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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Room temperature tensile ductility in polycrystalline B2 Ni-30Al-20Fe

A room-temperature tensile elongation of about 2.5 percent, where the only slip vector observed was the 100, has been determined for a double-extruded B2 Ni-30Al-20Fe alloy consisting of recrystallized equiaxed grains about 25 microns in diameter; these results suggest that 100-slip does not preclude limited ductility in polycrystalline B2 alloys in tension at low temperatures. A suppression of ordering through resort to rapid solidification, in other words, is not necessary for ductility, since the cast and as-extruded alloy presently examined is ordered.

Guha, Sumit↗
NASA NTRS1989

Observations on the brittle to ductile transition temperatures of B2 nickel aluminides with and without zirconium

The effect of a zirconium addition (0.05 at. pct) to a stoichiometric NiAl alloy on the brittle-to-ductile transition temperature (BDTT) of this alloy was investigated. Constant velocity tensile tests were conducted to fracture between 300 and 1100 K under initial strain rate 0.00014/sec, and the true stress and true strain values were determined from plots of load vs time after subtracting the elastic strain. The inelastic strain was measured under a traveling microscope. Microstructural characterization of as-extruded and fractured specimens was carried out by SEM and TEM. It was found that, while the addition of 0.05 at. pct Zr strengthened the NiAl alloy, it increased its BDTT; this shift in the BDTT could not be attributed either to variations in grain size or to impurity contents. Little or no room-temperature ductility was observed for either alloy.

Raj, S. V.↗
NASA NTRS1991

Lithospheric extension near Lake Mead, Nevada - A model for ductile flow in the lower crust

Small variations in gravity anomalies and topographic elevation observed in areas that have undergone highly variable amounts of upper crustal thinning can be satisfactorily explained by ductile flow of lower crustal material under the proper conditions. The boundary between the unextended Colorado Plateau and a strongly extended domain in the Basin and Range Province in the Lake Mead (Nevada) region is examined. Finite element modeling of Newtonian flow and power law creep shows that flow over the length scale of the eastern Basin and Range (500) km or more) corresponding to upper crustal extension by a factor of 1.4-3 over 10 million years requires effective viscosities less than 10 to the 18th - 10 to the 20th Pa s for ductile channels 10-25 km thick. Modeling suggests that these effective viscosities may be sustained by lower crustal material deforming at laboratory-derived power law creep rates. The longer-scale flow may require elevated crustal temperatures (more than 700 C), depending on the composition and material properties assumed. Under the boundary conditions assumed in this study the linear viscous flow models yield a satisfactory approximation to deformation by power law creep. This work suggests that flow in the lower crust may be a viable mechanism for producing small variations in total crustal thickness between strongly extended and less extended regions, and thereby explaining the relative uniformity in gravity and topography between such regions.

Kruse, Sarah↗
NASA NTRS1990

The potential for ductility enhancement from surface and interface dislocation sources in NiAl

Limited ductility and toughness of NiAl and related aluminides near room temperature pose major problems in their potential application as structural materials. An analysis of these problems is presented as part of a review of the flow and fracture behavior of binary NiAl. Following this discussion is a demonstration that conditions of elastic and plastic constraint associated with phase boundaries afforded by surface films, internal lamellae, or precipitates may introduce sufficient densities of mobile dislocations to enhance the ductility of NiAl-based materials by significant amounts. Examples of this behavior are presented for several model materials, including 001- and 123-oriented single crystals of oxide-coated NiAl, directionally solidified beta-gamma-prime (Ni70Al30) and beta-gamma (Ni50Fe30Al20) in situ composites, and several NiAl/precipitate systems. The nature of the resulting dislocation substructures and the effects of several materials variables are described.

