Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Stress Modeling”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Transient Creep of a Composite Lower Crust: A Polymineralic Basis for Rapidly Evolving Postseismic Deformation Modes - 2

Postseismic horizontal strain and displacement following the June 28, 1992, Landers, California, earthquake (M(sub W) 7.3) is broad scale and cannot be explained solely by delayed afterslip located at the rupturing fault trace. Both the observed strain at Pifion Flat Observatory (PFO) and observed Global Positioning System receiver velocities evolve rapidly after the Landers-Big Bear earthquake sequence. The observed exponential decay of these motions, with timescales of 4-34 days, may reflect a soft creep rheology in the lower crust and brittle-ductile transition zone or even within the seismogenic crust itself. Here a simple model of a two-dimensional screw dislocation in a layered Maxwell viscoelastic Earth is employed in conjunction with a composite rheology to demonstrate that the short timescale transient response modes (approx. = 4-34 days) are consistent with the behavior of a biviscous lower crust. The lowest viscosity of this system is derivable from laboratory experimental data on the long-term creep of natural quarztites, and the highest viscosity is consistent with isostasy-related lower crustal flow in a continental extensional tectonic environment. The model predicts significant stress relaxation at the base of the seismogenic crust. Near the base of the seismogenic zone, and about 4 km away from the mainshock, the rate of predicted relaxation is of the order of 0.01 MPa/ d during the first 20 days of postseismic flow. Oblate spheroidal inclusions at 5% concentration levels that are both aligned and fairly flat in shape and that have a viscosity of 3-4 x 10(exp 15) Pa s are consistent with both the amplitude and decay time of horizontal crustal strain observed at PFO after the Landers mainshock. It is speculated that the structures exposed in cross sections and in seismic reflection profiles of the lower crust that have mylonitic associations are, in part, the cause of such rapid postseismic evolution in southeastern California. Unmylonitized quartz-rich rock at sufficiently elevated temperatures could also contribute to the rapid decay modes.

Ivins, Erik R.↗
NASA NTRS2000

A Numerical Evaluation of Icing Effects on a Natural Laminar Flow Airfoil

As a part of CFD code validation efforts within the Icing Branch of NASA Glenn Research Center, computations were performed for natural laminar flow (NLF) airfoil, NLF-0414. with 6 and 22.5 minute ice accretions. Both 3-D ice castings and 2-D machine-generated ice shapes were used in wind tunnel tests to study the effects of natural ice is well as simulated ice. They were mounted in the test section of the Low Turbulence Pressure Tunnel (LTPT) at NASA Langley that the 2-dimensionality of the flow can be maintained. Aerodynamic properties predicted by computations were compared to data obtained through the experiment by the authors at the LTPT. Computations were performed only in 2-D and in the case of 3-D ice, the digitized ice shape obtained at one spanwise location was used. The comparisons were mainly concentrated on the lift characteristics over Reynolds numbers ranging from 3 to 10 million and Mach numbers ranging from 0.12 to 0.29. WIND code computations indicated that the predicted stall angles were in agreement with experiment within one or two degrees. The maximum lift values obtained by computations were in good agreement with those of the experiment for the 6 minute ice shapes and the minute 3-D ice, but were somewhat lower in the case of the 22.5 minute 2-D ice. In general, the Reynolds number variation did not cause much change in the lift values while the variation of Mach number showed more change in the lift. The Spalart-Allmaras (S-A) turbulence model was the best performing model for the airfoil with the 22.5 minute ice and the Shear Stress Turbulence (SST) turbulence model was the best for the airfoil with the 6 minute ice and also for the clean airfoil. The pressure distribution on the surface of the iced airfoil showed good agreement for the 6 minute ice. However, relatively poor agreement of the pressure distribution on the upper surface aft of the leading edge horn for the 22.5 minute ice suggests that improvements are needed in the grid or turbulence models.

