bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Effect of Elevated Temperature on Shot Peened 403 Stainless Steel
Authors: Childs WH 
Published: February 2009

This paper presents the results of an experiment to determine the effect of elevated temperature on residual stresses present in, and the fatigue life of, shot peened 403 stainless steel. The first step involved testing simulated Almen A strips made from strip quench and tempered to 229–235 HB. The strips were shot peened to 8–10 A and subjected to temperatures ranging from 150 to 595°C (300 to 1100°F) for up to 1000 h. The amount of relaxation of the height of each sample was then measured at several intervals during the test. The data revealed that the change at 150°C (300°F) after 50 h was equal to that at 260°C (500°F). This drop was unexpected, as a review of available literature indicated residual stresses in carbon steel would not start to drop until 260°C (500°F), with stainless steels resistant to a much higher temperature. Measurement via x-ray diffraction showed the residual stress dropped from -529 MPa (-76.7 ksi) at room temperature to -269 MPa (-39 ksi) after exposure to 150°C (300°F) and to -112 MPa (-16.3 ksi) after exposure to 595°C (1100°F).
The second part of the paper presents the results of testing shot peened 403 stainless steel rotating beam fatigue test bars at room temperature, 260, and 400°C (500°F and 750°F). The data shows the endurance limit increases by 16 percentage points at room temperature and 6 percentage points at 260 and 400°C (500 and 750°F).
Mass Spectrometric Studies of Laser Damage in Calcium Fluoride
Authors: Nogar NS , Apel EC , Estler RC 
Published: February 2009

Both electron impact- and laser ionization-mass spectrometry have been used to probe the material spalled from CaF2 surfaces by the fundamental(1.06μ) and harmonic (355 nm and 266 nm) outputs from a Q-switched Nd:YAG laser. We have identified a number of gas phase products, including Ca, CaF and tentatively, CaF2, and have measured their translational and internal energy distributions.
Our results suggest that while the 1.06μ experiments can be adequately modeled in terms of a single damage mechanism (likely avalanche breakdown), the short-wavelength results suggest the onset of second mechanism, perhaps multiphoton absorption. This is consistent with both the observed bimodal velocity distribution following short-wavelength damage, and with the decrease in CaF vibrational and rotational excitation.
CaF2: An ESCA Study
Authors: Raj T , Law M 
Published: February 2009

This paper describes two observations made on CaF2 during electron spectroscopy for chemical analysis (ESCA) studies. The first observation is that an ion-etched CaF2 surface adsorbs several layers of water even in an ultrahigh vacuum (UHV) chamber (P ∼ 2×10-10 torr). This water at the sputter-etched surface is responsible for the presence of oxygen peaks in the ESCA data. The presence of oxygen in the ESCA data can easily be misinterpreted as an impurity in the CaF2 bulk. This observation is detailed in Part I of the paper.
The second observation is that CaF2 (whether substrate, source material or coating) in a UHV environment releases a small amount of fluorine-containing gas. This is discussed in Part II of the paper.
Production Oriented Laser Damage Testing at Hughes Aircraft Company
Authors: Mordaunt DW , Arenberg JW , Frink ME 
Published: February 2009

This paper describes the laser damage test station used by Hughes Aircraft Company for production support and incoming inspection of optics. It is emphasized that this is a high volume production station which is utilized almost full time for lot sample testing and related production support activities.
The evolution of damage testing at Hughes over a 15 year period is described from early efforts with ruby lasers to the current facility used in support of our Nd:YAG laser programs. The test station and procedures are described in detail including the use of a reference optic as a standard of comparison. Also discussed is the long term success of this test in providing usable components which are acceptable in actual hardware. Plans are presented for the development of the next generation of production related damage test station which incorporates more sophisticated diagnostics and the potential for almost complete automation of the actual damage test.
Amorphous Silicon for CO2 Laser Mirror Coatings
Authors: Dutois F , Mouchart J , Pointu B , Villela G 
Published: February 2009

