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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

GENOA-PFA: Progressive Fracture in Composites Simulated Computationally

GENOA-PFA is a commercial version of the Composite Durability Structural Analysis (CODSTRAN) computer program that simulates the progression of damage ultimately leading to fracture in polymer-matrix-composite (PMC) material structures under various loading and environmental conditions. GENOA-PFA offers several capabilities not available in other programs developed for this purpose, making it preferable for use in analyzing the durability and damage tolerance of complex PMC structures in which the fiber reinforcements occur in two- and three-dimensional weaves and braids. GENOA-PFA implements a progressive-fracture methodology based on the idea that a structure fails when flaws that may initially be small (even microscopic) grow and/or coalesce to a critical dimension where the structure no longer has an adequate safety margin to avoid catastrophic global fracture. Damage is considered to progress through five stages: (1) initiation, (2) growth, (3) accumulation (coalescence of propagating flaws), (4) stable propagation (up to the critical dimension), and (5) unstable or very rapid propagation (beyond the critical dimension) to catastrophic failure. The computational simulation of progressive failure involves formal procedures for identifying the five different stages of damage and for relating the amount of damage at each stage to the overall behavior of the deteriorating structure. In GENOA-PFA, mathematical modeling of the composite physical behavior involves an integration of simulations at multiple, hierarchical scales ranging from the macroscopic (lamina, laminate, and structure) to the microscopic (fiber, matrix, and fiber/matrix interface), as shown in the figure. The code includes algorithms to simulate the progression of damage from various source defects, including (1) through-the-thickness cracks and (2) voids with edge, pocket, internal, or mixed-mode delaminations.

Murthy, Pappu L. N.↗
NASA NTRS1992

Sparse Matrices in MATLAB: Design and Implementation

The matrix computation language and environment MATLAB is extended to include sparse matrix storage and operations. The only change to the outward appearance of the MATLAB language is a pair of commands to create full or sparse matrices. Nearly all the operations of MATLAB now apply equally to full or sparse matrices, without any explicit action by the user. The sparse data structure represents a matrix in space proportional to the number of nonzero entries, and most of the operations compute sparse results in time proportional to the number of arithmetic operations on nonzeros.

Gilbert, John R.↗
NASA NTRS2021

Latent Cure Epoxy Resins for Reliable Joints in Secondary-Bonded Composite Structures

In high-performance polymer matrix composite assemblies, adhesive bonding is generally superior to mechanical fastening in structural performance and manufacturing efficiency. However, adhesive bonds are susceptible to minute levels of contamination accumulated during assembly that can lead to unpredictable, weak bonds. Current methods of measuring bond strength are all destructive mechanical tests. To overcome these challenges, redundant load paths (e.g., mechanical fasteners) are often implemented in secondary-bonded, primary-structures, which can greatly reduce structural performance. This study investigated reformulated aerospace epoxy matrix resins with stoichiometric offset to inhibit cure of the matrix resin prior to assembly. Inhibited resins can reflow and mix across the joint interface, which eliminates the material discontinuity and forms a homogenous joint with reliable fracture properties. The goal of this study was to develop and demonstrate secondary composite assemblies that are mechanically and microscopically indistinguishable from a co-cured composite joint. This article describes the development of latent epoxy resins, the fabrication of test articles, and the mechanical properties measured from experimental joints compared with conventional, co-cured laminates. Methods of in-line quality control using and infrared spectroscopy and post-assembly forensics are also described. The final mode-II fracture toughness measured from precracked AERoBOND specimens was similar to that measured from co-cured laminates indicating that later cure epoxy materials could be a suitable replacement for secondary bonding.

Polymer-matrix composites (PMCs)↗
NASA NTRS1995

The strength of a calcified tissue depends in part on the molecular structure and organization of its constituent mineral crystals in their organic matrix

High-voltage electron-microscopic tomographic (3D) studies of the ultrastructural interaction between mineral and organic matrix in a variety of calcified tissues reveal different crystal structural and organizational features in association with their respective organic matrices. In brittle or weak pathologic or ectopic calcifications, including examples of osteogenesis imperfecta, calciphylaxis, calcergy, and dermatomyositis, hydroxyapatite crystals occur in various sizes and shapes and are oriented and aligned with respect to collagen in a manner which is distinct from that found in normal calcified tissues. A model of collagen-mineral interaction is proposed which may account for the observed crystal structures and organization. The results indicate that the ultimate strength, support, and other mechanical properties provided by a calcified tissue are dependent in part upon the molecular structure and arrangement of its constituent mineral crystals within their organic matrix.

