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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

A novel concept for a combined-load test apparatus

An original concept for a combined-load test machine is presented in the paper. The concept employs a circular test specimen which may be rotated with respect to the biaxially applied loads. The ability to rotate the specimen and to vary the applied loads allows for limitless combinations of in-plane normal and shear loads. The loads generated in the test section reference frame are calculated from simple Mohr's circle relationships. In this paper, the concept is evaluated for isotropic, orthotropic, and discretely stiffened panels using elasticity and finite element methods. Strengths and weaknesses of the test machine concept are also discussed and evaluated.

Martin, Carl J.↗
NASA NTRS1989

Recent results concerning the stability of viscoelastic shear deformable plates under compressive edge loading

Some recent results obtained by the authors are summarized concerning the stability of transversely isotropic flat panels whose materials exhibit a viscoelastic behavior and whose edges are subjected to in-plane biaxial compressive loads. Two transversely isotropic type materials, largely used in advanced technology, are considered: (1) the pyrolytic-graphite type, used in the thermal protection of aerospace vehicles, and (2) the type corresponding to unidirectional fiber-reinforced composites. In the former case, the planes of isotropy are parallel at each point to the midplane of the plate. In the latter case, they are normal to the fiber directions. The micromechanical relations developed by Aboudi (1984, 1986, 1987) are considered in conjunction with the correspondence principle of linear viscoelastic theory in order to predict the macroscopic viscoelastic properties of a material composed of uniaxial elastic fibers embedded in a linear viscoelastic matrix.

Librescu, L.↗
NASA NTRS1988

Cyclic fatigue damage characteristics observed for simple loadings extended to multiaxial life prediction

Fully reversed uniaxial strain controlled fatigue tests were performed on smooth cylindrical specimens made of 304 stainless steel. Fatigue life data and cracking observations for uniaxial tests were compared with life data and cracking behavior observed in fully reversed torsional tests. It was determined that the product of maximum principle strain amplitude and maximum principle stress provided the best correlation of fatigue lives for these two loading conditions. Implementation of this parameter is in agreement with observed physical damage and it accounts for the variation of stress-strain response, which is unique to specific loading conditions. Biaxial fatigue tests were conducted on tubular specimens employing both in-phase and out-of-phase tension torsion cyclic strain paths. Cracking observations indicated that the physical damage which occurred in the biaxial tests was similar to the damage observed in uniaxial and torsional tests. The Smith, Watson, and Topper parameter was then extended to predict the fatigue lives resulting from the more complex loading conditions.

Jones, David J.↗
NASA NTRS2013

Thermal and Structural Performance of Woven Carbon Cloth For Adaptive Deployable Entry and Placement Technology

Arcjet testing and analysis of a three-dimensional (3D) woven carbon fabric has shown that it can be used as a thermal protection system and as a load bearing structural component for a low ballistic coefficient hypersonic decelerator called ADEPT (Adaptive Deployable Entry and Placement Technology). Results of arcjet tests proved that the 3D woven carbon fabric can withstand flight-like heating while under flight-like biaxial mechanical loads representative of those encountered during shallow entry flight path angles into the atmosphere of Venus. Importantly, the arcjet test results have been used to extend a preliminary material thermal response model based on previous testing of the same 3D woven carbon fabric under uni-axial mechanical loading.

Carbon fabric↗
DOE OSTI2022

Strain dependent electronic and optical responses of penta-BCN monolayer

We report here, structural, dynamic, and mechanical stability in pentagonal boron carbon nitride (p-BCN) monolayer, a new member of direct bandgap two-dimensional (2D) semiconductor. The identified visible range bandgap with excellent mechanical strength allows it to be a promising candidate material in optoelectronics, nanomechanics, and optomechanical sensors. By employing density functional theory (DFT), we reveal a unique geometrical reconstruction with rigidity in B–N and C–N bond lengths with applied strain. These quasi-sp 3 hybridized short and strong covalent bonding and unique geometry support the monolayer to possess extraordinary mechanical response. The desired bandgap is manipulated by loading the biaxial strain. Most importantly, our predictions on p-BCN show excellent optical response such as good static dielectric constant and refractive index, strong optical absorption (up to 1.08 x 10 5 cm -1 in VR and 7.01 x 10 cm -1 in UV) with small energy loss and reflectance both appearing in visible and ultraviolet regions (UV). The desired optical response along with the blue and red shift is demonstrated by tailoring with tensile and compressive strain. The predicted strong optical anisotropy provides it’s application in polarized photodetection.

