SEARCH · Engineering Papers

Results for “Microstructures, and Modelling”

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.

SourceResearch connectionFrom yearThrough year

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

At least 91 records · Page 5

All sources NASA NTRS DOE OSTI

NASA NTRS1982

Edge softening of the Shuttle TPS strain isolation pad

Tensile tests and an analytical investigation were performed to characterize the edge softening behavior of the strain isolation pad (SIP) between the Orbiter skin and thermal protection system. The tensile tests were carried out with varying sizes of disk-shaped specimens bonded between aluminum disks. The specimens strength and stiffness were determined on the basis of specimen size, and an analytical model of the microstructural stress-strain characteristics was developed. Strength and stiffness were found to decrease near the free edges because through-the-thickness fibers located there were not anchored. No size dependence at maximum load was observed in specimens between 0.75-4.0 in. thick. In-plane and out-of-plane coupling in deformation was detected. The model gave accurate predictions of the tensile behavior of the SIP as a function of distance to a free edge.

Ransone, P. O.↗

NASA NTRS1996

Analysis of New Composite Architectures

Efficient and accurate specialty finite elements methods to analyze textile composites were developed and are described. Textile composites present unique challenges to the analyst because of the large, complex 'microstructure'. The geometry of the microstructure is difficult to model and it introduces unusual free surface effects. The size of the microstructure complicates the use of traditional homogenization methods. The methods developed constitute considerable progress in addressing the modeling difficulties. The details of the methods and attended results obtained therefrom, are described in the various chapters included in Part 1 of the report. Specific conclusions and computer codes generated are included in Part 2 of the report.

Whitcomb, John D.↗

NASA NTRS1981

Propagation in a shearing plasma. III - Magnetic field effects and pulsar microstructure periods

Effects of a magnetic field on wave and pulse propagation in a shearing plasma are investigated. Equations for the wave fields are derived from Maxwell's equations and the Minkowski relations for an anisotropic medium, when the magnetic field is parallel to the shearing velocity. The independent propagation modes are elliptically polarized in the stationary frame and vary with the velocity of the medium. Numerical calculations are presented which show the propagation of waves and pulses through a plane-parallel shearing plasma in the case of weak and strong fields. It is found that in a weak field, propagation effects are very similar to those previously found in field-free models: the transmitted pulses acquire temporal modulations whose period is frequency dependent. In a strong field, the period of the temporal modulations is independent of frequency. Transmitted pulses can also undergo polarization changes as a result of phase differences between modes. These results are discussed in relation to their significance to propagation in a pulsar magnetosphere and, in particular, to a model for pulse microstructure.

Harding, A. K.↗

NASA NTRSDate not supplied

Cathode Modeling of Solid-State Batteries

The search for safe, reliable, and compact high-capacity energy storage devices has led to increased interest in all-solid-state battery research. The use of solid electrolytes provides enhanced safety and durability due to their reduced flammability and increased mechanical strength compared to organic liquid electrolytes. Still, the use of solid electrolytes remains challenging. Computational modeling plays a substantial role in addressing these challenges. A particle dynamics electromechanical model for simulating electrochemical processes in a solid-state battery cathode will be presented. The model presents cathode microstructure at the particle level as a mixture of ionically conductive solid electrolyte particles, electrically conductive carbon additives, and cathodic reactant particles. After densification, the particle connectivity is analyzed to reconstruct the complex electric network connecting reactant particles with an anodic and cathodic current collectors through the electrolyte and carbon particles. The Kirchhoff’s matrix equation describing this electric network, is solved to obtain values of various critical parameters, such as the overall conductivity of the cathode for lithium ions and electrons, cathodic reactant material utilization, and the distribution of the electric current and voltages within the cathode. In addition, by representing the reactant particles as electrolyte or galvanic microcells governed by the Butler-Volmer electrochemical equation, the overall performance of battery cells during charge or discharge processes, respectively, can be predicted for a given cathodic powder composition. The presented model, executed on a high-performance computing architecture, essentially provides a valuable guidance in designing and developing future solid-state batteries.