High power CO2 laser require mirrors with high reflectivity, high laser damage threshold and efficient mechanical and chemical protection. Enhanced metallic coatings are generally used.
Amorphous silicon thin films are hard, with low porosity and have a high refractive index: unfortunately the low absorption at 10.6 μm is however too high for quarterwave layer at that wavelength.
When associated with a classical transparent but softer high index material such as ZnSe or ZnS, amorphous silicon can nevertheless be used in order to design the last composite high index quaterwave. Theoretical calculations predict an optimum reflectance for a fixed a : Si : H thickness.
The amorphous silicon thickness is thin enough to obtain a high reflectivity coating although its absorption, but thick enough to provide a good chemical and mechanical protection. Besides, experimentally determined that such enhanced coatings have a high laser damage threshold level.
Change of Dislocation Structures and Macroscopic Conditions from Initial State to Fatigue Crack Nucleation
Authors: Murakami Y , Mura T , Kobayashi M 
Published: February 2009

Dislocation structures in fatigue were investigated with special consideration given to the compatibility of the macroscopic observation by an optical microscope and the microscopic observation by a transmission electron microscope (TEM). First, previous works are reviewed from this point of view, that is, the compatability of macro- and microscopic observations. It is postulated that this viewpoint is very important for both the elucidation of fatigue mechanism and the construction of crack nucleation models. Second, the experiments are planned and carried out, and the results are discussed in this direction. Copper polycrystalline sheets with a thickness of 0.1 mm are used for the preparation of specimens for fatigue testing. The specimen contains an artificial hole of 200 μm diameter. The fatigue processes at the edge of the hole were observed successively with an optical microscope. In the early stage of the fatigue test, slipbands initiated at the hole edge and subsequently cracks nucleated after stress cycles of N ≅ 8 × 105. The foil specimens for TEM observation were prepared from the sheet specimens that were tested for various numbers of cycles, say, N = 2 × 105, 4 × 105, and 8 × 105. Every effort was made to show the correspondence between the site of TEM observation and that of macroscopic observation. Since it was very difficult to thin the edge of a hole sufficiently, only a few specimens were available for TEM observation though more than 100 sheet specimens were tested. The first part of the paper poses five fundamental questions; especially considered in the direction described above are (1) the relationship between vein structures and persistent slipbands (PSBs), (2) the relationship between crack nucleation and PSBs, and (3) dislocation structure at the stress concentration or stress gradient.Conclusions may be summarized as follow: (1) Vein structures and ladder structures in PSBs are closely related. (2) In the fatigued copper polycrystal specimens with no hole, PSBs with ladder structure can develop in certain grains of the specimen. (3) At the edge of a hole of the specimens which contain a hole, however, PSBs with ladder structure are unlikely to be formed. (4) The crack nucleation sites at the edge of a hole are PSBs without ladder structure.
Crystallographic Study of the Fatigue Crack Nucleation Mechanism in Pure Iron
Authors: Tanaka T , Kosugi M 
Published: February 2009

The fundamental question posed in this study is, What crystallographic conditions are satisfied at fatigue crack nucleation sites in polycrystalline iron? To answer this question it is vital to establish an effective technique to determine the crystallographic orientation of each grain under observation. This problem was solved by developing an etch pit method of grain orientation analysis. Stereographic projection geometry was successfully applied in determining the orientation of each grain with great accuracy from the measured angles between ridge lines of sharp-edged etch pit patterns on the film. The critical experiment, then, is to examine the geometrical relationship between the nucleated fine cracks and the orientations of surrounding grains on fatigued specimen surfaces. The final step is to extract such crystallographic conditions as are commonly satisfied at the sites of crack nucleation.
Electrolytically polished commercial base pure iron plate specimens were tested under completely reversed plane bending stress in the high-cycle fatigue range. Tests were interrupted at about half of the fracture life, and the crystallographic configuration of microcracks with respect to the grain orientation was thoroughly examined by making use of the newly developed technique. Cracks were observed to nucleate only along grain boundaries on the specimen surface. And it was found that there are five conditions satisfied at those cracked sites. These conditions concern the favorable configuration of slip systems, Schmid factor, grain size, and the direction of grain boundaries. Three more conditions were added from information pertaining to the crystallographic structure below the surface gained by observation after removal of the surface layer and of cross sections containing a crack. A brief discussion is also given on some statistical aspects of important parameters.
Use of Nondestructive Evaluation Techniques in Studies of Small Fatigue Cracks
Authors: Resch MT , Nelson DV , Yuce HH , London BD 
Published: February 2009

