Explosive-induced shock damage in copper and recompression of the damaged region
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36 MATERIALS SCIENCE↗
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The impact of contamination and aging effects on the long-term laser-damage resistance of SiO 2 /HfO 2 /TiO 2 high-reflection coatings for 1054nm
The laser damage thresholds of optical coatings can degrade over time due to a variety of factors, including contamination and aging. Optical coatings deposited using electron beam evaporation are particularly susceptible to degradation due to their porous structure. In a previous study, the laser damage thresholds of optical coatings were reduced by roughly a factor of two from 2013 to 2017. The coatings in question were high reflectors for 1054 nm that contained SiO 2 and HfO 2 and/or TiO 2 layers, and they were stored in sealed PETG containers in a class 100 cleanroom with temperature control. At the time, it was not certain whether contamination or thin film aging effects were responsible for the reduced laser damage thresholds. Therefore, to better understand the role of contamination, the coatings were recleaned and the laser damage thresholds were measured again in 2018. Here, the results indicate that contamination played the most dominant role in reducing the laser damage thresholds of these optical coatings, even though they were stored in an environment that was presumed to be clean.
42 ENGINEERING↗
Characterization of swift heavy ion irradiation damage in ceria
We have examined microstructural evolution in irradiated ceria (CeO2) using swift heavy ion irradiation, electron microscopy, and atomistic simulation. CeO2, a UO2 fuel surrogate, was irradiated with gold ions at an energy of 1 GeV to fluences up to 1x1014 ions/cm2. Transmission electron microscopy accompanied by electron energy loss spectroscopy showed that the ion tracks were of similar size at all fluences, and that there was no chemical change in the ion track core. Classical molecular dynamics simulations of thermal spikes in CeO2 with energy deposition of 12 and 36 keV/nm show damage consisting of isolated point defects at the lower energy and defect clusters at 36 keV/nm, with no amorphization at either energy. Inferences are drawn from modeling about density changes in the ion track and the formation of interstitial loops that shed light on features observed by electron microscopy of swift heavy ion irradiated ceria.
Yablinsky, Clarissa↗
Numerical study of damage in particulate composites during high-strain rate loading using novel damage model
Not provided.
Materials Science↗
Cationic Dependence of X-ray Induced Damage in Strontium and Barium Nitrate
The response of solids to x-ray irradiation is not well understood, in part, because the interactions between x-rays and molecules in solids depend on the intra- and/or inter-molecular electronic properties of the material. Our previous work demonstrated that x-ray induced damage of certain ionic salts depends on the irradiating photon energy, especially when irradiated with photons of energy near the cation’s K-edge. To advance understanding of the cationic dependence of x-ray photochemistry, we present studies of x-ray induced damage of barium nitrate and strontium nitrate. Polycrystalline samples of barium and strontium nitrate were irradiated with high flux monochromatic synchrotron x-rays at selected energies near the K-edge of the respective cations. The damage processes were studied with powder x-ray diffraction, and irradiation products, NO 2 and O 2 , were characterized via Raman spectroscopy. Our results demonstrate that irradiating barium and strontium nitrate with photons of energy greater than the K-edge of the cation promotes high rate of decomposition compared to that observed when irradiating with photons of energy below the K-edge. Additionally, differences in x-ray induced damage between the two compounds are examined and discussed, and evidence of the diffusion of irradiation products is presented.
36 MATERIALS SCIENCE↗
High-pressure-assisted X-ray-induced damage as a new route for chemical and structural synthesis
A novel structural and chemical synthesis of Cs–O derived materials has been demonstrated via X-ray irradiation of Cs 2 C 2 H 2 O 5 at high pressure.
Evlyukhin, Egor↗
Repair of a mirror coating on a large optic for high laser damage applications using ion milling and over-coating methods
Here, when an optical coating is damaged, deposited incorrectly, or is otherwise unsuitable, the conventional method to restore the optic often entails repolishing the optic surface, which can incur a large cost and long lead time. We propose three alternative options to repolishing, including (i) burying the unsuitable coating under another optical coating, (ii) using ion milling to etch the unsuitable coating completely from the optic surface and then recoating the optic, and (iii) using ion milling to etch through a number of unsuitable layers, leaving the rest of the coating intact, and then recoating the layers that were etched. Repairs were made on test optics with dielectric mirror coatings according to the above three options. The mirror coatings to be repaired were quarter wave stacks of HfO 2 and SiO 2 layers for high reflection at 1054 nm at 45 deg incidence in P-polarization. One of the coating layers was purposely deposited incorrectly as Hf metal instead of HfO2 to evaluate the ability of each repair method to restore the coating’s high laser-induced damage threshold (LIDT) of 64.0 J/cm 2 . The repaired coating with the highest resistance to laser-induced damage was achieved using repair method (ii) with an LIDT of 49.0 to 61.0 J/cm 2 .
