Unstressed Sample Research Articles

Study on the magnetic domain and anisotropy of FeCoSiB amorphous films fabricated by strained growth method

The effect of stress on the magnetic domain and anisotropy of FeCoSiB amorphous films is investigated. It is observed that the unstressed sample consists of irregular domain while the stressed samples show the strip domain. The strip domain of the sample under tensile stress aligns parallel to the direction of the stress while that of the sample under compressive stress aligns perpendicular to it. The variation of the magnetic domain is explained with the magnetoelastic anisotropy induced by the stress, which has been verified by the hysteresis loops, remanences and the anisotropy field. It is also obtained that the stress-induced anisotropy increases with the increase of the stress. The effects of the stress on the magnetic properties of the FeCoSiB films have been discussed.

Assessment of Indentation Fracture Toughness Based on a Direct Measurement of Crack-Driving Residual Stress

A direct measurement of the crack-driving stress has been attempted by applying a nanoindentation-combined, stress-probing technique to the expected crack routes ahead of a Vickers impression. The nanoindentation curves close to the remnant indent were compared to those of an unstressed bare sample and were interpreted into quantitative stress values. In detail, from the difference of two stress distributions measured from uncracked and cracked indentation corners, the driving stress for the radial cracking was estimated; a rapid decaying response with a distance to the Vickers indent center with the peak value 406.7MPa. The fracture toughness of soda-lime glass, estimated by taking into account the results measured in this study was 0.74 ± 0.15 2 / 1 m MPa × and was comparable with that of the literature.

Use of an atomic force microscope to measure surface deformations in polymeric systems

An atomic force microscope is used to image an unstressed sample which is subsequently stressed and re-imaged. An image analysis program is described which allows mapping of surface deformations from the images. In order to show the scope of the present analysis of deformation in plastics, three load conditions showing deformation in a glassy plastic have been selected. In the first a simple tensile load is applied and the image is obtained at low magnification. These images show the general, homogeneous deformation expected with a general elongation in the load direction, an obvious Poisson contraction in the surface plane normal to the load direction and some slight suggestion of Poisson contraction in the through-thickness direction. This loading configuration is intended to reproduce the predicted deformations to illustrate the applicability of the method under simple load conditions. The second loading condition, of a tensile specimen containing a hole, is intended to illustrate the applicability of the system to more complex loading conditions where stress concentrations modify the deformation pattern. The third loading condition is around the tip of a crack propagating in a predictable way in a standard fracture toughness specimen. These images are intended to show the usefulness of the method in characterizing deformations in a complex stress field during failure of the material.

Use of an atomic force microscope to measure surface deformations in polymeric systems

An atomic force microscope is used to image an unstressed sample which is subsequently stressed and re-imaged. An image analysis program is described which allows mapping of surface deformations from the images. In order to show the scope of the present analysis of deformation in plastics, three load conditions showing deformation in a glassy plastic have been selected. In the first a simple tensile load is applied and the image is obtained at low magnification. These images show the general, homogeneous deformation expected with a general elongation in the load direction, an obvious Poisson contraction in the surface plane normal to the load direction and some slight suggestion of Poisson contraction in the through-thickness direction. This loading configuration is intended to reproduce the predicted deformations to illustrate the applicability of the method under simple load conditions. The second loading condition, of a tensile specimen containing a hole, is intended to illustrate the applicability of the system to more complex loading conditions where stress concentrations modify the deformation pattern. The third loading condition is around the tip of a crack propagating in a predictable way in a standard fracture toughness specimen. These images are intended to show the usefulness of the method in characterizing deformations in a complex stress field during failure of the material.

Nanoindentation technique for measuring residual stress field around a laser-induced crack in fused silica

A nanometre scale indentation technique using microprobe indentations to measure residual stresses at selected positions near u.v.-laser-induced cracks in fused silica is presented. The approach is based on the observation that the nanoindentations' penetration depths are affected by the residual stress field emanating from the laser-induced crack. A simple theoretical model based on the change of the nanoindentation penetration depth as well as the change in Young's modulus and hardness of the material is derived. The results show good agreement with the inclusion model [15] suggesting that the residual stress field around a laser-induced crack in fused silica is of shear nature. An exploratory test made on an unstressed sample (free of a laser-induced crack), yielding values for Young's modulus and hardness in accordance with handbook values, shows the high accuracy of this nanoindentation diagnostic.

