bluuebunny/crossref_metadata_2025 huggingface dataset:
The Use of Thermomechanical Analysis as a Viable Alternative for the Determination of the Tensile Heat Distortion Temperature of Polymer Films
Authors: Moscato MJ
Published: March 2009

The results of an attempt to determine the tensile heat distortion temperature of polymer films using a DuPont 943 thermomechanical analyzer in the tensile mode are presented. The results are compared to those obtained using an apparatus that was designed in house to conform to the specifications in ASTM Tensile Heat Distortion Temperature of Plastic Sheeting (D 1637-83, discontinued 1990). The thermomechanical analysis (TMA) was temperature calibrated by a two-point method using fine grade, high purity foils of indium (melting point [mp] 156.6°C) and lead (mp 327.5°C) as standards. Films of polyethylene terephthalate (PET) and cellulose acetate, some of which were made under different processing conditions, were used in this study. The data indicate that TMA is a viable alternative to the ASTM D 1637 method when conducted under identical experimental conditions. The data from the additional experiments, which involved the variation of both the tensile load and heating rate, demonstrate the ease and flexibility of using TMA as an alternative technique.
Glass Transition Determination by Thermomechanical Analysis, a Dynamic Mechanical Analyzer, and a Differential Scanning Calorimeter
Authors: Cassel B , Twombly B
Published: March 2009

A suitable specimen was selected to compare the glass transition measurement by several thermal analysis techniques. The specimen, an epoxy composite, was analyzed by Thermal mechanical analysis (TMA) using three different methods, including flexure, expansion, and stress relief, as a function of temperature. A dynamic mechanical analyzer (DMA) was then performed at three frequencies. A portion of the specimen was then selected for differential scanning calorimeter (DSC) analysis. Special care was taken to ensure that the specimen pre-treatment was identical and that thermal lag errors were corrected for, so that a direct glass transition comparison could be made between analytical techniques.

The best agreement in Tg values between the various measurement methods was obtained between: DSC heat flow midpoint; TMA onset of expansion, flexure or stress relief; and the onset of the storage modulus for DMA data taken at 0.1 Hz. These were all within one degree of 122°C. The best correlations with the DSC and TMA data to be obtained from a 1-Hz DMA run was that of the onset of the loss modulus peak (121.7°C). The methods employed are described, and the results discussed.
Application of Thermal Mechanical Analysis to Organic Coatings
Authors: Schoff CK , Kamarchik P
Published: March 2009

The performance of an organic coating is highly dependent on its physical and mechanical properties and their variation with temperature. A variety of thermal mechanical methods may be used to define these properties. This paper demonstrates the importance of penetration/indentation methods in the characterization of organic coatings. The use of a thermal mechanical analyzer (TMA) and the ICI Microindentometer to establish softening points, degree of cure, elastic modulus, and indentation hardness and creep is described. Dynamic methods have tended to take over from penetration/indentation techniques in recent years, but the latter still are the only ones that can be used on most field samples (for example, specimens cut from beer cans, car hoods, and washing machines, pieces of metal siding from buildings, chunks of outboard motor castings, and so forth). Typical measurements and their significance in problem solving and coatings evaluation are presented and discussed. The difficulties of dealing with thin films (25 μm or less) and multicoat systems also are addressed. The paper closes with a discussion of the interfacing of a TMA with a computer for better data collection and analysis.
The Use of Thermal Mechanical Analysis to Characterize Ethylene-Propylene-Diene Terpolymer (EPDM) Roofing Membrane Materials
Authors: Gaddy GD , Rossiter WJ , Eby RK
Published: March 2009

This study was conducted to provide baseline data on the applicability of thermal mechanical analysis (TMA) for characterizing ethylene propylene diene terpolymer (EPDM) roofing membrane materials. TMA has not been used extensively for the analysis of such materials. Three black and three white membrane materials were analyzed before and after exposure to the heat, ozone, and ultra violet (UV) conditions described in ASTM Specification for Vulcanized Rubber Sheet Used in Single Ply Roof Membrane (D 4637), as well as to outdoor exposure. Load-elongation was conducted as a comparison to the TMA results. The results indicated that (1) TMA can be applied to the characterization of EPDM membrane materials showing differences in glass transition temperature between various brand name products; (2) changes in glass transition temperatures induced by the exposure conditions were relatively low and covered the same range for both the black and white membrane materials; and (3) in contrast to the TMA testing, the percent elongation values displayed relatively large changes.
An Interferometric Technique for the Concurrent Determination of Thermo-optic and Thermal Expansion Coefficients
Authors: Jewell JM , Askins C , Aggarwal ID
Published: March 2009

An interferometric technique is described that uses a Fabry-Perot type configuration to measure the coefficient of thermal expansion (CTE) and the thermo-optic coefficient (dn/dT) of transparent materials concurrently. A number of measurements of the CTE and dn/dT are made for both oxide and fluoride based glasses. These measurements show that the technique is accurate, reproducible, and is very effective in determining the temperature dependence of both the thermo-optic and thermal expansion coefficients.
Refractive Index Measurement Capabilities at the National Institute of Standards and Technology
Authors: Dodge MJ
Published: March 2009

