PSI - Issue 13

Koji Uenishi et al. / Procedia Structural Integrity 13 (2018) 769–774

772

4

Uenishi and Goji / Structural Integrity Procedia 00 (2018) 000–000

at a frame rate of 50,000 frames per second and the experimental observations show the presence of (i) one dimensional, unidirectional stress transfer, which is similar to force chains often found in quasi-static cases and may lead to granular mass flow (Figs. 2(a) and 3(a)), and (ii) wide, two-dimensional wave radiation that can result in separation of the slope face only (similar to toppling failure) (Figs. 2(b) and 3(b)), and whichever occurs seems to be dependent on the profile (e.g. duration of supply, amount) of energy imparted to the slope by the impact. a b

Projectile

10 mm

Aluminum

Photoelastic particle

Slope face separation, similar to toppling failure

Opening away from the position of impact

Opening beneath the position of impact, leading to mass flow

Fig. 2. Experimentally taken photographs indicate the movement of each particle in two-dimensional model slopes and also the isochromatic fringe patterns inside the photoelastic particles (the fringe order is proportional to the maximum in-plane shear stress) that are induced by (a) free fall of button-shaped aluminum (diameter 20 mm, thickness 10 mm, mass 8.4 grams, impact velocity 3.5 m/s) and (b) a projectile launched by an airsoft gun (sphere of diameter 6 mm, mass 0.2 grams, impact velocity 76 m/s). The topmost pictures correspond to the stage just before dynamic impact. The time elapsed after the topmost snapshot is (a) 600, 1200, 1800 and 4000  s and (b) 300, 600, 900 and 2000  s, respectively.