Subsidence‐Derived Volumetric Strain Models for Mapping Extensional Fissures and Constraining Rock Mechanical Properties in the San Joaquin Valley, California
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Grace Carlson↗
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Results for “volumetric strain”
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The effects of confining pressure and stress difference on static fatigue of granite
Samples of Barre granite were creep tested at room temperature at confining pressures up to 2 kilobars. The time to fracture increased with decreasing stress difference at every pressure, but the rate of change of fracture time with respect to the stress difference increased with pressure. At 87% of the short-term fracture strength, the time to fracture increased from about 4 minutes at atmospheric pressure to longer than one day at 2 Kb of pressure. The inelastic volumetric strain at the onset of tertiary creep, delta, was constant within 25% at any particular pressure but increased with pressure in a manner analogous to the increase of strength with pressure. At the onset of tertiary creep, the number of cracks and their average length increased with pressure. The crack angle and crack length spectra were quite similar, however, at each pressure at the onset of tertiary creep.
Kranz, R. L.↗
Computer-aided analysis for the Mechanics of Granular Materials (MGM) experiment, part 2
Computer vision based analysis for the MGM experiment is continued and expanded into new areas. Volumetric strains of granular material triaxial test specimens have been measured from digitized images. A computer-assisted procedure is used to identify the edges of the specimen, and the edges are used in a 3-D model to estimate specimen volume. The results of this technique compare favorably to conventional measurements. A simplified model of the magnification caused by diffraction of light within the water of the test apparatus was also developed. This model yields good results when the distance between the camera and the test specimen is large compared to the specimen height. An algorithm for a more accurate 3-D magnification correction is also presented. The use of composite and RGB (red-green-blue) color cameras is discussed and potentially significant benefits from using an RGB camera are presented.
Parker, Joey K.↗
A Nonlinear Viscoelastic Model for Ceramics at High Temperatures
High-temperature creep behavior of ceramics is characterized by nonlinear time-dependent responses, asymmetric behavior in tension and compression, and nucleation and coalescence of voids leading to creep rupture. Moreover, creep rupture experiments show considerable scatter or randomness in fatigue lives of nominally equal specimens. To capture the nonlinear, asymmetric time-dependent behavior, the standard linear viscoelastic solid model is modified. Nonlinearity and asymmetry are introduced in the volumetric components by using a nonlinear function similar to a hyperbolic sine function but modified to model asymmetry. The nonlinear viscoelastic model is implemented in an ABAQUS user material subroutine. To model the random formation and coalescence of voids, each element is assigned a failure strain sampled from a lognormal distribution. An element is deleted when its volumetric strain exceeds its failure strain. Element deletion has been implemented within ABAQUS. Temporal increases in strains produce a sequential loss of elements (a model for void nucleation and growth), which in turn leads to failure. Nonlinear viscoelastic model parameters are determined from uniaxial tensile and compressive creep experiments on silicon nitride. The model is then used to predict the deformation of four-point bending and ball-on-ring specimens. Simulation is used to predict statistical moments of creep rupture lives. Numerical simulation results compare well with results of experiments of four-point bending specimens. The analytical model is intended to be used to predict the creep rupture lives of ceramic parts in arbitrary stress conditions.
Powers, Lynn M.↗
The JPL advanced propulsion module motor chamber
A Kevlar 49/epoxy chamber has been developed for the advanced propulsion module motor. This chamber was successfully designed, fabricated, and hydroproof-tested at 511.6 N/sq cm. The fabrication, interior dimensional inspection, and proof test are discussed, showing that the chamber will be capable of achieving the design burst pressure of 639.8 N/sq cm. The projected chamber growth at 448.2 N/sq cm is presented based on the strain gage and volumetric growth data collected in that proof test.