solid-state battery↗

NASA NTRS2012

Investigation of Effects of Material Architecture on the Elastic Response of a Woven Ceramic Matrix Composite

To develop methods for quantifying the effects of the microstructural variations of woven ceramic matrix composites on the effective properties and response of the material, a research program has been undertaken which is described in this paper. In order to characterize and quantify the variations in the microstructure of a five harness satin weave, 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 and collect relevant statistics such as within ply tow spacing. This information was then used to build two dimensional finite element models that approximated the observed section geometry. With the aid of geometrical models generated by the microstructural characterization process, finite element models were generated and analyses were performed to quantify the effects of the microstructure and its variation on the effective stiffness and areas of stress concentration of the material. The results indicated that the geometry and distribution of the porosity appear to have significant effects on the through-thickness modulus. Similarly, stress concentrations on the outer surface of the composite appear to correlate to regions where the transverse tows are separated by a critical amount.

Goldberg, Robert K.↗

NASA NTRS1990

U.S.-Japan Workshop on Smart/Intelligent Materials and Systems, Honolulu, HI, Mar. 19-23, 1990, Proceedings

Topics presented include the concept of intelligent materials, the molecular engineering of channel proteins, the prospects, limitations, and requirements of intelligent micro motion systems, the modeling of a shape memory integrated actuator for vibration control of large space structures, and intelligent materials for future electronics. Also presented are the slewing of an active structure, the health monitoring of control system components, the numerical modeling of the microstructure of crystals with symmetry-related variants, and the intelligent material system concept.

Ahmad, Iqbal↗

NASA NTRS2011

Thermal Cycling and Isothermal Deformation Response of Polycrystalline NiTi: Simulations vs. Experiment

A recent microstructure-based FEM model that couples crystal-based plasticity, the B2<-> MB190 phase transformation and anisotropic elasticity at the grain scale is calibrated to recent data for polycrystalline NiTi (49.9 at.% Ni). Inputs include anisotropic elastic properties, texture and differential scanning calorimetry data, as well as a subset of recent isothermal deformation and load-biased thermal cycling data. The model is assessed against additional experimental data. Several experimental trends are captured - in particular, the transformation strain during thermal cycling monotonically increases and reaches a peak with increasing bias stress. This is achieved, in part, by modifying the martensite hardening matrix proposed by Patoor et al. [Patoor E, Eberhardt A, Berveiller M. J Phys IV 1996;6:277]. Some experimental trends are underestimated - in particular, the ratcheting of macrostrain during thermal cycling. This may reflect a model limitation that transformation-plasticity coupling is captured on a coarse (grain) scale but not on a fine (martensitic plate) scale.

Manchiraju, Sivom↗

NASA NTRS2012

Multiscale Modeling of Ultra High Temperature Ceramics (UHTC) ZrB2 and HfB2: Application to Lattice Thermal Conductivity

We are developing a multiscale framework in computational modeling for the ultra high temperature ceramics (UHTC) ZrB2 and HfB2. These materials are characterized by high melting point, good strength, and reasonable oxidation resistance. They are candidate materials for a number of applications in extreme environments including sharp leading edges of hypersonic aircraft. In particular, we used a combination of ab initio methods, atomistic simulations and continuum computations to obtain insights into fundamental properties of these materials. Ab initio methods were used to compute basic structural, mechanical and thermal properties. From these results, a database was constructed to fit a Tersoff style interatomic potential suitable for atomistic simulations. These potentials were used to evaluate the lattice thermal conductivity of single crystals and the thermal resistance of simple grain boundaries. Finite element method (FEM) computations using atomistic results as inputs were performed with meshes constructed on SEM images thereby modeling the realistic microstructure. These continuum computations showed the reduction in thermal conductivity due to the grain boundary network.