36 MATERIALS SCIENCE↗
Defect interactions with stepped CeO{sub 2}/SrTiO{sub 3} interfaces: Implications for radiation damage evolution and fast ion conduction
Due to reduced dimensions and increased interfacial content, nanocomposite oxides offer improved functionalities in a wide variety of advanced technological applications, including their potential use as radiation tolerant materials. To better understand the role of interface structures in influencing the radiation damage tolerance of oxides, we have conducted atomistic calculations to elucidate the behavior of radiation-induced point defects (vacancies and interstitials) at interface steps in a model CeO{sub 2}/SrTiO{sub 3} system. We find that atomic-scale steps at the interface have substantial influence on the defect behavior, which ultimately dictate the material performance in hostile irradiation environments. Distinctive steps react dissimilarly to cation and anion defects, effectively becoming biased sinks for different types of defects. Steps also attract cation interstitials, leaving behind an excess of immobile vacancies. Further, defects introduce significant structural and chemical distortions primarily at the steps. These two factors are plausible origins for the enhanced amorphization at steps seen in our recent experiments. The present work indicates that comprehensive examination of the interaction of radiation-induced point defects with the atomic-scale topology and defect structure of heterointerfaces is essential to evaluate the radiation tolerance of nanocomposites. Finally, our results have implications for other applications, such as fast ion conduction.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Metabolite Damage and Metabolite Damage Control in Plants
It is increasingly clear that (a) many metabolites undergo spontaneous or enzyme-catalyzed side reactions in vivo, (b) the damaged metabolites formed by these reactions can be harmful, and (c) organisms have biochemical systems that limit the buildup of damaged metabolites. These damage-control systems either return a damaged molecule to its pristine state (metabolite repair) or convert harmful molecules to harmless ones (damage preemption). Because all organisms share a core set of metabolites that suffer the same chemical and enzymatic damage reactions, certain damage-control systems are widely conserved across the kingdoms of life. Relatively few damage reactions and damage-control systems are well known. Uncovering new damage reactions and identifying the corresponding damaged metabolites, damage-control genes, and enzymes demands a coordinated mix of chemistry, metabolomics, cheminformatics, biochemistry, and comparative genomics. This review illustrates the above points using examples from plants, which are at least as prone to metabolite damage as other organisms.
cheminformatics↗
Heterogeneous energetic material damage simulator (HEDS): A deep learning approach to simulate damage–sensitivity linkages
Damage in the microstructures of energetic materials (EMs), such as propellants and plastic bonded explosives (PBXs), can significantly alter their response to external loads. Both sensitization and desensitization can occur, causing concerns with safety and performance in the field; predictive models that connect damage and the sensitivity of EMs can enable design and provide confidence in their robustness and reliability. However, modeling of damage evolution is challenging for real microstructures of EMs; samples of damaged EMs are difficult to obtain, thereby hindering experiments and direct numerical simulations to determine the sensitivity of EMs at various stages of damage. Here, we develop an approach to generate synthetic, i.e., in silico produced, damaged microstructures for use in simulations to connect damage levels to sensitivity. The development of the present workflow to generate and impose varying levels of damage in microstructures, known as HEDS (Heterogeneous Energetic Material Damage Simulator), begins with a small set of images of damaged PBXs and combines a collection of deep neural network techniques to generate microstructures with varying levels of damage. By making the synthetic microstructures conform closely to those observed in available real, imaged microstructures, we develop an ensemble of damaged microstructures that can be used for in silico shock experiments. HEDS develops these microstructure ensembles as level set fields, which are directly employed in a sharp interface Eulerian hydrocode where shock simulations are performed to quantify the energy release rate from hotspot fields generated in the microstructure. These capabilities can be useful for the analysis and assessment of changes in the sensitivity of EMs and to design formulations that are less susceptible to damage-induced changes in sensitivity and performance.
Fang, Irene (ORCID:0009000844557122)↗
A thermodynamics-based damage model for the non-linear mechanical behavior of SiC/SiC ceramic matrix composites in irradiation and thermal environments
A damage model is developed and validated with experimental data for the non-linear mechanical behavior of SiC/SiC composite materials in nuclear applications. Cyclic thermal and mechanical loading associated with neutron irradiation effects of these composites leads to wide-spread and progressive micro-cracking that leads to loss of thermal conductivity and further enhancement of thermo-mechanical damage. A physics-based model of wide-spread micro-cracking is developed within the thermodynamic framework of continuum damage mechanics. Evolution equations for damage parameters that describe the growth of continuum damage are developed, where the material variables are obtained from experiments. The model novelty is in coupling mechanical, thermal, and irradiation damage through a consistent thermodynamic framework, including loss of thermal conductivity due to the evolution of mechanically induced micro-cracks. A number of thermo-mechanical experiments were conducted to confirm model assumptions. The model is shown to be validated with out-of-pile experiments, and then implemented using commercial finite element code COMSOL to the fuel cladding problem with normal and high radiation dose cases.
