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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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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Laser Welded Edge Seals for Glass/Glass Modules

Polymers used in module construction are often involved in degradation mechanisms and hamper recycling. This project explores femtosecond (fs) laser welding of glass/glass modules to enable polymer-free modules. We are utilizing the knowledge base of the industrial laser community to apply glass/glass fs laser welding technology to solar modules. Experimentally measured stress intensity factors for glass welds are input into a COMSOL model of a full-size module to test weld failure under static loading. If successful, fs laser welding could enable modules that are polymer-free that will extend module warrantees, allow hermetically sealed glass/glass modules for moisture-sensitive semiconductors, and improve module recyclability.

COMSOL finite element model↗
DOE OSTI2019

Interfacial Strength Evaluation of Oxide Films on Carbon Steel by Using the Laser Shock Adhesion Test

We investigate the adhesion strength (interfacial strength) of the oxide film formed on a carbon steel substrate by using a laser shock adhesion test (LaSAT). A rolled carbon steel (SS400) plate is first heated at high temperature (700 °C) under the atmosphere (heat treatment) to cause the formation of oxide films about 20-50 μm thick on the steel surface. The film consisted of multiple layers, including wustite (FeO), magnetite (Fe{sub 3}O{sub 4}), and hematite (Fe{sub 2}O{sub 3}). Next, the x-ray diffraction method was used to measure the residual stress in the film. We find that compression stress develops in the film because of a mismatch of thermal strain in between the film and substrate after the heat treatment. With LaSAT, strong elastic wave generates by a pulsed laser ablation of the substrate backside, and results in interfacial fractures in the oxide films. To monitor the normal (out-of-plane) displacement of the top surface film, a laser ultrasonic interferometer is simultaneously utilized, such that we detect film delamination and determine the critical laser energy for interfacial fracture to obtain the critical stress (interfacial strength). Furthermore, additional pulsed laser irradiation is conducted against a pre-delaminated specimen in order to examine the growth of delamination area and evaluate the interfacial fracture toughness. Finally, elastic wave propagation in the sample is computed using the finite element method (FEM) in order to evaluate the interfacial stress field, accurately. For the FEM, multiple layers in the oxide film are modeled, and the residual stress due to thermal strain mismatch is introduced. The FEM computations reveal the stress distribution around the interface and evaluate the critical stress and critical stress intensity factor for delamination. We thus quantitatively evaluate the interfacial strength and interfacial fracture toughness of the oxide film formed on carbon steel. The mechanism of interfacial fracture is also discussed on the basis of microstructures in a film with multiple layers. This result may be useful for understanding the adhesion quality of oxide film during the hot-rolling process.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Laser 3D Printing of Fe-Based Bulk Metallic Glass: Microstructure Evolution and Crack Propagation

This work presents a comprehensive study of microstructure evolution, crack development and hardness performance of Fe-based bulk metallic glass parts processed by laser 3D printing. The combination of a low scan speed and high energy density generates a low temperature gradient, leading to supercooling and the formation of coarse dendrite and cellular crystal microstructure. Columnar dendrites grow in a single direction with large stress, and cracks are easily formed between the dendrites. The stress intensity factor (SIF) caused by the crack surface tension is small, the crack healing effect is weak, and it is difficult to prevent crack propagation. Cellular grain growth is uniform and more easily accommodates the strain, preventing crack initiation and propagation. In contrast, use of a high scan speed with low energy input produces a fine and uniform dendrite or even nanocrystalline, microstructure with microcracks. The SIF caused by the crack surface tension is large, and the crack healing effect is strong and prevents crack initiation and propagation. For low energy density, the hardness of the sample is similar to the hardness of the cast amorphous. This result indicates that the printing sample retained some amorphous characteristics.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Investigation of Mode I Notch Toughness of Zr{sub 41.2}Ti{sub 13.8}Cu{sub 10}Ni{sub 12.5}Be{sub 22.5} Metallic Glass under Dynamic Loading Conditions

