Edge stresses in bonded armor system for divertor plate

To safely manage the high heat loads expected in the next fusion devices, efforts have been focused on the development of the actively cooled divertor plate which consists of graphite armor tiles bonded to copper structural members. Residual stresses in the interface region were evaluated for the graphite/copper bonded system. Eigenvalue analysis was performed to investigate the favorable free-edge geometry for the interface. Results for a joint having half-plane free-edge geometry indicated no stress singularity for θ₁~120°, where θ₁ is the angle between the traction free surface of the graphite and the bonding interface. Thermal stresses in a joint having a conical bonding interface with inner and outer free edges were also examined for a sequence consisting of cooling from the brazing temperature and service with a pulsed heat load of 10 MW/m²-5 s. The normal stress on the bonding interface calculated for graphite was tensile only in the neighborhood of the interface edges. This normal stress decreased but the high stress region expanded during heat loading. The Von Mises stress in the interface edge region decreased without apparent increase in plastic strain at two different times in the thermal cycle