Buckling of axially compressed cylinders with eccentric longitudinal stiffeners.
Longitudinal stiffeners eccentricity /one- sidedness/ effect on buckling strength of axially compressed cylinders
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Results for “COMPRESSION STRENGTH”
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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The Pack Method for Compressive Tests of Thin Specimens of Materials Used in Thin-Wall Structures
The strength of modern lightweight thin-wall structures is generally limited by the strength of the compression members. An adequate design of these members requires a knowledge of the compressive stress-strain graph of the thin-wall material. The "pack" method was developed at the National Bureau of Standards with the support of the National Advisory Committee for Aeronautics to make possible a determination of compressive stress-strain graphs for such material. In the pack test an odd number of specimens are assembled into a relatively stable pack, like a "pack of cards." Additional lateral stability is obtained from lateral supports between the external sheet faces of the pack and outside reactions. The tests seems adequate for many problems in structural research.
Aitchison, C S↗
Effect of grain size on iron-boride nanoglasses
Metallic nanoglasses are made of amorphous grains that are separated by lower-density amorphous boundaries, which have been proposed to enhance plasticity through the deflection of cracks and shear bands at interfaces. It has been difficult to experimentally control grain size and interfacial structure to understand their roles in plastic deformation. Here, we fabricate bulk nanoglasses via compaction and sintering of colloidally synthesized amorphous iron-boride nanoparticles. These nanoglasses have amorphous grains with diameters from 116nm to 576nm and were tested using nanoindentation and micropillar compressions. The nanoglass with a grain size of 576 nm shows the highest elastic modulus and hardness of 101 GPa and 7.4GPa, respectively. Transmission electron microscopy reveals that nanocrystals form within the nanoglasses during compaction. Higher nanocrystal density correlates with higher nanoparticle crystallization enthalpy, an increase in plasticity, and a decrease in yield strength. Plastic strain of 5.0%, yield strength of 3.8GPa, and ultimate compressive strength of 2.7–3.8GPa were achieved. Here we show that the compaction of colloidal metallic glass nanoparticles results in robust bulk samples, with mechanical properties similar to that of other iron-based bulk metallic glasses.
36 MATERIALS SCIENCE↗
Finding evidence for inflation and the origin of galactic magnetic fields with CMB surveys
The origin of the μG magnetic fields observed in galaxies is unknown. One promising scenario is that magnetic fields generated during inflation, larger than 0.1 nG on Mpc scales, were adiabatically compressed to μG strengths in galaxies during structure formation. Thus, detecting a scale-invariant primordial magnetic field (PMF) above 0.1 nG on Mpc scales just after recombination would indicate an inflationary origin of galactic magnetic fields. Furthermore, this would also provide compelling evidence that inflation occurred since only an inflationary mechanism could generate such a strong, scale-invariant magnetic field on Mpc scales. In contrast, constraining the scale-invariant PMF strength to be below 0.1 nG would imply an inflationary scenario is not the primary origin, since such weak PMFs cannot be amplified enough via adiabatic compression to produce the strength of the galactic fields we observe today. We find that measurements of anisotropic birefringence by future CMB surveys will be able to improve the sensitivity to Mpc-scale inflationary PMFs by an order of magnitude, and, in particular, that CMB-HD would lower the upper bound to 0.072 nG at the 95% C.L., which is below the critical 0.1 nG threshold for ruling out a purely inflationary origin. If inflationary PMFs exist, we find that a CMB-HD survey would be able to detect them with about 3σ significance or higher, providing evidence for inflation itself.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Improvement microstructural and damage characterization of ceramic composites Y{sub 2}O{sub 3} – V{sub 2}O{sub 5} with MgO nano particles
Compacted samples of Y{sub 2}O{sub 3}-V{sub 2}O{sub 5} – MgO Nano – particles wt. % sintered at different sintering temperature (700, 900, 1100, 1300) ) C° for 2 hours under static air were investigated by x-ray diffraction and differential thermal analysis(DTA), to identify the phase present .Microstructure examination achieved by scanning electron microscopy .Sintered density and porosity were measured for all sintered samples .Compression was tested too and the Brake down voltage and dielectric strength were measure for all sintered samples .The clear improvement were noticed in both microstructure and damage characterization respectively after existing the MgO Nano-particles, by increasing in about 30% in sintered density and 25% for the compressive strength .The improvement also noticed on both brake down voltage and dielectric strength.
