Meaning
Mechanical structures undergo repetitive expansion and contraction when exposed to alternating high and low temperatures. During engine operation, thermal stress cycling generates internal stress gradients that can lead to microcracking and structural failure.
Material Degradation
Microscopic voids and microcracks form along grain boundaries as the temperature varies. The material degradation is driven by the mismatch in thermal expansion coefficients between different phases or joined components. This internal friction weakens the microstructural bonds until the component can no longer carry the designed mechanical loads.
Thermal Fatigue
Repeated temperature fluctuations cause plastic deformation at localized hot spots where expansion is constrained. The thermal fatigue life decreases when the temperature range is wide or the transition rate is rapid. Components in gas turbines are particularly susceptible to this damage mechanism because of the extreme operating environment.
Testing Protocol
Laboratory simulations use specialized environmental chambers to alternate the temperature of the specimen between extreme limits. The testing protocol requires precise control over the dwell times and heating rates to mimic real-world operating conditions. Committing to a production design before completing these thermal cycles risk expensive field failures and warranty recalls.
High-reliability electronics and turbine blades must survive thousands of these cycles during the design verification phase.
