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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.

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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Elastic properties of suspended black phosphorus nanosheets

The mechanical properties of black phosphorus (BP) nanosheets suspended over circular holes were measured by an atomic force microscope nanoindentation method. The continuum mechanic model was introduced to calculate the elastic modulus and pretension of BP nanosheets with thicknesses ranging from 14.3 to 34 nm. Elastic modulus of BP nanosheets declines with thickness, and the maximum value is 276 ± 32.4 GPa. Besides, the effective strain of BP ranges from 8 to 17% with a breaking strength of 25 GPa. Our results show that BP nanosheets serve as a promising candidate for flexible electronic applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Deep-Learning Interatomic Potential Connects Molecular Structural Ordering to the Macroscale Properties of Polyacrylonitrile

Polyacrylonitrile (PAN) is an important commercial polymer, bearing atactic stereochemistry resulting from nonselective radical polymerization. As such, an accurate, fundamental understanding of governing interactions among PAN molecular units is indispensable for advancing the design principles of final products at reduced processability costs. While ab initio molecular dynamics (AIMD) simulations can provide the necessary accuracy for treating key interactions in polar polymers, such as dipole–dipole interactions and hydrogen bonding, and analyzing their influence on the molecular orientation, their implementation is limited to small molecules only. Herein, we show that the neural network interatomic potentials (NNIPs) that are trained on the small-scale AIMD data (acquired for oligomers) can be efficiently employed to examine the structures and properties at large scales (polymers). NNIP provides critical insight into intra- and interchain hydrogen-bonding and dipolar correlations and accurately predicts the amorphous bulk PAN structure validated by modeling the experimental X-ray structure factor. Furthermore, the NNIP-predicted PAN properties, such as density and elastic modulus, are in good agreement with their experimental values. Overall, the trend in the elastic modulus is found to correlate strongly with the PAN structural orientations encoded in the Hermans orientation factor. In conclusion, this study enables the ability to predict the structure–property relations for PAN and analogues with sustainable ab initio accuracy across scales.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Frenkel pairs cause elastic softening in zirconia: theory and experiments

Abstract Recent results from molecular dynamics simulations have shown that significant concentrations of Frenkel pairs can be introduced by the proliferation of phonons lying at the edge of the Brillouin zone and when above the Debye temperature. Following the work of Granato (2014 Eur. Phys. J. B 87 18) we extend those calculations to the influence of Frenkels on the elastic modulus. Significant softening is predicted which is confirmed by in situ measurements of the elastic modulus during flash. Frenkel pairs have been proposed to play a central role in the flash phenomena.

Physics↗
NASA NTRS1993

Internal strain analysis of ceramics using scanning laser acoustic microscopy

Quantitative studies of material behavior characteristics are essential for predicting the functionality of a material under its operating conditions. A nonintrusive methodology for measuring the in situ strain of small dimeter (to 11 microns) ceramic fibers under uniaxial tensile loading and the local internal strains of ceramics and ceramic composites under flexural loading is introduced. The strain measurements and experimentally observed mechanical behavior are analyzed in terms of the microstructural development and fracture behavior of each test specimen evaluated. Measurement and analysis of Nicalon silicon carbide (SiC) fiber (15 microns diameter) indicate that the mean elastic modulus of the individual fiber is 185.3 GPa. Deviations observed in the experimentally determined elastic modulus values between specimens were attributed to microstructural variations which occur during processing. Corresponding variations in the fracture surface morphology were also observed. The observed local mechanical behavior of a lithium alumino-silicate (LAS) glass ceramic, a LAS/SiC monofilament composite, and a calcium alumino-silicate (CAS)/SiC fully reinforced composite exhibits nonlinearities and apparent hysteresis due to the subcritical mechanical loading. Local hysteresis in the LAS matrices coincided with the occurrence of multiple fracture initiation sites, localized microcracking, and secondary cracking. The observed microcracking phenomenon was attributed to stress relaxation of residual stresses developed during processing, and local interaction of the crack front with the microstructure. The relaxation strain and stress predicted on apparent mechanical hysteresis effects were defined and correlated with the magnitude of the measured fracture stress for each specimen studied. This quantitative correlation indicated a repeatable measure of the stress at which matrix microcracking occurred for stress relief of each material system. Stress relaxation occurred prior to the onset of steady state cracking conditions. The relaxation stress occurred at 18.5 percent of the fracture stress in LAS and 11.0 percent of the yield stress in CAS/SiC. The relaxation stress ratio was dependent upon the dominant fracture mode of the LAS/SiC specimens. Relaxation stress ratios greater than 0.30 were observed for specimens which fractured due to shear at the fiber matrix interface; specimens which fracture due to tensile cracking had relaxation stress ratios less than 0.30. The stress relaxation ratio appeared to be a specific characteristic of the glass ceramic material. The measured stress relaxation for LAS indicated a measure of the inherent residual stresses in the material due to processing and suggested localized toughening mechanisms for brittle material structures.

