• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.560-563
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• 2008

A condensed model is proposed for the simulation of forming of sandwich sheet with pyramid core. A corresponding finite element analysis for L-type bending is carried out to prove the accuracy and the effectiveness. Simulation results are compared with those of experiment. Deformation shape and post-buckling behavior by simulation are in good agreement with those of experiment for the considerable range of deformation. From the comparison of force-displacement curve, it is shown that the proposed model shows good prediction of the forming force compared to the experiment. Thus, the effectiveness of the proposed method is sufficiently demonstrated.

• Journal of the Korean Wood Science and Technology
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• v.18 no.4
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• pp.26-40
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• 1990

The plane trees(Platanus occidentalis L.) have been grown in Korea very widely as ornamental garden or street trees but they have not been used as manufacturing materials The proportion of imported wood has been now over 85% of raw materials needed in the wood industry, and therefore, many of studies on the substitution of domestic wood for imported wood and on the increasing the utilization rate of domestic species have been attempted and considered as very important projects to solve. From a this point of view, this study was carried out to investigate solid wood bending properties of plane trees and then to develop their end-uses, and the size of specimens tested was $15\times15\times350mm$ for steaming treatment and they were dried to $15\pm1%$ before bending. The results obtained were as follows: 1. The optimum conditions for solid wood bending processing of Platanus occidentalis are showed in Table 7. 2. The minimum solid-bending radii of Platanus occidentalis were 40mm in steaming treatment. 3. The effect of knots, diagonal grain and decay on the degradation of bending processing properties were very severe. 4. The bending stress was setted successfully through $80^{\circ}C$-15hrs drying after bending and the spring back for 24hr-exposing time was only about 1%.

• Journal of Korean Neurosurgical Society
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• v.46 no.2
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• pp.144-151
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• 2009

Objective: To compare two testing protocols for evaluating range of motion (ROM) changes in the preloaded cadaveric spines implanted with a mobile core type Charite$^{TM}$ lumbar artificial disc. Methods: Using five human cadaveric lumbosacral spines (L2-S2), baseline ROMs were measured with a bending moment of 8 Nm for all motion modes (flexion/extension, lateral bending, and axial rotation) in intact spine. The ROM was tracked using a video-based motion-capturing system. After the Charite$^{TM}$ disc was implanted at the L4-L5 level, the measurement was repeated using two different methods: 1) loading up to 8 Nm with the compressive follower preload as in testing the intact spine (Load control protocol), 2) loading in displacement control until the total ROM of L2-S2 matches that when the intact spine was loaded under load control (Hybrid protocol). The comparison between the data of each protocol was performed. Results: The ROMs of the L4-L5 arthroplasty level were increased in all test modalities (p < 0.05 in bending and rotation) under both load and hybrid protocols. At the adjacent segments, the ROMs were increased in all modes except flexion under load control protocol. Under hybrid protocol, the adjacent segments demonstrated decreased ROMs in all modalities except extension at the inferior segment. Statistical significance between load and hybrid protocols was observed during bending and rotation at the operative and adjacent levels (p< 0.05). Conclusion: In hybrid protocol, the Charite$^{TM}$ disc provided a relatively better restoration of ROM, than in the load control protocol, reproducing clinical observations in terms of motion following surgery.

• Journal of the Korean Wood Science and Technology
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• v.43 no.3
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• pp.287-294
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• 2015

Relationship between growth rate and wood quality was investigated by mechanical properties with Alnus glutinosa L. (24 years old) from 4 different origins of seeds (Bulgary, Italy, United Kingdom and Yugoslavia). Compression strength was in the range of $231{\sim}326kgf/cm^2$, and there was some differences among different origins of seed. Wood cultivated from the seeds of Italy, United Kingdom, and Bulgary showed higher growth rate and had lower compression strength and compression young's modulus. Wood from Yugoslavia seed had the fastest growth rate with higher strength than other three origins of seed. Bending strength was in the range of $426{\sim}727kgf/cm^2$, and there was some differences among the origin of seed. Higher growth rate wood showed higher bending strength and young's modulus than other woods. Trees cultivated from Yugoslavia seed had two times in diameter than other different origins of seeds, also have compressive strength, bending strength than other origins, which can be recommended as best cultivar in Alnus glutinosa L.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.2
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• pp.169-177
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• 2011

In this paper, the natural frequency of a cracked cantilever L-beams with a coupled bending and torsional vibrations is investigate by theory and experiment. In addition, a method for detection of crack in a cantilever L-beams is presented based on natural frequency measurements. The governing differential equations of a cracked L-beam are derived via Hamilton's principle. The two coupled governing differential equations are reduced to one sixth order ordinary differential equation in terms of the flexural displacement. Futher, the dynamic transfer matrix method is used for calculation of a exact natural frequencies of L-beams. The crack is assumed to be in the first mode of fracture and to be always opened during vibrations. In this study, the differences between the actual and predicted positions and sizes of crack are less than about 10 % and 39.5 % respectively.

