THERMAL FLUCTUATIONS LIMIT THE COHESIVE STRENGTH OF COMPLIANT SOLIDS

摘要

The cohesive strength, of an interface, σ_o is on the order of W_(ad)/δ_o, where W_(ad) is the work of fracture and δ_o is a characteristic length representing the separation between the two surfaces. If one imagines that the bodies are separated as rigid entities, the characteristic length δ_o derives from the inter-surface potential and is of order nanometer to angstroms. Even for weak van der Waals types of interactions, W_(ad) is about 50-100mJ/m~2. Using these numbers, the intrinsic cohesive strength σ_o is found to be in the range 10~2-10~3MPa. For stiff materials, defined here as those with elastic modulus much greater than intrinsic strength, such a value poses no problem.