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DOE OSTI2021

Stepwise Dynamic Calibration of a Hydromechanical Simulation Using Time-Lapse Vertical Seismic Profile

This study aims to develop a methodology for calibrating subsurface stress changes through time-lapse Vertical Seismic Profiling (VSP) integration. The selected study site is the 13-10A injector well within the ongoing CO2-EOR operation of the Farnsworth Field Unit. The Time-lapse VSP dataset carries the combined effects of fluid substitution and mean effective stress changes, thereby providing a dataset amenable for the calibration of production and injection-induced stress changes. The concept is similar to calibrating a reservoir simulation model in that the process honor real field data to set up an inverse problem. The solution optimizes the independent and impactful geomechanical parameters that replicate the observed time-lapse seismic velocity changes. This stress calibration is enabled by 4D geomechanical modeling and the VSP Integration workflow. This calibration benefits from extensive geological, geophysical and geomechanical characterization through 3D seismic data, geophysical well logs, and core assessed as part of the 1D MEM conducted on the 13-10A subject well. These data are used to develop a site-specific rock physics model. The Biot Gassmann workflow combines rock physics and reservoir simulation outputs to determine the fluid substitution contribution to seismic velocity change. Additionally, modeled seismic velocity attributed to mean effective stress are determined from the geomechanical simulation outputs, and the stress-velocity relationship developed from the ultrasonic seismic velocity measurements on the extracted Morrow B core. A penalty function is then formed between the modeled seismic velocities and the observed time-lapse VSP dataset. Four independent and impactful geomechanical parameters have been determined. These are the bulk modulus and shear modulus for zero porosity and the shear and compressional seismic velocity to mean effective stress derivatives. The dataset of numerous coupled hydromechanical- geomechanical simulation realizations is built by combining variations of the four stated geomechanical parameters. A machine learning-assisted workflow comprised of an artificial neural network and a particle swarm optimizer are used to converge on the optimal geomechanical parameters. The successful execution of this workflow has affirmed the suitability of acoustic time-lapse measurements for 4D-VSP geomechanical stress calibration pending measurable stress sensitivities within the anticipated effective stress changes and the availability of suitable and reliable datasets for petroelastic modeling.

02 PETROLEUM↗

DOE OSTI2018

Phosphocreatine attenuates endoplasmic reticulum stress-mediated hepatocellular apoptosis ameliorates insulin resistance in diabetes model

Highlights: • PCr decrease blood glucose level improve body weight. • PCr protected liver tissues against STZ/MGO caused apoptosis. • PCr attenuates hepatic endoplasmic reticulum stress markers. • PCr ameliorates insulin resistance. Diabetes mellitus (DM) associated liver damage is a major health burden. Hepatocellular-damage in DM characterized with elevated endoplasmic reticulum stress (ER) and may enhanced insulin-resistance. Phosphocreatine (PCr) a rapidly high-energy-reserve molecule of phosphates naturally occurs in liver, brain and skeletal muscle. This study aimed to investigate the protective effect of PCr on the liver-injury-associated with DM and to report the mechanism involved. Wistar rat's diabetes model was induced using streptozotocin (STZ), and the animals were treated with 20 mg/kg, or 50 mg/kg PCr injection. Blood glucose level, and body wt were recorded. Liver tissues homogenate were analyzed for liver damage markers alanine transaminase (ALT), aspartate transaminase (AST). Liver tissues proteins further evaluated for apoptosis, endoplasmic reticulum stress (ER), and insulin resistance biomarkers using western blotting. Our results revealed that PCr reduced blood glucose level, improved body wt, ameliorates liver function enzymes. Furthermore, PCr upregulates anti-apoptotic Bcl2 proteins expression, and down-regulates significantly pro-apoptotic casp3 and Bax proteins expression in vivo and invitro. Moreover, ER stress CHOP, GRP78 and ATF4 biomarkers level were significantly attenuated in PCr treated animals comparing to STZ diabetes associated liver-damage model with significant improving in insulin-resistance Akt and IRS-1. Our results revealed that treating with PCr in diabetes-associated liver injury models decreased blood glucose level and possess protective effect in-vitro and in-vivo, which could be suggested as potential therapeutic strategy for diabetes associated liver injury patients.