Chung, James J.↗
NASA NTRS2002

Computational Simulation of the High Strain Rate Tensile Response of Polymer Matrix Composites

A research program is underway to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to high strain rate impact loads. Under these types of loading conditions, the material response can be highly strain rate dependent and nonlinear. State variable constitutive equations based on a viscoplasticity approach have been developed to model the deformation of the polymer matrix. The constitutive equations are then combined with a mechanics of materials based micromechanics model which utilizes fiber substructuring to predict the effective mechanical and thermal response of the composite. To verify the analytical model, tensile stress-strain curves are predicted for a representative composite over strain rates ranging from around 1 x 10(exp -5)/sec to approximately 400/sec. The analytical predictions compare favorably to experimentally obtained values both qualitatively and quantitatively. Effective elastic and thermal constants are predicted for another composite, and compared to finite element results.

Goldberg, Robert K.↗
NASA NTRS2003

Computation of Transverse Injection Into Supersonic Crossflow With Various Injector Orifice Geometries

Computational results are presented for the performance and flow behavior of various injector geometries employed in transverse injection into a non-reacting Mach 1.2 flow. 3-D Reynolds-Averaged Navier Stokes (RANS) results are obtained for the various injector geometries using the Wind code with the Mentor s Shear Stress Transport turbulence model in both single and multi-species modes. Computed results for the injector mixing, penetration, and induced wall forces are presented. In the case of rectangular injectors, those longer in the direction of the freestream flow are predicted to generate the most mixing and penetration of the injector flow into the primary stream. These injectors are also predicted to provide the largest discharge coefficients and induced wall forces. Minor performance differences are indicated among diamond, circle, and square orifices. Grid sensitivity study results are presented which indicate consistent qualitative trends in the injector performance comparisons with increasing grid fineness.

Foster, Lancert↗
NASA NTRS2005

Assessment of NASA Dual Microstructure Heat Treatment Method Utilizing Ladis SuperCooler(trademark) Cooling Technology

The intent of this investigation was to demonstrate the NASA DMHT method with a tailored Ladish SuperCool(Trademark) cooling method on a Rolls-Royce AE2100, stage 3 disk shape. One disk each of two alloys, LSHR and ME3, were successfully converted as shown by macrostructure. DMHT heating time selection and cooling rate was aided by finite element modeling analysis. Residual stresses were also predicted and reported. Detailed microstructural analysis was performed by NASA and included in this report. Mechanical property characterization, also planned by NASA, is incomplete at this time and not part of this report.

Lemsky, Joe↗
NASA NTRS2006

Estimating Temperature Retrieval Accuracy Associated With Thermal Band Spatial Resolution Requirements for Center Pivot Irrigation Monitoring and Management

This study explores the use of synthetic thermal center pivot irrigation scenes to estimate temperature retrieval accuracy for thermal remote sensed data, such as data acquired from current and proposed Landsat-like thermal systems. Center pivot irrigation is a common practice in the western United States and in other parts of the world where water resources are scarce. Wide-area ET (evapotranspiration) estimates and reliable water management decisions depend on accurate temperature information retrieval from remotely sensed data. Spatial resolution, sensor noise, and the temperature step between a field and its surrounding area impose limits on the ability to retrieve temperature information. Spatial resolution is an interrelationship between GSD (ground sample distance) and a measure of image sharpness, such as edge response or edge slope. Edge response and edge slope are intuitive, and direct measures of spatial resolution are easier to visualize and estimate than the more common Modulation Transfer Function or Point Spread Function. For these reasons, recent data specifications, such as those for the LDCM (Landsat Data Continuity Mission), have used GSD and edge response to specify spatial resolution. For this study, we have defined a 400-800 m diameter center pivot irrigation area with a large 25 K temperature step associated with a 300 K well-watered field surrounded by an infinite 325 K dry area. In this context, we defined the benchmark problem as an easily modeled, highly common stressing case. By parametrically varying GSD (30-240 m) and edge slope, we determined the number of pixels and field area fraction that meet a given temperature accuracy estimate for 400-m, 600-m, and 800-m diameter field sizes. Results of this project will help assess the utility of proposed specifications for the LDCM and other future thermal remote sensing missions and for water resource management.

