PSI - Issue 2_B

Аlexandre Divakov et al. / Procedia Structural Integrity 2 (2016) 460 – 467 A.K. Divakov, Yu.I. Meshcheryakov, N.M. Silnikov/ Structural Integrity Procedia 00 (2016) 000–000

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the shock-wave tests under uniaxial strain conditions are sufficiently informative. For example, as shown above, the instability threshold stress can be precisely determined. In this situation, the results obtained in planar collision experiments can be taken as strength-component of resistance of target to penetration R : R = σ inst = 0.5 ρ C pl U inst , (4) where C pl is а velocity of plastic front in uniaxial strain tests and U inst is the particle velocity corresponding to loss of structural stability under compression. The results of calculations of R for set of constructional materials are provided in Table 1. The values of R determined by using the Tate’s procedure with Eqs (2) - (3) and dynamic instability threshold σ inst obtained under planar tests with Eq (4) are seen to be practically identical. This means that strength-component of resistance of material to high-velocity penetration has a concrete physical meaning – its value is determined by the structural instability threshold of material under uniaxial strain conditions. Furthermore, the structural instability under shock compression is initiated only in the case when particle velocity dispersion at the mesoscale-1 as a mean for relaxation of internal stresses, is entirely exhausted. At that moment, the relaxation of stresses at higher scale level, mesoscale-2 (50-500 µm) is initiated. This occurs in different manner depending on the kind of material - brittle or ductile.

Table 1. Comparison of strength-component of resistance to high-velocity penetration R and instability threshold σ inst for three kinds of constructional materials Material σ HE L , GPa R (Tate), GPa C pl , mm/µs U inst , m/s σ inst , GPa D16 Al alloy 40 0.6 5.35 80 0.58 M2 copper 5 2.44 4.38 132 2.54 38KHN3MFA 75 4.01 5.0 210 3.96

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