Issue 41

E. Tolmacheva (Lyapunova) et alii, Frattura ed Integrità Strutturale, 41 (2017) 552-561; DOI: 10.3221/IGF-ESIS.41.65 556 S AMPLE DISPLACEMENT CALCULATION ccording to [13], the longitudinal displacement of the sample initiated by the elastic compression wave traveling through the long aluminum rod can be calculated as:   0 0 t i r d c dt      (1) where 0 c is the sound speed in aluminum taken as 5080 m/s, i  and r  are the incident and reflected elastic impulses registered by strain gauges 5 in Fig. 3. Due to the selected experimental scheme the sample displacement is equal to the depth of indenter penetration into the sample. Fig. 5,a illustrates typical experimental signals from the strain gauges. The elastic compression wave, initiated by the striker moves through the rod and is registered by strain gauges as the first negative peak (Fig. 5,a). After being reflected from the free end of the loading rod, the elastic wave changes into a tensile wave, which increases the displacement of the free end of the rod with glued-on sample affording thus its deeper penetration into the fixed indenter. The elastic tension wave is registered by the strain gauges as a positive peak (Fig. 5,a). Typical displacement of the sample calculated by formula (1) is shown in Fig. 5,b. (a) (b) Figure 5 : а) Strain gauges signal (1) and load sensor signal (2) initiated by the strike of small aluminum alloy rod accelerated to 8 m/s, b) displacement of the long rod rare surface. L OAD CALCULATION n the dynamic indentation experiments at a maximum load up to 500 N (first experimental scheme) the force acting on the indenter was directly registered by the piezoelectric load sensor (Fig. 5,a, curve 2). However, in the second experimental scheme we applied additional long aluminum alloy rod with another line of strain gauges in order to overcome load restrictions on the load sensor and to achieve (and detect) higher values of loading impulses. In this case, according to [13] the load acting on the indenter can be calculated as: F = E S ε t (2) where E and S are the elastic modulus and cross-section area of the aluminum alloy rod denoted by 1 in Fig. 3,b, ε t is the transmitted deformation impulse registered by the strain gauges 2 in Fig. 3,b. These data were used to construct the loading curve for dynamic indentation process in the form of the “load acting on the sample versus indenter displacement” plot. A I