Serpentine Transmitted Bar

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Schematic of coaxially embedded serpentine bar. [1]

< Intermediate Strain Rate Bar

When an intermediate strain rate test is performed, the stress experienced in the test specimen is transmitted to the serpentine bar in the form of a stress wave. This stress wave travels the length of the transmitted bar and is measured by a strain gauge. Challenges arise with gathering data via the strain gauge. The stress wave created when the test is initiated hits the end of the transmitted bar and is reflected back to the strain gauge before the specimen fails. Therefore, the transmitted bar needs to be as long enough to avoid seeing the reflected wave before the specimen fails. Many national labs and research facilities do not have the footprint available to house a long bar. The original patented design of the serpentine bar features three concentric tubes welded together at the ends. This design allows for the stress wave to propagate through all of the tubes before it reflects back. Therefore, the serpentine bar has an effective length much greater than its physical length creating a more efficient footprint.

References

  1. Whittington, W. R., Oppedal A. L., Francis, D. K., Horstemeyer, M. F., A novel ISR testing device: The serpentine transmitted bar, International Journal of Impact Engineering, 2015, vol. 81, pp. 1-7.
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