A bulge test based methodology for characterizing ultra-thin buckled membranes

Abstract

Buckled membranes become ever more important with further miniaturization and development of ultra-thin film based systems. It is well established that the bulge test method, generally considered the gold standard for characterizing freestanding thin films, is unsuited to characterize buckled membranes, because of compressive residual stresses and a negligible out-of-plane bending stiffness. When pressurized, buckled membranes immediately start entering the ripple regime, but they typically plastically deform or fracture before reaching the cylindrical regime. In this paper the bulge test method is extended to enable characterization of buckled freestanding ultra-thin membranes in the ripple regime. In a combined experimental-numerical approach, the advanced technique of digital height correlation was first extended towards the sub-micron scale, to enable measurement of the highly varying local 3D strain and curvature fields on top of a single ripple in a total region of interest as small as ~25 μm. Subsequently, a finite element (FE) model was set up to analyze the post-buckled membrane under pressure loading. In the seemingly complex ripple configuration, a suitable combination of local region of interest and pressure range was identified for which the stress-strain state can be extracted from the local strain and curvature fields. This enables the extraction of both the Young's modulus and Poisson's ratio from a single bulge sample, contrary to the conventional bulge test method. Virtual experiments demonstrate the feasibility of the approach, while real proof of principle of the method was demonstrated for fragile specimens with rather narrow (~25 μm) ripples.

Experimental characterisation of the local mechanical behaviour of cellulose fibres: an in-situ micro-profilometry approach

“…( 2). For more details on the strain calculation procedure, the reader is referred to Shafqat et al (2018).…”

Hydrodynamic Bulge Testing: Materials Characterization Without Measuring Deformation

“…Then, the governing differential equations Eqs. (15) for Φ X and U are a set of coupled, inhomogeneous, ordinary differential equations (ODEs) in X with constant coefficients. Based on the definition of λ from Eq.…”

“…Several techniques have been proposed to improve the accuracy of "traditional" bulge tests. These improvements include, but are not limited to, accounting for the film's bending stiffness [13], accounting for pre-stress in the film [2,14], considering the possibility of buckling [15] and better prediction of the stress distribution near edges [16] by using elastically clamped (instead of the traditional rigidly clamped) boundary conditions [10,11].…”

Application of the bulge test combined with 3D-DIC for biaxial characterization of PLA films and defect detection

“…This is due to the limited dimensions of these structures, which prevent using standardized tests typically used for bulk specimens. 4,[9][10][11][12] Bulge test is widely used in industries such as microelectronics, where thin films are commonly used to manufacture electronic devices, nano-devices, coating applications, and biomedical devices, where the properties of soft tissues and biomaterials are of interest. 9,[13][14][15] Bulge test was also used to investigate the plastic behavior of metallic sheets to understand their formability or to obtain model parameters for predicting thermoforming behavior of plastic or metallic sheets.…”