Ryan, Robert E.↗
NASA NTRS2011

Microcoil Spring Interconnects for Ceramic Grid Array Integrated Circuits

As integrated circuit miniaturization trends continue, they drive the need for smaller higher input/output (I/O) packages. Hermetically sealed ceramic area array parts are the package of choice by the space community for high reliability space flight electronic hardware. Unfortunately, the coefficient of thermal expansion mismatch between the ceramic area array package and the epoxy glass printed wiring board limits the life of the interconnecting solder joint. This work presents the results of an investigation by Marshall Space Flight Center into a method to increase the life of this second level interconnection by the use of compliant microcoil springs. The design of the spring and its attachment process are presented along with thermal cycling results of microcoil springs (MCS) compared with state-of-the-art ball and column interconnections. Vibration testing has been conducted on MCS and high lead column parts. Radio frequency simulation and measurements have been made and the MCS has been modeled and a stress analysis performed. Thermal cycling and vibration testing have shown MCS interconnects to be significantly more reliable than solder columns. Also, MCS interconnects are less prone to handling damage than solder columns. Future work that includes shock testing, incorporation into a digital signal processor board, and process evaluation of expansion from a 400 I/O device to a device with over 1,100 I/O is identified.

Strickland, S. M.↗
NASA NTRS2005

Upgrades of Two Computer Codes for Analysis of Turbomachinery

Major upgrades have been made in two of the programs reported in "ive Computer Codes for Analysis of Turbomachinery". The affected programs are: Swift -- a code for three-dimensional (3D) multiblock analysis; and TCGRID, which generates a 3D grid used with Swift. Originally utilizing only a central-differencing scheme for numerical solution, Swift was augmented by addition of two upwind schemes that give greater accuracy but take more computing time. Other improvements in Swift include addition of a shear-stress-transport turbulence model for better prediction of adverse pressure gradients, addition of an H-grid capability for flexibility in modeling flows in pumps and ducts, and modification to enable simultaneous modeling of hub and tip clearances. Improvements in TCGRID include modifications to enable generation of grids for more complicated flow paths and addition of an option to generate grids compatible with the ADPAC code used at NASA and in industry. For both codes, new test cases were developed and documentation was updated. Both codes were converted to Fortran 90, with dynamic memory allocation. Both codes were also modified for ease of use in both UNIX and Windows operating systems.

Chima, Rodrick V.↗
NASA NTRS2012

Two-Dimensional Nonlinear Finite Element Analysis of CMC Microstructures

A research program has been developed to quantify the effects of the microstructure of a woven ceramic matrix composite and its variability on the effective properties and response of the material. In order to characterize and quantify the variations in the microstructure of a five harness satin weave, chemical vapor infiltrated (CVI) SiC/SiC composite material, specimens were serially sectioned and polished to capture images that detailed the fiber tows, matrix, and porosity. Open source quantitative image analysis tools were then used to isolate the constituents, from which two dimensional finite element models were generated which approximated the actual specimen section geometry. A simplified elastic-plastic model, wherein all stress above yield is redistributed to lower stress regions, is used to approximate the progressive damage behavior for each of the composite constituents. Finite element analyses under in-plane tensile loading were performed to examine how the variability in the local microstructure affected the macroscopic stress-strain response of the material as well as the local initiation and progression of damage. The macroscopic stress-strain response appeared to be minimally affected by the variation in local microstructure, but the locations where damage initiated and propagated appeared to be linked to specific aspects of the local microstructure.

