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At least 1,297 records · Page 72
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Shock recompaction of spall damage

Spall fracture is a high strain-rate damage phenomenon associated with shock or impulsive loading events. When a material that has been subjected to shock compression is allowed to release, rarefaction waves propagate into the sample and reduce the internal stress to zero. If multiple rarefaction waves intersect, they generate tension which, if sufficient, can nucleate voids in the material. It has been observed in several works investigating spall fracture that although the shock-wave profiles suggested spall occurred, imaging of the recovered sample revealed no voids or cracks. In this study, we aim to determine whether a second shock event could recompact existing spall damage, and if so, what form does the microstructure at the recompaction interface have? Through a series of gas-gun flyer-plate impact experiments, we demonstrate that modest shock stresses of 2 GPa–3 GPa are enough to both fully compact a damaged copper target back to a state of zero porosity and, furthermore, drive recrystallization of the interface such that there is a new bond formed where the free surfaces were brought together.

42 ENGINEERING↗
DOE OSTI2022

Few-cycle optical field breakdown and damage of gallium oxide and gallium nitride

Both gallium oxide and gallium nitride have great potential for use as high power transparent conducting oxide materials for a wide range of optoelectronic applications. It is, therefore, important to determine the dynamic optical field breakdown for these materials. Here, we report laser damage thresholds for Ga 2 O 3 and GaN using 9 fs few-cycle pulses with a center wavelength near 760 nm. We determine laser-induced damage thresholds (LIDTs) for both single pulse and multi-pulse exposures, with multi-pulse LIDT showing significant reduction compared to single pulse LIDT (in some cases, >50%), possibly due to laser-induced defects. We show that Ga 2 O 3 and GaN have an ultrafast optical field breakdown of 23 and 18 GV/m when nearly polarized along their [010] and [111] planes, respectively, extending their suitability for high power applications to the ultrashort pulse regime. To accurately characterize the excited carrier density criteria in which apparent laser damage occurs, carrier excitation dynamics for the entire laser pulse interaction were simulated using a modified Keldysh ionization model. For the measured single-shot threshold fluences, the plasma critical density was surpassed by 2 orders of magnitude and 2D finite-difference time-domain simulations were employed to understand the pulse interaction near the surface.

Tripepi, Michael↗
DOE OSTI2022

Use of a non-collinear wave mixing technique to image internal microscale damage in concrete

This research demonstrates the feasibility of using a non-collinear wave mixing technique to image internal microscale damage throughout the interior volume of a relatively large (28 cm thick) concrete component. By exploiting the underlying mechanics of nonlinear wave mixing, it is possible to mix two incident waves with frequencies low enough to propagate without being scattered by the inherently heterogenous, concrete microstructure, while still being sensitive to damage features with length scales well below these incident wavelengths. For this study, scanning and imaging is accomplished by manually adjusting the locations of the two incident waves, while a knowledge of the wave speeds in concrete plus synchronization identifies the location of the mixing zone—the specific volume of concrete being imaged. The viability of the proposed technique is demonstrated by examining a concrete prism specimen with known, embedded internal microscale damage.

