Dynamic Behavior of Concrete: Experimental Aspects - Dynamic Behavior of Concrete and Seismic Engineering - page 26

Figure 1.12. Hopkinson bar compression test input and output rates
A one-dimensional transient elastic calculation simulates the test quite well. The
incident wave being known, we calculate the reflected and transmitted waves during
the first 45 P s, after which the result of the calculation suddenly deviates from the
measurements. From this, we can infer that failure takes place after 45 P s at the
latest. This instant is more or less synchronous with the output load peak. For this
calculation, the apparent elastic modulus is 7.8 GPa. This “modulus” is quite weak
and can probably be explained by concentrated strains at the interfaces between the
specimen and bar surfaces: these cannot be neglected in statics either when
considering the specific strains on a specimen. If we only consider this phase of the
trial, we notice a time shift between the maximum of the load, equal to about half
the 45 P s.