60 APPLIED LIFE SCIENCES↗

NASA NTRS2002

High-Fidelity Generalization Method of Cells for Inelastic Periodic Multiphase Materials

An extension of a recently-developed linear thermoelastic theory for multiphase periodic materials is presented which admits inelastic behavior of the constituent phases. The extended theory is capable of accurately estimating both the effective inelastic response of a periodic multiphase composite and the local stress and strain fields in the individual phases. The model is presently limited to materials characterized by constituent phases that are continuous in one direction, but arbitrarily distributed within the repeating unit cell which characterizes the material's periodic microstructure. The model's analytical framework is based on the homogenization technique for periodic media, but the method of solution for the local displacement and stress fields borrows concepts previously employed by the authors in constructing the higher-order theory for functionally graded materials, in contrast with the standard finite-element solution method typically used in conjunction with the homogenization technique. The present approach produces a closed-form macroscopic constitutive equation for a periodic multiphase material valid for both uniaxial and multiaxial loading. The model's predictive accuracy in generating both the effective inelastic stress-strain response and the local stress said inelastic strain fields is demonstrated by comparison with the results of an analytical inelastic solution for the axisymmetric and axial shear response of a unidirectional composite based on the concentric cylinder model, and with finite-element results for transverse loading.

Aboudi, Jacob↗

DOE OSTI2019

Metabolic effects of vitamin B12 on physiology, stress resistance, growth rate and biomass productivity of Cyanobacterium stanieri planktonic and biofilm cultures

Although synthesized only by bacteria and archaea, cobalamin (vitamin B 12 ) is essential for virtually all living cells. One major function is its role in methionine synthesis, as a co-factor for the B 12 -dependent methionine synthase MetH. However, a large number of microbes avoid requirements for B 12 by encoding cobalamin-independent enzymes, such as the B 12 -independent methionine synthase MetE. Interestingly, many such microbes retain transporters for exogenous B 12 , produced by neighboring microbes. We hypothesize that selection for retention of B 12 transport suggests preservation of unrevealed but critical roles for cobalamin in photoautotroph fitness. As such, to identify the impacts of B 12 on photoautotrophic metabolism, we studied the physiological and transcriptional adaptation of Cyanobacterium stanieri HL-69 to varying irradiance and oxidative stress in the presence and absence of B 12 . The metabolic flexibility of C. stanieri , which possesses both MetH and MetE, allows comparative analysis of cobalamin impacts on its global metabolism. As anticipated, B 12 availability governed transcription of cobalamin transporter btuB , metH and a number of genes involved in the methionine-folate cycle. Surprisingly, however, B 12 impacted the cell integrity, growth rate and biomass productivity of C. stanieri under conditions of likely oxidative stress due to biofilm growth or under high partial pressures of O 2 . Furthermore, C. stanieri response to B 12 globally rewired cellular metabolic networks, including nitrogen metabolism, energy metabolism, redox homeostasis and oxidative stress response. These findings demonstrate previously-unappreciated roles for B 12 metabolism beyond methionine synthesis and reveal how interactions with cobalamin-producing heterotrophs may affect phytoplankton function and dynamics in natural microbial communities. Further comprehension and mastering of the natural oxidative stress resistance mechanisms modulated by cobalamin could be used for the design and implementation of more robust algal bioprocesses retaining high biomass productivities especially under stress conditions.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2019

Fatigue-resistant high-performance elastocaloric materials made by additive manufacturing

Elastocaloric cooling, a solid-state cooling technology, displays the latent heat released and absorbed by stress-induced phase transformations. Hysteresis associated with transformation, however, is detrimental to efficient energy conversion and functional durability. Here, we have created thermodynamically efficient, low-hysteresis elastocaloric cooling materials by means of additive manufacturing of nickel-titanium. The utilization of a localized molten environment and near-eutectic mixing of elemental powders has led to the formation of nanocomposite microstructures composed of a nickel-rich intermetallic compound interspersed among a binary alloy matrix. The microstructure allowed extremely small hysteresis in quasi-linear stress-strain behaviors—enhancing the materials efficiency by a factor of four to seven—and repeatable elastocaloric performance over 1 million cycles. Implementing additive manufacturing to elastocaloric cooling materials enables distinct microstructure control of high-performance metallic refrigerants with long fatigue life.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Experimental evolution reveals nitrate tolerance mechanisms in Desulfovibrio vulgaris

