PSI - Issue 6

Author name / Structural Integrity Procedia 00 (2017) 000 – 000

7

Yurii Meshcheryakov et al. / Procedia Structural Integrity 6 (2017) 146–153

152

5. Discussion and concludes. It seems to be very interesting to testify the physical meaning of proportionality coefficient R in Eq.(3) which links the particle velocity variance D and strain rate dε/dt . As the frequency of oscillations are determined from the experimental profiles, Eq.(14) can be used to calculate this coefficient R . From Eq(14) the frequency of oscillations equals:   2 2 2 2 2 l l p C C C R      . (15) The velocity of plastic wave can be calculated by using the delay Δt between elastic precursor and middle of plastic front (see Fig.4): t p t h С  (16)

h t C  

l

The characteristics of aluminum alloys and parameters of shock front are provided in Table 1. Table 1. Parameters, C l C p

Rise time of front Period of oscillation Shear modulus

material

mm/µs mm/µs

ns

ns

GPa

Al. alloy 1565 6,34 Al. alloy 1561 6.4

5.59 5.53

7 61

5.1 47.3

27 27

Calculations of coefficient R yield: 1. Aluminum alloy 1561: R = 340 µ m, aluminum alloy 1565: R = 34.32 µ m. 2. The space duration of plastic front measured at the free surface velocity profiles equals: Aluminum alloy 1561: L f = 337,3 µ m; aluminum alloy 1565: L f = 39 µ m. Thus, for both studied alloys the coefficient R in Eq. (3) is seen to practically coincide with the space dimensions of plastic front. Microstructure investigations of post-shocked specimens show that the space period of oscillations, L osc , do not coincides with the grain size for both alloys. On the another hand side, the space periods are found to be very close to dimensions of structural elements, L cell . The structural elements looks as horizontal steps which are nucleated only during the shock-wave propagation (see Fig.6).