Lightweight Structural Members Research Articles

적층구성 변화에 따른 경량화 구조부재의 에너지 흡수 특성

In this study, one type of circular shaped composite tube was used, combined with reinforcing foam and without foam. Furthermore, CFRP (Carbon Fiber Reinforced Plastic) circular member manufactured from CFRP prepreg sheet for lightweight design. CFRP is an anisotropic material which is the most widely adapted lightweight structural member. The crashworthy behavior of circular composite material tubes subjected to static axial compression under same conditions is reported in this paper. The collapse mode during the failure process were observed and analyzed. The behavior of polymeric foams to the tubes crashworthiness were also investigated.

Buckling Behavior of Sinusoidal Web for Composite Wood I-Joist with Elastically Restrained Loaded Edges under Compression

AbstractWood I-joists are efficient and lightweight structural members that are well suited for long-span floor and rafter applications. However, because of the thin-wall nature of the web and relatively low stiffness, local web buckling of the joist is an issue that must be considered. To increase the buckling capacity of these joists, investigators at West Virginia Univ. and Univ. of Idaho developed web panels with a sinusoidal geometry, instead of the flat web panels commonly used for prefabricated I-joists. This study presents analytical modeling, experimental testing, and finite-element (FE) analysis of the local buckling capacities of these sinusoidal web panels under compression. The flanges and web are not rigidly connected; thus, this problem can be described as the instability of a sinusoidal shell with two rotationally restrained loaded edges under compression. Using an energy method, the critical compression buckling stresses were obtained in terms of the elastic rotational restraint stiffness...

대단면 스킨팀버의 휨 성질에 관한 연구

최근 들어 한옥에 대한 수요과 공급이 계속해서 늘고 있다. 이러한 한옥이 가지고 있는 가장 심각한 문제는 과도한 지붕구조의 무게와 이로 인해 늘어날 수밖에 없는 구조부재의 대형화이다. 따라서 겉으로는 대단면 목재 부재이면서 다량의 목질부를 제거하여 무게의 경량화를 이루고 감소하는 강도적 성질은 부재의 하이브리드화를 통해 보충할 수 있는 실대재 대단면 스킨팀버를 제작하였다. 소나무와 낙엽송 두 수종을 사용하여 실대재 스킨팀버를 제작하였다. 두 수종에 대해 정각형 스킨팀버와 원통형 스킨팀버 각각을 제작하여 휨성능을 평가하였다. 가공기계의 정밀도 부족으로 인해 부재에 과도한 손상이 발생하여 의도한 정도의 강도적 성질을 얻지 못하였다. 하지만 가공기계의 정밀도 향상을 도모하고 추가적인 하이브리드 구조체 제작을 첨가한다면 경량의 대단면 구조부재의 생산이 가능할 것으로 판단된다. 본 연구에서 실제 제작한 낙엽송과 소나무 실대재 스킨팀버에서는 수종간의 휨성능 차이는 나타나지 않아 적절히 혼용 가능한 것으로 나타났다. 낙엽송의 MOR 기준에서만 정각형과 원통형간에 성능 차이가 인정되어 구분하여 사용해야 할 필요가 있고 나머지에 있어서는 차이가 인정되지 않아 혼용이 가능하다고 판단되었다. 본 연구의 목적이 어느 정도의 강도를 지닌 경량의 대단면 구조재 개발에 있으므로 목질계 우드세라믹이나 경량철골 등을 이용한 하이브리드 구조체를 개발한다면 한옥이나 실내인테리어재료 그리고 기둥-보 공법의 재료 등으로 활용 가능할 것이다. Recently, the demand and supply on the Hanok have been increased. However, Hanok should be requested larger section of structural members because of excessive roof weight. So, structural skin-timber was manufactured to get a lightweight structural member. The structural skin-timber has exterior shape with larger section but a great volume of wood be removed. The reduced strength of structural skin-timber can be supplemented by hybridizaion of structural member. Japanese larch and Domestic pine were used to manufacture the structural skin-timber. Structural skin-timbers of rectangular shape and cylinder shape were manufactured and tested to evaluate the bending properties. The intended strength property could not be obtained because member had been suffered severe damage by precision deficiency of manufacturing machine. However, if precision of manufacturing machine would be improved and additional hybridizaion of structural skin-timber would be done, lightweight structural member will be able to be manufactured. Structural skin-timber did not showed statistical significancy between two species, so it is possible to use pine mixed with larch. Only MOR of larch showed statistical significancy between rectangular shape and cylinder shape, so it is necessary to use of those as separate things. However, the rest of skin-timber can be judged mixed using because of non statistical significancy. The objective of this study was the development of lightweight larger structural member with relatively strength. If hybrid member of skin-timber could be developed with wood-ceramics, lightweight steel and more, it can be possible to be used as a building material of Hanok, interior material, post & beam construction material and more.

