• Journal of the Korea Concrete Institute
• /
• v.25 no.2
• /
• pp.187-194
• /
• 2013

Fiber reinforced polymer (FRP) has been gathering interest from designers and engineers for its possible usage as a replacement reinforcement of a steel reinforcing bar due to its advantageous characteristics such as high tensile strength, non-corrosive material, etc. Since it is manufactured with various contents ratios, fiber types, and shapes without any general specification, test results for concrete members reinforced with these FRP reinforcing bars could not be systematically used. Moreover, since investigations for FRP reinforced members have mainly focused on short-term behavior, the purpose of this study is to evaluate long-term behaviors of glass FRP (GFRP) reinforcing bar and concrete beams reinforced with GFRP. In this paper, test results of tensile and bond performance of GFRP reinforcing bar and creep behavior are presented. In the creep tests, results showed that 100 years of service time can be secured when sustained load level is below 55% of tensile strength of GFRP reinforcing bar. A modification factor of 0.73 used to calculate long-term deflection of GFRP reinforced beams was acquired from the creep tests for GFRP reinforced concrete beams. It is expected that these test results would give more useful information for design of FRP reinforced members.

• Composites Research
• /
• v.34 no.4
• /
• pp.241-248
• /
• 2021

As the electric vehicle market grows, there is an issue of light weight vehicles to increase battery efficiency. Therefore, it is going to replace the battery module cover that protects the battery module of electric vehicles with high strength/high heat-resistant polymer composite material which has lighter weight from existing aluminum materials. It also aims to respond to the early electric vehicle market where technology changes quickly by combining 3D printing technology that is advantageous for small production of multiple varieties without restrictions on complex shapes. Based on the composite material mechanics, the critical length of glass fibers in short glass fiber (GF)/polycarbonate (PC) composite materials manufactured through extruder was derived as 453.87 ㎛, and the side feeding method was adopted to improve the residual fiber length from 365.87 ㎛ and to increase a dispersibility. Thus, the optimal properties of tensile strength 135 MPa and Young's modulus 7.8 MPa were implemented as GF/PC composite materials containing 30 wt% of GF. In addition, the filament extrusion conditions (temperature, extrusion speed) were optimized to meet the commercial filament specification of 1.75 mm thickness and 0.05 mm standard deviation. Through manufactured filaments, 3D printing process conditions (temperature, printing speed) were optimized by multi-optimization that minimize porosity, maximize tensile strength, and printing speed to increase the productivity. Through this procedure, tensile strength and elastic modulus were improved 11%, 56% respectively. Also, by post-processing, tensile strength and Young's modulus were improved 5%, 18% respectively. Lastly, using the FEA (finite element analysis) technique, the structure of the battery module cover was optimized to meet the mechanical shock test criteria of the electric vehicle battery module cover (ISO-12405), and it is satisfied the battery cover mechanical shock test while achieving 37% lighter weight compared to aluminum battery module cover. Based on this research, it is expected that 3D printing technology of polymer composite materials can be used in various fields in the future.

• The Research Journal of the Costume Culture
• /
• v.3 no.2
• /
• pp.241-260
• /
• 1995

