Ductile-brittle fracture of amorphous glassy polymers

Date

2024-9-5

Author

Başdemir, Selçuk

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Amorphous glassy polymers are extensively used in industrial sectors like microelectronics, medical devices, and aerospace. Their design and application have become crucial due to their varying fracture responses, which can range from ductile to brittle depending on factors such as entanglement density, temperature, and loading rate. Ductile responses are driven by diffuse shear zones exhibiting volume-preserving inelastic deformations, while brittle responses are manifested by small crack-like defects with fibrillar bridges separated by micro-voids, indicating void formation through nucleation and propagation. This thesis focuses on describing shear yielding and crazing phenomena through evolution equations. It also extends the modeling of fracture using a crack phase-field approach, allowing for the simultaneous consideration of ductile and brittle failure. This approach is based on a novel failure criterion that features both a critical amount of plastic strain and void volume fraction, making it more physically grounded than current models. Additionally, a coupled thermo-mechano-fracture model for amorphous glassy polymers is introduced, enabling simultaneous treatment of ductile and brittle fracture. Constitutive formulations for shear yielding, crazing, and void volume fraction are derived, starting with the local and conductive components of the dissipation inequality. The model’s governing equations integrate mechanics with the crack phase-field and temperature evolution, addressing the global thermal problem—a key focus of this research. The model’s performance is evaluated using local and global Newton-type update algorithms, tested against experimental data from homogeneous and inhomogeneous tests, revealing significant temperature dependency on failure type and interaction between loading rate and temperature due to dissipative heating.

Subject Keywords

Amorphous glassy polymers, Crack phase-field, Crazing, Finite thermo-viscoplasticity, Void growth

URI

https://hdl.handle.net/11511/111063

Collections

Graduate School of Natural and Applied Sciences, Thesis