Stretchability enables the device to be patched to a curved surface or to be folded several times to maximize usability. Among many methods, the pre-strain method is advantageous in that the stretchability as much as the pre-strain applied to the substrate is guaranteed even without material improvement. When the pre-strain is restored to its original state, the thin film gets wrinkled or the substrate gets buckled. Wrinkles and buckling that appear in this way are affected by the physical properties and dimensions of the substrate, and it is necessary to analyze their effect. In this study, a theoretical approach was used and a nonlinear post-buckling analysis was performed using a finite element method. The analysis was divided into two steps: the pre-strain step and the recovery step. According to the analysis results, it was possible to predict and analyze the wrinkle and buckling behavior due to pre-strain according to the physical properties and dimensions of the substrate. The pre-strain analysis method can be applied to multi-layer structures with three or more layers and can be used as a method to analyze wrinkle suppression and wrinkle shape control in future studies.

Recently, porous structures of nano/microfibers are receiving great attention because of their excellent mechanical properties, surface area to volume ratio, and permeability. In this study, thick microfiber mats were fabricated using a melt-electrospinning process in a controlled manner. A melt-electrospinning equipment including a three-axis precision motion control with pneumatic dispensing was constructed. The diameter and deposition pattern of melt-electrospun microfibers with respect to the barrel temperature and pressure were investigated. Based on identified effects of process conditions on microfiber geometry, thick microfiber mats with various properties were successfully fabricated using melt-electrospinning with snake scanning and iterative layering. Their mechanical properties and porosities were then compared and analyzed.

It is generally accepted that mechanical properties of sandwich composite are affected by curing pressure variation. For the present study, the effects of curing pressure variation on the compressive properties of balsa wood sandwich composite were investigated. For this purpose, a compressive test was conducted using balsa wood and honeycomb core sandwich composite, applying 40 psi and 60 psi curing pressure conditions. The results showed that compressive load of balsa wood sandwich composite applying 60 psi curing pressure condition is higher than applying a 40-psi curing condition. This phenomenon is due to an increase in the adhesive strength of the balsa wood sandwich composite as the curing pressure increases, thereby improving the compressive strength. Deboning and local buckling were observed on fracture surfaces of all balsa wood sandwich composite, but only global buckling was observed at honeycomb core sandwich composite.