Kim, Jin-Yeon (ORCID:0000000255180032)↗
DOE OSTI2016

APE2 Zf-GRF facilitates 3'-5' resection of DNA damage following oxidative stress

The Xenopus laevis APE2 (apurinic/apyrimidinic endonuclease 2) nuclease participates in 3'-5' nucleolytic resection of oxidative DNA damage and activation of the ATR-Chk1 DNA damage response (DDR) pathway via ill-defined mechanisms. Here we report that APE2 resection activity is regulated by DNA interactions in its Zf-GRF domain, a region sharing high homology with DDR proteins Topoisomerase 3α (TOP3α) and NEIL3 (Nei-like DNA glycosylase 3), as well as transcription and RNA regulatory proteins, such as TTF2 (transcription termination factor 2), TFIIS, and RPB9. Biochemical and NMR results establish the nucleic acid-binding activity of the Zf-GRF domain. Moreover, an APE2 Zf-GRF X-ray structure and small-angle X-ray scattering analyses show that the Zf-GRF fold is typified by a crescent-shaped ssDNA binding claw that is flexibly appended to an APE2 endonuclease/exonuclease/phosphatase (EEP) catalytic core. Structure-guided Zf-GRF mutations impact APE2 DNA binding and 3'-5' exonuclease processing, and also prevent efficient APE2-dependent RPA recruitment to damaged chromatin and activation of the ATR-Chk1 DDR pathway in response to oxidative stress in Xenopus egg extracts. Collectively, our data unveil the APE2 Zf-GRF domain as a nucleic acid interaction module in the regulation of a key single-strand break resection function of APE2, and also reveal topologic similarity of the Zf-GRF to the zinc ribbon domains of TFIIS and RPB9.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Sprain energy consequences for damage localization and fracture mechanics

The 2023 smooth Lagrangian Crack-Band Model (slCBM), inspired by the 2020 invention of the gap test, prevented spurious damage localization during fracture growth by introducing the second gradient of the displacement field vector, named the “sprain,” as the localization limiter. The key idea was that, in the finite element implementation, the displacement vector and its gradient should be treated as independent fields with the lowest ( C 0 ) continuity, constrained by a second-order Lagrange multiplier tensor. Coupled with a realistic constitutive law for triaxial softening damage, such as microplane model M7, the known limitations of the classical Crack Band Model were eliminated. Here, we show that the slCBM closely reproduces the size effect revealed by the gap test at various crack-parallel stresses. To describe it, we present an approximate corrective formula, although a strong loading-path dependence limits its applicability. Except for the rare case of zero crack-parallel stresses, the fracture predictions of the line crack models (linear elastic fracture mechanics, phase-field, extended finite element method (XFEM), cohesive crack models) can be as much as 100% in error. We argue that the localization limiter concept must be extended by including the resistance to material rotation gradients. We also show that, without this resistance, the existing strain-gradient damage theories may predict a wrong fracture pattern and have, for Mode II and III fractures, a load capacity error as much as 55%. Finally, we argue that the crack-parallel stress effect must occur in all materials, ranging from concrete to atomistically sharp cracks in crystals.

Science & Technology - Other Topics↗
DOE OSTI2017

Radiation damage free ghost diffraction with atomic resolution

The x-ray free electron lasers can enable diffractive structural determination of protein nanocrystals and single molecules that are too small and radiation-sensitive for conventional x-ray diffraction. However the electronic form factor may be modified during the ultrashort x-ray pulse due to photoionization and electron cascade caused by the intense x-ray pulse. For general x-ray imaging techniques, the minimization of the effects of radiation damage is of major concern to ensure reliable reconstruction of molecular structure. Here in this paper, we show that radiation damage free diffraction can be achieved with atomic spatial resolution by using x-ray parametric down-conversion and ghost diffraction with entangled photons of x-ray and optical frequencies. We show that the formation of the diffraction patterns satisfies a condition analogous to the Bragg equation, with a resolution that can be as fine as the crystal lattice length scale of several Ångstrom. Since the samples are illuminated by low energy optical photons, they can be free of radiation damage.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2021

Atomistic modeling of radiation damage in crystalline materials

This review discusses atomistic modeling techniques used to simulate radiation damage in crystalline materials. Radiation damage due to energetic particles results in the formation of defects. The subsequent evolution of these defects over multiple length and time scales requiring numerous simulations techniques to model the gamut of behaviors. This work focuses attention on current and new methodologies at the atomistic scale regarding the mechanisms of defect formation at the primary damage state.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Ion-damage-free planarization or shallow angle sectioning of solar cells for mapping grain orientation and nanoscale photovoltaic properties

