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At least 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Importance of Considering Near-Surface Attenuation in Earthquake Source Parameter Estimation: Insights from Kappa at a Dense Array in Oklahoma

ABSTRACT Separating earthquake source spectra from propagation effects is challenging. The propagation effect contains a site-dependent term related to the high attenuation of shallow sediments. Neglecting the site-dependent attenuation can cause large biases and scattering in the corner-frequency (fc) estimates, resulting in significant stress-drop deviations. In this study, we investigate shallow attenuation at the LArge-n Seismic Survey in Oklahoma (LASSO) and site-related biases and scattering in source parameter measurements due to simplified attenuation models. We measure the high-frequency spectral decay parameter kappa on the vertical acceleration spectra of regional earthquakes (125 km away). The site-dependent kappa (κ0,acc) suggests that attenuation increases rapidly at shallow depth and is highly site-dependent. 10%–75% of the attenuation is site-dependent for S waves and even larger for P waves. The quality factor for S waves (QS) ranges from 10 to 100 in the upper 400 m. QP for P waves is mostly below 10 within the same depth. The Quaternary sediments tend to be more attenuating (QS<30), but the Permian rocks also can have high attenuation. We demonstrate that using a non-site-dependent attenuation model in single-spectra fitting leads to large scattering in fc estimates among stations with apparent good fits. The apparent fc can significantly deviate when the range of site-dependent kappa is large or with a higher assumed source spectral fall-off rate n. The biases in apparent fc depend on site condition and distance; however, the correlation between fc and these factors might not be obvious, depending on model assumptions. An apparent increase of stress drop with magnitude in a previous study for local microearthquakes (1.3

Chang, Hilary↗
DOE OSTI2022

Towards 20 T Hybrid Accelerator Dipole Magnets

We report the most effective way to achieve very high collision energies in a circular particle accelerator is to maximize the field strength of the main bending dipoles. In dipole magnets using Nb-Ti superconductor the practical field limit is considered to be 8-9 T. When Nb 3 Sn superconductor material is utilized, a field level of 15-16 T can be achieved. To further push the magnetic field beyond the Nb 3 Sn limits, High Temperature Superconductors (HTS) need to be considered in the magnet design. The most promising HTS materials for particle accelerator magnets are Bi2212 and REBCO. However, their outstanding performance comes with a significantly higher cost. Therefore, an economically viable option towards 20 T dipole magnets could consist in an “hybrid” solution, where both HTS and Nb3Sn materials are used. We discuss in this paper preliminary conceptual designs of various 20 T hybrid magnet concepts. After the definition of the overall design criteria, the coil dimensions and parameters are investigated with finite element models based on simple sector coils. Preliminary 2D cross-section computation results are then presented and three main layouts compared: cos-theta, block, and common-coil. Both traditional designs and more advanced stress-management options are considered.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

Forecasting the Decay of Hybrid Perovskite Performance Using Optical Transmittance or Reflected Dark-Field Imaging

The practicality and economic viability of hybrid perovskite solar cells hinge on their operational lifetime, and methods for forecasting the performance of perovskites under different operational stresses are urgently needed. Here, we explore the evolution of material-level optoelectronic properties as MAPbI 3 degrades and discover universal behaviors where the carrier diffusion length (L D ) decays before quasi-Fermi-level splitting (ΔE F ), regardless of the specific stress protocol (oxygen, humidity, thermal stress, or a combination). We employ a machine learning greedy feature selection model that uses initially measured properties to predict the time it takes L D to decrease to 85% of its initial value with a prediction accuracy of 12.8%. This model reveals a strong correlation between the initial rate of transmittance change and the time until loss of transport. We translate this material-level finding to photovoltaic device-level forecasting by demonstrating that the rate of change of transmittance is equivalent to the rate of change of the spatial standard deviation of dark-field image intensity (i.e., scattered light intensity) collected in reflection mode (and thus applicable to devices with opaque contacts). Furthermore, this work demonstrates that transmittance and scattering methods are highly effective for accelerated material (and device) stability evaluation and forecasting.

