• Composites Research
• /
• v.16 no.2
• /
• pp.18-25
• /
• 2003

The tensile properties of short nylon6 fiber reinforced NR and SBR have been investigated as functions of fiber aspect ratio(AR), diameter ratio(DR), interphase condition, and fiber content. The tensile strength increased with increasing fiber AR(20 min.) and good interphase conditions. The short-fiber(DR=3 and AR=20 min.) reinforced SBR did not show the dilution effect for all interrhase conditions. And the short-fiber(DR=3 and AR=20min.) reinforced NR did not show the dilution effect except for the no-coating. The tensile moduli were significantly improved due to fiber AR. fiber content, and good interphase at same DR. The better interphase condition showed the higher pull-out force at same DR. Also, the stress analysis near the fiber end carried out using axisymmetric FEA to be convinced of the reinforcing mechanism. It is found that the fiber AR, interphase and DR have an important effect on tensile properties.

• Composites Research
• /
• v.16 no.2
• /
• pp.33-40
• /
• 2003

In order to overcome one of the most pronounced shortcomings of conventional laminated composites, such as the low damage tolerance due to delamination, the thermoplastic materials and 3D (three-dimensional) preforms have been utilized in the manufacture of composite materials. From the newly developed process termed as the co-braiding, hybrid yarns of the thermoplastic fibers (PEEK) and reinforcing fibers (carbon) have been fabricated. In order to further enhance the delamination suppression, through thickness fibers have been introduced by way of 3D weaving technique in the fabrication of textile preforms. The preforms have been thermoformed to make composite materials. Complete impregnation of the PEEK into the carbon fiber bundles has been confirmed. For the comparison of mechanical performance of 3D woven composites, quasi-isotropic laminates using APC-2/AS4 tapes have been fabricated. Tensile and compressive properties of both the composites have been determined. Furthermore. the open hole, impact and CAI(Compression After Impact) tests were also carried out to assess the applicability of 3D woven textile reinforced thermoplastic composites in aerospace structures.

• Composites Research
• /
• v.13 no.6
• /
• pp.39-46
• /
• 2000

Electrical discharge machining (EDM) cuts metal by discharging electric current across a thin gap between tool and workpiece. Electrical discharge wire cutting, a special form of EDM, uses a continuously moving conductive wire as an electrode, and is widely used for the manufacture of punches, dies and stripper plates. In the wire cutting process, the moving wire is usually supported by cantilever arm and wire guides. As the wire traveling speed has been increased in recent years to improve productivity, the vibration of the cantilever arm occurs, which reduces the positional accuracy of the machine. Therefore, the design and manufacture of the cantilever arm with high dynamic characteristics have become important as the machining speed increases. In this paper, the cantilever arm for guiding the moving wire was designed and manufactured using carbon fiber epoxy composite in order to improve the static and dynamic characteristics. Specimens for the composite cantilever arm were manufactured and tested to investigate the effect of the number of reinforcing plies and length fitted to steel flange on the load capacity. Also, the finite element analysis using layer and contact elements was performed to compare the calculated results with the experimental ones. From the results, the prototype of the composite cantilever arm for the electrical discharge wire cutting machine was manufactured and the static and dynamic characteristics were compared with those of the conventional steel cantilever arm.

• Composites Research
• /
• v.24 no.5
• /
• pp.34-38
• /
• 2011

Carbon nanotubes (CNTs) have been widely investigated as reinforcements of CNT/polymer nanocomposites to enhance mechanical and electrical properties of polymer matrices since their discovery in the early 90's. Furthermore, the number of studies about incorporating CNTs into carbon fiber reinforced plastics (CFRP) to reinforce their polymer matrices is increasing recently. In this study, single-walled carbon nanotubes (SWNT) were dispersed in epoxy with 0.2 wt.% and 0.5 wt.%. Then, the SWNT/epoxy mixtures were processed to carbon fiber composites by a vacuum assisted resin transfer molding (VARTM) and a wet lay up method. The processed composite samples were tested for the interlaminar shear strength (ILSS). The relationship between the interlaminar shear strengths and processing, and the reinforcement mechanism of carbon nanotubes were investigated. CNT/epoxy nanocomposite specimens showed the increased tensile properties. However, the ILSS of carbon fiber composites was not enhanced by reinforcing the matrix with CNTs because of processing issues caused by increased viscosity of the matrix due to addition of CNTs particularly for a VARTM method.

• Composites Research
• /
• v.26 no.1
• /
• pp.1-6
• /
• 2013

CNT-polypropylene (PP) composites were compounded by solvent dispersion method with uniform dispersion by using twin screw extruder. Damage sensing effects based on conductive carbon nanotubes (CNT) were evaluated to monitor the internal damage of CNT-PP composites using electrical resistance measurement. Mechanical and interfacial properties of CNT-PP composites were investigated and compared with neat PP. The mechanical properties of PP matrix were improved after adding CNT, because of the reinforcing effect of CNT fillers. In order to monitor the internal damage of CNT-PP composite, the change in electrical resistance of the composites was measured under fatigue loading and bending tests. CNT fillers exhibited good sensing under electrical resistance measurements. It is shown that CNT-PP composites with low CNT contents allow identifying critical cyclic loading, which are found to be accompanied with the internal failure.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.32 no.6
• /
• pp.465-473
• /
• 2008

Type II compressed natural gas(CNG) storage vessels for automobiles have been acknowledged for their excellence and have recently become established in local regions. Their supply is not only to automakers in Korea such as Hyundai Motors but they are being increasingly exported. Although the available products have undergone safety evaluations and are certified by an authorized institution they are still short of the optimal design that is possible for such storage vessels. This research investigates the shape and thickness of the dome with the aim of optimizing the type II CNG storage vessels by using a finite element analysis technique. CNG storage vessels can be largely divided into 3 parts namely, the hear part, the cylinder part and the dome part. The head part is designed by means of a hot spinning process and this method is safer than that used in the design of the dome part even though its shape is similar. The thickness of the liners and reinforcing materials was optimized based on the requirements of the cylinder and dome parts. In addition, the shape of the dome, which is most suitable for Type II CNG storage vessels, is proposed by a process of review and analysis of various existing shape, and then conducting a structural stability evaluation to ensure the optimal design plan.

