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

Shakiba, Maryam; Najmeddine, Aimane

doi:10.48550/arxiv.2104.09001

Cited by 2 publications

(5 citation statements)

References 47 publications

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“…In a previous work by the authors (Shakiba & Najmeddine, 2021), it was confirmed that the crosslinking events in an elastomer induced by thermo-chemical aging contribute significantly to the changes manifested in the free energy. The authors adopted the AB hyperelastic free energy and concluded that thermo-chemical aging causes the number of Kuhn monomers per chain in the AB description to decrease.…”

Section: Bulk Hyperelastic Energymentioning

confidence: 62%

“…The effect of thermo-chemical aging on the Helmholtz free energy can be accounted for by describing appropriate evolution functions for the rubber modulus and the number of Kuhn monomers with respect to the change in crosslink density. Shakiba & Najmeddine (2021) showed that the evolution of the rubber modulus during thermo-chemical aging can be given by the following micro-mechanically motivated expression…”

Section: Bulk Hyperelastic Energymentioning

confidence: 99%

“…Next, the total number of crosslinks per volume times the number of Kuhn segments per chain must remain constant in order to satisfy the conservation of mass principle. Therefore, the number of Kuhn monomers per chain at the current state of aging, 𝑁 (𝑡 𝑎 ) , can be obtained according to (Shakiba & Najmeddine, 2021)…”

Section: Bulk Hyperelastic Energymentioning

confidence: 99%

“…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. A similar approach was employed in the work of Najmeddine et al (2022) who proposed a stand-alone constitutive framework to capture the mechanical response of photo-oxidatively aged semi-crystalline polymers based on the change in the polymer's crystallinity and mass loss.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Bulk Hyperelastic Energymentioning

confidence: 62%

Section: Bulk Hyperelastic Energymentioning

confidence: 99%

Section: Bulk Hyperelastic Energymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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

Najmeddine¹,

Shakiba²

2022

Preprint

Self Cite

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“…Many researchers have developed models to simulate the response of polymeric and elastomeric materials to environmental conditions (e.g., Soares et al (2008Soares et al ( , 2010; Vieira et al (2014Vieira et al ( , 2011; Breche et al (2016a,b); Wang et al (2010); Han & Pan (2009); Zhao & Zikry (2017); Johlitz et al (2014); Abdelaziz et al (2019); Shakiba & Najmeddine (2021); Xiao & Nguyen (2016); Shakiba et al (2016); Zhao et al (2020)).…”

Section: Introductionmentioning

confidence: 99%

Physics-based Constitutive Modeling of Photo-oxidative Aging in Semi-Crystalline Polymers based on Chemical Characterization Techniques

Najmeddine,

Xu,

Liu

et al. 2021

Preprint

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This paper proposes a physio-chemically-based constitutive framework to simulate and predict the response of semi-crystalline low-density polyethylene (LDPE) to severe photo-oxidation. Photo-oxidation induced by exposure to Ultra-Violet (UV) light and oxygen is the dominant degradation mechanism affecting the lifespan of LDPE. In this work, we propose evolution functions for the material properties in the constitutive equations of Boyce et al. (2000) to incorporate the effects of photo-oxidation on the mechanical response of LDPE. The evolution functions are based on chemically verified processes that are responsible for material degradation, namely the change in crystallinity and mass loss relative to the initial pristine films over exposure time. Changes in crystallinity and mass loss are characterized by Differential Scanning Calorimetry (DSC) and Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D) experiments, respectively. Connecting the physio-chemical processes affecting polymer network evolution to the mechanical response of LDPE bypasses the need for defining fitting parameters that carry no physical meaning. The developed constitutive framework is validated with respect to a series of in-house uniaxial tensile tests performed on LDPE aged for different UV exposure times. Comparison of the constitutive frame-

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

Cited by 2 publications

References 47 publications

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

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

Physics-based Constitutive Modeling of Photo-oxidative Aging in Semi-Crystalline Polymers based on Chemical Characterization Techniques

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