arXiv subjects

Sung Hoon Kang

Publications and source records attributed to Sung Hoon Kang.

4 recordsLinked to original sources

arXiv2025

Tension-Induced Soft Stress and Viscoelastic Bending in Liquid Crystal Elastomers for Enhanced Energy Dissipation

Architected materials that exploit buckling instabilities to reversibly trap energy have been shown to be effective for impact protection. The energy-absorbing capabilities of these architected materials can be enhanced further by incorporating viscoelastic material behavior into the buckling elements using liquid crystal elastomers (LCE). In addition to conventional viscoelastic behavior, LCEs also exhibit a highly dissipative rate-dependent soft stress response from mesogen rotation under a mechanical load. However, the buckling elements cannot take advantage of this dissipation mechanism because buckling occurs at strains below the threshold for mesogen rotation. In this study, we investigate tension-induced soft stress behavior as an additional dissipation mechanism in horizontal members of lattice structures composed of tilted LCE beams under compression. Viscoelastic properties of LCEs with two crosslinking densities were characterized experimentally, and a nonlinear viscoelastic model was implemented in Abaqus/Standard as a user-defined element to simulate finite-strain behavior of monodomain LCEs, including soft stress response. Simulations and experiments revealed a non-monotonic dependence of energy dissipation on the thickness ratio between horizontal and tilted LCE members. Optimized structures with stretchable horizontal bars dissipated 2-3 times more energy than rigid-bar counterparts by balancing tension-driven soft stress with viscoelastic beam bending. These findings demonstrate a new design strategy for LCE-based architected materials to enhance energy dissipation.

cond-mat.soft↗

arXiv2021

Synergistic Energy Absorption Mechanisms of Architected Liquid Crystal Elastomers

Here, we report the rate-dependent energy absorption behavior of a liquid crystal elastomer (LCE)-based architected material consisting of repeating unit cells of bistable tilted LCE beams sandwiched between stiff supports. Viscoelastic behaviors of the LCE material cause the energy absorption to increase with strain rate according to a power-law relationship, which can be modulated by changing the degree of mesogens alignment during synthesis. For a strain rate of 600 s-1, the unit cell structure shows up to a 5 MJ/m3 energy absorption density, which is two orders of magnitude higher than the same structure fabricated from Polydimethylsiloxane (PDMS), and is comparable to the dissipation from irreversible plastic deformation exhibited by denser metals. For a stacked structure of unit cells, viscoelasticity also produces nonuniform buckling of the LCE beams, causing the energy absorption density to increase with the stacking number n up to n=3. Varying the beam geometry further promotes the nonuniform buckling behavior allowing the energy absorption density to increase with stacking number without bounds. We envision that our study can lead to the development of lightweight extreme energy-absorbing materials.

cond-mat.soft↗

arXiv2019

Bioinspired Materials with Self-Adaptable Mechanical Properties

Natural structural materials, such as bone and wood, can autonomously adapt their mechanical properties in response to loading to prevent failure. They smartly control the addition of material in locations of high stress by utilizing locally available resources guided by biological signals. On the contrary, synthetic structural materials have unchanging mechanical properties limiting their mechanical performance and service life. Here, a material system that autonomously adapts its mechanical properties in response to mechanical loading is reported inspired by the mineralization process of bone. It is observed that charges from piezoelectric scaffolds can induce mineralization from media with mineral ions. The material system adapts to mechanical loading by inducing mineral deposition in proportion to the magnitude of the loading and the resulting piezoelectric charges. Moreover, the mechanism allows a simple one-step route for making graded materials by controlling stress distribution along the scaffold. The findings can pave the way for a new class of self-adaptive materials that reinforce the region of high stress or induce deposition of minerals on the damaged areas from the increase in stress to prevent/mitigate failure. They can also contribute to addressing the current challenges of synthetic materials for load-bearing applications from self-adaptive capabilities.

physics.app-ph↗

arXiv2016

Harnessing Geometric Frustration to Form Band Gaps in Acoustic Channel Lattices

We demonstrate both numerically and experimentally that geometric frustration in two-dimensional periodic acoustic networks consisting of arrays of narrow air channels can be harnessed to form band gaps (ranges of frequency in which the waves cannot propagate in any direction through the system). While resonant standing wave modes and interferences are ubiquitous in all the analyzed network geometries, we show that they give rise to band gaps only in the geometrically frustrated ones (i.e. those comprising of triangles and pentagons). Our results not only reveal a new mechanism based on geometric frustration to suppress the propagation of pressure waves in specific frequency ranges, but also opens avenues for the design of a new generation of smart systems that control and manipulate sound and vibrations.

physics.class-ph↗