scholarly journals Micromechanically informed reaction-induced damage and fracture in polymers due to oxidation

2020 ◽  
Author(s):  
Shabnam Konica ◽  
Trisha Sain
Keyword(s):  
Network Structure ◽  
Phase Field ◽  
Network Theory ◽  
Three Dimensional ◽  
Diffusion Reaction ◽  
Temperature Oxidation ◽  
Oxidative Aging ◽  
Coupled Diffusion ◽  
Damage And Fracture ◽  
Amorphous Network

High temperature oxidation in polymers is a complex phenomenon, driven by the coupled diffusion-reaction process, causing changes in the amorphous network structure and resulting in property degradation. Prolonged oxidation in polymers results in the formation of a coarse, oxide layer on the outer surface and induces spontaneous cracking inside the material. In this paper, we present a chemical reaction-driven evolving network theory coupled with phase-field fracture to describe the effect of oxidation in polymers across different length scales. The theory considers the coupling between oxygen diffusion, chemical reactions, large deformation of polymers, and phase-field fracture in a thermodynamically consistent way. Guided by the statistical mechanics, the network theory has been introduced to model the reaction induced chain scissions and crosslinking events causing significant changes in the three-dimensional network structure. Further, these microscale events have been considered as the reason behind macroscopic mechanical property degradation, namely oxidative embrittlement. Finally the network theory is coupled with a phase-field fracture model to capture the macroscale damage and fracture in the polymer under stress-coupled oxidation conditions. We derive the specific constitutive forms for all the physical-chemical processes based on the thermodynamic inequality conditions, and numerically implement the theory in finite elements by writing ABAQUS user-defined element (UEL) subroutine. To present the model's capability, numerical examples with standard fracture geometries have been studied. The simulation results have demonstrated the model's capability of predicting the effect of oxidative aging on the polymer's response.

scholarly journals Coupled diffusion and phase transition: Phase fields, constraints, and the Cahn–Hilliard equation

Meccanica ◽  
2021 ◽  
Author(s):  
Fernando P. Duda ◽  
Adel F. Sarmiento ◽  
Eliot Fried
Keyword(s):  
Phase Field ◽  
Mass Fraction ◽  
Three Dimensional ◽  
The Body ◽  
Hilliard Equation ◽  
Coupled Diffusion ◽  
Phase Fields ◽  
Cahn Hilliard Equation ◽  
Distinguishing Features

AbstractWe develop a constrained theory for constituent migration in bodies with microstructure described by a scalar phase field. The distinguishing features of the theory stem from a systematic treatment and characterization of the reactions needed to maintain the internal constraint given by the coincidence of the mass fraction and the phase field. We also develop boundary conditions for situations in which the interface between the body and its environment is structureless and cannot support constituent transport. In addition to yielding a new derivation of the Cahn–Hilliard equation, the theory affords an interpretation of that equation as a limiting variant of an Allen–Cahn type diffusion system arising from the unconstrained theory obtained by considering the mass fraction and the phase field as independent quantities. We corroborate that interpretation with three-dimensional numerical simulations of a recently proposed benchmark problem.

scholarly journals A thermodynamically consistent chemo-mechanically coupled large deformation model for polymer oxidation

2019 ◽  
Author(s):  
Shabnam Konica ◽  
Trisha Sain
Keyword(s):  
Large Deformation ◽  
Diffusion Reaction ◽  
Deformation Model ◽  
Ambient Conditions ◽  
Temperature Oxidation ◽  
Reaction Behavior ◽  
Oxidative Aging ◽  
Consistent Model ◽  
Irreversible Effect

In this work, we present a continuum-level thermodynamically consistent model for high temperature oxidation inpolymers, that incorporates the coupling between diffusion, chemical reaction and large deformation behavior ofpolymers. The specific constitutive forms are derived based on the thermodynamic inequality conditions and thekinetics of the oxidative reactions are considered. Oxidative shrinkage has also been considered in the kinematics asan irreversible effect. Subsequently, the model is implemented in ABAQUS/Standard to analyze numerically thecoupled diffusion-reaction behavior of polymers undergoing oxidation. Several numerical simulations are performed tounderstand the effect of various material parameters on the oxidative response. The model is capable of predicting theheterogeneous oxidation profile within a thick polymer sample. It can also track the growth of oxide layer in the case ofa long-term thermo-oxidative aging process. The model can be used to simulate the oxidation process involvingcomplex geometries (as fiber reinforced composites) fairly easily under various ambient conditions.