Non-NASA Center↗
NASA NTRS1988

Structural analyses of engine wall cooling concepts and materials

The severe thermal environments under which hypersonic aircraft such as the National Aerospace Plane (NASP) will operate require cooling of the engine walls, especially in the combustor. A preliminary assessment is made of some candidate materials based on structural analyses for a number of convective cooling configurations. Three materials were studied: graphite/copper and tungsten/copper composite alloys with 50 percent fiber volume fractions and a wrought cobalt-base superalloy, Haynes 188. Anisotropic mechanical and thermal properties for the composites were obtained from a computer code, ICAN, which determines the composite material properties from the individual properties of the fiber and matrix materials. The structural analyses were performed by using the MARC nonlinear finite element code. Heat transfer analyses were conducted to calculate the metal temperature distributions.

Kaufman, Albert↗
NASA NTRS2016

Optimization of a Hot Structure Aeroshell and Nose Cap for Mars Atmospheric Entry

The National Aeronautics and Space Administration (NASA) is preparing to send humans beyond Low Earth Orbit and eventually to the surface of Mars. As part of the Evolvable Mars Campaign, different vehicle configurations are being designed and considered for delivering large payloads to the surface of Mars. Weight and packing volume are driving factors in the vehicle design, and the thermal protection system (TPS) for planetary entry is a technology area which can offer potential weight and volume savings. The feasibility and potential benefits of a ceramic matrix composite hot structure concept for different vehicle configurations are explored in this paper, including the nose cap for a Hypersonic Inflatable Aerodynamic Decelerator (HIAD) and an aeroshell for a mid lift-to-drag (Mid L/D) concept. The TPS of a planetary entry vehicle is a critical component required to survive the severe aerodynamic heating environment during atmospheric en- try. The current state-of-the-art is an ablative material to protect the vehicle from the heat load. The ablator is bonded to an underlying structure, which carries the mechanical loads associated with entry. The alternative hot structure design utilizes an advanced carbon-carbon material system on the outer surface of the vehicle, which is exposed to the severe heating and acts as a load carrying structure. The preliminary design using the hot structure concept and the ablative concept is determined for the spherical nose cap of the HIAD entry vehicle and the aeroshell of the Mid L/D entry vehicle. The results of the study indicate that the use of hot structures for both vehicle concepts leads to a feasible design with potential weight and volume savings benefits over current state-of-the-art TPS technology that could enable future missions.

Langston, Sarah L.↗
NASA NTRS1989

Mini-mast dynamic analysis using the truss-beam model

The Mini-Mast is a generic space truss designed by Astro Aerospace Corp. A 210 meter truss located in the Structural Dynamics research Lab of NASA Langley is used in comprehensive active vibration control experiments on a realistic large space structure. Some predictions of the natural frequencies and mode shapes were made based on the Finite Element model. The purpose here is to use the Truss-Beam model developed by Elias G. Abu-Saba to predict the natural frequencies of the Mini-Mast and then compare the results with those obtained from the FE model. Imperfections of the joints are modeled, and joint contribution to the flexibility matrix of the structure is noted. The natural frequencies are obtained. An iterative procedure is used to enhance the Truss-Beam model by comparing these results with experimental ones.

Abu-Saba, Elias G.↗
DOE OSTI2026

Effects of Cooling Rates on Self-Reinforced Polyethylene Composites via Multiscale Experimental Characterizations

This study investigates cooling rate effects on self-reinforced polyethylene composites (PE-SRCs), focusing on macroscopic thermal and mechanical properties, and micro- to sub-micron morphologies. Unlike conventional fiber-reinforced composites (e.g., carbon and glass fiber based), cooling rate effects on SRCs remain less studied. PE-SRCs were fabricated from ultrahigh molecular weight polyethylene (UHMWPE) fabric and high-density polyethylene (HDPE) matrix with cooling rates from 0.76°C/min to 425°C/min. Tensile properties, including modulus (~9.5 GPa), strength (~360 MPa), and ultimate elongation (~6%), showed no significant cooling rate dependence. However, thermal analysis revealed melting temperature of HDPE matrix decreased from ~130°C to ~126.5°C with total crystallinity reducing from 84% to 75%. Wide-angle X-ray scattering confirmed decreasing crystallinity but at lower values (67%–59%), as thermal analysis might overestimate crystallinity. Small-angle X-ray scattering showed long period decreased from 24.3 to 17.4 nm, attributed to thinner lamellae and closer packing, suggesting limited crystal growth and faster nucleation. While cooling rates alter melting point and crystalline structures of HDPE matrix, these changes do not translate to substantial impact on macroscale mechanical properties of PE-SRCs. This insensitivity might be related to low interfacial shear strength at PE/PE interfaces, enabling process optimization while maintaining mechanical performance.

