Thermo-mechanical hot-spot formation and damage accumulation in tungsten monoblock divertor targets

The thermo-mechanical integrity of tungsten monoblock divertor targets limits high heat-flux operation in present and future fusion devices. A coupled thermo-mechanical model is presented to examine hot-spot formation, yield exceedance, and damage accumulation in water-cooled tungsten monoblocks under steady and cyclic heat loading. The model accounts for heat conduction, elastoplastic stress response, and geometry-induced mechanical constraint, with interfacial heat transfer represented through an effective contact conductance that can degrade with thermo-mechanical loading. Baseline calculations reveal a clear separation between thermal and mechanical hot-spots. Peak temperatures are controlled primarily by heat-extraction pathways and thermal resistance, whereas the highest failure ratios and plastic strains develop near material interfaces in mechanically constrained regions above the cooling channel. Parametric variations show pronounced trade-offs between thermal and mechanical margins: geometric changes that reduce peak temperature can increase yield exceedance, while configurations with higher temperatures may exhibit reduced mechanical constraint. Sensitivity and uncertainty analyses indicate that variability in peak temperature and failure ratio is dominated by a small number of geometric parameters, particularly those governing coolant pipe position and interlayer geometry. Under cyclic loading, plastic strain progressively localises near the cooling channel and accumulates through ratcheting. In the coupled model, this accumulation degrades interfacial heat transfer, leading to increased thermal resistance and amplification of thermo-mechanical hot-spots. While the magnitude of these effects depends on phenomenological degradation assumptions, the results demonstrate that temperature-based metrics alone do not capture structural risk. Mechanical constraint and interface behaviour play a central role in governing damage localisation and divertor performance. • A thermo-mechanical model is developed for tungsten monoblock divertor targets. • Thermal and mechanical hot-spots are shown to be spatially decoupled. • Interface contact degradation strongly amplifies peak stress and temperature. • Geometric changes produce competing thermal and mechanical design trends. • Cyclic loading leads to plastic strain localisation near the cooling channel.