14 SOLAR ENERGY↗
DOE OSTI2022

Multimode Characterization Approach for Understanding Cell-Level PV Performance and Degradation

Cell-level degradation processes impact the economic viability and large-scale deployment prospects for both established and emerging photovoltaic (PV) technologies. This project addresses the need to develop experimental and device-modeling approaches for studying cell-level degradation processes in photovoltaic (PV) devices using a variety of characterization techniques that provide access to complementary material and device properties. Our results demonstrate that by coupling characterization results with device modeling it is possible to develop comprehensive understanding of processes leading to performance limitations and degradation. This project developed a suite of novel measurement techniques including pulsed-light-bias operando X-ray and photoelectron spectroscopy (popXPS), light-biased scanning microwave impedance microscopy (sMIM), and near-field transport imaging (TI). In addition, operando characterization methodologies and in situ stressing capabilities have been developed and applied for techniques including electron-beam-induced current (EBIC), cathodoluminescence (CL), and Kelvin probe force microscopy (KPFM). Device-physics models were developed and applied to simulate correlative, multi-mode measurements to extract material and device parameters that control performance degradation. These characterization and modeling techniques were applied in a multi-mode approach to probe cell-level degradation mechanisms in Cd(Se,Te) and hybrid perovskite PV devices. Together these efforts contribute to foundational PV degradation science by establishing a framework for understanding PV performance degradation at the cell level and benefit the U.S. PV industry by providing resources in the form of novel experimental capabilities, knowledge gained, and available expertise that can accelerate research and development of improved PV device materials and architectures. The project provided a comprehensive understanding of degradation in baseline Cd(Se,Te) solar cells provided by our collaborators at Colorado State University (CSU). EBIC and CL-based measurements and revealed unusual collection and recombination profiles in these devices, which underwent significant changes with during stressing. KPFM and operando XPS measurements showed that device stressing permanently alters energy-band alignments at the (Mg,Zn)O/Cd(Se,Te) interface, which in turn account for an observed loss in fill factor. Studies on hybrid perovskite devices were hampered to a significant extent by delays related to the pandemic. Nevertheless, a set of hybrid perovskite devices (supplied through an NREL-industry partnership) were stress tested and characterized with techniques including EBIC, sMIM, popXPS/popUPS and optically excited TI. Available results from these measurements informed the device modeling effort and suggest that defects and related band offsets at the C60/LiF/hybrid perovskite interface are the primary source of degradation in these devices.