• Journal of the Korean Wood Science and Technology
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• v.32 no.3
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• pp.59-65
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• 2004

This paper reports the mechanical properties of bending, compression and hardness of woodceramics manufactured at different carbonizing temperatures (600℃, 800℃, 1000℃, 1200℃ and 1500℃) in a vacuum sintering furnace using sawdust boards of Pinus densiflora, Pinus koraiensis and Larix kaemferi. The highest values of bending MOR (MOR_b) were 104 kgf/cm² (1200℃), 91 kgf/cm² (1500℃) and 86 kgf/cm² (1500℃), the highest values of compression strength were 152 kgf/cm²(1200℃)), 160 kgf/cm²(1000℃) and 189 kgf/cm²(1000℃), the highest values of hardness were 2.00 kgf/mm²(800℃), 2.01 kgf/mm² (1200℃) and 2.28 kgf/mm² (1000℃) in P. densifora, L. kaemferi and P. koraiensis, respectively. The carbonizing temperature of 600℃ was not proper to the mechanical properties for three kinds of sawdust boards and the highest values of mechanical properties were different from the kinds of mechanical properties and species of sawdust boards. Therefore, it is necessary to manufacture woodceramics at a proper temperature for particular species of sawdust boards to obtain good mechanical properties.

• Journal of the Korean Society of Clothing and Textiles
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• v.20 no.6
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• pp.1116-1124
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• 1996

The factors to presume the shapes of bending and draping were examined in this study, by applying the similar phenomenon and theory of analysis. The findings were as followings: 1. The value of deflection angle (f) of deflection curve were almost consistent with those of K number and the shapes of deflection curve were congruent, under the condition of that the values of EI/w are almost similar and the lengths of samples are consistent. 2. The values of drape area, drape coefficient, mean of deflection angle, and $\pi$ number were consistently estimated and the shapes of drape were almost the same, under the condition of that the values of EI/w are similar and the diameter of samples are consistent. 3. In using the samples with different values of EI/w, scale factor, kl, was obtained from the formula, the shapes of bending of the referent samples and compsactive smaples was geometrically similar, which the lengths of samples were 1,1'and were satisfied with the formula, hi: L'11, and their $\pi$ number were also consistent. 4. In applying the samples with different values of Rllw, scale factor (kl) was obtained and then, when semidiameter of samples was adjusted to be satisfied with the formula, k1=L/L, the shapes of draping of referent samples and comparative samples were geometrically similar. Furthermore, their $\pi$ number was also consistent. 5. The shares of bending and draping could be changed in terms of three factors such as the lengths of samples, bending ridigity, and weigths per unit area. $\pi$ number was obtained from theory of similar phenomenon, which was index to presume shapes of bending and the shapes of draping getting from the three factors.

• Transactions of Materials Processing
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• v.23 no.7
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• pp.405-412
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• 2014

As a major type of heat exchanger, the steam generator (SG) produces steam from heat energy of a nuclear power plant reactor. The steam produced by the steam generator flows into a turbine, and plays an important role in electric power generation. The heat transfer tubes in the steam generator consist of approximately 10,000 U-shaped tubes, which perform a structural role and act as thermal boundaries. The heat transfer tubes conduct the thermal energy between the primary coolant (about $320^{\circ}C$, $157kgf/cm^2$) obtained from the reactor and the secondary coolant (about $260^{\circ}C$, $60kgf/cm^2$) as part of the secondary system. Recently, the heat transfer tubes in the steam generator of the pressurized water reactor (PWR) are primarily produced from Alloy 600 and Alloy 690 seamless tubes. As a pilot study to find process parameters for the cold U-bending process using rotary draw bending, numerical and experimental investigations were conducted to produce U-shaped tubes from long straight SUS304L seamless tubes. 3D finite element simulations were run using ABAQUS Explicit with consideration of the elastic recovery. The process parameters studied were the angular speed, the operation period and the bending angle. Experimental verifications were conducted to insure the suitability of the final U-shaped configurations with respect to both ovality and wall thickness.

• Journal of the Korean Wood Science and Technology
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• v.23 no.3
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• pp.73-82
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• 1995

Black locust trees(Robinia pseudo-acacia L.) are growing widely in Korea and have been used to get honey and animal feed, but they have seldom been used as manufacturing materials. This study was carried out to evaluate the possibility of using black locust as bent-wood furniture materials. Softening methods were steaming and micro-wave heating. The specimens of 15${\times}$15${\times}$350mm were all air-dried. For softening, specimens were steamed at 100$^{\circ}C$ for 7 min, or microwave heated for 35 seconds. It is known that microwave heating softens wood much faster than steaming. The bending processing conditions are showed in Table 7. The minimum solid-bending radii of black locust were 40mm for steaming and 150mm for micro-wave heating, respectively. In conclusion the steamed black locust, showed very good solid bending properties, but the bending properties of micro-wave heated black locust were not sufficient for bent-wood furniture.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.9 no.6
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• pp.78-86
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• 2010

This paper aims to investigate the natural frequency of a cracked cantilever L-beams with a coupled bending and torsional vibrations. In addition, a theoretical method for detection of the crack position and size in a cantilever L-beams is presented based on natural frequencies. Based on the Euler-Bernoulli beam theory, the equation of motion is derived by using extended Hamilton's Principle. The dynamic transfer matrix method is used for calculation of a exact natural frequencies of L-beams. In order to detect the crack of L-beams, the effect of spring coefficients for bending moment and torsional force is included. In this study, the differences between the actual data and predicted positions and sizes of crack are less than 0.5% and 6.7% respectively.