Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “softening”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Alloy hardening and softening in binary molybdenum alloys as related to electron concentration.

Determination of the effects of alloy additions of Hf, Ta, W, Re, Os, Ir, and Pt on the hardness of Mo. Special emphasis was placed on alloy softening in these binary Mo alloys. A modified microhardness test unit permitted hardness determinations at homologous temperatures ranging from 0.02 to 0.15, where alloy softening normally occurs in bcc alloys. Results showed that alloy softening was produced by those elements having an excess of s + d electrons compared to Mo while those elements having an equal number or fewer s + d electrons than Mo failed to produce alloy softening. The magnitude of the softening and the amount of solute element at the hardness minimum diminished rapidly with increasing test temperature. At solute concentrations where alloy softening was observed, the temperature sensitivity of hardness was lowered. For solute elements having an excess of s + d electrons or fewer s + d electrons than Mo, alloy softening and alloy hardening can be correlated with the difference in number of s + d electrons of the solute element and Mo.

Stephens, J. R.↗
NASA NTRS1976

Alloy softening in binary iron solid solutions

An investigation was conducted to determine softening and hardening behavior in 19 binary iron-alloy systems. Microhardness tests were conducted at four temperatures in the range 77 to 411 K. Alloy softening was exhibited by 17 of the 19 alloy systems. Alloy softening observed in 15 of the alloy systems was attributed to an intrinsic mechanism, believed to be lowering of the Peierls (lattice friction) stress. Softening and hardening rates could be correlated with the atomic radius ratio of solute to iron. Softening observed in two other systems was attributed to an extrinsic mechanism, believed to be associated with scavenging of interstitial impurities.

Stephens, J. R.↗
NASA NTRS1992

The topography of impact craters in 'softened' terrain on Mars

The technique of photoclinometry is applied here to Viking orbiter images of Mars in order to derive topographic profiles across Martian craters on both softened and unsoftened terrain. The results demonstrate that craters on the two kinds of terrain are in fact topographically distinct. Both simple and complex softened craters are characterized by more convex-upward crater walls than are unsoftened craters, and both simple and complex softened craters have rounder crater rims. Softened complex craters have modestly smaller crater depths than unsoftened complex craters. Both the rim heights and bowl depths are reduced, with the rim heights reduced more. Softened simple craters have much smaller crater depths than unsoftened simple craters. Both the rim heights and bowl depths are reduced, with the bowl depths reduced more.

Jankowski, David G.↗
NASA NTRS1972

Alloy softening in binary molybdenum alloys

An investigation was conducted to determine the effects of alloy additions of Hf, Ta, W, Re, Os, Ir, and Pt on the hardness of Mo. Special emphasis was placed on alloy softening in these binary Mo alloys. Results showed that alloy softening was produced by those elements having an excess of s+d electrons compared to Mo, while those elements having an equal number or fewer s+d electrons than Mo failed to produce alloy softening. Alloy softening and hardening can be correlated with the difference in number of s+d electrons of the solute element and Mo.

Stephens, J. R.↗
NASA NTRS1972

Alloy hardening and softening in binary molybdenum alloys as related to electron concentration

An investigation was conducted to determine the effects of alloy additions of hafnium, tantalum, tungsten, rhenium, osmium, iridium, and platinum on hardness of molybdenum. Special emphasis was placed on alloy softening in these binary molybdenum alloys. Results showed that alloy softening was produced by those elements having an excess of s+d electrons compared to molybdenum, while those elements having an equal number or fewer s+d electrons that molybdenum failed to produce alloy softening. Alloy softening and alloy hardening can be correlated with the difference in number of s+d electrons of the solute element and molybdenum.

Stephens, J. R.↗
NASA NTRS1972

Alloy softening in binary molybdenum alloys.

An investigation was conducted to determine the effects of alloy additions of Hf, Ta, W, Re, Os, Ir, and Pt on the hardness of Mo. Special emphasis was placed on alloy softening in these binary Mo alloys. Results showed that alloys softening was produced by those elements having an excess of s+d electrons compared to Mo, while those elements having an equal number or fewer s+d electrons than Mo failed to produce alloy softening. Alloy softening and alloy hardening can be correlated with the difference in number of s+d electrons of the solute element and Mo.

