Thermo-Mechanical Fatigue Assessment of Cylinder Heads Using Advanced Simulation Techniques

Thermo-mechanical fatigue (TMF) is a critical durability concern for cylinder heads in internal combustion engines, particularly under severe cyclic thermal and mechanical loads. TMF-induced damage often initiates in geometrically constrained regions with high thermal gradients and can significantly reduce component life. As performance demands increase, understanding and mitigating TMF becomes essential to ensure the structural integrity and long-term reliability of engine components. This study presents a simulation methodology for evaluating thermo-mechanical fatigue (TMF), a temperature-dependent low-cycle fatigue (LCF) mechanism that arises from repeated thermal expansion and contraction under mechanical constraints, leading to cyclic plastic deformation and damage. The methodology consists of two key phases. Phase I involves global finite element (FE) simulations—both thermal and structural—to obtain temperature and displacement fields under rated and idle engine conditions, which together define the TMF heating-cooling cycle. In Phase II, a non-linear transient FE analysis is performed on a detailed sub-model (cake model), where the temperature and displacement results from Phase I are applied as boundary conditions. This sub-model uses an advanced material model that includes combined strain hardening, back stress evolution, and creep behavior. Subsequently, fatigue life is predicted using Sehitoglu’s framework, which distinguishes the individual contributions of mechanical fatigue, creep, and oxidation damage. Material characterization for this analysis was carried out through tensile, strain-controlled fatigue, creep, and TMF testing, each providing critical model parameters. This TMF assessment methodology was applied on a cast iron engine head development program. Critical valve bridge locations in the fire deck were identified and addressed through targeted design modifications to achieve TMF life time targets. The final prototype design was validated through physical testing, showing no TMF-related failure and aligning well with simulation predictions. The study highlights the importance of TMF evaluation for enhancing cylinder head durability under elevated thermal loads.