Kent, Renee M.↗
DOE OSTI2012

Microstrain temperature evolution in beta-eurcryptite ceramics: Measurement and model

Mechanisms of microcracking and stress release in {beta}-eucryptite ceramics were investigated by applying a combination of neutron diffraction (ND), dilatometry and the Integrity Factor Model (IFM). It was observed that the macroscopic thermal expansion of solid samples closely follows the lattice thermal expansion as a function of temperature, and both are dominated by microcracks closing (during heating) and opening (during cooling). Analogous experiments on powders showed that the stresses that manifest peak shift are indeed relieved by comminution, and that the resulting lattice thermal expansion can be considered as unconstrained. By means of Rietveld refinement of the ND data, the evolution with temperature of peak width parameters linked to strain distributions along the basal, pyramidal and axial planes could also be extracted. The peak width parameters S{sub HKL} correlated well with the strains calculated by peak shift and with the model results. Furthermore, while the peak shifts showed that the powders are basically stress free, the S{sub HKL} showed a strong evolution of the peak width. Powders carry, therefore, a measurable strain distribution inside the particles, owing to the thermal expansion anisotropy of the crystallites. The IFM allowed this behavior to be rationalized, and the effect of microcracking on thermal expansion to be quantified. Experimental data allowed accurate numerical prediction of microcracking on cooling and of the evolution of microstresses. They also allowed the derivation of the material elastic modulus from bulk thermal expansion curves through the IFM concept. Ultrasound resonance measurements of the elastic modulus strongly support these theoretical predictions.

36 MATERIALS SCIENCE↗
NASA NTRS2019

Stress Intensity Factors for Layered Pressure Vessel Inner Layer Through Cracks

A difficulty encountered when performing Fitness-for- Service assessments for layered pressure vessels (LPVs) is the lack of stress intensity factor solution in literature that produce accurate results for inner layer longitudinal through cracks. Using surrogate solutions such as a through crack in a plate or cylinder produce results that can be overly conservative especially for longer cracks. This is largely due to the ability of a layered pressure vessel to redistribute hoop load to other layers, the restricted radial movement of the cracked layer, and the friction forces applied in the cracked region. To understand this problem, a parametric finite element model (FEM) generator was developed that is capable of producing layered pressure vessel models with inner layer through cracks. The results from the FEMs were used to create a dataset of inner layer through crack stress intensity factors (KI) for layered pressure vessels corresponding to variations of internal pressure, radius, layer thicknesses, friction factor, and crack length. The elastic modulus of the material also has an effect on KI but, for this dataset, the elastic modulus was fixed at the typical value for steel - 29,500 ksi (203 GPa). Finally, a non-dimensional model was developed and calibrated using the dataset. This allows KI to be calculated without the need of a FEM using a closed-form equation. The results of the closed-form solution were then compared to FEM results showing accuracy was generally within 10%.

Hobbs, Joel R.↗
DOE OSTI2014

Nanoscale dynamics and aging of fibrous peptide-based gels

Solutions of the aromatic dipeptide derivative molecule fluorenylmethoxycarbonyl-diphenylalanine (Fmoc-FF) in dimethyl sulfoxide produce fibrous gels when mixed with water. We study the evolution of density fluctuations of this three-component system using X-ray photon correlation spectroscopy (XPCS) and compare these results to the macroscopic rheology of the gels and optical observations of the microstructure evolution. At the investigated scattering angles, the intensity autocorrelation functions do not follow behavior expected for simple diffusion of individual Fmoc-FF molecules localized within cages of nearest neighbors. Instead, the dynamics are associated with density fluctuations on length scales of ∼10–100 nm arising from disaggregation and reformation of fibers, leading to an increasingly uniform network. This process is correlated with the growth of the elastic modulus, which saturates at long times. Autocorrelation functions and relaxation times acquired from XPCS measurements are consistent with relaxation rates of structures at dynamic equilibrium. This study provides further support to the concept of exploring peptide-based gelators as valence-limited patchy particles capable of forming equilibrium gels.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Physics-informed neural networks for identification of material properties using standing waves

