• Structural Engineering and Mechanics
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• 제49권2호
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• pp.273-283
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• 2014

According to deformation features of pre-twisted bar, its elastic bending and torsion buckling equation is developed in the paper. The equation indicates that the bending buckling deformations in two main bending directions are coupled with each other, bending and twist buckling deformations are coupled with each other as well. However, for pre-twisted bar with dual-axis symmetry cross-section, bending buckling deformations are independent to the twist buckling deformation. The research indicates that the elastic torsion buckling load is not related to the pre-twisted angle, and equals to the torsion buckling load of the straight bar. Finite element analysis to pre-twisted bar with different pre-twisted angle is performed, the prediction shows that the assumption of a plane elastic bending buckling deformation curve proposed in previous literature (Shadnam and Abbasnia 2002) may not be accurate, and the curve deviates more from a plane with increasing of the pre-twisting angle. Finally, the parameters analysis is carried out to obtain the relationships between elastic bending buckling critical capacity, the effect of different pre-twisted angles and bending rigidity ratios are studied. The numerical results show that the existence of the pre-twisted angle leads to "resistance" effect of the stronger axis on buckling deformation, and enhances the elastic bending buckling critical capacity. It is noted that the "resistance" is getting stronger and the elastic buckling capacity is higher as the cross section bending rigidity ratio increases.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2000년도 추계학술대회논문집 - 한국공작기계학회
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• pp.255-261
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• 2000

Tube bending is one of the conventional manufacturing process. Recently, tube bending was highlighted in automotive industry by hydroforming. Tube hydroforming process is divided into pre-bending process and hydroforming process. It's initial state is very important in die cavity of first hydroforming process. So tube bending is important factor of the hydroforming process. In this paper, two pre-bending simulations, by a rotary draw bending machine and a bend die. This paper presents the simulation results in pre-bending process that is used to form an automotive part, tie-bar.

• Journal of Welding and Joining
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• 제33권2호
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• pp.62-68
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• 2015

This study investigates the appropriate range of reverse bending load for the CTOD test of thick weld by observing improvement of pre-crack shape and determination of the limit applicable load. In order to do it, the effect of the amount of the reverse bending load on the maximum deviation of the pre-crack length was investigated by the extensive tests, and the variation of plastic zone size in way of the crack tip under reverse bending load were evaluated by FEA. With the results obtained by the experiments and FEA, the proper range of reverse bending load was suggested. The effectiveness of the reverse bending method was verified by examining the pre-crack straightness after CTOD tests of thick weld specimens with various thickness and strength.

• 대한기계학회논문집
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• 제18권5호
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• pp.1144-1149
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• 1994

Damage caused in CFRP laminates by low energy impact of steel ball are investigated ultrasonically. Two types of laminated specimens having different stacking sequence are used as a target material. The effects of pre-bending on the behaviors of impact damage are specifically discussed. The initiation and progagation behaviors of delamination were largely dependent upon the bending rigidity of each specimen. Specimen C having higher bending rigidity produced larger delamination damage than the Specimen D having relatively low bending rigidity, however it was little for the Specimen C. Application of pre-bending increased the apparent bending rigidity of target during impacting, it produced delamination at lower impact energy level compared to the case of no preload.

• 소성∙가공
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• 제26권1호
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• pp.41-47
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• 2017

Cyclic behavior of advanced high strength steel sheets was measured using an inverse-optimization approach with pre-straining and bending. First, tensile specimens were pre-strained, and three-point bending was conducted for the pre-strained specimens. By using the inverse finite element optimization, the combined isotropic-kinematic hardening parameters that minimize the error between the measured and predicted bending force-displacement curves. The measured cyclic behavior agreed well with the cyclic behavior measured by sheet tension-compression test, which confirms the validity of the measuring procedure based on inverse optimization.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.244-247
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• 2009

Hydroformed parts have higher dimensional accuracy, structural strength, and dimensional repeatability. Particularly in the automotive industry, manufacturing of parts with complex shapes from tubular materials sometimes requires one or more pre-forming operations such as bending before the hydroforming process. The pre-bending process is an important factor for successful hydroforming in the case where the perimeter of the blank is nearly the same as that of final product. The bendability of a tube depends on the parameters such as the bending radius, variation of the diameter, thickness, hardness. This study shows the analysis of bending through the stainless steel tubes bent to rotary draw bending machine.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 춘계학술대회 논문집
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• pp.874-877
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• 2000

Pre-coated sheet materials are a cost-effective and environmentally attractive alternative to conventional sheet materials coated after forming. At present but the high scratch sensitivity of coating used for pre-coated metal sheet is a major limitation to use of these materials. Because of high scratch sensitivity, products made by pre-coated metal sheet are not formed by conventional design method. This study has been performed to investigate scratch characteristic of non-vinyl pre-coated metal (PCM) sheet. Using the simple U-bending test equipment, three non-vinyls PCM's were tested. This paper provides the results of bending tests showing the influence of sheet surface texture, tool material and process conditions. It was found that the influence of punch, die clearance and tool material had an effect upon the scratch characteristic.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2001년도 추계학술대회(한국공작기계학회)
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• pp.85-90
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• 2001

Recent general Press brake has many problems in cutting high accurate products in the progress of industry. Previous hand-operated press brake needs many pre-processing works to adjust bending ang1e and marking-off works to calculate bending length. Also, the hand-operating work makes many geometric errors and has difficulty for variety-mass production. To solve these problems, this paper proposes Computer Numerical Control (CNC) general press brake and development of servo-control system based on database for reduction of geometric errors and pre-processing work time and high accuracy bending work.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.71-74
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• 2005

In manufacturing automotive parts, such as engine cradles, frame rails, subframes, cross-members, and other parts from circular tubes, pre-bending and pre-forming operations are often required prior to the subsequent tubular hydroforming process. During some pre-forming operations, the cross section of a bent circular tube is crushed into an oval-like shape to ensure proper geometry and sufficient clearance in the hydroforming dies. For such applications, the use of oval Instead of circular tubes could be an effective means of eliminating the pre-forming step. The oval tube could also be produced with less thinning and with less strain on the outside of the bend when controlled by a booster system without the use of mandrel. Hence, the understanding of the issues that occur in the bending of oval tubes is worthy of Investigation. This paper presents parametric studies on the bending of oval tubes without a mandrel. The finite element modeling technique is used to examine the deformation characteristics for both circular and oval tubes. In the simulations, the bending process parameters of bend radius, aspect ratio of the tube ovalness, and tube wall thickness are varied. Observations are made to obtain a hoop-buckle limit diagram in terms of a non-dimensional shape degradation factor. Suggestions based upon developed criteria are made on the acceptability of bend tubes suitable for hydroforming applications without the need ofa pre-forming step or the used of a mandrel.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 춘계학술대회논문집
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• pp.262-265
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• 2003

In the present study, subframe was developed using hydroforming technology. The manufacturing process for subframe consists of tube bending, pre-forming and hydroforming. The effects of bending process for manufacturing hydroformed subframe were researched. And the variables of bending process were studied by FEM simulation. The bending method is rotary draw bending that is the most popular, cost-effective bending method for thin walled tubes.