36 MATERIALS SCIENCE↗
DOE OSTI2025

A generalizable machine learning-assisted fast Fourier transform algorithm to simulate the large strain phenomena in polycrystalline materials

Machine learning methods have shown initial promise in constitutive modeling for single crystals or homogenized polycrystals, delivering notable computational efficiency. However, existing machine learning-based constitutive models often lack generalizability, limiting their application across diverse boundary value problems. This study introduces a thermodynamics-informed artificial neural network model to accelerate rate-tangent crystal plasticity fast Fourier transform simulations for cross-scale deformation behaviors of polycrystals under complex loading. Our model integrates microstructural variability and local interactions effectively. To address local effects in each grain, we employ K-means clustering to group Gauss points within the microstructure into clusters assumed to be in similar mechanical states. This approach, based on self-clustering analysis, extends model scope from macroscopic stress response to the granular level, capturing mechanical responses and orientation evolution across grains. This reduces the number of nonlinear problems to solve, with cluster responses propagated throughout each group. The thermodynamics-based artificial neural network-extracted features are further processed using local material state clusters to account for history-dependent deformation and evolving microstructures. Additionally, representative volume element simulations with rate-tangent crystal plasticity fast Fourier transform provide reliable datasets for model training. The proposed model demonstrates high efficiency, accuracy, self-consistency, and enhanced generalizability in predicting strain–stress responses and orientation evolution at both individual grain and aggregate scales under complex loading conditions, such as biaxial tension and arbitrary loading scenarios.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Fracture toughness evaluations for spent nuclear fuel dry storage canister welds and spent nuclear fuel clad-pellet structures

Integrity of spent nuclear fuel (SNF) interim storage canisters is very important to the safety of the back-end nuclear fuel cycle. Stress corrosion cracking (SCC) potential of interim storage canister has been considered as a high priority. Because no post-weld heat treatment was required for forming these canisters, the high tensile residual stress existed within these canister welds. This can change the fracture resistance capacity significantly as well as increase SCC potential. Due to relative thin shell thickness of a canister weldment, the spiral notch torsion test (SNTT) method was used to estimate the canister weldment fracture toughness. SNTT was developed to measure the intrinsic fracture toughness of structural materials using small specimens. The SNTT method has been applied to a wide variety of structural materials, such as low-alloy steels, stainless steel, aluminum alloy, ceramics, concrete, and composites. The SNTT system operates by applying pure torsion to cylindrical specimens with a notch line that spirals around the specimen at a 45° pitch. In order to carry out pure torsion load mode, biaxial tension/torsion tester was developed accordingly to perform SNTT protocol. Moreover, applying fracture mechanics approach to SNF system reliability investigation is warranted due to the inherent flaws and hydride structures existed in a SNF system after nuclear reactor operation. However, none of the existing fracture toughness data deal with fuel cladding specific geometry or spent fuel material conditions, such as cladding structure with the pellet-inserts and the associated pellet clad mechanical interactions induced mixed-mode damage mechanisms. Thus, the development of an intrinsic fracture mechanics approach that is suitable for SNF materials is needed. Furthermore, due to thin wall and small dimension of clad tubing structure, the SNTT method was used to estimate the clad tubing structure fracture toughness. Fracture testing were performed on the received stainless steel canister weldment, most SNTT weld samples fracture initiation sites are at heat-affected zone (HAZ) regions. The estimated fracture toughness J Q ’ for the baseline SS304 steel is at 283 kJ/m². The estimated JQ’ for the SS304/308 weld and baseline metals are 148 kJ/m 2 and 459 kJ/m 2 , respectively. Out of cell fracture testing for spent fuel structure were carried out on the surrogate rods made of Zr-4 clad and alumina inserts, the estimated fracture toughness values for baseline Zr-4 cladding with alumina-pellet inserts are: (1) For SNTT samples with a short or medium crack length, between 5.4-mm and 8-mm, the estimate J IQ upon fracture initiation for the baseline Zr-4 cladding is at 50 kJ/m 2 with 2-sigma uncertainty of 3.26 kJ/m 2 , and the associated K IQ is at 67.46 MPa$\sqrt{m}$; and (2) For SNTT samples with a long crack length, around 13-mm, the crack initialization is deviated from that of the Mode-I tensile fracture and appears to be a mixed-mode fracture of Mode I - tensile stress and Mode III - out of plane shear stress; the estimated J MQ is at 18.9 kJ/m 2 , the associated K MQ is at 41.4 MPa$\sqrt{m}$.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1975

Biaxial compression test technique

Fixture and technique have been developed for predicting behavior of stiffened skin panels under biaxial compressive loading. Tester can load test panel independently in longitudinal and transverse directions. Data can also be obtained in combined mode.

