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Results for “Effects of defects”

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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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Environmental and high strain rate effects on composites for engine applications

The complex environmental and loading conditions experienced by many turbine engine components impose severe durability and damage tolerance requirements for component materials. Programs are being conducted to establish the structural performance of composite materials under anticipated engine operating environments. A description is presented of the results obtained in connection with several of these programs. A comparison of predicted and measured hygrothermal effects is considered along with hygrothermal effects on defect growth, high strain rate effects on composite mechanical properties, dynamic stress intensity factors for composites, and the indentation laws for composite impact analysis.

Chamis, C. C.↗
NASA NTRS1990

Effective actions for bosonic topological defects

A gauge field theory is considered which admits p-dimensional topological defects, expanding the equations of motion in powers of the defect thickness. In this way an effective action and effective equation of motion is derived for the defect in terms of the coordinates of the p-dimensional worldsurface defined by the history of the core of the defect.

Gregory, Ruth↗
NASA NTRS1987

The effects of wall surface defects on boundary-layer transition in quiet and noisy supersonic flow

The design of supersonic vehicles with laminar flow control and vehicles such as the Space Shuttle requires information on allowable transition tolerances to fabrication defects such as discrete surface roughness and waviness. A relatively large data base on the effects of discrete roughness on transition exists for subsonic and supersonic speeds. The existing supersonic wind tunnel transition data are contaminated by wind tunnel noise emanating from the turbulent boundary layers on the nozzle walls. Roughness and waviness transition data obtained in a quiet Mach 3.5 supersonic wind tunnel are compared with those obtained in conventional noisy flows.

Morrisette, E. Leon↗
DOE OSTI2021

Nanoscale friction of CVD single-layer MoS 2 with controlled defect formation

Two-dimensional (2D) layered nanomaterials such as graphene, molybdenum disulfide (MoS 2 ), or tungsten disulfide offer a promising solution in areas of solid-state lubrication, due to their excellent mechanical properties as well as low friction. However, defects can influence their friction and reduce their superior tribological properties. Thus, it is crucial to understand the effects of defects on sliding behavior in 2D nanomaterials, to foster a functional strategy for utilizing 2D nanomaterials as solid-state tribological films. In this study, frictional effects of defects, grain boundaries, and atomic-scale structural defects were explored on chemical vapor deposition (CVD) grown single layer MoS 2 . Selective patterning of defects into MoS 2 was accomplished via controlled irradiation of helium ions with varying ion doses. The friction of MoS 2 was characterized by friction force microscopy (FFM) and was found that friction depends on the defect formation controlled by helium ion irradiation. This approach offers a correlation between surface topography, defects and friction. Understanding the relative friction of MoS 2 in the presence of different levels of defects is foundational to studying tribological properties of a single layer MoS 2 at both nanoscales and macroscales.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Tunable chemical complexity to control atomic diffusion in alloys

Abstract In this paper we report a new fundamental understanding of chemically-biased diffusion in Ni–Fe random alloys that is tuned/controlled by the intrinsic quantifiable chemical complexity. Development of radiation-tolerant alloys has been a long-standing challenge. Here we show how intrinsic chemical complexity can be utilized to guide the atomic diffusion and suppress radiation damage. The influence of chemical complexity is shown by the example of interstitial atom (IA) diffusion that is the most important defect in radiation effects. We use μs-scale molecular dynamics to reveal sluggish diffusion and percolation of IAs in concentrated Ni–Fe alloys. We develop a mean field diffusion model to take into account the effect of migrating defect energy properties on diffusion percolation, which is verified by a new kinetic Monte Carlo approach addressing detailed processes. We demonstrate that the local variations in the ground state energy of IA configurations in alloys, reflecting the chemical difference between alloying components, drives the percolation effects for atomic diffusion. Percolation, chemically-biased and sluggish diffusion are phenomena that are directly related to the chemical complexity intrinsically to multicomponent alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Effects of strain and defects on the topological properties of HfTe 5

Manipulating topological states is a topic of vigorous research. However, the impact of such topological phase transitions on the quasiparticle dynamics remains elusive. Here, in this work, we present the effects of a transition from a strong to weak topological insulator in HfTe 5 as a function of Te vacancy concentration. We observed a significant transition from distinct sharp surface states and Dirac crossing to a Fermi-liquid-like quasiparticle state in which these surface-localized features are heavily suppressed. Additionally, by inducing the same effect through applied uniaxial stress, we demonstrate that changes in the lattice constants play the foremost role in determining the electronic structure, self-energy, and topological states of HfTe 5 . Our results demonstrate the possibility of using both defect chemistry and strain as control parameters for topological phase transitions and associated many-body physics.

