• Transactions of Materials Processing
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• v.13 no.3
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• pp.190-204
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• 2004

The objective of this study is to develop a highly accurate micro tool alignment system applicable to the micro machining technology. In a specific application such as micro hole punching, radial clearance between micro tools is order of a few micron. Under this micron scale tool clearance, accuracy of tool alignment is very important for ensuring hole quality. In the present study, a two-way image acquisition system was developed, which can produce overlapped image of both micro tools that face each other, and applied to the tool alignment in the micro punching. Also, to meet alignment accuracy of tools within $1\mu\textrm{m}$, the cross correlation image processing algorithm was employed. With this system, $25\mu\textrm{m}$ punching tools with $1\mu\textrm{m}$ radial clearance could be accurately aligned.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.151-152
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• 2010

The objective of this study is to propose the new punching shear model for two-way concrete slabs of building structures and bridge decks structures reinforced with FRP or steel rebars. To do this, two evaluating methods are applied here. One is the ratio of test to model and the other is probability analysis with probabilistic uncertainties. In conclusion, it shows that the proposed punching shear model evaluates the tested punching shear strength as conservative with stability and it exhibits better probabilistic characteristics than existing punching shear models.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2002.02a
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• pp.239-244
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• 2002

In this study, we developed the manufacturing technology of micro-hole and micro-shaft for micro punching system using micro electrical discharge machining and micro electro chemical machining. Micro punching dies of tungsten carbide with $55\;{\mu}m\;and\;110\;{\mu}m$ diameter and $250\;{\mu}m$ depth were made by micro electrical discharge machining. The form accuracy and surface roughness of die hole were pretty good and it was shown that the punched hole quality was fine. WC micro-shaft with $30\;{\mu}m$ diameter was made by the multistep micro electro chemical machining. The developed technologies can be effectively used in precision manufacturing of micro punching die and mass production of micro-shaft.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.362-365
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• 2005

The hub hole is usually formed with a flanging process followed by a blanking process of a ]tole. Since the hole is made by blanking, the blanked surface is so rough that the formability in the region is rather poor. The emerging task is to identify the formability of the blanked region in the forming simulation and to relate the criterion to the real forming process by experiments. In this paper, hole expansion tests are carried out with respect to various hole conditions to verify the hole condition effect on the hole expansion ratio. The hole of specimens is made by machining or punching. In the case of punching, two different punching clearances are used for making the hole. From the results of test, fracture mechanism of the hole expansion is explained.

• Journal of Ocean Engineering and Technology
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• v.18 no.1
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• pp.1-6
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• 2004

In this paper, the performance of a wave absorbing system using an inclined punching plate, was investigated. Using the multi-domain boundary element method (BEM), the reflection coefficients of an inclined punching plate were tested with various design parameters, such as inclined angle, porosity, and wave frequencies. To confirm the numerical solutions, the systematic model test was conducted at 2-D tank and square tank. The numerical results were in good agreement with the experimental results within the entire frequency range. It was found that an inclined punching plate had an excellent wave absorbing efficiency, compared to a horizontal one. Also, the optimal range of an inclined angle had an excellent wave absorbing efficiency, compared to a horizontal one the optimal range of the inclined angle is 10°<β<20°. The developed wave absorber was installed at KRISO's square basin, and is working effectively for various model tests.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.7
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• pp.70-75
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• 2004

The shearing process for the sheet metal is normally used in the precision elements such as a lead frame of IC chips. In these precision elements, the burr formation brings a bad effect on the system assembly and demands the additional deburring process. In this paper, we developed the small size precision punching system to investigate burr formation mechanism and to present kinematically punch-die aligning methodology between the rectangular shaped punch and die. The punch is driven by an air cylinder and the sheet metal is moving on the X-Y table system which is driven by two stepping motors. The whole system is controlled by microprocessor and is communicated with each other by RS232C serial communication protocol. Punching results are measured manually using the SEM photographs and are compared aligning result with miss aligning one.

