• Transactions of Materials Processing
• /
• v.8 no.3
• /
• pp.221-221
• /
• 1999

Warm deep drawability in a square cup drawing was investigated using a newly developed high-strength steel sheet with retained austenite that was transformed into martensite during formation. For this investigation, six different temperatures between room temperature and 250℃, and five different drawing ratios ranging from 2.2 to 2.6 were considered. The results showed that the maximum drawing force and the drawing depth were affected by the change in temperature, and a more stable thickness strain distribution was observed at elevated temperatures. However, blue shortness occurred at over 200℃. FEM analysis using the LS-DYNA code was used to compare the experimental results with the numerical results for the thickness strain distribution.

• Journal of Welding and Joining
• /
• v.25 no.4
• /
• pp.65-71
• /
• 2007

Laser weldability of the aluminized steel for the full penetration welding will be described in this paper. We focused on the effect of Al coating conditions on weld strength. For these objectives, aluminized steel sheets that have various thickness and coating weight were prepared for laser welding. And then, tensile-shear and hardness test were carried out. At the same time, Al contents in weld after laser welding were analyzed and their correlations with mechanical properties were investigated. Besides, as removing partially coating layer, weldability has been investigated according to the position of coating layer. As a result of this study, tensile-shear strength was decreased with increasing Al contents in weld, and Al of coating layer caused grain growth.

• Journal of the Korea Institute of Building Construction
• /
• v.8 no.5
• /
• pp.43-51
• /
• 2008

This study examines shear capacity performance and structural characteristics of reinforced concrete beam using carbon fiber sheet(CFS), g)ass fiber sheet(GFS), glass fiber steel plate(GSP) and carbon fiber bar CB) which are reinforcing materials for reinforced concrete beam in order to produce similar condition to repair and reinforce actual structure and aims to provide data available In designing and constructing reinforced concrete structures under the structural damage. This study obtains the following conclusions. After considering the shear experiment results. it was indicated that the CB reinforced test object was the best in the shear capacity improvement and ductility capacity as it was contained in the concrete and was all operated, Also, GFS reinforced test object indicated the reduced flexural capacity but good shear capacity. GSP reinforced test object had bigger reinforcing strength than other reinforcing test objects. On the other hand, it showed the lowest reinforcement effect as compared section thickness of reinforced material because it showed the bigger relativity a section thickness of reinforced material. If the adherence to the concrete is improved, it will seem to show bigger reinforcement effect.

• Transactions of Materials Processing
• /
• v.25 no.5
• /
• pp.301-305
• /
• 2016

The manual modification of stamping die has widely been used in order to reduce springback after sheet metal forming. When UHSS (Ultra High Strength Steel) is used in sheet metal forming, the die design considering springback compensation is more difficult because higher strength sheet has more springback. In this study, the optimization method was used in order to design die geometry considering springback compensation after forming of 1.2GPa UHSS. Die geometries were defined as design variables and the springback distance from the die surface was conducted as object function in optimization process. The optimized die geometry considering springback compensation was performed using finite element and optimization analysis. The simulation results such as thickness distribution and springback amount were compared with measured data using 3D optical measurement system (GOM ARGUS, ATOS). And the prediction of springback amount showed a good agreement within test results.

• Journal of the Korean Society for Precision Engineering
• /
• v.29 no.8
• /
• pp.840-844
• /
• 2012

Roll forming process is a sheet metal forming process where the forming occurs with rolls in several steps, often from an undeformed sheet to a product ready to use. And each pair of forming rolls installed in a forming machine operates a particular role in making up the required final cross-section. This process used to many industry manufactures and recently apply to automotive industry. This study, FEM simulation applied bumper reinforcement using SHAPE-RF software and analyzed about total effective strain, longitudinal strain, thickness according to the roll-pass.

• Journal of the Korean Society of Safety
• /
• v.25 no.1
• /
• pp.1-8
• /
• 2010

The tensile and fatigue experiments were conducted with tensile-shear specimens for investigating the strength of adhesive bonded and mechanical press joints of SPCC steel sheet used in the field of the automobile industry. The optimal punch press force was evaluated 50kN for combining epoxy adhesive bonding and mechanical press joining with a diameter of 8.3mm using SPCC sheet with a thickness of 0.8mm. The combining epoxy adhesive bonding and mechanical press joining exhibits the maximum tensile force of 750N. The fatigue strengths of the combination of adhesive bond and mechanical press joint and pure adhesive joint were evaluated 370N and 320N at 106cycles, respectively. These values correspond to 22% and 20% of their maximum tensile forces, respectively. However, the fatigue strength of the combination of adhesive bond and mechanical press joining was much lower than that of pure mechanical press joining.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2001.04a
• /
• pp.138-145
• /
• 2001

