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Optical properties and electronic transitions in solid crystals as function of temperature using infrared and Raman techniques
Load separation is the representation of the load in the test records of geometries containing cracks as a multiplication of two separate functions: a crack geometry function and a material deformation function. Load separation is demonstrated in the test records of several two-dimensional geometries such as compact tension geometry, single edge notched bend geometry, and center cracked tension geometry and three-dimensional geometries such as semi-elliptical surface crack. The role of load separation in the evaluation of the fracture parameter J-integral and the associated factor eta for two-dimensional geometries is discussed. The paper also discusses the theoretical basis and the procedure for using load separation as a simplified yet accurate approach for plastic J evaluation in semi-elliptical surface crack which is a three-dimensional geometry. The experimental evaluation of J, and particularly J(sub pl), for three-dimensional geometries is very challenging. A few approaches have been developed in this regard and they are either complex or very approximate. The paper also presents the load separation as a mean to identify the blunting and crack growth regions in the experimental test records of precracked specimens. Finally, load separation as a methodology in elastic-plastic fracture mechanics is presented.
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Unifying empirical data with predictive models can enable engineering cost-savings through certification by analysis and reliability-based design. Both concepts require rigorous uncertainty quantification (UQ) and robust understanding and treatment of relevant physics. Combining sampling-based UQ algorithms with high-fidelity simulations creates a computational bottleneck that is often alleviated through the use of machine learning (ML). ML can be used to create computationally efficient surrogates for simulations of complex or high-dimensional physical interactions (e.g., multi-phase interactions associated with melt pools in laser powder bed fusion or spatially-dependent material properties in functionally graded materials). However, negative side effects of ML may include a lack of interpretability and negative correlation between event rarity and simulation accuracy due to a lack of training data. As such, it is important to infuse ML algorithms with physics-based guardrails to provide confidence in their predictions. This talk will provide a brief review of recent NASA research at this intersection of physics-based simulation, ML, and UQ with a focus on certification and reliability analysis.
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A method of fabricating an coating includes providing a coating comprising a base material. The base material is coated with an inorganic material using at least one of an atomic layer deposition (ALD), a molecular layer deposition (MLD), or sequential infiltration synthesis (SIS) process. The SIS process includes at least one cycle of exposing the coating to a first metal precursor for a first predetermined time and a first partial pressure. The first metal precursor infiltrates at least a portion of the base material and binds with the base material. The coating is exposed to a second co-reactant precursor for a second predetermined time and a second partial pressure. The second co-reactant precursor reacts with the first metal precursor, thereby forming the inorganic material on the base material. The inorganic material infiltrating at least the portion of the base material. The inorganic material is functionalized with a material.
Functionally graded materials are an emergent method for designing components with programmable site-specific material properties. These materials are typically fabricated using metal additive manufacturing tools by simultaneously feeding multiple wire and/or powder feedstocks at various rates to achieve spatial composition change. The wire-powder-directed energy deposition (WP-DED) technique is of particular interest for many functionally graded material applications by balancing the low raw materials cost of wire with the high resolution of powder. However, feeding wire and powder are inherently different processes since all extruded wire enters the melt pool, while much of the blown powder is scattered, which makes determining the composition of the build challenging. In this study, we devise a simple area-based measurement method for estimating the composition of WP-DED structures. WP-DED single beads are printed using 309L stainless steel wire and commercially pure Fe powder at five wire feed rates (0.5, 0.75, 1.00, 1.25, 1.50 mm/mm) and five powder feed rates (2, 4, 6, 8, 10 rpm). Characteristic defects including interface gaps and macrosegregation (lack of mixing) tendencies are examined. High powder feed rates (8, 10 rpm) result in interface gaps at all wire feed rates, but smooth deposition and complete mixing is achieved at low powder feed rates, particularly with lower wire feed rates as well. The area-based composition measurement method is within ±20% of energy dispersive x-ray spectroscopy measurements for all samples, showing its effectiveness as a rapid composition estimate for WP-DED materials development.
Porous materials are ubiquitous, from biological tissues (skin, cartilage, bones, heart tissue), to manufactured materials (paper, functional porous materials, batteries, drug delivery systems, diapers), to environmental materials (rocks, soils, plants). Because these materials are composed of multiple phases, the effects of flow, heat transfer, chemical reactions, and deformations including swelling and shrinking are more complex than that for a single phase such as a gas, liquid, or solid. The realization that porous materials, regardless of the application, have commonalities in modeling approaches, experimental methods, and numerical methods was the impetus of this journal, Transport in Porous Media (founded by Jacob Bear in 1986) and of the International Society for Porous Media (InterPore, interpore.org), which at its roots, originated in 2006. The growth of TIPM and of InterPore mirrors the explosive interest in porous media research that is now recognized as a field of research in and of itself. It is in the honor of InterPore’s 10th anniversary, celebrated at the InterPore 10th Annual Meeting and Jubilee in 2018 in New Orleans, USA, that this special issue was conceived.