Elevated nitrate in the environment inhibits sulfate reduction by important microorganisms of sulfate-reducing bacteria (SRB). Several SRB may respire nitrate to survive under elevated nitrate, but how SRB that lack nitrate reductase survive to elevated nitrate remains elusive. To understand nitrate adaptation mechanisms, we evolved 12 populations of a model SRB (i.e., Desulfovibrio vulgaris Hildenborough, DvH) under elevated NaNO 3 for 1000 generations, analyzed growth and acquired mutations, and linked their genotypes with phenotypes. Nitrate-evolved (EN) populations significantly (p < 0.05) increased nitrate tolerance, and whole-genome resequencing identified 119 new mutations in 44 genes of 12 EN populations, among which six functional gene groups were discovered with high mutation frequencies at the population level. In this work, we observed a high frequency of nonsense or frameshift mutations in nitrosative stress response genes (NSR: DVU2543, DVU2547, and DVU2548), nitrogen regulatory protein C family genes (NRC: DVU2394-2396, DVU2402, and DVU2405), and nitrate cluster (DVU0246-0249 and DVU0251). Mutagenesis analysis confirmed that loss-of-functions of NRC and NSR increased nitrate tolerance. Also, functional gene groups involved in fatty acid synthesis, iron regulation, and two-component system (LytR/LytS) known to be responsive to multiple stresses, had a high frequency of missense mutations. Additionally, mutations in those gene groups could increase nitrate tolerance through regulating energy metabolism, barring entry of nitrate into cells, altering cell membrane characteristics, or conferring growth advantages at the stationary phase. This study advances our understanding of nitrate tolerance mechanisms and has important implications for linking genotypes with phenotypes in DvH.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2019

Microbiomes of Velloziaceae from phosphorus-impoverished soils of the campos rupestres, a biodiversity hotspot

The rocky, seasonally-dry and nutrient-impoverished soils of the Brazilian campos rupestres impose severe growth-limiting conditions on plants. Species of a dominant plant family, Velloziaceae , are highly specialized to low-nutrient conditions and seasonal water availability of this environment, where phosphorus (P) is the key limiting nutrient. Despite plant-microbe associations playing critical roles in stressful ecosystems, the contribution of these interactions in the campos rupestres remains poorly studied. Here we present the first microbiome data of Velloziaceae spp. thriving in contrasting substrates of campos rupestres . We assessed the microbiomes of Vellozia epidendroides , which occupies shallow patches of soil, and Barbacenia macrantha , growing on exposed rocks. The prokaryotic and fungal profiles were assessed by rRNA barcode sequencing of epiphytic and endophytic compartments of roots, stems, leaves and surrounding soil/rocks. We also generated root and substrate (rock/soil)-associated metagenomes of each plant species. We foresee that these data will contribute to decipher how the microbiome contributes to plant functioning in the campos rupestres , and to unravel new strategies for improved crop productivity in stressful environments.

59 BASIC BIOLOGICAL SCIENCES↗

NASA NTRS1998

The Coupling of Solution Chemistry to Plant Nutrient Demand in an on Demand Nutrient Delivery System

The goal of the proposal will be to determine the suitability of the DASI instrument in providing a signal that can be recognized and be utilized as an indicator of plant stress. The method to be utilized for evaluating stress is the presentation of an every increasing level of nutrient deficiency and salinity stress (addition of salt (NACl) or increasing concentration of balanced nutrient) while simultaneously recording spectral reflectance using the DASI instrument and monitoring the traditional processes of gas exchange and nutrient uptake parameters. In this manner, we will be able to directly compare the DASI measurements with known stresses as determined by the traditional gas exchange and nutrient uptake measures of stress. We anticipate that the DASI will provide a sensitive identifier of plant stress; recording signals of the resulting changes in plant metabolism in real time, far before any visible effects of stress could be observed. Thus, there is a potential for very early management intervention to correct a stress condition before damage could develop. The present response time for the observation of visual symptoms of plant stress is considerable and only provides an indication that a stress is present after it has been present for an extended period of time. Thus, the impact of a plant-based life support function will have already been significant. An additional benefit of this research to regenerative life support will be the characterization of a potential recovery scenario from various degrees of stress. The experimental approach to be employed includes the removal of the stress at various points in the stress gradient and the characterization of plant performance and reflectance spectra during recovery from various degrees of stress. Spectral reflectance imaging techniques have been developed and used to measure the biochemical composition of plants and relate these characteristics to the fluxes of biochemical elements within the ecosystem.