This paper presents F.E.M. analysis result about the behavior of R.C. beam repaired with steel plate and fiber sheet. The effect of repairing varies with reinforcement ratio of R.C. beam, plate thickness, numbers of fiber sheet, and repairing length, etc. F.E.M. analysis using a program, DIANA, was carried out taking these factors as parameter in this study. Analysis result shows that repaired R.C. beam behaves differently according to parameters and certain cases imply that repairing is useless or may lay structure in dangerous condition. F.E.M. model considers that interfacial behavior between different two parts of repaired beam is rigid based on an assumption that adhesive failure does not appear before yielding of reinforcement and its analysis shows the result coincides with that of experiment.

• Transactions of Materials Processing
• /
• v.10 no.2
• /
• pp.101-110
• /
• 2001

The thermal problem of press work is classified into two cases. First, the temperature of forming die passively rises due to the heating effect of plastic deformation. The warm forming is the second case in which the external heating is applied to the die and blank holder. So, the purpose of this study is to provide database for the forming characteristics at various temperature conditions. In this study, the tensile test was carried out for the commercial steel sheets such as SCPI and SCP3C with the thickness of 0.7mm and 1.4mm respectively. The tensile strength, total elongation, Lankford value and the flow curve have been obtained at the temperature of $25^{\circ}C$, $50^{\circ}C$, $100^{\circ}C$, $150^{\circ}C$, $200^{\circ}C$, $250^{\circ}C$ and $300^{\circ}C$, respectively. From the results, we can see that both the tensile strength and total elongation decrease as the temperature increases. In the light of anisotropy, the effect of thickness is dominant than the material specs. For the temperature dependency of flow curves, there are only small differences for the work-hardening exponent, and the strength intensity decreases monotonically as temperature increases. The present results we useful as input data for the analysis of sheet metal forming processes with the various temperature conditions.

• Journal of the Korean Society for Precision Engineering
• /
• v.27 no.11
• /
• pp.46-56
• /
• 2010

The present research works investigated into the low velocity impact characteristics of DP 780 high strength steel sheet with 1.7 mm in thickness subjected to free boundary condition using three-dimensional finite element analysis. Finite element analysis was carried out via ABAQUS explicit code. Hyper-elastic model and the damping factor were introduced to improve an accuracy of the FE analysis. An appropriate FE model was obtained via the comparison of the results of the FE analyses and those of the impact tests. The influence of the impact energy and nose diameter of the impact head on the force-deflection curves, impact time, absorption characteristics of the impact energy, deformation behaviours, and stress-strain distributions was quantitatively examined using the results of FE analysis. The results of the FE analysis showed that the absorption rate of impact energy lies in the range of the 70.7-77.5 %. In addition, it was noted that the absorption rate of impact energy decreases when the impact energy increases and the nose diameter of the impact head decreases. The local deformation of the impacted region was rapidly increased when the impact energy was larger than 76.2 J and the nose diameter was 20 mm. A critical impact energy, which occur the instability of the DP780, was estimated using the relationship between the plastic strain and the impact energy. Finally, characteristics of the plastic energy dissipation and the strain energy density were discussed.

• Laser Solutions
• /
• v.9 no.2
• /
• pp.1-9
• /
• 2006

In this paper, we investigated the characteristics of fatigue fracture on TB(Tailored Blank) weldment by comparing the fatigue crack propagation characteristics of base metal with those of TB welded sheet used for vehicle body panels. We also investigated the influence of center crack on the fatigue characteristic of laser weld sheet of same thickness. We conducted an experiment on fatigue crack propagation on the base metal specimen of 1.2mm thickness of cold-rolled metal sheet(SPCSD) and 2.0mm thickness of hot-rolled metal sheet(SAPH440) and 1.2+2.0mm TB specimen. We also made an experiment on fatigue crack propagation on 2.0+2.0mm and 1.2+1.2mm thickness TB specimen which had center crack. The characteristics of fatigue crack growth on the base metal were different from those on 1.2+2.0mm thickness TB specimen. The fatigue crack growth rate of the TB welded specimens is slower in low stress intensity factor range $({\Delta}K)$ region and faster in high${\Delta}K$ region than that of the base metal specimens. The slant crack angle slightly influenced the crack propagation of the TB specimen of 2.0+2.0mm thinkness.