bluuebunny/crossref_metadata_2025_split huggingface dataset:
Vane Shear Test Apparatus: A Reliable Tool for the Soft Soil Exploration
Authors: Nagarkar PK , Rode SV , Shurpal TW , Dixit GL 
Published: February 2009

There are deposits of fine clays on coastal areas in India. Those soils are soft, highly saturated, of low density, and low shear strength, sensitive, and normally consolidated. Such soils are generally termed as marine clays. Reliable undisturbed sampling of desired size in marine clays is generally difficult, and laboratory tests for determination of shear strength are also difficult for designing foundations of earth fills. In contrast, the vane shear test is a simple as well as reliable method in the hands of research workers.
Five sites for reclamation of dykes and road embankments around Bombay (India) were tackled. The height of the dykes and embankments varied from 2.5 to 7.97 m, and the depths of the marine clay deposits varied from 6 to 16 m.
During the foundation soil exploration, undisturbed soil samples were collected in open tube samplers from drilled holes. The vane shear test with its slow gear arrangement was carried out in the adjacent boreholes. The vane shear tests with vane borer (vane guard) were also conducted at one of the five sites.
Designing of the embankments, by the sliding block analysis method, was based on the average undrained shear strength determined during the vane shear tests. The settlement performance of the above embankments was studied and found to be satisfactory.
Comparison of In-Situ Vane, Cone Penetrometer, and Laboratory Test Results for Gulf of Mexico Deepwater Clays
Authors: Johnson GW , Hamilton TK , Ebelhar RJ , Mueller JL , Pelletier JH 
Published: February 2009

Site investigations were recently performed offshore at three prospective plat-form sites in water depths between 400 and 500 m in the Gulf of Mexico. Soil conditions at the sites generally range from very soft clays near the seafloor to very stiff clays at 120- to 150-m penetration. Analyses of stress history indicate the soils at these locations are generally normally consolidated. Laboratory tests were performed on recovered specimens to deter-mine the undrained shear strength. Standard laboratory miniature vane shear tests and unconsolidated-undrained triaxial tests were performed in addition to consolidated-undrained tests using stress history and normalized soil engineering properties (SHANSEP) procedures. Tests performed in the field included in-situ vane and cone penetrometer. Cone factors Nk were computed using in-situ vane shear strengths as the reference strength.
This paper compares the results of consolidated-undrained (SHANSEP) laboratory and in-situ tests to determine a relationship that may be used to correlate these results. The effects of soil strength and plasticity are examined and used to correlate shear strength with the liquidity index. A comparison is also made between peak and residual in-situ vane strengths.
This paper further describes how a combination of these in-situ and laboratory tests can be used to characterize a deepwater site for foundation design. Recommendations for future site investigations are also discussed.
X-ray Diffraction and Acoustic Emission Study of Fatigue Damage in Aluminum Alloys
Authors: Bathias C , Bonnafe JP , Lebrun JL , Maeder G 
Published: February 2009

The damage that leads to crack initiation under fatigue loading generally occurs at or near the surface. The macrostresses and microstrains induced by machining and surface treatments such as shot peening play an important role in the initiation process. The initial distribution and subsequent evolution of these stresses and strains also influence the growth of fatigue damage. A detailed study, carried out using two aluminum alloys (2024 T351 and 7075 T7351) with electrolytically polished, milled, or shot peened surfaces, has been undertaken at microscopic and macroscopic levels by X-ray measurements of residual stresses at each step of damage development. Acoustic emission has been used to detect the three stages of damage growth: plastic deformation of the surface, microcrack formation, and macrocracking.
The experiment pointed to the conclusion that the damage leading to crack initiation occurs in the following manner: (1) cyclic cold working of the surface with a rapid evolution of residual stresses, (2) stabilization of these stresses and plastic deformation of the surface layers, (3) the appearance of the first microcracks without any change in the residual stresses, and then, (4) the ascendency of one or two macrocracks with complete relaxation of the macrostresses in the close neighborhood of this macrocrack.
Fatigue Crack Propagation and Residual Stress in a Quenched and Tempered C-Mn-B Steel
Authors: Fletcher AJ , Geary W , King JE 
Published: February 2009

