Session: 12-29-01: Mechanics of Soft Materials

Paper Number: 150254

150254 - Cavitation Growth Versus Crack Nucleation/propagation in Confined Thin Layers of Soft Solids 

Thin layers of soft solids are used in various applications, such as pressure-sensitive adhesives, protective coatings, barrier packaging films, flexible electronics, and many biomedical applications. Their mechanical response has been widely investigated in the literature, both experimentally and theoretically. Thin layers of soft solids bonded to two rigid plates demonstrate interesting and unusual failure response that depends on various material and geometrical parameters. The prevailing notion in the literature is that these layers fail by two different mechanisms: (i) internal/external crack nucleation and propagation, and (ii) elastic cavity growth that leads to fibrillation and then failure. The first mechanism is thought to be an energy-release-rate-governed phenomenon, while the second cavitation mechanism is considered a stress-governed phenomenon.

 

In this talk, we will demonstrate that these two mechanisms are actually one and the same, and both need to be described as fracture processes. The analysis makes use of the recently established theory which showed that cavitation is predominantly a fracture process, and not a purely elastic one as conjectured for decades. This theory, put forth by Kumar et al. (2018), is a comprehensive theory of fracture -- regularized, of phase-field type, that can model not only the cavitation phenomenon but also the other experimental results accumulated in the literature in the last 100 years on the nucleation and propagation of cracks within the bulk of elastic brittle elastomers as well as from pre-existing cracks, notches and other sources of stress concentrations.  With this theory, quantitative comparisons have been recently conducted with the so-called poker-chip experiments in natural rubber and synthetic silicone, which show very good agreement. We will discuss the theory in detail and show experimental validation with a recent set of high spatial-temporal resolution experiments.

 

The reason cavitation fracture growth appears distinct in the experiments on thin confined layers is because it involves crack growth through the thickness of the layer and parallel to the direction of the loading. This unusual sideways fracture process depends on material properties like the Poisson's ratio, elasto-adhesive length scale of the bulk, strength as well as the degree of confinement of the layer. Comprehensive numerical analysis is performed using a recently developed complete phase-field model of fracture. Further insight is gained through energy release rate calculations with the J-integral. It is concluded that two mechanics of fracture identified in the experiments both involve crack nucleation and propagation and are controlled by the material's strength as well as their critical energy release rate.

Presenting Author: Aditya Kumar Georgia Institute of Technology

Presenting Author Biography: Assistant Professor

Authors:

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