Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Performance Rating Method”

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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Accelerated simulation of stochastic particle removal processes in particle-resolved aerosol models

Stochastic particle-resolved methods have proven useful for simulating multi-dimensional systems such as composition-resolved aerosol size distributions. While particle-resolved methods have substantial benefits for highly detailed simulations, these techniques suffer from high computational cost, motivating efforts to improve their algorithmic efficiency. Here we formulate an algorithm for accelerating particle removal processes by aggregating particles of similar size into bins. We present the Binned Algorithm for particle removal processes and analyze its performance with application to the atmospherically relevant process of aerosol dry deposition. We show that the Binned Algorithm can dramatically improve the efficiency of particle removals, particularly for low removal rates, and that computational cost is reduced without introducing additional error. In simulations of aerosol particle removal by dry deposition in atmospherically relevant conditions, we demonstrate about 50-times increase in algorithm efficiency.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Analysis of reaction schemes using maximum rates of constituent steps

Significance The design of active and selective catalysts is essential for a wide range of industrial applications and societal issues. A fundamental approach is to identify the key elementary steps and to elucidate the predicted reaction kinetics for potential reaction mechanisms. We present a methodology to analyze analytically the performance of catalytic reaction schemes by calculation of the maximum rates of the constituent steps. This proposed methodology can be used to identify the important transition states and adsorbed species, such that more detailed calculations can be carried out for these species, whereas more approximate methods can be used for the remaining species, thereby substantially reducing the computational time required to elucidate how catalyst performance is controlled by the fundamental surface chemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Application of machine learning techniques for fast MeV x-ray spectra unfolding from filter stack spectrometer data

Recovery of MeV x-ray spectra from detector signals is difficult because the response matrix inversion is ill-conditioned and current methods are too slow for high-repetition-rate experiments. In this work, we make use of neural networks to unfold MeV x-ray spectra from measurements obtained with a filter stack spectrometer at rates of near 40 Hz. The neural network was trained on synthetic data and tested on both synthetic and experimental data, the latter obtained in two separate experiments performed at the Omega EP laser facility. We show here that this unfolding method has good performance on synthetic data and that it is a promising option for experimental data of up to 40 MeV. The accuracy on experimental data is verified by using a simple forward model to compare against measured values.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Investigation of an Ultrafast Harmonic Resonant RF Kicker

