• Advances in materials Research
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• v.6 no.2
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• pp.169-184
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• 2017

Electro-Discharge machining (EDM) is a thermal process comprising a complex metal removal mechanism. This method works by forming of a plasma channel between the tool and the workpiece electrodes leading to the melting and evaporation of the material to be removed. EDM is considered especially suitable for machining complex contours with high accuracy, as well as for materials that are not amenable to conventional removal methods. However, several phenomena can arise and adversely affect the surface integrity of EDMed workpieces. These have to be taken into account and studied in order to optimize the process. Recently, artificial neural networks (ANN) have emerged as a novel modeling technique that can provide reliable results and readily, be integrated into several technological areas. In this paper, we use an ANN, namely, the multi-layer perceptron and the back propagation network (BPNN) to predict the mean surface roughness of electro-discharge machined surfaces. The comparison of the derived results with experimental findings demonstrates the promising potential of using back propagation neural networks (BPNNs) for getting a reliable and robust approximation of the Surface Roughness of Electro-discharge Machined Components.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.4
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• pp.383-391
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• 2011

The hot-stamping technique is used to manufacture high-strength parts by press forming by heating at a temperature above the Austenite transformation temperature and then rapid cooling. Boron steel, which contains a very small amount of boron, is one of the materials used for hot stamping. The purpose of this study is to show the microstructures and to investigate the mechanical properties under different heat-treatment conditions. The heat treatment of water quenching was conducted at the various temperatures and different elapsed times. These can be practical data useful when boron steels are used for hot stamping. Furthermore, the microstructures and mechanical properties of the spot-welded specimen with coatings and counterpart materials (SPRC 340, SPRC 590) is investigated in order to determine the welding characteristics of boron steel at different welding condition.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.12
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• pp.1373-1377
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• 2014

Hot-stamping is a method of obtaining ultrahigh-strength steel by simultaneously forming and cooling boron steel in a press die after it has been heated at $900^{\circ}C$ or above. After heat treatment, boron steel has a strength of 1500 MPa or more. This material ensures a high level of quality because it overcomes the spring-back phenomenon, which is a problem associated with high-strength steel materials, and the degree of dimensional precision is improved by 90 or more because of the good formability compared with existing types of steel. In this study, the welding characteristics were identified through the butt and lap welding of hot-stamped steel using a disk laser. Full penetration was obtained at a faster speed with butt welding compared to lap welding, and a white band was observed in every specimen.

• Geomechanics and Engineering
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• v.23 no.4
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• pp.327-338
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• 2020

The role of precise prediction of subsurface fluids and discrimination among them cannot be ignored in reservoir characterization and petroleum prospecting. A suitable rock physics model should be build for the extraction of valuable information form seismic data. The main intent of current work is to present a rock physics model to analyze the characteristics of seismic wave propagating through a cracked porous rock saturated by a three phase fluid. Furthermore, the influence on wave characteristics due to variation in saturation of water, oil and gas were also analyzed for oil and water as wet cases. With this approach the objective to explore wave attenuation and dispersion due to wave induce fluid flow (WIFF) at seismic and sub-seismic frequencies can be precisely achieved. We accomplished our proposed approach by using BISQ equations and by applying appropriate boundary conditions to incorporate heterogeneity due to saturation of three immiscible fluids forming a layered system. To authenticate the proposed methodology, we compared our results with White's mesoscopic theory and with the results obtained by using Biot's poroelastic relations. The outcomes reveals that, at low frequencies seismic wave characteristics are in good agreement with White's mesoscopic theory, however a slight increase in attenuation at seismic frequencies is because of the squirt flow. Moreover, our work crop up as a practical tool for the development of rock physical theories with the intention to identify and estimate properties of different fluids from seismic data.

• Wind and Structures
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• v.20 no.5
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• pp.643-660
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• 2015

The wind tunnel test of large-scale sectional model and computational fluid dynamics (CFD) are employed for the purpose of studying the aerodynamic appendices and mechanism on suppression for the vortex-induced vibration (VIV). This paper takes the HongKong-Zhuhai-Macao Bridge as an example to conduct the wind tunnel test of large-scale sectional model. The results of wind tunnel test show that it is the crash barrier that induces the vertical VIV. CFD numerical simulation results show that the distance between the curb and crash barrier is not long enough to accelerate the flow velocity between them, resulting in an approximate stagnation region forming behind those two, where the continuous vortex-shedding occurs, giving rise to the vertical VIV in the end. According to the above, 3 types of wind fairing (trapezoidal, airfoil and smaller airfoil) are proposed to accelerate the flow velocity between the crash barrier and curb in order to avoid the continuous vortex-shedding. Both of the CFD numerical simulation and the velocity field measurement show that the flow velocity of all the measuring points in case of the section with airfoil wind fairing, can be increased greatly compared to the results of original section, and the energy is reduced considerably at the natural frequency, indicating that the wind fairing do accelerate the flow velocity behind the crash barrier. Wind tunnel tests in case of the sections with three different countermeasures mentioned above are conducted and the results compared with the original section show that all the three different countermeasures can be used to control VIV to varying degrees.

