The wrinkling of a stiff thin film bonded on a soft elastic layer and subjected to an applied or residual compressive stress is investigated in the present paper. A three-dimensional theoretical model is presented to predict the buckling and postbuckling behavior of the film. We obtained the analytical solutions for the critical buckling condition and the postbuckling morphology of the film. The effects of the thicknesses and elastic properties of the film and the soft layer on the characteristic wrinkling wavelength are examined. It is found that the critical wrinkling condition of the thin film is sensitive to the compressibility and thickness of the soft layer, and its wrinkling amplitude depends on the magnitude of the applied or residual in-plane stress. The bonding condition between the soft layer and the rigid substrate has a considerable influence on the buckling of the thin film, and the relative sliding at the interface tends to destabilize the system.
Low-velocity dynamic compression tests were performed to reveal the failure mechanism and the energy absorption capacity of the integrated woven sandwich composite. Shear deformations were induced by the tilting of fiber piles in the core of the integrated woven sandwich composite. Ductile load–displacement curves are featured by a long deformation plateau originated from rotations of the core piles. Densification is apparent in the later stage of compression. Stout piles in the core also lead to plastic compression failure mode accompanying with much smaller rotations of core piles. Controlled by the latter failure mode, the dynamic strength and the energy absorption of the panel are stronger. In dynamic compression experiments, the integrated woven sandwich composite panels exhibit similar failure modes with those observed in quasi-static compression tests. The dynamic strength is much greater and the corresponding deformation plateau is much more stable, which leads to greater energy absorption. The dynamic effects of the strength and the energy absorption were explained by the dynamic buckling of the woven struts in the core. The tests suggest that the integrated woven sandwich composite is ideal to serve as a lightweight anti-impact material in engineering structures.
For soft films with a thickness on the order of microns or nanometers, the long-range surface∕interface interaction can be sufficiently strong to induce their surface instability or even rupture. By using the bifurcation theory of elasticity, we here present a three-dimensional theoretical model to study the spontaneous surface instability of a soft elastic thin film supported by a rigid substrate. By accounting for the competition of van der Waals interaction energy with elastic strain energy and surface energy, we obtain the analytical solutions for the critical conditions of three-dimensional surface morphology instability. The effects of surface energy, thickness, and elastic properties of the film on the characteristic wavelength of surface wrinkling are examined. It is found that the characteristic wavelength of the deformation bifurcation mode depends on the film thickness via an exponential relation, with the power index in the range of 0.75–1.0, which mainly depends on the ratio between the surface energy and shear modulus of the film but not on the nature of the surface∕interface interaction. Furthermore, it is shown that the interface condition between the film and the substrate significantly influences the critical condition of surface bifurcation. The theoretical solution proves to be a good agreement with the corresponding experiment results.
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