Codes
Developed By: Amir Bahrololoumi
(If you use these files, please cite Bahrololoumi et al. 2021)
A multi-physics model is proposed to predict the changes in the constitutive behavior of cross-linked polymeric systems due to damages induced by deformation, oxidation, moisture, and temperature. Coupling the concept of network evolution, hydrolysis, and thermo-oxidation aging, we hypothesize that the synergized effects of deformation-induced damage, as well as different environmental factors such as humidity, temperature, and oxygen, can be taken into account through a generic model. Deformation-induced damage is due to the chain breakage while hygrothermal aging results from the interaction of elastomeric components with moisture in the presence of oxygen and temperature. Results indicate that hygrothermal aging can be considered as a consequence of damage accumulation of two concurrent aging mechanisms, namely; i) thermo-oxidative, and ii) hydrolytic aging. In order to capture the mutual effects of thermo-oxidative and hydrolytic aging, the assumption has been made that each of the aging phenomena can be superimposed upon each other. In fact, each of them acts independently, and as a result, they can propagate hygrothermal aging in collaboration. In view of multiple kinetics involved in hygrothermal aging, its effect has been induced by the concurrent effects of three micro-mechanisms; i) chain scission due to the presence of temperature, ii) reduction of cross-links attributed to the attendance of water, and iii) formation of cross-links as a repercussion of oxygen present in the environment. Utilizing the theory of network decomposition, all phenomena and their correlation were modeled, and thus, the strain energy function of the polymer matrix is written with respect to four independent mechanisms; i) the shrinking original matrix that has neither been attacked by water nor oxygen, ii) conversion of the first network to two new networks due to reduction and formation of cross-links, and iii) energy loss from network degradation due to water attrition to polymer active agents. The proposed model cannot consider variation in oxygen density since it has been derived for cases where there is abundant oxygen. Apropos, the model is valid for a slow aging process that occurs in super-thin samples. Finally, the model is validated with respect to extensive sets of our experimental data. In view of its interoperability, precision, and deep insight it provides into the nature of the aging phenomenon, the model is a good choice for advanced implementation in FE applications.
For the tutorial please find the uploaded video file under the master branch. You need the x265 decoder to play the video.
A Physically-Based Model for Thermo-Oxidative and Hydrolytic Aging of Elastomers (Github)
(If you use these files, please cite Bahrololoumi et al. 2021)
Developed By: Amir Bahrololoumi
A computationally efficient model is proposed to capture the loss of mechanical performance due to chemical aging that are formed as the competition of chain scission and cross-link formation/dissolution, such as thermo-oxidative aging or hydrolytic aging. The model should be considered an extension of our recent models which further simplifies the matrix behavior based on the assumption of independence of environmental and mechanical damage. The model uses this assumption to reduce the necessary material parameters needed to model constitutive and inelastic behavior of elastomers during aging. To this end, the model can provide accurate predictions of the material performance with the significantly fewer number of fitting parameters. The model is relevant for all decay mechanisms formed by the occurrence of two simultaneous micro-mechanisms; (i) formation/reduction of the cross-links, and (ii) chain scission, both of which are present in thermo-oxidation and hydrolytic aging. Assuming the alteration of the chain density along the aging trajectory is identical to the peroxide cross-link density for thermo-oxidation, and the change of the average molecular weight for hydrolysis, the strain energy of polymer matrix can be rewritten as a function of deformation, deformation history, storage time and aging temperature. Next, the modified network alteration model is formulated for implementation into Finite Element (FE) simulations. %The model is based on the assumption of homogeneous diffusion of water/oxygen and thus is mainly relevant for relatively thin samples exposed to environmental loads for a long time. The model is built on the presumption of homogeneous and consistent oxygen/water absorption and thus is mainly relevant for relatively thin samples exposed to environmental loads for a long time. The proposed model includes only six physically inspired material parameters. Thus, while it is computationally efficient, it shows good agreement with own experimental data, which performed on various range of accelerated aging temperatures and times. With respect to its computational efficiency, simplicity, accuracy, and interpret-ability, the model is the right choice for advanced implementations in FE programs.
A tutorial has been uploaded under the name of "output.mp4". You need x265 codec to play this video. I suggest use "PotPlayer" software.
Network Evolution
Developed By: Vahid Morovati
(If you use these files, please cite Morovati and Dargazany 2019)
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