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김종훈(Jonghun Kim),남경목(Gyung Mok Nam),조민재(Minjae Cho),윤상희(Sang-Hee Yoon) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11
The exfoliating nature of graphite is critically important to a variety of engineering applications. Graphite exfoliation is still, however, controversial about the processes and the related mechanophysical parameters. Here, we characterize the expansion behavior of graphite in the microwave-assisted exfoliation where KMnO4 and HNO3 are used as oxidant and intercalation agent, respectively. The expansion ratio of graphite is quantitatively measured as a function of: (1) mixing ratio of graphite, KMnO4, and HNO3; (2) mixing time; (3) graphite physical properties (form, type, and size). A fluid-dynamics-based model is also built to explain the relation between graphite expansion ratio and graphite physical properties.
초기변형률에 의한 피부조직의 미소바늘관통저항 감소에 관한 연구
김종훈(Jonghun Kim),박성민(Sungmin Park),김도훈(Dohoon Kim),남경목(Gyung Mok Nam),윤상희(Sang-Hee Yoon) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
Despite all the recent advances made in the biodegradable microneedle field, the mechanical failure of a microneedle during insertion remains a major technical hurdle in the path of large scale commercialization. A controllable reduction in the microneedle puncture resistance of skin tissues is therefore an essential requirement for developing a biodegradable microneedle. Here, we consider unidirectional or multidirectional prestress on skin tissues as a critical stimulus to reducing the microneedle puncture resistance, and investigate the effect of prestress on the changes in microneedle insertion behavior (e.g., puncture resistance, insertion force, etc.) in a quantitative way. For pork skin tissues similar to human ones, microneedle insertion behavior is characterized with a z-axis motorized stage equipped with a load cell, together with microindenters; the experimental apparatus provides a force-time curve which contains information on microneedle puncture and insertion into skin tissues. The experimental results lead to quantifying the relation between microneedle insertion behavior and prestrain. The findings of this study will lead to better understanding of skin tissue biomechanics.