This paper reports progress to date in the development of an ultrasonic surface acoustic wave (SAW) technique to monitor in situ the depth of small cracks as they grow, as well as the stresses required to cause the cracks to begin to open and to fully open.
Two SAW transducers (transmitter and receiver) are used to monitor crack reflection signals. The surface length is measured by conventional methods. Based on new acoustic theory, the reflection signal and length data are used to infer crack depth below the surface. Acoustically determined depth is compared with that obtained by destructive examination of specimens, and agreement is good.
The crack opening stress determined acoustically is compared with opening stress determined by scanning electron microscope (SEM) measurements of crack mouth opening displacement versus applied stress. This comparison requires specimens small enough to fit inside an SEM chamber. Preliminary results demonstrate the ability of the acoustic measurements of crack opening to detect behavior below the surface not detected by SEM measurements. Acoustically determined changes in crack opening behavior as a function of constant-amplitude and variable-amplitude stress histories are also presented.
Development of a Criterion for the Effect on the J-R Curve of Elastic Unloadings
Authors: Joyce JA 
Published: February 2009

A criterion is proposed which allows estimation of the fraction of cyclic damage which would be expected from a given number of partial or complete unloadings applied during the course of a J-R curve fracture toughness test. The criterion requires both geometry and material inputs, but for the special case of a steel compact specimen, an upper-bound criterion is developed and presented graphically.Data from a series of compact specimens of a 3% nickel alloy steel are used to verify both the model used and the resulting fractional damage criterion developed.
Ultrafine Polishing of Tungsten and Molybdenum Mirrors for Co 2 Laser
Authors: Yamashita M , Hara S , Matsunaga H 
Published: February 2009

A study has been performed experimentally to determine the polishing methods for high-power laser mirrors. This paper presents ultrafine polishing of tungsten (W) and molybdenum (Mo) which cannot be turned by a diamond tool.
Samples were prepared by five methods: lapping with SiC abrasives of 4000-grit size; lapping with 3 μm diamond powder; float polishing with SiO2 powder; Ar ion beam etching; and electrolytic polishing. The finished surfaces are characterized using several techniques, including profilometry, electron probe microanalysis, X-ray diffraction, calorimetric technique with cw CO2 laser and so on.
The surfaces lapped with 3 μm diamond powder have damaged layers of about 2 μm deep in the case of W and about 3 μm deep in the case of Mo. In either case, however, if about 1 μm thickness of the damaged layer is removed by float polishing from the lapped surface, the layer which increases absorptance at 10.6 μm wavelength will be almost removed.
Laser Induced Particle Emission as a Precursor to Laser Damage
Authors: Domann FE , Stewart AF , Guenther AH 
Published: February 2009

Mass spectrometry was used to investigate particle emission, specifically contaminant species, as a possible precursor to laser damage. Experiments were carried out in a clean ultra-high vacuum chamber with a background pressure of 4×10-8Pa. Both pulsed (8 ns) and CW Nd:YAG lasers operating at 1.06 microns were used to irradiate a variety of samples which included uncoated Si, fused silica coated with films of Al2O3, MgF2, or ZrO2, and Si coated with a SiO2/ZrO2 stack. In the pulsed laser experiments, both 1-on-1 and N-on-1 irradiations were investigated. Emitted particles were mass analyzed with a quadruple mass spectrometer which recorded the partial pressure of a given species as a function of time.
Single pulse damage thresholds found in this study were consistent with those reported in the literature. Important differences are exhibited in pulse radiation data depending upon whether the laser fluence is above or below the damage threshold as well as upon the type of sample irradiated. In CW laser experiments, fluence was sufficient to cause damage only in the SiO2/ZrO2multilayered coating due to absorption by the Si substrate. CW irradiation also resulted in desorption signals at lower fluences than was possible with pulsed radiation.
Ion Emission Kinetics of Laser Damage to Semiconductor and Dielectric Thin Film Surfaces
Authors: Trisnadi JI , Jee Y , Walser RM , Becker MF 
Published: February 2009

