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Photoelastic measurements of residual strains are used extensively in the QC and inspection of transparent materials. A new method of measurements, based on Spectral Contents Analysis, is described in this paper. The method uses a personal computer for photoelastic data acquisition, eliminating personal skill and subjectivity. the new tool should make the measurements of residual strains for QC simpler and more reliable.
In the United States, extreme heat is the most deadly weather-related hazard. In the face of a warming climate and urbanization, which contributes to local-scale urban heat islands, it is very likely that extreme heat events (EHEs) will become more common and more severe in the U.S. This research seeks to provide historical and future measures of climate-driven extreme heat events to enable assessments of the impacts of heat on public health over the coterminous U.S. We use atmospheric temperature and humidity information from meteorological reanalysis and from Global Climate Models (GCMs) to provide data on past and future heat events. The focus of research is on providing assessments of the magnitude, frequency and geographic distribution of extreme heat in the U.S. to facilitate public health studies. In our approach, long-term climate change is captured with GCM outputs, and the temporal and spatial characteristics of short-term extremes are represented by the reanalysis data. Two future time horizons for 2040 and 2090 are compared to the recent past period of 1981- 2000. We characterize regional-scale temperature and humidity conditions using GCM outputs for two climate change scenarios (A2 and A1B) defined in the Special Report on Emissions Scenarios (SRES). For each future period, 20 years of multi-model GCM outputs are analyzed to develop a 'heat stress climatology' based on statistics of extreme heat indicators. Differences between the two future and the past period are used to define temperature and humidity changes on a monthly time scale and regional spatial scale. These changes are combined with the historical meteorological data, which is hourly and at a spatial scale (12 km), to create future climate realizations. From these realizations, we compute the daily heat stress measures and related spatially-specific climatological fields, such as the mean annual number of days above certain thresholds of maximum and minimum air temperatures, heat indices and a new heat stress variable developed as part of this research that gives an integrated measure of heat stress (and relief) over the course of a day. Comparisons are made between projected (2040 and 2090) and past (1990) heat stress statistics. Outputs are aggregated to the county level, which is a popular scale of analysis for public health interests. County-level statistics are made available to public health researchers by the Centers for Disease Control and Prevention (CDC) via the Wideranging Online Data for Epidemiologic Research (WONDER) system. This addition of heat stress measures to CDC WONDER allows decision and policy makers to assess the impact of alternative approaches to optimize the public health response to EHEs. Through CDC WONDER, users are able to spatially and temporally query public health and heat-related data sets and create county-level maps and statistical charts of such data across the coterminous U.S
In the United States, extreme heat is the most deadly weather-related hazard. In the face of a warming climate and urbanization, which contributes to local-scale urban heat islands, it is very likely that extreme heat events (EHEs) will become more common and more severe in the U.S. This research seeks to provide historical and future measures of climate-driven extreme heat events to enable assessments of the impacts of heat on public health over the coterminous U.S. We use atmospheric temperature and humidity information from meteorological reanalysis and from Global Climate Models (GCMs) to provide data on past and future heat events. The focus of research is on providing assessments of the magnitude, frequency and geographic distribution of extreme heat in the U.S. to facilitate public health studies. In our approach, long-term climate change is captured with GCM outputs, and the temporal and spatial characteristics of short-term extremes are represented by the reanalysis data. Two future time horizons for 2040 and 2090 are compared to the recent past period of 1981- 2000. We characterize regional-scale temperature and humidity conditions using GCM outputs for two climate change scenarios (A2 and A1B) defined in the Special Report on Emissions Scenarios (SRES). For each future period, 20 years of multi-model GCM outputs are analyzed to develop a 'heat stress climatology' based on statistics of extreme heat indicators. Differences between the two future and the past period are used to define temperature and humidity changes on a monthly time scale and regional spatial scale. These changes are combined with the historical meteorological data, which is hourly and at a spatial scale (12 km) much finer than that of GCMs, to create future climate realizations. From these realizations, we compute the daily heat stress measures and related spatially-specific climatological fields, such as the mean annual number of days above certain thresholds of maximum and minimum air temperatures, heat indices, and a new heat stress variable developed as part of this research that gives an integrated measure of heat stress (and relief) over the course of a day. Comparisons are made between projected (2040 and 2090) and past (1990) heat stress statistics. Outputs are aggregated to the county level, which is a popular scale of analysis for public health interests. County-level statistics are made available to public health researchers by the Centers for Disease Control and Prevention (CDC) via the Wide-ranging Online Data for Epidemiologic Research (WONDER) system. This addition of heat stress measures to CDC WONDER allows decision and policy makers to assess the impact of alternative approaches to optimize the public health response to EHEs. Through CDC WONDER, users are able to spatially and temporally query public health and heat-related data sets and create county-level maps and statistical charts of such data across the coterminous U.S.
