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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 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Numerical Simulation of Bulging Deformation for Wide-Thick Slab Under Uneven Cooling Conditions

In the present work, the bulging deformation of a wide-thick slab under uneven cooling conditions was studied using finite element method. The non-uniform solidification was first calculated using a 2D heat transfer model. The thermal material properties were derived based on a microsegregation model, and the water flux distribution was measured and applied to calculate the cooling boundary conditions. Based on the solidification results, a 3D bulging model was established. The 2D heat transfer model was verified by the measured shell thickness and the slab surface temperature, and the 3D bulging model was verified by the calculated maximum bulging deflections using formulas. The bulging deformation behavior of the wide-thick slab under uneven cooling condition was then determined, and the effect of uneven solidification, casting speed, and roll misalignment were investigated.

36 MATERIALS SCIENCE↗
DOE OSTI2019

A Method for Three-Dimensional Deformation Predictions in the Rolling of Steel Strips

In order to achieve a better accuracy-speed balance in the three-dimensional (3-D) deformation calculations of strip rolling, especially for cold rolling of comparatively thin and wide steel strips, a new integrative method is developed. The basic and related mathematic equations and the coupling algorithm are given in detail. To test the approach and prove its effectiveness, four examples are calculated by the proposed method and the models based on the traditional influence function method, taking a six-high strip finishing mill and the rolled piece of a certain specification as research objects. The lateral distributions of front tensile stress that is closely related to the 3-D plastic deformation of the rolled metal and the flatness in the four cases are presented and discussed. The comparison of computational expense and analysis of the results preliminarily confirms that it is workable for this purpose.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of 0.1 wt.% Co on the Hot Deformation and Toughness of Fine-Grained Low-Carbon Steel at Sub-zero Temperatures

The effect of 0.1 wt.% Co on the hot deformation behavior of fine-grained low-carbon microalloyed steel was investigated at temperatures of 850-1200 °C and a strain rate of 5 s{sup −1}. Furthermore, the toughness of the steel with and without Co at sub-zero temperatures was evaluated. The results suggest that the addition of 0.1 wt.% Co increases the flow stress and delays the occurrence of dynamic recrystallization (DRX) at the same deformation temperature and strain. The DRX fraction of steel specimens without and with 0.1 wt.% Co was about 67.4 and 43.9% at 850 °C, respectively. Then, it increased to 100% at 1100 °C. Compared with steel without Co, cementite particles in the tempered sorbite of steel with 0.1 wt.% Co decreased in size but increased in quantity, yield strength increased from 756 to 787 MPa, and Charpy V-notch energy at − 20 and − 50 °C improved from 69 and 41 to 102 and 65 J, respectively. The fracture morphology and crack propagation characteristics were consistent with the variation in impact energy.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Effect of Aluminum Alloying on the Hot Deformation Behavior of Nano-bainite Bearing Steel

Interest in using aluminum in nano-bainite steel, especially for high-carbon bearing steel, is gradually growing. In this study, GCr15SiMo and GCr15SiMoAl steels are introduced to investigate the effect of Al alloying on the hot deformation behavior of bearing steel. Results show that the addition of Al not only notably increases the flow stress of steel due to the strong strengthening effect of Al on austenite phase, but also accelerates the strain-softening rates for its increasing effect on stacking fault energy. Al alloying also increases the activation energy of deformation. Two constitutive equations with an accuracy of higher than 0.99 are proposed. The constructed processing maps show the expanded instability regions for GCr15SiMoAl steel as compared with GCr15SiMo steel. This finding is consistent with the occurrence of cracking on the GCr15SiMoAl specimens, revealing that Al alloying reduces the high-temperature plasticity of the bearing steel. On the contrary, GCr15SiMoAl steel possesses smaller grain size than GCr15SiMo steel, manifesting the positive effect of Al on bearing steel. Attention should be focused on the hot working process of bearing steel with Al.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Deformation Temperature on Dynamic Recrystallization and CSL Grain Boundary Distribution of Fe-36%Ni Invar Alloy

This paper investigated the effect of deformation temperatures on microstructure evolution and grain boundary character distribution (GBCD) of Fe-36%Ni Invar alloy during hot compression tests. The isothermal hot deformation tests were carried out in a temperature range of 850-1100 °C and a strain rate of 0.01 s{sup −1}. The grain boundary character distribution was based on the Σ3{sup n} (n = 1, 2, 3,…) coincidence site lattice (CSL) boundaries. The experimental results show that the extent of dynamic recrystallization significantly expanded at the strain rate of 0.01 s{sup −1} with the increase in temperature and this phenomenon was consistent with the evolution tendency of Σ3{sup n} boundaries. To some degree, the increasing proportion of typical low-ΣCSL boundaries, especially the increasing trend of Σ3, positively promoted the wider process of dynamic recrystallization.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Constitutive Model for Hot Deformation of the Cu-Zr-Ce Alloy

