A High-Throughput Testbed for Parallelized Thermal Fatigue Characterization

Thermal fatigue is a key life-limiting failure mechanism in turbomachinery. This problem is especially severe in the turbine of turbopumps that power new reusable staged-combustion rocket engines, which subject the turbine to extreme thermal transients upon engine startup and shutdown. A candidate approach to mitigating thermal fatigue is to select intrinsically fatigue-resistant materials. However, reliable thermal fatigue data is scarce and can be expensive and time-consuming to collect. This work addresses this lack of design-relevant data using a high-throughput approach for parallelized thermal fatigue testing. The test rig uses a rotating disk specimen, with edge notches of varying radii uniformly spaced around its perimeter. The specimen is subjected to thermal cycling using induction heating followed by forced convection cooling while the edge notches are imaged with white-light and IR thermography. The imaging results are processed using digital image correlation to resolve the displacement and strain fields around the notch. By tracking the strain at the notch roots and observing the cycles to crack initiation, a single disk specimen can be used to collect a complete strain-life curve. In this talk I will describe the design, development, and successful implementation of this high-rate test method. I will also present results from an ongoing DARPA-funded test campaign where we aim to characterize the thermal fatigue properties of 150 alloy variants. The talk will conclude with a discussion of how these experimental results will be used to design fatigue-resistant turbine rotors for reusable rocket engines.