Ion beam milling is the most common modern method for preparing specific features for microscopic analysis, even though concomitant ion implantation and amorphization remain persistent challenges, particularly as they often modify materials properties of interest. Atomic force microscopy (AFM), on the other hand, can mechanically mill specific nanoscale regions in plan-view without chemical or high energy ion damage, due to its resolution, directionality, and fine load control. As an example, AFM-nanomilling (AFM-NM) is implemented for top-down planarization of polycrystalline CdTe thin film solar cells, with a resulting decrease in the root mean square (RMS) roughness by an order of magnitude, even better than for a low incidence FIB polished surface. Subsequently AFM-based property maps reveal a substantially stronger contrast, in this case of the short-circuit current or open circuit voltage during light exposure. Furthermore, electron back scattering diffraction (EBSD) imaging also becomes possible upon AFM-NM, enabling direct correlations between the local materials properties and the polycrystalline microstructure. Smooth shallow-angle cross-sections are demonstrated as well, based on targeted oblique milling. As expected, this reveals a gradual decrease in the average short-circuit current and maximum power as the underlying CdS and electrode layers are approached, but a relatively consistent open-circuit voltage through the diminishing thickness of the CdTe absorber. AFM-based nanomilling is therefore a powerful tool for material characterization, uniquely providing ion-damage free, selective area, planar smoothing or low-angle sectioning of specimens while preserving their functionality. This then enables novel, co-located advanced AFM measurements, EBSD analysis, and investigations by related techniques that are otherwise hindered by surface morphology or surface damage.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2019

Focused-helium-ion-beam blow forming of nanostructures: radiation damage and nanofabrication

Targeted irradiation of nanostructures by a finely focused ion beam provides routes to improved control of material modification and understanding of the physics of interactions between ion beams and nanomaterials. Here, we studied radiation damage in crystalline diamond and silicon nanostructures using a focused helium ion beam, with the former exhibiting extremely long-range ion propagation and large plastic deformation in a process visibly analogous to blow forming. We report significant dependence of damage morphology on material, geometry, and irradiation conditions (ion dose, ion energy, ion species, and location). In this work, we suggest that our approach and findings will not only improve the understanding of radiation damage in isolated nanostructures, but will also support the design of new engineering materials and devices for current and future applications in nanotechnology.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

Low-cost sensor-based damage localization for large-area monitoring of FRP composites

Abstract In recent years, there has been growing interest in self-sensing structural materials across research and industry sectors. Detecting and locating structural damage typically requires numerous sensors wired to a data acquisition (DAQ) circuit, rendering implementation impractical in real structures. This paper proposes an innovative, cost-effective sensor network for damage detection and localization in fiber-reinforced polymer composites. The innovation encompasses three key elements: (1) utilizing carbon fiber tows within the composite as piezoresistive sensors, eliminating the need for additional foreign sensor devices; (2) introducing a novel sensor layout wherein sensor tow branches with varied resistance values are connected in parallel, reducing the number of connections to the DAQ circuit and cutting manufacturing costs significantly; (3) developing a practical sensor terminal fabrication technique to minimize manufacturing expenses. The proposed design methodology for the branch resistance values is first validated using a demonstration panel. Subsequently, the overall strategy is assessed by conducting impact tests on carbon and glass fiber-reinforced composite specimens. Results validate the sensor’s ability to accurately detect and locate structural damage.

Demo, Luke B. (ORCID:0000000208806522)↗
DOE OSTI2020

Measurements with silicon photomultipliers of dose-rate effects in the radiation damage of plastic scintillator tiles in the CMS hadron endcap calorimeter

