Toughening mechanisms and damage tolerance of bioinspired interfaces

Abstract

Biologically inspired designs were deployed into selective laser sintering of polyamide substrates to study the mechanics of adhesion and debonding of adhesive bonded structural interfaces. In particular, through extensive series of experiments and simulations, the present study covers the effect of hollow channels, mimicking the base plate of the Amphibalanus amphitrite, and of sinusoidal interfaces, resembling those observed in sutures joints, on the mechanics of crack propagation in adhesive bonds. A model material system comprising adhesively bonded 3D printed substrates in the Double Cantilever Beam (DCB) configuration was selected for the analyses. Adhesive bonding and subsequent mechanical tests revealed the occurrence of a crack trapping effect, which hinders crack propagation and enhances energy dissipation with respect to the baseline interface. The use of bioinspired structures is shown to improve the performances of adhesive joints, enabling damage tolerance and, in the case of subsurface channels, also a weight reduction. Numerical simulations, carried out using finite element analysis (FEA) with interface elements, were also executed to gain a deep understanding of all mechanisms observed experimentally. The simulations were able to mimic the serrated behavior observed in experimental load-displacement responses, which was due to the snap-through interfacial cracking mechanism, i.e., a sudden and almost instantaneous growth of apparently stable cracks. Moreover, the mechanisms of fracture observed in the experiments (e.g., nucleation of a secondary crack at the interface) were reproduced with good accuracy in finite element simulations. The overall analysis demonstrates that is possible to improve joints effective fracture toughness by modifying joints architecture, even without any modification of adhesive type and/or interface properties (e.g., surface energy). This study further confirms that additive manufacturing represents a powerful platform for the experimental study of bio-inspired materials