Cohesive behavior of soft biological adhesives: Experiments and modeling

Teleost fish scales amongst the toughest collagenous materials

“…It is in fact likely that the inelastic region spreads across the entire scale ahead of the notch before or shortly after crack propagation occurs. Nevertheless, the results from the experimental setup used here directly reflect the traction-separation behavior of the material, and we have indeed recently used a similar setup to determine cohesive laws of various adhesive in the past, with modeling and validation against independent toughness measurements (Dastjerdi et al, 2012. In this experimental configuration, the energy dissipated up to failure can therefore be used to compute work of fracture and toughness, even if the inelastic region extends along the entire sample.…”

“…This calculation yielded a toughness of 38.679.8 J m À 2 . For comparison this delamination toughness is about twenty times higher than office tape on a glass substrate (Dastjerdi et al, 2012), and more than ten times higher than the toughness of the interfaces in nacre . The delamination toughness is 400 times lower than the toughness of the whole scale measured above which is beneficial, considering that low interfacial toughness is a requirement for pullout, delamination and defibrillation of the collagen in the fracture process of the whole scale in the A-P, L-L and P-A directions.…”

“…Slippage at the clamp is also limited, because large surfaces of the scale are used for clamping. The test geometry is similar to the rigid double cantilever beam (RDCB) fracture test, which we recently developed to measure the fracture toughness of biological proteins and engineering adhesives (Dastjerdi et al, 2012). Here the fracture samples were prepared by punching six holes (1 mm in diameter) though the scale: two pairs of holes were used as screw holes to clamp the scale with the two pairs of rigid steel fixtures, while the other pair was used as pin holes to exert opening forces with the miniature loading machine (Fig.…”

Overcoming the brittleness of glass through bio-inspiration and micro-architecture

“…4f) had a bell-shape characteristic of stable crack propagation in tough materials. We then used an integration method to obtain the traction-separation curve of the interface from the force-opening curve 47 (Methods section). Figure 4g shows typical traction-separation curves: the initial response (stage I) is linear elastic up to about 2 MPa, at which point the interface fails in a brittle fashion (sudden drop).…”

The quest for stiff, strong and tough hybrid materials: an exhaustive exploration

“…For example, our models only considered failure of the hard or the soft phase. Debonding between the hard and soft phases could also be introduced and modelled, for example, with cohesive elements [34,35]. Other features such as anisotropy, heterogeneities or even functionally graded properties may be introduced and modelled in the hard and soft phases, these features being present in natural materials.…”