An Energy Recovery Linac (ERL) based multi-turn electron Circulator Cooler Ring (CCR) is envisaged in the proposed Jefferson Lab Electron Ion Collider (JLEIC) to cool the ion bunches with high energy (55 MeV), high current (1.5 A), high repetition frequency (476.3 MHz), high quality magnetized electron bunches. A critical component in this scheme is a pair of ultrafast kickers for the exchange of electron bunches between the ERL and the CCR. The ultrafast kicker should operate with the rise and fall time in less than 2.1 ns, at the repetition rate of ~10s MHz, and should be able to run continuously during the whole period of cooling. These -and-fall time being combined together, are well beyond the state-of-art of traditional pulsed power supplies and magnet kickers. To solve this technical challenge, an alternative method is to generate this high repetition rate, fast rise-and-fall time short pulse continuous waveform by summing several finite number of (co)sine waves at harmonic frequencies of the kicking repetition frequency, and these harmonic modes can be generated by the Quarter Wave Resonater (QWR) based multifrequency cavities. Assuming the recirculator factor is 10, 10 harmonic modes (from 47.63 MHz to 476.3 MHz) with proper amplitudes and phases, plus a DC offset are combined together, a continuous short pulse waveform with the rise-and-fall time in less than 2.1 ns, repetition rate of 47.63 MHz waveform can be generated. With the compact and matured technology of QWR cavities, the total cost of both hardware development and operation can be reduced to a modest level. Focuse on the technical scheme, three main topics will be discussed in this thesis: the synthetization of the kicking pulse, the design and optimization of the deflecting QWR multi-integer harmonic frequency resonator and the fabrication and bench measurements of a half scale copper prototype. In the kicking pulse synthetization part, we begin with the Fourier Series expansion of an ideal square pulse, and get a Flat-Top waveform which will give a uniform kick over the bunch length of the kicked electron bunches, thus the transverse emittance of these kicked electron bunches can be maintained. By using two identical kickers with the betatron phase advance of 180 degree or its odd multiples, the residual kick voltage wave slopes at the unkicked bunch position will be totally cancelled out. Flat-Top waveform combined with two kicker scheme, the transverse emittance of the cooling electron bunches will be conserved during the whole injection, recirculation, and ejection processes. In the cavity design part, firstly, the cavity geometry is optimized to get high transverse shunt impedance thus less than 100 W of RF losses on the cavity wall can be achieved for all these 10 harmonic modes. To support all these 10 harmonic modes, group of four QWRs are adopted with the mode distribution of 5:3:1:1. In the multi-frequency cavities such as the five-mode-cavity and the three-mode-cavity, tunings are required to achieve the design frequencies for each mode. Slight segments of taper design on the inner conductor help to get the frequencies to be exactly on the odd harmonic modes. Stub tuners equal to the number of resonant modes are inserted to the outer conductor wall to compensate the frequency shifts due manufacturing errors and other perturbations during the operation such as the change of the cavity temperature. Single loop couple is designed for all harmonic modes in each cavity. By adjusting its loop size, position and rotation, it is possible to get the fundamental mode critical coupled and other higher harmonic modes slightly over coupled. A broadband circulator will be considered for absorbing the reflected power. Finally in this part, multipole field components due to the asymmetric cylindrical structure around the beam axis of the cavity as well as the beam-induced higher order mode (HOM) issues will be analyzed and discussed in this thesis. A half-scale copper prototype cavity (resonant frequencies from 95.26 MHz to 857.34 MHz) was fabricated to validate the electromagnetic characteristics. With this half scale prototype, the tuning processes of multiple harmonic frequencies, unloaded quality factor measurements of each mode, and bead-pull measurements are performed. The bench measurement results matched well with the simulation results, which have validated our cavity design and construction methods. Finally, a simple mode combining experiment with five separate signal generators was performed on this prototype cavity and the desired fast rise/fall time (1.2 ns), high repetition rate (95.26 MHz) waveform was captured, which finally proved our design of this ultrafast harmonic kicker.

43 PARTICLE ACCELERATORS↗
DOE OSTI2018

A computational fluid dynamics simulation framework for ventricular catheter design optimization

OBJECTIVE Cerebrospinal fluid (CSF) shunts are the primary treatment for patients suffering from hydrocephalus. While proven effective in symptom relief, these shunt systems are plagued by high failure rates and often require repeated revision surgeries to replace malfunctioning components. One of the leading causes of CSF shunt failure is obstruction of the ventricular catheter by aggregations of cells, proteins, blood clots, or fronds of choroid plexus that occlude the catheter’s small inlet holes or even the full internal catheter lumen. Such obstructions can disrupt CSF diversion out of the ventricular system or impede it entirely. Previous studies have suggested that altering the catheter’s fluid dynamics may help to reduce the likelihood of complete ventricular catheter failure caused by obstruction. However, systematic correlation between a ventricular catheter’s design parameters and its performance, specifically its likelihood to become occluded, still remains unknown. Therefore, an automated, open-source computational fluid dynamics (CFD) simulation framework was developed for use in the medical community to determine optimized ventricular catheter designs and to rapidly explore parameter influence for a given flow objective. METHODS The computational framework was developed by coupling a 3D CFD solver and an iterative optimization algorithm and was implemented in a high-performance computing environment. The capabilities of the framework were demonstrated by computing an optimized ventricular catheter design that provides uniform flow rates through the catheter’s inlet holes, a common design objective in the literature. The baseline computational model was validated using 3D nuclear imaging to provide flow velocities at the inlet holes and through the catheter. RESULTS The optimized catheter design achieved through use of the automated simulation framework improved significantly on previous attempts to reach a uniform inlet flow rate distribution using the standard catheter hole configuration as a baseline. While the standard ventricular catheter design featuring uniform inlet hole diameters and hole spacing has a standard deviation of 14.27% for the inlet flow rates, the optimized design has a standard deviation of 0.30%. CONCLUSIONS This customizable framework, paired with high-performance computing, provides a rapid method of design testing to solve complex flow problems. While a relatively simplified ventricular catheter model was used to demonstrate the framework, the computational approach is applicable to any baseline catheter model, and it is easily adapted to optimize catheters for the unique needs of different patients as well as for other fluid-based medical devices.

