Dynamic Behavior of Concrete: Experimental Aspects - Dynamic Behavior of Concrete and Seismic Engineering - page 18

The plate - plate test is a relatively pure trial. However, it has to be interpreted, is
difficult to implement, and only can only inform us about concrete compaction
behavior at very high strain rates (above 10 5 s -1 ).
1.2.2.2. Hopkinson bar tests with strong confinement
This test was developed at the LMS in co-operation with LMT Cachan [GAR
99]. A cylindrical specimen is confined within a metal cylinder (Figure 1.5). It is
loaded using a large diameter (80 mm) steel Hopkinson bar, which allows the use of
test samples large enough in comparison with aggregate size to be adequately
representative of the material.
Figure 1.5. Confined sample for Hopkinson bar test (from [GAR 99])
The complete collection and analysis of the signals recorded on the bars
(described in section 1.1.2.2) allows the measurement of the forces and
displacements applied on both faces of the sample.
When the input and output forces are equal (which is the case shown in Figure
1.6) and we can assume an homogenous state of stress and strain, the stresses,
strains and axial strain speeds can be deduced.