The fatigue crack propagation and threshold behavior of a C-Mn-B steel has been examined at strength levels appropriate to the use of this material in haulage chain. Two austenitizing temperatures have been used, 1250°C and 900°C, with tempering temperatures up to 400°C. Threshold values at R = 0.2 ranged from about 4 to 6 MPa ∙ m1/2. They tended to be somewhat higher in material austenitized at 900°C, than in material treated at 1250°C. In the material austenitized at 900°C and tempered at low temperatures (up to about 350°C), the fatigue crack fronts were markedly curved, being held up in the center of the fatigue specimens and advanced at the quarter-section positions. This was due to the residual stress distribution resulting from the volume changes associated with cooling and transformation during the quench.
Good agreement was obtained between the residual stress distribution measured by monitoring the change in strain on the bottom face of a fatigue specimen as successive layers of material were removed from the opposite face, and the predicted distribution after the 900°C austenitizing treatment. The predicted residual stress distribution was determined by a viscoelastic-plastic mathematical model. Both methods showed a tensile stress in the region immediately below the surface and a compressive stress towards the center of the fatigue specimens, as anticipated from the crack front curvature.
Testing at R = 0.8 reduced the crack-front curvature very significantly. In material austenitized at 1250°C, the crack front curvature was less marked than it was following the 900°C treatment.
Measured and predicted residual stress distributions for material as-quenched from 900°C and 1250°C are presented, and the relationship between the stress distribution present and the effects of such factors as mean stress and tempering temperature is discussed in terms of crack closure behavior.
Thresholds for and Time Dependence of UV-Photon-Induced Desorption of Lithium Atoms from Lithium-Fluoride Single Crystals
Authors: Haglund RF , Tolk NH 
Published: February 2009

The rapid pace of development in short-wavelength light sources — ranging from available excimer lasers to projected vuv and xuv free-electron lasers — is stimulating investigations of the electronic photon-materials interactions which may be the rate-limiting processes in catastrophic optical damage.
We have measured photon-energy thresholds for ground-state neutral Li desorption from single-crystal LiF under ultrahigh vacuum conditions using laser-induced fluorescence, and found that as much as one-fourth of the total yield is traceable to photons with energies less than the LiF band gap. Moreover, time-resolved measurements of the desorption process have enabled us to identify the specific excitonic channels which lead to diffusion-driven, defect-induced desorption in this material. Excitonic energy-transfer mechanisms of this type are characteristic features not only of the alkali halides, but also of alkaline-earth halides, fused silica and many metal oxides.
Our results demonstrate that mobile surface and near-surface defects can be produced even by low-energy photons, and that the diffusion of these defects drives the formation of metal-rich overlayers in LiF and probably in many other short-wavelength optical dielectrics.
Radiation Hardness of Nd:YAG and Nd:Cr:GSGG Laser Rods
Authors: Acharekar MA , Kaplan MM , McCarthy DP 
Published: February 2009

Gadolinium scandium gallium garnett (GSGG) co-doped with neodymium (Nd) and chromium (Cr), shows higher efficiency and optical damage threshold than commonly used neodymium doped yttrium aluminum garnet (Nd:YAG) laser rod. Nd:YAG and Nd:Cr:GSGG laser rods were irradiated with gamma radiation from Cobalt-60 source. Passive electronic and vibrational spectra of the laser materials were obtained before and after radiation. The near ultraviolet (NUV), visible (VIS) and near infrared (NIR) spectra were obtained using a Varian Model 2300 spectrophotometer. The infrared (IR) spectra were obtained using a Perkin-Elmer Model 783 Infrared Spectrophotometer and Model 7500 Infrared Data System. The active laser tests were conducted to study the effects of irradiation on the efficiency of the laser materials.
The data collected indicates that the Nd:YAG laser rod had transient radiation effects while the Nd:Cr:GSGG laser rod appeared to be resistant to the effects of the radiation dose in terms of the laser's output energy.
Chemically Strengthened Slab Laser Glass with Optical Surface Quality
Authors: Hata C , Inazumi T , Izumitani T 
Published: February 2009