A metallic structure in its initial stage of failure involves plastic deformation or environmental degradation that changes the elastic modulus and density. This work presents the detection of change in wave velocity (a function of elastic modulus and density) as a system identification problem. A physics-informed neural network (PINN) is proposed to solve the system identification problem. The PINN takes the spatial coordinates of scanning locations and time as inputs and provides the displacement and wave velocity as outputs. The governing partial differential equation of standing waves in a rod is incorporated into the neural network as physics in the form of a loss function. The wave velocity vector is randomly initiated. During the training of the network, physics is used to determine and update the wave velocity target vector from the network’s displacement predictions. The measured data, comprising sparse displacement response on the rod structure, are used to train the PINN. The wave velocity at the sparse locations on the rod is learned from the predicted displacements during the training. Using the predictions of the trained network, the response of free vibration or material property variation can be reconstructed at unscanned locations on the structure to obtain high-resolution maps for full-field imaging to detect and localize the changes caused by plastic deformation. The PINN’s sparse scanning and simultaneous prediction capability during training can lead to high scanning and data-processing speeds. This capability yields a nondestructive evaluation system that can predict the presence of degraded material locations as the structural vibrations are scanned and processed in real time.

Rathod, Vivek↗
DOE OSTI2018

Recrystallization Behavior and Super-Elasticity of a Metastable β-Type Ti-21Nb-7Mo-4Sn Alloy During Cold Rolling and Annealing

Based on the d-electron alloy design theory, a new metastable β-type titanium alloy for biomedical applications, Ti-21Nb-7Mo-4Sn (wt.%) was designed in this article. This theory predicted this alloy was a metastable single β-type titanium alloy with low elastic modulus at room temperature, and the β-phase transition (β to α″) would be easy to occur during the cold rolling. The evolution of microstructure and mechanical properties of this alloy during cold rolling plus annealing were investigated by means of x-ray diffraction, optical microscope, transmission electron microscope and mechanical properties test. The results indicate that only β phase can be identified in this alloy before cold rolling, while a large amount of lath martensite (α″ phase) appears after cold rolling due to stress-induced martensitic transformation, which is in accordance with the prediction of the d-electron alloy design theory. The recrystallization nucleation occurs preferentially in the martensite lath region during the subsequent annealing process, and this region forms a large number of nano-crystals and microcrystals, showing that cold rolling plus annealing can become a new process for refining grains. Compared with casting and cold rolling samples, the annealing materials at 923 K for 10 min have excellent comprehensive mechanical properties with lower elastic modulus (58 GPa) and higher elastic recovery rate (35.39%).

36 MATERIALS SCIENCE↗
DOE OSTI2022

Ultrasonic Elastography for Nondestructive Evaluation of Dissimilar Material Joints

Dissimilar material joints or multilayered metals have become inevitable in the manufacturing industry due to the increasing demand for multifunctional materials with variable mechanical, thermal, or electrical characteristics in a single assembly. Lattice mismatch of materials at the interface of dissimilar materials leads to inferior mechanical characteristics. In particular, the mismatch in elastic properties indicated by a large initial elastic deformation is critical to determine the extent of variation in stress. However, nanoindentation, the most common and accepted technique to measure elastic modulus, is destructive, time-consuming, and can only examine mechanical properties within a limited area. A non-invasive elastographic mapping technique evaluates the mechanical properties using ultrasonic elastography to study incompressibility. The dissimilar joint between steel and copper was obtained via friction stir welding. The variation of the stress developed at the welded joint of the two different metals was evaluated from the dynamic bulk modulus map. A tensile test of the involved workpiece confirmed a good agreement with our analysis based on the dynamic bulk modulus elastographic mapping results. This study provides a rapid and non-invasive technique for the bulk metallurgic elastic modulus inspection to overcome the limitations of conventional methods.