Mital, Subodh K.↗
NASA NTRS2006

Metallurgical Design and Development of NASA Crawler/Transporter Tread Belt Shoe Castings

The NASA Crawler/Transporters (CT-1 and CT-2) used to transport the Space Shuffles are one of the largest tracked vehicles in existence today. Two of these machines have been used to move space flight vehicles at Kennedy Space Center since the Apollo missions of the 1960's and relatively few modifications have been made to keep them operational. In September of 2003 during normal Crawler/Transporter operations cracks were observed along the roller pad surfaces of several tread belt shoes. Further examination showed 20 cracked shoes on CT-1 and 40 cracked shoes on CT-2 and a formal failure analysis investigation was undertaken while the cracked shoes were replaced. Six shoes were cross-sectioned with the fracture surfaces exposed and it was determined that the cracks were due to fatigue that initiated on the internal casting web channels at pre-existing casting defects and propagated through thickness both transgranularly and intergranularly between internal shrinkage cavities, porosity, and along austenitic and ferritic grain boundaries. The original shoes were cast during the 1960's using a modified 861330 steel with slightly higher levels of chromium, nickel and molybdenum followed by heat treatment to achieve a minimum tensile strength of 11 Oksi. Subsequent metallurgical analysis of the tread belt shoes after multiple failures showed excessive internal defects, alloy segregation, a nonuniform ferritic/ bainitic/martensitic microstructure, and low average tensile properties indicative of poor casting and poor heat-treatment. As a result, NASA funded an initiative to replace all of the tread belt shoes on both crawler/transporters along with a redesign of the alloy, manufacturing, and heat-treatment to create a homogeneous cast structure with uniform mechanical and metallurgical properties. ME Global, a wholly owned subsidiary of ME Elecmetal based in Minneapolis, MN was selected as manufacturing and design partner to develop the new shoes and this paper describes the research, development, and manufacturing that resulted in the successful delivery of 1044 new Crawler/Transporter tread belt shoes all meeting rigid metallurgical and mechanical design criteria derived from finite element modeling of the stress loads required for safe space shuttle transport.

Parker, Donald S.↗
NASA NTRS2013

Experimental Identification and Simulation of Time and/or Rate Dependent Reversible and Irreversible Deformation Regions for both a Titanium and Nickel Alloy

In this paper time and/or rate dependent deformation regions are experimentally mapped out as a function of temperature. It is clearly demonstrated that the concept of a threshold stress (a stress that delineate reversible and irreversible behavior) is valid and necessary at elevated temperatures and corresponds to the classical yield stress at lower temperatures. Also the infinitely slow modulus, (Es) i.e. the elastic modulus of the material if it was loaded at an infinitely slow strain rate, and the "dynamic modulus", modulus, Ed, which represents the modulus of the material if it is loaded at an infinitely fast rate are used to delineate rate dependent from rate independent regions. As demonstrated at elevated temperatures there is a significant difference between the two modulus values, thus indicating both significant time-dependence and rate dependence. In the case of the nickel-based super alloy, ME3, this behavior is also shown to be grain size specific. Consequently, at higher temperatures viscoelastic behavior exist below k (i.e., the threshold stress) and at stresses above k the behavior is viscoplastic. Finally a multi-mechanism, stress partitioned viscoelastic model, capable of being consistently coupled to a viscoplastic model is characterized over the full temperature range investigated for Ti-6-4 and ME3.

Arnold, Steven M.↗
NASA NTRS2017

Structural Design Exploration of an Electric Powered Multi-Propulsor Wing Configuration

