PSI - Issue 61

118 4

Koji Uenishi et al. / Procedia Structural Integrity 61 (2024) 115–121 Uenishi and Kato / Structural Integrity Procedia 00 (2024) 000 – 000

a

b

10 mm

Single impact

Stress transfer

Relatively unstable due to the existence of a free surface

Mechanically stable area

Fig. 2. (a) Photographs of the first experiment (Fig. 1(a)) at a shorter interval. (b) Difference of colors between the photographs before and after the single dynamic impact clearly indicates the lines of unidirectional stress transfer in the granular medium. Below the lines of stress transfer the particles are stable and no large movement is expected while above these lines, due to the presence of the top free surface nearby, stresses cannot be transferred easily into the far field and hence relatively large movement of particles and fragmentation of the granular medium near the point of impact are possible. The time elapsed since the impact is, from top to bottom, 300, 600, 900, 1,200 or 1,800 microseconds (  s).