Cooling rate↗
NASA NTRS1974

Connective stability of nonlinear matrix systems

Consideration of stability under structural perturbations of free dynamic systems described by the differential equation dx/dt = A(t,x)x, where the matrix A(t,x) has time-varying nonlinear elements. The concept of 'connective stability' is introduced to study the structural properties of competitive-cooperative nonlinear matrix systems. It is shown that stability reliability in such systems is high and that they remain stable despite time-varying (including 'on-off') interaction among individual agents present in the system. The results obtained can be used to study stability aspects of mathematical models arising in as diverse fields as economics, biology, arms races, and transistor circuits.

Siljak, D. D.↗
NASA NTRS1979

High resolution transmission electron microscopy of two stony meteorites - Murchison and Kenna

Matrix material from the Murchison C2(M) carbonaceous chondrite and less than micrometer-size pyroxene inclusions in an olivine from the Kenna ureilite have been characterized using high resolution transmission electron microscopy. A diversity of textures and mineral associations, including serpentine-type and brucite-type mixed-layering, occur in the Murchison matrix. Such mixed layer structures are new types of layer silicate. Their presence in the matrix may prove to be genetically significant. The Kenna inclusions, formed at the olivine grain margins, are of two types: (1) a disordered orthopyroxene-clinopyroxene which may have inverted from protopyroxene and (2) a pigeonite with narrow anti-phase domains (80 A to 250 A) and boundaries parallel to (100).

Mackinnon, I. D. R.↗
NASA NTRS1991

Closed-form solutions for linear regulator design of mechanical systems including optimal weighting matrix selection

Vibration in modern structural and mechanical systems can be reduced in amplitude by increasing stiffness, redistributing stiffness and mass, and/or adding damping if design techniques are available to do so. Linear Quadratic Regulator (LQR) theory in modern multivariable control design, attacks the general dissipative elastic system design problem in a global formulation. The optimal design, however, allows electronic connections and phase relations which are not physically practical or possible in passive structural-mechanical devices. The restriction of LQR solutions (to the Algebraic Riccati Equation) to design spaces which can be implemented as passive structural members and/or dampers is addressed. A general closed-form solution to the optimal free-decay control problem is presented which is tailored for structural-mechanical system. The solution includes, as subsets, special cases such as the Rayleigh Dissipation Function and total energy. Weighting matrix selection is a constrained choice among several parameters to obtain desired physical relationships. The closed-form solution is also applicable to active control design for systems where perfect, collocated actuator-sensor pairs exist.

Hanks, Brantley R.↗
DOE OSTI2024

Osteocytic oxygen sensing: Distinct impacts of VHL and HIF-2alpha on bone integrity

Skeletal fracture resistance emerges from multiple components of bone structure like microarchitecture, matrix mineralization, and organization. These characteristics are engendered via mechanisms like the hypoxia-inducible factors (HIF) pathway, involving two paralogs, HIF-1α and HIF-2α. Under normoxia, HIF-α is targeted for degradation via von-Hippel Lindau (VHL); hypoxia enables HIF-α stabilization and induction of target genes. We previously showed that osteocytic Vhl deletion or expression of degradation-resistant HIF-2α cDR female mice each produced high bone mass, whereas degradation-resistant osteocytic HIF-1α produced no overt phenotype. We report within that Vhl cKO increased bone strength, while HIF-2α cDR displayed markedly reduced bone strength below Cre-negative controls. This suggests that VHL and HIF-2α drive distinct responses that promote disparate effects on bone strength. Both Vhl deletion or HIF-2α accumulation generated two discrete bone morphologies: an outer lamellar cortex and a woven, poorly mineralized endocortex that imparted dramatically different functional outcomes. Our studies reveal novel influence of osteocytic HIF-2α signaling on collagen matrix organization, mineralization, and bone strength.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

Mild chemical recycling of carbon fiber-reinforced epoxy composites in aqueous buffers and development of hydrothermally recyclable vitrimer composites from recyclates

Carbon fiber-reinforced polymer (CFRP) composites have gained widespread adoption across diverse industries. However, their inherent stability, stemming from the crosslinked structure of the matrix resin, poses a significant challenge in managing the growing volume of CFRP waste. Consequently, there is a pressing need for an eco-friendly upcycling method that effectively recovers and reuses both the valuable carbon fibers and the polymer matrix from CFRP waste. This study presents a novel approach for upcycling CFRP waste under environmentally friendly conditions. Firstly, CFRP waste with an amine-cured epoxy matrix was completely decomposed in aqueous buffer solutions under mild conditions (≤ 220 °C, pH = 4.8). Further, decomposed matrix polymer (DMP) was employed to transform conventional epoxy resins into recyclable vitrimers. Lastly, new composites that can be hydrothermally recycled were fabricated using both DMP and recovered carbon fibers. As a result, this work proposes a novel strategy for achieving a circular economy within the CFRP industry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Additive manufacturing of an ultrastrong, deformable Al alloy with nanoscale intermetallics