Advancements in aircraft electric propulsion may enable an expanded operational envelope for electrically powered vehicles compared to their internal combustion engine counterparts. High aspect ratio wings provide additional lift and drag reduction for a proposed multi-propulsor design, however, the challenge is to reduce the weight of wing structures while maintaining adequate structural and aeroelastic margins. Design exploration using a conventional design-and-build philosophy coupled with a finite element method (FEM)-based design of experiments (DOE) strategy are presented to examine high aspect ratio wing structures that have spanwise distributed electric motors. Multiple leading-edge-mounted engine masses presented a challenge to design a wing within acceptable limits for dynamic and aeroelastic stability. Because the first four primary bending eigenmodes of the proposed wing structure are very sensitive to outboard motor placement, safety-of-flight requirements drove the need for multiple spars, rib attachments, and outboard structural reinforcements in the design. Global aeroelasticity became an increasingly important design constraint during the on-going design process, with outboard motor pod flutter ultimately becoming a primary design constraint. Designers successively generated models to examine stress, dynamics, and aeroelasticity concurrently. This research specifically addressed satisfying multi-disciplinary design criteria to generate fluid-structure interaction solution sets, and produced high aspect ratio primary structure designs for the NASA Scalable Convergent Electric Propulsion Technology and Operations Research (SCEPTOR) project in the Aeronautic Research Mission Directorate at NASA. In this paper, a dynamics-driven, quasi-inverse design methodology is presented to address aerodynamic performance goals and structural challenges encountered for the SCEPTOR demonstrator vehicle. These results are compared with a traditional computer aided design based approach.

Moore, James B.↗
NASA NTRS2016

Tidal Disruption of Phobos as the Cause of Surface Fractures

Phobos, the innermost satellite of Mars, displays an extensive system of grooves that are mostly symmetric about its sub-Mars point. Phobos is steadily spiraling inward due to the tides it raises on Mars lagging behind Phobos' orbital position and will suffer tidal disruption before colliding with Mars in a few tens of millions of years. We calculate the surface stress field of the deorbiting satellite and show that the first signs of tidal disruption are already present on its surface. Most of Phobos' prominent grooves have an excellent correlation with computed stress orientations. The model requires a weak interior that has very low rigidity on the tidal evolution time scale, overlain by an approximately 10-100 m exterior shell that has elastic properties similar to lunar regolith as described by Horvath et al. (1980).

Hurford, T. A.↗
NASA NTRS2021

ED1: Design and Prototype of a 3D Printed Wind Tunnel Model with Integrated Force Measurement

Wind tunnel testing using conventionally manufactured force measurement systems (balances) is able to yield precise and accurate results. These balances are delicate, complex instruments. Due to the nature of this high-precision complexity, balances are expensive and time-consuming to produce. These factors can limit the design potential of the model because using conventionally manufactured balances generally means that the model is designed to accommodate balances that already exist. Ideally, engineers would be able to design a measurement system that is tailored to fit the needs of the model, rather than the other way around. The goal of this research project was to determine if it is possible to overcome these drawbacks by designing a wind tunnel model with a modifiable integrated force measurement system that leverages additive manufacturing. This was undertaken by utilizing the existing UT-63 wind tunnel balance (measurement system), integrating it with a model based on the existing AGARD-B model, and performing stress analysis to optimize the design. Due to time constraints, the result of this endeavor is currently incomplete. Continued analysis and optimization are required to have a thorough understanding of the success or failure of the attempted design. As additive manufacturing technology evolves, the ability for it to become the primary method of fabrication for sensitive measurement systems increases. This project contributes to this by providing one method for design, a framework for optimizing existing balances for additive manufacturing, and resources for performing necessary stress analysis.

Callie Ellsworth↗
NASA NTRSDate not supplied

Thermal Performance of Perovskite-Based Photovoltaics for Operation in Low Earth Orbit

Perovskite-based photovoltaics are attractive for applications in space. The space environment is harsh with extreme temperatures, atomic oxygen, ionizing radiation, UV radiation, and thermal cycling. Here, we evaluate the thermal performance of a perovskite active layer and perovskite photovoltaic devices in low earth orbit. We determine that a 1 µm layer of silicon oxide coupled with a 500 nm zirconia thin film aid in cell thermal management. We model the residual stresses between various layers in the device and prove that thermally induced mechanical failure of the perovskite (t > 460 years) is unlikely during the operating lifetime of a space mission. We identify target power conversion efficiencies to manage operating temperature of a perovskite-based photovoltaic.

