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At least 1,477 records · Page 82
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Bio-reinforced composite development for additive manufacturing: Nanocellulose-PLA

Additive manufacturing (AM) is transitioning from being only a prototyping method towards becoming a manufacturing technique for the quick production of parts with complex geometries. For the complete realization of this transition, the mechanical properties of the printed parts have to meet the requirements of actual load-bearing structural components. Integration of a reinforcing second phase into a polymer is a viable approach for the improvement of resins mechanical performance. Addition of carbon fibers into acrylonitrile-butadiene-styrene (ABS) has already been shown to improve its mechanical properties compared to the neat ABS resin (both additively manufactured), and led to the manufacture of world s first 3D-printed car. However, both ABS resin and carbon fibers are petroleum-based products, and there is a continuous search for alternative, bio-sourced, renewable materials as a feedstock for manufacturing. Towards this direction, we have investigated the potential of cellulose nanofibril-reinforced polylactic acid (PLA) resin systems as an alternative. CNF-PLA composite systems with up to 40 wt% CNF loadings were prepared via compression molding technique and tested. Significant improvements in both tensile strength (80%) and elastic modulus (128%) were observed. Filaments prepared from the same compositions were also successfully 3D-printed into tensile testing specimens with up to 30% CNF concentrations, and showed similar improvements in mechanical performance. Although CNFs were not individually dispersed in PLA matrix, they were observed to be well blended with the polymer based on SEM micrographs. In summary, preparation and 3D-printing of a 100% bio-based feedstock material with the mechanical properties comparable to the carbon fiber-ABS system was successfully demonstrated that it can open up new window of opportunities in the additive manufacturing industry. Acknowledgement Research sponsored by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office, under contract DE-AC05-00OR22725 with UT-Battelle, LLC.

09 BIOMASS FUELS↗
NASA NTRS1980

Effect of thermal cycling on ZrO2-Y2O3 thermal barrier coatings

A study was made of the comparative life of plasma sprayed ZrO2-Y2O3 thermal barrier coatings on NiCrAlY bond coats on Rene 41 in short (4 min) and long (57 min) thermal cycles to 1040 C in a 0.3 Mach flame. Short cycles greatly reduced the life of the ceramic coating in terms of time at temperature as compared to longer cycles. Appearance of the failed coating indicated compressive failure. Failure occurred at the bond coat-ceramic coat junction. At heating rates greater than 550 kw/sq m, the calculated coating detachment stress was in the range of literature values of coating adhesive/cohesive strength. Methods are discussed for decreasing the effect of high heating rate by avoiding compressive stress.

Mcdonald, G.↗
NASA NTRS1983

Failure analysis of composite laminates including biaxial compression

This report describes a continued effort on the development and application of the tensor polynomial failure criterion for composite laminate analysis. In particular, emphasis is given to the design, construction and testing of a cross-beam laminate configuration to obtain "pure' biaxial compression failure. The purpose of this test case was to provide to permit "closure' of the cubic form of the failure surface in the 1-2 compression-compression quadrant. This resulted in a revised set of interaction strength parameters and the construction of a failure surface which can be used with confidence for strength predictions, assuming a plane stress state exists. Furthermore, the problem of complex conjugate roots which can occur in some failure regions is addressed and an "engineering' interpretation is provided. Results are presented illustrating this behavior and the methodology for overcoming this problem is discussed.

Tennyson, R. C.↗
NASA NTRS1988

Magnetic ULF fluctuations in the compressional zone of AMPTE's artificial comets

The two Ba releases in the solar wind, termed artificial comets (the first in interplanetary space, the second in the terrestrial magnetosheath), showed a number of common magnetic features. Both times a magnetic cavity was detected and a field pile-up observed with magnitudes several times the ambient field strength upstream of the cavity. The magnetic fluctuations in the compressed region are generally enhanced by a factor comparable to the amount of field pile-up. There is a peak in the spectra of both events around 0.1 Hz in the component which is perpendicular to the solar-wind velocity vector and almost field-aligned. This magnetosonic wave has been interpreted as the fundamental mode of resonance oscillations of the compression zone. For frequencies beyond 2 Hz the spectra decrease more steeply in the case of the second 'comet' than in the first. This is due to the interaction of the supersonic solar wind with the first comet. The spectra obtained during the first comet at the solar-wind/ion-cloud interface are identical to those observed during bow-shock crossings.