Jin, Yuqi↗
DOE OSTI2019

Elasticity and yielding of mesophases of block copolymers in water–oil mixtures

Here, amphiphilic block copolymers self-assemble at the water/oil interface to form different mesomorphic structures, such as lamellar, micellar cubic, normal hexagonal, and reverse hexagonal structures. Usually, these structures are polycrystalline and the value of their elastic modulus depends on the average orientation of their constituent's single crystals. We introduce a model to predict the elastic modulus and yielding of mesophases from their characteristic length and intermicellar interactions. Shear modulus of each structure is measured as a function of deformation (strain). Zero-shear modulus, G 0 , depends on the inverse of the intermicellar distance with a power law model. The power law index for each structure is approximately n + 2 where n is the degree of confinement in the mesophase: 1 for lamellar, 2 for both normal and reverse hexagonal, and 3 for micellar cubic structures. Rheological properties of different mesophases of Pluronic P84 in the presence of water and p -xylene are used as a case study. The model is found to be in good agreement with experimental data in the linear viscoelastic region. When compared to experimental data, the yield strain value obtained from the model is one order of magnitude higher than the limit of the linear viscoelastic regime and close to the strain at the cross-over point of storage and loss moduli. Frequency sweep measurements are done to characterize the relaxation and cooperative model behaviors of each mesophase structure.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Stress Profile in Coating Layers of TRISO Fuel Particles in Contact with One Another

This work presents a discussion on a series of finite element analyses that assess stress evolution in the coating layers of tristructural isotropic (TRISO) particles in contact with each other while embedded in a matrix. The initial simulations were of applied uniaxial pressure versus matrix elastic modulus. These simulations predicted increasing stress in the silicon carbide coating layers of the TRISO particles with decreasing matrix elastic modulus. The second set of simulations focused on the effects of heating and cooling and the associated dimensional change on the state of stress in the coating layers. The general finding was that there was no significant difference below the coating layer’s deposition temperature. Although, above the deposition temperature, the contacting particles had higher stress compared with those that were separated. The third set of simulations focused on the effects of irradiation, specifically, creep, dimensional change, and swelling. An interface debonding model was introduced since these potential effects have a significant bearing on predicted stresses.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Effect of Composition on Mechanical Properties and Conductivity of the Dual-Ion Conductor Na 1+ x Mn x /2 Zr 2– x /2 (PO 4 ) 3 for Solid-State Batteries

Here we report the dependence of mechanical properties and ionic conductivity of the Na 1+ x Mn x /2 Zr 2– x /2 (PO 4 ) 3 (designated as NMZP) ionic conductor on its composition (with x = 0.5, 1.0, 1.5, and 2.0). Local mechanics was studied by instrumented nanoindentation, and the properties of interest included the elastic modulus, hardness, and fracture toughness. Overall, the material becomes more compliant and soft with the increase in the Na content. The elastic modulus reduces from 120 to 80 GPa, and nanoindentation hardness reduces from 7.8 to 4.2 GPa when x changes from 0.5 to 2.0. The relationship with fracture toughness ( K C ) is highly nonlinear: fracture toughness first decreases and then increases with the increase in the sodium content, reaching a maximum value of 0.89 MPa × m 1/2 at x = 2.0. Such a relationship was found to correlate with the formation of a glassy phase in NMZP at intermediate Na concentration. The maximum ionic conductivity coincides with the maximum fracture toughness in this material.

25 ENERGY STORAGE↗
DOE OSTI2015

Atomic force microscopy based nanoindentation study of onion abaxial epidermis walls in aqueous environment

An atomic force microscopy based nanoindentation method was employed to study how the structure of cellulose microfibril packing and matrix polymers affect elastic modulus of fully hydrated primary plant cell walls. The isolated, single-layered abaxial epidermis cell wall of an onion bulb was used as a test system since the cellulose microfibril packing in this cell wall is known to vary systematically from inside to outside scales and the most abundant matrix polymer, pectin, can easily be altered through simple chemical treatments such as ethylenediaminetetraacetic acid and calcium ions. Experimental results showed that the pectin network variation has significant impacts on the cell wall modulus, and not the cellulose microfibril packing.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructure, Phase Transformation, Mechanical Behavior, Bio-corrosion and Antibacterial Properties of Ti-Nb-xSn (x = 0, 0.25, 0.5 and 1.5) SMAs

