• Journal of Ocean Engineering and Technology
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• v.19 no.1 s.62
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• pp.57-63
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• 2005

The objective of this research is to investigate the mechanical characteristics of the hybrid fiber reinforced composite rebar, which is manufactured from a braidtrusion process. Braidtrusion is a direct composite fabrication technique, utilizing in-line brading and the pultrusion process. hz order to obtain the mechanical behavior of the glass fiber, carbon fiber, and kevlar fiber, the tensile tests are carried out. The results of the fibers are compared with that of steel. Hybrid rebar specimens with various diameters, ranging from model size (3 mm) to full-scale size (9.5 mm), and various cross sections, such as solid and hollow shape, have been manufactured from the braidtrusion process. The tensile and bending tests for the case of the hybrid rebar, the conventional GFRP rebar, and the steel bar have been carried out. The results of the experiments show that the hybrid rebar is superior to the conventional GFRP rebar and the steel bar, from the viewpoint of tensile and bending characteristics.

• Progress in Superconductivity and Cryogenics
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• v.24 no.1
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• pp.8-12
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• 2022

Recently, research on applying composite materials to various industrial fields is being actively conducted. In particular, composite materials fabricated by Fused Deposition Modeling 3D printers have more advantages than existing materials as they have fewer restrictions on manufacturing shape, reduce the time required, weight. With these advantages, it is possible to consider utilizing composite materials in cryogenic environments such as the application of liquid oxygen and liquid hydrogen, which are mainly used in an aerospace and mobility. However, FDM composite materials are not verified in cryogenic environments less than 150K. This study evaluates the characteristics of composite materials such as tensile strength and strain using a UTM (Universal Testing Machine). The specimen is immersed in liquid nitrogen (77 K) to cool down during the test. The specimen is fabricated using 3D print, and can be manufactured by stacking reinforced fibers such as carbon fiber, fiber glass, and aramid fiber (Kevlar) with base material (Onyx). For the experimental method and specimen shape, international standards ASTM D638 and ASTM D3039 for tensile testing of composite materials were referenced.

• Design & Manufacturing
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• v.16 no.4
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• pp.7-16
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• 2022

A helmet is essential for safety when operating personal mobility. However, user's actual helmet wear rate is low due to the inconvenience of wearing and poor ventilation. In this study, a new helmet structure with improved ventilation for personal mobility devices was designed. To design a new structure with improved breathability compared to the existing helmet while satisfying the safety regulations for the helmet, a generative design method was applied to the shock-absorbing liner of the helmet. In addition, other materials were applied to create a structure with improved ventilation while maintaining safety. The generated design result was verified for shock absorption through simulation. As a result of the study, EPS, the current material was replaced with CFRP and Kevlar, and the structure was changed. This design was judged to satisfy safety regulations against impact. The new helmet structure is expected to improve the helmet usability for personal mobility and increase the helmet wear rate of users.

• Journal of the Korean Society of Propulsion Engineers
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• v.27 no.1
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• pp.9-16
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• 2023

This paper investigated the method to predict a thermal response of internal insulation in a solid rocket motor considering both thermal decomposition and ablation. Changes in properties due to the thermal decomposition, swelling of char layer and movement of decomposition gases inside the material were considered during a modeling. And radiative/convective heat flux from the exhaust gas were applied as boundary conditions, while the chemical ablation of the material surface is modeled with algebraic equations. Test SRM with thermocouples was solved for a validation purpose. The results showed that predicted temperatures have identical trends and values compared to the experimental values. And an error of predicted thermal destruction depth was around 0.1 mm.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.10
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• pp.1526-1533
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• 2004

The needs of walking assistant device such as the Ankle Foot Orthosis (A.F.O) are getting greater than before. However, most of the A.F.O are generally imported rather than domestic manufacturing. The major reason of high import reliability is the rack of impact properties of domestic commercial products. Therefore, this research is going to focus on the evaluation of impact properties of the A.F.O which has the high import reliability. Unfortunately, these kinds of researches are not performed sufficiently. This research is going to evaluate impact energy behavior in composite materials such as the glass/epoxy (S-glass, [0/90]sub 2S/) and the aramid/epoxy (Kevlar-29, woven type, 8 ply) of ankle foot orthosis. The approach methods were as follows. 1) The history of impact load and impact energy due to the various velocities. 2) Relationship between the deflection and damage shape according to the impact velocities. 3) The behavior of absorbed energy and residual strength rate due to the various impact velocities.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.2
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• pp.147-156
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• 2016