Jensen, W. M.↗
NDT and SHM of Carbon Fiber Composites using Linear Drive MWM-Arrays
Carbon fiber composites are used in a wide range of structural applications due to their excellent specific strength and stiffness. However, the anisotropic mechanical and electrical properties associated with the fibers within each composite layer present challenges, and opportunities, for Nondestructive Testing (NDT) methods used to characterize and assess the structure condition. This includes composite condition after manufacture (such as fiber orientation and density, porosity, delamination, and bond strength) and during usage (such as damage from impact, fiber breakage, thermal exposure or applied stress). Ultrasonic and thermographic methods can address some of these challenges, but eddy current methods provide an alternative method for composite structures that contain a conducting material, such as carbon fibers or a metallic liner. This presentation reviews recent advances in the development of eddy current sensors and arrays for carbon fiber composite NDT and Structural Health Monitoring (SHM) applications. The focus is on eddy current sensor constructs with linear drive windings, such as MWM -Arrays, that induce currents primarily within the linear fibers of the composite. By combining this type of sensor construct with micromechanical models that relate composite constituent properties to measurable sensor responses, insight is obtained into the volumetric distribution of electrical properties within the composite and the associated manufacturing, damage, or strain conditions. With knowledge of the fiber layup, this MWM-Array technology is able to detect damage and strain/stress as a function of depth and fiber orientation. This work has been funded by NASA, NA V AIR and the Army for applications ranging from composite overwrapped pressure vessels (COPVs) to aircraft structures and rotorcraft blades. This presentation will specifically present background on the MWM-Array technology, results from the micromechanical modeling effort, and results from ongoing efforts for high resolution imaging and volumetric strain sensing.
Washabaugh, Andrew↗
Diaphragm Pump With Resonant Piezoelectric Drive
A diaphragm pump driven by a piezoelectric actuator is undergoing development. This pump is intended to be a prototype of lightweight, highly reliable pumps for circulating cooling liquids in protective garments and high-power electronic circuits, and perhaps for some medical applications. The pump would be highly reliable because it would contain no sliding seals or bearings that could wear, the only parts subject to wear would be two check valves, and the diaphragm and other flexing parts could be designed, by use of proven methods, for extremely long life. Because the pump would be capable of a large volumetric flow rate and would have only a small dead volume, its operation would not be disrupted by ingestion of gas, and it could be started reliably under all conditions. The prior art includes a number piezoelectrically actuated diaphragm pumps. Because of the smallness of the motions of piezoelectric actuators (typical maximum strains only about 0.001), the volumetric flow rates of those pumps are much too small for typical cooling applications. In the pump now undergoing development, mechanical resonance would be utilized to amplify the motion generated by the piezoelectric actuator and thereby multiply the volumetric flow rate. The prime mover in this pump would be a stack of piezoelectric ceramic actuators, one end of which would be connected to a spring that would be part of a spring-and-mass resonator structure. The mass part of the resonator structure would include the pump diaphragm (see Figure 1). Contraction of the spring would draw the diaphragm to the left, causing the volume of the fluid chamber to increase and thereby causing fluid to flow into the chamber. Subsequent expansion of the spring would push the diaphragm to the right, causing the volume of the fluid chamber to decrease, and thereby expelling fluid from the chamber. The fluid would enter and leave the chamber through check valves. The piezoelectric stack would be driven electrically to make it oscillate at the resonance frequency of the spring and- mass structure. This frequency could be made high enough (of the order of 400 Hz) that the masses of all components could be made conveniently small. The resonance would amplify the relatively small motion of the piezoelectric stack (a stroke of the order of 10 m) to a diaphragm stroke of the order of 0.5 mm. The exact amplification factor would depend on the rate of damping of oscillations; this, in turn, would depend on details of design and operation, including (but not limited to) the desired pressure rise and volumetric flow rate. In order to obtain resonance with large displacement, the damping rate must be low enough that the energy imparted to the pumped fluid on each stroke is much less than the kinetic and potential energy exchanged between the mass and spring during each cycle of oscillation. To minimize the power demand of the pump, a highly efficient drive circuit would be used to excite the piezoelectric stack. This circuit (see Figure 2) would amount to a special-purpose regenerative, switching power supply that would operate in a power-source mode during the part of an oscillation cycle when the excitation waveform was positive and in a power-recovery mode during the part of the cycle when the excitation waveform was negative. The circuit would include a voltage-boosting dc-to-dc converter that would convert between a supply potential of 24 Vdc and the high voltage needed to drive the piezoelectric stack. Because of the power-recovery feature, the circuit would consume little power. It should be possible to build the circuit as a compact unit, using readily available components.