Based on dynamic three-point bending tests, the dynamic notch toughness (K{sub Q}{sup d}) of Zr{sub 41.2}Ti{sub 13.8}Cu{sub 10}Ni{sub 12.5}Be{sub 22.5} (Vit 1) bulk metallic glass (BMG) was found to be sensitive to stress intensity factor rate ( K-dot {sub Q}{sup d}), which varied from 5.21 to 31.90 MPa m{sup 1/2}. The number of shear bands (N{sub s}) in the notch tip plastic zone was quantitatively analyzed. The phenomenon wherein N{sub s} decreased with increasing loading rate was explained based on the theory of the shear transformation zone and the softening mechanism. Then, power law relationships were established among N{sub s}, K{sub Q}{sup d} and K-dot {sub Q}{sup d}. The results showed that shear bands can affect K{sub Q}{sup d} and K-dot {sub Q}{sup d} and act as a bridge connecting K{sub Q}{sup d} and K-dot {sub Q}{sup d}. The sensitivity of K{sub Q}{sup d} to K-dot {sub Q}{sup d} in BMGs can be well explained by the variation of N{sub s} with loading rate.

36 MATERIALS SCIENCE↗
DOE OSTI2022

The Fracture Toughness of Nuclear Graphite Grades, Revision 1

New measurements of graphite mode I critical stress intensity factor, K Ic (commonly referred to as the fracture toughness) and the mode II critical shear stress intensity, K IIc , are reported and compared with prior data for K Ic and K IIc . The new data are for graphite grades PCEA, IG-110 and 2114. Variations of K Ic and acoustic emission (AE) data with graphite texture are reported and discussed. The Codes and Standards applications of fracture toughness, K Ic , data are also discussed. A specified minimum value for nuclear graphite K Ic is recommended.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2022

Mechanisms of Mitigating Chloride-Induced Stress Corrosion Cracking of Austenitic Steels by Laser Shock Peening

This study investigates the effect of laser shock peening (LSP) on the chloride-induced stress corrosion cracking (SCC) of 304 austenitic steels. LSP can induce a high compressive residual stress to a depth of 700 µm and plastic deformation structures of dislocations, deformation twins, and stacking faults. Constant-load SCC tests in MgCl2 solution suggested that LSP can retard the crack initiation and slow the crack growth. LSP-treated subsurface layers experience ductile fracture while the central regions exhibit intergranular SCC. The LSP-induced deformation structures may impede dislocation slips, while the LSP-induced compressive residual stress can lessen the stress intensity factor of crack tips and decrease the local stress for film rupture.

Materials Science↗
DOE OSTI2026

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.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Sound Assisted Low Temperature Spalling: Upscaling and Throughput

In evaluating the state-of-the-art spalling techniques, the key factor that is missing is the control of crack propagation, which is responsible for low quality wafers due to high surface roughness and Total Thickness Variation, TTV. This project has shown that acoustic waves can alter the conditions at the crack tip during thermal spalling, modifying the propagation speed and the stress field around it (stress intensity factor, K). Both factors are directly related to the roughness of the spalled surface, so as we control speed and stress, we can fine-tune the surface roughness through the entire wafer as suggested by Arakawa.

42 ENGINEERING↗
DOE OSTI2019

Simulating the Fracture of Notched Mortar Beams through Extended Finite-Element Method and Peridynamics

This paper simulates fracture in notched mortar beams under three-point bending using extended finite element method (XFEM) and peridynamics. A three-phase microstructure (i.e., cement paste, aggregates, and paste-aggregate interface) is used for constitutive modeling of the mortar to obtain the elastic properties for simulation. In the XFEM approach, the simulated homogenized elastic modulus is used along with the total fracture energy of the cement mortar in a damage model to predict the fracture response of the mortar including crack propagation and its fracture parameters (Mode I stress intensity factor, K IC and critical crack tip opening displacement, CTOD C ). The damage model incorporates a maximum principal stress-based damage initiation criteria and a traction-separation law for damage evolution. In the peridynamics approach, a bond-based model involving a prototype microelastic brittle (PMB) material model is used. The elastic properties and fracture energy release rates are used as inputs in the PMB model, along with the choice of peridynamic horizon size. Comparison with experimental fracture properties ( K IC , CTOD C ) as well as crack propagation paths from digital image correlation show that both the approaches yield satisfactory results, particularly for K IC and crack extension. Furthermore, both these methods can be adopted for fracture simulation of cement-based materials.