36 MATERIALS SCIENCE↗
Effects of partial interlaminar bonding on impact resistance and loaded-hole behavior of graphite/epoxy quasi-isotropic laminates
A partial-bonding interlaminar toughening concept was evaluated for resistance to impact and for behavior of a loaded hole. Perforated Mylar sheets were interleaved between all 24 plies of a graphite/epoxy quasi-isotropic lay-up. Specimens were impacted by aluminum spheres while under tensile or compressive loads. Impact-failure thresholds and residual strengths were obtained. Loaded-hole specimens were tested in three configurations that were critical in bearing, shear, or tension. Partial bonding reduced the tensile and compressive strengths of undamaged specimens by about one-third. For impact, partial bonding did not change the threshold for impact failure under tensile preload. However, under compressive preload, partial bonding caused serious degradation of impact resistance. Partial bonding reduced the maximum load-carrying capacity of all three types of loaded-hole specimens. Overall, partial bonding degraded both impact resistance and bearing strength of holes.
Illg, W.↗
Pressure core analysis of geomechanical and fluid flow properties of seals associated with gas hydrate-bearing reservoirs in the Krishna-Godavari Basin, offshore India
Physical properties of the sediment directly overlying a gas hydrate reservoir provide important controls on the effectiveness of depressurizing that reservoir to extract methane from gas hydrate as an energy resource. The permeability of overlying sediment determines if a gas hydrate reservoir’s upper contact will provide an effective seal that enables efficient reservoir depressurization. Compressibility, stiffness and strength indicate how overlying sediment will deform as the in situ stress changes during production, providing engineering data for well designs. Assessing these properties requires minimally-disturbed sediment. India’s National Gas Hydrates Program Expedition 2 (NGHP-02) provided an opportunity to study these seal sediment properties, reducing disturbance from gas exsolution and bubble growth by collecting a pressure core from the seal sediment just above the primary gas hydrate reservoir at Site NGHP-02-08 in Area C of the Krishna-Godavari Basin. The effective stress chamber (ESC) and the direct shear chamber (DSC) devices in the suite of Pressure Core Characterization Tools (PCCTs) were used to measure permeability, compressibility, stiffness and shear strength at the in situ vertical stress. Geotechnical properties of the predominantly fine-grained seal layer at in situ vertical stress are in typical clay sediment ranges, with low measured permeability (0.02 mD), high compressibility (C c = 0.26 – 0.33) and low shear strength (404 kPa). Though pressure and temperature were maintained throughout the collection and measurement process to stabilize gas hydrate, the lack of effective stress in the pressure core storage chamber and the chamber pressurization with methane-free water caused core expansion and gas hydrate in a thin coarser-grained layer to dissolve. The PCCTs can reapply in situ stress with incremental loading steps during a consolidation test to account for sediment compaction. Lastly, gas hydrate dissolution can be limited by storing cores just above freezing temperatures, and by using solid spacers to reduce the storage chamber’s free volume.
