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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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Critical design load case fatigue and ultimate failure simulation for a 10-m H-type vertical-axis wind turbine
While previous studies investigating critical VAWT design load cases have focused on large and relatively flexible Darrieus designs, the bulk of current commercial products seeking certification fall in the relatively small, stiff, and H-type configuration, such as the XFlow Energy Corporation turbine that this study compares against. Understanding the critical design load case impacts for both fatigue and ultimate failure for this size and type of VAWT are imperative for certification. The abil
Inclusion of tearing parameter failure capabilities in modular failure
The tearing parameter criterion and failure propagation method currently used in the multilinear elastic-plastic constitutive model was added as an option to modular failure capabilities. Currently, this implementation is only available to the J 2 plasticity model due to the formulation of the failure propagation approach. The implementation was verified against analytical solutions for both a uniaxial tension and a pure shear boundary-value problem. Possible improvements to, and necessary generalizations of, the failure method to extend it as a modular option for all plasticity models are highlighted.
Failure diagnosis and trend‐based performance losses routines for the detection and classification of incidents in large‐scale photovoltaic systems
Abstract Fault detection and classification in photovoltaic (PV) systems through real‐time monitoring is a fundamental task that ensures quality of operation and significantly improves the performance and reliability of operating systems. Different statistical and comparative approaches have already been proposed in the literature for fault detection; however, accurate classification of fault and loss incidents based on PV performance time series remains a key challenge. Failure diagnosis and trend‐based performance loss routines were developed in this work for detecting PV underperformance and accurately identifying the different fault types and loss mechanisms. The proposed routines focus mainly on the differentiation of failures (e.g., inverter faults) from irreversible (e.g., degradation) and reversible (e.g., snow and soiling) performance loss factors based on statistical analysis. The proposed routines were benchmarked using historical inverter data obtained from a 1.8 MWp PV power plant. The results demonstrated the effectiveness of the routines for detecting failures and loss mechanisms and the capability of the pipeline for distinguishing underperformance issues using anomaly detection and change‐point (CP) models. Finally, a CP model was used to extract significant changes in time series data, to detect soiling and cleaning events and to estimate both the performance loss and degradation rates of fielded PV systems.
Fast Diagnosis of Failure Mechanisms and Lifetime Prediction of Li Metal Batteries
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Development of a Ductile Rupture Failure Surface for PH13-8Mo H950 Steel Using the Xue-Wierzbicki Failure Model
The ability to model ductile rupture in metal parts is critical in highly stressed applications. The initiation of a ductile fracture is a function of the plastic strain, the stress state, and stress history. This paper develops a ductile rupture failure surface for PH13-8Mo H950 steel using the Xue-Wierzbicki failure model. The model is developed using data from five tensile specimen tests conducted at -40⁰C and 20⁰C. The specimens are designed to cover a Lode parameter range of 0 and 1 with a stress triaxiality range from zero in pure shear to approximately 1.0 in tension. The failure surface can be implemented directly into the finite element code or used as a post processing check.
Probing the Failure Mechanism of SnO{sub 2} Nanowires for Sodium-Ion Batteries
Nonlithium metals such as sodium have attracted wide attention as a potential charge carrying ion for rechargeable batteries. Using in situ transmission electron microscopy in combination with density functional theory calculations, we probed the structural and chemical evolution of SnO{sub 2} nanowire anodes in Na-ion batteries and compared them quantitatively with results from Li-ion batteries (Huang, J. Y.; et al. Science 2010, 330, 1515-1520). Upon Na insertion into SnO{sub 2}, a displacement reaction occurs, leading to the formation of amorphous Na{sub x}Sn nanoparticles dispersed in Na{sub 2}O matrix. With further Na insertion, the Na{sub x}Sn crystallized into Na{sub 15}Sn{sub 4} (x = 3.75). Upon extraction of Na (desodiation), the Na{sub x}Sn transforms to Sn nanoparticles. Associated with the dealloying, pores are found to form, leading to a structure of Sn particles confined in a hollow matrix of Na{sub 2}O. These pores greatly increase electrical impedance, therefore accounting for the poor cyclability of SnO{sub 2}. DFT calculations indicate that Na{sup +} diffuses 30 times slower than Li{sup +} in SnO{sub 2}, in agreement with in situ TEM measurement. Insertion of Na can chemomechanically soften the reaction product to a greater extent than in lithiation. Therefore, in contrast to the lithiation of SnO{sub 2} significantly less dislocation plasticity was seen ahead of the sodiation front. This direct comparison of the results from Na and Li highlights the critical role of ionic size and electronic structure of different ionic species on the charge/discharge rate and failure mechanisms in these batteries.