Kloecker, N.↗
NASA NTRS2000

Comparison of The Dimensional Stability of Kel-F 81 and Neoflon CTFE M400H Polychlorotrifluoroethylenes Used in Valve Seat Application

The dimensional stability of polychlorotrifluoroethylene (PCTFE) valve seats used in oxygen regulator applications was determined by thermomechanical analysis (TMA). Two traceable grades of PCTFE were tested; Kel-F 81 and Neoflon CTFE M400H. For these particular resins, the effect of percent crystallinity, zero strength time (ZST) molecular weight, resin grade, process history (compression-molded versus extruded) on the dimensional stability and annealing behavior was determined. In addition to the traceable Kel-F 81 and Neoflon CTFE M400H grades, actual PCI'PH valve seats of differing geometry and design were tested by TMA. The PCTFE valve seats were of unspecified resin grade, although certain inferences about the grade could be drawn based on knowledge of the valve seat fabrication date. Results consistently revealed dimensional instability of varying magnitude at temperatures ranging from 40 to 70 degrees Celsius. Furthermore, some of the pre- 1 995 seats appeared to be more dimensionally stable than those fabricated after 1995. The TMA results are discussed in the context of several proposed ignition mechanisms; namely, particle impact, presence of contaminant oils and fibers, and localized heating by flow friction and/or resonance. The effect of metal constraint on the dimensional stability of PCTFE is also discussed. Finally, the effect of percent crystallinity, ZST molecular weight, resin grade, process history (compression-molded versus extruded) on the AIT, delta Hc and impact sensitivity of various types of Neoflon CTFE M400H was determined using Kel-F 81 as a control. Results show that the AIT, delta Hc and impact sensitivity were essentially independent of Neoflon CTFE process history and structure.

Waller, Jess M.↗
DOE OSTI2022

Characterization of Tri-lab β-Tin (Sn)

This report documents details of the microstructure and mechanical properties of -tin (Sn), that is used in the Tri-lab (Los Alamos National Laboratory (LANL), Lawrence Livermore National Laboratory (LLNL), Sandia National Laboratories (SNL)) collaboration project on Multi-phase Tin Strength. We report microstructural features detailing the crystallographic texture and grain morphology of as-received -tin from electron back scatter diffraction (EBSD). Temperature and strain rate dependent mechanical behavior was investigated by multiple compression tests at temperatures of 200K to 400K and strain rates of 0.0001 /s to 100 /s. Tri-lab tin showed significant temperature and strain rate dependent strength with no significant plastic anisotropy. A sample to sample material variation was observed from duplicate compression tests and texture measurements. Compression data was used to calibrate model parameters for temperature and rate dependent strength models, Johnson-Cook (JC), Zerilli-Armstrong (ZA) and Preston-Tonks-Wallace (PTW) strength models.

36 MATERIALS SCIENCE↗
NASA NTRS1996

Elevated Temperature Compressive Properties of Zr-Modified Nial

Small Zr additions are known to substantially affect the deformation behavior and strength of polycrystalline NiAl, yet little information is currently available regarding the high-temperature properties of such alloys. Utilizing prealloyed powder technology, a series of four NiAl alloys have been produced containing from 0.05 to 0.7 at. pct Zr. The creep behavior of these alloys was characterized in compression between 1000 and 1400 K at strain rates ranging from approx. O.1 to 10(exp -9)/ sec. All the Zr-modified alloys were significantly stronger than binary NiAl under lower temperature and faster strain-rate conditions; however, the single-phase materials (Zr less than or equal to 0.1 at. pct) and binary NiAl had similar strengths at high temperatures and slow strain rates. The two-phase NiAl-Ni, AlZr alloys containing 0.3 and 0.7 at. pct Zr had nearly identical strengths. While the two-phase alloys were stronger than the single-phase materials at all test conditions, the degree of microstructural damage in the two-phase alloys due to internal oxidation during testing appeared to increase with Zr level. Balancing the poor oxidation behavior with the consistent strength advantage of the two-phase alloys, it is concluded that optimum elevated-temperature properties could be obtained in Heusler-strengthened NiAl containing between 0.1 and 0.3 at. pct Zr.