Effects of swirl on the development of an axisymmetric turbulent mixing layer have been studied. The development of the zero swirl case is found to be consistent with that of a single-stream mixing layer developing from a tripped boundary layer. In particular, the consistency of the measured stress levels shows the accuracy of the measurement system. Swirl increases all the Reynolds stress levels with the increased scaling with swirl number. The shear stresses are found to be affected significantly more than the normal stresses. The stress increases are partly explained by considering extra production terms in the transport equations that are activated by the presense of the swirl. The thickness and growth rate for the lower swirl rate are found to be comparable to the zero swirl case, while those for the higher swirl rate are increased significantly, in line with the increased Reynolds stresses.
Thermal and pressure stress measurements for photoelastic model of Algol rocket nozzle
Geomechanical risks of injection have raised concerns regarding secure CO 2 storage. In this work, a combined monitoring and modeling approach is used to assess the stress changes and surface uplift associated with CO 2 injection into a depleted carbonate reef of the Michigan basin. A site-scale geomechanical model is built by assigning mechanical properties of formations using well-log and experimental data. Gravity load is applied to the model to estimate the vertical component of stress as well as different lateral boundary displacement scenarios to estimate horizontal stresses. We used a poroelastic pressure-dependent model (instead of a linear elastic mechanical earth model) to calibrate initial stresses using hydraulic fracture test data measured at depleted reservoir status. Multi-phase fluid flow-geomechanical simulations are performed to estimate the poroelastic response during (1) primary depletion (2) field-scale CO 2 injection phase (3) a hypothetical forecast scenario in which well bottom hole pressure (BHP) reach 45000 KPa. The predicted surface uplift is less than 1 mm at the end of the field-scale CO 2 injection phase which is in good agreement with Interferometric Synthetic Aperture Radar (InSAR) uplift measurement. Although the InSAR data shows an insignificant uplift, hydromechanical modeling of injection shows that CO 2 injection still causes reservoir deformation emphasizing the role of carbonate overburden and reservoir formation mechanical properties and limited size of reef on diminishing the surface deformation. Modeling indicates poroelastic response of caprock matters to estimate uplift. The lower permeability of the top two layers provides additional barrier to large uplift. Also, history of subsidence due to production should be accounted to predict uplift due to a follow up injection correctly. This report shows the significance of combining a calibrated geomechanical model with field measured stresses and monitoring data to be used as a tool to ensure the safety of CO 2 storage.
The Munson-Dawson (MD) constitutive model was originally developed in the 1980's to predict the thermomechanical behavior of rock salt. Since then, it has been used to simulate the evolution of the underground in nuclear waste repositories, mines, and storage caverns for gases and liquids. This report covers three enhancements to the MD model. (1) New transient and steady-state rate terms were added to capture salt's creep behavior at low equivalent stresses (below about 8 MPa). These new terms were calibrated against a series of triaxial compression creep experiments on salt from the Waste Isolation Pilot Plant. (2) The equivalent stress measure was changed from the Tresca stress to the Hosford stress. By varying a single exponent, the Hosford stress can reduce to the Tresca stress, the von Mises stress, or a range of behaviors in-between. This exponent was calibrated against true triaxial compression experiments on salt hollow cylinders. (3) The MD model's numerical implementation was overhauled, adding a line search algorithm to the implicit solution scheme. The new implementation was verified against analytical solutions, and benchmarked against a pre-existing implementation on a room closure simulation. The new implementation pre- dicted virtually identical room closure, yet sped up the simulation by 16x . (The source code of the new implementation is included in an appendix of this report.)
Elastic moduli of five glass types and the glass-ceramic Zerodur, exposed to a near-earth orbit environment on the Long Duration Exposure Facility (LDEF), were compared to that of unexposed samples. A double exposure speckle photography technique utilizing 633 nm laser light was used in the production of the speckle pattern. Subsequent illumination of a double exposed negative using the same wavelength radiation produces Young's fringes from which the in-plane displacements are measured. Stresses imposed by compressive loading produced measurable strains in the glasses and glass-ceramic.
Gas turbine components such as combustor liners or turbine vanes are subject to regions of high stress-concentration, e.g., attachment to the frame or at cooling holes. Ceramic matrix composites (CMCs) are potential materials for high temperature applications in gas turbines. They offer some capability to relieve stress at regions of high stress-concentration via matrix damage accumulation. In this study notch sensitivity was examined for woven SiC fiber reinforced, melt-infiltrated SiC matrix composites with a BN interphase, utilizing either Hi-Nicalo(TM) fibers or the stiffer Sylramic fibers. The double-edge notched tensile test approach was used for a wide range of notch sizes and specimen widths. Both composite systems exhibited mild notch sensitivity similar to other CMC systems. Acoustic emission, detected during the tensile tests, indicated that matrix cracking occurred around notches at net-section stresses below the stress where matrix cracking first occurs in unnotched specimens. However, thermoelastic stress analysis did not show any measurable stress relief around notches after the specimens were preloaded.