Stephens, J. R.↗
NASA NTRS1975

The role of electron concentration in softening and hardening of ternary molybdenum alloys

An investigation was conducted to determine softening and hardening behavior in ternary Mo alloys and to correlate these effects with electron concentration. Results showed that the hardness behavior of ternary Mo alloys could be correlated with results anticipated from binary data based upon expressions involving the number of s + d electrons contributed by the solute elements. It was further shown that combining alloying elements at concentrations that produce the maximum amount of softening in Mo does not result in additive softening in ternary Mo alloys. Once a critical electron concentration is exceeded, only alloy hardening is observed. A comparison of hardness behavior with literature data on Hall coefficient and magnetic susceptibility for W-Re alloys showed that hardness minima occur at Re concentrations where minima are observed for the physical property measurements. These observations, and the correlation of hardness with electron concentration, support the hypothesis that alloy softening in Group VI metals is an intrinsic characteristic of these metals and that electron concentration plays the dominant role in controlling hardness.

Stephens, J. R.↗
NASA NTRS1976

Alloy softening in binary iron solid solutions

An experimental study was conducted to determine whether alloy softening in Fe alloys is dependent on electron concentration and to provide a direct comparison of alloy softening and hardening in several binary Fe alloy systems having the same processing history. Alloy additions to Fe included the elements in the Periods 4-6 and the Groups IV-VIII with the exception of technetium. A total of 19 alloy systems was investigated, and hardness testing was the primary means of evaluation. Testing was carried out at four temperatures over a homologous temperature range of 0.043-0.227 times the absolute melting temperature of unalloyed Fe. Major conclusions are that the atomic radius ratio of solute-to-Fe is the key factor in controlling low-temperature hardness of the binary Fe alloys and that alloy softening rates at 77 K and alloy hardening rates at 411 K are correlated with this atomic radius ratio for 15 of the binary alloy systems. Mechanisms of alloy softening and hardening are proposed.

Stephens, J. R.↗
NASA NTRS1999

Boom Softening and Nacelle Integration on an Arrow-Wing High-Speed Civil Transport Concept

During the last cycle of concept design and wind-tunnel testing, the goal of the low-boom- shaped HSCT concepts (the B-935, the LB-16, and the LB- 1 8) was to meet mission requirements and generate shaped, ground-level pressure signatures with nose shock strengths of 1.0 psf or less. The wind-tunnel tests of these concepts produced results that were partially successful and encouraging although not fully up to expectations. In spite of this, however, these conceptual designs were overly optimistic and not acceptable because: the wing planforms had excessive area; the wing structural aspect ratio was too high; one concept had aft-fuselage rather than under-the-wing engines; and the gross takeoff weights were unrealistically low because of engines that were early, high-tech versions of later, revised, more-realistic engines. The need for reducing the ground-level overpressure shock strengths still existed; a need to be met within more restrictive guidelines of mission performance and gross takeoff weight limitations. Therefore, it was decided that the next conceptual design cycle would focus on decreased nose shock strengths, "boom softening," in the signatures of the Boeing and the McDonnell Douglas baseline concepts rather than low-boom concepts with shaped-signature designs. Overly-optimistic results were not the only problem with these low-sonic-boom concepts. Papers given at the 1994 Sonic-Boom Workshop had demonstrated that the problem of successful nacelle integration on HSCT concepts had only been partially solved. Wind-tunnel pressure signature data, from the HSCT-11B (a.k.a. the LB-18) wind-tunnel model, showed that the Langley HSCT design and analysis method had been successful in reducing the nacelle-volume disturbances in the flow field. This was due.to the engine nacelles mounted behind the wing trailing-edge on the aft fuselage so that no nacelle-wing interference-lift flow-field disturbances were generated. While acceptable from a sonic-boom research point of view, this concept was unacceptable from several practical and structural considerations. Preliminary wind-tunnel pressure signature data from the LB-16 wind-tunnel model, which had the engine nacelles mounted under the wings (the usual location), indicated that the application of the Langley nacelle-integration method had been only partially successful in the reduction of the nacelle-volume with nacelle-wing interference-lift pressure disturbances. So, "boom softening" had to also address the task of successful integration of the engine nacelles, with the engines in the required under-the-wing location. Unless this problem was solved, low-sonic-boom and low-drag modifications to the wing planform, the airfoil shape, and the fuselage longitudinal area distribution could be nullified if the nacelle disturbances added increments to the nose-shock strengths that were removed through component tailoring. In this paper, an arrow-wing boom-softened HSC7 concept which incorporated modifications to a baseline McDonnell Douglas concept is discussed. The analysis of the concept's characteristics will include estimates of weight, center of gravity, takeoff field length, mission range, and predictions of its ground-level sonic-boom pressure signature. Additional modifications which enhanced the softened-boom performance of this concept are also described as well as estimates of the performance penalties induced by these modifications.