A performative network theory of attitudes

2020 ◽  
Author(s):  
Michael Quayle
Keyword(s):  
Attitude Change ◽  
Network Structure ◽  
Network Theory ◽  
Social Group ◽  
Group Structure ◽  
Social Identities ◽  
Bipartite Network ◽  
Identity Change ◽  
Multilayer Network ◽  
Dynamic Phenomena

In this paper I propose a network theory of attitudes where attitude agreements and disagreements forge a multilayer network structure that simultaneously binds people into groups (via attitudes) and attitudes into clusters (via people who share them). This theory proposes that people have a range of possible attitudes (like cards in a hand) but these only become meaningful when expressed (like a card played). Attitudes are expressed with sensitivity to their potential audiences and are socially performative: when we express attitudes, or respond to those expressed by others, we tell people who we are, what groups we might belong to and what to think of us. Agreement and disagreement can be modelled as a bipartite network that provides a psychological basis for perceived ingroup similarity and outgroup difference and, more abstractly, group identity. Opinion-based groups and group-related opinions are therefore co-emergent dynamic phenomena. Dynamic fixing occurs when particular attitudes become associated with specific social identities. The theory provides a framework for understanding identity ecosystems in which social group structure and attitudes are co-constituted. The theory describes how attitude change is also identity change. This has broad relevance across disciplines and applications concerned with social influence and attitude change.

scholarly journals Phase-field modeling of grain evolutions in additive manufacturing from nucleation, growth, to coarsening

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Min Yang ◽  
Lu Wang ◽  
Wentao Yan
Keyword(s):  
Additive Manufacturing ◽  
Phase Field ◽  
Field Model ◽  
Three Dimensional ◽  
Phase Field Model ◽  
Nucleation Theory ◽  
Experimental Result ◽  
Classical Nucleation Theory ◽  
Validation Experiment ◽  
Powder Particles

AbstractA three-dimensional phase-field model is developed to simulate grain evolutions during powder-bed-fusion (PBF) additive manufacturing, while the physically-informed temperature profile is implemented from a thermal-fluid flow model. The phase-field model incorporates a nucleation model based on classical nucleation theory, as well as the initial grain structures of powder particles and substrate. The grain evolutions during the three-layer three-track PBF process are comprehensively reproduced, including grain nucleation and growth in molten pools, epitaxial growth from powder particles, substrate and previous tracks, grain re-melting and re-growth in overlapping zones, and grain coarsening in heat-affected zones. A validation experiment has been carried out, showing that the simulation results are consistent with the experimental results in the molten pool and grain morphologies. Furthermore, the grain refinement by adding nanoparticles is preliminarily reproduced and compared against the experimental result in literature.

scholarly journals Mathematical Modeling and Numerical Simulation of Atherosclerosis Based on a Novel Surgeon’s View

2021 ◽  
Author(s):  
Meisam Soleimani ◽  
Axel Haverich ◽  
Peter Wriggers
Keyword(s):  
Mathematical Modeling ◽  
Inflammatory Response ◽  
Phase Field ◽  
Mechanical Response ◽  
Type Equation ◽  
The Body ◽  
Vasa Vasorum ◽  
Diffusion Reaction ◽  
Dust Particles ◽  
Driving Mechanism