The refractometry program at the National Institute of Standards and Technology (NIST) was abandoned ten years ago, because of a lack of support. A serious attempt is being made to reestablish this program, and to upgrade the existing refractometers and the measurement capabilities to meet the present needs of the optical community. The purpose of this paper is to present the current status of the refractive-index-measurement capabilities at NIST, the immediate plans for the future, and the results of some recent measurements. Refractive index data will be given from 0.5461 to 1.083 μm for three samples of zinc selenide from different manufacturers.
High-Power Transmission Through Step-Index, Multimode Fibers
Authors: Setchell RE , Meeks KD , Trott WM , Klingsporn P , Berry DM
Published: March 2009

Motivated by interest in optical firing systems for initiating explosives, laser-induced damage thresholds have been investigated in step-index, multimode fibers having pure fused silica cores. A compact, multimode Nd/YAG laser operated at a pulsewidth of 16 ns was used for the experiments. The focusing geometry for introducing the beam into the fiber was chosen to avoid damage along the core/cladding interface as observed in previous studies. Five lots of twenty fibers each were tested, with polishing steps varied between successive lots to produce improved finishes on the fiber end surfaces. Each fiber was subjected to a sequence of progressively increasing energy densities up to a value more than 80 J/cm2. Initial damage was monitored by observing scattered HeNe laser light from the fiber faces using magnified video cameras.

The majority of the fibers damaged initially at the rear fiber face, once a “laser conditioning” process at the front fiber face was completed. In this process, a visible plasma was generated at the front face for one or more laser shots. Rather than produce progressive damage at the front surface, this process apparently improved the surface finish in nearly all cases, resulting in improved resistance to damage. Other modes of damage along the fiber length were observed either at locations of handling stresses or at the location of highest static tensile stress corresponding to the fiber's minimum bend radius. A fraction of the fibers in each lot never damaged, and this fraction increased as the successive lots were tested. The fibers that did not damage in the final lot were subjected to an additional series of laser shots at the maximum input conditions, and the majority still did not damage. These results, together with some insights into the dominant damage processes suggested by previous studies, are encouraging in terms of realizing high damage thresholds in this type of optical fiber. However, several important areas for further study are indicated.
Ion Beam Milling of Fused Silica for Window Fabrication
Authors: Wilson SR , Reicher DW , Kranenberg CF , McNeil JR , White PL , Martin PM , McCready DE
Published: March 2009

Ion beam figuring has been demonstrated to be a deterministic, efficient, flexible technique for removing material from optical surfaces. Recent interest in using this process to produce high quality optical components has driven the need to fully characterize the resulting surfaces. We have performed a polishing parameter matrix investigation to optimize fused silica (Corning 7957) surfaces for subsequent ion milling. Samples were characterized for surface scatter, surface absorption, surface roughness, subsurface damage, and laser damage as a function of mill depth. Small defects (pits) were evident on surfaces after milling a few microns, with pit density dependent to some degree upon the surface preparation technique. The defects were often in lines, apparently following a surface or subsurface scratch in the material. Surface scatter decreased significantly (up to 10X), and laser damage threshold increased in some cases by 400%. Laser damage was not correlated with defects in the material.
Ion-Exchange Strengthening of High Average Power Phosphate Laser Glass
Authors: Lee HC , Meissner HE
Published: March 2009

Thermal stress induced fracture limits the power output of high average power glass laser slabs1. The fracture of laser glass is initiated by the onset of unstable propagation of subsurface microcracks in which local tensile stress exceeds the critical level. The production of subsurface flaws is inevitable for a standard high precision fabrication process. Applying a compressive stress surface layer can be used to counterbalance the thermal tensile stress imposed upon the surface during operation. We have developed an ion-exchange process submerging the phosphate glass into a mixed alkali nitrate salt melt. An ionic size differential induces a compressive layer of tens of microns. The process avoids water corrosion and preserves the finished optical surface quality during ion-exchange. Furthermore, we have optimized the process taking into account network relaxation as well as ion-exchanged concentration profile. To characterize the surface compressive stress, we have employed a biaxial flexure bending test. We have found that a finished HAP-4 laser glass with a tensile breaking strength of 200MPa can be strengthened to twice its original strength, namely 400MPa.

