Spontaneous formation and morphology of telephone cord blisters in thin films: The Ω formulae

Abstract

Telephone cord blisters (TCBs) are frequently observed in film/substrate material systems. They nucleate and propagate forward with wavy boundaries between the film and the substrate like worms. The current study views the problem from a completely new angle: It is discovered that the spontaneous formation and morphology of TCBs in thin films under biaxial compressive residual stresses can be accurately explained and determined by assuming the existence of a pocket of energy concentration (PEC) instead of the existence of a separation of critical size. For the first time, completely-analytical formulae-the 'Ω formulae'-are derived for the two local morphology parameters of TCBs of any shape, that is, width and height, and for the two global morphology parameters of TCBs of sinusoidal shape, that is, the wavelength and transverse amplitude. Mechanical conditions are also given for the first time for the formation of TCBs. Predictions for the four morphology parameters of the developed theory agree very well with extensive experimental results. In addition, by reversing the calculation, the residual stress and the film/substrate interface fracture toughness are also accurately determined from measurements of the TCB morphology parameters.

Determination of residual stress and interface adhesion toughness of thin films by blisters

“…Experimental observations, however, show no such preexisting delamination. Wang et al have recently proposed that spontaneous formation of blisters is driven by pockets of energy concentration (PECs) . Predictions of blister morphology from these PEC‐driven models are in excellent agreement with independent experimental results.…”

“…Yuan et al have developed a completely analytical model to determine the four morphology parameters based on the PECs theory . The theoretical predictions are again in excellent agreement with extensive independent experimental data.…”

“…Spontaneous formation of circular and TCBs in thin films can occur when the parameter Ω, that is, the ratio between the plane‐strain residual strain energy density and the adhesion toughness, is larger than 3/2. By measuring the blister morphology parameters, the authors' PEC‐driven mechanical models provide an accurate method to determine the residual stresses in a thin film and the adhesion toughness at the interface between the film and its substrate. This method is of considerable value as it can be used in both laboratory tests and with in situ measurements.…”

Swelling-induced telephone cord blisters in hydrogel films

“…Although Takahashi et al [20,21] performed systematic research to identify the parameters determining the formation and development of 3D architectures, quantitative analysis upon the correlations with the film thickness, cross-linking density, swelling ratio, and the geometry of the non-adhesive interface is still required for the design of microfluidic devices via artificially controlling the morphology parameters. Particularly, when the critical condition for conventional buckling is not satisfied, i.e., the magnitude of swelling-induced compressive stress is smaller than the critical value, or alternatively the width of the non-adhesive region at the interface is small, the 'Ω-formulae' for the TCB in equilibrium developed by Yuan et al [22] can be used to quantify the morphology parameters. It is noted that the Ω-formulae are based on a novel mechanical hypothesis originally proposed in Refs.…”

Determinação de propriedades mecânicas de filmes de DLC (Diamond-Like carbon) por meio de estruturas formadas por delaminação espontânea

“…A figura 2.3 mostra alguns dos tipos mais comuns de estruturas em filmes sob tensão de compressão. Usualmente, todos esses modos de delaminação, bem como modos de rachadura são caracterizados pelo seguinte parâmetro adimensional: 52,53…”