In this paper, optimal designs of bicycle frame were studied for weight reduction of bicycle using carbon-fiber-reinforced plastic (CFRP), glass-fiber-reinforced plastic (GFRP) and Kevlar-fiber-reinforced plastic (KFRP), respectively. Based on the anisotropic properties of FRP material, stacking angle and thickness optimization were performed under the safety reference of European committee for standardization (CEN) to ensure the stability of bicycle frame. Finally, performances of FRP bicycle frame was evaluated by digital logic method based on the optimized results of weight, strength properties and cost. Then, the optimized bicycle frame composed of each FRPs were evaluated and ranked by total performance values.

• Steel and Composite Structures
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• v.26 no.4
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• pp.473-484
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• 2018

Free vibration of cross-ply laminated plates using a higher-order shear deformation theory is studied. The arbitrary number of layers is oriented in symmetric and anti-symmetric manners. The plate kinematics are based on higher-order shear deformation theory (HSDT) and the vibrational behaviour of multi-layered plates are analysed under simply supported boundary conditions. The differential equations are obtained in terms of displacement and rotational functions by substituting the stress-strain relations and strain-displacement relations in the governing equations and separable method is adopted for these functions to get a set of ordinary differential equations in term of single variable, which are coupled. These displacement and rotational functions are approximated using cubic and quantic splines which results in to the system of algebraic equations with unknown spline coefficients. Incurring the boundary conditions with the algebraic equations, a generalized eigen value problem is obtained. This eigen value problem is solved numerically to find the eigen frequency parameter and associated eigenvectors which are the spline coefficients.The material properties of Kevlar-49/epoxy, Graphite/Epoxy and E-glass epoxy are used to show the parametric effects of the plates aspect ratio, side-to-thickness ratio, stacking sequence, number of lamina and ply orientations on the frequency parameter of the plate. The current results are verified with those results obtained in the previous work and the new results are presented in tables and graphs.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.5
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• pp.448-455
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• 2018

Glass wool is an eco-friendly materials that is manufactured through a continuous process by processing waste glass. This materials is low cost compared with another materials and has excellent thermal conductivity. For this reason, glass wool is installed as insulation system for LNG carriers and as insulation of building wall as well as various industries. The mechanism of insulation of glass wool is the conduction of the wool itself and convection by space between fibers. Therefore, in order to develop the enhanced thermal conductivity of glass wool is necessary to reduce its own conduction or to insert additional material after manufacturing as well as prevent convection. In this respect, many researchers have been actively studying to decrease thermal conductivity of polyurethane foam using by inserted glass wool or change the chemical component of glass wool. However, many research are aiming reduction of glass wool itself. This study focus on post-processing and inserted different materials; silica-aerogel, kevlar fiber 1mm, 6mm and glass bubble. Experimental results show that the thermal conductivity almost decreases with the addiction of glass bubble and silica aerogel.

• Journal of Aerospace System Engineering
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• v.14 no.3
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• pp.10-16
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• 2020

We propose a capture mechanism based on the principles of fishing nets that can be mounted on the drone using cable. The gripper mechanism, mainly proposed for the drone is heavy, and is limited to catch standardized objects. In contrast, the proposed capture device in this paper is light, flexible, and can capture various types of objects from a long distance. The theoretical relationships between cables and mechanisms were analyzed. Finally, the capture device was designed and manufactured to be installed in the drone (DJI S900) to conduct capturing experiments for various objects and verify the validity.

• Composites Research
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• v.32 no.5
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• pp.290-295
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• 2019

In the present study, composite insulation mat was reinforced over polyurethane foam (PUF) to improve the thermal performance and impact resistance of the PUF applied to the liquefied natural gas carrier insulation system. The composite insulation mat used Kevlar, aerogel, and cryogel composite mat that can be applied in a cryogenic environment. The thermal conductivity was measured at $20^{\circ}C$ to investigate the thermal performance, and the drop impact test was carried out under impact energy of 30 J at $20^{\circ}C$, $-163^{\circ}C$ to investigate the impact resistance. The measured thermal performance was compared with neat PUF through effective thermal conductivity theoretical value. The shock resistance was evaluated of contact force, contact time, and absorb energy. In experimental results, cryogel composite mat was the best performance in terms of thermal performance, and aerogel composite mat was the best performance in terms of impact resistance.