The process has been scaled up to production in which large laser glass slabs or most other phosphate glass can be treated routinely. We have strengthened polished HAP-4 slabs(42cm × 14cm × 1cm) to up to twice their original thermal shock resistance without deteriorating their optical surface quality.
Subsurface Polishing Damage of Fused Silica: Nature and Effect on Laser Damage of Coated Surfaces
Authors: Tesar AA , Brown NJ , Taylor JR , Stolz CJ
Published: March 2009

The nature of subsurface damage incurred during polishing of fused silica varies greatly with the polishing process. Although subsurface damage is known to lower laser damage thresholds for fused silica surfaces1,2, the effect on thresholds of coated dielectric surfaces has not been previously documented. This study describes features of subsurface damage due to polishing by ten commercial fabricators and compares laser damage thresholds of a high reflection coating on these surfaces.
Characterization of Subsurface Damage in Glass and Metal Optics
Authors: Polvani RS , Evans CJ
Published: March 2009

Even unusual care in polishing, leads to optics with somewhat damaged working faces. The question is, to what degree? the physical nature of this damage depends on the ductility or plasticity of the construction material. Glassy materials (glass, brittle metals and semiconductors) fracture, while ductile materials work harden. Beryllium suffers from both modes. To physically model damage, we oversimplify and picture a surface layer with two features, a depth and an intensity of the bulk property changes. A statistical alternative to intensity is the visible flaw density. We use a variety of analytical methods, but mainly x-ray diffraction, metallography and instrumented microindentation, and frequently use them in combination. Our problem is to develop a general basis and means of characterizing subsurface damage. To illustrate the diversity, difficulty and our progress with the problem, we will report experiences with a variety of examples. The talk will consider damage in “ductile regime” ground, classically polished fused silica BK-7, pyrex optics, “super” polished BK-7, precision ground silicon nitride and alumina ceramics, and precision CBN turned beryllium.7
Laser Raman Measurements of Dielectric Coatings as a Function of Temperature
Authors: Exarhos GJ , Hess NJ , Ryan S
Published: March 2009

Single crystal Raman spectra of the anatase phase of titania have been acquired as a simultaneous function of temperature and pressure in a heated diamond anvil cell. Measured data are used to construct frequency contours in P,T space for particular allowed vibrational modes. The magnitude of stress in thin films deposited on various substrates and its temperature evolution have been evaluated from correlations between the P,T frequency maps and measured temperature-dependent mode frequencies exhibited by the films. A simple anharmonic oscillator model has been used to relate the temperature-dependence of the square of the mode frequency to the first order anharmonic contribution to the potential energy from which the thermal expansion coefficient (α) of polycrystalline films may be estimated. The stress dependence of α for bulk titania has been determined from this data and is compared with the predicted response of several stressed titania films.
Optical Characterization of Damage Resistant “kilolayer” Rugate Filters
Authors: Elder ML , Jancaitis KS , Milam D , Campbell JH
Published: March 2009

Multilayer dielectric optical coatings produced by high temperature plasma-assisted chemical vapor deposition (PCVD) have been previously shown to have very high surface and bulk damage thresholds (above 40 J/cm2). Because these experimental coatings are deposited on tubular substrates, conventional wavelength scanning cannot accurately measure the coating peak reflectance and bandwidth. Measurement of the variation of transmittance with incidence angle at fixed wavelength permits analysis of the coating spectral response. The results indicate that the PCVD coatings behave as nearly “ideal” rugate filters. Their optical performance agrees well with that predicted for a rugate by Southwell's coupled-wave theory and by the characteristic-matrix model. These 1000-layer-pair filters have maximum reflectances exceeding 99.9%, peak reflectance wavelengths within 0.5% of the design wavelength, and FWHM bandwidths narrower than 10 nm. Minor perturbations to the ideal rugate sinusoidal profile donot appreciably affect the coating optical performance. Comparison with calculations suggest that the only significant deviation of the PCVD structure from that of an ideal rugate is a small (0.7%) drift in the index period. Excellent optical performance and high damage resistance makes PCVD rugate coatings potentially useful for several high power laser applications.
Development of Damage Resistant Optics for KrF Excimer Lasers
Authors: Boyer JD , Mauro BR , Sanders VE
Published: March 2009

At excimer wavelengths, the photon energy either exceeds or is comparable to bandgap energies of most materials. This severely limits the materials suitable for optical coatings and is also responsible for the rapid decrease in observed damage threshold fluences as laser wavelength drops. Most materials traditionally used in coating fabrication are unsuitable at the shorter excimer wavelengths. For longer wavelength coatings, materials are chosen for properties such as index contrast and ease of deposition. We are currently reevaluating the suitability of selected materials for damage resistant optical coatings at the KrF excimer wavelength. The low and medium index fluorides are promising as is aluminium oxide. We report the results of damage experiments on both single layer films and dielectric reflectors fabricated from promising combinations of these materials.
Defect Enhancement of Local Electric Fields in Dielectric Films
Authors: Risser SM , Ferris KF
Published: March 2009

Different film deposition techniques have been found to generate distinct grain morphologies and defect distributions, which can result in a wide distribution of local field intensities. We have developed a lattice element model of an inhomogeneous medium, which we use to self-consistently determine the local internal electric field and polarization. We use this method to show the sensitivity of the polarization to defect shape. The results of this method predict the local field to have a large range of values within the film and have been used to identify regions where the local field is a maximum.
Investigation of Neutral Atom and Ion Emission During Laser Conditioning of Multilayer HfO2-SiO2 Coatings
Authors: Schildbach M , Chase LL , Hamza AV
Published: March 2009