Noebe, R. D.↗
NASA NTRS1990

Ductility enhancement from interface dislocation sources in a directionally solidified beta + gamma + gamma-prime Ni-Fe-Al composite alloy

A directionally solidified beta + gamma + gamma-prime Ni-Fe-Al in situ composite alloy of composition Ni50Fe30Al20 has been used to investigate the effect of a plastically soft second phase on the mechanical behavior of a B2 ordered intermetallic alloy. This material exhibits extensive plasticity during compressive deformation at room temperature and fails in shear with extensive gamma + gamma-prime lamellar or rod pullout. The material also exhibits about 10 percent tensile elongation to fracture at room temperature, with final fracture that includes substantial necking of the gamma + gamma-prime lamellae or rods. Observation of slip lines and dislocation substructures discloses that the normally brittle beta matrix undergoes extensive plasticity in order to deform compatibly with the more ductile gamma phase. The plasticity of the beta matrix is accomplished by the generation of glissile dislocations into the beta matrix from the beta/gamma interface region and is enhanced because of a favorable beta-gamma orientation relationship for slip transfer. Ductility enhancement from interface-generated mobile dislocations generated from beta-gamma interfaces is compared to that observed in film-coated beta-NiAl single crystals and FeAl polycrystals.

Larsen, M.↗
NASA NTRS1993

Deformation mechanisms of NiAl cyclicly deformed near the brittle-to-ductile transition temperature

The intermetallic compound NiAl is one of many advanced materials which is being scrutinized for possible use in high temperature, structural applications. Stoichiometric NiAl has a high melting temperature, excellent oxidation resistance, and good thermal conductivity. Past research has concentrated on improving monotonic properties. The encouraging results obtained on binary and micro-alloyed NiAl over the past ten years have led to the broadening of NiAl experimental programs. The purpose of this research project was to determine the low cycle fatigue properties and dislocation mechanisms of stoichiometric NiAl at temperatures near the monotonic brittle-to-ductile transition. The fatigue properties were found to change only slightly in the temperature range of 600 to 700 K; a temperature range over which monotonic ductility and fracture strength increase markedly. The shape of the cyclic hardening curves coincided with the changes observed in the dislocation structures. The evolution of dislocation structures did not appear to change with temperature.

Cullers, Cheryl L.↗
NASA NTRS1991

Transverse ductility of metal matrix composites

The role of the fiber matrix interface bond on the transverse ductility of continuous fiber reinforced composites has been investigated. Two specific systems have been considered: an Aluminum alloy matrix reinforced by Alumina fibers, characterized by a strong interface and a Titanium alloy reinforced by coated Silicon Carbide fibers, characterized by a weak interface. A micro-mechanical study indicates that the bond condition has a significant effect on the state of stress in the matrix which in turn dictates the available matrix ductility. The micro-mechanical predictions are in good agreement with the experimental results for the two systems.

Gunawardena, S. R.↗
NASA NTRS1995

An investigation of the loss of ductility in hydrogen charged beta-Ti alloys

The high strength, low density, and good corrosion resistance of Ti-based alloys make them candidate materials for a number of applications in the aerospace industry. A major limitation in the use of these alloys in the advanced hypersonic flight vehicle program is their susceptibility to hydrogen embrittlement. This study focuses on the hydrogen sensitivity of TIMETAL 21S beta-Ti alloy. The material received was in the form of grip-ends of failed tensile test samples which had been exposed to different charging conditions (combinations of hydrogen pressure and temperature). The samples received, the charging conditions, and their fracture mode are discussed. It can be seen that the fracture behavior changes from ductile to brittle with increasing hydrogen content, but the transition in behavior occurs for a small increase in hydrogen concentration. The aim of this program was to assess the microstructural differences between the ductile and brittle alloys to ascertain the embrittlement mechanism. A range of tools which included x-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used.

Robertson, Ian M.↗
NASA NTRS2000

Material Characterization for Ductile Fracture Prediction

The research summarized in this document provides valuable information for structural health evaluation of NASA infrastructure. Specifically, material properties are reported which will enable calibration of ductile fracture prediction methods for three high-toughness metallic materials and one aluminum alloy which can be found in various NASA facilities. The task of investigating these materials has also served to validate an overall methodology for ductile fracture prediction is currently being employed at NASA. In facilitating the ability to incorporate various materials into the prediction scheme, we have provided data to enable demonstration of the overall generality of the approach.