各種断面形状押出形材の回転引き曲げ加工限界

Extruded aluminum alloy sections are advanced materials composed of lightweight structural members. A secondary forming process such as bending is required when these materials are utilized for practical use. Some undesirable deformations such as flattening distortion, wrinkling and splitting occur during the bending process of light gauge tubes. Thus, the working limits for the shape and dimension of such sections are very important in designing lightweight constructions. In this study, a square tube, a square tube with a lateral direction rib, a square tube with a radial direction rib, an asymmetric channel, a hat channel and a channel were used in rotary draw bending with axial tension. Mandrels were selected to match the characteristics of the sections. The working limits for some thickness ratio and materials such as A6061S-O, A6061S-T6, A6063S-O and A6063S-T5 were introduced. This study shows that a working limit that depends on the type of cross section and on thickness ratio, and the application of axial tension to the draw bending of light gauge tubes are very effective in preventing wrinkling in rotary draw bending.

How to Build Flexible Design Automation Systems for Manufacturability Analysis of the Draw Bending of Aluminum Profiles

Manufacturing companies continually need to develop and produce products faster, cheaper, and of better quality to meet requirements from customers and investors. One key factor in meeting these requirements is the efficiency of the product development and the production preparation processes. Design automation is a powerful tool for increasing the efficiency of these two processes. The benefits of automating manufacturability analyses, a part of the production preparation process, are shortened lead time, improved product performance, and ultimately decreased cost. Further, the automation is beneficial as it increases the ability to adapt products to new specifications since production preparations are done in few or in a single step. Extruded sections of aluminum (aluminum profiles) have many advantages, especially for light weight structural members, and are used in many products. Many times a secondary forming process, such as bending, is required when these materials are used. The intention of the work presented in this article has been to investigate how to automate the process of finding manufacturing limits of the rotary draw bending of aluminum profiles with focus on the system architecture needed to make such systems flexible. Finding the forming limits of an aluminum profile is not a trivial task. This is because the limits depend not only on the profile shape but also on the layout of the tool. Hence, simulations have to be done to evaluate different designs. A prototype system was developed to explore what was needed to automate simulation of the rotary draw bending of aluminum profiles, and subsequently, analyze the simulated production outcome with respect to wrinkling and developed length.

In-Plane Load-Deflection Behavior and Buckling of Pressurized Fabric Arches

This study focuses on the in-plane load-deflection and buckling response of pressurized fabric arches of constant circular cross section. These lightweight portable structural members support tents used for temporary medical facilities, disaster-relief shelters, and military applications. A quadratic Timoshenko beam element is developed for materially and geometrically nonlinear analysis based on a virtual work principle that includes work done by internal pressure due to deformation-induced volume changes. The inability of the arch fabric to carry compressive stress is addressed with a nonlinear moment-curvature relationship that captures the effect of fabric tensile stiffness, internal pressure, and axial load. A corotational formulation and cylindrical arc-length solver are used to permit large displacement analysis and the tracking of postbuckling softening response. A convergence study demonstrates the good performance of the element and the solver. Results of laboratory load tests on a 9.5 m-span semicircular inflated fabric arch are presented, and shown to agree well with the model predictions. Parametric studies are conducted to examine the significance of inflation pressure and lateral restraint on arch deflections and buckling under the action of code-specified snow loads. The numerical studies show that the work done by the confined air significantly increases arch load capacity, and that shear deformations of woven fabrics can significantly reduce arch capacity.

Study of Intrusion Bending for Steel Tubes with Thin Wall Thickness

In regard to light-weight structural members for automobiles, attention to hydroforming has been increasing. Intrusion-bending method is well suited to the preliminary bending of hydroformed structural members of automobiles, because straight tubes can be bent into three-dimensional forms by this new method. However, in the case of tubes with a thin wall thickness, wrinkling remains a problem. In this report, application of intrusion bending method to tubes with extremely low ratios of wall thickness to outer diameter (from 1.2 to 1.9%), and whose steel grades are SSPDX, SAFC440R, and SAFC590T was investigated. A summary of this study is as follows. Effects of steel grades and wall thickness ratios on wrinkle formation, eccentricity, and ovality are studied. Relationships between wrinkle generation and gyro movement are investigated.