It has been recently shown that the optical damage thresholds of multilayer coatings can be increased by up to a factor of two by conditioning the coating at laser fluences below the optical damage threshold. We have investigated the laser conditioning mechanism of HfO2-SiO2 coatings by observing the laser-induced emission of neutral constituents of the coatings during laser conditioning. We observe the ejection of Hf, Si and oxygen (O or O2, or both) neutrals starting at fluences of about 10 J/cm2, considerably below our measured unconditioned damage threshold of about 16–18 J/cm2. We observed a threshold pulse fluence for laser conditioning, which is also about 10 J/cm2. This identical threshold for neutral emission and laser conditioning suggests that the neutral emission is caused by the laser conditioning process. The emitted neutrals have extremely high kinetic energies, on the order of several tens of eV. On the basis of this information, we propose that the laser conditioning process is caused by microscopic damage that involves cracking of the coating layers, resulting in the ejection of the high-energy particles via a “fractoemission” process. This microscopic damage apparently raises the damage threshold by either reducing the absorption of coating defects or by relieving the thermal stresses that cause cracking, particle emission, and possible plasma formation by laser ionization of the neutrals.
A Novel Perfluorinated AR and Protective Coating for KDP and other Optical Materials
Authors: Thomas IM , Campbell JH
Published: March 2009

A new commercially available perfluorinated organic polymer has been used to prepare a combined quarterwave AR and protective coating for KDP and other optical materials. Coatings are applied from solution at room temperature by spin or dip, they are fully dense and have a refractive index of 1.29. The laser damage threshold at 1064 nm and 355 ran is the highest that we have ever measured for an AR coating material.
High Laser Damage Threshold and Low Cost Sol-Gel Coated Epoxy-Replicated Mirrors
Authors: Floch HG , Berger M , Novaro M , Thomas IM
Published: March 2009

In a collaborative effort with some french industrial and university laboratories and also in contact with our colleagues from the Lawrence Livermore National Laboratory (LLNL), we have developed at Limeil-Valenton National Laboratory (LVNL) various laser-performant and inexpensive dielectric mirrors made of a resin-replicated substrate and a specific colloidal sol-gel coating. To date, we have obtained 8″ to 12″ diameter molded optical surfaces with a flatness as good as λ/10 peak to valley at 633-nm wavelength with a roughness ranging 10–15 Å RMS. We have been able to acheive coating-reflectivity exceeding 99 % using room temperature spin-coating deposition of alternate silica and alumina quarterwave layers, and conserving the original substrate flatness. Such sol-gel coated replicated mirrors averaged 13.5 J/cm2 in a single shot irradiation mode and 15.1 J/cm2 with a laser-annealing procedure at 1064-nm and with 3-ns pulses. The present cost of such a product is about 4–6 times cheaper than a similar component conventionally e-beam coated.
Laser-Induced Damage of Diamond Films
Authors: Read HE , Merker M , Gurtman GA , Wilson RS
Published: March 2009

The laser-induced damage thresholds of diamond films deposited on silicon substrates were investigated. Experiments were performed with both CW and pulsed lasers operating at a wavelength of 10.6 μm. Analytical studies were conducted to determine the thermal and thermomechanical states, as well as the electric field strengths, of the films and the substrates at the damage thresholds in an effort to identify the damage mechanism. The evidence suggests that the diamond films are damaged by stress-induced cracking which occurs when the underlying silicon approaches melt.
Ion Assisted Deposition of Graded Index Silicon Oxynitride Coatings
Authors: Al-Jumaily GA , Gagliardi FJ , McColl P , Mizerka LJ
Published: March 2009

Graded index coatings of silicon oxynitride have been deposited using ion assisted deposition (IAD). During the IAD process the coated surface is bombarded with low energy reactive ions such that the chemical properties of the coating can be changed in a controlled fashion. We have shown that the chemical composition of SiNXOY can be varied continuously from silicon nitride to silicon oxide. As a result, the index of refraction of the coatings can be varied between 2.1 and 1.45 by varying the gas mixture in the coating system. The process has been used to deposit graded index antireflection coatings and rugate filters. Several diagnostic techniques were employed to examine the optical, mechanical, and chemical properties of the coatings.
The Effects of Polishing Materials on the Laser Damage Threshold of Optical Coatings
Authors: Crase R
Published: March 2009

This paper reports the effects of polishing material on the laser damage threshold of optical coatings. Two identical sets of BK-7 glass windows were polished to a laser quality surface finish. One set was polished with cerium dioxide (CeO2) and the second set was polished with a soft zirconia (ZrO2).