14 SOLAR ENERGY↗
DOE OSTI2016

Thermal Aging Degradation of Cast Stainless Steels in LWR Systems

Cast austenitic stainless steels (CASSs) have been extensively used for the large components of light water reactor (LWR) power plants such as primary coolant piping and pump casing. Since a large number of massive CASS components are installed in every modern nuclear power plant, any significant degradation of CASS components will raise serious concerns on the integrity of the entire power plant. Upon the presumption that the replacement cost of such massive components is prohibitive, therefore, thorough scientific understanding and systematic monitoring the thermal aging degradation of CASS components should be essential requirements for assessing the plant safety. In the past few decades many researches have concluded that the formation of Cr-rich α-phase by Spinoidal decomposition of δ-ferrite phase, which is formed in high temperature region during cooling, is the primary mechanism for the thermal embrittlement. Cracking mechanism in the thermally-embrittled duplex stainless steels consists of cleavage initiation at ferrite and crack propagation via separation of ferrite-austenite interphase. It has been known, however, that such thermal aging embrittlement is observed only in accelerated aging conditions and the cast stainless steel grades used in nuclear plants have performed well without experiencing real embrittlement. It has been speculated that long-term thermal aging for ≥ 60 years could lead to further decomposition of designed phases and increase of precipitation. This will result in significantly increased susceptibility to embrittlement or other degradation due to thermal aging-radiation synergistic effect, irradiation-induced degradation, stress-corrosion cracking, and general corrosion. Currently, therefore, the thermal embrittlement of CASS components is one of the most serious concerns for extended operation of nuclear power plants. A scientific research is underway to address the issues related to the thermal aging degradation of CASS components. The research aims to provide knowledge-based conclusive prediction for the integrity of the CASS components of LWR power plants during extended operation up to and beyond 60 years. This presentation intends to provide an introductory overview on the thermal aging phenomena in LWR relevant conditions and discussion on the measurements of mechanical property degradation after accelerated and LWR relevant thermal aging treatments. First, the thermal aging effect on toughness is discussed in terms of the causes of embrittlement and influential parameters. Second, the talk will include a comprehensive discussion on the thermal aging effects in different CASS grades (i.e., CF3, CF3M, CF8, and CF8M), which will focus on the influence of alloying elements such as molybdenum and carbon. Third, approximate analysis on thermal reaction in CASS was carried out using Arrhenius equation to decide the effective temperature range for accelerated aging experiments to simulate 60 and 80 years of services in limited time frame. The results will provide valuable insights in the degree of thermal aging. Fourth, calculation on equilibrium precipitation was performed for model CASS alloys using the CALPHAD program, and the results will be used to describe the precipitation behaviors in association with the degradation in mechanical properties. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2019

Mechanical Utility Structure for Testing High Field Superconducting Dipole Magnets

The U.S. Magnet Development Program (MDP) collaboration is designing a utility mechanical structure for testing various high-field superconducting dipole coils. The design uses a shell-based structure concept, which allows applying preload in two steps: During a room temperature assembly and during a cool down to a cryogenic temperature. The structure is designed to accommodate various coil designs - including Nb 3 Sn Cosine Theta (CT) and Canted CT magnets as well as hybrid magnets with high temperature superconductor cables. Superconducting coils, enclosed by bolted pads to form an octagonal coil pack, will be inserted into a reusable yoke-shell subassembly and precisely preloaded during the assembly using a bladder-and-key technology. Due to a differential thermal contraction between an external aluminum shell and the magnet core, the coil preload increases during the cool down up to level required for 17-T excitation. Such a reusable structure will serve as a testing fixture supporting goals of the MDP program, decreasing cost and simplifying coil performance testing at different preload levels. We present a finite-element analysis of the structure preloading various coil designs and examine the predicted coil stress at each step of the magnet assembly and excitation.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

Development and test of a large-aperture Nb3Sn cos-theta dipole coil with stress management

The stress-managed cos-theta (SMCT) coil is a new concept which was proposed and is being developed at Fermilab in the framework of US Magnet Development Program (US-MDP) for high-field and/or large-aperture accelerator magnets based on low-temperature and high-temperature superconductors. A 120-mm aperture two-layer Nb3Sn SMCT dipole coil has been developed at Fermilab to demonstrate and test the SMCT concept including coil design, fabrication technology and performance. The first SMCT demo coil was fabricated and assembled with 60-mm aperture Nb3Sn coil inside a dipole mirror configuration and tested separately and in series with the insert coil. This paper summarizes the design, parameters, and quench performance of the 120-mm aperture SMCT coil in a dipole mirror configuration.

43 PARTICLE ACCELERATORS↗
DOE OSTI2018

Residual Stress Measurements of Front Window Welds in a Prototypical Spallation Neutron Source Target Module

Spallation Neutron Source (SNS) target modules are fabricated from 316L stainless steel by welding together sections of machined components using electron beam welding. The failure of the tenth operational SNS target (Target 10) at an electron beam weld prompted an investigation into the residual stress remaining in the weld joint after joining to determine if welding procedures for SNS target fabrication produce detrimental residual stresses in or near the welds. Due to an issue with fabrication, the front section of an SNS target was removed from fabrication and made available for residual stress measurements. The residual stresses in an electron beam weld joining the front window and front body of the target prototype was measured at several locations near EBW2 weld between outer window and front body using the VUCLAN instrument. Different stress free d hkl 0 methods were used to calculated the residual strain and residual stress. Furthermore, the results show tensile residual stress up to 350MPa along the weld direction which peaked at weld location.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Next Generation Hydrogen Storage Vessels Enabled by Carbon Fiber Infusion with a Low Viscosity, High Toughness System