Neurosciences & Neurology↗
DOE OSTI2022

Low level coupling scheme between neutronics and thermal-hydraulics based on Anderson acceleration

The simulation of nuclear reactors is a multiphysics problem mixing, amongst other fields, neutron transport and thermal-hydraulics. The simplest and most used approach in multiphysics simulation is based on the coupling of single-physics codes in a black-box fashion. However, in order to reduce the computational time needed for such simulations, case-dependent optimizations are often required. In this paper, we aim at reducing the computational time required to solve a coupled neutronic/thermal-hydraulic steady-state problem on a simplified Pressurized Water Reactor (PWR) core. The idea is to deal simultaneously with the coupling of the energy groups of the deterministic neutronic description of the core and its thermal-hydraulic description with the Anderson acceleration. By doing so, the fission source terms are directly accelerated instead of the power map as done in most cases. The power method used to solve the k-eigenvalue problem inside the neutronic solver is thus accelerated with the Anderson acceleration. The numerical experimentations conducted in this work are performed using APOLLO3 and THEDI, and indicate that such coupling strategy improves the convergence rates in terms of number of iterations required and the total computational time. (authors)

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2019

Design of Energy Storage Friendly Regulation Signals using Empirical Mode Decomposition

This paper presents an energy storage friendly regulation signal design method based on empirical mode decomposition (EMD). Battery energy storage systems (BESS) have a very fast response rate and excellent ramping capability, making them ideal resources for providing fast regulation services. However, the limitation in energy storage capacity prevents the BESS from following non-energy neutral signals for prolonged durations. The existing BESS-friendly regulation signal design uses the filter-based approach, which cannot guarantee the resultant fast changing signals are energy neutral. The EMD-based approach decomposes the raw regulation signal into an energy-neutral, fast-changing component and a slow-changing component. The fast and slow regulation signals obtained using the proposed method are compared with the PJM RegD and RegA signals. Simulation results and cost-benefit analysis demonstrate that both generators and BESSs have achieved better performance in terms of revenue, response rate, and lifetime when responding to the EMD-based regulation signals compared with the filter-based RegA and RegD signals.

Meng, Yao↗
DOE OSTI2017

Development of the Advanced D1S for Shutdown Dose Rate Calculations in Fusion Reactors

The assessment of the shutdown dose rate due to neutron activation is fundamental for shielding design, materials selection, licensing and planning of maintenance operations in high performances fusion devices. The shutdown dose rate calculations require the combined use of radiation transports and inventory codes. The typical approach consists in a two steps procedure. A pure neutron transport simulation is performed in a first step to calculate the spatial distribution of neutron spectra. The results are used as input for an activation calculation that provides the decay gamma source used in a second step for a pure gamma transport simulation (rigorous-two step, R2S). The Direct 1-Step (D1S) approach has been developed more than ten years ago by ENEA and the ITER team: this technique relies on a coupled neutron-decay gamma transport in a single simulation. It is based on the use of a modified version of the MCNP5 Monte Carlo code with specially tailored nuclear cross-section data for transport and FISPACT inventory code for temporal behaviour. The 'Advanced-D1S' is an improved version of D1S in which additional computational features have been introduced, such as the mesh tally capability and continuous time evolution assessment of the dose rate in single run dose. It has been validated through measurements at JET tokamak and comparison with R2S codes and a future benchmark experiment during next high performance deuterium-tritium campaign is in preparation at JET. It has also been extensively used for ITER calculations and recently applied to DEMO assessment. Present limitations and in progress code improvement strategy are described and discussed in this paper.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2016

SU-F-R-47: Quantitative Shape Relationship Analysis of PTV Modification for Critical Anatomy Sparing and Its Impact On Pathologic Response for Neoadjuvant Stereotactic Radiotherapy for Pancreatic Cancer