The effect of thermal stressing on perfluoropolyalkylethers at elevated temperatures

Fultz et al. have reported that the thermo‐oxidative properties of linear PFPAEs can be improved by stressing the fluid at elevated temperature (371°C) in the presence of air. A study of M‐50 steel coupons exposed to unstressed and stressed linear PFPAE fluids at 260 °C and 330 °C each reveal complex surface layers. For the coupon exposed to the unstressed fluid at 260 °C, a subsurface layer is observed between the iron oxide and iron substrate that has been characterized as being composed of FeF2. In contrast, the coupon exposed to the stressed fluid has a marked increase in the iron oxide thickness ∼2–3 times) when compared to the unstressed sample and shows no evidence of a buried fluorine‐containing layer. An increase in temperature (330 °C) in the stressed fluid O–C test was required to form a subsurface FeF2 layer. It is proposed that the elimination of the fluorine layer found on the M‐50 substrate increases the upper temperature limit found from the oxidation–corrosion studies. The increase in the oxide layer thickness implies that the FeF2 layer found in the unstressed sample acts like a diffusion barrier which inhibits the outward movement of Fe0 and the decreased rate of iron oxide growth.

Optical characterization of tin diffusion and defect generation in strained GaAs

The effects of strain on tin diffusion in GaAs were studied by using laser Raman and photoluminescence spectroscopies. It was found that an increase of compressive strain on GaAs causes an increase of the carrier concentration while a decrease of compressive strain or an increase of tensile strain causes a decrease of the carrier concentration at the surface of GaAs. The results are due to the decrease of the diffusion coefficient of tin in GaAs with compressive strain and the increase of it with tensile strain. Photoluminescence data showed that the peak due to Ga antisite defects increased with increase of compressive stress. This indicates a decrease of Ga vacancy concentration from the equilibrium concentration in an unstressed sample. On the other hand, photoluminescence data from the tensile stressed sample showed an increase of Ga vacancy concentration from the equilibrium concentration in an unstressed sample. Thus, the change of the diffusion coefficient with strain seems to be related to Ga vacancy. It was also found that the diffusion coefficient decreased exponentially with compressive strain and increased exponentially with tensile strain with the result that the activation energy of tin diffusion in GaAs varied linearly with strain.

Uniaxial compaction creep of wet gypsum aggregates

The uniaxial compaction creep behavior of wet, granular gypsum is investigated under both chemically closed (i.e., drained) and open (i.e., flow through) conditions known to favor pressure solution. The experiments were performed using applied stresses of 0.5 to 2.5 MPa and grain sizes of 32–280 μm, at room temperature, using pore fluids saturated with respect to unstressed sample material. All wet‐tested samples crept rapidly. In contrast, control experiments using dry and oil‐saturated samples showed no measurable creep. The microstructures developed in the wet tests provide classical evidence for the operation of grain boundary diffusional pressure solution. To enable detailed comparison with theory, it is demonstrated that despite minor effects of the water of crystallization, conventional pressure solution creep models, for closed systems, are applicable to gypsum. However, the mechanical behavior observed in the closed‐system experiments does not fully match these models for either dissolution, diffusion, or precipitation control. Nonetheless, independent crystal growth data suggest that precipitation is most likely to be rate controlling. Additional evidence for this was provided by the experiments with through‐flowing solution. In such experiments, precipitation can no longer control the rate of deformation, so that dissolution or diffusion are expected to take over as the rate‐limiting process, thus enhancing the creep rate. Indeed, a 10 to 30 times increase in compaction creep rate was observed in the flow‐through tests, confirming that creep in the closed‐system case probably occurred by precipitation‐controlled grain boundary diffusional pressure solution.

Raman spectroscopic analysis of stress on GaAs-SiO2 interface and the effect of stress on tin diffusion in GaAs

Stress generated on GaAs-SiO2 interface during annealing and the effect of this stress on tin diffusion in GaAs have been investigated using laser Raman spectroscopy. It was found that compressive stress exists on the surface of GaAs after annealing, which increases with increase of the SiO2 cap layer thickness. The compressive stress on GaAs is generated during annealing and is due to the difference of the thermal expansion coefficients between GaAs and SiO2. The increase of compressive stress on the surface of GaAs decreases the diffusion coefficient of tin in GaAs. This occurs due to the reduction of Ga vacancy in a compressively stressed sample from the equilibrium Ga vacancy of an unstressed sample.

