Strain Deconcentration in Thin Films Patterned With Circular Holes

Abstract

It is well known that a circular hole in a blanket thin film causes strain concentration near the hole edge when the thin film is under tension. The increased strain level can be as high as three times of the applied tension. Interestingly, we show that, by suitably patterning an array of circular holes in a thin film, the resulting strain in the patterned film can be decreased to only a fraction of the applied tension, even at the hole edges. The strain deconcentration in the film originates from the following deformation mechanism: while initially planar, the film patterned with circular holes elongates by deflecting out of plane, so that a large tension induces only small strains. Using finite element simulations, we investigate the effects of geometric parameters (i.e., hole size, spacing, and pattern) and loading direction on the resulting strain in patterned thin films under tension. The large deformability of the patterned film is independent of materials and length scale, and thus sheds light on a potential architecture concept for flexible electronics.

Microstructured Silicone Substrate for Printable and Stretchable Metallic Films

“…Two-micrometer-diameter pillars on the substrate surface with height greater than the print thickness lead to the inclusion of similarly sized circular holes in the printed conductor. This type of feature has been studied numerically by Tucker et al as a mechanism of strain relief in thin metallic films . It was demonstrated that if the film can stretch only in-plane then strain localization occurs at the rim of the holes in a thin metallic film and promotes crack formation in the film.…”

Extremely compliant and highly stretchable patterned graphene

“…It has been shown that suitable patterning can significantly increase the stretchability of various materials under the similar deformation mechanism. 41,42 In the second stage, the applied elongation further straightens and stretches the graphene nanoribbon network (Fig. 2(f)) until the final fracture of the GNM at about 50% elongation (Fig.…”

“…The significantly enhanced stretchability and ultra-high compliance of suitably patterned structures, such as GNM and other materials, 6,41,42,45,46 find their origin in the deformation mechanism of bending and twisting, instead of pure stretching, to accommodate elongation. Such a deformation mechanism is essentially geometric, and thus independent of length scale.…”

Lightweight, strong, moldable wood via cell wall engineering as a sustainable structural material

“…In the contour plot, the outer part of the severely folded region is under tension and the inner part is under compression, with a neutral area (zero strain) near the middle plane along the thickness direction of the Moldable Wood. It has been previously shown that circular holes (e.g., the distributed vessels in Moldable Wood) can effectively reduce the strain level in a material subject to large deformation (45). As further shown in Fig.…”

“…S8B) is extremely low, with a maximum tensile and compressive strain of 0.47% and 2.66%, respectively, when the Moldable Wood is subjected to a 60% nominal strain (corresponding to the maximum strain level at the outer and inner most parts of the Moldable Wood when it is folded 180˚). Such remarkable strain mitigation is derived from the wrinkled cell wall structure, which can accommodate large elongation and compression by flattening the cell wall wrinkles through cell wall bending instead of pure stretching, and thus results in substantially low strain in the cell walls (45).…”