Hot compressive deformation behavior of the Cu-Zr-Ce alloy has been investigated according to the hot deformation tests in the 550-900 °C temperature range and 0.001-10 s{sup −1} strain rate range. Based on the true stress–true strain curves, the flow stress behavior of the Cu-Zr-Ce alloy was investigated. Microstructure evolution was observed by optical microscopy. Based on the experimental results, a constitutive equation, which reflects the relationships between the stress, strain, strain rate and temperature, has been established. Material constants n, α, Q and ln A were calculated as functions of strain. The equation predicting the flow stress combined with these materials constants has been proposed. The predicted stress is consistent with experimental stress, indicating that developed constitutive equation can adequately predict the flow stress of the Cu-Zr-Ce alloy. Dynamic recrystallization critical strain was determined using the work hardening rate method. According to the dynamic material model, the processing maps for the Cu-Zr and Cu-Zr-Ce alloy were obtained at 0.4 and 0.5 strain. Based on the processing maps and microstructure observations, the optimal processing parameters for the two alloys were determined, and it was found that the addition of Ce can promote the hot workability of the Cu-Zr alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Constitutive Behavior and Processing Map of T2 Pure Copper Deformed from 293 to 1073 K

The deformation behavior of T2 pure copper compressed from 293 to 1073 K with strain rates from 0.01 to 10 s{sup −1} was investigated. The constitutive equations were established by the Arrhenius constitutive model, which can be expressed as a piecewise function of temperature with two sections, in the ranges 293-723 K and 723-1073 K. The processing maps were established according to the dynamic material model for strains of 0.2, 0.4, 0.6, and 0.8, and the optimal processing parameters of T2 copper were determined accordingly. In order to obtain a better understanding of the deformation behavior, the microstructures of the compressed samples were studied by electron back-scattered diffraction. The grains tend to be more refined with decreases in temperature and increases in strain rate.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Hot Roll Bonding of Aluminum to Twin-Roll Cast (TRC) Magnesium and Its Subsequent Deformation Behavior

In an experiment in which twin-roll cast AZ31 magnesium alloy and commercial purity aluminum (AA 1050) sheets were bonded by hot rolling as Al/Mg/Al laminate composites, it was found that increasing the preheating temperatures up to 400 °C enhances the bonding strength of composites. Further increases in the preheating temperatures accelerate the magnesium oxide growth and thus reduce the bonding strength. The influence of the reduction ratio on the bonding properties was also studied, whereby it was observed that increasing the rolling reduction led to an increase in the bonding strength. The experimental results show that the optimum bonding strength can be obtained at rolling temperatures of 375-400 °C with a 50-60% reduction in thickness. On the other hand, the subsequent deformation behavior of composite was assessed using plane strain compression and deep drawing tests. We demonstrate that the composites produced using the optimum roll bonding conditions exhibited sufficient bonding during subsequent deformation and did not reveal any debonding at the bonding interface.

36 MATERIALS SCIENCE↗
DOE OSTI2018

X-ray Diffraction Investigation of Annealing Behavior of Peened Surface Deformation Layer on Precipitation Hardening Stainless Steel

In order to investigate the recrystallization behavior of peened surface deformation layer of precipitation hardening stainless steel, a classic x-ray diffraction line profile analysis, Voigt method, was carried out on peened 17-4PH with different isothermal annealing temperatures. The activation energy of domain boundary migration (Q{sub a}) and the activation energy of microstrain relaxation (Q{sub b}) were calculated by regression analysis in different annealing temperature conditions. The results show that the value of Q{sub a} decreases with annealing temperature increasing, which is due to the influence of precipitation (ε-Cu) size on the movements of grain and subgrain boundaries. The maximum growth rate of ε-Cu particles occurs during 400 to 500 °C interval. Compared with growth behavior of domain size, microstrain relaxation behavior is less sensitive to precipitation particle size. The effects of annealing temperature and time on dislocation density are both significant when annealing temperature is lower than 500 °C. However, the effect of annealing temperature on dislocation density becomes insignificant when annealing temperature is higher than 500 °C. 300 °C annealing temperature only leads to the microstrain relaxation but nearly cannot lead to the domain size growth even if prolonging annealing time. Microstructure enhancement effect still exists in plastic deformation layer when 300 °C annealing temperature lasts for 60 min but nearly disappears when 600 °C annealing temperature lasts for 20 min.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Analyses of Small Punch Creep Deformation Behavior of 316LN Stainless Steel Having Different Nitrogen Contents

