Structural and Fatigue Twin
A structural twin reconstructs the stresses in load-bearing components and integrates them into an accumulated-damage estimate over the machine's life.
Tracking mechanical health
Fusion machines subject their structures to large, cyclic, and sometimes sudden loads: magnetic forces on coils and supports, thermal stresses from temperature swings, and pressure loads in coolant systems. A structural twin reconstructs the stresses in load-bearing components from measurements and load estimates, then integrates them into an accumulated-damage figure that tracks how close each part is to a structural limit.
The loads
- Magnetic forces, which are enormous in high-field regions and vary with operation
- Thermal stresses from heating and cooling cycles
- Pressure loads in coolant and vacuum boundaries
- Transient loads from events such as disruptions in a tokamak
Fatigue accumulation
Cyclic loading accumulates fatigue damage even when each cycle is well within the static strength. A common approach counts stress cycles and sums their damage contributions toward a limit, with the material's fatigue curve setting how many cycles of a given amplitude a part can survive. The twin performs this counting on the reconstructed, as-operated stresses rather than on nominal assumptions, giving a per-component damage ledger.
Reconstructing stress
The highest stresses often occur at internal features, welds, and stress concentrations where no gauge can sit. The twin reconstructs them from surface strain measurements, load estimates from the magnet and thermal twins, and a structural model. Where the full model is too slow, a reduced-order or surrogate structural model provides fast estimates, with high-fidelity finite-element analysis run offline for detail. See component-life tracking.
In the Kronos machines
The magnet supports of both machines are prime targets, given the fields involved, an on-axis 8 tesla and 16.84 tesla peak in the Hyperion breeder, and 26.49 tesla in the burner plug. For the breeder, the twin also tracks transient loads from potential disruptions and the effect of neutron damage on material strength. These methods are built on validated structural and materials models today; real fatigue data accrues only once the machines cycle, after first tritium near 2030. See magnet system twin and remaining useful life.