AbstractThis paper deals with the mathematical modeling of atherosclerosis based on a novel hypothesis proposed by a surgeon, Prof. Dr. Axel Haverich (Circulation 135(3):205–207, 2017). Atherosclerosis is referred as the thickening of the artery walls. Currently, there are two schools of thoughts for explaining the root of such phenomenon: thickening due to substance deposition and thickening as a result of inflammatory overgrowth. The hypothesis favored here is the second paradigm stating that the atherosclerosis is nothing else than the inflammatory response of of the wall tissues as a result of disruption in wall nourishment. It is known that a network of capillaries called vasa vasorum (VV) accounts for the nourishment of the wall in addition to the natural diffusion of nutrient from the blood passing through the lumen. Disruption of nutrient flow to the wall tissues may take place due to the occlusion of vasa vasorums with viruses, bacteria and very fine dust particles such as air pollutants referred to as PM 2.5. They can enter the body through the respiratory system at the first place and then reach the circulatory system. Hence in the new hypothesis, the root of atherosclerotic vessel is perceived as the malfunction of microvessels that nourish the vessel. A large number of clinical observation support this hypothesis. Recently and highly related to this work, and after the COVID-19 pandemic, one of the most prevalent disease in the lungs are attributed to the atherosclerotic pulmonary arteries, see Boyle and Haverich (Eur J Cardio Thorac Surg 58(6):1109–1110, 2020). In this work, a general framework is developed based on a multiphysics mathematical model to capture the wall deformation, nutrient availability and the inflammatory response. For the mechanical response an anisotropic constitutive relation is invoked in order to account for the presence of collagen fibers in the artery wall. A diffusion–reaction equation governs the transport of the nutrient within the wall. The inflammation (overgrowth) is described using a phase-field type equation with a double well potential which captures a sharp interface between two regions of the tissues, namely the healthy and the overgrowing part. The kinematics of the growth is treated by classical multiplicative decomposition of the gradient deformation. The inflammation is represented by means of a phase-field variable. A novel driving mechanism for the phase field is proposed for modeling the progression of the pathology. The model is 3D and fully based on the continuum description of the problem. The numerical implementation is carried out using FEM. Predictions of the model are compared with the clinical observations. The versatility and applicability of the model and the numerical tool allow.

scholarly journals Enhanced bacterial disinfection by CuI–BiOI/rGO hydrogel under visible light irradiation

RSC Advances ◽  
2021 ◽  
Vol 11 (33) ◽  
pp. 20446-20456
Author(s):  
Xi Ma ◽  
Ziwei Wang ◽  
Haoguo Yang ◽  
Yiqiu Zhang ◽  
Zizhong Zhang ◽  
...  
Keyword(s):  
Electron Transport ◽  
Visible Light ◽  
Network Structure ◽  
Visible Light Irradiation ◽  
Three Dimensional ◽  
Light Irradiation ◽  
Transport Capacity ◽  
Highly Efficient ◽  
Dimensional Network ◽  
Bacterial Disinfection

Compared with traditional layered graphene, graphene hydrogels have been used to construct highly efficient visible light-excited photocatalysts due to their particular three-dimensional network structure and efficient electron transport capacity.

scholarly journals Effect of Oat β-Glucan on the Rheological Characteristics and Microstructure of Set-Type Yogurt

Molecules ◽  
2021 ◽  
Vol 26 (16) ◽  
pp. 4752
Author(s):  
Xiaoqing Qu ◽  
Yuliya Nazarenko ◽  
Wei Yang ◽  
Yuanyang Nie ◽  
Yongsheng Zhang ◽  
...  
Keyword(s):  
Sensory Evaluation ◽  
Network Structure ◽  
Theoretical Basis ◽  
Fermentation Process ◽  
Three Dimensional ◽  
Rheological Characteristics ◽  
Fermentation Time ◽  
Spherical Aggregate ◽  
Dimensional Network ◽  
Solid Liquid

The oat β-glucan (OG) was added into set-type yogurt as a functional ingredient, in order to evaluate effects on the rheological characteristics and microstructure of set-type yogurt. When the OG concentration increased from 0 to 0.3%, the WHC gradually increased. At 0.3% OG, the set-type yogurt had the highest WHC of 94.67%. Additionally, the WHC continuously decreased, reaching the lowest WHC (about 80%) at 0.5% OG. When 0.3% OG was added, the highest score of sensory evaluation was about 85. The rheological result showed that the fermentation process went through the changes as follows: solid → liquid → solid → liquid. The addition of 0.3% OG decreased the fermentation time of set-type yogurt by about 16 min, making yogurt more inclined to be liquid. The acidity of set-type yogurt with OG was slightly higher. The result of microstructure showed that the addition of OG destroyed the three-dimensional network structure of yogurt, and some spherical aggregate particles could be clearly observed at 0.3% OG. Overall, this study provided a theoretical basis for the application of OG in set-type yogurt.

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