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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
DOE OSTI2023

Faster-than-real-time Simulation with Demonstration for Resilient DER Integration

The US electric grid is facing operational, stability, and security challenges. Transmission system operators need some measure of visibility into distribution system renewable generation. Distribution system generation needs to support transmission system voltage. The grid is experiencing an expansion in measurement systems. How to take full advantage of this expansion and defend against attacks, both cyber and physical, poses additional challenges. The Faster-than-real-time Simulation with demonstration for Resilient DER Integration project set out to do the following: a. Flatten the voltage profile through the feeders and system for cost saving and voltage stabilization needs. b. Increase the amount of intermittent distributed energy resources (IDERs) that could be deployed on a utility feeder and provide 100% or more energy needed for the demands on that feeder, and c. based on an accurate model (Digital Twin) of the utilities system, be able to detect any abnormalities on the utilities distribution system. To manage the voltage and increase IDER penetration (a,b), Graph Trace Analysis is employed in a time-series, optimal power flow to coordinate the time-varying feedback control setpoints of a distribution feeder’s utility control devices. Under the coordinated control are a Load Tap Changing Transformer, a voltage regulator, and five switched capacitor banks. The feeder serves over 2000 customers, the feeder secondaries are modeled, and the feeder has 2.3 MW of PV generation, corresponding to a 17.4% penetration of PV generation. The feeder model has over 12,000 components, where every customer load bus and PV generator are modeled. The accuracy of the power flow solution is compared against historical meter voltage measurements, the improvement in conservation voltage reduction energy savings as a function of the coordinated control desired voltage profile is investigated, and the increase in PV penetration of the coordinated control over the existing control is presented. To achieve improved control performance while observing system operation constraints, bellwether Advanced Metering Infrastructure (AMI) voltage measurements are used to adjust the desired voltage profile used by the optimal power flow analysis. To detect and alleviate or negate attacks or failures on the distribution and transmission utility grids (c) the grid needs to be resilient and self-healing. In this project software was designed to do just that. At the center of the software is an Integrated System Model (ISM) that spans from transmission to secondary distribution. The ISM is employed in real-time abnormality detection, voltage stability forecasting, and multi-mode control. Testing results are presented for: 1—attacks on utility infrastructure; 2—energy savings from optimal control; 3—distribution system control response during a low voltage transmission system event; 4—cyber-attacks on PV inverters, where physical inverters are used in hard-ware-in-the-simulation-loop studies. Contributions of this work include real-time analysis that spans from three-phase transmission through secondary distribution; an approach for detecting abnormalities that employs measurements from three independent measurement systems; and a multi-mode distribution system control that responds to cyber-attacks, physical attacks, equipment failures, and transmission system needs.

Integrated System Model, Graph Trace Analysis, Adv↗
DOE OSTI2014

Development of a system model for advanced small modular reactors.

This report describes a system model that can be used to analyze three advance small modular reactor (SMR) designs through their lifetime. Neutronics of these reactor designs were evaluated using Monte Carlo N-Particle eXtended (MCNPX/6). The system models were developed in Matlab and Simulink. A major thrust of this research was the initial scoping analysis of Sandia s concept of a long-life fast reactor (LLFR). The inherent characteristic of this conceptual design is to minimize the change in reactivity over the lifetime of the reactor. This allows the reactor to operate substantially longer at full power than traditional light water reactors (LWRs) or other SMR designs (e.g. high temperature gas reactor (HTGR)). The system model has subroutines for lifetime reactor feedback and operation calculations, thermal hydraulic effects, load demand changes and a simplified SCO2 Brayton cycle for power conversion.