Hansard, E. T.↗
NASA NTRS1975

NOLIN: A nonlinear laminate analysis program

A nonlinear, plane-stress, laminate analysis program, NOLIN, was developed which accounts for laminae nonlinearity under inplane shear and transverse extensional stress. The program determines the nonlinear stress-strain behavior of symmetric laminates subjected to any combination of inplane shear and biaxial extensional loadings. The program has the ability to treat different stress-strain behavior in tension and compression, and predicts laminate failure using any or all of maximum stress, maximum strain, and quadratic interaction failure criteria. A brief description of the program is presented including discussion of the flow of information and details of the input required. Sample problems and a complete listing of the program is also provided.

Kibler, J. J.↗
NASA NTRS1977

Experimental studies of graphite-epoxy and boron-epoxy angle ply laminates in shear

The nonlinear/inelastic response under inplane shear of a large variety of graphite-epoxy and boron-epoxy angle-ply laminates was tested. Their strength allowables were obtained and the mechanisms which govern their mode of failure were determined. Two types of specimens for the program were chosen, tested, and evaluated: shear panels stabilized by an aluminum honeycomb core and shear tubes. A modified biaxially compression/tension loaded picture frame was designed and utilized in the test program with the shear panels. The results obtained with this test technique categorically prefer the shear panels, rather than the tubes, for adequate and satisfactory experimental definition of the objectives. Test results indicate the existence of a so-called core-effect which ought to be considered when reducing experimental data for weak in shear laminates.

Weller, T.↗
NASA NTRS1985

Concurrent processing for nonlinear analysis of hollow rectangular structural sections

A concurrent processing algorithm is developed for a materially nonlinear analysis of hollow square and rectangular structural sections and implemented on a special purpose multiprocessor computer at NASA Langley Research Center referred to as the 'Finite Element Machine'. The cross sectional thrust-moment-curvature relations are generated concurrently using a tangent stiffness approach and yield surfaces are obtained which represent the interaction between axial load and biaxial moments. For the study, a maximum speed-up factor of 7.69 is achieved on eight processors.

Darbhamulla, S. P.↗
NASA NTRS1986

Constitutive modeling for isotropic materials (HOST)

The results of the third year of work on a program which is part of the NASA Hot Section Technology program (HOST) are presented. The goals of this program are: (1) the development of unified constitutive models for rate dependent isotropic materials; and (2) the demonstration of the use of unified models in structural analyses of hot section components of gas turbine engines. The unified models selected for development and evaluation are those of Bodner-Partom and of Walker. A test procedure was developed for assisting the generation of a data base for the Bodner-Partom model using a relatively small number of specimens. This test procedure involved performing a tensile test at a temperature of interest that involves a succession of strain-rate changes. The results for B1900+Hf indicate that material constants related to hardening and thermal recovery can be obtained on the basis of such a procedure. Strain aging, thermal recovery, and unexpected material variations, however, preluded an accurate determination of the strain-rate sensitivity parameter is this exercise. The effects of casting grain size on the constitutive behavior of B1900+Hf were studied and no particular grain size effect was observed. A systematic procedure was also developed for determining the material constants in the Bodner-Partom model. Both the new test procedure and the method for determining material constants were applied to the alternate material, Mar-M247 . Test data including tensile, creep, cyclic and nonproportional biaxial (tension/torsion) loading were collected. Good correlations were obtained between the Bodner-Partom model and experiments. A literature survey was conducted to assess the effects of thermal history on the constitutive behavior of metals. Thermal history effects are expected to be present at temperature regimes where strain aging and change of microstructure are important. Possible modifications to the Bodner-Partom model to account for these effects are outlined. The use of a unified constitutive model for hot section component analyses was demonstrated by applying the Walker model and the MARC finite-element code to a B1900+Hf airfoil problem.

Chan, Kwai S.↗
NASA NTRS1990

A real time neural net estimator of fatigue life

A neural net architecture is proposed to estimate, in real-time, the fatigue life of mechanical components, as part of the Intelligent Control System for Reusable Rocket Engines. Arbitrary component loading values were used as input to train a two hidden-layer feedforward neural net to estimate component fatigue damage. The ability of the net to learn, based on a local strain approach, the mapping between load sequence and fatigue damage has been demonstrated for a uniaxial specimen. Because of its demonstrated performance, the neural computation may be extended to complex cases where the loads are biaxial or triaxial, and the geometry of the component is complex (e.g., turbopump blades). The generality of the approach is such that load/damage mappings can be directly extracted from experimental data without requiring any knowledge of the stress/strain profile of the component. In addition, the parallel network architecture allows real-time life calculations even for high frequency vibrations. Owing to its distributed nature, the neural implementation will be robust and reliable, enabling its use in hostile environments such as rocket engines. This neural net estimator of fatigue life is seen as the enabling technology to achieve component life prognosis, and therefore would be an important part of life extending control for reusable rocket engines.