Measurements are presented of the reduction of signal output due to radiation damage for two types of plastic scintillator tiles used in the hadron endcap (HE) calorimeter of the CMS detector. The tiles were exposed to particles produced in proton-proton (pp) collisions at the CERN LHC with a center-of-mass energy of 13 TeV, corresponding to a delivered luminosity of 50 fb−1. The measurements are based on readout channels of the HE that were instrumented with silicon photomultipliers, and are derived using data from several sources: a laser calibration system, a movable radioactive source, as well as hadrons and muons produced in pp collisions. Results from several irradiation campaigns using 60Co sources are also discussed. The damage is presented as a function of dose rate. Within the range of these measurements, for a fixed dose the damage increases with decreasing dose rate.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2011

Radiation damage in protein serial femtosecond crystallography using an x-ray free-electron laser

X-ray free-electron lasers deliver intense femtosecond pulses that promise to yield high resolution diffraction data of nanocrystals before the destruction of the sample by radiation damage. Diffraction intensities of lysozyme nanocrystals collected at the Linac Coherent Light Source using 2 keV photons were used for structure determination by molecular replacement and analyzed for radiation damage as a function of pulse length and fluence. Signatures of radiation damage are observed for pulses as short as 70 fs. Parametric scaling used in conventional crystallography does not account for the observed effects.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Does sink efficiency unequivocally characterize how grain boundaries impact radiation damage?

The role of grain boundaries in limiting irradiation damage in nanocrystalline materials is often correlated with the grain boundary sink efficiency. Here, we demonstrate on a tungsten material system (which has very distinct vacancy and interstitial mobilities) that sink efficiency does not unequivocally describe how grain boundaries impact irradiation damage. Rather, it reflects a particular defect diffusion equation that can change if any of the bulk conditions change. Even when denuded zone formation does not occur and grain boundaries have zero sink efficiencies, grain boundaries still impact the performance of nanocrystalline materials under irradiation by acting as a saturable defect storage site. However, denuded zone formation can occur under a necessary requirement of extra defect recombination at the grain boundaries (which, for example, is not possible when vacancy migration does not occur). These insights provide answers to several outstanding questions regarding the sink efficiency of a grain boundary and assist in parametrizing the role of grain boundaries in limiting irradiation damage in nanocrystalline materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Hard X-ray-induced damage on carbon–binder matrix for in situ synchrotron transmission X-ray microscopy tomography of Li-ion batteries

The electrode of Li-ion batteries is required to be chemically and mechanically stable in the electrolyte environment for in situ monitoring by transmission X-ray microscopy (TXM). Evidence has shown that continuous irradiation has an impact on the microstructure and the electrochemical performance of the electrode. To identify the root cause of the radiation damage, a wire-shaped electrode is soaked in an electrolyte in a quartz capillary and monitored using TXM under hard X-ray illumination. The results show that expansion of the carbon–binder matrix by the accumulated X-ray dose is the key factor of radiation damage. For in situ TXM tomography, intermittent X-ray exposure during image capturing can be used to avoid the morphology change caused by radiation damage on the carbon–binder matrix.

Lim, Cheolwoong↗
DOE OSTI2022

Miniature Crack or Damage Detection on Cable Insulation and Jacket Using Conformal Surface Wave Reflectometry

This letter introduces the study and application of a conformal surface wave launcher array to detect miniature insulation and/or jacket damage on unshielded cables. Here simulation and experimental results are presented that demonstrate that with the proposed concept very small instances of damage at various distances along power cables can be detected. Effects of damage detection feasibility in the presence of other cables in proximity and for cables containing semiconducting screen are also presented.

42 ENGINEERING↗
DOE OSTI2023

A study of Cell Cracks Formation During Freight Shipping : Monitoring Shock and Temperature in Real-Time & Assessing Damages With Pre and Post-Transit Characterizations of PV Modules