Source record↗
DOE OSTI2021

Recurrence analysis of friction based dry-couplant ultrasonic Lamb waves in plate-like structures

Here, in this study, the effect of friction on the generation of dry-coupled Lamb waves is experimentally investigated. Recurrence analysis is performed to analyze the complex behavior of friction based dry-coupled Lamb waves. In particular, the effect of the normal force, which is necessary for a stronger dry-coupled Lamb wave generation and the friction, on the transmission of mechanical energy and determinism characteristics of Lamb waves are investigated. The results verify that larger friction coefficient and friction force are crucial for generation and propagation of strong Lamb waves supporting the fact that the main mechanism to transfer mechanical energy using dry-couplant is friction. The sensitivity of Lamb waves to the friction coefficient, highlights the importance of designing specific pads with respect to condition of the surface. Besides, the results show that the normal force and friction coefficient can change the determinism characteristics behavior of multimode Lamb waves. Furthermore, it is shown that the determinism value is sensitive to the friction coefficient and normal force. A similar trend is observed in the determinism values and friction coefficient. In general, a smaller friction coefficient indicates smaller determinism value. Additionally, it is shown that a normal load can change the behavior of a system, as observed from recurrence plots, owing to changes in the Lamb waves trajectories in the phase-space domain. In addition, it is shown that recurrence plots enable the detection of mode transitions in multimode Lamb waves. Recurrence analysis is a complementary tool to frequency domain methods for accurate analysis of multimode Lamb waves behavior.

42 ENGINEERING↗
DOE OSTI2017

Stress Models of the Annual Hydrospheric, Atmospheric, Thermal, and Tidal Loading Cycles on California Faults: Perturbation of Background Stress and Changes in Seismicity

Stresses in the lithosphere arise from multiple natural loading sources that include both surface and body forces. The largest surface loads include near-surface water storage, snow and ice, atmosphere pressure, ocean loading, and temperature changes. The solid Earth also deforms from celestial body interactions and variations in Earth's rotation. We model the seasonal stress changes in California from 2006 through 2014 for seven different loading sources with annual periods to produce an aggregate stressing history for faults in the study area. Our modeling shows that the annual water loading, atmosphere, temperature, and Earth pole tides are the largest loading sources and should each be evaluated to fully describe seasonal stress changes. In California we find that the hydrological loads are the largest source of seasonal stresses. We explore the seasonal stresses with respect to the background principal stress orientation constrained with regional focal mechanisms and analyze the modulation of seismicity. Our results do not suggest a resolvable seasonal variation for the ambient stress orientation in the shallow crust. When projecting the seasonal stresses into the background stress orientation we find that the timing of microseismicity modestly increases from an ~8 kPa seasonal mean-normal-stress perturbation. The results suggest that faults in California are optimally oriented with the background stress field and respond to subsurface pressure changes, possibly due to processes we have not considered in this study. At any time a population of faults are near failure as evident from earthquakes triggered by these slight seasonal stress perturbations.

58 GEOSCIENCES↗
DOE OSTI2012

Recovery Act: Adaptive Environmentally Contained Power and Cooling IT Infrastructure for the Data Center (Final Technical Report)

The objectives of this program were to research and develop a fully enclosed Information Technology (IT) rack system for 100 kilowatts (KW) of IT load that provides its own internal power and cooling with High Voltage Alternating Current (HVAC defined as 480 volt) and chilled water as the primary inputs into the system and accepts alternative energy power sources such as wind and solar. For maximum efficiency, internal power to the IT equipment uses distributed High Voltage Direct Current power (HVDC defined as 360-380 volt) from the power source to the IT loads. The management scheme aggressively controls energy use to insure the best utilization of available power and cooling resources. The solution incorporates internal active management controls that not only optimizes the system environment for the given dynamic IT loads and changing system conditions, but also interfaces with data center Building Management Systems (BMS) to provide a complete end-to-end view of power and cooling chain. This technology achieves the goal of a Power Usage Effectiveness (PUE) of 1.25, resulting in a 38% reduction in the total amount of energy needed to support a 100KW IT load compared to current data center designs.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2018

Increased mechanical loading through controlled swimming exercise induces bone formation and mineralization in adult zebrafish