The small punch creep (SPC) behavior of 316LN stainless steel (SS) containing 0.07, 0.11 and 0.14 wt.% nitrogen has been investigated at 923 K. The transient and tertiary SPC deformation of 316LN SS with various nitrogen contents have been analyzed according to the equation proposed for SPC deflection, δ=δ{sub 0}+δ{sub T}(1−e{sup −κt})+ δ-dot {sub s}t+δ{sub 3}e{sup [φ(t−t{sub r})]}. The relationships among the rate of exhaustion of transient creep (κ), steady-state deflection rate ( δ-dot {sub s}) and the rate of acceleration of tertiary creep (φ) revealed the interrelationships among the three stages of SPC curve. The first-order reaction rate theory was found to be applicable to SPC deformation throughout the transient as well as tertiary region, in all the investigated steels. The initial and final creep deflection rates were decreased, whereas time to attain steady-state deflection rate increased with the increase in nitrogen content. By increasing the nitrogen content in 316LN SS from 0.07 to 0.14 wt.%, each stage of SPC was prolonged, and consequently, the values of κ, δ-dot {sub s} and φ were lowered. Using the above parameters, the master curves for both transient and tertiary SPC deflections were constructed for 316LN SS containing different nitrogen contents.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A Review of Texture Evolution Mechanisms During Deformation by Rolling in Aluminum Alloys

The current understanding of texture evolution during deformation by rolling in aluminum alloys was summarized. This included understanding the evolution mechanisms and several key factors of initial texture, microstructure, alloy composition, deformation temperature, stress–strain condition, and rolling geometry. Related models on predicting texture evolution during rolling were also discussed. Finally, for this research field, the recommendations for controlling the formation of rolling textures were proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Physics-based Constitutive Model for the Hot Deformation of 2Cr11Mo1VNbN Martensitic Stainless Steel

The hot deformation behavior of 2Cr11Mo1VNbN martensitic stainless steel is investigated through isothermal compression tests between 1173 and 1423 K with strain rates of 0.005-5 s{sup −1}. Based on experimental results, the work hardening–dynamic recovery stage and dynamic softening stage are evaluated, and a couple-stage constitutive model is developed to describe the work hardening–dynamic recovery and dynamic softening behaviors. Phenomenological constitutive models, which consider temperature, strain and strain rate, are established. A comparison between the predicted and experimental flow stress values indicates that the established models accurately describe the hot deformation behaviors for the studied supercritical steel.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Experimental Study on the Hot Deformation Characterization of Low-Carbon Nb-V-Ti Microalloyed Steel

X80 steel, as typical low-carbon Nb-V-Ti microalloyed steel, is getting more and more attention in oil and gas transmission pipeline manufacturing. In this paper, the hot deformation behavior of X80 steel has been investigated. Hot compression tests of the steel were conducted under different temperatures and strain rates. Based on the experimental data, the flow stress constitutive equations were established. It is found that the hot deformation activation energy of this steel is higher than C-Mn and low-carbon steel. Then, the kinetics model and grain size model of dynamic recrystallization were developed according to the flow curves and the optical microstructures. In addition, the processing maps were developed to analyze the workability of X80 steel at elevated temperature. The analysis results show that the optimum processing window is at the temperature of 1300-1473 K and the strain rate of 0.01-10 s{sup −1}. The microstructure observation indicates that the optimum processing parameters are applicable to the tested steel.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Analytical Model of High-Velocity Impact of a Deformable Projectile Against Textile-Based Composites