In these experiments we used time-of-flight energy analysis to determine the kinetic processes occurring at laser damage on surfaces. A triaxial charge collector of relatively large area was designed for use in the target vacuum chamber. It could be biased in several ways to detect either positive or negative charge, and it could resolve charged particle time-of-flight over a field free region of about 6 cm. The laser system was a Q-switched Nd:YAG laser with 10 ns pulses at 1064 nm. Measurements were made on single crystal germanium wafers and on half-wave delectric thin film samples of ThF2 and MgF2 on fused silica.
On germanium, ion emission was only detected when the surface morphology indicated boiling. This occurred at about 1 J/cm2 or a little over twice the melt or damage onset fluence. For thin film samples, ion emission correlated with surface damage. For all samples, ion velocity distributions and the observed correlation between kinetic energy and ion flux were characteristic of laser heated plasma processes following charge emission.
High Power Continuous Wave and Repetitive Pulsed Thermal Shock Laser Damage to Metallic Reflective Optics
Authors: Palmer JR 
Published: February 2009

Thermal shock damage may be a precursor to the melting and disordering of metallic reflector surfaces. A number of investigators have reported in these proceedings the phenomena of slip fracture on the surfaces of both polished and diamond turned optics. In this paper, a model is presented using elastic-plastic technique coupled with the transient thermal response of an optical surface.
Equations are presented to reflect the thermal shock threshold for major metals that are commonly used for high power laser reflective optics. The models for the continuous wave and repetitive pulsed conditions have some similarities in evaluating the strain and rupture. However, because of the two cycle nature of the Repetitive Pulse condition, the thresholds are demonstrably lower than those that are shown for the Continuous Wave situation.
Deformation and Fatigue Damage in 1070 Steel under Thermal Loading
Authors: Karasek ML , Sehitoglu H , Slavik DC 
Published: February 2009

The fatigue lives of 1070 steel (Class U wheel steel) under (1) isothermal loading, (2) thermo-mechanical constant amplitude loading, and (3) thermo-mechanical block loading have been examined. Fatigue lives for these three cases were compared based on the same mechanical strain range and maximum temperature level, with similar strain rates. Predictions of thermo-mechanical block loading cases were nonconservative based on isothermal data, while the predictions improved to within a factor of 1.5 of experimental lives when thermo-mechanical constant amplitude data were utilized.
Oxide scales readily formed at high temperatures (&gt;500°C) and resulted in increased damage due to a localized high strain state and an inherent lack of ductility. Oxides of different composition and morphology form depending on the temperature and type of loading. Stratified and non-stratified oxide layers (predominantly Fe3O4) were identified in the experiments.
Growth of Small Cracks and an Evaluation of Low Cycle Fatigue Life
Authors: Hatanaka K , Fujimitsu T 
Published: February 2009

Smooth and through-thickness cracked specimens of JIS S35C medium carbon and SNCM 439 alloy steels, heat-treated in several conditions, were low cycle fatigued. The growth rates of small surface and through-thickness large cracks, da/dN, were analyzed in terms of the cyclic J-integral range, ΔJ, and the strain intensity factor range, ΔKϵ.
The crack growth rates plotted against ΔJ and ΔKϵ are expressed by straight lines on a log-log diagram. The fairly large scatter inherent in a small crack problem hides some difference in the relations of da/dN versus ΔJ and the da/dN versus ΔKϵ plots between different materials. These relations in a small surface crack are slightly different from those in the through-thickness large crack.
The equations derived from combining these two relations and the cyclic stress-strain curve express well the fatigue life curves, of which slopes decrease in the lower plastic strain range in materials having a high strength and a low ductility, as well as the usual Coffin-Manson plot.
Elevated-Temperature Low Cycle and Thermomechanical Fatigue Properties of AISI H13 Hot-Work Tool Steel
Authors: Engberg G , Larsson L 
Published: February 2009