Savage, Wayne↗

DOE OSTI2022

A High-Voltage High-Reliability Scalable Architecture for Electric Vehicle Power Electronics (Final Report)

This project developed and demonstrated new composite converter technologies that lead to high power density (> 20 kW/L) at power levels of 10s of kW, 100s of kW, or possibly higher, with fundamental advances in converter efficiency and Q that lead to substantial increases in mean time to failure (MTTF). These advantages were realized through development of new composite converter topologies that perform buck, boost, or other conversion functions and that are scalable to higher voltage and power levels through sharing of voltage and current stresses among multiple dissimilar partial-power converter modules. The project led to experimental demonstration of a125 kW multifunction electric vehicle power conversion system having in-creased dc bus voltage (950 V nominal, 1200 V peak) that interfaces a 200 V to 400 V battery pack, and that includes integrated level 2 wired charging and wireless charging functions. The project incorporated SiC MOSFET modules having switching frequencies in excess of 100 kHz, planar magnetics, a hierarchical control architecture that enables scaling to higher voltages and powers with additional converter modules, and a high-power density in excess of 20 kW/L. The research demonstrated how a more complex converter approach can increase mean-time-to-failure, even though the number of elements is increased. This is achieved through significant reduction of temperature rise through fundamentally superior converter circuit topologies. The research also demonstrated new high power planar magnetics that increase power density. The technology is appropriate to a variety of applications including EV power trains, EV charging, PV inverters, battery storage, and similar areas. These systems potentially can be manufactured in the U.S.

33 ADVANCED PROPULSION SYSTEMS↗

NASA NTRS1997

The Spectral and Statistical Properties of Turbulence Generated by a Vortex/Blade-Tip Interaction

The perpendicular interaction of a streamwise vortex with the tip of a lifting blade was studied in incompressible flow to provide information useful to the accurate prediction of helicopter rotor noise and the understanding of vortex dominated turbulent flows. The vortex passed 0.3 chord lengths to the suction side of the blade tip, providing a weak interaction. Single and two-point turbulence measurements were made using sub-miniature four sensor hot-wire probes 15 chord lengths downstream of the blade trailing edge; revealing the mean velocity and Reynolds stress tensor distributions of the turbulence, as well as its spanwise length scales as a function of frequency. The single point measurements show the flow downstream of the blade to be dominated by the interaction of the original tip vortex and the vortex shed by the blade. These vortices rotate about each other under their mutual induction, winding up the turbulent wakes of the blades. This interaction between the vortices appears to be the source of new turbulence in their cores and in the region between them. This turbulence appears to be responsible for some decay in the core of the original vortex, not seen when the blade is removed. The region between the vortices is not only a region of comparatively large stresses, but also one of intense turbulence production. Velocity autospectra measured near its center suggests the presence quasi-periodic large eddies with axes roughly parallel to a line joining the vortex cores. Detailed two-point measurements were made on a series of spanwise cuts through the flow so as to reveal the turbulence scales as they would be seen along the span of an intersecting airfoil. The measurements were made over a range of probe separations that enabled them to be analyzed not only in terms of coherence and phase spectra but also in terms of wave-number frequency (kappa-omega) spectra, computed by transforming the measured cross-spectra with respect to the spanwise separation of the probes. These data clearly show the influence of the coherent eddies in the spiral wake and the turbulent region between the cores. These eddies produce distinct peaks in the upwash velocity kappa-omega spectra, and strong anisotropy manifested both in the decay of the kappa-omega spectrum at larger wave-numbers and in differences between the kappa-omega spectra of different components. None of these features are represented in the von Karman spectrum for isotropic turbulence that is often used in broadband noise computations. Wave-number frequency spectra measured in the cores appear to show some evidence that the turbulence outside sets tip core waves, as has previously been hypothesized. These spectra also provide for the first time a truly objective method for distinguishing velocity fluctuations produced by core wandering from other motions.

Devenport, William J.↗

DOE OSTI2025

Nitrogen limitation causes a seismic shift in redox state and phosphorylation of proteins implicated in carbon flux and lipidome remodeling in Rhodotorula toruloides