Porous Ti-Nb-xSn shape memory alloys (SMAs) are fabricated by microwave sintering technology. The microstructures exhibit needle-like morphologies, β{sub (N)} (normal straight and crossed needles along with needle-like morphology that resembles spaghetti or irregular lines with α-phases in between) as well as plate-like morphologies [normal straight plate-like morphology, α′′ and dendritic plate-like morphology, β{sub (D)}]. Increases in Sn addition significantly induce an increase in the density of the α-phase. XRD patterns exhibited three phases, namely the β-main phase with smaller intensities of α′′ and α. Further, the addition of 0.25% Sn led to more effective improvement in the intensity of the α′′-phase compared with 0.5% and 1.5% Sn addition. Additions of Sn also enhanced the fracture strength and its corresponding strain along with the shape memory effect (SME), where the best enhancement was achieved at 0.25% Sn. The corrosion rate (Ri) was reduced by rising Sn content, while both corrosion resistance and antibacterial zones were increased. The lower elastic modulus, as well as the robust mechanical properties and bioactivity, made these SMAs rather suitable for biomedical application purposes, where the low elastic modulus had value in terms of avoiding the problem of “stress shielding.”.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Distributed strain sensing using Bi-metallic coated fiber optic sensors embedded in stainless steel

Silica fiber optic sensors are resistant to corrosive environments and high temperatures, making them attractive candidates for harsh conditions found in nuclear and aerospace industries. Moreover, fibers can be deployed remotely for continuous measuring of spatially distributed temperatures and strains. Here, this study investigated embedding a Ni/Cu bi-metallic coated fiber in a stainless-steel 316 (SS316) matrix using laser powder bed fusion towards functionalizing metal components for site-specific health monitoring. The embedded fiber was continuously interrogated during controlled heating to 1000°C. The measured fiber strains were similar to the expected differential thermal strains between the fiber and the SS316 matrix, until divergent behavior was observed at temperatures >500°C. No debonding at the matrix–coating–fiber interfaces was observed during microscopy, but significant interactions between the coatings and matrix resulted in diffusion-driven chemistry variations and Kirkendall void formation. Applying the strain-lag theory revealed plastic behavior in the Ni coating at temperatures >500°C, limiting the strain transfer to the fiber at higher temperatures. It was estimated that the elastic modulus in the Ni coating had decreased from ~200 GPa at room temperature to below 40 GPa, starting at 600°C. The low elastic modulus above 600°C is within the margin of what the tangent modulus would be in the case of bilinear isotropic hardening. Regardless of the divergent strain transfer at higher temperatures, the fiber was exposed to the equivalent of 1.9 % engineering strain at 1000°C, but measured only a 0.7 % engineering strain due to the poor strain transfer. Although compensating for the plastic behavior of Ni proved challenging, the bonding of a brittle silica fiber to a metal matrix surviving to 1000°C invites potential iterations on coating material for future application. For example, the embedded fiber is sufficient for acoustic energy transfer, realizing high temperature distributed acoustic sensing.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Room temperature mechanical properties of electron beam welded zircaloy-4 sheet

Room temperature mechanical properties of electron beam welded and plain Zircaloy-4 sheet (1.6mm thick) have been measured and compared. Various welding parameters were utilized to join sheet material. Electron beam welded specimens and as-received sheet specimens show comparable mechanical properties. Zr-4 sheet displays anisotropy; tensile properties measured for transverse display higher elastic modulus, yield strength, reduction of area and slightly lower ductility than for the longitudinal (rolling direction). Higher welding power increases the alloy’s hardness, elastic modulus and yield strength, with a corresponding decrease in tensile strength and ductility. The hardness measured at weld is comparable to the parent metal hardness. Hardness at heat-affected-zone is slightly higher. Electron microscopic examination shows distinct microstructure morphology and grain size at the weld zone, HAZ and parent metal. A correlation between welding parameters, mechanical properties and microstructural features was established for electron beam welded Zircaloy-4 sheet material.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