• Computers and Concrete
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• v.23 no.3
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• pp.217-233
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• 2019

This paper describes the numerical modelling of an interior slab-column connection to investigate the punching shear resistance of reinforced concrete (RC) slabs under fire conditions. Parameters of the study were the fire direction, flexural reinforcement ratio, load levels, shear reinforcement and compressive strength of concrete. Moreover, the efficiency of the insulating material, gypsum, in reducing the heat transferred to the slab was assessed. Validation studies were conducted comparing the simulation results to experiments from the literature and common codes of practice. Temperature dependencies of both concrete and reinforcing steel bars were considered in thermo-mechanical analyses. Results showed that there is a slight difference in temperature endurance of various models with respect to concrete with different compressive strengths. It was also concluded that compared to a slab without gypsum, 10-mm and 20-mm thick gypsum reduce the maximum heat transferred to the slab by 45.8% and 70%, respectively. Finally, it was observed that increasing the flexural reinforcement ratio changes the failure mode from flexural punching to brittle punching in most cases.

• Computers and Concrete
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• v.27 no.1
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• pp.41-54
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• 2021

This paper introduced three new strengthening systems for isolated footings: BFRP wrapping system, CFRP wrapping system, and steel jacketing system. The proposed systems are more practical than the current traditional methods, which involves installing many dowel bars and splicing reinforcing steels to join new and old concrete segments. In the proposed three new systems, BFRP wraps, CFRP wraps, or steel jackets are installed on the exterior surface of the enlarged footing, with construction adhesive or a few steel dowels being applied to the contact surfaces. To investigate the effectiveness of three systems, forty-four models were constructed in ABAQUS, with different parameters being considered. All footings investigated failed in punching shear, including original and retrofitted footings. According to FEA results and parametric studies, the three strengthening systems were capable of improving the punching shear resistance of footings. By introducing a new factor η, the punching shear equation in Eurocode 2 was modified to predict the punching shear resistances of the strengthened footings. A linear formula was developed to present the relationship between the new factor η and the investigated parameters.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.5
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• pp.1183-1192
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• 1993

Since the punching time is strongly related to the productivity in sheet metal stamping, there have been a lot of efforts to obtain the optimal tool path. However, most of the conventional efforts have the basic limitations to provide the global optimal solution because of the inherent difficulties of the NP hard combinatorial optimization problem. The existing methods search the optimal tool path with limiting tool changes to the minimal number, which proves not to be a global optimal solution. In this work, the turret rotation time is also considered in addition to the bed translation time of the NCT machine, and the total punching time is minimized by the simulated annealing algorithm. Some manufacturing constraints in punching sequences such as punching priority constraint and punching accuracy constraint are incorporated automatically in optimization, while several user-interactions to edit the final tool path are usually required in commercial systems.

• Structural Engineering and Mechanics
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• v.1 no.1
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• pp.75-86
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• 1993

The punching shear strength of concrete flat plates is one of the topics of intensive research in recent years by various concrete structures researchers. This paper reviews four current methods of analysing the punching shear strength at the corner-and edge-column positions of reinforced concrete flat plates. They include those recommended in the Australian Standard AS3600-1988, the American Concrete Institute ACI318-89 and the British Standard on Concrete Practices (BS8110) as well as the approach developed at the University of Wollongong, Australia. Based on half-scale model test results, a comparative study of these four analysis methods is made with regard to their limitation, accuracy and reliability. It is found that the Wollongong approach in general gives the best performance in predicting the punching shear strength of flat plates with torsion strips and those with spandrel beams. The Australian Standard procedure performs just as satisfactorily for flat plates with torsion strips but tends to be unsafe for those with spandrel beams. Both the ACI and the British methods are applicable only to flat plates with torsion strips; they also tend to give unsafe predictions for the punching shear strength.