Thermo-mechanical fatigue (TMF) consists of cyclic temperature in addition to cyclic loads, but TMF testing is often norotiously slow. For example, thermal cycles on the order of 3 minutes when applied to tests on the order of 2000 cycles can take 100 hours to collect a single data point on an S-N curve. Due to the highly stochastic nature of TMF testing, tests must be repeated under each new operating condition. This increases already lengthy testing times for qualify new structural materials and processes.In this work, a high-throughput concept is presented in which multiple specimens are tested simultaneously, thus reducing the total testing time. A segmented assembly is presented which uses four segments connected in series with varying cross sections. The same force is applied to the assembly which creates a different stress in each specimen due to the varied cross-sectional areas. The first specimen is cycled until failure, during which the remaining specimens accumulate the same number of cycles, thus reducing their remaining number of cycles until failure. When one specimen fails it is removed and sometimes replaced with a specimen of the same or different cross-sectional area, and testing resumes.Tests were performed in a Gleeble 1500D Thermomechanical simulator. The Gleeble has a 50 kN load cell and uses Joule heating. The displacement could not be measured directly by The Gleeble 1500D because a strain measurement was needed for each of the segments individually. Instead, Digital Image Correlation (DIC) was used to measure displacement in each specimen separately. &nbsp;DIC is a measurement system which uses cameras to image the specimens throughout the deformation. The images are compared to determine the displacement of the specimen. Full field strain is then calculated for each specimen.A series of 4 tests were performed. First the four segments were each test individually. Second, the four segments were tests in series, but when one segment failed it was removed, and testing resumed with a shorter assembly consisting of the remaining segments. Third, the four segments were tested in series and when one segment failed it was removed and replaced with a segment having identical cross-sectional area until each segment had failed at least once, after which segments were no longer replaced. Fourth, the four segments were tested in series and when one segment failed it was replaced by a segment having a different cross-sectional area. &nbsp;The tests in which failed specimens were removed and replaced are shown to complete the same number of cycles up to 3.66 times faster compared to testing each specimen individually, thus greatly accelerating the qualification of new materials to withstand fatigue.

A High-Throughput Assembly to Accelerate Thermo-Mechanical Fatigue Testing

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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