Numerical study of impact phenomena due to cavitation bubble collapse on metals and polymers

Metals and polymers are the materials most frequently used in hydromachinery components that are prone to cavitation damage. This study examined the damage mechanism of metals (titanium, SUS304, Al2024, and magnesium) and polymers (nylon, Teflon, Adiprene, epoxy, and polyethylene) due to cavitation bubble collapse by utilizing a coupled fluid–solid hydrocodes solver. An air bubble was positioned adjacent to solid material within a long and narrow water-filled channel. A planar shockwave was utilized to create instability within the air bubble, causing a nonspherical collapse that is often observed in cavitation bubbles. By analyzing the wave propagation behavior of bubble collapse impact load (BCIL) acting on the surface, it was revealed that in metals, the impact load is primarily transmitted as elastic waves of compression and shear. Hence, the cavitation damage on metals can be defined by BCIL and acoustic impedance. On the other hand, the BCIL on polymers generates an excessive plastic deformation, so called cavitation pit. An image analysis on cavitation pit growth demonstrated a strong correlation between the pit's volume and depth with the polymer's yield strength.