Understanding decay functions and their contribution in modeling of thermal-induced aging of cross-linked polymers

Mohammadi, Hamid; Morovati, Vahid; Poshtan, Emad A.; Dargazany, Roozbeh

doi:10.1016/j.polymdegradstab.2020.109108

Cited by 35 publications

(27 citation statements)

References 40 publications

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“…Since polymer radicals are highly reactive, these broken chains can get re-attached via the termination reactions (IV, V and VI). These new attachments or bonds are formed with a much lower energy compared to the original bonds in the virgin networks as reported in [66]. Thus, one can consider that, the final oxidative product has more cross-linked network of smaller chains compared to the virgin polymer with longer cross-linked network.…”

Section: A Reaction-dependent Network Theory Based On the Statistical Mechanics Of Polymer Chainsmentioning

confidence: 83%

“…The DLO predictions showed that when the rate of reaction is greater than that of oxygen diffu-sion, the reaction gets contained within the surface instead of spreading toward the sample core [20,21,71]. Recently, a micro-mechanical model based on the competition between chain-scission and crosslinking events occurring at the polymer network during oxidation was reported to predict the changes in the constitutive behavior of polymers by [66]. On the other hand, a thermodynamically consistent continuum model to predict the constitutive response based on high-temperature oxidation behavior was found in the work of [46,47].…”

Section: Introductionmentioning

confidence: 99%

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

Konica¹,

Sain²

2020

Preprint

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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.

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Section: A Reaction-dependent Network Theory Based On the Statistical Mechanics Of Polymer Chainsmentioning

confidence: 83%

Section: Introductionmentioning

confidence: 99%

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

Konica¹,

Sain²

2020

Preprint

View full text Add to dashboard Cite

show abstract

“…Moreover, phenomenological and thermodynamic-based frameworks were proposed to combine diffusion and reaction expressions to link the mechanical responses to chemical kinetics (e.g., Wise et al (1997a,b); Lion & Johlitz (2012); Wineman & Shaw (2019); Konica & Sain (2021)). Furthermore, micro-mechanical constitutive equations based on statistical mechanics of polymer structure have been introduced (e.g., Mohammadi et al (2020); Mohammadi & Dargazany (2019); Beurle et al (2020); Konica & Sain (2021)). Recently, Shakiba & Najmeddine (2021) proposed a self-contained constitutive relationship to predict the stiffening response of thermo-oxidatively aged elastomers based solely on the evolution of the macromolecular network characterized by the change in the crosslink density.…”

Section: Introductionmentioning

confidence: 99%

Physics and chemistry-based constitutive framework for thermo-chemically aged elastomer using phase-field approach

Najmeddine¹,

Shakiba²

2022

Preprint

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We propose a physics and chemistry-based constitutive framework to predict the stress responses of thermo-chemically aged elastomers and capture their brittle failure using the phase-field approach. High-temperature aging in the presence of oxygen causes the macromolecular network of elastomers to undergo complex chemical reactions inducing two main mechanisms: chain-scission and crosslinking. Chemical crosslinking contributes to the stiffening behavior characterizing the brittle response of aged elastomers. In this work, we first modify the Helmholtz free energy to incorporate the effect of thermo-chemically-driven crosslinking processes. Then, we equip the constitutive description with phase-field to capture the induced brittle failure via a strain-based criterion for fracture. We show that our proposed framework is self-contained and requires only four main material properties whose evolution due to thermo-chemical aging is characterized entirely by the change of the crosslink density obtained based on chemical characterization experiments. The developed constitutive framework is first solved analytically for the case of uniaxial tension in a homogeneous bar to highlight the interconnection between all four material properties. Then, the framework is numerically implemented within a finite element (FE) context via a user-element subroutine (UEL) in the commercial FE software Abaqus to simulate more complicated geometries and loading states. The framework is finally validated with respect to a set of experimental results available in the literature. The comparison confirms that the proposed constitutive framework can accurately predict the mechanical response of thermo-chemically aged elastomers. Further numerical examples are provided to demonstrate the effects of evolving material properties on the response of specimens containing pre-existing cracks.

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“…Moreover, micro-mechanical constitutive equations based on statistical mechanics of polymer structure were developed (e.g., Mohammadi et al (2020);Beurle et al (2020); Konica & Sain (2021)). Mohammadi et al (2020) developed a micromechanical model based on the competition between chain-scission and crosslinking events occurring at the polymer network during oxidation. Konica & Sain (2021) developed an oxidation reaction-informed evolving network theory to connect the microscale network evolution with macroscopic damage occurring in polymers.…”

Section: Introductionmentioning

confidence: 99%

Physics-based Constitutive Equation for Thermo-Chemical Aging in Elastomers based on Crosslink Density Evolution

Shakiba,

Najmeddine

2021

Preprint

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This paper presents a physics-based constitutive equation to predict the thermo-chemical aging in elastomers. High-temperature oxidation in elastomers is a complex phenomenon. The macromolecular network of elastomers' microstructures undergoes chain scission and crosslinking under high temperature and oxygen diffusion conditions. In this work, we modify the network stiffness and the chain extensibility in the Arruda-Boyce well-known eight-chain constitutive equation to incorporate the additional Helmholtz free energy due to network changes in elastomers' microstructures. The effect of network evolution due to aging in changing the shear modulus and the number of chain monomers is considered. The modification is based on chemical characterization tests, namely the equilibrium swelling experiment to measure the crosslink density evolution. The developed constitutive equation predicts the mechanical responses of thermo-chemically aged elastomers independent of any mechanical tests on aged samples. The proposed constitutive equation is validated with respect to a comprehensive set of experimental data available in the literature that were designed to capture thermo-chemical aging effects in elastomers. The comparison showed that the constitutive equation can accurately predict the intermittent tensile tests based on crosslink density evolution input. The developed constitutive equation is physics-based, simple, and includes minimal material parameters.

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Understanding decay functions and their contribution in modeling of thermal-induced aging of cross-linked polymers

Cited by 35 publications

References 40 publications

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

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

Physics and chemistry-based constitutive framework for thermo-chemically aged elastomer using phase-field approach

Physics-based Constitutive Equation for Thermo-Chemical Aging in Elastomers based on Crosslink Density Evolution

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