Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “SLIP”

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 1,747 records · Page 97
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Fatigue Failure Characteristics of Single-Crystal Fe-3%Al Alloy

To obtain a better understanding of the mechanical properties and failure characteristics of the single-crystal Fe-3%Al alloy (SC), tensile and fatigue properties of the SC and polycrystalline Fe-3%Al alloy (PC) have been investigated. The tensile strength and fracture strain for the SC samples were different depending on the loading direction, i.e., 〈111〉, 〈110〉 and 〈100〉, which could be explained by the Schmid factor. Fatigue strength for the SC samples was basically correlated with their tensile strength. Different fatigue properties were obtained for the PC sample, e.g., the high fatigue strength was obtained in the early fatigue stage, and significant reduction in the fatigue strength was appeared in the later fatigue stage, e.g., low endurance limit at 10{sup 7} cycles. The reason for this was caused by the material brittleness due to the accumulated dislocation at the grain boundaries. Because the high ductile SC samples made severe plastic deformation ahead of the crack tip, the crack growth rate did not enhance even if the high stress intensity factor range was applied in Region II (da/dN versus ΔK). The crack growth rate dropped just before the final fracture. Effective stress intensity factor range was estimated using the crack closure model, but the crack growth rate is found to be affected strongly by the slip system of SC sample.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effects of Postweld Heat Treatment on Microstructure and Properties of Laser-Welded Ti-24Al-15Nb Alloy Joint

The microstructure evolution and mechanical properties of laser-welded joints of Ti-24Al-15Nb alloy under different postweld heat treatment (PWHT) conditions were systematically investigated. The results show that the microstructure is very sensitive to PWHT temperatures. The weld zone consists of B2 and O phases after PWHT. With the PWHT temperatures increasing from 850 to 1000 °C, the amount of O phase decreases gradually, while the grains of O precipitates become coarser. After PWHT, there are some thin acicular O precipitates in heat-affected zone (HAZ), and the decomposition of α{sub 2}-phase caused by niobium diffusion can be observed in the HAZ. The PWHT can significantly increase the microhardness of joints, resulting from O phase precipitation hardening effect. The tensile strength and elongation of joints can be remarkably improved after PWHT, which was closely related to the strengthening effect of O precipitates and slip transmission between O and B2 phases. In addition, the results indicate that the best mechanical properties can be achieved only when the number and size of O phase and B2 phase are the best match.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Design, Processing, and Properties of WTaCrV-Hf Multi-principal Element Alloys

Refractory multi-principal element alloys are candidates for high-temperature structural components due, in part, to their high strength and high melting points. Single-phase materials are initially preferred for isotropic material properties as a function of time and temperature in service conditions. This work outlines a computational rank-ordering and experimental validation methodology for single-phase body-centered-cubic phase stability in WTaCrV-Hf alloys using order–disorder transition temperature. Eight compositions were fabricated by arc-melting and heat-treated at 1400 °C for 24 hrs. X-ray diffraction, energy-dispersive x-ray spectroscopy, and Vickers hardness testing showed alloys with order–disorder transition temperatures below 600 °C formed a single-phase body-centered-cubic structure during solidification and remained single-phase after heat-treatment. The sample possessing the lowest order–disorder transition temperature exhibited slip traces suggestive of room-temperature plastic deformation under Vickers indentation, with both heat-treated single-phase samples exhibiting hardnesses over 800 HV with little cracking compared to tungsten. These results establish order–disorder transition temperature as a viable predictive parameter for multi-principal element alloy phase stability. The methodology outlined in this work provides a framework for future design, fabrication, and characterization of high-temperature structural multi-principal element alloys.

