Finite Element Model For Interfaces In Compatibilized Polymer Blends

A Comparative Study on the Mixed-Mode Response of Cohesive Zone Models Implemented With Small and Large Displacement Assumptions

Master thesis (2022)

Authors

S.N.R. Mudunuru Mechanical Engineering

Contributors

M.A. Bessa Team Georgy Filonenko - Mechanical, Maritime and Materials Engineering (supervisor 1)
Albert Turon Travesa University of Girona (supervisor 2)
B. Y. Chen Aerospace Structures & Computational Mechanics - Aerospace Engineering (supervisor 2)
Faculty
Mechanical Engineering
Copyright: © 2022 Nanditha Mudunuru
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Published Date

30-03-2022

Language

English

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Faculty

Mechanical Engineering

Abstract

Designing and modeling compatibilized polymer blends require accurate interface model. In addition, it is possible that crazing occurs during failure of the interfaces leading to large deformation prior to complete failure and therefore must be accounted for by the interface model.

A preliminary literature review showed that existing formulations for the large
deformation account for the nonlinearity by adjusting the assumptions. For example, Van den Bosch et al. (2007) proposed redefining the local basis at each integration point. In contrast, Reinoso and Paggi (2014) argued that this did not account for geometric nonlinearity and proposed including the first derivative of rotation vector in the finite element equation. However, the mixed-mode responses of the models were not characterized and validated thoroughly. Therefore, we studied the response from standardized mixed-mode tests to compare the large displacement formulation with the commonly used small-displacement formulation of the cohesive zone model.

The standardized tests used by Moreira et al. (2020) for characterizing the mixed-mode behavior of ductile interfaces inspired the tests used in this study. When implemented with the BK criteria, the mode partitioning method used by Moreira et al. (2020) results in a wider spread of the mean predicted mode ratio and the mean predicted fracture toughness. However, the corresponding mode ratio predictions are similar when the predicted fracture toughness is close to expected. Therefore, while the power-law is better for implementing the mode partitioning method, we can use the predictions from the mode partitioning method implemented with the power-law to find the BK parameter.

Further, simulating the mixed-mode fracture tests with properties presented by
Moreira et al. (2020) showed that bulk materials with high modulus or stiffness, such as carbon fiber reinforced plastics, do not undergo nonlinear deformation to require the large deformation formulation. However, for bulk materials with lower modulus or stiffness, the responses of the two formulations in question are different. Additionally, for a given load case, a cohesive zone with anisotropic fracture properties experiences a different mode ratio when implemented with the large displacement formulation than the small displacement formulation. Moreover, more significant influence of the stronger mode on the load case results in greater difference between the mode ratio experienced at the interface. Nevertheless, the large displacement formulation is also applicable for stronger mode-II interfaces. However, a further investigation involving physical experiments is required to compare the response of the two formulations to the behavior of real material systems.