A device to fracture soft solids at high speeds

We describe the development of a device for high-rate, pneumatic fracture. The Small-scale Ballistic Cavitation (SBC) device uses a high pressure reservoir to generate cavities within ultrasoft solids (moduli < 100 kPa) in bursts as short as 5 ms. Flow accelerates through a needle embedded within a soft solid, reaching the speed of sound at the tip before delivery to the sample. The energy density of the air pulse matches that of handgun projectiles, enabling ballistic-like temporary cavities, but on a benchtop scale. We validate the device using mass transfer measurements and find good agreement without the use of fit parameters between experiments and theory at the required operational pressures ranging from ∼30 to 160 atm. Independent control of pressure, needle diameter, and valve cycle time provides flexibility in experimental control variables (e.g., energy density, rate) that is not present in other ultrasoft solid cavitation techniques. We demonstrate the device's experimental flexibility via the application of constant energy density with variable loading rate conditions that illustrate the importance of rate on fracture morphology in soft solids.