Exercise promotes gain in bone mass through adaptive responses of the vertebrate skeleton. This mechanism counteracts age- and disease-related skeletal degradation, but remains to be fully understood. In life sciences, zebrafsh emerged as a vertebrate model that can provide new insights into the complex mechanisms governing bone quality. To test the hypothesis that musculoskeletal exercise induces bone adaptation in adult zebrafsh and to characterize bone reorganization, animals were subjected to increased physical exercise for four weeks in a swim tunnel experiment. Cellular, structural and compositional changes of loaded vertebrae were quantifed using integrated high-resolution analyses. Exercise triggered rapid bone adaptation with substantial increases in bone-forming osteoblasts, bone volume and mineralization. Clearly, modeling processes in zebrafsh bone resemble processes in human bone. This study highlights how exercise experiments in adult zebrafsh foster in-depth insight into aging-related bone diseases and can thus catalyze the search for appropriate prevention and new treatment options.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Development of a smart DC grid model

Smart grid and distributed generation should be the solution of the global climate change and the crisis energy of the main source of electrical power generation which is fossil fuel. In order to meet the rising electrical power demand and increasing service quality demands, as well as reduce pollution, the existing power grid infrastructure should be developed into a smart grid and distributed power generation which provide a great opportunity to address issues related to energy efficiency, energy security, power quality and aging infrastructure systems. The conventional of the existing distributed generation system is an AC grid while for a renewable resources requires a DC grid system. This paper explores the model of smart DC grid by introducing a model of smart DC grid with the stable power generation give a minimal and compressed circuitry that can be implemented very cost-effectively with simple components. The PC based application software for controlling was developed to show the condition of the grid and to control the grid become ‘smart’. The model is then subjected to a severe system perturbation, such as incremental change in loads to test the performance of the system again stability. It is concluded that the system able to detect and controlled the voltage stability which indicating the ability of power system to maintain steady voltage within permissible rangers in normal condition.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2024

Value of Nuclear Energy to the Reliability of the North American Power System: Results for Western and Eastern Interconnections

This report documents the fulfillment of a milestone for the United States (U.S.) Department of Energy Office of Nuclear Energy Light Water Reactor Sustainability Program: completing a baseline study of regional impact of nuclear power plants and hydrogen production in maintaining grid services and power quality. Models have been comprehensively demonstrated for the Western Interconnection, or Western Electric Coordinating Council area, and in the Eastern Interconnection for scenarios representative of past extreme events (e.g., drought and heat waves). Understanding the impact on the reliability of the bulk electric system of any reduction in generation capacity from nuclear power, for any reason, is the motivation of this work. Factors that might lead to the premature or unplanned closure of nuclear plants, extended outages, or repurposing of nuclear power include: • Aging infrastructure: Many nuclear power plants in the U.S. are nearing the end of their designed operating lives. Upgrading aging infrastructure can be expensive, and some utilities may choose to retire plants rather than invest in costly upgrades. • Low wholesale electricity prices: The deregulation of the electricity market in many states has led to increased competition and driven down wholesale electricity prices, causing nuclear power operators to seek other revenue sources for their heat and power such as clean hydrogen production. • Renewables growth: The rapid growth of renewable energy sources like solar and wind power is posing a challenge to traditional generation sources like nuclear. While many see renewables as a key part of the clean energy transition, their intermittent nature requires additional grid solutions for reliable power supply. • The potential for regulatory decisions to be in conflict: In its 2021 rulemaking, EPA rule (86 FR 880), the Environmental Protection Agency (EPA) set a compliance date for the ban on processing and distribution in commerce of Decabromodiphenyl Ether (DecaBDE). Since DecaBDE is in many components, particularly wiring, of nuclear power plants which are deemed safety-related or important to safety, three plants would not have been able to restart after their 2023 spring outages, and numerous others would have faced issues in the near future. Fortunately, in this case, the EPA provided relief to the nuclear energy industry. The report provides a summary of the significant role nuclear energy plays in the United States’ power generation mix, supplying around 20% of the nation’s electricity generation, spread across 28 U.S. states. Nuclear power is reliable, mostly unaffected by weather and seasonal changes, and provides a consistent source of baseload power. In terms of capacity, nuclear power plants account for as much as 26% of balancing area power generation capacity. Nuclear power also provides a substantial contribution (e.g., 10% of the inertia in the Eastern Interconnection) of the synchronous spinning mass/inertia that buffers the rate at which frequency changes when a load and generation imbalance occurs (e.g., a large plant trips or a load is suddenly shed due to a transmission outage). This contribution is critical for maintaining grid stability during sudden changes in load or generation.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2015