09 BIOMASS FUELS↗
Strength and structural phase transitions of gadolinium at high pressure from radial X-ray diffraction
Lattice strength and structural phase transitions of gadolinium (Gd) were determined under nonhydrostatic compression up to 55 GPa using an angle-dispersive radial x-ray diffraction technique in a diamond-anvil cell at room temperature. Three new phases of fcc structure, dfcc structure, and new monoclinic structure were observed at 25 GPa, 34 GPa, and 53 GPa, respectively. The radial x-ray diffraction data yield a bulk modulus K{sub 0} = 36(1) GPa with its pressure derivate K{sub 0}′ = 3.8(1) at the azimuthal angle between the diamond cell loading axis and the diffraction plane normal and diffraction plane ψ = 54.7°. With K{sub 0}′ fixed at 4, the derived K{sub 0} is 34(1) GPa. In addition, analysis of diffraction data with lattice strain theory indicates that the ratio of differential stress to shear modulus (t/G) ranges from 0.011 to 0.014 at pressures of 12–55 GPa. Together with estimated high-pressure shear moduli, our results show that Gd can support a maximum differential stress of 0.41 GPa, while it starts to yield to plastic deformation at 16 GPa under uniaxial compression. The yield strength of Gd remains approximately a constant with increasing pressure, and reaches 0.46 GPa at 55 GPa.
36 MATERIALS SCIENCE↗
Anisotropy, size, and aspect ratio effects on micropillar compression of Al-SiC nanolaminate composites
Metal-ceramic nanolaminate composites show promise as high strength and toughness materials. Micropillar compression was used to characterize the mechanical behavior of AlSiC multilayers in different orientations including loading at 0°, 45° and 90° with respect to the direction of the layers. The 0° orientation showed the highest strength while the 45° orientation showed the lowest strength. Each orientation showed unique deformation behavior. Effects of pillar size and aspect ratio were also studied. Higher compressive strengths were observed in smaller pillars for all orientations. This effect was shown to be due to a lower probability of flaws using Weibull statistics. Additionally, changes in the aspect ratio was shown to have no significant effect on the behavior except an increase in the strain to failure in the 0° orientation. In conclusion, finite element analysis (FEA) was used to simulate and understand the effect of these parameters on the deformation behavior.
36 MATERIALS SCIENCE↗
Damage Characteristics and Residual Strength of Composite Sandwich Panels Impacted with and Without Compression Loading
The results of an experimental study of the impact damage characteristics and residual strength of composite sandwich panels impacted with and without a compression loading are presented. Results of impact damage screening tests conducted to identify the impact-energy levels at which damage initiates and at which barely visible impact damage occurs in the impacted facesheet are discussed. Parametric effects studied in these tests include the impactor diameter, dropped-weight versus airgun-launched impactors, and the effect of the location of the impact site with respect to the panel boundaries. Residual strength results of panels tested in compression after impact are presented and compared with results of panels that are subjected to a compressive preload prior to being impacted.
McGowan, David M.↗
Concepts for improving the damage tolerance of composite compression panels
The residual strength of specimens with damage and the sensitivity to damage while subjected to an applied inplane compression load were determined for flatplate specimens and blade-stiffened panels. The results suggest that matrix materials that fail by delamination have the lowest damage tolerance capability. Alternate matrix materials or laminates which are transversely reinforced suppress the delamination mode of failure and change the failure mode to transverse shear crippling which occurs at a higher strain value. Several damage-tolerant blade-stiffened panel design concepts are evaluated. Structural efficiency studies conducted show only small mass penalties may result from incorporating these damage-tolerant features in panel design. The implication of test results on the design of aircraft structures was examined with respect to FAR requirements.
Rhodes, M. D.↗
Micromechanics of compression failures in open hole composite laminates
The high strength-to-weight ratio of composite materials is ideally suited for aerospace applications where they already are used in commercial and military aircraft secondary structures and will soon be used for heavily loaded primary structures. One area impeding the widespread application of composites is their inherent weakness in compressive strength when compared to the tensile properties of the same material. Furthermore, these airframe designs typically contain many bolted or riveted joints, as well as electrical and hydraulic control lines. These applications produce areas of stress concentration, and thus, further complicate the compression failure problem. Open hole compression failures which represent a typical failure mode for composite materials are addressed.