Textile-based composites are used in manufacturing of ballistic shields due to their favorable combination of mechanical properties which enables weight saving and efficiency while retaining or even improving ballistic performance. Predictive models are an important tool in reducing experimental tests which are still an important step in ballistic shield design. Among those, analytical models provide less accurate results but require far less computational cost than numerical models and can be used for preliminary analyses. Many authors in the literature have developed analytical models for high-velocity impact on textile-based composites based on wave propagation theory and an energy equilibrium approach. The main limitation of these models is the assumption of rigid projectile which leads to the underestimation of the ballistic limit for soft core projectiles, which are a very common type of threat for this kind of protection. For this reason, an enhanced version of these models is reported in this paper, which releases the assumption of rigid projectile and adds erosion and deformation of the projectile to the formulation. Ballistic tests were performed on panels manufactured from layers of Kevlar 29 plain weave fabric embedded in an epoxy matrix. An insight into the different kinds of energy absorption considered by the model shows that projectile deformation plays an important role in the dissipation of the kinetic energy of the projectile in case of intermediate impact velocity. For this reason, the present model delivers more accurate results than the models present in the literature. In particular, the estimation of the ballistic limit is drastically improved which is a key step in ballistic shields optimization.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effects of Environmental Conditions on the Mechanical and Degradation Behavior of Polyurethane Foam Subjected to Various Deformation Histories

Since its development, polyurethane foam (PUF) has been widely used as an insulator, including in the marine industry. Liquefied natural gas (LNG) carriers have the highest market share in the LNG-related shipbuilding industry. PUF is used as an insulator in membrane-type cargo containment systems (CCSs) as one of the most important components of LNG carriers. Because PUF is subjected to constant load and deformation when used in insulation for LNG CCSs and is exposed to the cryogenics of the seawater environment for extended times, it is essential to evaluate the mechanical behavior of PUF in such environments. In this study, to investigate the effects of applying an initial strain and of immersion in various media on the mechanical properties of PUF, compression tests were carried out at ambient and cryogenic temperature using a universal testing machine. The mechanical behavior of PUF after deformation recovery upon subjection to various initial strain levels was estimated experimentally. In addition, the microstructure of the PUF specimen prior to testing was analyzed to investigate the effects of the initial strain level and immersion in different media on the mechanical behavior of PUF.

36 MATERIALS SCIENCE↗
DOE OSTI2019

A kinematic comparison of meshfree and mesh-based Lagrangian approximations using manufactured extreme deformation fields

Meshfree methods for solid mechanics have been in development since the early 1990's. Initial motivations included alleviation of the burden of mesh creation and the desire to overcome the limitations of traditional mesh-based discretizations for extreme deformation applications. Here, the accuracy and robustness of both mesh-free and meshbased Lagrangian discretizations are compared using manufactured extreme-deformation fields. For the meshfree discretizations, both moving least squares and maximum entropy are considered. Quantitative error and convergence results are presented for the best approximation in the H 1 norm.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

In-situ high-energy X-ray characterization of neutron irradiated HT-UPS stainless steel under tensile deformation

Here, the tensile deformation behavior of a high-temperature, ultrafine-precipitate strengthened (HT-UPS) stainless steel was characterized in-situ with high-energy X-ray diffraction at 20 and 400 °C. The HT-UPS samples were neutron irradiated to 3 dpa at 400 °C. Significant irradiation hardening and ductility loss were observed at both temperatures. Lattice strain evolutions of the irradiated samples showed a strong linear response up to near the onset of the macroscopic yield, in contrast to the unirradiated HT-UPS which showed a pronounced non-linear behavior well below the macroscopic yield. While the room temperature diffraction elastic moduli in the longitudinal direction increased after irradiation, the 400 degrees C moduli were similar before and after irradiation. The evolution of the {200} lattice strain parallel to the loading axis (ε L {200} ) showed unique characteristics: in the plastic regime, the evolution of (ε L {200} ) after yield is temperature-dependent in the unirradiated specimens but temperature-independent in the irradiated specimens; and the value of (ε L {200} ) at the yield is an irradiation-sensitive, temperature-independent . parameter. The evolution of (ε L {200} ) corresponds well with the dislocation density evolution, and is an effective probe of the deformation-induced long-range internal stresses in the HT-UPS steel.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Hierarchically-structured large superelastic deformation in ferroelastic-ferroelectrics

Large superelastic deformation in ferroelastic-ferroelectrics (FMs) is a complex phenomenon involving multiple mechanisms operating simultaneously. Understanding how these mechanisms contribute corporately is critical to apply this useful property to the intrinsically brittle FMs, which can therefore display both excellent functional and mechanical performance. Here, we have directly observed and quantitatively analyzed in situ in a transmission electron microscope the three main mechanisms of twinning domain, phase transformation and mobile point defect contributing to extremely large superelastic deformation in single-crystal BaTiO 3 (5.0% strain) and Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 (10.1% strain). Finally, our results reveal the hierarchical origin of large recoverable strain in “brittle” FMs.

36 MATERIALS SCIENCE↗