Purpose: Stereotactic body radiation therapy (SBRT) may be used to increase surgery candidacy in borderline resectable (BRPC) and locally advanced (LAPC) pancreatic cancer. However, the planning target volume (PTV) may need to be limited to avoid toxicity when the gross tumor volume (GTV) is anatomically involved with surrounding critical structures. Our study aims to characterize the coverage of GTV and investigate the association between modified PTV and pathologic (pCR) or near pathologic (npCR) complete response rates determined from the surgical specimen. Methods: Patients treated with neoadjuvant pancreas SBRT followed by surgery from 2010–2015 were selected from Oncospace. Overlap volume histogram (OVH) analysis was performed to determine the extent of compromise of the PTV from both the GTV and a standard target (GTV+3mm). Subsequently, normalized overlap volume (%) was calculated for: (1) GTV-PTV, and (2) GTV+3mm expansion-PTV. A logistic regression model was used to identify the association between the overlap ratios and ≥ npCR(pCR/npCR) stratified by active breathing control (ABC) versus free-breathing status. Results: Eighty-one (BRPC: n=42, LAPC: n=39) patients were available for analysis. Nearly 40% (31/81) had ≥npCR and 75% (61/81) were able to complete ABC. Mean coverage of the GTV-PTV was 92.6% (range, 59.9%–100%, SD = 8.68) and coverage of the GTV+3mm expansion-PTV was 85. 2% (range, 59.9% −100.0%, SD= 8.67). Among the patients with ABC, every 10% increase in GTV coverage doubled the odds to have ≥npCR (OR = 1.82, p=0.06). Coverage of GTV+3mm expansion was not associated with ≥npCR regardless of ABC status. Conclusion: Preferential sparing of critical anatomy over GTV-PTV coverage with ABC management suggests worse ≥npCR rates for neoadjuvant SBRT in BRPC and LAPC. Limiting the GTV and GTV+3mm expansion in free-breathing patients was not associated with pathologic response perhaps due to larger GTV definitions as a result of motion artifacts in free-breathing CT scans. Collaboration with Toshiba, Elekta, and Phillips.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Operating a commercial building HVAC load as a virtual battery through airflow control

Virtual battery (VB) is an innovative method to model flexibility of building loads and effectively coordinate them with other resources at a system level. Unlike a real battery with a dedicated power conversion system for charging control, methods are required for operating building loads to deviate from the baseline to respond to grid signals. This paper presents a VB control for a commercial heating, ventilation, and air conditioning (HVAC) system to follow the desired power consumption in real-time by adjusting zonal airflow rates. The proposed method consists of two parts. At the system level, a mixed feedforward and feedback control is used to estimate the desired total airflow rate. At the zone level, two priority-based algorithms are then proposed to distribute the total airflow rate to individual zones. In particular, a zonal airflow limit estimation method is proposed using machine-learning techniques, in contrast to physics-based thermal models in existing studies, to more accurately capture zonal thermal dynamics and improve temperature control performance. An office building on the Pacific Northwest National Laboratory campus is implemented in EnergyPlus, and used to illustrate and validate the proposed control.

Wang, Jiyu↗
DOE OSTI2022

Measuring the maximum capacity and thermal resistances in phase-change thermal storage devices

Thermal energy storage can increase the efficiency of the electric grid by adding flexibility to thermal systems. The value of thermal storage is a function of its energy and power density, which are driven by the capacity and thermal resistances in the storage device. Measuring these properties in-situ at the device level is an important step to understanding the performance and improving the design of thermal storage systems. Here, we present methods to measure the total capacity and thermal resistances in heat exchangers with integrated phase change materials. These methods are demonstrated on two thermal storage devices - a 570-kWh ice-based storage tank and a 0.35-kWh graphite-tetradecane composite device. The results show how thermal resistances evolve with the state of charge and discharge rate in these devices and quantify the impact of applied pressure on the contact resistance in composite phase change material heat exchangers. The proposed method allows for easy comparison between different systems and provides information on the thermal bottlenecks limiting performance. Ultimately, these measurements will allow designers to make robust, high-performance thermal storage devices for next-generation thermal systems.

25 ENERGY STORAGE↗
DOE OSTI2022

TRISO SiC Failure Probability for Reactivity Initiated Accidents in High-Temperature Gas-Cooled Reactors

