form of the damage cone and a relatively big residue remains back. Above this velocity, however, the cracks spanning the entire disc result in the break-up of the residue into smaller pieces, see Fig. \[snapshots\]d. Later on it will be shown that the behavior of the system quantitatively changes at this velocity, which we call critical velocity. At impact velocities larger than the critical value, secondary cracks are generated roughly perpendicular to the oblique cracks. Secondary cracks from neighboring oblique cracks may merge with each other as can be seen in Fig. \[snapshot\]c. Also at higher impact velocities, vertical cracks with a direction nearly perpendicular to the target plate are more prominent as the intensity of stress concentration near the tip region of the cone is high as compared to other parts.

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   ![\[snapshot\] Final reassembled states of the break-up process of a disc of radius $30$ cm at different impact velocities dropped on a hard frictionless plate. (a) $v_0 = 100$ cm/sec. The cone is not fully developed and only few oblique cracks are present. (b) $v_0 = 200$ cm/sec. More oblique cracks develop and travel a greater distance. (c) $v_0 = 600$ cm/sec. Both oblique cracks 