The determination of lattice parameters and strains in stressed thin films using X-ray diffraction with Seeman-Bohlin focusing

A method is presented that allows the simultaneous direct determination of the lattice parameter a 0 and the strains of stressed thin films, independently of an unstressed reference sample with the same value of a 0. The method employs a thin film Guinier camera in subtracting backscattering geometry using Seemann-Bohlin focusing. A wide range of diffraction angles is covered. The strain is measured over a range of angles, not just normal to the layer. Applications of the method to evaporated silver, gold, Nb 3Ge, niobium and vanadium films are presented.

Site-dependent post-trial effects of intracranial substance P and electrical stimulation on learning

The SACROC field, located in west Texas in the Permian Basin, is t he oldes t CO2 enhanced oil recovery site in the United States, with over 93 milli on tons of CO2 injected as of 2007. Recently, t he Na tional Energy Technology Labora tory (NETL) of the United Sta tes Department of Energy has begun to support an enhanced oil recovery project at the SACROC field in north central Texas, working in close collaboration with the Bureau of Economic Geology in Austin, Texas. The project requires the injection of CO2 at a depth of approximately 2040 meters into a reef structure. This project involves both repeat reflection seismic surveys and rock physics based analysis of core material. In the SACROC field, hydrocarbons were flooded out using water, and will be flooded w ith liquid CO2 during the summer of 2008. An experiment is planned whereby we first image fluid floods through reservoir rock using a CT scanner at NETL in order to see what the residual saturations of the previous fluids are. We th en plan to conduct velocity measurements in this order, so that we can obtain a good estimate of conditions in different parts of the reservoir. W e will then measure the P and S wave velo cities, porosity, and permeability at varying pressures and temperatures that simulate reservoir conditions after each successive flood. In addition to velocity ulus, Poisson’s ratio, and stress and strain measuremen ts, we will measure porosity, permeability, Young’s Mod measuremen t under simulate d in situ reservoir conditions. Preliminary P and S wave velocity measurements were made in dry Berea sandstone samples in order to have a base r eference material to compare our results to. Our Berea measurements were 2402 m/s for Vp, 1688 m/s for Vs, and 0.703 for Vs/Vp for an unstressed sample, which agrees well with the literature. The measured ve locities, the P and S waveforms, the velocity vs. confining pressure will be used to calibrate our acoustical measurements both in dry and saturated samples of the carbonate SACROC reservoir rock using oil, gas, water, and CO2. We then plan on doing the first of several seismic surveys in the SACROC field in west Texas. The first survey will be comple ted during the summer of 2008, and presented at this meeting. Using our velocity measurement s, we hope to be able to discern the difference between areas of the reservo ir rock that are saturated with different pore - filling phases. With repeated surveys over the next few years, we hope to be able to observe the area of extent of various floods of CO2 that are scheduled to be injected into several wells in the area using the laboratory me asurements we collected.

Fluage du pyrocarbone sous irradiation

Three massive samples of pyrocarbon were irradiated at 1100°C for a maximum fast-neutron dose of 1.6 × 10 21 DNE. They were subjected to stresses in the range 1.33 × 10 2–2 × 10 2 Kg/cm 2. The pyrocarbon was deposited from methane in a rotating furnace. Its density, its isotropy, its structure according to X-rays and TEM relate closely to its homologue deposited from methane in fluidised conditions. A study of creep under irradiation showed that a brief stage of primary creep is followed by a stage which is linear with respect to both stress and fast-neutron dose. Creep is thus well represented by an expression of the form ϵ = Kσφ, where K is 2 × 10 −25 (Kg · cm −2. DNE) −1, which is a value ten times greater than previously estimated. Irradiation is accompanied by densification, a slight increase in anisotropy and a reduction in L c (apparent crystallite size measured along the c axis). The variation of these parameters with dose does not, however, differ appreciably between the three creep samples and the unstressed sample.

The effect of stress on the microstructure of neutron irradiated cold worked type 316 stainless steel

