A model for static friction in a film-terminated microfibril array

We model the response of a film-terminated microfibril array subjected to shear through contact with a rigid cylindrical indenter. Our model determines the shear force acting on the indenter for a fixed normal indenter force before the onset of uniform sliding. Consistent with experiment, our model shows that (1) the contact area increases only slightly with the applied shear and (2) the fibrils inside the contact zone are subjected to tension at intermediate to large applied shear displacement despite the fact that the applied normal load is compressive. These features can be explained by the fact that in our samples the continuous terminal film supports tension. The model accurately matches the experimentally measured shear force response. With the use of an independently measured critical energy release rate for unstable release of the contact, the model shows how this architecture achieves a strong enhancement in static friction.