Onboard hydrogen storage for fuel cell vehicles holds considerable commercial promise which could be accelerated by lower cost storage vessels. In past years, the use of lower cost reinforcing fiber had been studied as an intuitive avenue to reduce vessel costs. Although the matrix resin does not play a large role in bearing stress loads in many areas of a filament wound pressure vessel, the matrix is relied upon for stress transfer between fibers and appears to play an important role in certain regions of the vessel construction such as the “tangent region” where the cylinder section transitions to the dome. Also, the matrix resin can play a role in the damage tolerance of vessels after impact events. Furthermore, the effect of dry spots or voids in the laminate can affect stress transfer between fibers in a manner that is challenging to quantify. Therefore, excess fiber must be used to account for this variability in performance. Unfortunately, in the case hydrogen pressure vessels the cost of the vessel is strongly dependent on the amount of carbon-fiber used in the design and manufacturing. An extensive investigation on the use of non-traditional fabrication processes enabled by an ultra-low viscosity thermoset resin (<10 cP) with high fracture toughness was conducted to determine the opportunity to reduce carbon-fiber usage and the associated high cost. The hypothesis was based on enabling a lower variation in vessel performance from a reduction in void defects (often found with traditional wet-winding) and a more defect-tolerant vessel resulting from use of a matrix resin with high fracture toughness. These two features were anticipated to justify a more aggressive design approach to the vessel winding pattern. From the work in this project, the potential use of the vacuum infusion approach to produce high quality vessels was validated. However, the team recognized the need to re-optimize the design, the dry-process, and the vacuum infusion process at each scale-up stage. During the planning phase, the critical need to re-optimize at this frequency was under-estimated. Also, the team identified the lack of industry testing standards on subscale parts for providing predictive value of vessel performance. Therefore, significant effort is needed to produce statistically significant numbers of vessels. To produce such numbers of vessels the project needed in retrospect to partner closely with a series vessel manufactures to develop a proof of concept production line to make the vessels. However, without the appropriate data, a manufacturing partner was challenging to fully engage during this timeline. New technologies relying on changing raw materials and manufacturing processes carry inherent risks. This project did not reach its ultimate objectives of demonstrated a vessel with lower carbon-fiber. But some companies expressed interest in learning from the partial successes of this project for future challenges in pressure vessel applications.

08 HYDROGEN↗
DOE OSTI2019

Thermal Test of 29 mm and 12 mm Targets

NorthStar medical isotopes are planning to produce important medical radioisotope molybdenum-99 (Mo-99) through photonuclear reaction on molybdenum-100 (Mo-100). In this approach, multiple thin disks of enriched molybdenum metal will be bombarded with a 40-MeV electron beam. Because enriched Mo-100 is expensive, we intend to use as much beam power as possible to achieve maximum production yield and minimize the size of the target. This requirement leads to very high beam power density (heat deposition in the target),which sets challenging requirements for cooling. Together with scientists at Los Alamos National Laboratory, a team at Argonne National Laboratory has developed and demonstrated a cooling approach using pressurized helium, which allows for efficient heat removal. One of the challenges in this approach is the management of the heat load on the target window. The target window separates the high-pressure helium atmosphere inside the target from the vacuum in the beamline so it is constantly under stress from differential pressure. Also, the window is cooled only by the helium gas flow from one side, making the window design challenging. To validate calculation models, the team performed a series of tests at Argonne’s Low Energy Accelerator Facility (LEAF). This report describes additional tests for two target designs: a full-scale target 29 millimeters in diameter and a scaled-down version, 12 millimeters in diameter. We compared the results of the window temperature measurements and cooling system parameters obtained in the experiments with those predicted by analytical calculations and Computation Flow Dynamic (CFD) simulations. Results of the experiments and calculations are presented below.

