Adhesion and Debonding of Soft Elastic Films:  Crack Patterns, Metastable Pathways, and Forces

Abstract

We study the phenomenon of debonding in a thin soft elastic film sandwiched between two rigid plates as one of the plates is brought into intimate contact and then pulled away from contact proximity by application of a normal force. Nonlinear simulations based on minimization of total energy (composed of stabilizing elastic strain energy and destabilizing adhesive interaction energy) are employed to address the problems of contact hysteresis, cavitation, crack morphology, variation of contact area, snap-off distance, pull-off force, work done, and energy loss. Below a critical distance (d(c)) upon approach, simulations show the formation of columnar structures and nonrandom, regularly arranged nanocavities at the soft interface at a length scale of approximately 3h (h being the thickness of the film). The persistence of such instability upon withdrawal (distance >>d(c)) indicates a contact hysteresis, which is caused by an energy barrier that separates the metastable states of the patterned configuration and the global minimum state of the flat film. The energy and the pull-off force are found to be nonequilibrium and nonunique properties depending on the initial contact, defects, noise, etc. Three broad pathways of debonding leading to adhesive failure of the interface, depending on the stiffness of the film, step size of withdrawal, and the imposed noise, are identified: a catastrophic column collapse mode, a peeling mode involving a continuous decrease in the contact area, and a column splitting mode. The first two modes are caused by a very high stress concentration near the cavity edges. These metastable patterned configurations engender pull-off forces that are orders of magnitude smaller than that required to separate two flat surfaces from contact.

Debonding of confined elastomeric layer using cohesive zone model

“…For both the elastic and the viscoelastic layers, the wavelength to thickness ratio for ϕ near region III is found to be larger and dependent on ϕ than that when ϕ is near region II. It is noteworthy that at the larger ϕ value, shapes of the nucleated cavities change before they coalesce as was computed by Sarkar et al [24]. Our numerical experiments suggest that the response becomes more mesh-dependent as ϕ is increased (see Appendix C).…”

“…Since the use of the CZM coupled with the finite element method (FEM) by Hillerborg et al [19] to study fracture problems, significant progress has been made in modeling interfacial debonding/delamination of a polymer interlayer [20][21][22][23]. However, there has been limited research [8,24,25] on capturing progressive interfacial debonding undulations using the CZM. The formation of debonding undulations (such as fingering in a peeling problem) adds to the complexity of the mechanics of the demolding process.…”

Effect of confinement and interfacial adhesion on peeling of a flexible plate from an elastomeric layer

“…Multiple debonds initiate over the CZ resulting in traction-free regions separated by portions of the damaged interface. The average spacing between these debonds is approximately 3 h, which agrees with the results of the interfacial instability ( Mönch and Herminghaus, 2001 ;Sarkar et al, 2005 ;Ghatak, 2006 ). A comparison of our computed results for φ = 4 and φ = 5 suggests that the threshold value, ( φ c ), of φ is in the range (4, 5).…”

“…Recalling that the spacing ( λ) between the adjacent undulation peaks ( Mönch and Herminghaus, 2001 ;Sarkar et al, 2005 ;Ghatak, 2006 ) is expected to be ≈ 3 h , the size of the CZ in a plane strain analysis must be >> 3 h to capture the undulatory debonding phenomenon. Our numerical experiments reveal that the size of this CZ decreases with an increase in φ and a decrease in α.…”

Soft and Hard Adhesion

“…Equation (16) is a simplified version of an expression presented earlier by Webber et al [10], who used the more exact form of the elastic energy in the film as provided by Shenoy and Sharma [30,32,35,36]. Considering only a single Fourier mode of interfacial perturbation, u z ðxÞ ¼ d cosð2px=kÞ, the expression for the elastic energy of the film becomes [36]:…”