Lawson, John W.↗

NASA NTRS2012

Multiscale Modeling of UHTC: Thermal Conductivity

Lawson, John W.↗

NASA NTRS2012

ISS-Experiments of Columnar-to-Equiaxed Transition in Solidification Processing

The main topic of the research project CETSOL in the framework of the Microgravity Application Promotion (MAP) programme of the European Space Agency (ESA) is the investigation of the transition from columnar to equiaxed grain growth during solidification. Microgravity environment allows for suppression of buoyancy-driven melt flow and for growth of equiaxed grains free of sedimentation and buoyancy effects. This contribution will present first experimental results obtained in microgravity using hypo-eutectic AlSi alloys in the Materials Science Laboratory (MSL) on-board the International Space Station (ISS). The analysis of the experiments confirms the existence of a columnar to equiaxed transition, especially in the refined alloy. Temperature evolution and grain structure analysis provide critical values for the position, the temperature gradient and the solidification velocity at the columnar to equiaxed transition. These data will be used to improve modeling of solidification microstructures and grain structure on different lengths scales.

Sturz, Laszlo↗

NASA NTRS2013

The Effect of Prior Exposures on the Notched Fatigue Behavior of Disk Superalloy ME3

Environmental attack has the potential to limit turbine disk durability, particularly in next generation engines which will run hotter; there is a need to understand better oxidation at potential service conditions and develop models that link microstructure to fatigue response. More efficient gas turbine engine designs will require higher operating temperatures. Turbine disks are regarded as critical flight safety components; a failure is a serious hazard. Low cycle fatigue is an important design criteria for turbine disks. Powder metallurgy alloys, like ME3, have led to major improvements in temperature performance through refractory additions (e.g. Mo,W) at the expense of environmental resistance (Al, Cr). Service conditions for aerospace disks can produce major cycle periods extending from minutes to hours and days with total service times exceeding 1,000 hours in aerospace applications. Some of the effects of service can be captured by extended exposures at elevated temperature prior to LCF testing. Some details of the work presented here have been published.

Sudbrack, Chantal K.↗

NASA NTRS2015

Ultra High Temperature (UHT) SiC Fiber (Phase 2)

Silicon-carbide fiber-reinforced silicon-carbide ceramic matrix composites (SiCSiC CMC) are emerginglightweight re-usable structural materials not only for hot section components in gas turbine engines, but also for controlsurfaces and leading edges of reusable hypersonic vehicles as well as for nuclear propulsion and reactor components. Ithas been shown that when these CMC are employed in engine hot-section components, the higher the upper usetemperature (UUT) of the SiC fiber, the more performance benefits are accrued, such as higher operating temperatures,reduced component cooling air, reduced fuel consumption, and reduced emissions. The first generation of SiCSiC CMC with a temperature capability of 2200-2400F are on the verge of being introduced into the hot-section components ofcommercial and military gas turbine engines.Today the SiC fiber type currently recognized as the worlds best in terms ofthermo-mechanical performance is the Sylramic-iBN fiber. This fiber was previously developed by the PI at NASA GRC using patented processes to improve the high-cost commercial Sylramic fiber, which in turn was derived from anotherlow-cost low-performance commercial fiber. Although the Sylramic-iBN fiber shows state-of-the art creep and rupture resistance for use temperatures above 2550oF, NASA has shown by fundamental creep studies and model developmentthat its microstructure and creep resistance could theoretically be significantly improved to produce an Ultra HighTemperature (UHT) SiC fiber.This Phase II Seedling Fund effort has been focused on the key objective of effectively repeating the similar processes used for producing the Sylramic-iBN fiber using a design of experiments approach to first understand the cause of the less than optimum Sylramic-iBN microstructure and then attempting to develop processconditions that eliminate or minimize these key microstructural issues. In so doing, it is predicted that that theseadvanced process could result in an UHT SiC fiber with 20 times more creep resistance than the Sylramic-iBN fiber,which in turn would allow SiCSiC CMC to operate up to 2700oF and above, thereby further enhancing the performancebenefits of SiCSiC components in aero-propulsion engines. It was also envisioned that the fiber processes developedduring Phase II efforts would not only reduce production costs for the UHT fiber by using low-cost precursor fibers andcombined processes, but also allow the UHT fibers to be directly produced in preforms of the precursor fibers, possibly atthe facilities of the CMC fabricator.

