  There are a multitude of applications in which structural materials would be
desired to be nondestructively evaluated, while in a component, for plasticity
and failure characteristics. In this way, safety and resilience features can be
significantly improved. Nevertheless, while failure can be visible through
cracks, plasticity is commonly invisible and highly microstructure-dependent.
Here, we show that an equation-free method based on principal component
analysis is capable of detecting yielding and tertiary creep onset, directly
from strain fields that are obtained by digital image correlation, applicable
on components, continuously and nondestructively. We demonstrate the
applicability of the method to yielding of Ni-based Haynes 230 metal alloy
polycrystalline samples, which are also characterized through electron
microscopy and benchmarked using continuum polycrystalline plasticity modeling.
Also, we successfully apply this method to yielding during uniaxial tension of
Hastelloy X polycrystalline samples, and also to the onset of tertiary creep in
quasibrittle fiber composites under uniaxial tension. We conclude that there
are key features in the spatiotemporal fluctuations of local strain fields that
can be used to infer mechanical properties.