The solar photovoltaic (PV) industry often experiences module damage during transportation. PV modules stacked horizontally and strapped on wooden pallets may develop failures impacting their efficiency (glass shattering, cracks, frame indentation, etc.), especially when modules are not packed by professionals. The appearance of failures during the shipment from one laboratory to another can be detrimental to research studies. In this study, we tested a reusable plastic pallet designed to ship modules vertically. Five technologies of commercial PV modules were shipped together from Arizona to Florida including: glass/glass bifacial modules (framed and frameless), glass/transparent backsheet bifacial modules and glass/white backsheet modules (framed). Each module technology has a different physical size. Some modules had pre-existing cell-cracks allowing for the study of cell-crack formation and propagation during shipment. Dark current-voltage (I-V), light I-V and electroluminescence characterization were performed before and after shipment. A datalogger was used to monitor shocks and ambient temperature throughout the shipment and identify when the modules were more susceptible to damage. The modules were tilted upon receipt and the pallet were damaged but with no shattered modules. Time series shock data provided by the datalogger were used to determine potential responsible events. Our results reveal a few new post-transportation cracks for some modules. Modules parameters before and after shipment are also compared regarding the module constructions and their position in the pallet.

14 SOLAR ENERGY↗
DOE OSTI2020

Muscone suppresses inflammatory responses and neuronal damage in a rat model of cervical spondylotic myelopathy by regulating Drp1‐dependent mitochondrial fission

Abstract Cervical spondylotic myelopathy (CSM) is a common cause of disability with few treatments. Aberrant mitochondrial dynamics play a crucial role in the pathogenesis of various neurodegenerative diseases. Thus, regulation of mitochondrial dynamics may offer therapeutic benefit for the treatment of CSM. Muscone, the active ingredient of an odoriferous animal product, exhibits anti‐inflammatory and neuroprotective effects for which the underlying mechanisms remain obscure. We hypothesized that muscone might ameliorate inflammatory responses and neuronal damage by regulating mitochondrial dynamics. To this end, the effects of muscone on a rat model of chronic cervical cord compression, as well as activated BV2 cells and injured neurons, were assessed. The results showed that muscone intervention improved motor function compared with vehicle‐treated rats. Indeed, muscone attenuated pro‐inflammatory cytokine expression, neuronal‐apoptosis indicators in the lesion area, and activation of the nod‐like receptor family pyrin domain‐containing 3 inflammasome, nuclear transcription factor‐κB, and dynamin‐related protein 1 in Iba1‐ and βIII‐tubulin‐labeled cells. Compared with vehicle‐treated rats, compression sites of muscone‐treated animals exhibited elongated mitochondrial morphologies in individual cell types and reduced reactive oxygen species. In vitro results indicated that muscone suppressed microglial activation and neuronal damage by regulating related‐inflammatory or apoptotic molecules. Moreover, muscone inhibited dynamin‐related protein 1 activation in activated BV2 cells and injured neurons, whereby it rescued mitochondrial fragmentation and reactive oxygen species production, which regulate a wide range of inflammatory and apoptotic molecules. Our findings reveal that muscone attenuates neuroinflammation and neuronal damage in rats with chronic cervical cord compression by regulating mitochondrial fission events, suggesting its promise for CSM therapy. image

Zhou, Long‐yun↗
DOE OSTI2018

Damage Precursor Assessment in Aerospace Structural Materials

The focus of this study was to apply a robust inspection technique for monitoring damage nucleation and propagation in 7075 aluminum alloy specimens exposed to cyclic loading. A previously developed specimen, linearly tapered in width along the length, was subjected to a sinusoidal tension-tension load while conductivity and strain were measured in-situ. Ex-situ measurements of modulus, hardness, surface potential, digital image correlation strain field, and neutron diffraction were made as a function of fatigue cycles. It is hypothesized that varying levels of induced stress along the length due to equal-force but varying area along the length will create a record of damage which can be probed to intuit a temporal history for the specimen. Baseline, intermediate, and failure sensor measurements for several specimens were compared and analyzed as a function of applied stress (varied linearly along the length) and fatigue cycles (constant). Mechanisms of damage nucleation and propagation due to fatigue cycling are discussed with an emphasis on which inspection methods are most promising for improving structural durability and state monitoring.

Cole, Daniel↗