in 109 for scattering sites smaller than the pixel size (50 microns). The dc sensitivity of the instrument is roughly one part in 106 (1 ppm).
The instrument has been successfully used in inspecting mirror substrates before and after coating and in developing cleaning techniques. Operation of the system and some data will be presented.
The Growth and Stability of Ag Layers on Cu(110) Monitored by Second-Harmonic Generation
Authors: Muenchausen RE , Hoffbauer MA , Taylor TN 
Published: February 2009

Understanding the fundamental limits for laser/optical mirror fabrication is directly relevant to the development of mirrors with improved durability and damage thresholds. Ag layers deposited in ultra-high vacuum on a well characterized, single-crystal Cu(llO) substrate as a function of substrate temperature have been analyzed using Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED) in order to answer questions concerning substrate overlayer formation and film degradation at the early stages of growth (̃ 10 monolayers).
Another aspect of this work has centered on developing diagnostics transferable from UHV to “real-world” environments. Optical second-harmonic generation (SHG) was chosen due to its surface specificity and experimental simplicity. The observed SH intensity as a function of Ag deposition even at submonolayer coverages. A comparison between the observed SH intensity and polarization dependence with the AES and LEED analysis indicates that optics SHG provides a fingerprint of the nucleation of Ag clusters.
Super-Polished Silicon Carbide Mirror for XUV Radiation
Authors: Yoshida K , Kato Y , Nakai S , Kurosawa K , Sasaki W 
Published: February 2009

We have coated a large silicon carbide (SiC) thin film on the graphite substrate by thermal CVD method. The surface of the SiC is first lapped and then polished with a precision ring-polisher. The roughness of super-polished SiC surface was about 5 Arms. This super-polished SiC surface is expected to be useful as a grazing incidence mirror for XUV radiation.
We have applied this SiC as a high reflectance mirror for the argon excimer laser (λ=126 nm), and obtained peak output power of more than 14 MW (MgF2 output mirror and 3 mm in beam diameter) without any damage on the SiC mirror surface. The output power and power density on the cavity mirror are the highest in comparison to the previous results obtained with other mirrors.
UV Light Cleaning of Silica Surfaces for Improved Laser Damage of AR Coatings
Authors: Yoshida K , Yoshida H , Kato Y , Nakai S , Ohtani M 
Published: February 2009

The glass substrates for the optical coatings have many contaminations on the surface which can not be removed by standard optical cleaning techniques. Especially, it is very difficult to remove the polishing compound which is buried into the silica substrates.
In this report, the improvement of laser damage threshold due to UV light cleaning is presented. The excimer laser, Xe flashlamps, and Xe arc-lamp have been used as UV light sources. The damage threshold of the AR coating on the silica surface which was cleaned with KrF laser light has increased by 50% at 355 nm.
Wavelength Dependence of Edge Filter Absorption
Authors: Basegio LJ , von Gunten MK 
Published: February 2009

Laser isotope separation and free electron laser programs have driven the need for optical coatings which function in environments of high average power density. Low absorption is the key requirement for these coatings to prevent catastrophic laser damage and to minimize wavefront deformation caused by localized heating of the coating and substrate. Dichroic edge filters have been utilized in wavelength separation applications; however, the intrinsic absorption of these designs at the edge limits their power handling capability for closely spaced wavelengths. In order to fully understand the absorption behavior and to optimize the performance of these designs, measurement of absorption as a function of wavelength has been undertaken, with particular emphasis on the transition region.
The absorption measurements have been performed with a calorimeter which utilizes a matched thermistor bridge and an ultra-precision instrumentation amplifier in conjunction with both discrete and tunable laser sources. Several types of edge filter coatings have been measured. These measurements have been performed over the wavelength region from the stopband through the edge region into the passband. This empirical data is compared to theoretical predictions.
Deposition with Ultra-Fine Particles
Authors: Day AC 
Published: February 2009

A study has been initiated into the possible uses of deposition with ultra-fine particles and/or clusters. The starting point was the Ionized Cluster Beam technique reported by Takagi et. al. Experimental studies in this laboratory strongly suggest that clusters cannot, in general, be formed in an adiabatic expansion of a pure metal vapor as had been claimed, although other mechanisms cannot be ruled out. Numerical simulations have also been carried out which support our conclusion.
However, it is well known that small particles or clusters can be condensed in a low pressure quenching gas. Work is now being directed toward exploiting these particles to produce materials composed of nanometer-sized “splats” somewhat analogous to those in plasma spray coatings. It is hoped this radical departure from the usual columnar structures of deposited materials can lead to improved damage thresholds in many types of optical coatings. The feasibility of this new approach will be discussed along with its potential merits.
Operational Limits for ZnSe/ThF4 Multilayer Mirrors in the Los Alamos Free-Electron Laser Oscillator
Authors: Newnam BE , Bender SC 
Published: February 2009

The Los Alamos free-electron oscillator is driven by an rf linear accelerator at an energy of ̃20 MeV. This L-band linac delivers electrons in a 100-μs-long train of micropulses (̃10-ps width) each separated by 46 ns. A semi-confocal resonator (g1g2 = 0.87 to 0.95) is used to maximize the optical intensity within the magnetic undulator by which extraction of energy from the electrons and optical gain are maximized.
For operation in the spectral range of 8 to 12 μm. multilayer dielectric reflectors of ZnSe/ThF4 on ZnSe substrates have been used for the end mirrors. At moderate laser power, these reflectors have performed without evidence of deterioration in the multiple environment of laser photons, gamma rays and neutrons [1]. However, when the time-average optical intensity on the mirrors exceeded the range of 500 to 700 kW/cm2, the resonator losses increased and the output power dropped [2]. Post inspection revealed coating damage in the form of a collection of many elongated pits plus one or two larger (1 × 1 mm2) pits penetrating to the ZnSe substrate. The damage mechanism most consistent with the observed morphology is heating of microscopic absorbing defects leading to film rupture by excessive stress.
Laser Induced Damage Measurements of Free Electron Laser Optical Components
Authors: Jolin LJ , Sanders VE , Salazar SJ 
Published: February 2009

A study of free electron laser (FEL) related optical damage is currently under way at Los Alamos National Laboratory. A single burst of the FEL has been simulated using a Nd:YAG laser system operating at 1064 nm. Thfe laser is a modelocked, 100 microsecond, pulse selected system operating at 10 pulses per second.
Damage thresholds for conventionally deposited dielectric high reflectors as well as bare metals have been studied and the results are reported. Some high reflectors have demonstrated laser induced damage thresholds of greater than 5 megawatts/cm2 average pulse power.
Also, reported are damage data for a non-modelocked laser configuration.