42 ENGINEERING↗
DOE OSTI2023

Nonmonotonic effect of chemical heterogeneity on interfacial crack growth at high-angle grain boundaries in Fe-Ni-Cr alloys

Here, an intermittent pattern is observed in the modeling of interfacial cyclic-loading crack growth at high-angle grain boundaries in ternary Fe-Ni-Cr alloys. Different from conventional wisdom of stress-intensity factor, the abrupt crack advances are found driven by extreme value statistics—namely, the aggregation of atoms with most compressive residual stresses. In addition, inherently non-affine atomic stress fluctuations are discovered, and the fluctuations peak at intermediate level of chemical heterogeneity, causing the fastest crack growth. Implications of such nonmonotonic mechanism in regard to the origin of intermediate-temperature embrittlement phenomena are also discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Large Plate Experiment of Chloride-induced Stress Corrosion Cracking in Spent Nuclear Fuel Storage Canisters

This report provides a description of the testing (in progress at the Savannah River National Laboratory) to evaluate the corrosion behavior of a large section of welded plate material harvested from the Sandia National Laboratories’ full-size mockup of a spent nuclear fuel (SNF) dry storage canister. The details of the establishment of this plate test, the interim corrosion results (from visual examination), and the general plan for examination of the plate in CY21 to evaluate crack growth behavior (if any) are provided. This work is intended to inform aging management programs for SNF canisters under conditions of extended dry storage. A “large plate” (approximately 51 x 46 cm with thickness 16 mm and weight about 30 kg) and containing a circumferential weldment from the mockup is the test specimen. The knowledge of the salt, temperature, humidity conditions for chloride-induced stress corrosion cracking (CISCC) including the threshold stress intensity factor, K iscc , were used to setup the large plate test in which a set of part-through-wall and through-wall electrical discharge machined (EDM) defects were positioned in the weld residual stress field of the welded plate material from the mockup canister. A marine salt solution was applied to this plate specimen with an air-brush spray, then dried, and then exposed to a sustained 71-73% RH condition at an ambient room temperature of 22 °C. The salt loading and environmental condition is expected to be aggressive to cause CISCC

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2022

Efficient co-solution of time step size and independent state in simulations of fluid-driven fracture propagation with embedded meshes

Here we present an efficient time-continuation scheme for fluid-driven fracture propagation problems in the extended finite element method framework. The approach applies a monolithic solution strategy to a fully coupled and implicit approximation of hydro-mechanical systems in conjunction with simultaneous linear elastic propagation of multiple fractures. At the end of each time step, the process ensures that the weakest fracture tip is in an equilibrium propagation regime. Furthermore, the solution process provides an initialization procedure for the newly created fracture spaces and an a priori estimate of the stress intensity factor growth rate, improving simulation robustness, and efficiency. The solution process is validated using the Kristianovich-Geertsma-de Klerk analytical solution under the toughness- and viscosity-dominated regimes. It is also extended to and demonstrated on problems with multiple fractures undergoing simultaneous propagation with stress shadow interactions. Numerical examples demonstrate that the solution process can reduce the required computational cost by one order of magnitude compared to other existing methods.