SiC Ceramic Fiber↗

NASA NTRS2016

Separating the Influence of Environment from Stress Relaxation Effects on Dwell Fatigue Crack Growth in a Nickel-Base Disk Alloy

Both environmental embrittlement and crack tip visco-plastic stress relaxation play a significant role in determining the dwell fatigue crack growth (DFCG) resistance of nickel-based disk superalloys. In the current study performed on the Low Solvus High Refractory (LSHR) disk alloy, the influence of these two mechanisms were separated so that the effects of each could be quantified and modeled. Seven different microstructural variations of LSHR were produced by controlling the cooling rate and the subsequent aging and thermal exposure heat treatments. Through cyclic fatigue crack growth testing performed both in air and vacuum, it was established that four out of the seven LSHR heat treatments evaluated, possessed similar intrinsic environmental resistance to cyclic crack growth. For these four heat treatments, it was further shown that the large differences in dwell crack growth behavior which still persisted, were related to their measured stress relaxation behavior. The apparent differences in their dwell crack growth resistance were attributed to the inability of the standard linear elastic fracture mechanics (LEFM) stress intensity parameter to account for visco-plastic behavior. Crack tip stress relaxation controls the magnitude of the remaining local tensile stresses which are directly related to the measured dwell crack growth rates. It was hypothesized that the environmentally weakened grain boundary crack tip regions fail during the dwells when their strength is exceeded by the remaining local crack tip tensile stresses. It was shown that the classical creep crack growth mechanisms such as grain boundary sliding did not contribute to crack growth, but the local visco-plastic behavior still plays a very significant role by determining the crack tip tensile stress field which controls the dwell crack growth behavior. To account for the influence of the visco-plastic behavior on the crack tip stress field, an empirical modification to the LEFM stress intensity parameter, Kmax, was developed by incorporating into the formulation the remaining stress level concept as measured by simple stress relaxation tests. The newly proposed parameter, Ksrf, did an excellent job in correlating the dwell crack growth rates for the four heat treatments which were shown to have similar intrinsic environmental cyclic fatigue crack growth resistance.

Dwell crack growth↗

NASA NTRS2003

Arc Jet Testing of Hafnium Diboride Based Ultra High Temperature Ceramics

Hafnium Diboride (HFB,) based materials have shown promise for use in a number of high temperature aerospace applications, including rocket nozzles and as leading edges on hypersonic reentry vehicles. The stability of the materials in relevant environments is key to determining their suitability for a particular application. In this program we have been developing HfB2/SiC materials for use as sharp leading edges. The program as a whole included processing and characterization of the HfBJSiC materials. The specific work discussed here will focus on studies of the materials oxidation behavior in simulated reentry environments through arc jet testing. Four flat face models were tested to examine the influence of heat flux and stagnation pressure on the materials oxidation behavior. The results from arc jet testing of two HfB2/SiC cone models will also be discussed. Each cone model was run multiple times with gradually increasing heat fluxes. Total run times on a single cone model exceeded 80 minutes. For both the flat face and cone models surface temperatures well in excess of 2200 C were measured. Post test microstructural examination of the models and correlations with measured temperatures will be discussed.