07 ISOTOPE AND RADIATION SOURCES↗
NASA NTRS1979

High G pyrotechnic shock simulation using metal-to-metal impact

A technique for simulating high g level pyrotechnic shocks is described and the results of applying the technique to obtain the MIL-STD-1540A shock spectrum with a maximum acceleration of 18,000g at 2,000 Hz are presented. Designing the resonant beam and plate on which the test unit is mounted, and generating a proper impulsive load on them, were the essentials of the technique. One dimensional stress wave and Euler equations were employed in the design. A metal pendulum hammer was used to generate the impulsive load.

Bai, M.↗
NASA NTRS1983

Preliminary scramjet design for hypersonic airbreathing missile application

A conceptual design study of a scramjet engine was conducted for a hypersonic surface to air missile (HYSAM). The definition of the engine was based upon the requirements of accelerating the HYSAM from Mach 4 at 20,000 feet to Mach 6 at 100,000 feet and the cruise conditions at Mach 6. The resulting external and internal environmental conditions were used by various engineering disciplines performing design, stress and heat transfer analysis. A detailed structural analysis was conducted along with an indepth thermal analysis. Structurally all the components within the system exhibit positive margins of safety. A feasible concept was defined which uses state-of-the-art materials and existing TMC technology. The engine basically consists of a three dimensional carbon/carbon combustor/nozzle secured to an FS-85 columbium inlet. The carbon/carbon liner is sheathed with carbon felt insulation to thermally protect the FS-85 structure and skin. The thermal analysis of the engine indicates that a thermally viable configuration exists.

Carlson, C. H.↗
NASA NTRS2025

Physics-Based Modeling and Simulation of Self-Reacting Friction Stir Welding Using Computational Fluid Dynamics

A physics-based model was developed to simulate the behavior of material in a self-reacting friction stir welding (SR-FSW) process for the joining of metals. This steady-state model builds upon fundamental computational fluid dynamic (CFD) principles within Ansys Fluent to solve the discretized equations. The effective viscosity is calculated using a viscoplastic model using a Sheppard-Wright formulation of flow stress. Numerous advancements have been made in the incorporated physics including (1) temperature-dependent material properties; (2) locally adaptable flow and thermal boundary conditions; and (3) adapting material properties in nugget in response to microstructural changes. Simulation strategies to accelerate computation and improve numerical stability include adapting the mesh refinement and solver relaxation factors during simulation. The result is a highly robust and computationally efficient model capable of providing the material flow and temperature history across the domain. As material history determines the local microstructure and ultimately weld strength, an accurate and detailed physics-based model has the potential to accelerate SR-FSW process development. The model is highly adaptable to changes in process parameters, tool design, or alloy.

Process Modeling↗
DOE OSTI2018

Angptl2 deficiency attenuates paraquat (PQ)-induced lung injury in mice by altering inflammation, oxidative stress and fibrosis through NF-κB pathway

