A remarkable high fracture toughness is sometimes observed for interfaces
between materials with a large elastic mismatch, which is reported to be
caused by the fibrillar microstructure appearing in the fracture process zone.
In this work, this fibrillation mechanism is investigated further to investigate
how this mechanism is dissipating energy. For that purpose, thermoplastic
urethane(TPU)-copper interfaces are delaminated at various rates in a peel
test experimental setup. The fracture process zone is visualized in situ at
the meso scale using optical microscopy and at the micro scale using Environmental Scanning Electron Microscopy (ESEM). It is shown that the
geometry of the fracture process zone is insensitive to the delamination rate,
while the interface traction scales logarithmically with the rate. This research
has revealed that, the interface roughness is shown to be pivotal in initiating the fibrillation delamination process, which facilitates the high fracture
toughness. The multi-scale experimental approach identified two mechanism
responsible for this high fracture toughness. Namely, the viscous dissipation
of the TPU at the high strain levels occurring in the fibrils and the loss of
stored elastic energy which is disjointed from the propagation due to the size
of the process zone.