  The mussel thread-plaque system exhibits strong adhesion and high ductility,
allowing it to adhere to various surfaces. While the microstructure of plaques
has been thoroughly studied, the effect of their unique porous structure on
ductility remains unclear. This study firstly investigated the porous structure
of mussel plaque cores using scanning electron microscopy (SEM).
Two-dimensional (2D) porous representative volume elements (RVEs) with scaled
distribution parameters were generated, and the calibrated phase-field
modelling method was applied to analyse the effect of the pore distribution and
multi-scale porous structure on the failure mechanism of porous RVEs. The SEM
analysis revealed that large-scale pores exhibited a lognormal size
distribution and a uniform spatial distribution. Simulations showed that
increasing the normalised mean radius value of the large-scale pore
distribution can statistically lead to a decreasing trend in ductility,
strength and strain energy, but cannot solely determine their values. The
interaction between pores can lead to two different failure modes under the
same pore distribution: progressive failure mode and sudden failure mode.
Additionally, the hierarchical structure of multi-scale porous RVEs can further
increase ductility by 40%-60% compared to single-scale porous RVEs by reducing
stiffness, highlighting the hierarchical structure could be another key factor
contributing to the high ductility. These findings deepen our understanding of
how the pore distribution and multi-scale porous structure in mussel plaques
contribute to their high ductility and affect other mechanical properties,
providing valuable insights for the future design of highly ductile biomimetic
materials.