Timothy S. Krause↗
DOE OSTI2020

Modeling of deformation of battery cells using thick shell element formulation

Here, we describe a new approach for modeling nonlinear deformation and stress distribution of battery cells using a new thick shell finite element formulation with a through-thickness calculation of stresses and strains that satisfy equilibrium conditions. Battery cells are transversely layered materials that contain numerous thin layers in a repeating sequence. The layers are made of materials with significantly different mechanical responses. Explicit discretization of the layers is computationally impractical except for very small domains, while homogenized material models cannot account for stress and strain variations and partition through the thickness. The new formulation allows for calculation of the transverse and interlayer stresses based on the material properties of the individual cell layers. The application to problems where the transverse stresses have strong influence is also possible.

25 ENERGY STORAGE↗
DOE OSTI2022

Fluctuations and power-law scaling of dry, frictionless granular rheology near the hard-particle limit

Here the flow of frictionless granular particles is studied with stress-controlled discrete element modeling simulations for systems varying in size from 300 to 100,000 particles. The volume fraction and shear-stress ratio μ are relatively insensitive to system size for a wide range of inertial numbers I. Second-order effects in strain rate, such as normal stress differences, require large system sizes to accurately extract meaningful results, notably a nonmonotonic dependence in the first normal stress difference with strain rate. The rheological response represented by the μ(I) scalar model works well at describing the lower-order aspects of the rheology, except near the quasistatic limit of these stress-controlled flows. The pressure is varied over five decades, and a pressure dependence of the coordination number is observed, which is not captured by the inertial number. Large fluctuations observed for small systems N≤1000 near the quasistatic limit can lead to the arrest of flow resulting in challenges to fitting the data to rheological relationships. The inertial number is also insufficient for capturing the pressure-dependent behavior of property fluctuations. Fluctuations in the flow and microstructural properties are measured in both the quasistatic and inertial regimes, including shear stress, pressure, strain rate, normal stress differences, volume fraction, coordination number, and contact fabric anisotropy. The fluctuations in flow properties scale self-similarly with pressure and system size. A transition in the scaling of fluctuations of stress properties and contact fabric anisotropy are measured and proposed as a quantitative identification of the transition from inertial to quasistatic flow.

36 MATERIALS SCIENCE↗
NASA NTRS1991

Differential continuum damage mechanics models for creep and fatigue of unidirectional metal matrix composites

Three multiaxial isothermal continuum damage mechanics models for creep, fatigue, and creep/fatigue interaction of a unidirectional metal matrix composite volume element are presented, only one of which will be discussed in depth. Each model is phenomenological and stress based, with varying degrees of complexity to accurately predict the initiation and propagation of intergranular and transgranular defects over a wide range of loading conditions. The development of these models is founded on the definition of an initially transversely isotropic fatigue limit surface, static fracture surface, normalized stress amplitude function and isochronous creep damage failure surface, from which both fatigue and creep damage evolutionary laws can be obtained. The anisotropy of each model is defined through physically meaningful invariants reflecting the local stress and material orientation. All three transversely isotropic models have been shown, when taken to their isotropic limit, to directly simplify to previously developed and validated creep and fatigue continuum damage theories. Results of a nondimensional parametric study illustrate (1) the flexibility of the present formulation when attempting to characterize a large class of composite materials, and (2) its ability to predict anticipated qualitative trends in the fatigue behavior of unidirectional metal matrix composites. Additionally, the potential for the inclusion of various micromechanical effects (e.g., fiber/matrix bond strength, fiber volume fraction, etc.), into the phenomenological anisotropic parameters is noted, as well as a detailed discussion regarding the necessary exploratory and characterization experiments needed to utilize the featured damage theories.

Arnold, S. M.↗