Ellerby, Don↗

NASA NTRS1989

Nonlinear mesomechanics of composites with periodic microstructure

This work is concerned with modeling the mechanical deformation or constitutive behavior of composites comprised of a periodic microstructure under small displacement conditions at elevated temperature. A mesomechanics approach is adopted which relates the microimechanical behavior of the heterogeneous composite with its in-service macroscopic behavior. Two different methods, one based on a Fourier series approach and the other on a Green's function approach, are used in modeling the micromechanical behavior of the composite material. Although the constitutive formulations are based on a micromechanical approach, it should be stressed that the resulting equations are volume averaged to produce overall effective constitutive relations which relate the bulk, volume averaged, stress increment to the bulk, volume averaged, strain increment. As such, they are macromodels which can be used directly in nonlinear finite element programs such as MARC, ANSYS and ABAQUS or in boundary element programs such as BEST3D. In developing the volume averaged or efective macromodels from the micromechanical models, both approaches will require the evaluation of volume integrals containing the spatially varying strain distributions throughout the composite material. By assuming that the strain distributions are spatially constant within each constituent phase-or within a given subvolume within each constituent phase-of the composite material, the volume integrals can be obtained in closed form. This simplified micromodel can then be volume averaged to obtain an effective macromodel suitable for use in the MARC, ANSYS and ABAQUS nonlinear finite element programs via user constitutive subroutines such as HYPELA and CMUSER. This effective macromodel can be used in a nonlinear finite element structural analysis to obtain the strain-temperature history at those points in the structure where thermomechanical cracking and damage are expected to occur, the so called damage critical points of the structure.

Walker, Kevin P.↗

NASA NTRS2019

Estimating Alpine Snow Depth by Combining Multi-Frequency Passive Radiance Observations with Ensemble Snowpack Modeling

This paper presents a physically-based snow depth retrieval algorithm adapted for deep mountainous snowpack and airborne multifrequency (10.7, 18.7, 37.0 and 89.0 GHz) passive microwave (PM) radiance observations from a single flight. The algorithm employs a single forecast-analysis cycle of a traditional sequential assimilation scheme. It uses an ensemble of multi-layer snowpack model runs to resolve snow microstructure and melt-refreeze crusts, andmicrowave radiative transfer models to relate snow properties to microwave measurements.Snow depth was retrieved at a 120 m spatial resolution over three 1 km2 Intensive Study Area (ISA) within the Rabbit Ears Meso-Cell Study Area (MSA) from the NASA Cold Land Processes Experiment (CLPX) in Colorado (United States) for one date in February 2003. When evaluated against in situ observations, root mean square error (RMSE) of the snow depth from the assimilation was 13.3 cm for areas with low (<5 %) forest cover, which was a reduction of 48 % in the RMSE compared with the modeled snow depth when the PM observations were not assimilated; indicating a ~5% relative error of the posterior snow depth with respect to the average snow depth (200 cm) measured at these pixels. For pixels with forest cover ranging from 5-15% and 15-30%, results were improved (R2 increased from 0.65 to 0.71 and from 0 to 0.38, respectively) by introducing a forest radiative transfer model during the assimilation.

Airborne Multifrequency↗

NASA NTRS1987

A 2000-hour cyclic endurance test of a laboratory model multipropellant resistojet

The technological readiness of a long-life multipropellant resistojet for space station auxiliary propulsion is demonstrated. A laboratory model resistojet made from grain-stabilized platinum served as a test bed to evaluate the design characteristics, fabrication methods, and operating strategies for an engineering model multipropellant resistojet developed under contract by the Rocketdyne Division of Rockwell International and Technion Incorporated. The laboratory model thruster was subjected to a 2000-hr, 2400-thermal-cycle endurance test using carbon dioxide propellant. Maximum thruster temperatures were approximately 1400 C. The post-test analyses of the laboratory model thruster included an investigation of component microstructures. Significant observations from the laboratory model thruster are discussed as they relate to the design of the engineering model thruster.

Morren, W. Earl↗

NASA NTRS1987

2000-hour cyclic endurance test of a laboratory model multipropellant resistojet

Morren, W. Earl↗