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At least 1,153 records · Page 64

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DOE OSTI2025

Hierarchically Structured Vitrimer Biocomposites for Sustainable Manufacturing

Polymers containing dynamic covalent bonds (DCBs) exhibit thermoplastic-like flow above their topology freezing temperature (T v ) while maintaining thermoset-like properties below it, making them promising for sustainable manufacturing. However, their large-scale adoption remains limited due to challenges in accurately determining T v and achieving efficient fiber-matrix bonding in composite applications. Here, hierarchically structured epoxy-anhydride-based polyester vitrimer composites reinforced with cellulosic filaments is demonstrated, where hydroxyl groups on fiber surfaces participate directly in transesterification with the matrix. Further, this dynamic interfacial bonding delivers exceptional mechanical properties, including ≈70 MPa shear strength and >10% strain-to-failure, while enabling thermal malleability. Using a combination of nuclear magnetic resonance and nano-infrared spectroscopies, direct evidence is provided that chemical bond exchange begins well below the conventionally measured T v , supporting the hypothesis that rheologically determined T v reflects a combination of chemical exchange and frictional dynamics rather than a discrete transition. The composites demonstrate excellent processability through vacuum-assisted resin transfer molding and maintain >90% of their mechanical properties after multiple thermal reforming cycles. These findings advance both the fundamental understanding of vitrimeric transitions and the practical development of sustainable, high-performance composite materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2014

Approximate Hessian for accelerating ab initio structure relaxation by force fitting

We present a method to approximate the Hessian matrix of the Born-Oppenheimer energy landscape by using a simple force field model whose parameters are fitted to on-the-flight ab initio results. The inversed Hessian matrix is used as the preconditioner of conjugate gradient algorithms to speed up the atomic structure relaxation, resulting in a speedup factor of 2 to 5 on systems of bulk, slab, sheets, and atomic clusters. Because the force field model employed is simple and general, the parameter fitting is straightforward; the method is applicable to a variety of complicated systems for minimum structure relaxation. In the metal cluster new structure search, the new method yields better structures than the one obtained before with conventional algorithms.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Achieving ultra-high bearing strength of tungsten nanoribbons in a transforming metal matrix

Nanowires (or nanoribbons) were identified as the most potential structural reinforcements for composites due to their ultrahigh strength, but it is difficult to transcribe their ultrahigh strength into the composite. Here, an in-situ W nanoribbbons-NiTi matrix composite was fabricated by mechanical reduction of a W-NiTi ingot, and the micromechanical deformation behavior was studied by in-situ high energy X-ray diffraction during tensile loading-unloading. It is revealed that the large elastic deformation of the W nanoribbons in a NiTi matrix is dictated by and synchronized with the martensitic transformation of the matrix. The bearing strength of the W nanoribbons, up to 11.6 GPa, was achieved in this composite. A significant load transfer took place from the matrix to the nanoribbons, exhibiting the characters of locality and rapidity. In conclusion, the stress fraction carried by the W nanoribbons with the volume fraction of 3% is up to 45% for the strength of the composite.

36 MATERIALS SCIENCE↗

NASA NTRS1991

Structural reliability analysis of laminated CMC components

For laminated ceramic matrix composite (CMC) materials to realize their full potential in aerospace applications, design methods and protocols are a necessity. The time independent failure response of these materials is focussed on and a reliability analysis is presented associated with the initiation of matrix cracking. A public domain computer algorithm is highlighted that was coupled with the laminate analysis of a finite element code and which serves as a design aid to analyze structural components made from laminated CMC materials. Issues relevant to the effect of the size of the component are discussed, and a parameter estimation procedure is presented. The estimation procedure allows three parameters to be calculated from a failure population that has an underlying Weibull distribution.