Samples of each type were coated with electron beam evaporated dielectric coatings. After coating, the samples were then tested to determine their relative damage threshold. The results for each polish type were then compared. Implications for the use of zirconia as an alternative polishing material for high power laser optics is presented.
Physics of Multishot Laser Damage to Optical Materials
Authors: Manenkov AA , Nechitailo VS
Published: March 2009

Fundamental aspects of multishot laser damage are considered: thermal instability in an optical medium due to pulse-to-pulse accumulation of absorbing defects,mechanisms of laser induced defect generation. Effective methods of suppressing a defect formation to increase laser damage resistance are discussed and illustrated by experimental data for various type optical materials.
Dispersion of n2 in Solids
Authors: Sheik-Bahae M , Hutchings DC , Hagan DJ , Soileau MJ , Van Stryland EW
Published: March 2009

We recently performed an extensive series of measurements of the bound electronic nonlinear refractive index n2 of a variety of solids at several wavelengths. We found that as the photon energy approached Eg (the band-gap energy), that n2 changed from positive to negative. This observed wavelength dispersion of n2 can be well explained for wavelengths well below the fundamental absorption edge using a Kramers-Kronig transformation on the two-photon absorption coefficient β which we had previously studied. While this theory fit the data well for 0.1Eg<ℏω<0.8Eg (Eg is the band-gap energy), there was a significant deviation toward larger negative values of n2 near the fundamental absorption edge. We speculated that the AC Stark effect could account for this deviation. Here we extend the data to photon energies nearer the gap and redo the Kramers-Kronig calculation to include the AC Stark (virtual band-blocking), and electronic Raman contributions to the imaginary part of the third order susceptibility. Indeed the fit obtained for n2 as calculated by Kramers-Kronig is amazingly good for a five orders of magnitude change of n2 including a change in sign. The change in sign from positive to negative with increasing frequency occurs midway between the two-photon absorption edge and the fundamental absorption edge. Thus, we now have a comprehensive theory that allows prediction of n2 at any wavelength below the band edge given only Eg and the linear index of refraction. Such information is useful for a variety of applications including optical limiting, laser-induced damage, and all-optical switching.
Damage Resistant Optics for a Mega-Joule Solid-State Laser
Authors: Campbell JH , Rainer F , Kozlowski M , Wolfe CR , Thomas I , Milanovich F
Published: March 2009

Research on Inertial Confinement Fusion (ICF) has progressed rapidly in the past several years. As a consequence, LLNL is developing plans to upgrade the current 120 kj solid state (Nd+3-phosphate glass) Nova laser to a 1.5 to 2 megajoule system with the goal of achieving fusion ignition. The design of the planned Nova Upgrade is briefly discussed.

Because of recent improvements in the damage resistance of optical materials it is now technically and economically feasible to build a megajoule-class solid state laser. Specifically, the damage threshold of Nd+3-doped phosphate laser glass, multilayer dielectric coatings, and non-linear optical crystals (e.g., KDP) have been dramatically improved. These materials now meet the fluence requirements for a 1.5–2 MJ Nd3+-glass laser operating at 1054 and 351 nm and at a pulse length of 3 ns. The recent improvements in damage thresholds are reviewed; threshold data at both 1064 and 355 nm and the measured pulse length scaling are presented.
Contributions of π' Bonding to the Nonlinear Optical Properties of Inorganic Polymers
Authors: Ferris KF , Risser SM
Published: March 2009

Inorganic polymers are characterized by both in-plane π' and out-of-plane π bonding interactions, in contrast to organic materials where π effects dominate the optical properties. Involvement of the π' bonding system results in higher electronic transition energies with the first transition being a π'⃗ π* process. Second hyperpolarizabilities are affected by both π bonding systems, and are reduced by higher transition energies and lower transition probabilities. In this paper, we present electronic structure calculations of the static hyperpolarizabilities of a series of model compounds for inorganic polymers to illustrate the relationship between their electronic structure and nonlinear optical properties.
Damage to InAs Surface from Long Pulse 10.6μm Laser Radiation
Authors: Kovalev VI
Published: March 2009

Laser induced damage to InAs — the material of interest for use as a nonlinear medium for the dinamic holography, phase conjugation etc. at 10.6μm — was studied. Damage thresholds of InAs surfaces both bare and antireflectin coated have been measured for single pulses of 20μs duration and beam spot diameter ⩾/0.5cm. The dependence of thresholds on the surface preparation procedure was found. The performed investigations of damaged sites with help of optical and scanning electron microscopes and X-ray microprobe analiser made evident that the surface heating leaded to the damage. The role of surface absorption and reflectivity are exposed.
Effect of Polarization on Two Color Laser-Induced Damage
Authors: Becker W , McIver JK , Guenther AH
Published: March 2009