Whittenberger, J. Daniel↗
NASA NTRS1939

The Column Strength of Two Extruded Aluminum-Alloy H-Sections

Extruded aluminum-alloy members of various cross sections are used in aircraft as compression members either singly or as stiffeners for aluminum-alloy sheet. In order to design such members, it is necessary to know their column strength or, in the case of stiffeners, the value of the double modulus, which is best obtained for practical purposes from column tests. Column tests made on two extruded h-sections are described, and column formulas and formulas for the ratio of the double modulus to Young's modulus, based on the tests, are given.

Osgood, William R↗
DOE OSTI2018

A Low-Cost Lightweight Entropic Alloy with High Strength

In this study, a series of lightweight Al–Mg system entropic alloys containing Zn, Cu, and Si were designed based on the order/disorder or entropy, and eutectic concepts. The alloys of Al{sub 58.5}Mg{sub 31.5}Zn{sub 4.5}Cu{sub 4.5}Si{sub 1}; Al{sub 63}Mg{sub 27}Zn{sub 4.5}Cu{sub 4.5}Si{sub 1}; Al{sub 66.7}Mg{sub 23.3}Zn{sub 4.5}Cu{sub 4.5}Si{sub 1}; Al{sub 80}Mg{sub 14}Zn{sub 2.7}Cu{sub 2.7}Si{sub 0.6}; Al{sub 85}Mg{sub 10.5}Zn{sub 2.025}Cu{sub 2.025}Si{sub 0.45}; and Al{sub 90}Mg{sub 7}Zn{sub 1.35}Cu{sub 1.35}Si{sub 0.3} were prepared by induction melting under a high-purity argon atmosphere and then casted into stainless steel molds. The microstructures which were tested in the as-cast state exhibited multiphases and contained apparent volume fractions of intermetallic compounds and solid solutions. Then, the compressive mechanical properties of the alloys were measured, and high fracture strengths of 577, 677, 590, 498, 814, and 794 MPa, respectively, were determined. Strong hardening phenomena were observed in the Al{sub 80}Mg{sub 14}Zn{sub 2.7}Cu{sub 2.7}Si{sub 0.6}, Al{sub 85}Mg{sub 10.5}Zn{sub 2.025}Cu{sub 2.025}Si{sub 0.45}, and Al{sub 90}Mg{sub 7}Zn{sub 1.35}Cu{sub 1.35}Si{sub 0.3} alloys at room temperature, with amazing plasticity percentages of 13.8, 24.8, and 32.7%, respectively. The property differences in the lightweight alloys were analyzed using the following parameters: the critical values of the enthalpy of mixing; atomic size differences; ratio of entropy to enthalpy; valence electron concentration (VEC); and Pauling electronegativity difference. Finally, three of the aforementioned parameters (atomic size difference, enthalpy of mixing, and Pauling electronegativity difference) were regarded in this study as the crucial rules for the lightweight multicomponent alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Structure property correlations in wet-spun textile PAN fibers for cost-effective carbon fibers applicable in H 2 storage tank manufacturing