36 MATERIALS SCIENCE↗
DOE OSTI2022

The Potential Energy Hotspot: Effects of Impact Velocity, Defect Geometry, and Crystallographic Orientation

In energetic materials, the localization of energy into “hotspots” is known to dictate the initiation of chemical reactions and detonation. Recent all-atom simulations have shown that more energy is localized as internal potential energy (PE) than can be inferred from the kinetic energy (KE) alone. The mechanisms associated with pore collapse and hotspot formation are known to depend on pore geometry and dynamic material response such as plasticity. Therefore, we use molecular dynamics (MD) simulations to characterize shock-induced pore collapse and the subsequent formation of hotspots in 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), a highly anisotropic molecular crystal, for various defect shapes, shock strengths, and crystallographic orientations. We find that the localization of energy as PE is consistently larger than the KE in cases with significant plastic deformation. Additionally, an analysis of MD trajectories reveals the underlying molecular- and crystal-level processes that govern the effect of orientation and pore shape on PE localization. We find that the regions of highest PE relate to the areas of maximum plastic deformation, while KE is maximized at the point of impact. Comparisons against octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) reveal less energy localization in TATB, which could be a contributing factor to the latter’s insensitivity.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Band-edge Engineering to Eliminate Radiation-Induced Defect States in Perovskite Scintillators

Under radiative environments such as extended hard X- or γ-rays, degradation of scintillation performance is often due to irradiation-induced defects. To overcome the effect of deleterious defects, novel design mitigation strategies are needed to identify and design more resilient materials. The potential for band-edge engineering to eliminate the effect of radiation-induced defect states in rare-earth-doped perovskite scintillators is explored, taking Ce 3+ -doped LuAlO 3 as a model material system, using density functional theory (DFT)-based DFT + U and hybrid Heyd–Scuseria–Ernzerhof (HSE) calculations. Furthermore, from spin-polarized hybrid HSE calculations, the Ce 3+ activator ground-state 4f position is determined to be 2.81 eV above the valence band maximum in LuAlO 3 . Except for the oxygen vacancies which have a deep level inside the band gap, all other radiation-induced defects in LuAlO 3 have shallow defect states or are outside the band gap, that is, relatively far away from either the 5d 1 or the 4f Ce 3+ levels. Finally, we examine the role of Ga doping at the Al site and found that LuGaO 3 has a band gap that is more than 2 eV smaller than that of LuAlO 3 . Specifically, the lowered conduction band edge envelopes the defect gap states, eliminating their potential impact on scintillation performance and providing direct theoretical evidence for how band-edge engineering could be applied to rare-earth-doped perovskite scintillators.

36 MATERIALS SCIENCE↗
NASA NTRS1981

Material and processing needs for silicon solar cells in space

The technical concerns of NASA in the area of space grade solar cells are summarized. Solar power needs are projected through 1987. The degradation of solar cell performance due to the effects of radiation on impurities and crystal defects and the improved performance of float zone silicon are illustrated. The reduction of oxygen and carbon in float zone silicon allows for much faster low temperature annealing of the defects. The effects of improved crystal purity on cell performance are summarized.

Brandhorst, H. W., Jr.↗
NASA NTRS1981

The effects of artificially-produced defects on the film thickness distribution in sliding EHD point contacts

Effects of artificially produced dents and grooves on the elastohydrodynamic film thickness profile in a sliding point contact are investigated using optical interferometry. Defects on the surface of a highly polished ball are held stationary at various locations within the vicinity of the contact region while the disk is rotating. It is shown that defects can dramatically change the film thickness which exists when no defects are present in or near the contact, and it is shown that the change in thickness is mainly a function of the position of the defects in the inlet region, the geometry of the defects, the orientation of the defects in the case of grooves, and the depth of the defect relative to the central film thickness.