Laser-induced damage of optical materials due to the presence of radiation at two different frequencies has received little attention in the literature even though this is not an uncommon occurrence in the laboratory. Recent studies on the multiphoton ionization of single atoms have shown that the ionization threshold depends strongly on the frequencies of the incident fields and their polarizations. In this paper we explore the extent to which these results can be applied to laser-induced damage. The results for a single atom are presented for the case where one field has a comparatively high frequency and low intensity. This field is responsible for the ionization. The other field has a higher intensity and much lower frequency such that it does not ionize by itself. However, it substantially modifies the ionization threshold due to the first field. Both fields are circularly polarized. The behavior of the ionization rate near the thresholds is found to depend strongly on whether the fields have the same or opposite circular polarizations. We also speculate on how these results will influence laser induced damage thresholds.
Crack-Mouth Displacements for Semielliptical Surface Cracks Subjected to Remote Tension and Bending Loads
Authors: Raju IS , Newman JC , Atluri SN
Published: March 2009

The exact analytical solution for an embedded elliptical crack in an infinite body subjected to arbitrary loading was used in conjunction with the finite element alternating method to obtain crack-mouth-opening displacements (CMOD) for surface cracks in finite plates subjected to remote tension. Identical surface-crack configurations were also analyzed with the finite element method using 20-noded element for plates subjected to both remote tension and bending. The CMODs from these two methods generally agreed within a few percent of each other. Comparisons made with experimental results obtained from surface cracks in welded aluminum alloy specimens subjected to tension also showed good agreement.

Empirical equations were developed for CMOD for a wide range of surface-crack shapes and sizes subjected to tension and bending loads. These equations were obtained by modifying the Green-Sneddon exact solution for an elliptical crack in an infinite body to account for finite boundary effects. These equations should be useful in monitoring surface-crack growth in tests and in developing complete crack-face-displacement equations for use in three-dimensional weight-function methods.
An Inverse Method for the Calculation of Through-Thickness Fatigue Crack Closure Behavior
Authors: Dawicke DS , Shivakumar KN , Newman JC , Grandt AF
Published: March 2009

An inverse technique was used to calculate through-thickness fatigue crack closure behavior. The through-thickness variation in crack opening stress-intensity factor was calculated by considering the variation in the three-dimensional stress-intensity factor, the variation in crack growth rate along the crack front, and a relationship between the crack growth rate and effective stress-intensity factor range (da/dN - ΔKeff). The three-dimensional stress-intensity factor variation was obtained from an elastic finite element analysis of specific crack front profiles observed experimentally. The variation in crack growth rate along the crack front was obtained experimentally from comparison of observed crack front changes. The da/dN - ΔKeff relationship was estimated from high stress ratio, constant load amplitude, fatigue crack growth tests. The through-thickness crack opening stress-intensity factor results agreed with crack opening measurements obtained from fatigue striations, near-tip strain gages, and remote strain and displacement gages.
Comparison of Mixed-Mode Stress-Intensity Factors Obtained Through Displacement Correlation, J-lntegral Formulation, and Modified Crack-Closure Integral
Authors: Bittencourt TN , Barry A , Ingraffea AR
Published: March 2009

This paper presents a comparison among stress-intensity factors for mixed-mode two-dimensional problems obtained through three different approaches: displacement correlation, J-integral, and modified crack-closure integral. All mentioned procedures involve only one analysis step and are incorporated in the post-processor page of a finite element computer code for fracture mechanics analysis (FRANC). Results are presented for a closed-form solution problem under mixed-mode conditions. The accuracy of these described methods then is discussed and analyzed in the framework of the their numerical results. The influence of the differences among the three methods on the predicted crack trajectory of general problems is also discussed.
The Application of Line Spring Fracture Mechanics Methods to the Design of Complex Welded Structures
Authors: Ritchie D , Voermans CWM , Bell M , deLange JF
Published: March 2009

Fracture mechanics-based fatigue crack growth prediction methods based on the line spring technique are presented. Developments in the line spring method are described that make it possible to apply the method to realistic welded structures for fatigue design studies. The line spring finite element described in the paper has been formulated to fit between isoparametric brick elements in order to allow shell-to-shell junctions to be represented more accurately. The effect of stress concentrations at weld toes has been also introduced. The accuracy of the line spring approach for the calculation of stress-intensity factors is demonstrated by comparison with three-dimensional finite element fracture mechanics results and empirically estimated values. Prediction of fatigue crack growth in girth welds and tubular connections is compared with observations of cracking in large-scale test specimens. An example of how the fatigue crack growth prediction methods could be applied to the design of welded joints is presented.
Crack-Tip Displacement Fields and JR-Curves of Four Aluminum Alloys
Authors: Dadkhah MS , Kobayashi AS , Morris WL
Published: March 2009

