posted on 2020-03-18, 13:55authored byTaylor
A. Stockdale, Daniel P. Cole, Jeffrey M. Staniszewski, Michael R. Roenbeck, Dimitry Papkov, Steve R. Lustig, Yuris A. Dzenis, Kenneth E. Strawhecker
The
processing conditions used in the production of advanced polymer
fibers facilitate the formation of an oriented fibrillar network that
consists of structures spanning multiple length scales. The irregular
nature of fiber tensile fracture surfaces suggests that their structural
integrity is defined by the degree of lateral (interfacial) interactions
that exist within the fiber microstructure. To date, experimental
studies have quantified interfacial adhesion between nanoscale fibrils
measuring 10–50 nm in width, and the global fracture energy
through applying peel loads to fiber halves. However, a more in-depth
evaluation of tensile fracture indicates that fiber failure typically
occurs at an intermediate length scale, involving fibrillation along
interfaces between fibril bundles of a few 100s of nanometers in width.
Interaction mechanisms at this length scale have not yet been studied,
due in part to a lack of established experimental techniques. Here,
a new focused ion beam-based sample preparation protocol is combined
with nanoindentation to probe interfaces at the intermediate length
scale in two high-performance fibers, a rigid-rod poly(p-phenylene terephthalamide) and a flexible chain ultrahigh molecular
weight polyethylene fiber. Higher interfacial separation energy recorded
in the rigid-rod fiber correlated with less intensive fibrillation
during failure and is discussed in the context of fiber chemistry
and processing. Power law scaling of the total absorbed interfacial
separation energy at three different scales in the polyethylene fiber
is observed and analyzed, and distinct energy absorption mechanisms,
featuring a degree of self-similarity, are identified. The contribution
of these mechanisms to the overall integrity of the fiber is discussed,
and the importance of the intermediate scale is elucidated. Results
from this study provide new insights into the mechanical implications
of hierarchical lateral interactions and will aid in the development
of novel fibers with further improved mechanical performance.