Date

2023-2-13

Author

Açıkgöz, Kemal

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Dilatational failure in terms of cavity formation and distortional failure guided by shear-type deformations are the two main failure modes of rubbery polymers. These modes correspond to deformations associated with the energetic/volumetric and entropic/shear responses under general loading conditions. This work proposes an energy-based failure criterion with a unique split of the free-energy function in terms of the first three invariants. Such an ansatz allows various failure modes under volumetric and shear deformations. The baseline hyperelasticity is described by the extended eight-chain model. As a novel aspect, we introduce distinct degradation mechanisms for shear and dilatational deformations that account for the transition from quasi-incompressible hyperelastic behavior to a porous compressible solid state prior to macro-crack formation. Herein, separate forms of a tunable Hermitian polynomial-based degradation function are applied to the free energy function's dilatational and distortional parts. The tunable nature of the Hermitian polynomials allow adjustment of the degradation of each term separately. Utilizing two distinct degradation functions for the volumetric and the entropic parts, the proposed generalized phase-field approach is shown to allow such transition and the degradation of the Poisson's ratio is captured. Furthermore, the proposed degradation function recovers the quadratic, cubic, and quadric degradation functions from the literature as its special cases. The aspects of the proposed energetic failure surface are discussed, and its predictive capability is demonstrated by comparing it to existing data from the literature. Apart from separate degradations of the volumetric and entropic parts, a finitely nonlinear viscoelastic theory is utilized to investigate the rate effects to the fracture. An adjustable contribution of the viscoelastic part to the history field is adopted. Finally, experimental investigations are performed on unfilled styrene-butadiene rubber to obtain the base material response, rate effects, and fracture behavior. The fracture behavior is investigated with special v-shape notched specimens. Various boundary value problems are solved and the results are compared to the experiments.

Subject Keywords

phase-field, rubber fracture, degradation of incompressibility, phase-field fracture, fracture characterization

URI

https://hdl.handle.net/11511/102551

Collections

Graduate School of Natural and Applied Sciences, Thesis