Research has recently shown that liquid crystal coating (LCC) color-change response to shear depends on both shear stress magnitude and direction. Additional research was thus conducted to extend the LCC method from a flow-visualization tool to a surface shear stress vector measurement technique. A shear-sensitive LCC was applied to a planar test surface and illuminated by white light from the normal direction. A fiber optic probe was used to capture light scattered by the LCC from a point on the centerline of a turbulent, tangential-jet flow. Both the relative shear stress magnitude and the relative in-plane view angle between the sensor and the centerline shear vector were systematically varied. A spectrophotometer was used to obtain scattered-light spectra which were used to quantify the LCC color (dominant wavelength) as a function of shear stress magnitude and direction. At any fixed shear stress magnitude, the minimum dominant wavelength was measured when the shear vector was aligned with and directed away from the observer; changes in the relative in-plane view angle to either side of this vector/observer aligned position resulted in symmetric Gaussian increases in measured dominant wavelength. Based on these results, a vector measurement methodology, involving multiple oblique-view observations of the test surface, was formulated. Under present test conditions, the measurement resolution of this technique was found to be +/- 1 deg for vector orientations and +/- 5% for vector magnitudes. An approach t o extend the present methodology to full-surface applications is proposed.
This dataset contains final reports regarding stress measurements, permeability measurements, and mechanical properties from the core testing of well 58-32, in PDF format, and spreadsheets containing tables from the reports as part of Utah FORGE Phase 2B. Please refer to the reports for full information regarding the tables in the spreadsheets. There is also a ReadMe.text with well coordinates.
Epitaxial cubic silicon carbide on silicon is of high potential technological relevance for the integration of a wide range of applications and materials with silicon technologies, such as micro electro mechanical systems, wide-bandgap electronics, and graphene. The hetero-epitaxial system engenders mechanical stresses at least up to a GPa, pressures making it extremely challenging to maintain the integrity of the silicon carbide/silicon interface. In this work, we investigate the stability of said interface and we find that high temperature annealing leads to a loss of integrity. High–resolution transmission electron microscopy analysis shows a morphologically degraded SiC/Si interface, while mechanical stress measurements indicate considerable relaxation of the interfacial stress. From an electrical point of view, the diode behaviour of the initial p-Si/n-SiC junction is catastrophically lost due to considerable inter-diffusion of atoms and charges across the interface upon annealing. Temperature dependent transport measurements confirm a severe electrical shorting of the epitaxial silicon carbide to the underlying substrate, indicating vast predominance of the silicon carriers in lateral transport above 25 K. This finding has crucial consequences on the integration of epitaxial silicon carbide on silicon and its potential applications.
Flapwise bending moments were calculated for a teetering rotor blade using a reasonably rapid theoretical method in which airloads obtained from wind-tunnel tests were employed. The calculated moments agreed reasonably well with those measured with strain gages under the same test conditions. The range of the tests included one hovering and two forward-flight conditions. The rotor speed for the test was very near blade resonance, and difficult-to-calculate resonance effects apparently were responsible for the largest differences between the calculated and measured harmonic components of blade bending moments. These differences, moreover, were largely nullified when the harmonic components were combined to give a comparison of the calculated and measured blade total- moment time histories. The degree of agreement shown is therefore considered adequate to warrant the use of the theoretical method in establishing and applying methods of prediction of rotor-blade fatigue loads. At the same time, the validity of the experimental methods of obtaining both airload and blade stress measurement is also indicated to be adequate for use in establishing improved methods for prediction of rotor-blade fatigue loads during the design stage. The blade stiffnesses and natural frequencies were measured and found to be in close agreement with calculated values; however, for a condition of blade resonance the use of the experimental stiffness values resulted in better agreement between calculated and measured blade stresses.
Characteristics of a liquid crystal system, comprised of a shear-sensitive cholesteric-monomer liquid crystal thin-film coated on a liquid-crystal polymer substrate, are described. The system provides stable Grandjean texture, a desirable feature for shear-stress measurements using selective reflection from the monomer liquid-crystal helix structure. Impingement of gas or air flow on the monomer liquid-crystal free surface changes the wavelength of the selective reflection for an incident white light from red toward blue with increase in the rate of gas flow. The contrast of the selectively reflected light improves considerably by providing a thin black coating of about 5 microns at the monomer-polymer interface. The coating thickness is such that the steric interactions are still sufficiently strong to maintain Grandjean texture. For a small angle of incidence of a monochromatic light, the measurement of the reflected light intensity normal to the monomer-polymer liquid-crystal interface enables the determination of the wavelength for selective reflection as a function of the gas-flow differential pressure applied in the plane of the interface. The variation of the wavelength with the pressure is linear with a slope of about 2 nm/mmHg. Furthermore, the shear-stress effects are reversible unlike for monomer liquid crystal-metal systems used for flow visualization on wind-tunnel model surfaces. The present system offers a suitable method for direct on-line measurement of shear stress field from measurements of the wavelength for selective reflection for an incident white light.
