Session: 13-11-01: Friction, Fracture, and Damage I

Paper Number: 172672

On Failure Mechanisms and Load-Parallel Cracking in Confined Elastomeric Layers 

Thin layers of elastomers bonded to two rigid plates demonstrate unusual failure response. Historically, it has been believed that strongly-bonded layers fail by two distinct mechanisms: (i) internal/external penny-shaped crack nucleation and propagation, and (ii) cavitation, that is, cavity growth leading to fibrillation and then failure. However, recent work has demonstrated that cavitation itself is predominantly a fracture process. While the equations describing cavitation from a macroscopic or top-down view are now known and validated with experiments, several aspects of the cavitation crack growth need to be better understood. Notably, cavitation often involves through-thickness crack growth parallel to the loading direction, raising questions about when it initiates instead of the more typical penny-shaped cracks perpendicular to the load. Understanding and controlling the two vertical and horizontal crack growth is key to developing tougher soft films and adhesives. The purpose of this talk is to provide an explanation for the load-parallel crack growth through a comprehensive numerical analysis and highlight the role of various material and geometrical parameters.

To identify the conditions that favor vertical crack growth over horizontal growth, we perform parametric study over a single nucleation event at the center of a thin, two-dimensional layer, leading to a cross-shaped crack with both horizontal and vertical fronts. The length of each crack is taken to be larger than the intrinsic fracture length scale, such that their growth is governed solely by the material’s critical energy release rate. This allows the calculation of the energy release rate for each crack over a wide range of deformations using the J-integral. To further highlight the impact of vertical versus horizontal crack growth on the layer’s failure properties, phase-field simulations using the complete nucleation model are performed for two cases where either vertical or horizontal growth dominates.

Results demonstrate that the preference of vertical crack growth over horizontal growth depends on both the material properties and the geometric properties of the elastomeric layer. In particular, higher degree of confinement and greater incompressibility result in cavitation-like behavior. Furthermore, for isolated horizontal and vertical nucleation events, the relative values of energy release rate are found to be dependent on the size of initial crack. Since it is also observed that vertical growth leads to a higher load-carrying capacity for the film, and greater energy dissipation, controlling these parameters to induce vertical crack growth holds the key to producing thin films and adhesives that are stronger and tougher.

Presenting Author: Aarosh Dahal Georgia Institute of Technology

Presenting Author Biography: Aarosh Dahal is a second year doctoral student at the School of Civil and Environmental Engineering at Georgia institute of Technology. His research areas include Fracture in Elastomers, Ductile Fracture and Homogenization.

Authors:

Aarosh Dahal Georgia Institute of Technology
Aditya Kumar Georgia Institute of Technology