The economic viability of high-strength carbon fibers is pivotal for their integration into Type IV compressed hydrogen storage tanks. Oak Ridge National Laboratory is advancing this objective by developing cost-effective, textile-grade polyacrylonitrile (PAN) precursor fibers through an optimized wet spinning-process to garner more microstructural control over the precursor fibers. Here, this study examines the microstructural characteristics of PAN fibers, particularly the crystalline orientation factor, and their impact on mechanical properties in both precursor and thermally converted carbon fibers (CFs). Three wet-spun PAN fibers, all having diameters of 12-13 µm but varying orientation factors were assessed. Comprehensive characterization using X-ray scattering and microscopy revealed that fibers with higher orientation factors exhibited enhanced crystallinity and optimized crystallite sizes. Mechanical testing demonstrated that the PAN fiber with the highest orientation factor achieved the greatest tensile strength (98 ksi) and modulus (1.60 Msi). Additionally optical and scanning electron microscopy confirmed smooth and defect-free surfaces across all samples. These findings indicate that manipulating spinning parameters to maximize orientation factor is more impactful in achieving high strength and modulus over factors attributed to crystallinity and crystallite sizes. Here, highest performing CFs, thermally processed in lab from textile-grade precursor averaged 558 ksi, a 10% increase over previous results.

36 MATERIALS SCIENCE↗
NASA NTRS1985

Investigation of instability, dynamic forces, and effect of dynamic loading on strength of cages for the bearings in the high pressure oxygen turbopumps for the space shuttle main engine

Experiments were performed to determine the effect of cyclic loading on bearing cage strength. A long term working tensile load of approximately 1300 N (300 lbs) was found to be the likely maximum. Higher loads caused a decrease in cage tensile strength after the 125,000 cycle testing period. Poisson's ratio in compression was found to be highly dependent upon the direction of the fiberglass plies. At room temperature the value was 0.15 with the plies and 0.68 across the plies. At -196 C (-321 F), the value with the plies was 0.20. The results of the analyses conducted have again demonstrated the critical need for improved lubrication in the high pressure oxygen turbopump bearings. Lubricant films with low shear strength and low friction coefficients promote cage stability and decrease ball/cage forces during marginal operating conditions. The analysis of the effect of combined bearing loads on ball/cage loads has identified a radial load of 3600 N (800 lbs) as the maximum for the current clearance of the balls and cage pockets. Liquid oxygen impinging on the cage in the direction of rotation was found to enhance cage stability.

Dufrane, K. F.↗
DOE OSTI2019

Elastic Precursor Decay and Spallation in Nonporous Tungsten Carbide Ceramics

To identify the possible contribution of relaxation processes to the resistance against high-rate deformation, evolution of shock-compression waves in tungsten carbide (WC) ceramics manufactured by spark-plasma sintering at a maximum compressive stress of 27 GPa is measured. Strong elastic precursor decay upon changing the thickness of the samples from 0.15 to 4 mm is revealed. At maximum shock compressive stresses twice exceeding the Hugoniot elastic limit, a decrease in the spall strength value by about 30% from its value in the elastic region is recorded.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Fabrication of Enhanced Pinch Weld Electrodes

Savannah River Site uses brazed copper / tungsten electrodes for a specialized weld referred to as a pinch weld. As part of an internally funded PDRD program, an alternative method to produce the pinch weld electrodes was sought to improve quality and to reduce the manufacturing steps. Back casting of pinch weld electrodes was selected as such a process. During preliminary testing, deformation of the electrodes was observed. A failure analysis was conducted, and the strength of the electrodes was found to be significantly less than required to enable welding of the tubes. This assessment includes compression testing metallographic analysis. The pinch weld electrodes fabricated by back casting do not meet the requirements with respect to strength. In addition, a minimum strength requirement for conventionally prepared electrodes is recommended.

42 ENGINEERING↗
NASA NTRS1991

Laboratory simulations of large scale fragmentation events

Results are presented from fragmentation experiments at elevated external pressure; the application of overpressure to a small target allows the experiment to match the lithospheric compressive stress of a larger body's interior. With increasing overpressure, the fragmentation undergoes a transition, from a material strength-dominated regime to one that is dominated by applied overpressure, analogous to the transition from strength to gravity effects. High pressure testing allows direct measurement of the energy/unit target mass requirement of catastrophic fragmentation due to compressive stresses.