Cusano, C.↗
NASA NTRS1997

Nondestructive Evaluation of Adhesively Bonded Joints by Acousto-Ultrasonic Technique and Acoustic Emission

Reliable applications of adhesively bonded joints require an effective nondestructive evaluation technique for their bond strength prediction. To properly evaluate factors affecting bond strength, effects of defects such as voids and disbonds on stress distribution in the overlap region must be understood. At the same time, in order to use acousto-ultrasonic (AU) technique to evaluate bond quality, the effect of these defects on dynamic response of single lap joints must be clear. The stress distribution in a single lap joint with and without defects (void or disbond) is analyzed. A bar-Theta parameter which contains adherend and adhesive thickness and properties is introduced. It is shown for bonded joints with bar-Theta greater than 10, that a symmetric void or disbond in the middle of overlap up to the 70 percent of overlap length has negligible effect on bond strength. In contrast frequency response analyses by a finite element technique showed that the dynamic response is affected significantly by the presence of voids or disbonds. These results have direct implication in the interpretations of AU results. Through transmission attenuation and a number of AU parameters for various specimens with and without defects are evaluated. It is found that although void and disbond have similar effects on bond strength (stress distribution), they have completely different effects on wave propagation characteristics. For steel-adhesive-steel specimens with voids, the attenuation changes are related to the bond strength. However, the attenuation changes for specimens with disbond are fairly constant over a disbond range. In order to incorporate the location of defects in AU parameters, a weighting function is introduced. Using an immersion system with focused transducers, a number of AU parameters are evaluated. It is found that by incorporating weighting functions in these parameters better sensitivities (AU parameters vs. bond strength) are achieved. Acoustic emission (AE) activities of steel-adhesive-steel specimens with bar-Theta equal to 3.4 are monitored. Two different formats of energy vs. time have resulted, each corresponding to the perfect specimens or the specimens with void or disbond. The relative acoustic energy and the number of events at failure are found to be a means for predicting the bond strength.

Nayeb-Hashemi, Hamid↗
NASA NTRS2022

Assurance Equations: A Cost and Criticality Model for Optimizing Quality Assurance Surveillance

The cost of quality vs cost of failure correction has been a long-running topic of discussion within the Aerospace community. It leads directly to concepts of “risk tolerance”, and risk-based decision-making. It would be valuable if there was a way to compute the optimal investment in customer-executed quality assurance activities using defect significance with respect to performance objectives, the activities’ defect detection effectiveness, and the cost-penalty for late discovery of impactful defects. This optimization is particularly of interest to projects whose budget constraints significantly limit their risk management options.The cost to fix defects (i.e., failure correction) escalates as the project matures. There have been studies attempting to determine the relative cost of fixing defects discovered during various phases of a project life cycle with important implications, all of which suggest growth factors are large. The commonly referred to 1:10:100 rule represents a cost multiplier for repair/rework across the Design to Fab to Test hardware development phases. Cost premiums for QA activities also accumulate when they are treated as mandatory (due to schedule drag) or are performed later than their assigned phase.This paper describes the modeling of development phase -dependencies in the conduct of typical customer-executed quality assurance activities. Our initial modeling encompasses:• Distinct phases of the production lifecycle• Multiple kinds of Defects, each with some a-priori likelihood of being present• Each defect’s impact on performance Objectives for a type of hardware• The cost and efficacy of assurance techniques at detecting such Defects• The costs of fixing those Defects detected in a given phase of the production lifecycleThe model captures assurance activities’ abilities to Detect defects. Upon detection it is assumed that the Defect is immediately fixed. Defects that “escape” detection by some activity may thereafter be detected by a later activity, but by then the cost of fixing the Defect may have escalated. Defects are related to the performance Objectives they would detract from, were those Defects to remain present in the operating system.We have constructed and are exploring, a model that relates the importance of hardware system elements to mission objectives, the impact of types of Defects on those hardware types, the cost of customer-executed assurance activities (i.e., supplier controls) and their effectiveness towards reducing an impactful quality escape, and the cost of Defect correction across production phase. We describe the approach taken to select the key model aspects, why they are relevant to our NASA mission, and our efforts to populate it with relevant and contemporary data. We use a notional example to illustrate model design and function.

