High intensity focused ultrasound for high strain rate material testing and delamination

High intensity focused ultrasound (HIFU) is a non-contact method of focusing energy through acoustic waves at high frequencies. HIFU is attractive in nature due to its ability to produce highly focused energy both spatially and temporally. Besides its biomedical applications such as tumor ablation, recently, HIFU has been proposed as a remote excitation mechanism for shape recovery and surface treatment of polymers, among others. However, HIFU has not received much attention as a dynamic characterization technique for materials 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 delaminated at the interface via HIFU, demonstrating its capacity as a compact and non-contact mechanism of shock wave generation. Acoustic intensity and duration are varied to understand the interaction of HIFU and adhesive interfaces without contact. This indicates that high strain rate material testing, which is typically performed at strain rates of 10^-3 s^-1, can be done at the high end of the strain rate regime (up to 10⁶ s^-1) using our method. Compared to existing techniques, HIFU therefore presents a key opportunity to induce and analyze impact stresses in materials in a low-cost, compact, and non-contact manner.