Postpolymerization functionalization of polymers can create new applications for existing materials, while retaining their most favorable, intrinsic properties. Polyvinyl chloride (PVC) is a widely used, commodity polymer that is particularly challenging to modify. We report a copper-catalyzed protocol that replaces a small fraction of the C-Cl bonds in PVC with C-B bonds to boronic esters. The reaction occurs with an inexpensive catalyst comprising copper(II) chloride and an NHC ligand derived from a common ionic liquid that is distinct from the N-heterocyclic carbene (NHC) used for the borylation of small alkyl halides. The resulting materials adhere strongly to common surfaces, such as glass and metals, even more strongly than do commercial glues.
It is necessary for Advanced Reactors to have highly advanced engineered material systems that can combine multiple functions to save weight and cost. Metamaterial structures can be used to achieve this function. Material properties that could feasibly be combined were identified and explored in the literature. They were then proposed for future studies gauging the effectiveness of these proposals.
We present a new level set model for representing multimaterial flows in multiple space dimensions. Instead of associating a level set function with a specific fluid material, the function is associated with a pair of materials and the interface that separates them. A voting algorithm collects sign information from all level sets and determines material designations. M(M ₋1)/2 level set functions might be needed to represent a general M-material configuration; problems of practical interest use far fewer functions, since not all pairs of materials share an interface. The new model is less prone to producing indeterminate material states, i.e. regions claimed by more than one material (overlaps) or no material at all (vacuums). It outperforms existing material-based level set models without the need for reinitialization schemes, thereby avoiding additional computational costs and preventing excessive numerical diffusion.
Fabrication of stretchable functional polymeric materials usually relies on the physical adhesion between functional components and elastic polymers, while the interfacial resistance is a potential problem. Herein, a versatile approach on the molecular-level intrinsically stretchable polymer materials with defined functionality is reported. The single-ion conducting polymer electrolytes (SICPEs) were employed to demonstrate the proposed concept along with its potential application in stretchable batteries/electronics with improved energy efficiency and prolonged cell lifetime. The obtained membranes exhibit 88–252% elongation before breaking, and the mechanical properties are well adjustable. The galvanostatic test of the assembled cells using the obtained SICPE membrane exhibited a good cycling performance with a capacity retention of 81.5% after 100 cycles. The applicability of a proposed molecular-level design for intrinsically stretchable polymer materials is further demonstrated in other types of stretchable functional materials, including poly(vinylcarbazole)-based semiconducting polymers and poly(ethylene glycol)-based gas separation membranes.
Cyanidometallate complexes are highly versatile building units for the generation of functional porous materials. Here we report five new pillared Hofmann layer compounds incorporating the tetracyanidometallates [MoO(CN){sub 4}]{sup 2-} and [MnN(CN){sub 4}]{sup 2-}. These metalloligands, which are new to this class of materials, have been combined with divalent 1st-row transition metals to produce Hofmann layers that are linked into three-dimensional frameworks by ditopic bridging dipyridyls. We report the structures and anomalous thermal expansion properties of five new materials: [Mn(H{sub 2}O)(bpy){sub 1/2}{l_brace}MoO(CN){sub 4}(bpy){sub 1/2}{r_brace}] {center_dot} 2H{sub 2}O (1), [Mn(H{sub 2}O)(bpy){sub 1/2}{l_brace}MnN(CN){sub 4}(bpy){sub 1/2}{r_brace}] {center_dot} 2H{sub 2}O (2), [Fe(H{sub 2}O)(bpy){sub 1/2}{l_brace}MnN(CN){sub 4}(bpy){sub 1/2}{r_brace}] {center_dot} 2H{sub 2}O (3), [Co(H{sub 2}O)(bpy){sub 1/2}{l_brace}MnN(CN){sub 4}(bpy){sub 1/2}{r_brace}] {center_dot} 2H{sub 2}O (4) and [{l_brace}Mn(H{sub 2}O){sub 2}{r_brace}{sub 1/2}{l_brace}Mn(bpa){sub 2}{r_brace}{sub 1/2}{l_brace}MoO(CN){sub 4}(bpa){sub 1/2}{r_brace}] {center_dot} MeOH (5), (where bpy = 4,4'-bipyridine and bpa = 4,4'-bipyridylacetylene).