CALPHAD↗
DOE OSTI2016

Correlations among void shape distributions, dynamic damage mode, and loading kinetics [Correlations among spall void shape distributions, damage mode and shock loading kinetics]

Here, three-dimensional x-ray tomography (XRT) provides a nondestructive technique to characterize the size, shape, and location of damage in dynamically loaded metals. A shape-fitting method comprising the inertia tensors of individual damage sites was applied to study differences of spall damage development in face-centered-cubic (FCC) and hexagonal-closed-packed (HCP) multicrystals and for a suite of experiments on high-purity copper to examine the influence of loading kinetics on the spall damage process. Applying a volume-weighted average to the best-fit ellipsoidal aspect-ratios allows a quantitative assessment for determining the extent of damage coalescence present in a shocked metal. It was found that incipient transgranular HCP spall damage nucleates in a lenticular shape and is heavily oriented along particular crystallographic slip directions. In polycrystalline materials, shape distributions indicate that a decrease in the tensile loading rate leads to a transition to coalesced damage dominance and that the plastic processes driving void growth are time dependent.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Probing the Effect of Hydrogen on Elastic Properties and Plastic Deformation in Nickel Using Nanoindentation and Ultrasonic Methods

Hydrogen effects on small-volume plasticity and elastic stiffness constants are investigated with nanoindentation of Ni-201 and sonic velocity measurements of bulk Ni single crystals. Elastic modulus of Ni-201, calculated from indentation data, decreases ~22% after hydrogen charging. This substantial decrease is independently confirmed by sonic velocity measurements of Ni single crystals; c 44 decreases ~20% after hydrogen exposure. Furthermore, clear hydrogen-deformation interactions are observed. The maximum shear stress required to nucleate dislocations in hydrogen-charged Ni-201 is markedly lower than in as-annealed material, driven by hydrogen-reduced shear modulus. Additionally, a larger number of depth excursions are detected prior to general yielding in hydrogen-charged material, suggesting cross-slip restriction. Together, these data reveal direct correlation between hydrogen-affected elastic properties and plastic deformation in Ni alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Deformation Mechanism Transition in Additively Manufactured Compositionally Graded Fe-Base Alloys

Microstructure-dependent deformation and fracture behavior was investigated for an additively manufactured compositionally graded alloy (CGA) printed using the laser-directed energy deposition (L-DED) method to explore an alternative approach for dissimilar metal joints in nuclear energy systems. The electron backscatter diffraction (EBSD) maps from scanning electron microscopy (SEM) display a clear microstructural transition with decreasing austenite-forming elements (Ni and Mn), from an austenite (γ) dominant structure, to a complex composite structure containing ferrite (α), martensite (α') and retained austenite, and then to a fully ferritic structure. EBSD data were recorded in situ during tensile testing in SEM, and the evolution of the deformation mechanism and microstructure was characterized using Kikuchi diffraction pattern analysis. Complementary analysis for high-resolution features was also performed using scanning transmission electron microscopy (STEM). The Ni/Mn-rich austenite-dominant microstructures showed a complex deformation mechanism of two-step martensitic transformation (γ→ε→α'), whereas the minor austenite phase retained in the ferrite and/or martensite matrix showed a single transformation route (γ→α'). Ordinary dislocation glide and twinning via partial dislocation glide were observed in the austenite deformation. Meanwhile, the ferrite and martensite grains deformed mainly by ordinary dislocation slips and grain rotation. Furthermore, static tensile fracture was also highly dependent on local composition and phase constituents.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Deformation and Fracture Behavior of Additively Manufactured 316L Stainless Steel

Tensile deformation and fracture behavior of an additively manufactured (AM) 316L stainless steel (SS) in the as-built, stress-relieved, and solution-annealed conditions was investigated using in situ tensile testing in a scanning electron microscope with an electron back scattering diffraction (SEM–EBSD) detector. Analyses were performed to discuss the characteristic deformation and fracture process of the fine-grained AM 316L SS with and without relaxation heat treatment. The as-built 316L showed the highest strength, and both post-build heat treatments lowered the strength of the alloy. Regardless of the post-build processing, the AM 316L SS showed overall higher strength but slightly lower ductility when compared to the wrought (WT) 316L SS. Analysis of EBSD data indicated that the characteristic microstructural features from AM, such as the complex and fine grain morphology, dislocation network, pores, and silicon-rich oxides, evolved and exerted various roles during the tensile deformation and fracture processes. Further, it was obvious that the interaction of dislocation slips with oxide particles and cavities (or pores) resulted in an accelerated cracking in AM 316L SS. Overall, however, their influence on mechanical behavior was limited, as the genuinely high ductility of 316L SS could help avoid any premature or brittle fracture.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Gas sorption and non-Darcy flow in shale reservoirs

