• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.11
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• pp.319-325
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• 2018

The use of 3D printing (Additive Manufacturing) technology has expanded from initial model production to the mass production of parts in the industrial field based on the continuous research and development of materials and process technology. As a representative polymer material for 3D printing, the polyamide-based material, which is one of the high-strength engineering plastics, is used mainly for manufacturing parts for automobiles because of its light weight and durability. In this study, the specimens were fabricated using Selective Laser Sintering, which has excellent mechanical properties, and the flexural characteristics were analyzed according to the temperature of the two types of polyamide 12 and glass bead reinforced PA12 materials. The test specimens were prepared in the directions of $0^{\circ}$, $45^{\circ}$, and $90^{\circ}$ based on the work platform, and then subjected to a flexural test in three test temperature environments of $-25^{\circ}C$, $25^{\circ}C$, and $60^{\circ}C$. As a result, PA12 had the maximum flexural strength in the direction of $90^{\circ}$ at $-25^{\circ}C$ and $0^{\circ}$ at $25^{\circ}C$ and $60^{\circ}C$. The glass bead-reinforced PA12 exhibited maximum flexural strength values at all test temperatures in the $0^{\circ}$ fabrication direction. The tendency of the flexural strength changes of the two materials was different due to the influence of the plane direction of the lamination layer depending on the type of stress generated in the bending test.

• Steel and Composite Structures
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• v.31 no.4
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• pp.373-385
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• 2019

This paper presents a useful in-plane structural analysis of low-rise blind-bolted composite frames with semi-rigid joints. Analytical models were used to predict the moment-rotation relationship of the composite beam-to-column flush endplate joints that produced accurate and reliable results. The comparisons of the analytical model with test results in terms of the moment-rotation response verified the robustness and reliability of the model. Abaqus software was adopted to conduct frame analysis considering the material and geometrical non-linearities. The flexural behaviour of the composite frames was studied by applying the lateral loads incorporating wind and earthquake actions according to the Australian standards. A wide variety of frames with a varied number of bays and storeys was analysed to determine the bending moment envelopes under different load combinations. The design models were finalized that met the strength and serviceability limit state criteria. The results from the frame analysis suggest that among lateral loads, wind loads are more critical in Australia as compared to the earthquake loads. However, gravity loads alone govern the design as maximum sagging and hogging moments in the frames are produced as a result of the load combination with dead and live loads alone. This study provides a preliminary analysis and general understanding of the behaviour of low rise, semi-continuous frames subjected to lateral load characteristics of wind and earthquake conditions in Australia that can be applied in engineering practice.

• PNF and Movement
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• v.17 no.1
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• pp.41-46
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• 2019

Purpose: Continuous use of a smartphone increases the angle of forward bending of the user's cervical vertebrae, causing pain in the shoulders and back, including the thorax, lumbar region, and vertebrae. Although there are many studies on changes in the cervical spine due to smartphone usage, the changes in the shoulders, thoracolumbar spine, and pelvic have rarely been compared. The purpose of this study is to investigate the change in the spinal segments, shoulders, and pelvic when using a smartphone with both hands while in the standing position. Methods: This study was conducted on 35 adults in their twenties. The selection criteria for the subjects were limited to those in a similar age group, thus excluding posture differences according to age, and to those who did not have specific diseases or pain in the spinal and musculoskeletal system for 12 months prior to the study. In this study, we used a 3D spinal diagnostic imaging system (Back Mapper, Frickenhausen) to compare the changing conditions in each vertebral segment before and during smartphone usage with both hands while in the standing position. Posture differences according to smartphone usage were compared using the paired t-test for the motion of each spinal segment. Results: This study showed that the thoracic and lumbar angle increased posteriorly during smartphone usage (p<0.05). In addition, the anterior rotation angle of the shoulder bone significantly increased, but no significant difference occurred in the pelvic region. Conclusion: Based on the results of this study, smartphone usage with both hands while in the standing position showed that the spine, as a whole, forms a kyphotic curve. Therefore, we propose to present a postural guideline for correct smartphone usage, considering the change in each vertebral segment.

• Steel and Composite Structures
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• v.6 no.6
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• pp.459-477
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• 2006

A theoretical research project is undertaken to develop integrated analysis and design tools for long span composite beams in modern high-rise buildings, and it aims to develop non-linear finite element models for practical design of composite beams. As the first paper in the series, this paper presents the development study as well as the calibration exercise of the proposed finite element models for simply supported composite beams. Other practical issues such as continuous composite beams, the provision of web openings for passage of building services, the partial continuity offered by the connections to columns as well as the behaviour of both unprotected and protected composite beams under fires will be reported separately. In this paper, details of the finite elements and the material models for both steel and reinforced concrete are first described, and finite element studies of composite beams with full details of test data are then presented. It should be noted that in the proposed finite element models, both steel beams and concrete slabs are modelled with two dimensional plane stress elements whose widths are assigned to be equal to the widths of concrete flanges, and the flange widths and the web thicknesses of steel beams as appropriate. Moreover, each shear connector is modelled with one horizontal spring and one vertical spring to simulate its longitudinal shear and pull-out actions based on measured load-slippage curves of push-out tests of shear connectors. The numerical results are then carefully analyzed and compared with the corresponding test results in terms of load mid-span deflection curves as well as load end-slippage curves. Other deformation characteristics of the composite beams such as stress and strain distributions across the composite cross-sections as well as distributions of shear forces and slippages in shear connectors along the beam spans are also examined in details. It is shown that the numerical results of the composite beams compare well with the test data in terms of various load-deformation characteristics along the entire deformation ranges. Hence, the proposed analysis and design tools are considered to be simple and yet effective for composite beams with practical geometrical dimensions and arrangements. Structural engineers are strongly encouraged to employ the models in their practical work to exploit the full advantages offered by composite construction.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.10
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• pp.6977-6984
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• 2015

It is faced with the necessity of multi roll forming process of the ball slide rail which is made by adding the separate manufacturing processes, piercing, bending, trimming, to the roll forming process of a continuous plastic deformation, to improve the quality. However, the vibration and noise of the press machine in this process leads to the quality degradation of slide rail manufactured in this process. In this study, the roll was designed considering the optimal strain rates by the roll forming program with finite element method. And to estimate the static stability of the multi process the Von-Mises stress and deformation on the press was calculated with a structural analysis program. Also, to avoid driving systems in the resonance region their natural frequencies in the 1st and 2nd mode were calculated through the modal analysis. To verify its dynamic stability improvement the magnitudes of noise and vibration in the existing and studied system were compared using a microphone and accelerometers. And the widths and surface roughnesses of the rails which had been produced in the existing and studied process were measured. Therefore, it is known that multi roll forming process is stable in the analytical and experimental study.