Mack, Robert J.↗
NASA NTRS1999

Langley's Computational Efforts in Sonic-Boom Softening of the Boeing HSCT

NASA Langley's computational efforts in the sonic-boom softening of the Boeing high-speed civil transport are discussed in this paper. In these efforts, an optimization process using a higher order Euler method for analysis was employed to reduce the sonic boom of a baseline configuration through fuselage camber and wing dihedral modifications. Fuselage modifications did not provide any improvements, but the dihedral modifications were shown to be an important tool for the softening process. The study also included aerodynamic and sonic-boom analyses of the baseline and some of the proposed "softened" configurations. Comparisons of two Euler methodologies and two propagation programs for sonic-boom predictions are also discussed in the present paper.

Fouladi, Kamran↗
NASA NTRS2004

Searching for Terrain Softening near Mercury's North Pole

In 1999, following the initial discovery of radar bright craters near both poles of Mercury measured the depth-todiameter (d/D) ratios of 170 impact craters in Mariner 10 images covering four different regions on Mercury s surface. Rapid softening of crater structure, indicated by lower d/D ratios, could indicate the possibility of subsurface water ice in Mercury's terrain originating from an internal source in the planet. Their study included 3 specific radar bright craters suggested to contain ice. They concluded that no terrain softening was apparent, and a rapidly emplaced exogenic water source was the most likely source for the proposed ice in these craters. Recent radar observations of the Mercurian North pole have pinpointed many additional radar bright areas with a resolution 10x better than previous radar measurements, and which correlate with craters imaged by Mariner 10. These craters are correlated with regions that are permanently shaded from direct sunlight, and are consistent with observations of clean water ice. We have expanded the initial study by Barlow et al. to include d/D measurements of 12 craters newly identified as radar bright at latitudes poleward of +80o. The radar reflectivity resemblances to Mars south polar cap and echoes from three icy Galilean satellites suggest that these craters too may have polar ice on Mercury. The effect of subsurface H20 on impact craters is a decrease in its d/D ratio, and softening of crater rims over a period of time. The study of Barlow et al., focused on determining the d/D ratios of 170 impact craters in the Borealis (north polar), Tolstoj (equatorial), Kuiper (equatorial), and Bach (south polar) quadrangles. This work focuses on the newly discovered radar bright craters, investigating their d/D ratios as an expansion of the earlier work..We compare our results to the statistical results from Barlow et al. here. With the upcoming Messenger spacecraft mission to Mercury, this is an especially timely study whose result could potentially help the Messenger team as they develop a mission strategy.

Cobian, P. S.↗
NASA NTRS1979

Low-temperature softening in body-centered cubic alloys

In the low-temperature range, bcc alloys exhibit a lower stress-temperature dependence than the pure base metals. This effect often leads to a phenomenon that is called 'alloy softening': at low temperatures, the yield stress of an alloy may be lower than that of the base metal. Various theories are reviewed; the most promising are based either on extrinsic or intrinsic models of low-temperature deformation. Some other aspects of alloy softening are discussed, among them the effects on the ductile-brittle transition temperature.