Slab laser glass was chemically etched to remove microcracks on the polished surface and increase the fracture strength. Xe lamp irradiation test showed dramatically high fracture strength for chemically etched surface compared to polished surface. However, the chemically etched surface is optically neither flat nor smooth. The new fabrication method, chemical polishing, was developed to get simultaneously both chemically strengthened and optically smooth surface.
The slab laser glass fabricated by the new method showed 2.5 times high bending strength as well as optical flat and smooth surface.
Long-Range Pulselength Scaling of 351 nm Laser Damage Thresholds
Authors: Foltyn SR , Jolin LJ 
Published: February 2009

In a series of experiments incorporating 351-nm pulselengths of 9, 26, 54, and 625 ns, it was found that laser damage thresholds increased as (pulselength)X, and that the exponent averaged 0.36 and ranged, for different samples, from 0.23 to 0.48. Similar results were obtained when only catastrophic damage was considered. Samples included Al2O3/SiO2 in both AR and HR multilayers, HR's of Sc2O3/SiO2 and HfO2/SiO2, and an Al-on-pyrex mirror; 9-ns thresholds were between 0.2-5.6 J/cm2.
When these data were compared with a wide range of other results — for wavelengths from 0.25 to 10.6 μm and pulselengths down to 4 ps — a remarkably consistent picture emerged. Damage thresholds, on average, increase approximately as the cube-root of pulselength from picoseconds to nearly a microsecond, and do so regardless of wavelength or material under test.
Time to Failure in Single Pulse Laser Induced Damage in Thin Film Optical Coatings
Authors: Boyer J 
Published: February 2009

Measurement of the time between the start of the laser pulse and the disruption of the irradiated surface provides information not available in traditional damage measurements. The importance of the rate of energy input versus the total energy deposited may be studied by varying the pulse energy and measuring the time at which damage is initiated. If the diagnostics are of adequate sensitivity, a damage threshold fluence can be assigned to each damage event and the fluence distribution of the defect population can be measured.
I will discuss the test configuration and diagnostics for both transmitting and reflecting coatings. Preliminary data at 248 nm with a 23 ns pulse length will be presented.
Scattering Distribution from Multilayer Mirrors -Theoretical Research of a Design for Minimum Losses
Authors: Amra C 
Published: February 2009

The vector theory of light scattering from slightly rough surfaces allows a prediction in the whole space of the scattering distribution from a high-reflecting multilayer coating. A comparison with experimental results concerning classical quarterwave multidielectric coatings enables us to point out the influence of the initial substrate roughness and that of the fine microstructure of the materials used for the coating. Some results are presented for two materials (TiO2, SiO2), and we specify the consequences of the microstructure “grain size” for each one.
In order to reduce scattering losses, it is interesting to know if it is possible to use non-quarterwave multilayer stacks. A theoretical search for solutions leads us to study the consequences of a protective layer deposited on a classical mirror. The influence of the optical thickness of this layer is first studied. Then we examine the case where the top layers of the stack are non-quarterwave layers, so that the electric field associated with the stationary wave is reduced. We can show that, in some particular cases, the total integrated scattering is perceptibly reduced. Nevertheless, this result is only obtained when the roughnesses of the successive interfaces are not correlated. From an experimental point of view, it is not obvious that we can meet this condition whatever the spatial frequency of the defects, and this leads us to study the effect of the cross-correlation coefficient between interfaces.
An Investigation of the Possibility that Laser-Induced Color Centers are Responsible for Multiple Pulse Damage
Authors: Kitriotis D , Merkle LD 
Published: February 2009