Background: Oleaginous yeast are prodigious producers of oleochemicals, offering alternative and secure sources for applications in foodstuff, skincare, biofuels, and bioplastics. Nitrogen starvation is the primary strategy used to induce oil accumulation in oleaginous yeast as part of a global stress response. While research has demonstrated that post-translational modifications (PTMs), including phosphorylation and protein cysteine thiol oxidation (redox PTMs), are involved in signaling pathways that regulate stress responses in metazoa and algae, their role in oleaginous yeast remain understudied and unexplored. Results: Towards linking the yeast oleaginous phenotype to protein function, we integrated lipidomics, redox proteomics, and phosphoproteomics to investigate Rhodotorula toruloides under nitrogen-rich and starved conditions over time. Our lipidomics results unearthed interactions involving sphingolipids and cardiolipins with ER stress and mitophagy. Our redox and phosphoproteomics data highlighted the roles of the AMPK, TOR, and calcium signaling pathways in regulation of lipogenesis, autophagy, and oxidative stress response. As a first, we also demonstrated that lipogenic enzymes including fatty acid synthase are modified as a consequence of shifts in cellular redox states due to nutrient availability. Conclusions: We conclude that lipid accumulation is largely a consequence of carbon rerouting and autophagy governed by changes to PTMs, and not increases in the abundance of enzymes involved in central carbon metabolism and fatty acid biosynthesis. Our systems-level approach sets the stage for acquiring multidimensional data sets for protein structural modeling and predicting the functional relevance of PTMs using Artificial Intelligence/Machine Learning (AI/ML). Coupled to those bioinformatics approaches, the putative PTM switches that we delineate will enable advanced metabolic engineering strategies to decouple lipid accumulation from nitrogen limitation.

Lipid Signalling↗

DOE OSTI2019

Effect of magnesium on reducing the UV‐induced oxidative damage in marrow mesenchymal stem cells

Abstract Oxidative stress could cause damage to lipids, proteins and DNA, which is induced by the imbalance between the production of reactive oxygen species (ROS) and the biological system ability to counteract or detoxify their harmful effects. The oxidative stress damage significantly contributes to a number of diseases. Magnesium (Mg) is endowed with a novel function of removing excess ROS by releasing H 2 during the degradation. In this study, in order to explore the property of anti‐oxidative damage of Mg metal, rat bone marrow mesenchymal stem cells (MSCs) oxidative damaged by ultraviolet (UV) radiation was employed to co‐culture with Mg metal. The effect of Mg metal on the response of antioxidant enzymes and mitochondria in MSCs was studied. We found that Mg metal could reduce the cellular oxidative stress damage and elevate the activities of antioxidant enzymes to maintain redox homeostasis. In addition, Mg metal could reduce the risk of UV‐induced cell apoptosis by increasing the ratio of Bcl‐2/Bax, elevating the mitochondrial membrane potential and blocking the release of cytochrome c. This finding showed Mg metal might have the potential for treating diseases caused by oxidative stress damage. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1253–1263, 2019.

Chen, Yangmei↗

NASA NTRS1975

Thermoelastic analysis of solar window of a vacuum chamber

It has been noted during space simulation test programs that the chamber penetration window becomes the limiting factor as the solar intensity increases. The temperature at the center of the window normally attains a level of 550 C, while the edge temperature remains at about 35 C. The stresses produced by this thermal gradient combined with the atmospheric pressure are studied within the framework of classical theory of elasticity. The solution for the problem is obtained by solving the static uncoupled thermoelastic equations for a circular blank, subjected to nonuniform heat on one face, by introduction of two auxiliary variables. The displacements are expressed in terms of Bessel functions and parameters of interest are computed at various mesh points of the window. The maximum principal stresses thus obtained show that even with steep temperature gradient, the safety factor is acceptable.

Amba-Rao, C. L.↗

DOE OSTI2021

Development of Time Lapse VSP Integration Workflow: A Case Study at Farnsworth CO2-EOR Project

Abstract This study aims to develop a 4D Vertical Seismic Profile (VSP) integration workflow to improve the prediction of subsurface stress changes. The selected study site is a 5-spot pattern within the ongoing CO2-EOR operations at the Farnsworth Field Unit FWU in Ochiltree County, Texas. The specific pattern has undergone extensive geological and geomechanical characterization through the acquisition of 3D seismic data, geophysical well logs, and core. This workflow constrains a numerical hydromechanical model by applying a penalty function formed between "modeled" versus "observed" time-lapse compressional and shear seismic velocity changes. Analyses of geophysical logs and ultra-sonic measurements on core exhibit measurable sensitivities to changes in both fluid saturation and mean effective stress. These data are used to develop a site-specific rock physics model and stress-velocity relationship, which inform the numerical models used to generate the "modeled" portion of the penalty function. The "observed" portion of the penalty function is provided by a novel elastic full-waveform inversion of the available 3D baseline and three monitor surveys to produce high-quality estimates of time-lapse compressional and shear seismic velocity changes. The modeling workflow accounts sequentially for fluid substitution and stress impacts. Hydrodynamic and geomechanical properties of the 3D coupled numerical model are estimated through geostatistical integration of well log and core data with 3D seismic inversion products. Changes in seismic velocities due to fluid substitution are computed using the Biot-Gassmann workflow and site-specific rock physics. Stress impacts on time-lapse seismic velocity changes are modeled from the effective stress output of the hydromechanical model and are initially based on the velocity versus effective stress relationship extracted from core mechanical testing. Based on the principle of superposition of seismic wavefields, seismic velocity changes attributed to fluid substitution and that due to changes in mean effective stress are treated as linearly additive. The modeled results are upscaled using Backus averaging to reconcile scale discrepancies between the modeled and measured datasets to formulate the penalty function. This manuscript presents the forward modeling process and concludes that for the base case, the seismic velocity changes due to mean effective stress dominates over the seismic velocity changes attributed to fluid substitution because of the extensive range of the pressure perturbations. Successful minimization of this penalty function calibrates the coupled hydrodynamic geomechanical numerical model and affirms the suitability of acoustic time-lapse measurements such as 4D-VSP for geomechanical calibration.

