Mechanics and Fracture of Structured Pillar Interfaces

Material architecture and geometry provide an opportunity to alter the fracture response of materials without changing the composition or bonding. Here, concepts for using geometry to enhance fracture resistance are established through experiments and analysis of the fracture of elastic-brittle, polymer specimens with pillar-structures along the fracture plane. Specifically, we investigate the fracture response of double cantilever beam specimens with an array of pillars between the upper and lower beams. In the absence of pillars, unstable crack growth and rapid catastrophic failure occur in the double cantilever specimens tested in displacement control. Introducing pillars at the interface by removing material via laser cutting yields a discontinuous interface and leads to a more gradual fracture process and an increase in the work of fracture. The pillar geometry affects the failure load and, notably, increasing the slenderness of the pillars leads to higher critical failure loads due to greater load sharing. The effect of pillar geometry on fracture is established through experiments and analysis, including analytical modeling and finite element simulations. An analytical model that includes the macro-scale response of the beam and the micro-scale response of the pillars is presented and describes the key effects of pillar geometry on fracture response.