Abstract 20% cold worked Type 316 stainless steel in the form of uniaxially stressed solid rod and pressurized tubes was irradiated at 450°C in the EBR-11. Five irradiated and three unirradiated specimens were examined by transmission electron microscopy to determine the effect of stress on microstructure and possible mechanisms related to creep occurring during fast reactor irradiation. The dislocation density markedly decreased during the interval of transient irradiation creep. The in-reactor creep of the steel1 occurred independent of swelling since cold work suppressed void formation in both the stressed and the unstressed irradiated material. For the conditions investigated, stress had only a minor effect on the final microstructure compared to that due to irradiation. Although uniaxial stress significantly affected the size of the irradiation induced Frank loops, irradiation creep does not appear to be controlled by the strain from stress biased Frank loop formation. Within a 90% certainty level the mean Frank loop size increases with the increase in the stress component normal to the {111} plane of the loop. The corresponding maximum diameter of these sessile loops was also stress dependent. While the loop size increased with an increase in the stress component normal to the loop plane, the loops which formed on planes having the uniaxial stress nearly parallel to the { 111} planes were smaller than loops produced in the unstressed irradiated sample. These results suggest that uniaxial stress influences the growth rate of Frank loops. A similar effect of stress on loop size was not observed in the sample biaxially stressed during irradiation. No significant effect of stress on loop nucleation could be determined. Effects of stress on loop number density might be masked by the large variations in the numbers of loops formed on the different { 111} planes.

Bestimmung der Mikroporenverteilung im Zementstein

The pore distribution in hardened cement samples were calculated from the water and alcohol sorption isotherms by the method of Barrett, Joyner and Halenda. The maximum of all curves lies at about 20 Å. The pore distribution curve of the desorption branch has a higher maximum than that of the adsorption branch, whereas the raddi of over 100 Å occur more frequently in the adsorption branch. This can be interpreted by means of the “ink-bottle” model of the pores. Pore distribution curves for hardened cement of the same age but different water/cement ratio show that the total porosity and the quantity of gel increase with the rise of W/Z ratio, whereas the porosity of the cement gel is independent of W/Z ratio. It is shown that for hardened cement with W/Z ratio of 0.3, the quantity of gel increases with age. The number of micropores larger than 100 Å increases for up to 28 days and then falls off. The pore distribution curves from the water and alcohol sorption isotherms differ in so far that Δv/Δr for water sorption is twice as large as that for alcohol sorption within the calculated distribution range. This is explained by the higher concentration of water in adsorption and by occlusion in interlayers. The pore distribution curves for stressed and unstressed samples differ only in the height of their maxima. The unstressed sample has a higher maximum in the distribution of the adsorption branch than the stressed sample. The reverse applies to the distribution of the desorption branch. On compression closure of some pores takes place.

Cerium: Anon. ( Brass World, viii, S, 294.)

The SACROC field, located in west Texas in the Permian Basin, is t he oldes t CO2 enhanced oil recovery site in the United States, with over 93 milli on tons of CO2 injected as of 2007. Recently, t he Na tional Energy Technology Labora tory (NETL) of the United Sta tes Department of Energy has begun to support an enhanced oil recovery project at the SACROC field in north central Texas, working in close collaboration with the Bureau of Economic Geology in Austin, Texas. The project requires the injection of CO2 at a depth of approximately 2040 meters into a reef structure. This project involves both repeat reflection seismic surveys and rock physics based analysis of core material. In the SACROC field, hydrocarbons were flooded out using water, and will be flooded w ith liquid CO2 during the summer of 2008. An experiment is planned whereby we first image fluid floods through reservoir rock using a CT scanner at NETL in order to see what the residual saturations of the previous fluids are. We th en plan to conduct velocity measurements in this order, so that we can obtain a good estimate of conditions in different parts of the reservoir. W e will then measure the P and S wave velo cities, porosity, and permeability at varying pressures and temperatures that simulate reservoir conditions after each successive flood. In addition to velocity ulus, Poisson’s ratio, and stress and strain measuremen ts, we will measure porosity, permeability, Young’s Mod measuremen t under simulate d in situ reservoir conditions. Preliminary P and S wave velocity measurements were made in dry Berea sandstone samples in order to have a base r eference material to compare our results to. Our Berea measurements were 2402 m/s for Vp, 1688 m/s for Vs, and 0.703 for Vs/Vp for an unstressed sample, which agrees well with the literature. The measured ve locities, the P and S waveforms, the velocity vs. confining pressure will be used to calibrate our acoustical measurements both in dry and saturated samples of the carbonate SACROC reservoir rock using oil, gas, water, and CO2. We then plan on doing the first of several seismic surveys in the SACROC field in west Texas. The first survey will be comple ted during the summer of 2008, and presented at this meeting. Using our velocity measurement s, we hope to be able to discern the difference between areas of the reservo ir rock that are saturated with different pore - filling phases. With repeated surveys over the next few years, we hope to be able to observe the area of extent of various floods of CO2 that are scheduled to be injected into several wells in the area using the laboratory me asurements we collected.