Izenson, Michael G.↗
Toughening mechanism in elastometer-modified epoxy resins: Part 1
Several plaques of Epon 828, cured with piperidine, modified with hycar(r) CTBN 1300X8, Hycar(R) CTBN 1300X13, and Hycar(R) CTBN 1300x15, and in some cases modified with biphenol A (BPA), yielded properly toughened epoxies with rubber particle diameters ranging from 0.1 to 10 microns. Fracture toughness experiments indicate that toughness was more a function of rubber content than the rubber particle size. Tensile volumetric behavior of the near resin exhibits two regions: an initial region where the increase in volume strain was due to the Poisson's effect, and a second region where a slower rate of increase in volume strain was due to shear deformation. Tensile volumetric deformation of an elastomer-modified epoxy exhibits the same type of behavior to that of the neat resin at low rates ( 3.2x0.01 sec(-1)). But at very high strain rates, which correspond more closely to the strain rates at the crack tip, there exists an increase in volume strain beyond the Poisson's effect. TEM, SEM and OM studies indicate that the rubber particles had voided. When a thin section from the deformed region is viewed under crossed-polarized light, shear bands are seen connecting voided rubber particles. From this information cavitation and enhanced shear band formation is proposed as the toughening mechanism.
Yee, A. F.↗
Lithium-ion Battery Strain Gauge Monitoring and Depth of Discharge Estimation
Lithium-ion battery diagnostics and prognostics rely on measurements of electrical impedance, capacity, and voltage to infer the internal state of the battery. Mechanical changes to the cell structure represent an additional measure of the battery’s state because these changes are related to the overall battery health. As lithium-ion batteries are charged and discharged, lithium ions are inserted or removed from the anode and cathode, a process called intercalation and de-intercalation. As lithium ions intercalate and de-intercalate, they can cause changes to the lattice of the electrode particles, resulting in volumetric changes. These volumetric changes cause mechanical stresses and strains on the lithium-ion battery electrodes, and subsequently, the whole cell’s thickness varies as it is charged and discharged. This paper presents a study on the use of surface-mounted strain gauges for in-situ measurement of structural changes to lithium-ion batteries, along with a characterization of the unit-to-unit differences in strain response. A neural network modeling structure is then used to predict the battery’s depth of discharge under dynamic discharge conditions.
Lithium-ion batteries, depth of discharge, strain ↗
Icing Formation Strains on Airfoil Skin
Aircraft icing has long presented a safety hazard to the aerospace industry. One problem inherent to aircraft icing is predicting the adhesive properties of the ice-aircraft interface; values commonly reported span multiple orders of magnitude, making shedding prediction and surface evaluation difficult. An effort has been undertaken at the NASA Glenn Research Center to understand the cause of the scatter in the data. Geometry dependencies, variation in testing procedures, and residual stresses in ice samples have previously been identified as significant contributors to the problem. Residual stresses were singled out for this study, which investigated the strains at the leading edge of a Common Research Model (CRM) wind tunnel model in the NASA Glenn Icing Research Tunnel. Sprays were conducted at a particle size median volumetric diameter (MVD) of 20 µm, with liquid water contents (LWC) spanning from 0.4 to 3.0 g/m3. Total temperatures were varied between 0 and -25 °C, and test section velocity between 51 and 118 m/s. The leading edge was instrumented with custom strain gages, resistance temperature detectors (RTDs), optical fibers, and a pressure mat. Results indicate Δ strains, which were the difference between recorded strains and those predicted from isotropic thermal expansion of aluminum, below -400 µε with consistent patterns of strain across a wide variety of tunnel conditions. Isotropic, linear elastic finite element analysis (FEA) was conducted by varying the temperature of simplified airfoil and ice geometries, producing similar strains to those observed in testing. This allowed induced stresses to be predicted. Predicted stresses were above the expected tensile strength for ice, and suggest a source for previously observed cracking in tunnel ice.