Abstract Light-weight, high-strength, aluminum (Al) alloys have widespread industrial applications. However, most commercially available high-strength Al alloys, like AA 7075, are not suitable for additive manufacturing due to their high susceptibility to solidification cracking. In this work, a custom Al alloy Al 92 Ti 2 Fe 2 Co 2 Ni 2 is fabricated by selective laser melting. Heterogeneous nanoscale medium-entropy intermetallic lamella form in the as-printed Al alloy. Macroscale compression tests reveal a combination of high strength, over 700 MPa, and prominent plastic deformability. Micropillar compression tests display significant back stress in all regions, and certain regions have flow stresses exceeding 900 MPa. Post-deformation analyses reveal that, in addition to abundant dislocation activities in Al matrix, complex dislocation structures and stacking faults form in monoclinic Al 9 Co 2 type brittle intermetallics. This study shows that proper introduction of heterogeneous microstructures and nanoscale medium entropy intermetallics offer an alternative solution to the design of ultrastrong, deformable Al alloys via additive manufacturing.

Science & Technology - Other Topics↗
DOE OSTI2025

Entropy is an important design principle in the photosystem II supercomplex

Photosystem II (PSII) can achieve near-unity quantum efficiency of light harvesting in ideal conditions and can dissipate excess light energy as heat to prevent the formation of reactive oxygen species (ROS) under light stress. Understanding how this pigment–protein complex accomplishes these opposing goals is a topic of great interest that has so far been explored primarily through the lens of the system energetics. Despite PSII’s known flat energy landscape, a thorough consideration of the entropic effects on energy transfer in PSII is lacking. In this work, we aim to discern the free energetic design principles underlying the PSII energy transfer network. To accomplish this goal, we employ a structure-based rate matrix and compute the free energy terms in time following a specific initial excitation to discern how entropy and enthalpy drive ensemble system dynamics. We find that the interplay between the entropy and enthalpy components differ among each protein subunit, which allows each subunit to fulfill a unique role in the energy transfer network. This individuality ensures that PSII can accomplish efficient energy trapping in the reaction center (RC), effective nonphotochemical quenching (NPQ) in the periphery, and robust energy trapping in the other-monomer RC if the same-monomer RC is closed. We also show that entropy, in particular, is a dynamically tunable feature of the PSII free energy landscape accomplished through regulation of LHCII binding. These findings help rationalize natural photosynthesis and provide design principles for more efficient solar energy harvesting technologies.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

A graphics processing unit accelerated sparse direct solver and preconditioner with block low rank compression

We present the GPU implementation efforts and challenges of the sparse solver package STRUMPACK. The code is made publicly available on github with a permissive BSD license. STRUMPACK implements an approximate multifrontal solver, a sparse LU factorization which makes use of compression methods to accelerate time to solution and reduce memory usage. Multiple compression schemes based on rank-structured and hierarchical matrix approximations are supported, including hierarchically semi-separable, hierarchically off-diagonal butterfly, and block low rank. Here, in this paper, we present the GPU implementation of the block low rank (BLR) compression method within a multifrontal solver. Our GPU implementation relies on highly optimized vendor libraries such as cuBLAS and cuSOLVER for NVIDIA GPUs, rocBLAS and rocSOLVER for AMD GPUs and the Intel oneAPI Math Kernel Library (oneMKL) for Intel GPUs. Additionally, we rely on external open source libraries such as SLATE (Software for Linear Algebra Targeting Exascale), MAGMA (Matrix Algebra on GPU and Multi-core Architectures), and KBLAS (KAUST BLAS). SLATE is used as a GPU-capable ScaLAPACK replacement. From MAGMA we use variable sized batched dense linear algebra operations such as GEMM, TRSM and LU with partial pivoting. KBLAS provides efficient (batched) low rank matrix compression for NVIDIA GPUs using an adaptive randomized sampling scheme. The resulting sparse solver and preconditioner runs on NVIDIA, AMD and Intel GPUs. Interfaces are available from PETSc, Trilinos and MFEM, or the solver can be used directly in user code. We report results for a range of benchmark applications, using the Perlmutter system from NERSC, Frontier from ORNL, and Aurora from ALCF. For a high frequency wave equation on a regular mesh, using 32 Perlmutter compute nodes, the factorization phase of the exact GPU solver is about 6.5× faster compared to the CPU-only solver. The BLR-enabled GPU solver is about 13.8× faster than the CPU exact solver. For a collection of SuiteSparse matrices, the STRUMPACK exact factorization on a single GPU is on average 1.9× faster than NVIDIA’s cuDSS solver.

97 MATHEMATICS AND COMPUTING↗