42 ENGINEERING↗
DOE OSTI2020

Residually Stressed Bimaterial Beam Specimen for Measuring Environmentally Assisted Crack Growth

Background: Subcritical crack growth can occur in a brittle material when the stress intensity factor is smaller than the fracture toughness if an oxidizing agent (such as water) is present at the crack tip. Objective: Here we present a novel bi-material beam specimen which can measure environmentally assisted crack growth rates. The specimen is “self-loaded” by residual stress and requires no external loading. Methods: Two materials with different coefficient of thermal expansion are diffusion bonded at high temperature. After cooling to room temperature a subcritical crack is driven by thermal residual stresses. A finite element model is used to design the specimen geometry in terms of material properties in order to achieve the desired crack tip driving force. Results: The specimen is designed so that the crack driving force decreases as the crack extends, thus enabling the measurement of the crack velocity versus driving force relationship with a single test. The method is demonstrated by measuring slow crack growth data in soda lime silicate glass and validated by comparison to previously published data. Conclusions: The self-loaded nature of the specimen makes it ideal for measuring the very low crack velocities needed to predict brittle failure at long lifetimes.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Effect of Specimen Thickness on Fracture Toughness and Plane Stress to Plane Strain Transition in Medium-Density Polyethylene

This study investigates the effect of specimen thickness on fracture toughness and the transition from plane stress to plane strain conditions in Medium-Density Polyethylene (MDPE) using Single Edge Notched Bend (SENB) specimens. Three thickness groups (7.5 mm, 9.0 mm, and 12.1 mm) were tested following ASTM D5045 protocol. Conditional stress intensity factors (KQ) increased from 2.2 MPavm to 2.8 MPavm with increasing thickness, demonstrating significant size dependency. Confocal microscopy revealed a 34% reduction in maximum crack tip opening displacement (CTOD) from 0.478 mm to 0.314 mm as thickness increased, with plastic zone lateral extent decreasing by 32%. This quantitative evidence validates Irwin's theoretical prediction of plastic zone size transition from plane stress r_y˜ (1/2p) (K_I/s_y )^2 to plane strain conditions r_y˜ (1/6p) (K_I/s_y )^2.Scanning electron microscopy confirmed progressive suppression of shear lips and evolution from ductile tearing with extensive polymer chain drawing in thin specimens to localized crazing in thick specimens. Despite all specimens satisfying the ASTM D5045 criterion (B = 2.5(KQ/s_y )^2 ) ,residual shear lips persisted even in the thickest specimens, demonstrating that nominal size requirements alone are insufficient for achieving complete plane strain conditions in highly ductile polymers. The findings emphasize the necessity of integrated analytical and morphological assessment for valid fracture toughness characterization, with critical implications for life assessment and integrity prediction in thick-section polymer components such as natural gas distribution pipelines.

Medium-Density Polyethylene↗
DOE OSTI2025

Evaluating methods to reduce duration of near-threshold fatigue crack growth rate measurements for low-alloy steels in hydrogen gas

Measurement of the near-threshold fatigue crack growth rate (da/dN) vs. stress-intensity factor range (∆K) relationship in hydrogen gas is essential for maximizing the calculated design fatigue life of high-pressure hydrogen storage vessels. However, such measurements are rarely performed, since the low cyclic loading frequencies applied in standard practice lead to prohibitively protracted test durations. The objective of this study was to demonstrate two means for reducing test durations when measuring near-threshold da/dN vs. ΔK relationships under decreasing ΔK for low-alloy pressure vessel steels in hydrogen gas: 1) imposing steeper K-gradients relative to the recommended limits in standards such as ASTM E647, and 2) increasing cyclic loading frequency relative to typical values applied during fatigue crack growth testing of low-alloy steels in hydrogen gas. Recognizing that steeper K-gradients could amplify loading-history effects, test methods employing this approach were designed to mitigate such effects by either maintaining constant K max or gradually increasing the K-gradient as the threshold was approached. Although the varying K-gradient method was vulnerable to loading-history effects in the form of plasticity-induced crack closure, particularly at lower stress ratio (R) and higher starting K max values, these effects could be compensated by applying the adjusted compliance ratio (ACR) method. Here, it was demonstrated that steeper K-gradients in concert with increased cyclic loading frequency reduced the duration of near-threshold fatigue crack growth tests in hydrogen gas by more than 99% relative to standard practices.

