Modified scheme for hole problems with surface tension and surface elasticity: stability conditions and effective moduli
摘要
The (linearized) complete Gurtin-Murdoch model offers an accessible way to describe the role of surface tension and surface elasticity in the elastic behavior of porous structures at small scales. Since the surface stress introduced from this model (incorporating surface tension as a finite quantity and the surface strain-related contribution as a small quantity) is represented in terms of the first-kind Piola stress for small deformations, this model fails to incorporate directly the surface stretch in representing surface tension-related traction exerted on the surrounding bulk. This, in turn, may lead to significant disparities between the theoretical solutions and related experimental results and particularly the loss of certain intrinsic phenomena (for example, surface tension-driven instabilities of porous structures). To address this deficiency, we revisit the determination of the stress field in an elastic medium enclosing a hole with surface tension and surface elasticity. Specifically, to capture the precise traction induced by surface tension imposed on the medium, we use an exact first-order formula for the deformation-induced change in the actual curvature of the hole’s boundary directly instead of the complete Gurtin-Murdoch model. In particular, we formulate the corresponding boundary condition and boundary value problem for an arbitrary shaped hole using the complex variable formalism of plane elasticity. Closed-form solutions are derived for the case of a circular hole embedded in an infinitely large medium undergoing uniform far-field loadings, and explicit expressions are obtained for the transverse effective properties of a porous structure containing circular cylindrical holes with surface tension and surface elasticity. Simple conditions are identified for the stability of a porous structure containing circular cylindrical holes and for a positive correlation between the effective shear modulus of the porous structure and the hole volume fraction, when both surface tension and surface elasticity are present. Numerical examples compare the current model with the complete Gurtin-Murdoch model in terms of stress concentration around the hole and effective moduli of the porous structure.