Duffy, Stephen F.↗

NASA NTRS1991

Structural reliability analysis of laminated CMC components

Duffy, Stephen F.↗

DOE OSTI2011

Selected Topics on Nuclear Structure in Rare Electroweak Processes

We analyze the active-shell occupation probabilities of {sup 76}Ge and their contribution to the single- and double-beta decay matrix elements of this isotope. Strength modifications of the nucleon spin-orbit interaction are introduced for a better comparison with experimental data. The relation of this spin-orbit interaction with the nucleon densities is explored, and the latter are analyzed for {sup 76}Ge in the context of parity-violating electron scattering as a tool to extract accurate experimental information on neutron distributions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2018

Precipitation behavior of stainless steel weld overlay cladding exposed to a long-term thermal aging

Highlights: • Silicide phase formation with G-phase was first time to be observed. • Precipitation behavior discrepancy existed at different locations of ferrite phase. • G-phase and silicide phase formed along dislocations and within ferrite matrix. • Heterogeneous distribution of elements induced silicide phase formation. - Abstract: Thermal aging behavior of stainless steel weld overlay cladding aged at 400 °C for 10,000 h was investigated. The results showed that the precipitates along the dislocation and within ferrite matrix contained the face-centered cubic structural G-phase and silicide phase. Silicide phase, supposed to be (Fe, Mn){sub 3}Si phase, preferred to form with G-phase along the dislocations and within ferrite matrix. Silicide phase showed a cube-on-cube relationship with ferrite phase and G-phase. Heterogeneous distribution of elements within Ni-Mn-Si clusters was responsible for silicide phase formation during thermal aging process, and the corresponding precipitation behavior discrepancy at different forming sites (dislocations, ferrite matrix and phase boundary) was discussed.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Solving a class of infinite-dimensional tensor eigenvalue problems by translational invariant tensor ring approximations

Here, we examine a method for solving an infinite-dimensional tensor eigenvalue problem Hx = λx, where the infinite-dimensional symmetric matrix H exhibits a translational invariant structure. We provide a formulation of this type of problem from a numerical linear algebra point of view and describe how a power method applied to e -Ht is used to obtain an approximation to the desired eigenvector. This infinite-dimensional eigenvector is represented in a compact way by a translational invariant infinite Tensor Ring (iTR). Low rank approximation is used to keep the cost of subsequent power iterations bounded while preserving the iTR structure of the approximate eigenvector. We show how the averaged Rayleigh quotient of an iTR eigenvector approximation can be efficiently computed and introduce a projected residual to monitor its convergence. In the numerical examples, we illustrate that the norm of this projected iTR residual can also be used to automatically modify the time step to ensure accurate and rapid convergence of the power method.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2021

Matrix Graphite Material Models In Pebbles and Compacts For Bison

The cores and reflectors in high-temperature gas-cooled reactors (HTGRs) are made of graphite materials, with the graphite acting as a moderator, a fuel host matrix, or the foundation for various structural components. This study aims to survey the models in the literature for graphite materials being used as host matrices in pebble/fuel compacts and to implement those surveyed models into Bison to conduct an early assessment of graphite's thermo-mechanical response under various reactor conditions. In this study, thermal (e.g., thermal conductivity, and specific heat capacity) and mechanical (e.g., elastic properties, thermal expansion, irradiation-induced dimensional changes, and irradiation-induced creep) material models for various graphite grades (e.g., H-451, IG-110, G-348, 2020, A3-3, and A3-27) are incorporated into Bison. Two benchmark problems are then exercised utilizing these new graphite-related capabilities: (1) modeling an Advanced Gas Reactor (AGR)-2 fuel compact, and (2) modeling the debonding of a particle-matrix interface.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

NASA NTRS1992

Transient thermal stress recovery for structural models

A method for computing transient thermal stress vectors from temperature vectors is described. The three step procedure involves the use of NASTRAN to generate an influence coefficient matrix which relates temperatures to stresses in the structural model. The transient thermal stresses are then recovered and sorted for maximum and minimum values. Verification data for the procedure is also provided.

