Cyclic loading of materials at high strain rates may lead to fatigue dynamics that markedly differ from those at conventional strain rates. Various methods have been developed to perform fatigue testing at intermediate to high strain rates, such as automated split-Hopkinson bar testing, or with high throughput, such as ultrasonic testing. However, combining high strain rates with a large number of load cycles remains challenging. Here, we introduce a laser-based technique to build up propagative strain waves at rates above 10^7 s^−1 and at a frequency limited only by the laser base frequency — 1 kHz in this work. The method is based on the additive superposition of individual laser-generated acoustic waves and can generate giant strain waves without damage to the excitation region. Using this technique, we investigate fracture dynamics in strontium titanate, a ceramic with a perovskite structure, in which surface acoustic waves with longitudinal strain amplitudes reaching up to 3 % can be generated — well within the regime of mechanical failure. We extract Wöhler curves into the high-cycle fatigue regime and use diagnostic methods on a shot-to-shot basis, which enables the identification of slip bands building up prior to failure. Finally, we study the anisotropy of fracture dynamics from orientation-dependent measurements and show that counter-propagating strain waves lead to qualitatively different behaviors due to the nonlinearity of the fracture process.
2025-04-09 09:00:00
