A mechanistic framework to differentiate nanoindentation-induced plasticity and fracture in layered materials

During nanoindentation of layered materials, a plethora of deformation mechanisms manifest in the load-displacement data as discrete displacement bursts, whose physical origins are often difficult to isolate from indentation data alone. This study develops a mechanistic framework to classify nanoindentation displacement bursts, also known as pop-ins, in layered materials and structures, enabling attribution of distinct pop-in populations to the underlying deformation mechanisms. Using muscovite (a mica-group phyllosilicate) as a model system, we conducted nanoindentation experiments normal to the basal plane over temperatures from ambient to 300 °C and extracted features from the load-displacement data, including pop-in velocities and energies. Here, we report that fracture and plastic deformation events are reliably distinguished using a statistically robust threshold in pop-in width. This new procedure revealed that with increasing temperature, the onset load for fracture-induced pop-ins decreased – consistent with declining fracture toughness – whereas the onset load for plasticity-induced pop-ins remained unchanged. This work provides a systematic approach to identify and isolate deformation mechanisms in layered materials during nanoindentation.