Fig.7 Failure mode of equivalent plastic strain Fig.8 Failure mode of equivalent plastic strain (v=300m/s) (v=400m/s) 4.3 The maximum principal strain fracture criterion Refering to quasi static tensile tests, The maximum principal strain was 0.33. Through the simulation, failure mode of the maximum principal strain in different velocities (v=300m/s, 400m/s) are showing in Fig.9 and 10. About thirty fragments produced in this process, and the fragment volume was larger than that of above two fracture criterions. Fig.9 Failure mode of the maximum principal strain Fig.10 Failure mode of the maximum principal strain (v=300m/s) (v=400m/s) 4.4 J-C fracture criterion The influence of the stress triaxiality in these models is based on the void growth equation proposed[6, 7].The expression of J-C fracture strain fε is [3] ( ) ( )( ) * 3 * * 1 2 4 5 1 ln 1 D f D De D DT σ ε ε ⎛ ⎞ = + + + ⎜ ⎟ ⎝ ⎠ & (2) 1D, 2D , 3D , 4D and 5D are material parameters； * eff kk eff p Rσ σ σ σ σ = =− =− ，pis pressure， eff σ is equivalent stress，Rσis stress triaxiality； * 0 ε ε ε =& &&is dimensionless plastic strain rate， 0ε& is Referenced plastic strain rate； * ( ) ( ) r m r T T T T T = − − , rT and mT are the room temperature and the material melting temperature. For Q235, D1=0.38, D2=1.47, D3=2.58, D4=-0.0015, D5=8.07. Through the simulation, failure modes of J-C in different velocities (v=300m/s, 400m/s) are showing in Fig.11 and 12.
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