Housen, Kevin R.↗
NASA NTRS1991

Effects of bolt-hole contact on bearing-bypass damage-onset strength

A combined experimental and analytical study was conducted to investigate the effects of bolt-hole contact on the bearing bypass strength of a graphite-epoxy laminate. Tests were conducted on specimens consisting of 16-ply quasi-isotropic T300/5208 laminates with a centrally located hole. Bearing loads were applied through a clearance-fit steel bolt. Damage onset strength and damage mode were determined for each test case. A finite element procedure was used to calculate the bolt-hole stresses and bolt contact for each test case. A finite element procedure was used to calculate the bolt-hole stresses and bolt contact for each measured damage-onset strength. For the tension bearing-bypass cases tested, the bolt contact half-angle was approximately 60 degrees at damage onset. For compression, the contact angle was 20 degrees as the bypass load increased. A corresponding decrease in the bearing damage onset strength was attributed to the decrease in contact angle which made the bearing loads more severe. Hole boundary stresses were also computed by superimposing stresses for separate bearing and bypass loading. Stresses at the specimen net section were accurately approximated by the superposition procedure. However, the peak bearing stresses had large errors because the bolt contact angles were not represented correctly. For compression, peak bearing stress errors of nearly 50 percent were calculated.

Crews, John H., Jr.↗
DOE OSTI2026

Correlation between microstructure and residual stress formation in friction stir welded armor steels characterized by neutron diffraction

Friction stir welding (FSW) is a solid-state joining process that minimizes the heat-affected zone (HAZ) compared with fusion-based arc welding, making it well suited for joining martensitic armor steels where hardness and ballistic resistance are critical. This study investigates residual stress formation in three defect-free FSW butt-joint configurations relevant to armored-vehicle fabrication: similar rolled homogeneous armor (RHA–RHA, Case 1), similar high-hardness armor (HHA–HHA, Case 2), and dissimilar HHA–RHA (Case 3) joints produced under temperature-controlled conditions (770 °C). Neutron diffraction was employed to quantify the magnitude and spatial distribution of residual stresses in the longitudinal, transverse, and normal directions and to correlate them with weld microstructure and hardness. Tensile residual stresses were concentrated in the softened HAZ, reaching approximately 300 MPa for Case 2 and 400 MPa for Case 1 (≈50–70 % of the base-metal yield strength; ∼581 MPa for RHA and ∼566 MPa for HHA), while compressive residual stresses dominated the stir zone. The spatial extent of tensile stresses scaled with the width of the softened HAZ, which was largest in the dissimilar HHA–RHA joint and smallest in the HHA–HHA joint. Full-width-at-half-maximum (FWHM) analysis revealed low microstrain in overtempered HAZ regions and high microstrain in the stir zone associated with severe plastic deformation and fresh martensite formation. This work demonstrates that residual stress evolution in FSW of martensitic armor steels is governed not primarily by peak temperature or thermal contraction, as inferred from fusion-welding analogies, but by the competition between transformation-induced volumetric expansion and tempering-induced stress relaxation. The relative dominance of these mechanisms is shown to depend on alloy hardenability and local thermal history, leading to more extensive HAZ softening and broader tensile stress regions in the lower-hardenability RHA steel. These findings establish a transferable mechanistic framework for optimizing solid-state joining strategies in high-strength steels and other transformation-hardening alloys beyond armor applications.

Friction stir welding↗
NASA NTRS2018

Validation of a Mesoscale Fiber Kinking Model Through Test and Analysis of Double Edge Notch Compression Specimens

Tests and analyses were conducted on a series of geometrically-scaled double edge notch compression specimens to validate the capability of the fiber-kinking model in the NASA continuum damage mechanics code for progressive damage analysis, CompDam. The tests and analyses focused on the fiber-kinking damage mechanism, which is of critical importance for predicting accurately longitudinal compression failure in carbon fiber reinforced polymer laminates. The fiber-kinking model in CompDam was augmented with a new capability to represent a hardening response once a kink band has fully formed, enabling prediction of band broadening. Correlation of the test and analysis results showed agreement in stiffness and strength with less than 10% error. The analysis predicts the same sequence of events leading to ultimate failure that was found in the test. The overall excellent correlation in terms of stiffness, strength, and failure process validates the capability of the model for predicting longitudinal compression failure in notched laminates with cross-ply layups.

Bergan, Andrew C.↗