Investigations of dual-purpose canister direct disposal feasibility - 15106

Direct disposal of commercial spent nuclear fuel (SNF) in dual-purpose canisters (DPCs) could avoid the cost and complexity of re-packaging spent fuel into smaller purpose-built containers, avoid disposing of the DPC hulls as low-level waste, and potentially decrease worker dose. Technical objectives for disposal are: 1) safety of workers and the public, 2) engineering feasibility; 3) thermal management; and 4) criticality control after permanent closure of a repository. The postclosure safety case for DPC direct disposal would resemble that for any repository-waste isolation would be enhanced by choosing host geology in which radionuclide transport is diffusion dominated, and for which transport properties and pathways are insensitive to the expected temperature history. Containment functions would be assigned to the disposal overpack, and published data show that suitable materials exist for most possible disposal environments. Earlier studies showed that DPC-based waste packages would be only slightly larger and heavier than those proposed for a repository in volcanic tuff. Engineered solutions are available for transporting and emplacing them underground, although some could be the largest of their kind. The cost of DPC direct disposal in various geologic settings has been compared to options involving a change to loading standardized multi-purpose canisters, or continuing to load DPCs and re-packaging all of them for disposal. In general DPC direct disposal would cost tens of billions of dollars less, in packaging and disposal costs. Calculations for emplacement in hard rock and sedimentary rock show that host rock peak temperature targets of 100 to 200 deg.C could be met by managing fuel age and burnup, with repository closure at up to 150 years from reactor discharge. For disposal in salt, DPC-based waste packages could be emplaced at only 50 to 100 years from discharge, depending on burnup. Sedimentary media such as shales pose special challenges especially if they have low thermal conductivity. If backfill is used around DPC-based packages its peak temperature could be 150 to 200 deg.C. Without flooding of waste packages with ground water, criticality can never occur. However, some small number of disposal overpacks could fail within the postclosure performance period due to corrosion or disruptive events. Once flooded, the aluminum-based neutron absorber materials used in most DPCs would readily degrade. Analysis has shown that even without neutron absorbers, virtually all DPCs could be subcritical if flooded with chloride brines such as would occur in a salt repository. The licensing basis for existing DPCs involves criticality analysis that may be conservative compared to fuel that is actually loaded, and the difference provides uncredited reactivity margin. Uncredited margin can offset increases in reactivity associated with flooding and basket degradation. For flooding with fresh water, with loss of neutron absorbers, many DPCs have been shown to be subcritical using uncredited margin. Significantly fewer are subcritical if the fuel basket also degrades. Thus, the materials of DPC basket construction (e.g., aluminum or carbon steel) could be deleterious if they fully corrode, along with the neutron absorbers, during the performance period. Logistical simulations are used to better understand the relationship between the needed DPC decay storage time for disposal, and the timing of future events such as the repository opening date, or a transition to loading multi-purpose (disposable) canisters at nuclear power plants. Results show that the maximum benefit from implementing a new canister design, with respect to shortening the cooling time for all SNF including that in DPCs, is associated with the earliest repository start date. As time passes more of the total SNF inventory will be in DPCs such that the value of a transition to multi-purpose canisters will decline, and the remaining options are DPC direct disposal and re-packaging in purpose-designed disposal canisters. Fuel age at emplacement is of interest to evaluate potential impacts from future changes in the fuel management system that could place fuel age limits on dry storage or transportation. The minimum fuel age at emplacement (best-case) is obtained by re-packaging all DPCs into smaller canisters for disposal, thus drastically decreasing the needed decay storage time for any geologic disposal setting. If the industry transitions to smaller, multi-purpose canisters, and without re-packaging, the fuel age at emplacement would be comparable to the best case if: 1) the emplacement power limit is high enough, or 2) both the transition and the repository start date occur early (e.g., 2036 was analyzed). Technical feasibility evaluation continues to show that direct disposal could be safe and cost effective, for some DPCs and in some geologic settings. Direct disposal of a substantial fraction of existing DPCs, limited mainly by thermal management, uncredited criticality margin, materials of DPC basket construction, and the salinity of ground water in the disposal environment, could be part of the overall waste management system. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Validation of high-fidelity ion cyclotron range of frequencies antenna coupling simulations in full 3D geometry against experiments in the ASDEX Upgrade tokamak

