Abstract
This work presents the stages of development of some innovative equipment, based on Hopkinson bar techniques, for performing large scale dynamic tests of concrete specimens. The activity is centered at the recently upgraded HOPLAB facility, which is basically a split Hopkinson bar with a total length of approximately 200 m and with bar diameters of 72 mm. Through pre-tensioning and suddenly releasing a steel cable, force pulses of up to 2 MN, 250 μs rise time and 40 ms duration can be generated and applied to the specimen tested. The dynamic compression loading has first been treated and several modifications in the basic configuration have been introduced. Twin incident and transmitter bars have been installed with strong steel plates at their ends where large specimens can be accommodated. A series of calibration and qualification tests has been conducted and the first real tests on concrete cylindrical specimens of 20cm diameter and up to 40cm length have commenced. Preliminary results from the analysis of the recorded signals indicate proper Hopkinson bar testing conditions and reliable functioning of the facility.
Highlights
This work presents the stages of development of some innovative equipment, based on Hopkinson bar techniques, for performing large scale dynamic tests of concrete specimens
Introduction developed in order to apply dynamic compression to the specimen starting from a tensile propagating wave
Often the data have been obtained by different experimental techniques and in dynamic testing such differences can be more marked because of the wave propagation and inertia effects [1]. For this reason it is essential that apparatuses capable of handling the wave propagation be used for the mechanical characterization of concrete at high strain-rates. It is the intention of this work to analyse the development and present some results of an innovative equipment, based on Hopkinson bar techniques, for performing dynamic compression tests on concrete specimens of large size
Summary
As shown in figure 2, the basic element of the new configuration is the introduction of the twin incident and. Transmitter bars with the strong steel plates at their ends, where large specimens can be mounted and compressed With this “motion inversion frame” the available tensile pulse is transformed into a compressive one on the specimen, which is crushed dynamically. There is a considerable departure from the standard one-dimensional geometry, which is inherent in the analysis of the Hopkinson bar technique [3, 4] This is due to both the distance between the twin bars (270 mm) and to the flexibility of the end plates. For this reason a numerical study of the new configuration has accompanied all steps of its development. These simulations have indicated that a Hopkinson bar type test would be reliably reproduced
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