PSI - Issue 14

Dipankar Bora et al. / Procedia Structural Integrity 14 (2019) 537–543 Author name / Structural Integrity Procedia 00 (2018) 000–000

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3.2. Effect of Lode angle on the ductile fracture of thin walled cylindrical tubes Figure 4 shows the comparison of the deformed configurations of the impacting tube with and without considering Lode angle. From the Fig. 4, it is very clear that the deformation increases if lode angle is taken into account. If the Lode angle is not considered the tube expands leading to mushrooming effect and subsequent fracture. However, no mushrooming effect and fracture is seen when the Lode angle effect is taken into consideration. Figure 5 shows the comparison of damage and equivalent plastic strain considering the Lode angle and without the Lode angle effect at point B (see Fig. 1). Figure 5 (a) shows that damage reaches the critical value very quickly after the impact when the Lode angle effect is considered, but it takes 10μ sec more to reach critical value when the Lode angle effect is not considered. However, from Fig. (5(b) it can be seen that there is not effect on the growth of equivalent plastic strain.

(a) With Lode angle at t= 11 µ sec

(b) Without Lode angle at t= 11 µ sec

(c) With Lode angle at t= 15 µ sec

(d) Without Lode angle at t= 15 µ sec

Fig. 4. Comparison of deformed configuration with and without Lode angle

4. Conclusion In the resent work, ductile fracture in thin walled cylindrical tubes impacting a rigid surface is simulated by incorporating the effect of Lode angle. The damage growth law, along with the element deletion technique, is implemented in Abaqus/Explicit through the user defined material subroutine VUMAT. The effect of the Lode angle on the ductile fracture is also studied. At an impact velocity of V = 350 m/s, the fracture is observed at the impacted end. The impacted end mushrooms but no buckling is observed. Damage reaches the critical value first at