We address the validation of finite elements ion cyclotron range of frequencies (ICRF) antenna coupling simulation against experiments performed in the ASDEX Upgrade tokamak. Measurements of the loading resistance in ICRF-heated, magnetically-perturbed 3D plasma discharges are compared against numerical predictions of the RAPLICASOL code. To this end, the 3D induction field and the 3D density profile are modeled by concatenating the PARVMEC, BMW and EMC3-EIRENE codes. The 3D density is input to RAPLICASOL, where full-wave simulations are performed on a finite element mesh retaining full 3D geometry in the ICRF antenna model and the plasma description. The results are further compared with RAPLICASOL simulations using a 1D density profile as measured at the outboard midplane in the same experiments. We find that simulations using a 1D density profile overestimate the change in loading resistance by a factor of ~197 -248%, while simulations using the full 3D density profile are in agreement with experiments within a factor ~16%.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Thermal Energy Storage Configurations for Small Modular Reactor Load Shedding

The increased penetration of intermittent renewable energy technologies such as wind and solar power can strain electric grids, forcing carbon-based and nuclear sources of energy to operate in a load follow mode. For nuclear reactors, load follow operation can be undesirable due to the associated thermal and mechanical stresses placed on the fuel and other reactor components. Various methods of Thermal Energy Storage (TES) can be coupled to nuclear (or renewable) power sources to help absorb grid variability caused by daily load demand changes and renewable intermittency. Two TES techniques are investigated as candidate thermal reservoirs to be used in conjunction with a Small Modular Reactor (SMR): a two-tank sensible heat storage system and a stratified chilled-water storage system. The goal when coupling the two systems to the SMR is to match turbine output and demand and bypass steam to the TES systems to maintain reactor power at approximately 100%. Simulations of IPWR dynamics are run in a high-fidelity FORTRAN model developed at NCSU. Both TES systems are developed as callable FORTRAN subroutines to model the time-varying behavior associated with different configurations of these systems when connected to the SMR simulator. Simulation results reveal the sensible heat storage system is capable of meeting turbine demand and maintaining reactor power constant, while providing enough steam to power four absorption chillers for chilled-water production and storage. Here,the stored chilled water is used to supplement cooling loads of an adjacent facility.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2025

Thermal and electric multidomain dynamic model for integration of power grid distribution with behind-the-meter devices