Gas sorption and non-Darcy flow are two important issues for shale gas reservoirs. The sorption consists of dissolution and adsorption. Dissolved gas and adsorbed gas are different. The former is dissolved in the shale matrix, while the latter is concentrated near the solid walls of pores. In this paper, the Langmuir equation is used to describe adsorption and Henry’s law is used to describe dissolution. The K coefficient in Henry’s law of 0.052 mmol/(MPa g TOC) is obtained by matching experimental data. The amount of dissolved gas increases linearly when pressure increases. Using only the Langmuir equation without considering dissolution can lead to a significant underestimation of the amount of sorbed gas in shales. For non-Darcy gas flow, the apparent permeability model for free gas is established by combining slip flow and Knudsen flow. For adsorbed gas, the surface diffusion effect is also considered in this model. Here, the surface diffusion coefficient is suggested to be of the same scale as the gas self-diffusion coefficient, and the corresponding effective permeability is derived. When

02 PETROLEUM↗
DOE OSTI2017

Tailoring the Properties of a Ni-Based Superalloy via Modification of the Forging Process: an ICME Approach to Fatigue Performance

Traditionally, material design and property modifications are usually associated with compositional changes. However, subtle changes in the manufacturing process parameters can also have a dramatic effect on the resulting material properties. In this work, an integrated computational materials engineering (ICME) framework is adopted to tailor the fatigue performance of a Ni-based superalloy, RR1000. An existing fatigue model is used to identify microstructural features that promote enhanced fatigue life, namely a uniform, fine grain size distribution, random orientation, a distinct grain boundary distribution (specifically high twin boundary density and limited low-angle grain boundaries). A deformation mechanism map and process models for grain boundary engineering of RR1000 are used to identify the optimal thermo-mechanical processing parameters to realize these desirable microstructural features. For validation, small-scale forgings of RR1000 were produced and heat-treated to attain fine grain and coarse grain microstructures that represent the conventionally processed and grain boundary engineered (GBE) conditions, respectively. For each of the four microstructural variants of RR1000, the twin density and grain size were characterized and were in agreement with the desired microstructural attributes. In order to validate the deformation mechanisms and fatigue behavior of the material, high-resolution digital image correlation was performed to generate strain maps relative to the microstructural features. The high density of twin boundaries was confirmed to inhibit the length of slip bands, which is directly attributed to extended fatigue life. Thus, this study demonstrated the successful role of models, both process and performance, in the design and manufacture of Ni-based superalloy disk forgings.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Data-Driven Constitutive Model for the Inelastic Response of Metals: Application to 316H Steel

Here, predictions of the mechanical response of structural elements are conditioned by the accuracy of constitutive models used at the engineering length-scale. In this regard, a prospect of mechanistic crystal-plasticity-based constitutive models is that they could be used for extrapolation beyond regimes in which they are calibrated. However, their use for assessing the performance of a component is computationally onerous. To address this limitation, a new approach is proposed whereby a surrogate constitutive model (SM) of the inelastic response of 316H steel is derived from a mechanistic crystal plasticity-based polycrystal model tracking the evolution of dislocation densities on all slip systems. The latter is used to generate a database of the expected plastic response and dislocation content evolution associated with several instances of creep loading. From the database, a SM is developed. It relies on the use of orthogonal polynomial regression to describe the evolution of the dislocation content. The SM is then validated against predictions of the dead load creep response given by the polycrystal model across a range of temperatures and stresses. When the SM is used to predict the response of 316H during complex non monotonic loading, extrapolating to new loading conditions, it is found that predictions compare particularly well against those from the physics-based polycrystal model.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Modeling and analysis of mixed convection stagnation point flow of nanofluid towards a stretching surface: OHAM and FEM approach