• Korean Journal of Adult Nursing
• /
• v.24 no.2
• /
• pp.171-182
• /
• 2012

Purpose: This study aimed to identify depression and its predictors among Korean community-dwelling elderly with mild cognitive impairment. Methods: Secondary data analyses of the data collected by the "Study on tailored integration program for reinforcing cognitive and physical function of the frail elderly. The study used data from one-to-one interviews using structured questionnaires. The subjects were 346 community-dwelling elderly who visited a healthcare center in Seoul, Korea. A descriptive correlational study design was utilized to explore depression and its predictors including physical factors and psychosocial factors among the elderly with mild cognitive impairment. Data were analyzed using t-test, Pearson's correlation, and hierarchical regression. Results: Mean score of depression was within normal limit $11.61{\pm}6.69$. Somatic symptoms, negative life events (severity), social support were shown as significant predictors of depression. The most influential predictor for depression was somatic symptoms (${\beta}$=.340, $p$ <.001). Conclusion: To prevent and relieve depression in the elderly with mild cognitive impairment, nursing intervention strategies which consider well-balanced physical and psychosocial aspects are needed. In particular, a specific nursing intervention strategy is required to improve physical health of the elderly with mild cognitive impairment.

• Journal of Korean Medical classics
• /
• v.33 no.3
• /
• pp.91-109
• /
• 2020

Objectives : The aim of this paper is to compare the mechanisms of the OP/LB method and the SSD treatment in 『Piweilun』. Methods : Wenbing texts, articles on the OP/LB method, and the 『Piweilun』 was examined for comparison of treatment mechanisms of SSD. Results : The mechanism of the OP/LB method in treating SSD was to treat the Spleen and Stomach separately, to restore the ascending/descending pattern of qi through simultaneous use of pungent and bitter flavors which raises and lowers, respectively. Moreover, the use of medicinals with contrary properties regulate the other's biased nature, and none of the medicinals create dampness. The pungent and bitter flavors play central roles, where the pungent flavor opens and communicates and the bitter flavor clears and lowers. The treatment method of SSD in the 『Piweilun』 treat the Spleen and Stomach together, with a focus on raising and dispersing through upraising yang and reinforcing qi by means of Wind medicinals with pungent and bitter flavors added to sweet and warm medicinals. Conclusions : Owing to the expansion of the OP/LB method concept by modern-contemporary scholars, the potential for treating SSD as can be seen in the 『Piweilun』 with the OP/LB method has emerged. The similarity between the OP/LB method and treatment of SSD in the 『Piweilun』 is that the objective of the formulas is to lower fire heat and communicate qi to help qi movement. This common objective allows for treatment of SSD within Wenbing and those in 『Piweilun』 with the said formulas through appropriate modification fit for each situation.

• Journal of Korean Society of Forest Science
• /
• v.94 no.4 s.161
• /
• pp.281-286
• /
• 2005

Trees enhance slope stability against down slope mass movement through the removal of soil water by transpiration and by the mechanical reinforcement of their roots. To assess the magnitude of this reinforcement on natural slope stability, direct shear tests were made on dry sand reinforced with different array types of roots. Pinus koraiensis was used as root specimens. The peak shear resistance at each normal stress level was measured on the rooted and unrooted soil specimens. Increased soil resistance(${\Delta}S$) by roots was calculated using parameters like internal friction angle and cohesion of tested soil and also evaluated the effects of root array in tested soil. As results, we find that shear resistance increased in tested soil shear box as diameters and arrayed numbers of root specimen increased and cross root array in tested soil had a much greater reinforcing effect than other root arrays. Comparison of traditional root-soil model with experiments showed that simulated reinforce strength by the model was different with those obtained by the experiment due to its linearity.

• Architectural research
• /
• v.20 no.3
• /
• pp.83-92
• /
• 2018

Recently, there has been inter-Korean exchanges are active, in company with an assertive international activity with North Korea and inter-Korean Summits. Thus, there is a growing possibility of Korean reunification. However, when the unification situation occurs, population inflow by North Korean residents will be expected, and it will be necessary to prepare a housing supply strategy. In addition, even if North Koreans are prevented from entering, a plan is necessary to ensure structural safety since most buildings in North Korea are aging and a recent natural disaster occurs frequently. In this research, we will try to present a temporary housing supply strategy and a short-term structural reinforcement plan based on analysis of the standard housing conditions in North Korea. In this research, we represent the analysis result of the existing construction level, supply status and structural performance of North Korea. When we consider the reinforcement period and social costs, a short-term reinforcement plan is recommended rather than the full reinforcement of the aged housing in North Korea. Furthermore, we examine the ways to secure the residential safety of North Koreans through a case study of domestic and overseas temporary residential facilities, until the permanent residential facilities were supplied. According to the analysis, the tent houses were used as a form of relief housing in overseas frequently. However, the tent house is difficult to apply for domestic country with clear seasons due to insulation and heating problems. Therefore, it is appropriate to develop a residential supply strategy as focusing on the temporary housing facilities in assembled or container from, in preparation for the future population inflow.