Dynamic response of free-end rod with consideration of wave frequency

Sang Yeob Kim, Jong Sub Lee, Erol Tutumluer, Yong Hoon Byun

Research output: Contribution to journalArticlepeer-review

Abstract

The energy transferred on drill rods by dynamic impact mainly determines the penetration depth for in-situ tests. In this study, the dynamic response and transferred energy of drill rods are determined from the frequency of the stress waves. AW-type drill rods of lengths 1 to 3 m are prepared, and strain gauges and an accelerometer are installed at the head and tip of the connected rods. The drill rods are hung on strings, allowing free vibration, and then impacted by a pendulum hammer with fixed potential energy. Increasing the rod length L increases the wave roundtrip time (2L/c, where c is the wave velocity), and hence the transferred energy at the rod head. At the rod tip, the first velocity peak is higher than the first force peak because a large and tensile stress wave is reflected, and the transferred energy converges to zero. The resonant frequency increases with rod length in the waveforms measured by the strain gauges, and fluctuates in the waveforms measured by the accelerometer. In addition, the dynamic response and transferred energy are perturbed when the cutoff frequency is lower than 2 kHz. This study implies that the resonant frequency should be considered for the interpretation of transferred energy on drill rods.

Original languageEnglish
Pages (from-to)25-33
Number of pages9
JournalGeomechanics and Engineering
Volume28
Issue number1
DOIs
Publication statusPublished - 2022 Jan 10

Keywords

  • Drill rod
  • Dynamic response
  • Free vibration
  • Resonant frequency
  • Transferred energy

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Geotechnical Engineering and Engineering Geology

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