PSI - Issue 2_B

Yurii Meshcheryakov et al. / Procedia Structural Integrity 2 (2016) 477–484 483 Yu.I. Meshcheryakov, A,K. Divakov, N.I. Zhigacheva, G.V. Konovalov/ Structural Integrity Procedia 00 (2016) 000–000 7

250

10 12

200

u fs

W

0 2 4 6 8

150

Fused quartz U'= 224,8 m/s, ht = 5,22 mm himp = 1,95 mm,

100

50

D

0

velocity variance, m/s

0 100 200 300 400 500 600 700 800

free surface velocity , m/s

time, v/s

Fig. 7. Free surface velocity and variance profiles for fused quartz at the impact velocity of 224.8 m/s.

250

W

200

2

150

100

1

50

0

0 200 400 600 800 1000 1200 1400

free surface velocity, m/s

time, ns

Fig. 8. Free surface velocity profiles for fused quartz loaded at impact velocity of 98.4 m/s (1) and 224.8 m/s (2)

Thus, the processes at the shock front in gabbro-diabase can be subdivided by two stages. The first stage corresponds to reversible nucleation of micro-cracks of size ~100 nm at the expense of velocity pulsation at the mesoscale-1 and second stage corresponding to nucleation and irreversible growth of cracks owing to motion of structural elements of mesoscale-2. At the plateau of compressive pulse the velocity oscillation are initiated, which results in ultimate brittle fracture of material with zero value of spall strength. The threshold of local instability at the mesoscale-2 for all the specimens of gabbro-diabase turns out to be identical and equals u fs ~ 75 m/s, which corresponds to local stress of

1 2

= - 0.5∙3.05 ∙6.25∙10

5 ∙75∙10 2 = - 0.715 GPa.

CU



 



2

1

ms

inst



In this work a statistical treatment of dimensions of structural elements after damage of gabbro-diabase targets was also performed. The distribution is found to correspond to hierarchic row L i / L i-1 = К . The results of statistical treatment are presented in Table 5.

Таble 5. Results of statistics for structural element sizes for gabbro-diabase. L i μ m 1 2.5 5 11 22

40

90

180

400 2.2

-

2.5

2

2.2

2

1.8

2.25

2

1 i i L L  is within the limits of 1.8÷2.5, which correlates with Sadovskii (1989).

Similarity coefficient К =