The Maori's traditional clothing materials, basic forms of dress, and the pattern and technique of tatoo were examined in the present study in order to deepen the appreciation of the cultural heritage of the Maori. The research method employed was the analysis of written materials. And a fild-trip was also made for the study. The study was limitted to the traditional culture of body adornment of the Maori including the clothing which is preserved and practicing by them at the present day, and the origin and the process of the historical development of those are not included in the scope of the present study. Followings are the results of the study: (1) By far the most widely used fiber for Maori clothing is abtained from what is commonly called New Zealand Flax. The fiber of kiekie(Freycinetia baueriana) and cabbage trees(Cordyline spp.) may also be used. The strong, long-lasting fiber of toi(cordyline indivisa) is used for a prestige warrior's cloak. Flat strips of ti kauka(Cordyline australi) are also used as thatch on rain cloaks. (2) Regardless of technique used, Maori weaving is always worked horizontally from left to right. Traditionally the work was suspended between two upright turuturu or weaving sticks. As the work progressed a second pair of uprights was used to keep the work off the ground. These uprights were moved forward as required. Because the weaver sat on the ground, the working edge was kept at a height that was comfortable to reach. No weaving tools are used, the wefts(aho) being manipulated by the fingers. The two main Maori weaving techniques are whatu aho patahi(single-pair twining) and whatu aho rua(double-pair twining). (3) The Maori wore two basic garments - a waist met and a cloak. The cloth of commoners were of plain manufacture, while those of people of rank were superior, sometimes being decorated with feather or dyed tags and decorated borders. Children ran more-or-less naked until puberty, being dressed only for special events. Some working dress consisted of nothing more than belts with leaves thrust under them. Chiefs and commoners usually went barefoot, using rough sandals on journeys over rough country (4) The adornment of men and women of rank was an important matter of tribal concern as it was in chiefly persons that prestige of the group was centred, The durable items of Maori persons adornment were either worn or carried. Ornaments of various kinds were draped about the neck or suspended from pierced earlobes. Combs decorated the head. Personal decorations not only enhanced the appearance of men and women, but many had protective magical function. The most evident personal ornament was the hei-tiki made of jade or other material. Maori weapons were treasured by their owners. They served on bottle and were also personal regalia. A man of rank was not fully dressed without a weapon in hand. Also weapons were essential to effective oratory. (5) No man or woman of rank went without some tattoo adornment except in extremely rare instances when a person was too sacred to have any blood shed. The untattooed were marked as beeing commoners of no social standing. This indelible mark of rank was begun, with appropriate rite and ritual, at puberty. And tattoo marked the person as being of a marriageable age. Maori tattoo was unlike most traditional tattoo in that its main line were 'engraved' on the face with deep cuts made by miniature bone chisels. The fill-in areas were not tattooed with cuts but with the multiple pricks of small bone 'combs' that only lightly penetrated the skin surface. The instrument of tattoo consisted of small pots of pumice or wood into which was placed a wetted black pigment made from burnt kauri gum, burnt vegetable caterpillars or other sooty materials. A bird bone chisel or comb set at right angles on a short wooden handle was dipped into the gigment, that a rod or stick was used to tap head of this miniature adze, causing penetration of the skin surface. Black pigment lodged under the skin took on a bluish tinge. A full made facial tattoo consisted of major spirals with smaller spirals on each side of the nose and sweeping curved lines radiating out from between the brows over the forehead and from the nose to the chin. The major patterns were cut deep, while the secondary koru patterns were lightly pricked into the skin.

• Journal of the Korean Chemical Society
• /
• v.37 no.8
• /
• pp.765-772
• /
• 1993

Two-dimensional potassium tetratitanate ($K_2Ti_4O_9$) and three-dimensional potassium hexatitanate ($K_2Ti_6O_{13}$) fibers have been prepared by the combined method consisting of the flux melting (1150$^{\circ}C$)-slow cooling (cooling rate = 5$^{\circ}C$/h) process from the starting raw materials of $K_2CO_3$, and $TiO_2$ with the flux of $K_2MoO_4$. It was found that the fiber growth reaction is strongly dependent upon the mole ratio of flux (F) to raw material (R), which is 7 : 3 (F : R) as for the optimum growth condition. Relatively long fibers (average length ${\thickapprox}$ 4 mm) with a mixture of $K_2Ti_4O_9$ (major) and $K_2Ti_6O_{13}$ (minor) could be obtained when the reaction was carried out for the $K_2MoO_4-$K_2O{\cdot}4TiO_2$ (F : R = 7 : 3) system, but for the $K_2$MoO_4$-$K_2O{\cdot}6TiO_2$ (F : R = 7: 3) one, only the short fibers with ${\thickapprox}$ 2 mm long could be grown as the mixed phase of $K_2Ti_6O_{13}$ and $K_2Ti_4O_9$.