As renewable energy sources like solar and wind power become more integrated into the grid, coordinated control of behind-the-meter devices is crucial for enhancing grid flexibility and reliability and for meeting cost targets, with standardized models being developed to support this transition. The increasing flexibility and uncertainty of integrated renewable energy grids, along with interactions between various subsystems, make traditional steady-state modeling insufficient to capture transient and dynamic behaviors. Current models (e.g., composite load and battery equivalent models) focus on thermodynamic or electrical characteristics but overlook critical electromechanical interactions. This limits the ability to share performance information for grid services and hampers fast dynamic simulations. In addition, motor stalling is usually triggered by a fault event and attributed to the characteristics of the mechanical torque of the motor, resulting in absorption of a large amount of reactive power during the stalling period. Further, this significant withdrawal of reactive power will deteriorate the dynamic voltage stability of power grids and cause delayed voltage recovery. Therefore, an in-depth modeling of the thermodynamics or mechanical torque is essential to study the impacts of the realistic torque characteristics of those behind-the-meter devices on power system voltage stability. This study developed a dynamic multidomain model for building HVAC systems, such as air-source heat pumps, to simulate their thermal and electrical responses to grid transients. The model can accurately predict power metrics with a mean absolute percentage error of 10%, by validating against with power system computer-aided design performance data. Case studies demonstrate the model capability of capturing the transient response to sudden voltage changes, rapid load fluctuations, and system shutdowns respectively. During a sudden voltage drop (30% for 0.1s), a fully loaded heat pump’s motor speed dropped, continued declining, and shut down after 3.6s, with severe power oscillations and a torque spike. A partially loaded unit experienced temporary oscillations but stabilized. Under higher building loads, compressor speed increased from 64% to 100%, with power and torque rising before stabilizing. In safety-triggered shutdowns, power decreased after minor fluctuations, and torque briefly spiked before dropping to zero.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2023

Distributed Energy Resource-Cognizant Upgrade Paths to the Traditional Restoration Strategy of Utilities for Improved Load Restoration

Climate change has resulted in increasingly impactful and more frequent occurrences of extreme weather events. This trend poses a significant challenge for distribution utilities and system operators to ensure that there is uninterrupted power supply to critical loads in their networks under fault scenarios; however, currently, utilities deploying the automated fault location, isolation and restoration (FLISR) function in their advanced distribution management system (ADMS) do not take into account the available generation and load-modification capabilities of distributed energy resources present in the disconnected network due to an upstream isolated fault. This results in the network reconfiguration and restoration to result in sub-optimal load restoration. Therefore, this paper presents two approaches that can upgrade the existing FLISR capabilities of distribution utilities to significantly increase the restoration of critical loads. The performance of the proposed approaches is evaluated on a numerical model of a real distribution feeder in Georgia, USA.

DER↗
DOE OSTI2024

Evaluating the Impact of Off-Design CHP Performance on the Optimal Sizing and Dispatch on Hybrid Renewable-CHP Distributed Energy Resources

The maturation of distributed energy resources (DER) has prompted the exploration of their deployment in commercial building applications due to their potential to supply energy at lower costs and emissions rates compared to centralized generation. While several software tools exist for evaluating the techno-economic potential of integrated renewable energy and combined heat and power (CHP) systems for distributed generation applications, many suffer from poor accuracy in capturing off-design (part load and changes in ambient air temperature and pressure) performance characteristics of microturbines, combustion turbines, or internal combustion engines. Thus, this paper presents a methodology for integrating these off-design characteristics in the mixed-integer linear program within REopt, a hybrid DER screening tool. The economic impact of the CHP off-design performance is observed through several application studies of various hybrid system configurations in different climates. Each study indicates how CHP off-design performance influences optimal sizing and dispatch decisions and therefore overall system economic value. We observe through case studies that modeling without the off-design effects, depending on the CHP prime mover and site, can result in Net Present Value predictions of hybrid systems that can be overoptimistic in frequently hot climates (up to 52%), too conservative in frequently cold climates (up to 11%), or unaffected (+/-1%) in temperate climates. Cases also highlight several advantages of hybrid systems relative to non-hybrid systems such as total economic value and the systems' ability to mitigate potentially negative consequences attributed to off-design performance.