Fatigue threshold↗
DOE OSTI2020

An Improved Fracture Mechanics-Informed Multiscale Thermomechanical Damage Model for Ceramic Matrix Composites

This paper extends recent work done by the authors in modeling length scale-dependent damage behavior of ceramic matrix composites (CMCs) to include effects of local anisotropy introduced by matrix cracking. This model captures scale-dependent damage initiation and propagation behavior of the brittle matrix by employing internal state variable (ISV) theory within a multiscale modeling framework to obtain damaged matrix stress/strain constitutive relationships at each length scale. The damage ISV captures the effects of matrix cracking and growth by using fracture mechanics and the self-consistent scheme to determine the reduced stiffness of the cracked matrix. Matrix cracks, which activate when stress intensity factors near manufacturing induced cavities exceed the fracture toughness of the material, are assumed to be transversely isotropic in the plane of the crack, and matrix anisotropy occurs when the damaged stiffness tensor is rotated from the crack plane to the global axes. The crack progression and temporal evolution of the damage ISV are governed by fracture mechanics and crack growth kinetics. The model effectively captures first matrix cracking, which is the first significant deviation from linear elasticity. The nonlinear predictive capabilities of the material model are demonstrated for monolithic silicon carbide (SiC) and a 2D woven five-harness satin (5HS) carbon fiber SiC matrix (C/SiC) CMC.

Skinner, Travis↗
DOE OSTI2019

In situ high energy X-ray diffraction measurement of strain and dislocation density ahead of crack tips grown in hydrogen

The deformation fields near fatigue crack tips grown in hydrogen and in air were measured using high-energy x-ray diffraction. A larger magnitude of elastic strain was observed in the hydrogen case compared to the air case. The magnitude of elastic strain was quantified through an effective crack tip stress intensity factor. The dislocation profile ahead of the crack was probed via x-ray line broadening and electron back-scatter diffraction was used to assess the crack path (intergranular vs. transgranular). Ahead of the crack tip grown in hydrogen, an order of magnitude lower dislocation density, compared to a baseline density far from the crack, was observed. This decrease in dislocation density was not observed in the air case. These differences are discussed in terms of two leading hydrogen embrittlement mechanisms, Hydrogen Enhanced Localized Plasticity (HELP) and Hydrogen Enhanced Decohesion (HEDE). We have observed a decrease in transgranular cohesion (transgranular HEDE), as well as an increase in intergranular fracture. The measurements of dislocation activity support a model of a decrease in intergranular cohesion (intergranular HEDE) which is likely facilitated by the HELP mechanism. Here, this suggests that the increase in fatigue crack growth rate is due to a sum of the two effects of hydrogen, in which the crack grows faster in the transgranular fracture mode and faster due to an increase in a new mode of intergranular fracture. Published by Elsevier Ltd on behalf of Acta Materialia Inc.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Investigation of dynamic fracture behavior of additively manufactured Al-10Si-Mg using high-speed synchrotron X-ray imaging

The dynamic tensile properties of additively manufactured (AM) and cast Al-10Si-Mg alloy were disccused using high-speed synchrotron X-ray imaging coupled with a modified Kolsky bar apparatus. A controlled tensile loading (strain rate ≈ 750 s -1 ) was applied using the Kolsky bar apparatus and the deformation and fracture behavior were recorded using the high-speed X-ray imaging setup. The CT and high-speed imaging results worked together to identify the location of the critical flaw and to capture the dynamics of crack propagation. In all experiments, the critical flaw was located on the surface of each specimen. The AM specimens displayed significantly higher crack propagation speed, yield strength, ultimate tensile strength, strain hardening coefficient, and yet lower ductility compared to the cast specimens under dynamic tension. Although the strength values were higher for the AM specimens, the critical mode I stress intensity factors were comparable for both specimens. The microstructures of the samples were characterized by synchrotron X-ray computed tomography (CT) and scanning electron microcopy. The correlation between the dynamic fracture behavior of the samples and the microstructure of the samples is analyzed and discussed.

36 MATERIALS SCIENCE↗