Ice Adhesion↗
Scale effects on the transverse tensile strength of graphite epoxy composites
The influence of material volume on the transverse tensile strength of AS4/3501-6 graphite epoxy composites was investigated. Tensile tests of 90 degree laminates with 3 different widths and 5 different thicknesses were conducted. A finite element analysis was performed to determine the influence of the grip on the stress distribution in the coupons and explain the tendency for the distribution of failure locations to be skewed toward the grip. Specimens were instrumented with strain gages and extensometers to insure good alignment and to measure failure strains. Data indicated that matrix dominated strength properties varied with the volume of material that was stressed, with the strength decreasing as volume increased. Transverse strength data were used in a volumetric scaling law based on Weibull statistics to predict the strength of 90 degree laminates loaded in three point bending. Comparisons were also made between transverse strength measurements and out-of-plane interlaminar tensile strength measurements from curved beam bending tests. The significance of observed scale effects on the use of tests for material screening, quality assurance, and design allowables is discussed.
Obrien, T. Kevin↗
Mechanical Properties of Friction Stir Welds in A12195-T8
An extensive study of the mechanical properties of friction stir welded Al-Li 2195 has been conducted by Lockheed Martin Michoud Space Systems under contract to NASA. The study was part of a development program in which weld parameters were defined for using FSW to assemble large-scale aluminum cryogenic tanks. In excess of 300 feet of 0.320 in. gage plate material was welded and tested. The tests include room temperature and cryogenic temperature tensile tests and surface crack tension (SCT) tests, nondestructive evaluation, metallurgical studies, and photostress analysis. The results of the testing demonstrated improved mechanical properties with FSW as compared to typical fusion welding processes. Increases in ultimate tensile strength, cryogenic enhancement and elongation were observed with the tensile test results. Increased fracture toughness was observed with the SCT results. Nondestructive evaluations were conducted on all welded Joints. No volumetric defects were indicated. Surface indications on the root side of the welds did not significantly affect weld strength. The results of the nondestructive evaluations were confirmed via metallurgical studies. Photostress analysis revealed strain concentrations in multi-pass and heat-repaired FSW's. Details of the tests and results are presented.
Kinchen, David G.↗
A review of ice accretion data from a model rotor icing test and comparison with theory
An experiment was conducted by the Helicopter Icing Consortium (HIC) in the NASA Lewis Icing Research Tunnel (IRT) in which a 1/6 scale fuselage model of a UH-60A Black Hawk helicopter with a generic rotor was subjected to a wide range of icing conditions. The HIC consists of members from NASA, Bell Helicopter, Boeing Helicopter, McDonnell Douglas Helicopters, Sikorsky Aircraft, and Texas A&M University. Data was taken in the form of rotor torque, internal force balance measurements, blade strain gage loading, and two dimensional ice shape tracings. A review of the ice shape data is performed with special attention given to repeatability and correctness of trends in terms of radial variation, rotational speed, icing time, temperature, liquid water content, and volumetric median droplet size. Moreover, an indepth comparison between the experimental data and the analysis of NASA's ice accretion code LEWICE is given. Finally, conclusions are drawn as to the quality of the ice accretion data and the predictability of the data base as a whole. Recommendations are also given for improving data taking technique as well as potential future work.
Britton, Randall K.↗
A review of ice accretion data from a model rotor icing test and comparison with theory
An experiment was conducted by the Helicopter Icing Consortium (HIC) in the NASA Lewis Icing Research Tunnel (IRT) in which a 1/6 scale fuselage model of a UH-60A Black Hawk helicopter with a generic rotor was subjected to a wide range of icing conditions. The HIC consists of members from NASA, Bell Helicopter, Boeing Helicopter, McDonnell Douglas Helicopters, Sikorsky Aircraft, and Texas A&M University. Data was taken in the form of rotor torque, internal force balance measurements, blade strain gage loading, and two dimensional ice shape tracings. A review of the ice shape data is performed with special attention given to repeatability and correctness of trends in terms of radial variation, rotational speed, icing time, temperature, liquid water content, and volumetric median droplet size. Moreover, an indepth comparison between the experimental data and the analysis of NASA's ice accretion code LEWICE is given. Finally, conclusions are shown as to the quality of the ice accretion data and the predictability of the data base as a whole. Recommendations are also given for improving data taking technique as well as potential future work.
