Final answer:
Thermal stress in a turbine disc can be relieved through a process called thermal cycling, which involves alternating periods of heating and cooling the disc.
Step-by-step explanation:
Thermal stress in a turbine disc can be relieved through a process called thermal cycling. Thermal cycling involves subjecting the turbine disc to alternating periods of heating and cooling. This helps to alleviate the stress caused by the expansion and contraction of the disc due to temperature changes. By gradually heating and cooling the disc the material properties can be better managed, reducing the risk of cracking and failure.