Thermal fatigue of the martensitic hot work tool steel AISI H13 is complicated by structural degradation which in turn is influenced by plastic deformation. These properties are dependent upon plastic deformation, temperature, and time, and thus it is of vital importance to find a description which allows inter- or extrapolation to the thermal load experienced in various practical applications.
Isothermal, low cycle fatigue testing was performed mainly at 500 and 600°C and also to a limited amount at 80, 300, and 750°C. The material was tempered to three different hardness levels (43, 47, and 51 HRC) prior to testing. The main bulk of tests were performed on the 47 HRC variant. At 600°C no difference in life was observed between the different hardness variants. The cyclic stress-strain curves, evaluated at half lives, were also almost identical. Softening is believed to cause this similarity, while the initial differences will only influence the behavior during a small fraction of the life after which all material differences will have vanished. Softening is due to particle coarsening and a decrease of the initially very high dislocation density. By assuming that Ostwald ripening takes place through volume diffusion, that the Orowan mechanism for particle strengthening is valid, and that the dislocation network spacing is directly proportional to the interparticle distance, a fair functional description of the experimental data is obtained. The temperature dependence of the solubility limit for the carbides and the activation energy for self-diffusion are nicely reflected by the data. The model predicts that a low solid solubility and a high volume fraction of the carbides will give rise to a low rate of softening as will a high strain-rate and of course a low temperature. Plastic deformation is found to increase particle coarsening significantly, but the extent is independent of the magnitude of the plastic strain within the limits investigated.
Thermomechanical fatigue testing (simultaneous cycling of both strain and temperature, half a period out of phase with one another) was performed with a maximum temperature of 600°C in the cycle. The minimum temperature, T-min, was varied from 80 to 400°C. In comparison to the isothermal 600°C data, life was reduced when T-min was less than or equal to 200°C, but remained fairly unaffected when a T-min of 400°C was used. As expected, softening increased with increasing minimum temperature.
The same hardness variants as described above were also tested with the 200 to 600°C cycle. No significant differences in life were obtained, although the cyclic stress-strain curves (maximum tensile stress at half life) differed. The Ostergren method for life prediction fit our data reasonably well if the plastic work is normalized with the cube of the shear-modulus.
Low Cycle Fatigue of Strain Aging Ferrous Alloys
Authors: Pickard SM , Guiu F , Blackie AP 
Published: February 2009

The fatigue behavior of two high purity Fe alloys, one with 75 ppm (by mass) of both N and C and the other with 0.1% (by mass) C, has been investigated at 5 Hz. These alloys were heat treated to retain different solute concentrations, and it was found that the effect of increasing solute concentration was to increase the fatigue life and to suppress the “knee” in the S-N curve. It is shown that the flat appearance of the S-N curve is due to dynamic strain aging of the alloys. The Coffin-Manson analysis of the data shows that dynamic strain aging hardly affects the fatigue ductility of the material but produces an increase in yield stress sufficient to increase the fatigue life.
Fatigue predeformation and static aging at 60°C for 16 h produces a precipitation of metastable nitrides, or carbides, both at matrix sites and dislocations and an increase in the yield stress of the alloys. On retesting at the same stress amplitude, the plastic strain is found to have been considerably reduced and the fatigue life greatly increased, with a return of a “knee” in the S-N curve. The Coffin-Manson analysis reveals a great loss in fatigue ductility, but it is found that the cumulative strain to failure remains nearly constant at each stress level. This suggests that the influence of the increased strength by strain aging on fatigue life is more important than the reduction in ductility. The dislocation substructures developed at different amplitudes both before and after aging are correlated with the formation of slip bands and the nucleation of fatigue cracks.