A theoretical study of mixed convection stagnation point flow towards a stretching surface is presented. The governing boundary layer equations are transformed into a set of highly nonlinear ordinary differential equations using suitable similarity transforms. The semi-analytical solution is obtained using optimal homotopy analysis method (OHAM) and the numerical solution is obtained via finite element method (FEM). Solutions obtained via two different approaches are in excellent agreement, which validates the accuracy of present analysis. In a special case, the present OHAM solution is also validated with the earlier available results. Effect of pertinent flow parameters on the skin friction coefficient and Nusselt number is presented in tabular form, whereas the velocity, temperature and nanoparticle distribution are presented in graphical forms. Further, a quadratic multiple regression analysis on numeric data of skin friction coefficient and Nusselt number is performed. The findings suggest that velocity slip assists the fluid motion in presence of buoyancy forces, whereas it exhibits a retarding nature on fluid motion when no buoyancy forces exist.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2016

Response characteristics of stable mixed-potential NH 3 sensors in diesel engine exhaust

Here, a mixed-potential, electrochemical sensor platform is extended to NH 3 sensing by the introduction of a new gold alloy working electrode. A planar, pre-commercial NH 3 sensor utilized LANL’s controlled interface approach, and a Pd-Au alloy working electrode was tested in exhaust of a GM 1.9 L diesel engine downstream of a diesel oxidation catalyst through a slipstream arrangement. A fraction of the exhaust was pulled across the sensor with a pump at 20 L/min. In order to simulate NH 3 slip inside of a full SCR emissions control system, NH 3 was injected immediately upstream of the sensor using a calibrated mass flow controller. The sensor response quantitatively tracked the NH 3 as measured via Fourier transform infrared (FTIR) analyzer. A calibration curve was obtained in the exhaust from an ammonia staircase response with the engine running at steady-state engine conditions resulting in low background concentrations of NO x and HC (<20 ppm) during calibration. Exhaust gas recirculation (EGR) switching and sweeps were used to evaluate the NH 3 sensor response under different amounts of total background NO x . The calibration curve was used to directly compare the [NH 3 ] calculated from sensor response to the gas phase composition measured via FTIR. In general, there was excellent quantitative agreement between the sensor response and the actual NH 3 in the exhaust gas, and fast response time such that transients (<5 ppm) could be easily discerned from baseline. A LANL pre-commercial NO x sensor was tested simultaneously with the NH 3 sensor and the extent of cross-sensitivity between the two sensors will be discussed.

47 OTHER INSTRUMENTATION↗
DOE OSTI2025

Doping Effects on the Ductility of a Lightweight Refractory High-Entropy Alloy: Grain Boundary and Bulk Lattice Aspects

Doping elements in small amounts often segregate to grain boundaries (GBs) in alloys and can significantly impact mechanical properties and performance. Refractory high-entropy alloys (RHEAs) are known for their poor ductility, especially at low temperatures. Promoting GB cohesion through segregation can be an effective approach to mitigate embrittlement. Here, in this study, first-principles density functional theory (DFT) calculations were performed to examine the effects of important interstitial dopants (O, B, C, and N) and substitutional dopants (Cr, Y, La, and Ce) on the Σ5(310) [001] tilt GB of a lightweight RHEA Nb 32.5 Ti 27.5 Mo 22.5 Ta 12.5 Hf 2.5 Zr 2.5 . The DFT calculations reveal that certain dopants, such as B, C, Cr, N, and Y, exhibit favorable GB strengthening effects by improving bonding interactions with the bulk alloy. The impact of doping on the ductility parameter of the bulk lattice, defined as the ratio of surface energy to unstable stacking fault energy for the {110} <111> slip system, was also studied; and the results show that doping reduces the intrinsic ductility of the alloy, decreasing the D-parameter from 2.90 to 2.55, depending on the specific dopant. The present findings provide a foundational understanding at atomic level of the effect of representative dopants on mechanical properties of RHEAs and can be used to guide future alloy design for improved mechanical properties.

deformation charge density↗
DOE OSTI2018

Computational Homogenization of Polycrystals

This paper reviews the current state of the art in the simulation of the mechanical behavior of polycrystalline materials by means of computational homogenization. The key ingredients of this modeling strategy are presented in detail starting with the parameters needed to describe polycrystalline microstructures and the digital representation of such microstructures in a suitable format to perform computational homogenization. The different crystal plasticity frameworks that can describe the physical mechanisms of deformation in single crystals (dislocation slip and twinning) at the microscopic level are presented next. This is followed by the description of computational homogenization methods based on mean-field approximations by means of the viscoplastic self-consistent approach, or on the full-field simulation of the mechanical response of a representative polycrystalline volume element by means of the finite element method or the fast Fourier transform-based method. Multiscale frameworks based on the combination of mean-field homogenization and the finite element method are presented next to model the plastic deformation of polycrystalline specimens of arbitrary geometry under complex mechanical loading. Examples of application to predict the strength, fatigue life, damage, and texture evolution under different conditions are presented to illustrate the capabilities of the different models. Lastly, current challenges and future research directions in this field are summarized.

