Research Overview
1. Multiscale fatigue crack initiation in hierarchical additively manufactured alloys
Most mechanical failures are caused by fatigue, where damage accumulates gradually during cyclic loading. Hierarchical microstructures enabled by additive manufacturing offer a promising route to systematically design alloys that resist fatigue. Here, using a dual-phase nanolamellar high-entropy alloy (AlCoCrFeNi2.1) as a model system, we show that fatigue initiation in hierarchical alloys is scale-dependent: nanoscale phase boundaries govern microscale failure, while mesoscale melt pool boundaries generated during manufacturing govern macroscale failure. By identifying fatigue initiation length scales set by the microstructure, we provide a parameter to guide the design of fatigue-resistant, additively manufactured alloys.
Luc N. Capaldi, J. Ford, S. Fulco, R.K. Rai, W. Yang, S. Ching, E.A. Stach, K.T. Turner, W. Chen, and O.A. Tertuliano. Proceedings of the National Academy of Sciences 2026 123 (20), e2522790123. DOI.
2. Mechanically triggered self-folding of 3D van der Waals mesostructures
Two-dimensional (2D) van der Waals materials exhibit exceptional mechanical and transport properties, but are challenging to sculpt into general shapes and structures. Here, we leverage nanoindentation to trigger the spontaneous formation of three-dimensional (3D) auto-kirigami. These structures self-fold, peel, and tear into functional 3D morphologies, establishing a route towards the rational design of self-assembled van der Waals devices.
Luc N. Capaldi, Li Yuan, Cangyu Qu, Daniel A. Sánchez, Robert W. Carpick, and Ottman A. Tertuliano. Nano Letters 2025 25 (10), 3964-3971. DOI. Featured in Penn Engineering News.
3. High-temperature oxidation of nanocrystalline silicon carbide fibers
Next-generation inflatable heat shields for space exploration rely on flexible silicon carbide (SiC) woven ceramics that rapidly embrittle (50% tensile strength reduction) and fracture under high-temperature oxidation. Using large-scale molecular dynamics simulations, we demonstrate that incoherent grain boundaries fundamentally alter oxidation kinetics within nanocrystalline SiC fibers. We identify a distinct kinetic transition at 1500 K, marked by a six-fold increase in activation energy driven by surface melting. These findings provide atomic-level insights into the environmental degradation of fracture resistance in advanced thermal protection systems.
Luc N. Capaldi and Frederic Sansoz. Acta Materialia 2023 258, 119229. DOI.