ambient de-rate↗
DOE OSTI2020

Evaluation of a Geotechnical Compaction Model to Estimate Sediment Deformation

When surface ruts from vehicle activity occur above archeological deposits, there is a potential for an impact to the archeological record to occur. While impacts to the soil surface are relatively straightforward to describe, sub-surface disturbances are more difficult to quantify. In particular, disturbances to buried archeological materials can be difficult to characterize. Materials can be damaged by surface disturbances, but they can also be impacted even if they stay intact. Interpretation of intact materials relocated within the sediment column can be problematic. Traditional characterization methods (e.g. excavation) can also disturb archaeological materials. Here, we present a geotechnical compaction model that can be used to assist with sub-surface characterization under vehicle ruts formed during off-road travel. The model is based on a Boussinesq analysis of stress increase below a surface load. The change in bulk density resulting from compaction is assumed to be proportional to the stress increase. The model results were compared against pilot scale tests conducted with homogeneous sediment and field scale in-situ tests. The results indicate that the model generally agreed with measurements to within 20%, although only a single soil type was evaluated in these studies, with a narrow range of initial bulk densities and rut depths. While application of the model across a broader matrix of soil types, bulk densities and rut depths would increase confidence in the model, it appears that the model may be suitable for use in archeological field investigations. Potential uses include both compliance and research based field applications.

Fritz, Brad G.↗
DOE OSTI2018

Optimization of Process Parameters for the Axial Distortion and Distortion Range During Die Quenching of a Spiral Bevel Gear

The strength of high-duty gears can be improved by carburizing and quenching processes. Quenching distortion is inevitable during the process, and it has direct effects on the precision of the gear. For spiral bevel gear with big diameter and small thickness, die quenching process is applied in the manufacturing to control the distortion in axial direction. Die quenching parameters must be optimized to minimize the distortion while considering non-uniformity of chemical compositions and loads. In this paper, material models of gear material (22CrMoH) built based on the phase transformation kinetics, static mechanical properties and phase transformation plasticity equations. Finite element analysis (FEA) models are conducted to study the whole die quenching process based on the production process. Die quenching experiments and testing of microstructures and distortions are conducted to verify the accuracy of the FEA models. The effects of loads and bottom die obliquity on the final distortion are studied to set the appropriate range and control distortion. The distortion was very sensitive to the bottom die obliquity and some part of load ranges. The distortion changes little when the load of inner die was in the range of 1.38-2.07 MPa and the load of outer die was in the range of 2.07-2.76 MPa. The distortion range is fitted the production requirements by setting the inclination angle of bottom die between 0.12° and 0.29°.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Molecular Dynamics Simulation Study of Uniaxial Ratcheting Behaviors for Ultrafine-Grained Nanocrystalline Nickel

In this paper, molecular dynamics (MD) simulation-based study of deformation behavior of ultrafine-grained nanocrystalline nickel under asymmetric cyclic loading having stress ratios (R) such as − 0.2, − 0.4 and − 0.6 for different temperatures, viz. 100, 300 and 500 K, has been performed using embedded atom method potential. The predicted ratcheting strain by MD simulation for nanocrystalline Ni varies from 15 to 30%. A significant increase in ratcheting strain has been observed with the increase in temperature. It has been observed that the number of vacancies increases, and the number of clusters decreases with the increase in temperature. Slight reduction in crystallinity is identified at the middle of the each loading cycle from the performed cluster analysis. Zigzag pattern of dislocation density has been observed and leads to the decrease in dislocation density with the increase in temperature. Stress ratio does not show any significant effect on the number of vacancies, clusters and dislocation density on structural evolution during the asymmetric cyclic loading. Slight change in the grain rotation has been observed with the increase in temperature, and there is almost no change in the final texture evolved. From the post-tensile tests, ultimate tensile strength that remains same may be due to constant average dislocation density.

36 MATERIALS SCIENCE↗