Hill, Michael R.↗
DOE OSTI2022

Dimensionless parameters to categorize the failure modes of ductile plate perforation

In this work, two dimensionless parameters were derived organically from impact mechanics equations to remove the need for empirical constants. These two dimensionless parameters effectively collapse the ballistic performance of ductile metal plates along two distinct loci, depending on the projectile geometry and the corresponding failure mode. Projectiles that initiate ductile hole enlargement via cavity expansion fall along a linear curve, while shear-plugging failure modes tend to fall along a cubic curve. Results were demonstrated for various projectiles of different calibers impacting aluminum and Ti-6Al-4V alloys. The main advantage of the approach in this work is to drastically reduce the number of features for input into machine learning algorithms.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Dimensionless parameters to categorize the failure modes of ductile plate perforation

In this work, two dimensionless parameters were derived organically from impact mechanics equations to remove the need for empirical constants. These two dimensionless parameters effectively collapse the ballistic performance of ductile metal plates along two distinct loci, depending on the projectile geometry and the corresponding failure mode. Projectiles that initiate ductile hole enlargement via cavity expansion fall along a linear curve, while shear-plugging failure modes tend to fall along a cubic curve. Results were demonstrated for various projectiles of different calibers impacting aluminum and Ti-6Al-4V alloys, and further explored for more complex target combinations. The main advantage of the approach in this work is to drastically reduce the number of features for input into machine learning algorithms.

36 MATERIALS SCIENCE↗
DOE OSTI2021

In situ synchrotron investigation of degenerate graphite nodule evolution in ductile cast iron

Ductile cast irons (DCIs) are of increasing importance in the renewable energy and transportation sectors. The distribution and morphology of the graphite nodules, in particular the formation of degenerate features during solidification, dictate the mechanical performance of DCIs. In situ high-speed synchrotron X-ray tomography was used to capture the evolution of graphite nodules during solidification of DCI, including degenerate features and the effect of the carbon concentration field. The degeneration of nodules is observed to increase with re-melting cycles, which is attributed to Mg-loss. The dendritic primary austenite and carbon concentration gradients in the surrounding liquid phase were found to control nodule morphology by locally restricting and promoting growth. A coupled diffusion-mechanical model was developed, confirming the experimentally informed hypothesis that protrusions form through liquation cracking of the austenite shell and subsequent localised growth. In conclusion, these results provide valuable insights into the solidification kinetics of cast irons, supporting the design of advanced alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Strong and ductile FeNiCoAl-based high-entropy alloys for cryogenic to elevated temperature multifunctional applications

The highly tunable properties of multi-principal element alloys, commonly known as high-entropy alloys (HEAs), provide a remarkable potential for the development of superior materials for critical structural applications that involve extreme conditions. However, the optimization of the properties of HEAs has been primarily limited to behavior at either low or high temperatures. We report on a non-equiatomic, heterostructured, high-entropy alloy FeNiCoAlTaB which possesses remarkable combinations of mechanical properties across a wide range of temperatures from 77 K to 1073 K. The current metastable alloy presents good ductility and superior engineering tensile strengths of 2.2 GPa, 1.4 GPa, 800 MPa, and 500 MPa at 77 K, 298 K, 873 K, and 1073 K, respectively. This behavior is achieved by a synergic sequence of individual mechanisms that are activated at different temperatures. The alloy even displays pseudoelasticity at 77 K with an applied load up to 2 GPa. This work provides a methodology for tailoring structural heterogeneity and metastability in the design and fabrication of multifunctional HEAs that will outperform known metals and alloys over a wide range of temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Attaining regularization length insensitivity in phase-field models of ductile failure

In this work, a cohesive phase-field model of ductile fracture in a finite-deformation setting is presented. The model is based on a free-energy function in which both elastic and plastic work contributions are coupled to damage. Using a strictly variational framework, the field evolution equations, damage kinetics, and flow rule are jointly derived from a scalar least-action principle. Particular emphasis is placed on the use of a rational function for the stress degradation that maintains a fixed effective strength with decreasing regularization length. The model is employed to examine crack growth in pure mode-I problems through the generation of crack growth resistance (J-R) curves. In contrast to alternative models, the current formulation gives rise to J-R curves that are insensitive to the regularization length. Numerical evidence suggests convergence of local fields with respect to diminishing regularization length as well.

