The Effect of Strain Gage Instrumentation Bandwidth when Decreasing Loading Times of a Brittle Material with a Mini-Kolsky Bar

The goal of this paper is to probe the effect of strain gage instrumentation bandwidth (BW) on the measured and calculated mechanical response of a brittle material under dynamic loading using a mini-Kolsky bar. If the BW on the strain gage instrumentation is too low, relative to the loading time, there will be a filtering effect whereby the true signals are not measured. As researchers miniaturize the Kolsky bar to increase the strain rate, anomalous data may be recorded, especially when testing brittle materials. The filtering effect was systematically studied by compressing a representative brittle material with progressively shorter loading times, while simultaneously recording the strain gage signals at two different bandwidths, 500/800 kHz (no filtering) and 100 kHz (possible filtering), to determine when deviations occur. The results show that there is only a small filtering effect but that it occurs at rise times that are greater than what would be expected based on the typically used BW-rise time relationship or from the frequency components of the measured waves. Concerningly, there is no obvious way to know if the signals are being inadvertently filtered, and the calculated stress-strain curves are only slightly affected. The filtering effect is discussed further in relation to Kolsky bar testing in general.

Automated summary

This paper investigates the effect of strain gage instrumentation bandwidth on the mechanical response of brittle materials under dynamic loading. The results show a filtering effect exists, but only when the rise time is greater than expected. Additionally, the calculated stress-strain curves are only slightly affected.