36 MATERIALS SCIENCE↗
DOE OSTI2013

The influences of temperature and microstructure on the tensile properties of a CoCrFeMnNi high-entropy alloy

An equiatomic CoCrFeMnNi high-entropy alloy, which crystallizes in the face-centered cubic (FCC) crystal structure, was produced by arc melting and drop casting. The drop-cast ingots were homogenized, cold rolled, and recrystallized to obtain single-phase microstructures with three different grain sizes in the range 4~160 m. Quasi-static tensile tests were then performed at temperatures between 77 and 1073 K. Yield strength, ultimate tensile strength and ductility all increased with decreasing temperature. During the initial stages of plasticity (up to ~2% strain), deformation occurs by planar dislocation glide on the normal FCC slip system {111} 110 at all temperatures and grain sizes investigated. Undissociated 1/2 110 dislocations were observed, as were numerous stacking faults, which imply the dissociation of several of these dislocations into 1/6 112 Shockley partials. At later stages ( 20% strain), nanoscale deformation twins were observed after interrupted tests at 77 K, but not in specimens tested at room temperature where plasticity occurred exclusively by dislocations which organized into cells. Deformation twinning, by continually decreasing the mean free path of dislocations during tensile testing, produces a high degree of work hardening and a significant increase in the ultimate tensile strength. This increased work hardening prevents the early onset of necking instability and is a reason for the enhanced ductility observed at 77 K. A second way in which twinning can contribute to ductility is by providing an additional deformation mode to accommodate plasticity. However, it cannot explain the increase in yield strength with decreasing temperature in our high-entropy alloy since twinning was not observed in the early stages of plastic deformation. Since strong temperature dependencies of yield strength are also seen in binary FCC solid solution alloys, it may be an inherent solute effect, which needs further study.

Deformation twinning↗
DOE OSTI2014

Plastic deformation in nanoindentation of tantalum: A new mechanism for prismatic loop formation

Here, the mechanisms of deformation under a nanoindentation in tantalum, chosen as a model body-centered cubic (bcc) metal, are identified and quantified. Molecular dynamics (MD) simulations and indentation experiments are conducted for [1 0 0], [1 1 0] and [1 1 1] normals to surface orientations. The simulated plastic deformation proceeds by the formation of nanotwins, which rapidly evolve into shear dislocation loops. It is shown through a dislocation analysis that an elementary twin (three layers) is energetically favorable for a diameter below ~7 nm, at which point a shear loop comprising a perfect dislocation is formed. MD simulations show that shear loops expand into the material by the advancement of their edge components. Simultaneously with this advancement, screw components of the loop cross-slip and generate a cylindrical surface. When opposite segments approach, they eventually cancel by virtue of the attraction between them, forming a quasi-circular prismatic loop composed of edge dislocation segments. This “lasso”-like mechanism by which a shear loop transitions to a prismatic loop is identified for both [0 0 1] and [1 1 1] indentations. The prismatic loops advance into the material along $\langle$1 1 1$\rangle$ directions, transporting material away from the nucleation site. Analytical calculations supplement MD and experimental observations, and provide a framework for the improved understanding of the evolution of plastic deformation under a nanoindenter. Dislocation densities under the indenter are estimated experimentally (~1.2 × 10 15 m -2 ), by MD (~7 × 10 15 m -2 ) and through an analytical calculation (2.6–19 × 10 15 m -2 ). Considering the assumptions and simplifications, this agreement is considered satisfactory. MD simulations also show expected changes in pile-up symmetry after unloading, compatible with crystal plasticity.

36 MATERIALS SCIENCE↗