Creep under high-temperature stress is a critical factor influencing the lifetime of materials in industries such as power generation, aerospace, and automotive. Creep strain curves based solely on stress and temperature may misestimate long-term lifetime due to stress breakdown, where the stress exponent varies with stress levels. Deformation mechanisms are unpredictable for long-term predictions, particularly when multiple mechanisms act simultaneously. Instead, the focus shifted to cavitation damage and fracture types, which are more reliable for mechanistic modelling. The existing cavitation model under development effectively describes cavity nucleation and growth but often overlooks the coalescence mechanism, which is critical during the late stages of rupture. This thesis presents the development of an advanced creep cavitation model that integrates partial coalescence prior to rupture. The thesis introduces a breakthrough hypothesis that captures coalescence dynamics, enabling predictions from the early stages through to the final rupture phase, with high accuracy (83%) in describing total cavitation damage evolution throughout the creep time for Brass alloy (Cu-40Zn-2Pb). This is further evidenced by its capability for lifetime prediction, achieving 98% accuracy using just 45% of the available creep lifetime data. Key findings include a novel interpretation of crack propagation driven by partial coalescence, wherein a large primary cavity and smaller secondary cavities simulate crack length and tip growth, respectively. Additionally, individual cavity growth was found to occur through a dual mechanism, combining constrained diffusion and plasticity.
| Date of Award | 25 Mar 2025 |
|---|
| Original language | English |
|---|
| Supervisor | Qiang Xu (Main Supervisor), Joan Lu (Co-Supervisor), Vladimir Vishnyakov (Co-Supervisor) & Haiyan Miao (Co-Supervisor) |
|---|