Troudet, T.↗
NASA NTRS1990

Postbuckling analysis of shear deformable composite flat panels taking into account geometrical imperfections

The effects of initial geometrical imperfections on the postbuckling response of flat laminated composite panels to uniaxial and biaxial compressive loading are investigated analytically. The derivation of the mathematical model on the basis of first-order transverse shear deformation theory is outlined, and numerical results for perfect and imperfect, single-layer and three-layer square plates with free-free, clamped-clamped, or free-clamped edges are presented in graphs and briefly characterized. The present approach is shown to be more accurate than analyses based on the classical Kirchhoff plate model.

Librescu, L.↗
NASA NTRS1990

A real time neural net estimator of fatigue life

A neural network architecture is proposed to estimate, in real-time, the fatigue life of mechanical components, as part of the intelligent Control System for Reusable Rocket Engines. Arbitrary component loading values were used as input to train a two hidden-layer feedforward neural net to estimate component fatigue damage. The ability of the net to learn, based on a local strain approach, the mapping between load sequence and fatigue damage has been demonstrated for a uniaxial specimen. Because of its demonstrated performance, the neural computation may be extended to complex cases where the loads are biaxial or triaxial, and the geometry of the component is complex (e.g., turbopumps blades). The generality of the approach is such that load/damage mappings can be directly extracted from experimental data without requiring any knowledge of the stress/strain profile of the component. In addition, the parallel network architecture allows real-time life calculations even for high-frequency vibrations. Owing to its distributed nature, the neural implementation will be robust and reliable, enabling its use in hostile environments such as rocket engines.

Troudet, T.↗
NASA NTRS1993

Design, analysis, and fabrication of a pressure box test fixture for tension damage tolerance testing of curved fuselage panels

A pressure box test fixture was designed and fabricated to evaluate the effects of internal pressure, biaxial tension loads, curvature, and damage on the fracture response of composite fuselage structure. Previous work in composite fuselage tension damage tolerance, performed during NASA contract NAS1-17740, evaluated the above effects on unstiffened panels only. This work extends the tension damage tolerance testing to curved stiffened fuselage crown structure that contains longitudinal stringers and circumferential frame elements. The pressure box fixture was designed to apply internal pressure up to 20 psi, and axial tension loads up to 5000 lb/in, either separately or simultaneously. A NASTRAN finite element model of the pressure box fixture and composite stiffened panel was used to help design the test fixture, and was compared to a finite element model of a full composite stiffened fuselage shell. This was done to ensure that the test panel was loaded in a similar way to a panel in the full fuselage shell, and that the fixture and its attachment plates did not adversely affect the panel.

Smith, P. J.↗
NASA NTRS1998

Development of a Flexible Seal for a 60 psi Cryogenic Pressure Box

A cryogenic pressure box test facility has been designed and fabricated for use at NASA Langley Research Center (LaRC) to subject 5 ft x 6 ft curved panels to cryogenic temperatures and biaxial tensile loads. The cryogenic pressure box is capable of testing curved panels down to -423 F (20 K) with 54 psig maximum pressure. The key challenge in the design and fabrication of the pressure box was the development of a seal that could remain flexible at -423 F and contain 60 psi gaseous helium as the pressurization gas. A C-shaped seal was developed using a Gore-tex woven fabric. Mechanical testing of the fabric at room and elevated temperature, liquid nitrogen temperature, and liquid helium temperature demonstrated the strength and creep resistance of the material over the desired operating range. A small scale cryogenic pressure box was used to test prototype seals at cryogenic temperatures up to 60 psi. Preliminary tests indicated that excessive leakage was present through the seal. As a result, an aluminized mylar liner was placed inside the Gore-tex seal to reduce leakage through the seal. The final seal configuration resulted in minimal pressure loss during seal testing.

Glass, David E.↗
NASA NTRS1999

Analysis and Design of the NASA Langley Cryogenic Pressure Box

A cryogenic pressure box was designed and fabricated for use at NASA Langley Research Center (LaRC) to subject 72 in. x 60 in. curved panels to cryogenic temperatures and biaxial tensile loads. The cryogenic pressure box is capable of testing curved panels down to -423 F (20K) with 54 psig maximum pressure on the concave side, and elevated temperatures and atmospheric pressure on the convex surface. The internal surface of the panel is cooled by high pressure helium as that is cooled to -423 F by liquid helium heat exchangers. An array of twelve independently controlled fans circulate the high pressure gaseous helium to provide uniform cooling on the panel surface. The load introduction structure, consisting of four stainless steel load plates and numerous fingers attaching the load plates to the test panel, is designed to introduce loads into the test panel that represent stresses that will he observed in the actual tank structure. The load plates are trace cooled with liquid nitrogen to reduce thermal gradients that may result in bending the load plates, and thus additional stresses in the test panel. The design of the cryogenic systems, load introduction structure, and control system are discussed in this report.

Glass, David E.↗