42 ENGINEERING↗
DOE OSTI2020

Discontinuous micro-fibers as intrinsic reinforcement for ductile Engineered Cementitious Composites (ECC)

Engineered Cementitious Composites (ECC) have demonstrated superior mechanical and durability performance than conventional concrete. In the micromechanical reinforcing system of ECC, fibers play a pivotal role in establishing the ultrahigh tensile ductility and autogenous crack width control. This article reviews the state-of-the-art of discontinuous micro-fibers as intrinsic reinforcement of ECC regarding technical performance as well as environmental and economic impacts. Mechanical properties of ECC made with different micro-fibers, man-made or natural, and their embodied energy, emissions and material cost, are comprehensively surveyed. Further, studies on fiber hybridization are discussed regarding the combination of different types of fibers to form synergetic reinforcements that mitigate total material cost, and potentially enhance the composite performance. Lastly, recommendations on fiber selections are highlighted and directions for future research are suggested.

42 ENGINEERING↗
DOE OSTI2022

Dynamic fracture of glass fiber-reinforced ductile polymer matrix composites and loading rate effect

Here, the dynamic fracture of S-2 glass fiber-reinforced polymer matrix composites (FRPMCs) was investigated in this study. The matrix ductility was improved by a recently developed network topology modification technique via mixing partially reacted substructures (mPRS). The composite material was manufactured and characterized by micro-CT scanning and scanning electron microscopy (SEM). Dynamic single-edge notched bending (d-SENB) experiments were performed on the composites by using a modified split-Hopkinson pressure bar. Each specimen’s fracture process was visualized by ultrafast X-ray imaging. Such in-situ radiography enabled identifying the damage initiation below 50-micron scale and inspecting its propagation through the internal structures of opaque composites, thereby accurately quantifying the composites’ mechanical properties. Furthermore, the identical d-SENB experiments were designed and the digital image correlation (DIC) was employed to monitor the stress wave propagation on the composite specimens. The force and deflection measurements were modified and correlated to the physical damage processes. Besides, quasi-static SENB experiments were conducted to identify the loading rate effects on the composites’ fracture behaviors. The force and deflection history, bending stiffness, energy dissipation, and fracture toughness at different loading rates were quantified and compared. Finally, post-fracture analysis by micro-CT scanning and SEM provided physical observations on the variation of the fracture morphology by different loading rates.

42 ENGINEERING↗
DOE OSTI2024

Damage evolution and ductile fracture of commercially-pure titanium sheets subjected to simple tension and cyclic bending under tension

This paper describes a study into the evolution of damage in commercial-purity titanium (CP–Ti) sheets subjected to cyclic bending under tension (CBT) and uniaxial tension (simple tension, ST). Sections were taken from sheets that were strained to various levels under both methods and were imaged using X-ray computed tomography (XCT) to reveal insights into the size, density, and distribution of microvoids in the sheets. Digital image correlation (DIC) was also used to observe the surface strain of CBT and ST sheets during testing. These results showed that elongation to failure (ETF) for CBT deformation is about 2.5× higher than for ST, local longitudinal strains in the bulk of the CBT sample are around 1.3× higher than the peak strain in the ST necked region, and 1.7× higher in the localized region of CBT failure. It was found that the volume-density of voids in both sheets followed a similar exponential increase with strain, reaching nearly 45× higher in the CBT than the ST sheets before the onset of failure, mainly due to the higher strain levels achieved. A higher volume density of voids developed in the center of sheets at high levels of strain, for both processes, with the density in the sheet center becoming approximately double that found near the edges. Scanning electron microscopy (SEM) was used to examine the fracture surface of CBT and ST sheets after failure. The observations are presented and discussed highlighting the CBT process as effective to delay ductile fracture of the CP-Ti sheets.

Commercially pure titanium↗
DOE OSTI2022

The relationship between grain size distribution and ductile to brittle transition temperature in FeCrAl alloys

A FeCrAl (Fe12Cr6Al2Mo) alloy was prepared by two methods, (a) traditional wrought and (b) powder metallurgy (PM). Further, both alloys exhibited the same average grain size (~40 um), but the PM alloy displayed a wider grain size distribution. Charpy impact testing showed that the ductile to brittle transition temperature width is dependent on the grain size distribution width.

36 MATERIALS SCIENCE↗