Significant challenges have been faced in the manufacturing of low-stress B 4 C films. Here, we demonstrate a set of process parameters for direct-current magnetron sputter deposition of smooth, high-purity, amorphous B 4 C films with near-zero total residual stress and with thicknesses up to 10 μm. Films are characterized by a combination of high-energy ion scattering, x-ray diffraction, electron microscopy, and stress measurements based on substrate curvature. In order to facilitate the process transfer to other sputtering geometries, the favorable deposition conditions are correlated with distributions of landing energies and incident angles of depositing species estimated by Monte Carlo simulations of ballistic collisions and gas phase atomic transport. Based on such simulations, a decrease in compressive stress with increasing Ar working gas pressure is attributed to the corresponding broadening of the angular distribution of depositing species and associated atomic shadowing effects.
The objective of this work is to deposit nanocrystalline stainless steel onto steel substrates (homometallic) for enhanced wear and corrosion resistance. Homometallic coatings provide superior adhesion, and it has been shown that ultrafine-grained materials exhibit the increased hardness and decreased permeability desired for protective coatings. Nanocrystals will be produced by controlling nucleation and growth and use of an ion beam during deposition by e-beam evaporation or sputtering. Phase I is depositing 31 6L nanocrystalline stainless steel onto 31 6L stainless steel substrates. These coatings exhibit hardnesses comparable to those normally obtained for ceramic coatings such ZrO2, and possess the superior adhesion of seamless, homometallic coatings. Hardening the surface with a similar material also enhances adhesion, by avoiding problems associated with thermal and lattice mismatch. So far we have deposited nanocrystalline homometallic 316L stainless steel coatings by varying the ions and the current density of the ion beams. For all deposition conditions we have produced smooth, uniform, superhard coatings. All coatings exhibit hardness of at least 200% harder than that of bulk materials. Our measurements indicate that there is a direct relationship between nanohardness and the current density of the ion beam. Stress measurements indicate that stress in the films is increasingly proportional to current density of the ion beam. TEM, XPS, and XRD results indicate that the coated layers consist of FCC structure nanocrystallites with a dimension of about 10 to 20 nm. The Ni and Mo concentration of these coating are lower than those of bulk 316L but the concentration of Cr is higher.
The contour method for residual stress measurement has seen significant development, but an experimental reproducibility study utilizing physical samples has not been published. A double-blind reproducibly study is reported, having scope beginning with EDM cutting and ending with residual stress calculation. A reinforced I-beam sample geometry is identified for its unique residual stress profile when extracted from residual stress bearing quenched aluminum bar (7050-T74). Contour measurements are prescribed on a midplane of symmetry with dimensions 24.0 mm by 50.0 mm. Fourteen identically prepared samples are fabricated from a single long bar with well characterized and uniform residual stress. Five samples throughout the bar are identified for planning measurements to validate sample uniformity and overall suitability of the residual stress field. The planning measurements employ a range of techniques: contour method, neutron diffraction, and hole-drilling. Eight samples are distributed to an international group of participants to execute their standard measurement practice. A double-blind process is followed to provide anonymity. Results are provided by eight participants: six being self-similar and two being quite different, the latter set aside as outliers. An average residual stress field is established from non-outlying results and the spatial distribution of reproducibility standard deviation is determined. The average stress field ranges from -60 to 70 MPa and the reproducibility standard deviation averages 8.1 MPa on the measurement plane. The average reproducibility standard deviation is about 3 × larger for points within 1.0 mm of plane boundaries (17.6 MPa) than for the remaining points (6.1 MPa). Reproducibility standard deviation (among different labs) for contour method residual stress measurement is found to be very similar to repeatability standard deviation (in a single lab) reported in prior work. The reproducibility observed here, for the entire measurement process, is also similar to that found in a prior reproducibility study limited to contour method data analysis.
Ocean surface wind (U) is air in motion and stress (τ) is the turbulent transport of momentum between the ocean and the atmosphere. While the strong wind of a tropical cyclone (TC) causes destruction at landfall, it is the surface stress that drags down the TC. There was almost no stress measurement except in dedicated field campaigns and the stress we used was almost entirely derived from wind through a drag coefficient (C(sub D)), as defined by C(sub D) = τ / ( ρ U(exp 2)). In TC, there is difficulty in measuring strong wind and large uncertainty in the drag coefficient.