The mechanisms responsible for multiple pulse laser damage in transparent solids are still not understood. Recent reports related to laser generation of point defects in fused silica and BK-7 glass raise the possibility that such defect generation is the cause of multiple pulse damage. The difference in defect generation between high-OH and low-OH fused silica offers a means to test this possibility.
We have compared multiple pulse damage properties of “wet” and “dry” fused silica at 1064 nm and 532 nm. Nearly identical behaviors are observed for the two materials. In addition we have studied laser damage in BK-7 X-irradiated to produce color centers. The presence of these centers lowers the damage threshold only modestly. We conclude that optical generation of color centers is not the primary mechanism in multiple pulse damage in these materials.
A Versatile Laser Glass Inspection and Damage Testing Facility
Authors: Marion JE , Greiner GJ , Campbell JH , Chaffee PH , Hildum JS , Grens JZ , Weinzapfel CL , Winfree SM , Milam D 
Published: February 2009

Most glass optical components for high power lasers are melted and homogenized in platinum-lined crucibles leading to the potential presence of microscopic platinum inclusions. In situations where large optics are exposed to high laser fluences, a significant problem can be created by an extremely low density of inclusions, as low as one per component. Previously, direct visual examination or optical microscopy was used to inspect for these particles, limiting reliable detection to inclusions greater than 10μm diameter. Unfortunately, much smaller inclusions can initiate damage in modern lasers operated at high fluences.
A test facility is described which detects small opaque inclusions in large transparent components by using a commercial laser which delivers high energy pulses to the test sample at moderate frequency in a small diameter beam. The sample is automatically scanned such that each point in the volume is irradiated with ten pulses at twice the inclusion damage threshold--an amount sufficient to cause visible damage at inclusion sites. This approach permits detection of opaque inclusions in the parts per trillion and lower concentration range. The specifics of the device design, and its performance are discussed in the context of automatic inclusion inspection and mapping in large laser optics.
Computer-Controlled Facility for Laser Switching and Damage Testing
Authors: Chivian JS , Cotten WD , Fuller DF , Hemphill RB , Scott MW 
Published: February 2009

Apparatus has been assembled for mostly-automatic laser switching and damage measurements in which dynamic events are followed in real time. Lasers, optical elements, and detectors are available for operation at 2.8 μm and at 10.6 μm. Sample exposure time is variable from 50 μs to cw. Sample positioning in X:Y:Z is controllable to 0.2 μm. Testing can be done with static beam position or with a scanning beam. Samples can be tested at ambient temperature, or from near 77°K to 370°K.
Software provides for test control, data processing, and graphic, hard copy output. Beam profiling can be done automatically at the sample position, and the profile fit to a Gaussian of the same 1/e2 width. Sample data acquisition is sequenced by the computer after an enable pulse is given at the discretion of the experimenter. The computer records and processes the incoming data, presents intermediate data display, completes data manipulation, and compares processed measurement data with internally available prediction models in graphic form. Representative output for a thin film nonlinear optical material is shown.
Damage Testing in Optics Production and Procurement
Authors: Seitel SC , Teppo EA 
Published: February 2009

Laser-induced damage studies reported at these symposia have emphasized basic understanding of the light-matter interaction physics, and development of new, more durable materials and coatings. This paper reports a parallel trend toward routine use of damage testing in the procurement and production of reliable optics for low energy, high peak power military and commercial laser systems. Materials and coating designs are conventional, and in practice, in-service failures are as often due to system design effects and contamination as to improper finishing or coating design errors.
The emerging roles of damage testing as a production process-control tool, in acceptance testing, and in failure diagnostics, are discussed and illustrated with specific examples and color photomicrographs. Particular attention is paid to the problems of (1) meeting widely varying test requirements, often on deliverable part of complex geometry, in timely and cost-effective fashion; and (2) relating calibrated single-mode damage test results to optics durability in highly multimode military systems. A brief review of a new repetitively pulsed dual-wavelength damage test station with exceptional configurational flexibility and advanced digital fluence profiling features is included.
A Computer Automated Laser Damage Laboratory
Authors: Sweet MR , Jolin LJ , Foltyn SR 
Published: February 2009