Highlights: • Angptl2 deficiency reduces inflammation and oxidative stress in lung of PQ-induced mice. • Angptl2 knockout reduces fibrosis in lung of PQ-induced mice. • Angptl2 knockdown alleviates PQ-induced inflammation, oxidative stress and fibrosis through inactivating NF-κB. Paraquat (PQ) is one of the most extensively used herbicides, possessing high toxicity for humans and animals. The lung is the main target organ by the poisoning of PQ resulting in acute lung injury. Nonetheless, molecular mechanisms underlying PQ-induced lung injury remain unclear. Here, we ask if angiopoietin-like protein 2 (Angptl2), a pro-inflammatory protein, contributes to inflammation that accelerates acute lung injury. The results indicated that abundant Angptl2 expression was observed in lung tissues of PQ-treated mice. Histological analysis revealed that PQ-induced histological changes were alleviated by Angptl2 knockout (Angptl2{sup −/−}). Angptl2{sup −/−} in PQ-treated mice attenuated acute lung injury progression by reducing the number of total cells, total leukocytes, neutrophils and macrophages in bronchoalveolar lavage fluid (BALF) and reducing inflammatory response through the inactivation of nuclear factor kappa B (NF-κB) pathway. Angptl2{sup −/−} reduced oxidative stress in PQ-treated mice, as evidenced by the enhanced superoxide dismutase (SOD) activity and reduced malondialdehyde (MDA) levels in serum or lung tissue samples, which was accompanied with increased expressions of nuclear respiratory factor 2 (Nrf-2), heme oxygenase-1 (HO-1) and NAD(P)H:quinone oxidoreductase 1 (NQO-1). PQ-induced fibrosis was also improved in Angptl2{sup −/−} mice by decreasing pulmonary transforming growth factor (TGF)-β1 expressions. In vitro, we found that Angptl2 knockdown-suppressed inflammation, oxidative stress and fibrosis was restored by increasing NF-κB activation in PQ-incubated A549 cells; however, the results above were significantly reversed by inactivating NF-κB using its inhibitor, Bay 11–7085 or LY2409881. Therefore, Angptl2 could provide therapeutic effects on PQ-induced acute lung injury through inhibiting inflammation, oxidative stress and fibrosis by regulating NF-κB pathway.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

DUSP14 knockout accelerates cardiac ischemia reperfusion (IR) injury through activating NF-κB and MAPKs signaling pathways modulated by ROS generation

Highlights: • DUSP14 expression is decreased in the infarcted area following myocardial I/R. • DUSP14 knockout aggregates cardiac function following myocardial I/R. • DUSP14 ablation intensifies inflammation in murine hearts with IR injury. • DUSP14 deficiency exacerbates MAPKs pathway and oxidative stress in murine hearts. Inflammation and oxidative stress are significantly involved in the progression of a variety of diseases, including myocardial ischemia/reperfusion (IR). In the present study, we hypothesized a protective role of dual-specificity phosphatase 14 (DUSP14) in myocardial IR, as well as the underlying molecular mechanism. The results indicated that DUSP14 was down-regulated following cardiac IR injury. Subsequently, the wild type (WT) and DUSP14-knockout (KO) mice were included to further reveal the potential role of DUSP14 in cardiac IR injury progression. DUSP14-KO mice exhibited increased infarction area and elevated apoptosis, as evidenced by the increased TUNEL-positive cells in ischemia heart following reperfusion compared to WT mice. Further, DUSP14-KO significantly aggregated cardiac dysfunction of mice after IR injury. Cardiac IR injury to DUSP14-KO mice led to markedly increased expression of pro-inflammatory cytokines and activated nuclear factor-κB (NF-κB) pathway in the heart in comparison to WT mice. Meanwhile, mitogen-activated protein kinases (MAPKs), including p38, ERK1/2 and JNK, were significantly activated by DUSO14-KO in mice after IR injury. Compared to WT mice, DUSP14-KO mice showed markedly increased oxidative stress markers in cardiac tissues, including malondialdehyde (MDA), NADPH oxidase-4 (NOX4) and p47, while decreased activities or expressions of anti-oxidants, such as glutathione (GSH), glutathione peroxidase (GPx), glutathion reductases (GR), superoxide dismutase (SOD) and hemeoxygenase-1 (HO-1). DUSP14-knockdown (KD) in primary cardiomyocytes using its specific siRNA sequence elevated hypoxia and reoxygenation (HR)-induced activation of NF-κB and MAPKs signaling pathways, and reactive oxygen species (ROS) generation. Intriguingly, pre-treatment of ROS scavenger, N-acetylcysteine (NAC), markedly abolished DUSP14-KD-augmented NF-κB and MAPKs activation in HR-stimulated primary cardiomyocytes. Together, the results above indicated that DUSP14 might be served as a positive regulator to attenuate cardiac IR injury. Suppressing DUSP14 exacerbated cardiac injury through activating NF-κB and MAPKs signaling pathways regulated by ROS production. Thus, DUSP14 could be a valuable target for developing treatments for myocardial IR injury.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Conceptual Design of 20 T Hybrid Accelerator Dipole Magnets