Investigations on the bearing behaviour and application potential of textile reinforced concrete

At present there is a rising interest of architects and engineers in the application of Textile Reinforced Concrete (TRC) as a construction material. Filigree, self-supporting and ventilated façade systems are state-of-the-art in the application of TRC. In current investigations potentials for light-weight structural members are developed. The required models for a secure design of structural members are deduced within the framework of the research activities in the collaborative research centre 532 at RWTH Aachen University [Collaborative Research Centre 532: Textile Reinforced Concrete–Development of a new technology. RWTH Aachen University, Germany. http://sfb532.rwth-aachen.de]. The article outlines fundamental research results as well as their realisation in first applications.

Model characterization and failure analysis of welded aluminium components including process history

There is currently a high level of interest in automotive and other industries to use aluminium extrusions for lightweight structural members. The preferred joining technology is robot controlled MIG welding to provide a fast, consistent, high-quality weld. The disadvantage, however, is that the high temperature fusion process causes metallurgical transformations adjacent to the weldline in the Heat Affected Zones (HAZ), which significantly reduce mechanical properties and provide lines of weakness. Under crash loading these zones are of special concern and techniques are needed to evaluate their performance. This paper investigates reduced mechanical properties in the HAZ of welded aluminium joints and proposes a failure law suitable for practical crash simulation of automotive structures. The work has necessitated a pragmatic approach in which a compromise is sought between the true representation of the void growth and fracture mechanisms that occur on a micro-scale and the need for a simplified macro-model appropriate for large scale CPU intensive structures. Simulation tools and techniques are also presented that enable the process history of the weld manufacture to be analyzed and results of the HAZ and modified mechanical properties to be mapped to the structural model for crash or failure analysis, thus limiting the need for extensive mechanical testing. Validation studies are presented on notched butt joints and dynamically loaded sectional welded joints.

Evaluation of compressive mechanical properties of Al-foams using electrical conductivity

Al-foam filled composite panels have enormous potential for application as light weight structural members as well as the energy absorber during crushing. In such applications the mechanical properties of foams are of paramount importance. In this study, Al alloy foams of composition Al–3 wt. %Si–2%Cu–2%Mg were produced using powder metallurgical method. Mechanical properties of foams of different density were measured using the uni-axial compression test and the measured properties such as elastic modulus and strength were compared with those of other existing commercial foams. The newly produced (Al–3%Si–2%Cu–2%Mg alloy) foams showed the elastic modulus and strength similar or sometimes higher than those of the other existing commercial foams. The electrical conductivity of the foams was measured and was found to follow a power law relationship, with an exponent value of 1.5, with the relative density. A set of mathematical relationships were deduced between electrical conductivity and various compressive properties of Al-foams with an aim to propose a nondestructive method for obtaining the elastic modulus, the compressive strength and the densification strain of foams using electrical conductivity. The curves obtained from derived relationships fit very well with the experimental results.

６０６３アルミニウム合金チャンネル材の回転引曲げ加工における変形特性

Extruded sections of aluminum have many advantages for lightweight structural members. A secondary forming process, such as bending, is required when these materials are used in these parts. In this paper, we investigated deformation property of tension-side open type 6063 aluminum alloy extruded sections in the rotary draw bending process. A6063S extruded sections having various thickness applied to the workpiece of this experiment. In the rotary draw bending process of these workpieces, undesirable phenomena such as flattening distortion, compression flange wrinkling and web wrinkling arise in the same way as square tube. Flattening distortion can be restrained principally by rigid mandrel and restriction guide for web displacement. Compression flange wrinkling can be restrained by additional axial tension. As a result of this study, it has been shown that applying these restriction tools and additional axial tension are very effective in preventing undesirable deformations. The bend degree H0/R0 reaches 0.24 without any defects in this bending process, the workpiece of A6063S–O with thickness ratio H0/t0 = 26.7.

押出角管の回転引曲げ加工における積層弾性心材の効果

Extruded aluminum alloy sections are advanced materials in use as lightweight structural members. A secondly forming process such as bending is required when these materials are used for structural members of automobiles. It is known that undesirable deformations as wrinkling and split tend to occur easily when some sections having light gauge are formed by the bending process. This report shows the working limit for the draw bending process of square tubes with a laminated elastic mandrel. A6063S and A6061S square tubes having various thickness are applied to this experiment. It is shown that applying laminated elastic mandrels to this draw bending process is very effective in preventing either primary distortion or wrinkling of compression flange and compressive region of webs. In consequence, higher working limit is obtained by this method. On the working conditions of the thickness ratio t0/H0=0.075 or 0.05 of A6063S–O and A6061S–O, the working degree R0/H0 reaches to 2.4 or 4.3 without any defects, where t0 and H0 mean thickness and the height of the tube respectively.