Walls, William↗

DOE OSTI2022

Benchmarking a 9Cr-2WVTa Reduced Activation Ferritic Martensitic Steel Fabricated via Additive Manufacturing

Reduced activation ferritic (RAF) martensitic steels are promising candidates for the first wall of fusion reactors. However, current manufacturing capabilities call for these components to be made by welding wrought plates. This limits design freedom and necessitates the use of post-weld heat treatments (PWHT) in accordance with the boiler and pressure vessel code. Additive manufacturing (AM) can offer a unique solution to solve this challenge by leveraging the layer-wise deposition strategy to come up with temper bead deposition techniques to eliminate post-processing heat treatments (PPHT). However, it is necessary to benchmark the properties of RAF steels fabricated by AM with their wrought counterparts to identify the process-structure-property correlation, which is the goal of this study. The study demonstrates that while tensile properties at room temperature and high temperatures are satisfactory, the as fabricated and samples after PPHT have significant heterogeneity in tensile elongation. This has been attributed to the presence of discontinuities in the build. The as-fabricated samples have an average tensile strength of 1190 + 12 MPa and an average elongation of 15 + 5% at room temperature and 658 ± 20 MPa ultimate tensile strength (UTS) and 14 ± 7% at 600 °C. After the post-weld heat treatment, mechanical properties decrease to around 600–650 MPa and an elongation between 20–25% at room temperature to 300 MPa UTS and 25–28% elongation at 600 °C. The characterization of microstructures at various length scales demonstrates that the as-fabricated structure has a significant fraction of delta ferrite in a lath martensitic matrix. No precipitates could be identified in the as-fabricated structure. PPHT led to a decrease in the area fraction of delta ferrite and precipitation of M 23 C 6 and MX. Detailed characterization clearly demonstrates that the lack of precipitates in the as-fabricated structure could be due to the slow tempering response of the alloy. Finally, the needs to develop new alloys to achieve the objectives stated above are articulated.

36 MATERIALS SCIENCE↗

NASA NTRS1988

Remote structural damage detection via substructuring

An approach to structural damage detection which utilizes the concept of a substructure transfer function matrix is proposed. The major advantage of this approach is that structural changes localized within a small volume can be detected by studying the changes in the transfer function for a relatively small substructure containing the damaged portion.

Walton, William B.↗

DOE OSTI2014

Oxidation induced amorphous stabilization of the subsurface region in Zr-Cu metallic glass

In the present study, we demonstrate that selective surface oxidation of Zr{sub 70}Cu{sub 30} metallic glass can stabilize the amorphous structure in the subsurface region of the matrix. The oxidation proceeds by selective oxidation of Zr, forming monoclinic ZrO{sub 2} layer on the surface, and the subsurface layer becomes Cu-enriched due to back diffusion of Cu atoms from the oxide layer. Interestingly, in this system, the composition change in the subsurface region leads to enhancement of glass stability, forming of a double layered surface structure consisted of inner amorphous layer and outer monoclinic ZrO{sub 2} layer even when the remaining matrix is completely crystallized.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2017

A Strategy Combining Higher Energy C-Trap Dissociation with Neutral Loss- and Product Ion-Based MS{sup n} Acquisition for Global Profiling and Structure Annotation of Fatty Acids Conjugates

Fatty acids conjugates (FACs) are ubiquitous but found in trace amounts in the natural world. They are composed of multiple unknown substructures and side chains. Thus, FACs are difficult to be analyzed by traditional mass spectrometric methods. In this study, an integrated strategy was developed to global profiling and targeted structure annotation of FACs in complex matrix by LTQ Orbitrap. Dicarboxylic acid conjugated bufotoxins (DACBs) in Venenum bufonis (VB) were used as model compounds. The new strategy (abbreviated as HPNA) combined higher-energy C-trap dissociation (HCD) with product ion- (PI), neutral loss- (NL) based MS{sup n} (n ≥ 3) acquisition in both positive-ion mode and negative-ion mode. Several advantages are presented. First, various side chains were found under HCD in negative-ion mode, which included both known and unknown side chains. Second, DACBs with multiple side chains were simultaneously detected in one run. Compared with traditional quadrupole-based mass method, it greatly increased analysis throughput. Third, the fragment ions of side chain and steroids substructure could be obtained by PI- and NL-based MS{sup n} acquisition, respectively, which greatly increased the accuracy of the structure annotation of DACBs. In all, 78 DACBs have been discovered, of which 68 were new compounds; 25 types of substructure formulas and seven dicarboxylic acid side chains were found, especially five new side chains, including two saturated dicarboxylic acids [(azelaic acid (C{sub 9}) and sebacic acid (C{sub 10})] and three unsaturated dicarboxylic acids (u-C{sub 8}, u-C{sub 9}, and u-C{sub 10}). All these results greatly enriched the structures of DACBs in VB. .

