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How random roughness arrests cracks in the contact of soft solids and the fracture of spring networks
Soft solids tend to stick : bringing two surfaces together lowers their surface energy, and separating them requires tensile forces. This simple energy balance, however, cannot explain why soft materials stick more strongly when we pull them apart than when they first come into contact—a phenomenon known as adhesion hysteresis. In the first part of this talk, I will show that adhesion hysteresis originates from the pinning of the contact perimeter by surface roughness. This mechanism connects adhesion hysteresis to broader phenomena such as contact angle hysteresis, fracture in heterogeneous materials, and the pinning of elastic lines.
In the second part, I shift from adhesive contacts to fracture in bulk disordered materials. Using numerical simulations of spring networks with randomly removed bonds, I will show that fracture toughness increases with the square root of the defect fraction. This counterintuitive effect highlights how disorder, rather than weakening, can reinforce materials by arresting cracks.