The UV Laser Damage Program has been in existence at Los Alamos for over five years. Recently, the damage laboratories have been upgraded by using a computer system to control and monitor testing parameters, and to display and store the damage data.
The system was designed around already existing testing equipment merged with an IBM-XT for cost effectiveness. The damage fluence is set by a programmable beam attenuator configured in a closed-loop control system with the computer and an energy meter. A matrix of damage sites is set up at the test plane such that the operator can move the sample sequentially between sites or pick sites at random. To aid the operator in choosing test fluence values, a damage plot may be generated on the monitor or on a high resolution plotter.
By automating the Laser Damage Laboratory with a computer, consistent results can be achieved over a short testing time.
U.V. Laser Beam Diagnostics using a Computer Controlled Video Frame Store System
Authors: Clark SE , Laidler I , Emmony DC , Omar BA , Shaw MJ 
Published: February 2009

In the past the spatial intensity profile of a laser beam has been measured using such techniques as scanning pinholes, detector arrays and photography.
This new system converts the Excimer beam into visible light using a glass fluorescer with a very small penetration depth giving a good 2D image of the beam. The fluorescence has been found to be linear over a wide range of input energy and is imaged by a CCD camera linked to the computer controlled video frame store.
The digitised information is then computer processed to yield such results as the intensity profile along an arbitary line, peak fluence, the difference between two images and various statistical values.
This new technique has been applied to beams with widely varying diameters including analysis in the focal region and in the early detection of damage in materials.
Platinum Particles in the Nd:doped Disks of Phosphate Glass in the Nova Laser
Authors: Milam D , Hatcher CW , Campbell JH 
Published: February 2009

The disks of Nd:doped phosphate glass in the amplifiers of the Nova laser contain platinum particles with sizes ranging from &lt;5μm (detection limit) to about lOOμm. The particle density varies from about 0.01 to 1.0 cm-3. These particles cause fractures when irradiated at fluences &gt;2.5 J/cm2 delivered in 1-ns, 1064-nm pulses. Under repeated irradiation at 5–7 J/cm2, damage from small (&lt; 5μm) particles asymptotically approaches a limiting size, but damage surrounding the larger particles grows steadily. The damage threshold fluence, 2.5 J/cm2, corresponds to operation of Nova at one-half the desired output for pulse durations longer than 1 nsec. Operation at higher fluences causes accumulation of damage in the output amplifiers and requires replacement of the disks in those amplifiers on an accelerated schedule.
Large-area damage tests have been used to characterize samples from recent melts made to reduce the number of platinum particles. The 500-J, 1-ns pulses available at the midpoint of an arm were used to produce fluences of 7–10 J/cm2 over test areas 6–9 cm in diameter. Similar irradiations of areas 25–30 cm in diameter were accomplished using 5-kJ, 1-ns pulses available at the output of an arm. Preliminary results from these experiments indicate that a significant reduction of the inclusion density can be obtained through changes in the vendor's glass melting conditions.
Picosecond Nonlinear Investigation of Accumulated Damage in Molecular Crystals
Authors: Kosic TJ , Hill JR , Dlott DD 
Published: February 2009

Accumulated damage in aromatic molecular crystals at low temperature is studied by a variety of novel picosecond laser techniques. Damage in these materials is qualitatively different than in fused quartz, where dielectric breakdown is the predominant mechanism. In the aromatic crystals, multiphoton ionization creates reactive chemical fragments which are stabilized by the low temperature crystal matrix. These species accumulate until a high concentration is reached. At that point, phonon and photon assisted interactions release enough energy to damage the crystal. In a sense the process can be viewed as a chemical explosion.
The picosecond YAG--dual dye laser system used for these experiments is described. With this system we have demonstrated new methods to study damage. Subnanosecond damage is time-resolved with a sampling technique. The mechanism of defect production and crystal destruction is probed using damage detected spectroscopy. Scattering of the optical phonons by the accumulating defects is detected via picosecond time-delayed coherent Raman scattering.