This work analyzes the failure process of the silicon carbide (SiC) layer in tristructural isotropic (TRISO) during reactivity-initiated accident scenarios for a high-temperature gas-cooled reactor (HTGR) with BISON. Two cases are considered—a group control rod withdrawal (CRW) and a control rod ejection (CRE)—reproduced from a previous study. Failure probability is modeled using Weibull statistics, and worst-case scenario Weibull parameters are adopted to simulate the envelopes in BISON with a one-dimensional TRISO model. CRW scenario results are characterized by higher values of maximum energy deposition and final temperature and volumetric strain with respect to the CRE ones, but the latter have remarkably higher SiC failure probability, mainly due to the offset in strain rates between the two cases. This work also confirms the validity and conservatism of the performance envelopes produced in a previous work by replicating the envelope formulation using RELAP5-3D and RAVEN with a different sampling technique and obtaining consistent results. A sensitivity analysis using the Sobol variance decomposition method on SiC failure probability is then performed involving a set of inputs on both CRW and CRE. The two most important parameters are Weibull modulus and characteristic stress, and their relative importance depends on the specific case. The proposed interpretation of the results is that both energy deposition and strain rate influence the relative degree of importance of the failure parameters. Computation of 95% confidence intervals around worst-case scenario SiC failure probability values is also carried out for four different sets of Weibull parameters. Heren a new criterion for SiC TRISO quality classification built upon safety-based ranges of Weibull parameters is proposed to be integrated in future Fuel-Production Quality Assurance Plans.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2019

Experimental and Numerical Investigations of Cyclic Plastic Deformation of Al-Mg Alloy

In this work, low-cycle fatigue (LCF) tests are performed on as-received and solution-treated Al-Mg alloy (AA 5754). Solution heat treatment of the as-received alloy is performed at 530 °C for 2 h and then quenched in water at room temperature. The low-cycle fatigue response of the as-received and solution-treated alloy is evaluated at five different strain amplitudes from 0.2 to 0.6%. The strain rate of 0.5 × 10{sup −3} s{sup −1} is kept constant in all the LCF tests. The LCF behavior of AA 5754 is modeled by finite element method (FEM) using Chaboche kinematic hardening cyclic plasticity model. Hardening behavior or fatigue life of as-received and solution-treated alloy is successfully simulated using this model. The results obtained by FEM simulations are compared with those obtained by LCF experiments. Microstructural studies are also performed for as-received and solution-treated alloy. The fracture surfaces obtained from LCF tests are analyzed by scanning electron microscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2013

On the connection of semiclassical instanton theory with Marcus theory for electron transfer in solution

We present a derivation of Marcus theory of electron transfer in solution starting from semiclassical instanton theory. The conventional semiclassical instanton theory provides an inadequate description of the electron transfer process in the inverted Marcus regime. This has been attributed to the lack of backscattering in the product region, which is represented as a semi-infinite continuum of states. For electron transfer processes in condensed phase, the electronic states in the acceptor well are bound, which violates the continuum assumption. We show by detailed analysis of the minimum action path of a model system for electron transfer that the proper tunneling coordinate is a delocalized, 'bead-count' mode. The tunneling mode is analytically continued in the complex plane as in the traditional derivation. Unlike the traditional analysis where the method of steepest descent is used, the tunneling coordinate is treated as a quasi-zero mode. This feature allows including the influence of backscattering in the acceptor well and leads to the recovery of the Marcus formula for the rate of electron transfer. The results have implications on the performance of ring polymer molecular dynamics for the study of electron transfer dynamics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

The preparation and characterization of iron fluorides polymorphs FeF{sub 3}·0.33H{sub 2}O and β-FeF{sub 3}∙3H{sub 2}O as cathode materials for lithium-ion batteries

Graphical abstract: Better rate capability and cycling performance were observed for β-FeF{sub 3}·3H{sub 2}O/C prepared by mechano-chemical synthesis. - Highlights: • A novel mechano-chemical preparation method. • The use of NH{sub 4}F as starting material. • Better electro-chemical performance in the case of β-FeF{sub 3}·3H{sub 2}O/C. - Abstract: Two kinds of iron fluorides, FeF{sub 3}·0.33H{sub 2}O and β-FeF{sub 3}∙3H{sub 2}O, have been synthesized by different chemical routes using Fe(NO{sub 3}){sub 3}·9H{sub 2}O and NH{sub 4}F as precursors and investigated as cathode materials for secondary lithium batteries. β-FeF{sub 3}·3H{sub 2}O was obtained via a mechano-chemical process and FeF{sub 3}·0.33H{sub 2}O was obtained by a precipitation reaction from ethanol solution. To further improve their electrochemical properties, a ball milling process with carbon has been used to form composites. The fluorides were characterized by X-ray diffraction (XRD), thermal analysis, FTIR spectroscopy, galvanostatic charge/discharge and cyclic voltammetry measurements. The results showed that the as-prepared β-FeF{sub 3}·3H{sub 2}O/C exhibited better rate performance and cycling stability. It exhibited an initial discharge capacity of 199.6 mA h g{sup −1} at a current density of 20 mA g{sup −1} in a voltage range of 1.8–4.5 V and still reserved a discharge capacity of about 146.5 mA h g{sup −1} after 10 cycles. Only a capacity loss of 15 mA h g{sup −1} and 7 mA h g{sup −1} was observed when the current density was at 40 mA g{sup −1} and 80 mA g{sup −1}, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Electrodeposited manganese dioxide nanostructures on electro-etched carbon fibers: High performance materials for supercapacitor applications