Characterization of electrically-active defects in ultraviolet light-emitting diodes with laser-based failure analysis techniques
Laser-based failure analysis techniques demonstrate the ability to quickly and non-intrusively screen deep ultraviolet light-emitting diodes (LEDs) for electrically-active defects. In particular, two laser-based techniques, light-induced voltage alteration and thermally-induced voltage alteration, generate applied voltage maps (AVMs) that provide information on electrically-active defect behavior including turn-on bias, density, and spatial location. Here, multiple commercial LEDs were examined and found to have dark defect signals in the AVM indicating a site of reduced resistance or leakage through the diode. The existence of the dark defect signals in the AVM correlates strongly with an increased forward-bias leakage current. This increased leakage is not present in devices without AVM signals. Transmission electron microscopy analysis of a dark defect signal site revealed a dislocation cluster through the pn junction. The cluster included an open core dislocation. Even though LEDs with few dark AVM defect signals did not correlate strongly with power loss, direct association between increased open core dislocation densities and reduced LED device performance has been presented elsewhere [M. W. Moseley et al., J. Appl. Phys. 117, 095301 (2015)].
Understanding Strain and Failure of a Knot in Polyethylene Using Molecular Dynamics with Machine-Learned Potentials
A neural network potential (NNP) has been developed by fitting to ab initio electronic structure data on hydrocarbons and is used to study failure of linear and knotted polyethylene (PE) chains. A linear PE chain must be highly strained before breaking as the stress is equally distributed across the chain. In contrast, the stress in a PE chain with a 31 or overhand knot, accumulates at the knot’s entrance/exit. We find the strain energy is greatest when the bond length and angle are strained simultaneously, and that the knot weakens the chain by increasing the variance of the C–C–C angle, thereby allowing rupture at lower bond strains. Here, we extend our analysis to both 51 and 52 knots and find that both break at the entrance/exit of a loop. Notably, molecular scale PE knots exhibit many of the same characteristics as knots in a macroscopic rope, with stick–slip phenomena upon tightening and similar points of failure.
Successes and failures of Hubbard-corrected density functional theory: The case of Mg doped LiCoO{sub 2}
We have evaluated the successes and failures of the Hubbard-corrected density functional theory approach to study Mg doping of LiCoO{sub 2}. We computed the effect of the U parameter on the energetic, geometric, and electronic properties of two possible doping mechanisms: (1) substitution of Mg onto a Co (or Li) site with an associated impurity state and (2) formation of impurity-state-free complexes of substitutional Mg and point defects in LiCoO{sub 2}. We find that formation of impurity states results in changes on the valency of Co in LiCoO{sub 2}. Variation of the Co U shifts the energy of the impurity state, resulting in energetic, geometric, and electronic properties that depend significantly on the specific value of U. In contrast, the properties of the impurity-state-free complexes are insensitive to U. These results identify reasons for the strong dependence on the doping properties on the chosen value of U and for the overall difficulty of achieving agreement with the experimentally known energetic and electronic properties of doped transition metal oxides such as LiCoO{sub 2}.
A novel post-processing method for progressive failure analysis of brittle composite compression
Finite element analysis of brittle materials in axial compression typically uses element deletion to allow continued global deformation post-element-failure. However, element deletion produces cyclic load-displacement curves that underestimate energy absorption and are not representative of a continuum system. Two key observations support the conclusion that results from an appropriately discretized model can be an adequate representation of a continuum system. Specifically, the frequency of the oscillations in the load-displacement curve is directly dependent upon element length in the loading direction, and the peak amplitudes of oscillations are mesh size independent. A method of post-processing the analysis results, by connecting the peak amplitudes of oscillations, is proposed and applied to a series of continuous carbon fiber composite crush tubes. The load-displacement curve, stable crushing load, and specific energy absorption of the post-processed results compare well to an experimental study of crush tubes with similar layups.