The JR-curves associated with small crack growth in 0.8-mm-thick 2024-T3, 2024-0, 5052-H32 aluminum and 2091-T3 aluminum-lithium cruciform specimens and 2024-T3 and 2024-0 aluminum single-edge-notched (SEN) specimens are presented. The cruciform specimens were loaded uniaxially and biaxially. The J-integral values were determined directly through contour integration of the stresses and strains using deformation theory of plasticity and power hardening law. The strains were computed from the measured in-plane displacements that were determined experimentally using moiré interferometry. Path independency of the J-integral values were verified by the 5% scatter band for the near- and far-field Js. The JR results differed substantially from the J-values computed by using the far-field formula of Shih, German, and Kumar. Also the measured crack-tip displacement and strain fields did not agree with the asymptotic solutions of Hutchinson, Rice, and Rosengren computed from the measured J-values. These findings suggest that the current formulas for J calculations may be incorrect and that J may not be a suitable parameter for characterizing the crack tip.
Application of the Hybrid Finite Element Method to Aircraft Repairs
Authors: Tong P , Greif R , Chen L
Published: March 2009

A hybrid finite element approach is presented for the analysis of cracked panels with riveted doublers in airframe structures. The method uses the super element developed by Tong to model the cracked panel with rivet holes, springs to model the rivets, and regular finite elements to model the doubler. The super element accurately models the crack and rivet holes of the skin while the regular finite element method provides the versatility to take into account the variety of doubler designs. Numerical results are presented to demonstrate the efficiency and accuracy of this approach, and to compare different doubler designs.
A Hybrid Numerical-Experimental Method for Caustic Measurements of the T*-lntegral
Authors: Nishioka T , Fujimoto T , Sakakura K
Published: March 2009

This paper presents a methodology of direct experimental measurement of the T*-integral, which has great potential as a nonlinear (elastoplastic) fracture mechanics parameter. A hybrid numerical-experimental method was developed to measure the T*-integral by the size of reflected caustic pattern. To this end, the formation process of the caustic pattern for an elastoplastic crack tip in a compact tension specimen was simulated by a previously developed finite element simulation technique aided by computerized symbolic manipulation. Experimental measurement of the caustic pattern in the compact tension specimen was also carried out. Both simulated and actual caustic patterns agreed very well. The relations between the T*-integral and the size of caustic pattern were obtained for various optical setup.
Experimental Study of Near-Crack-Tip Deformation Fields
Authors: Chiang F-P , Li S , Wang YY
Published: March 2009

Stationary crack-tip singularity fields of strain-hardening material, Al 2024-0, are investigated by combined moiré and moiré interferometry techniques as a crack goes through elastic and plastic deformation. The experimental results are compared with the corresponding theories at different stages, K field and HRR field, respectively. A two-dimensional finite element computation is also carried out at plastic deformation stage to aid the analysis.
An Engineering Approach for Crack-Growth Analysis of 2024-T351 Aluminum Alloy
Authors: Gu I
Published: March 2009

A simple methodology is suggested to analyze the crack growth of a body up to maximum load, by integrating the step-like increments of applied load and crack extension. The crack-growth criterion is the critical rate of crack-tip opening displacement (CTOD) increase versus effective crack extension of plastic-zone-size adjustment. Formulations of linear elastic fracture mechanics and limit-load expressions are used in the calculation. The analysis also presents a K-resistance (KR) curve equation, which is complete with constants of fracture initiation toughness and crack-growth resistance. The proposed method is applied to 2024-T351 aluminum alloy specimens in plane stress, for which experimental data are available. The calculated maximum loads are in reasonable agreement with the failure loads.
Evaluation of Three-Dimensional Singularities by the Finite Element Iterative Method (FEIM)
Authors: Barsoum RS , Chen T-K
Published: March 2009

The three-dimensional asymptotic singularity fields for surface cracks and corner at a bimaterial interface are evaluated by the finite element iterative method (FEIM). The FEIM approach to three-dimensional cases is described and extended to evaluate the second singular term. The results for the bimaterial surface crack are correlated with experimental results, and the implications of the corner singularity on adhesive failure are discussed. It is shown that surface singularities are stronger than two-dimensional singularities in both cases, which means that commonly used plain-strain conditions at interfaces are nonconservative.
Application of Micromechanical Models to the Prediction of Ductile Fracture
Authors: Sun D-Z , Kienzler R , Voss B , Schmitt W
Published: March 2009

The ductile fracture behavior of different specimens is analyzed by continuum damage-mechanics techniques. A model introduced by Gurson and modified by Needleman and Tvergaard has been implemented in the finite element program package, ADINA. The damage parameters of the model are measured and calculated from smooth tension tests, and the characteristic material distance is estimated from compact tension experiments.

A steel, ASTM A710, and a weld metal for the steel, ASTM A508, are investigated. The damage parameters determined from the smooth bars are used to predict the deformation and fracture behavior of notched round bars and of sidegrooved compact specimens. For the weld metal, a side-grooved WOL-X-specimen is also simulated. In every case, a satisfactory agreement of prediction and experiment is observed.