02 PETROLEUM↗

NASA NTRS1979

Time dependent deformation of a basalt at low differential stress

A detailed study of linear elastic deformation in Ralston basalt during triaxial loading has been made as a function of strain rate (8 x 10 to the -8th per sec to 5 x 10 to the -5th per sec) and moisture content under constant confining pressure (500 bars) and temperature (20 C). Young's modulus was found to be constant and independent of moisture content and strain rate; however, Poisson's ratio decreased 5.7 plus or minus 1.6% and 6.7 plus or minus 1.6% per order of magnitude increase in strain rate for two suites of dry samples and 1.4 plus or minus 1.2% per equivalent change in strain rate for one suite of wet rocks. Lateral expansion in dry rocks is therefore a more sensitive function of strain rate than it is in wet rocks. It is suggested that this strain-rate dependence is related to microcracking.

Brodsky, N.↗

DOE OSTI2023

Physiological Functions of Phospholipid:Diacylglycerol Acyltransferases

Abstract Triacylglycerol (TAG) is among the most energy dense storage forms of reduced carbon in living systems. TAG metabolism plays critical roles in cellular energy balance, lipid homeostasis, cell growth and stress responses. In higher plants, microalgae and fungi, TAG is assembled by acyl-CoA-dependent and acyl-CoA-independent pathways catalyzed by diacylglycerol (DAG) acyltransferase and phospholipid:DAG acyltransferase (PDAT), respectively. This review contains a summary of the current understanding of the physiological functions of PDATs. Emphasis is placed on their role in lipid remodeling and lipid homeostasis in response to abiotic stress or perturbations in lipid metabolism.

59 BASIC BIOLOGICAL SCIENCES↗

NASA NTRS1985

Orthotropic fracture using a singular isoparametric element

The six noded quarter point natural isoparametric triangular element is employed to obtain displacement and stress distributions in the vicinity of the crack tip in a center cracked tensile coupon of unidirectional graphite epoxy. The material is considered to be homogeneous, elastic and orthotropic. The finite element results are compared to the analytical solution of anisotropic elasticity. Convergence as a function of mesh parameters is studied for isotropic and orthotropic materials. It is shown that displacements converge faster than stresses and that meshes which are convergent for isotropic and orthotropic materials. It is shown that displacements converge faster than stresses and that meshes which are convergent for isotropic materials are not completely convergent for the highly orthotropic graphite epoxy.

Gregory, M. A.↗

DOE OSTI2024

Multiobjective Constrained Symbolic Regression for Predictive Modeling of Material Creep Behavior

When creep testing is repeated on samples of the same alloy under the same parametric conditions (i.e., stress and temperature), the resulting strain/time curves can vary from each other considerably as shown in Figure 1 [1]. The time required to creep test a material to rupture can extend to the order of years. Because of this, a numerical model that can quickly analyze the incomplete results of an ongoing experiment to predict 1) the incomplete portion of the strain/time curve leading up to the rupture point and 2) the rupture point itself would be of great utility to the materials community. Such a model has the potential to save 1) the time required to finish running the experiment to rupture 2) the associated monetary cost of finishing said experiment. Furthermore, it would be advantageous if the predictive model could give a parametric function modeling strain/time curves for material scientists to investigate the impact of the temperature and stress parameters on the resulting creep behavior. This work introduces a piecewise symbolic regression algorithm to predict the remainder of the strain/time curve. Preliminary results show good model performance.

36 MATERIALS SCIENCE↗