Multi-path Vibrometer-Based Strain Measurement Technique for Very High Cycle Fatigue (VHCF) Testing

This feasibility study evaluates the use of a laser Doppler vibrometer to measure strain. Specifically, it uses multipath laser Doppler vibrometry (MDV) to measure high-frequency strain required for high-cycle fatigue (HCF) and very high cycle fatigue (VHCF) testing on various engineered materials. As an indicator of higher durability, there is an emerging need to measure at higher number of cycles while keeping the measurement time to a minimum. One way to meet this diametrically opposed requirement is to perform the testing at higher frequencies. Conventional sensors have a limitation in terms of highest frequency and maximum temperature of operation which are addressed with the proposed method. In this research, we provide a detailed account of the motivation and the procedure to go from vibrational velocity to dynamic strain using MDV. Comparison is shown between strain measured with MDV, 3-dimensional scanning LDV and a strain gage. Results show a good agreement between these techniques.