Plante, Jeannette↗
DOE OSTI2022

Synergistic effect of microstructure and defects on the initiation of fatigue cracks in additively manufactured Inconel 718

Fatigue cracks in additively manufactured (AMed) Inconel 718 (IN-718) in machined surface condition often initiate from persistent slip bands (PSBs) unlike other popular AM alloys such as 17-4 PH stainless steel or Ti-6Al-4V, where fatigue crack initiation is exclusively from volumetric defects; therefore, a competition between PSB- vs. defect- mediated crack initiation clearly exists. To shed light on the factors governing the competition, this study investigates the characteristics of cyclic strain localization, PSB formation, and crack initiation via crystal plasticity (CP) modeling of cyclic loading on polycrystalline aggregates which are then validated by experiments. In this work, a physics-based, free slip distance (FSD) dependent slip strength evolution law is proposed, which is shown to enable the CP model to simulate the heterogeneous strain distribution in IN-718. Implementing a crack initiation criterion based on strain contrast, the locations and lives for crack initiation can also be calculated. It is shown that both FSD and resolve shear stress influence the strain localization and crack initiation behaviors. The distribution of a localization parameter calculated based on the multiplication of FSD and Schmid factor within a grain is found to correlate well with the locations of PSBs. The maximum values of the localization parameters within a microstructure are shown to correlate well with the experimentally obtained crack initiation lives. The presence of volumetric defects in IN-718 generally do not impact strain localization behavior unless their size is large compared to the grain size.

42 ENGINEERING↗
DOE OSTI2025

Development of interatomic potential and effect of ordering on defect properties in CrMnV

Developing materials that can withstand extreme environments, such as high radiation doses and elevated temperatures, is crucial for next-generation particle accelerators, including the 2.4 MW Long-Baseline Neutrino Facility. High-Entropy Alloys have emerged as promising candidates for beam window materials due to their superior mechanical strength, corrosion resistance, and radiation tolerance. In this study, we focus on the Cr–Mn–V alloy system, developing and employing machine-learning interatomic potentials (MLIPs) to investigate the formation of an ordered phase and its influence on defect properties. Using hybrid Monte Carlo-Molecular Dynamics simulations, we observe the formation of a B2-ordered phase at lower temperatures, consistent with Density Functional Theory (DFT) predictions. Ordered structures display a bimodal distribution of migration energies and reduced mean square displacement values, indicating suppressed vacancy diffusion. Our results also show that the migration energy barrier varies based on the atomic species, with Mn and V exhibiting the highest and lowest average barriers, respectively. These findings suggest that atomic ordering inhibits defect mobility, potentially enhancing the radiation resistance of CrMnV alloys. The validated MLIP provides a reliable framework for simulations that are faster than traditional DFT while maintaining the accuracy required to study defect and ordering properties.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Effect of macroscopic surface defects on dynamic damage: An experimental and numerical study

This study examines the impact of macroscopic surface defects on the dynamic ductile damage behavior of polycrystalline metals using plate-impact experiments. Defects of various shapes (flat, round, and point) were manufactured on the free or impact surfaces of annealed copper specimens. The experiments were diagnosed with photon Doppler velocimetry measurements and soft recovery techniques. The experimental results revealed that defect shape and location significantly affect velocity–time profiles and void distribution. In order to understand the dynamics of shock propagation and corresponding ductile damage evolution within the target specimens, the impact experiments were modeled with a calibrated Tepla model, a dynamic ductile damage model for polycrystalline metals [Nguyen et al., Int. J. Solids Struct. 329, 113833 (2026)]. Overall, our resulting simulated velocity showed good agreement with measured velocity, and our simulated porosity distributions qualitatively matched experimental data. Based on our simulation results, defects on the free surface were found to distort rarefaction waves and therefore the corresponding spall planes. On the other hand, defects on the impact surface generated a delayed shock when the flyer plate and the defected target area were in contact, leading to distortion of the spall plane. The distortion of the spall plane resulted in a non-uniform distribution of voids within the defected specimens. Lastly, we examined the role of local work hardening due to the defect manufacturing process on the velocity and porosity distribution, using Tepla simulations with a simplified representation of local hardening. This investigation highlights the importance of defect geometry, location, and local hardening associated with defect generation in dynamic ductile damage processes.

36 MATERIALS SCIENCE↗