Pink, E.↗
NASA NTRSDate not supplied

Softening the Gap between Wöhler and Paris – New Approaches for Fatigue Analysis –

Fatigue analysis tools can vary across industries. For example, automotive engineers often use the Wöhler (S-N) approach to design for safe-life, while aerospace engineers prioritize damage tolerance and inspection intervals, relying instead on crack growth models such as Paris’ law. Although both approaches may deal with the control of cracks in similar materials, their analysis tools and material characterizations are fundamentally distinct. This divide mirrors the classic split between stress-based strength analysis and linear elastic fracture mechanics. However, modern nonlinear models that incorporate material softening, such as cohesive laws, blur this boundary and capture fracture behaviors across scales. This presentation describes the CF23 fatigue model, which uses cohesive softening to link S-N crack initiation with crack propagation rates. CF23 spans the full fatigue spectrum, from initial propagation transients to steady-state growth and threshold conditions, offering a unified framework that bridges Wöhler and Paris-based methodologies. Example applications include fatigue crack propagation transients in adhesive interfaces and skin/stiffener separation.

cohesive elements↗
NASA NTRS2014

A Technique for Mapping Characteristic Lengths to Preserve Energy Dissipated via Strain Softening in a Multiscale Analysis

It is often advantageous to account for the microstructure of the material directly using multiscale modeling. For computational tractability, an idealized repeating unit cell (RUC) is used to capture all of the pertinent features of the microstructure. Typically, the RUC is dimensionless and depends only on the relative volume fractions of the different phases in the material. This works well for non-linear and inelastic behavior exhibiting a positive-definite constitutive response. Although, once the material exhibits strain softening, or localization, a mesh objective failure theories, such as smeared fracture theories, nodal and element enrichment theories (XFEM), cohesive elements or virtual crack closure technique (VCCT), can be utilized at the microscale, but the dimensions of the RUC must then be defined. One major challenge in multiscale progressive damage modeling is relating the characteristic lengths across the scales in order to preserve the energy that is dissipated via localization at the microscale. If there is no effort to relate the size of the macroscale element to the microscale RUC, then the energy that is dissipated will remain mesh dependent at the macroscale, even if it is regularized at the microscale. Here, a technique for mapping characteristic lengths across the scales is proposed. The RUC will be modeled using the generalized method of cells (GMC) micromechanics theory, and local failure in the matrix constituent subcells will be modeled using the crack band theory. The subcell characteristic lengths used in the crack band calculations will be mapped to the macroscale finite element in order to regularize the local energy in a manner consistent with the global length scale. Examples will be provided with and without the regularization, and they will be compared to a baseline case where the size and shape of the element and RUC are coincident (ensuring energy is preserved across the scales).

softening↗
NASA NTRS1975

Role of electron concentration in softening and hardening of ternary molybdenum alloys

Effects of various combinations of hafnium, tantalum, rhenium, osmium, iridium, and platinum in ternary molybdenum alloys on alloy softening and hardening were determined. Hardness tests were conducted at four test temperatures over the temperature range 77 to 411 K. Results showed that hardness data for ternary molybdenum alloys could be correlated with anticipated results from binary data based upon expressions involving the number of s and d electrons contributed by the solute elements. The correlation indicated that electron concentration plays a dominant role in controlling the hardness of ternary molybdenum alloys.

Stephens, J. R.↗
NASA NTRS1981

Cloud fluid compression and softening in spiral arms and the formation of giant molecular cloud complexes

With regard to the galactodynamics of the cloudy interstellar medium, the paper considers the response of such a gas to a forcing potential in the tight-winding density wave theory. The cloud fluid is treated in the hydrodynamic limit with an equation of state which softens at high densities. It is shown that in the inner regions of the galaxy, cooling of the cloud fluid in the arms can result in gravitational instability and the formation of large bound complexes of clouds which are identified with the giant molecular clouds (GMCs). Masses, dimensions, distributions, and scale heights of the GMCs are predicted by the theory. It is suggested that the interstellar gas density in the disk is regulated by the gravitational instability mechanism in the arms which siphons material into star formation. Implications for the evolution of individual GMCs and for galactic morphology are discussed.

Cowie, L. L.↗