Addressing failures in exascale computing
We present here a report produced by a workshop on “Addressing Failures in Exascale Computing” held in Park City, Utah, August 4–11, 2012. The charter of this workshop was to establish a common taxonomy about resilience across all the levels in a computing system; discuss existing knowledge on resilience across the various hardware and software layers of an exascale system; and build on those results, examining potential solutions from both a hardware and software perspective and focusing on a combined approach. The workshop brought together participants with expertise in applications, system software, and hardware; they came from industry, government, and academia; and their interests ranged from theory to implementation. The combination allowed broad and comprehensive discussions and led to this document, which summarizes and builds on those discussions.
ACT University Collaboration Proposal: Role of manufacturing defects on material failure under dynamic loading for developing enhanced failure models and theories (Final Report)
Research on the tensile behavior of additively manufactured 316L stainless steel coupon specimens at increasing strain rates was conducted over the past year at Penn State. Dynamic loading rates into the 1000 1/s loading rates were performed on specimens with nearly 1.32” gage lengths. Stress-strain plots show ductile and plastic behavior well beyond 12% strain with necked specimens, having smaller effective gage lengths showing up to 56% ultimate strain. Additional tests performed on compact tension specimens helped with simulation work to understand the deformation behavior. Using finite elements, it was possible to determine the feasibility of a comprehensive experimental validation study towards an improved model for AM material failure – specifically, the Bai-Wierzbicki approach which accounts for lode angle and triaxiality. A non-significant number of tests are projected for eight specific failure nodes, with additional replicates to provide strain-rate capabilities to the existing formulation. One such correction factor is explored for quasi-static, notched specimens. Finally, stress intensity factor was explored using a set of compact-tension specimens which would also provide useful validation data for any simulation work.
Lithium loss, resistance growth, electrode expansion, gas evolution, and Li plating: Analyzing performance and failure of commercial large-format NMC-Gr lithium-ion pouch cells
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Joule heating induced thermomigration failure in un-powered microbumps due to thermal crosstalk in 2.5D IC technology
Thermal-crosstalk induced thermomigration failure in un-powered microbumps has been found in 2.5D integrated circuit (IC) circuit. In 2.5D IC, a Si interposer was used between a polymer substrate and a device chip which has transistors. The interposer has no transistors. If transistors are added to the interposer chip, it becomes 3D IC. In our test structure, there are two Si chips placed horizontally on a Si interposer. The vertical connections between the interposer and the Si chips are through microbumps. We powered one daisy chain of the microbumps under one Si chip; however, the un-powered microbumps in the neighboring chip are failed with big holes in the solder layer. We find that Joule heating from the powered microbumps is transferred horizontally to the bottom of the neighboring un-powered microbumps, and creates a large temperature gradient, in the order of 1000 °C/cm, through the un-powered microbumps in the neighboring chip, so the latter failed by thermomigration. In addition, we used synchrotron radiation tomography to compare three sets of microbumps in the test structure: microbumps under electromigration, microbumps under thermomigration, and microbumps under a constant temperature thermal annealing. The results show that the microbumps under thermomigration have the largest damage. Furthermore, simulation of temperature distribution in the test structure supports the finding of thermomigration.
Electrode Edge Effects and the Failure Mechanism of Lithium-Metal Batteries
Lithium (Li) metal with very high specific capacity makes it one of the ideal anode for high energy batteries. However, Li dendrite growth and the formation of isolated (or “dead”) Li during repeated Li plating/stripping processes lead to its low Coulombic efficiency (CE). In this work, we discovered for the first time that part of Li CE loss can be attributed to the edge effect of the copper (Cu) substrate electrode in a conventional Li||Cu cell configuration. The “dead” Li formed on the edge of Cu substrate was systematically investigated through scanning electron microscopy, energy dispersive X-ray spectroscopy, and two-dimensional X-ray photoelectron spectroscopy. In order to minimize the Li loss at the edge of the Cu exposed to pressure-free space, modified Li||Cu cell configuration with a Cu electrode smaller than Li metal is preferred. It was clearly demonstrated that using an electrode configuration with minimal open space or “pressure-free space” across electrodes can reduce “dead” Li accumulated during cycling and increase Li CE. This phenomena was also verified in Li metal batteries (Li||LiNi1/3Mn1/3Co1/3O2) and should be considered in the design of practical Li metal batteries.
Comparison of Failure Mechanisms Due to Shock Propagation in Forged, Layered, and Additive Manufactured Titanium Alloy
Presentation describes research to understand failure mechanisms under shock loading as part of a broader effort to reduce the costs of materials science testing through use of additive manufactured materials.