Materials Science↗
Damage development in neutron-irradiated concrete in a test reactor: Hygro-thermal and mechanical simulations
This paper reports the development of a 3D mesoscale hygro-thermal-mechanical simulation approach to predict damage in concrete irradiated in a test reactor. This framework, developed in MOOSE, considers the effects of elevated temperature, moisture content, and high neutron fluence (energy threshold, E > 0.1 MeV) on the mortar and aggregates separately. The first-stage simulation implements hygro-thermal analysis to determine the temperature and RH inside the specimen as a function of imposed radiation energy. These are used as inputs to the second stage, which considers radiation-induced volumetric expansion (RIVE) of aggregates, and creep, shrinkage, and stress-strain response of mortar to predict the expansion, stresses, and damage in specimens made using different coarse aggregates and subjected to different irradiation times. The irradiation time-dependent damage in the mortar is expressed using an isotropic damage parameter. This multi-physics model serves as a predictive tool for damage quantification in concrete due to neutron irradiation.
36 MATERIALS SCIENCE↗
A directional microcrack damage theory for brittle solids based on continuous hyperplasticity
We present a novel microcrack-damage theory for brittle solids under compression. Instead of using internal variables like zeroth, second or fourth rank damage tensors, the state of material damage is represented by an internal function that encapsulates the information of direction, density and size of microcracks. Just like other internal variables, the evolution of this state function must obey the second law of thermodynamics for arbitrary loading paths. This is done by casting the model in the framework of continuous hyperplasticity and enforcing a non-negative dissipation rate functional. The proposed framework offers predictions on the continuous evolution of microcrack density and the induced material anisotropy along with the macroscopic stress-strain curves. The use of continuous damage function grants the model significantly enhanced resolution in characterizing the direction-dependent response of cracked solids compared to classical models that are based on damage tensors. Two scenarios are considered in developing the theory, one assumes frictionless cracks and the other incorporates friction between crack surfaces. The results highlight that inelasticity, pressure dependence, and loading-unloading hysteresis exhibited by brittle solids are natural consequences of frictional microcracks. The proposed theory offers a generic and versatile framework to upscale micromechanical processes operating at individual crack scale to explain the macroscopic behavior of cracked solids.
Materials Science↗
Molecular Dynamics Simulation of Fission Fragment Damage in Nuclear Fuel and Surrogate Material
We have performed classical molecular dynamics simulations of swift heavy ion damage, typical of fission fragments, in nuclear fuel (UO2) for energy deposition per unit length of 3.9 keV/nm. We did not observe amorphization. The damage mainly consisted of isolated point defects. Only about 1% of the displacements occur on the uranium sublattice. Oxygen Frenkel pairs are an order of magnitude more numerous than uranium Frenkel pairs in the primary damage state. In contrast, previous results show that the ratio of Frenkel pairs on the two sublattices is close to the stoichiometric ratio in ceria. These differences in the primary damage state may lead to differences in radiation response of UO2 and CeO2.
Molecular dynamics, radiation damage in materials,↗
Isochronal annealing effects on local structure, crystalline fraction, and undamaged region size of radiation damage in Ga-stabilized δ-Pu
The effects on the local structure due to self-irradiation damage of Ga stabilized δ-Pu stored at cryogenic temperatures have been examined using extended x-ray absorption fine structure (EXAFS) experiments. Extensive damage, seen as a loss of local order, was evident after 72 days of storage below 15 K. The effect was observed from both the Pu and the Ga sites, although less pronounced around Ga. Isochronal annealing was performed on this sample to study the annealing processes that occur between cryogenic and room temperature storage conditions, where damage is mostly reversed. Damage fractions at various points along the annealing curve have been determined using an amplitude-ratio method, a standard EXAFS fitting, and a spherical crystallite model, and provide information complementary to the previous electrical resistivity- and susceptibility-based isochronal annealing studies. The use of a spherical crystallite model accounts for the changes in EXAFS spectra using just two parameters, namely, the crystalline fraction and the particle radius. Together, these results are discussed in terms of changes to the local structure around Ga and Pu throughout the annealing process and highlight the unusual role of Ga in the behavior of the lowest temperature anneals.
36 MATERIALS SCIENCE↗
Correlations among void shape distributions, dynamic damage mode, and loading kinetics [Correlations among spall void shape distributions, damage mode and shock loading kinetics]
Here, three-dimensional x-ray tomography (XRT) provides a nondestructive technique to characterize the size, shape, and location of damage in dynamically loaded metals. A shape-fitting method comprising the inertia tensors of individual damage sites was applied to study differences of spall damage development in face-centered-cubic (FCC) and hexagonal-closed-packed (HCP) multicrystals and for a suite of experiments on high-purity copper to examine the influence of loading kinetics on the spall damage process. Applying a volume-weighted average to the best-fit ellipsoidal aspect-ratios allows a quantitative assessment for determining the extent of damage coalescence present in a shocked metal. It was found that incipient transgranular HCP spall damage nucleates in a lenticular shape and is heavily oriented along particular crystallographic slip directions. In polycrystalline materials, shape distributions indicate that a decrease in the tensile loading rate leads to a transition to coalesced damage dominance and that the plastic processes driving void growth are time dependent.
36 MATERIALS SCIENCE↗