Guynn, E. Gail↗
Fabrication and Testing of Durable Redundant and Fluted-Core Joints for Composite Sandwich Structures
The development of durable bonded joint technology for assembling composite structures is an essential component of future space technologies. While NASA is working toward providing an entirely new capability for human space exploration beyond low Earth orbit, the objective of this project is to design, fabricate, analyze, and test a NASA patented durable redundant joint (DRJ) and a NASA/Boeing co-designed fluted-core joint (FCJ). The potential applications include a wide range of sandwich structures for NASA's future launch vehicles. Three types of joints were studied -- splice joint (SJ, as baseline), DRJ, and FCJ. Tests included tension, after-impact tension, and compression. Teflon strips were used at the joint area to increase failure strength by shifting stress concentration to a less sensitive area. Test results were compared to those of pristine coupons fabricated utilizing the same methods. Tensile test results indicated that the DRJ design was stiffer, stronger, and more impact resistant than other designs. The drawbacks of the DRJ design were extra mass and complex fabrication processes. The FCJ was lighter than the DRJ but less impact resistant. With barely visible but detectable impact damages, all three joints showed no sign of tensile strength reduction. No compression test was conducted on any impact-damaged sample due to limited scope and resource. Failure modes and damage propagation were also studied to support progressive damage modeling of the SJ and the DRJ.
Lin, Shih-Yung↗
Enhanced densification strength and molecular mechanisms in shock compressed porous silicon.
Abstract not provided.
Lane, J. Matthew↗
Enhanced densification strength and molecular mechanisms in shock compressed porous silicon.
Abstract not provided.
Lane, J. Matthew↗
Optimum mass-strength analysis for orthotropic ring-stiffened cylinders under axial compression
An analysis was developed to calculate the minimum mass-strength curve for an orthotropic cylinder subjected to axial compressive loading. The analysis, which includes the effects of ring and stringer eccentricities, is in a general form so that various cylinder wall and stiffener geometries can be considered. Several different ring-stiffened orthotropic configurations were studied. The minimum mass-strength curves and the dimensions associated with these curves are presented for (in order of decreasing efficiency) a tubular double bead, a nonsymmetric double bead, a Z-stiffened skin, and a trapezoidal corrugation. A comparison of efficiencies of the configurations shows a tubular element cylinder to be more efficient than a 3-percent core-density honeycomb-sandwich cylinder. It was found that for an optimized Z-stiffened skin, the location of the Z-stiffeners (internal or external) made a negligible difference in efficiency.
Shideler, J. L.↗
Strength Tests of Thin-Walled Duralumin Cylinders in Compression
This report is the second of a series presenting the results of strength tests of thin-walled duralumin cylinders and truncated cones of circular and elliptic section. It contains the results obtained from compression tests on 45 thin-walled duralumin cylinders of circular section with ends clamped to rigid bulkheads. In addition to the tests on duralumin cylinders, there are included the results of numerous tests on rubber, celluloid, steel, and brass cylinders obtained from various sources.
Lundquist, Eugene E↗
Subsatellite measurements of the lunar magnetic field
The Apollo 15 subsatellite magnetometer data have been used to map the lunar magnetic field over a narrow band of the lunar surface. Within this band the magnetic field is generally stronger and more variable over the farside highlands than the nearside maria. The correspondence between the strong variable lunar field regions and the source regions for limb compressions suggests that limb compressions arise as the result of the deflection of the solar wind just upstream of the terminator by the lunar magnetic field. Using this apparent relationship between field strength and limb compression source regions, it is deduced that the field strength in the northern farside highlands is not as strong as in the southern hemisphere at similar longitudes. Simultaneous measurements of the interplanetary magnetic field obtained by Explorer 35 and the Apollo 15 subsatellite above the dayside hemisphere are essentially identical. Thus, both instruments are measuring the undisturbed interplanetary field.
Russell, C. T.↗