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

NASA NTRS1979

Modal testing with Asher's method using a Fourier analyzer and curve fitting

An unusual application of the method proposed by Asher (1958) for structural dynamic and modal testing is discussed. Asher's method has the capability, using the admittance matrix and multiple-shaker sinusoidal excitation, of separating structural modes having indefinitely close natural frequencies. The present application uses Asher's method in conjunction with a modern Fourier analyzer system but eliminates the necessity of exciting the test structure simultaneously with several shakers. Evaluation of this approach with numerically simulated data demonstrated its effectiveness; the parameters of two modes having almost identical natural frequencies were accurately identified. Laboratory evaluation of this approach was inconclusive because of poor experimental input data.

Gold, R. R.↗

NASA NTRS1994

Integrated design of structures, controls, and materials

In this talk we shall discuss algorithms and CAD tools for the design and analysis of structures for high performance applications using advanced composite materials. An extensive mathematical theory for optimal structural (e.g., shape) design was developed over the past thirty years. Aspects of this theory have been used in the design of components for hypersonic vehicles and thermal diffusion systems based on homogeneous materials. Enhancement of the design methods to include optimization of the microstructure of the component is a significant innovation which can lead to major enhancements in component performance. Our work is focused on the adaptation of existing theories of optimal structural design (e.g., optimal shape design) to treat the design of structures using advanced composite materials (e.g., fiber reinforced, resin matrix materials). In this talk we shall discuss models and algorithms for the design of simple structures from composite materials, focussing on a problem in thermal management. We shall also discuss methods for the integration of active structural controls into the design process.

Blankenship, G. L.↗

NASA NTRS2008

Measurement and Prediction of the Thermomechanical Response of Shape Memory Alloy Hybrid Composite Beams

An experimental and numerical investigation into the static and dynamic responses of shape memory alloy hybrid composite (SMAHC) beams is performed to provide quantitative validation of a recently commercialized numerical analysis/design tool for SMAHC structures. The SMAHC beam specimens consist of a composite matrix with embedded pre-strained SMA actuators, which act against the mechanical boundaries of the structure when thermally activated to adaptively stiffen the structure. Numerical results are produced from the numerical model as implemented into the commercial finite element code ABAQUS. A rigorous experimental investigation is undertaken to acquire high fidelity measurements including infrared thermography and projection moire interferometry for full-field temperature and displacement measurements, respectively. High fidelity numerical results are also obtained from the numerical model and include measured parameters, such as geometric imperfection and thermal load. Excellent agreement is achieved between the predicted and measured results of the static and dynamic thermomechanical response, thereby providing quantitative validation of the numerical tool.

Davis, Brian↗

DOE OSTI2011

Challenges for a reliable shell model description of the neutrinoless double beta decay matrix elements

Assuming that the neutrinos are Majorana particles and the neutrinoless double beta (0{nu}{beta}{beta}) decay is observed, a reliable 0{nu}{beta}{beta} matrix element is necessary to decide the neutrino mass hierarchy and the minimum neutrino mass. Many nuclear structure techniques, including the shell model, are presently used to calculate these matrix elements. In the last few years one could see a slow convergence of these results, but not yet at a level of 20 several shell model effective interactions and varying other parameters, finding results in a range that spans about 20In this contribution we describe challenges for obtaining reliable shell model 0{nu}{beta}{beta} matrix elements, with emphasis to {sup 76}Ge and {sup 82}Se decays.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