High intensity focused ultrasound for high strain rate spall testing

High-intensity focused ultrasound (HIFU) localizes energy at high frequencies by means of acoustic waves in a non-contact way. HIFU’s natural appeal stems from its ability to produce highly focused energy both spatially and temporally. Despite various biomedical applications such as tumor ablation, HIFU has not been explored as a dynamic force excitation mechanism for materials characterization techniques at high strain rates. Here, we report the potential of HIFU as a stress-generating apparatus for material testing. Specifically, we show that adhesively bonded thin-film laminates can be selectively spalled at the interface via HIFU, demonstrating its capacity to generate shock waves in a compact and non-contact fashion. Acoustic intensity and duration are varied to understand the interaction of HIFU shock waves and interfaces at depth in a laminate, without sample contact. This work demonstrates the potential for spall testing at the high end of the strain-rate regime (up to 10⁶ s^-1). Compared to existing techniques, HIFU presents a key opportunity to study high strain rate delamination in materials in a low-cost, compact, and non-contact manner.