Britton, Randall K.↗
The variation of magma discharge during basaltic eruptions
The rate at which basaltic magma is discharged during many eruptions varies substantially. An individual eruption has an eruption rate, which is the volumetric rate of discharge averaged over the whole or a major part of an eruption, and an effusion rate, which is the volumetric flux rate at any given time. In many cases, the effusion rate soon reaches a maximum after a short period of waxing flow (partly because of magmatic expansion); it then falls more slowly in the later parts of the eruption. The release of elastic strain energy from stored magma and the subvolcanic reservoir during eruption can give a waning flow of this type an exponential form. A comparison of the eruption rates of eruptions of Mauna Loa, Kilauea and Etna shows that for each volcano there is a trend of decreasing effusion rate with increasing duration of eruption. It is noted that this relationship is not predicted by a simple elastic model of magma release. Two other processes are invoked to explain the eruptive histories of these volcanoes: modification of the eruptive conduits and the continued supply of magma from depth during eruption.
Wadge, G.↗
Calculation of radiation induced swelling of uranium mononitride using the digital computer program CYGRO 2
Fuel volume swelling and clad diametral creep strains were calculated for five fuel pins, clad with either T-111 (Ta-8W-2.4Hf) or PWC-11 (Nb-1Zr-0.1C). The fuel pins were irradiated to burnups between 2.7 and 4.6%. Clad temperatures were between 1750 and 2400 F (1228 and 1589 K). The maximum percentage difference between calculated and experimentally measured values of volumetric fuel swelling is 60%.
Davison, H. W.↗
Integration of a Finite Element Model with the DAP Bone Remodeling Model to Characterize Bone Response to Skeletal Loading
NASA's Digital Astronaut Project (DAP) has developed a bone remodeling model that has been validated for predicting volumetric bone mineral density (vBMD) changes of trabecular and cortical bone in the absence of mechanical loading. The model was recently updated to include skeletal loading from exercise and free living activities to maintain healthy bone using a new daily load stimulus (DLS). This new formula was developed based on an extensive review of existing DLS formulas, as discussed in the abstract by Pennline et al. The DLS formula incorporated into the bone remodeling model utilizes strains and stress calculated from finite element model (FEM) of the bone region of interest. The proximal femur was selected for the initial application of the DLS formula, with a specific focus on the femoral neck. METHODS: The FEM was generated from CAD geometry of a femur using de-identified CT data. The femur was meshed using linear tetrahedral elements Figure (1) with higher mesh densities in the femoral neck region, which is the primary region of interest for the initial application of the DLS formula in concert with the DAP bone remodeling model. Nodal loads were applied to the femoral head and the greater trochanter and the base of the femur was held fixed. An L2 norm study was conducted to reduce the length of the femoral shaft without significantly impacting the stresses in the femoral neck. The material properties of the FEM of the proximal femur were separated between cortical and trabecular regions to work with the bone remodeling model. Determining the elements with cortical material properties in the FEM was based off of publicly available CT hip scans [4] that were segmented, cleaned, and overlaid onto the FEM.
Bone Remodeling↗
LES/RANS Simulation of a Supersonic Reacting Wall Jet
This work presents results from large-eddy / Reynolds-averaged Navier-Stokes (LES/RANS) simulations of the well-known Burrows-Kurkov supersonic reacting wall-jet experiment. Generally good agreement with experimental mole fraction, stagnation temperature, and Pitot pressure profiles is obtained for non-reactive mixing of the hydrogen jet with a non-vitiated air stream. A lifted flame, stabilized between 10 and 22 cm downstream of the hydrogen jet, is formed for hydrogen injected into a vitiated air stream. Flame stabilization occurs closer to the hydrogen injection location when a three-dimensional combustor geometry (with boundary layer development resolved on all walls) is considered. Volumetric expansion of the reactive shear layer is accompanied by the formation of large eddies which interact strongly with the reaction zone. Time averaged predictions of the reaction zone structure show an under-prediction of the peak water concentration and stagnation temperature, relative to experimental data and to results from a Reynolds-averaged Navier-Stokes calculation. If the experimental data can be considered as being accurate, this result indicates that the present LES/RANS method does not correctly capture the cascade of turbulence scales that should be resolvable on the present mesh. Instead, energy is concentrated in the very largest scales, which provide an over-mixing effect that excessively cools and strains the flame. Predictions improve with the use of a low-dissipation version of the baseline piecewise parabolic advection scheme, which captures the formation of smaller-scale structures superimposed on larger structures of the order of the shear-layer width.
Edwards, Jack R.↗