The propagation and coalescence processes of two initially semi-elliptical surface cracks in a plate at high temperature are predicted by using a modified creep-damage model implemented with the numerical method. The creep growth of multiple cracks during pre-coalescence and coalescence periods is investigated in detail. For the purpose of comparison, the step-by-step fracture-mechanics-based finite element technique is also employed. The results indicated that, before coalescence, the cracks grow steadily but relatively rapidly in the adjacent district; after the cracks coalesce, the concave positions of the newly combined crack front exhibit a considerably high growth rate. Compared with the fracture mechanics approach, the numerical approach based on the modified creep-damage model enables to give more detailed information on creep crack initiation and more reliable estimate of propagation. In addition, the combination rules given by existing standards are also examined.

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