PSI - Issue 6

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

4

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

149

Accordingly, change of plastic deformation can be written through the change of particle velocity: p l u C     .

(8)

Using the relationships (8) and (3) one obtains:   2 2 p l tt R C    

(9)

Substitution (9) and (6) into (5) yields:   2 2 2 0 2 0 tt l xx xxtt C R C          .

(10)

For the steady shock wave propagating with the velocity С р ., this equation transforms into equation   2 2 2 2 2 0; p l l C C R C           

(11)

which can be rewritten in the form   2 2 2 2 0 ( ) 2 0 p l C C R C         

(13)

    this equation transforms into equation for oscillator:   2 2 0 l R C   

After exchange

(14)

2 0 (

2 p

C C

) 2     

Note that this equation becomes unsteady when velocity of plastic front becomes higher than the sound velocity. Thus, if the stress relaxation in shock deformed medium is realized through the motion of mesoparticles, two scenario for the material behavior can occur: (i) oscillations and (ii) unsteadiness of plastic deformation 3. Shock test of aluminum alloys In the present work, in shock tests of two kinds of aluminum alloys - 1561 and 1565 aluminum alloys - an alternative mechanism for structural heterogenization has been revealed. The shock tests within impact velocity region of 250-700 m/s were conducted under uniaxial strain conditions by using light gas gun. The free surface velocity profiles were registered with two-channel velocity interferometer. Besides the free surface profile registered with interferometer, the velocity of impactor was measured in every and each shock test. This allows a difference between velocity of impactor and maximum free surface velocity at the plateau of compressive pulse to be found for each shot. This difference is accepted to be the velocity defect. The impactor velocity at which the velocity defect begins to grow very fast is considered to be a threshold of structural transition. In order to fix the transition to unstable state of structure, a set of the free surface velocity profiles was registered for each kind of aluminum alloys. In Fig.2 the transition to heterogeneous regime of dynamic deformation is indicated for both kinds of alloy. Transition to heterogenization is seen to occur at different impact velocities - 450 m/s for 1561 alloy and 650 m/s for 1565 alloy.