Highlights: • We report a facile method for fabrication of MnO{sub 2} nanostructures on electro-etched carbon fiber. • MnO{sub 2}-ECF electrode shows outstanding supercapacitive behavior even at high discharge rates. • Exceptional cycle stability was achieved for MnO{sub 2}-ECF electrode. • The coulombic efficiency of MnO{sub 2}-ECF electrode is nearly 100%. - Abstract: In this article we introduce a facile, low cost and additive/template free method to fabricate high-rate electrochemical capacitors. Manganese oxide nanostructures were electrodeposited on electro-etched carbon fiber substrate by applying a constant anodic current. Nanostructured MnO{sub 2} on electro-etched carbon fiber was characterized by scanning electron microscopy, X-ray diffraction and energy dispersive X-ray analysis. The electrochemical behavior of MnO{sub 2} electro-etched carbon fiber electrode was investigated by electrochemical techniques including cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. A maximum specific capacitance of 728.5 F g{sup −1} was achieved at a scan rate of 5 mV s{sup −1} for MnO{sub 2} electro-etched carbon fiber electrode. Also, this electrode showed exceptional cycle stability, suggesting that it can be considered as a good candidate for supercapacitor electrodes.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Fatigue crack growth rates of X100 steel welds in high pressure hydrogen gas considering residual stress effects

Fatigue crack growth rate (FCGR) data were measured in high pressure hydrogen gas versus stress intensity factor range (ΔK) in specimens removed from a X100 welded steel pipe. Three distinct regions of the pipe weld were examined: base metal, weld fusion zone, and heat affected zone. Tests were performed at a load ratio (R) of 0.5, frequency of 1 Hz, and at a hydrogen gas pressure of 21 MPa. Tests were also performed in air at 10 Hz as a reference. Fatigue crack growth rates were observed to be over an order of magnitude higher for tests performed in hydrogen compared to the rates from tests in air. Residual stress measurements were collected on identical specimens cut from the base metal, weld, and heat affected zone to account for their influence on measured FCGR data. The slitting method provided residual stress and residual stress intensity factor (K res ), the effect of which was removed from the FCGR data using K norm in order to provide a more direct comparison of crack growth resistance of the base metal, weld and heat affected zone. Prior to accounting for residual stress, FCGR in hydrogen gas appeared to be highest in the weld fusion zone. Furthermore, after accounting for residual stress effects, the weld fusion zone FCGR data converged to the base metal FCGR data, which underscores the importance of accounting for residual stress effects when assessing fatigue performance.

42 ENGINEERING↗
DOE OSTI2018

Inferring Strength of Tantalum from Hydrodynamic Instability Recovery Experiments

Hydrodynamic instability experiments allow access to material properties at extreme conditions, where strain rates exceed 105 s -1 and pressures reach 100 GPa. Current hydrodynamic instability experimental methods require in-flight radiography to image the instability growth at high pressure and high strain rate, limiting the facilities where these experiments can be performed. An alternate approach, recovering the sample after loading, allows measurement of the instability growth with profilometry. Tantalum samples were manufactured with different 2D and 3D initial perturbation patterns and dynamically compressed by a blast wave generated by laser ablation. The samples were recovered from peak pressures between 30 and 120 GPa and strain rates on the order of 107 s -1 , providing a record of the growth of the perturbations due to hydrodynamic instability. These records are useful validation points for hydrocode simulations using models of material strength at high strain rate. Recovered tantalum samples were analyzed, providing an estimate of the strength of the material at high pressure and strain rate.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