Hybrid magnets are currently under consideration as an economically viable option towards 20 T dipole magnets for next generation of particle accelerators. In these magnets, High Temperature Superconducting (HTS) materials are used in the high field part of the coil with so-called insert coils, and Low Temperature Superconductors (LTS) like Nb 3 Sn and Nb-Ti superconductors are used in the lower field region with so-called outsert coils. The attractiveness of the hybrid option lays on the fact that, on the one hand, the 20 T field level is beyond the Nb 3 Sn practical limits of 15-16 T for accelerator magnets and can be achieved only via HTS materials; on the other hand, the high cost of HTS superconductors compared to LTS superconductors makes it advantageous exploring a hybrid approach, where the HTS portion of the coil is minimized. Here we present in this paper an overview of different design options aimed at generating 20 T field in a 50 mm clear aperture. The coil layouts investigated include the Cos-theta design (CT), with its variations to reduce the conductor peak stress, namely the Canted Cos-theta design (CCT) and the Stress Management Cos-theta design (SMCT), and, in addition, the Block-type design (BL) including a form of stress management and the Common-Coil design (CC). Results from a magnetic and mechanical analysis are discussed, with particular focus on the comparison between the different options regarding quantity of superconducting material, field quality, conductor peak stress, and quench protection.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

The role of local strains from prior cold work on stress corrosion cracking of α-brass in Mattsson's solution

The dynamic strain rate ahead of a crack tip formed during stress corrosion cracking (SCC) under a static load is assumed to arise from the crack propagation. The strain surrounding the crack tip would be redistributed as the crack grows, thereby having the effect of dynamic strain. Recently, several studies have shown cold work to cause accelerated crack growth rates during SCC, and the slip-dissolution mechanism has been widely applied to account for this via a supposedly increased crack-tip strain rate in cold worked material. While these interpretations consider cold work as a homogeneous effect, dislocations are generated inhomogeneously within the microstructure during cold work. The presence of grain boundaries results in dislocation pile-ups that cause local strain concentrations. The local strains generated from cold working α-brass by tensile elongation were characterized using electron backscatter diffraction (EBSD). The role of these local strains in SCC was studied by measuring the strain distributions from the same regions of the sample before cold work, after cold work, and after SCC. Though, the cracks did not always initiate or propagate along boundaries with pre-existing local strains from the applied cold work, the local strains surrounding the cracked boundaries had contributions from both the crack propagation and the prior cold work. - Highlights: • Plastic strain localization has a complex relationship with SCC susceptibility. • Surface relief created by cold work creates its own granular strain localization. • Cold work promotes crack growth but several other factors are involved.

36 MATERIALS SCIENCE↗
NASA NTRS1978

Procedure for developing experimental designs for accelerated tests for service-life prediction

Recommended design procedures to reduce the complete factorial design by retaining information on anticipated important interaction effects, and by generally giving up information on unconditional main effects are discussed. A hypothetical photovoltaic module used in the test design is presented. Judgments were made of the relative importance of various environmental stresses such as UV radiation, abrasion, chemical attack, temperature, mechanical stress, relative humidity and voltage. Consideration is given to a complete factorial design and its graphical representation, elimination of selected test conditions, examination and improvement of an engineering design, and parametric study. The resulting design consists of a mix of conditional main effects and conditional interactions and represents a compromise between engineering and statistical requirements.

Thomas, R. E.↗