In order to investigate the influence of the stress state (constraint) in cracked specimens, a series of numerical computations of different specimen geometries and loading situations is performed utilizing the same set of parameters of the ASTM A710 steel. The slopes of the predicted J-resistance curves increase with increasing ratio of tension versus bending load and with decreasing relative crack length.
Analysis of Unidirectional and Cross-Ply Laminates Under Torsion Loading
Authors: Li J , Armanios EA
Published: March 2009

A simple analytical method using a sublaminate approach is introduced to analyze unidirectional and cross-ply laminates under torsion loading. Interlaminar stresses and total energy release rate are evaluated based upon a displacement field that includes shear deformation. Closed-form expressions for the interlaminar stresses and total strain energy release rate in terms of the laminate stiffness coefficients are provided. Two sublaminate models are used for the interlaminar stress analysis and for the delamination analysis. The method is applied to the analysis of [0]16 and [0/90]4s laminates made of IM6/3501-6 graphite/epoxy material. The interlaminar stress predictions are compared with a finite element simulation and an exact elasticity solution.
Problems of Interpretation and Representation in the Computerization of a Printed Reference Work on Materials Data
Authors: Grattidge W , Lund WB , Westbrook JH
Published: March 2009

Problems encountered during a recently completed computerization project of a massive reference work (MilHdbk 5E), capturing approximately 300 tables and 1000 graphs, are identified and their solution described. Some of these problems appeared at the data entry stage, others during the process of validation of the completeness and homogeneity of the final 18,000 database records. The major categories of problems identified and illustrated comprise:inconsistencies and ambiguities arising from excessive compression in the printed form, explicit linkages which are required between exhibits for the computerized version, incomplete linkages, and other errors and ambiguities. In addressing these problems, the computer itself is used insofar as possible. First, to identify the existence of the problem, and second, to apply constraints, perform linkages, implement denormalization routines, etc. to produce the desired set of searchable records used to form the database.
Quality and Reliability Issues in Materials Databases: ASTM Committee E 49.05
Authors: Kaufman JG
Published: March 2009

Recent action by ASTM Committee E 49.05 has renewed progress in addressing quality and reliability issues for materials databases. Three major thrusts, the development of a guide for the development and management of materials databases, standardization of specific quality indicators for data and databases, and standardization of database descriptions are being carried forward. An overview of these three activities is provided in this paper.
Standards for the Representation of Thermodynamic Data for Inorganic Materials
Authors: Barry TI , Rand MH
Published: March 2009

Thermodynamic data are now being used routinely in the calculation of chemical and metallurgical equilibria in multicomponent systems. For these purposes the data must all have been assessed using self-consistent reference data for the elements and key binary systems. International cooperation is vital in order to maintain the necessary standards and generate the required data. The paper describes the role of CODATA, IUPAC, SGTE, CALPHAD and APDIC in these activities, the principles of the methods and their relevance to the design, processing and application of engineering materials.
Online Access to Worldwide Sources of Materials Performance Data--1991 Update on the Materials Property Data Network (MPD Network)
Authors: Kaufman JG
Published: March 2009

The National Materials Property Data Network, Inc., or MPD Network, is a not-for-profit service for the international engineering and material science communities with the mission of providing single-point online access to reliable performance data for materials and for joints in those materials. MPD Network is the result of a cooperative approach to answering the critical need for better access to numeric/factual data that is being carried forward in association with a number of technical societies, government laboratories, universities, and more than 50 sponsors from private industry.

The MPD Network features direct access to numeric and factual databases, easy-to-use software for the occasional, non-professional searcher, and a metadata system to aid in dealing with the varied terminology, materials nomenclature, units, and abbreviations typical of this field. Users may download information to whatever PC, CD-ROM, or mainframe data management systems they employ in their internal system.

A pilot MPD Network system was developed in 1986–1988 in a joint program with the National Institute for Science and Technology (NIST), formerly the National Bureau of Standards (NBS), the Department of Energy (DOE), Lawrence Berkeley Laboratories (LBL), and Stanford University based upon the NIST technology and was used as the research system and for obtaining user feedback. The production MPD Network began operations in January 1991, on STN International, the worldwide scientific and technical information network.

The major features of the MPD Network system are • Direct access to numeric material property databases • Single point access to many sources • User-oriented menu interface to help you locate specific data • Integrated thesaurus to help deal with confusing terminology and nomenclature • Integrated directory of additional material property databases

This update includes background material on the types of data and databases included on the MPD Network and on the menu interface that makes the system useful to end-user engineers and scientists.
The Integration of Materials Information into Engineering Design
Authors: Newley RA
Published: March 2009

The correct selection and use of materials for aerospace products is one of the fundamental aspects of the design process which can provide the necessary competitive advantage to ensure a company's survival and success. At Dowty a number of steps are being taken towards integration of the selection of materials into engineering design - one of which is the creation of a Materials Information (Database) System. This paper describes the evolution of the Information System from the initial recognition of the need, and a specification for an engineering materials database is proposed. It is demonstrated that a Materials Information System will differ from conventional data processing applications in a number of important respects if it is to fully satisfy the requirements of design.