• Transactions of Materials Processing
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• v.11 no.8
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• pp.682-690
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• 2002

The formation of adiabatic shearband in tungsten heavy alloys(WHA) was studied in this investigation. Five prismatic specimens were loaded by high velocity impacts and treated as plane strain problems. To find out the effect of particle's volume ratio, specimens containing 81%, 93% and 97% volume percents of tungsten particles were used. Also the effects of particle's geometry and size on the formation of shearband were studied for 81% volume percent alloys by small size particle model, large size particle model and undulated particle models, and the results were discussed.be used to diagnose the causes of necking and fracture in industrial practice and to investigate whether these defects were caused by material property variation, changes in lubrication, or incorrect press settings. In non-axisymmetric deep drawing, three modes of forming regimes are found: draw, stretch, plane strain. The stretch mode for non-axisymmetric deep drawing could be defined when the major and minor strains are positive. The draw mode could be defined when the major strain is positive and minor strain is negative, and plane strain mode could be defined when the major strain is positive and minor strain is zero. Through experiments the draw mode was shown on the wall and flange are one of a drawn cup, while the plane strain and the stretch mode were on the punch head and the punch corner area respectively, We observed that the punch load of elliptical deep drawing was decreased according to increase of die corner radius and the thickness deformation of minor side was more large than major side.

• Transactions of Materials Processing
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• v.19 no.6
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• pp.337-343
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• 2010

Current need of weight reduction in automotive part increases the application for high strength steel (HSS). The various types of high strength steels have been used to produce chassis part, control arms and trailing arms for weight reduction and increasing of fatigue durability such as dual phase steel (DP) and ferrite bainite steel (FB). But, DP and FB steels have proven to show inferiority in durability as well as press formability. Edge cracking occurred often in flange forming and hole expansion processes is the major failure encountered. This paper discussed the behavior of edge stretchability of high strength steel of DP and FB steels. Experimental works have been conducted to study the effect of punch clearance and burr direction on hole expansion ratio (HER). Also finite element simulation (FEM) has been preformed to clarify the mechanism of flange crack and support the experimental results on HER of DP and FB steels. It was simulated the whole process of blanking process following by hole expansion process and ductile fracture criterion named the modified Cockcroft-Latham model which was used to capture the fracture initiation. From the hole expansion tests and FEM simulation studies it was concluded that ferrite bainite steel showed better stretch-flangeability than dual phase steel. It was attributed to the lower work hardening rate of ferrite bainite steel than dual phase steel at the sheared edge.

• Design & Manufacturing
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• v.14 no.3
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• pp.50-56
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• 2020

Ceramic tile is widely used as a floor or interior decoration of buildings. The main processes are raw material blending, molding, drying, firing, etc., and since dimensional and quality stability are very important, they are generally molded by a dry press method. In ceramic tile molds, there is a liner that can be easily replaced in case of wear. The liner is constantly abrasion due to a continuous pressing process during tile forming, and it is required to be replaced every certain period. Even in the liner, use a wear-resistant fitting material only in areas where wear is concentrated. However, there was a risk that the fitting material was applied to large-sized tile molding due to problems such as damage to the molding machine and decrease in productivity when detached during the actual tile molding process due to weak fitting strength with the liner. Therefore, in this study, thermal-structural analysis for fitting tolerance analysis and structural analysis for fitting force analysis were performed for the shrink fit process of the fitting material.

• Design & Manufacturing
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• v.14 no.3
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• pp.17-22
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• 2020

As devices such as smartphones, tablet PC, and wearable devices have been miniaturized, the connectors that go into the devices are also designed to be very small. The connector combines the plug and the receptacle to transfer electricity. As devices are miniaturized, the contact shape is formed by partially thinning the thickness of the raw material of the terminal in order to lower the coupling height of the plug and receptacle. The product used in this study is a receptacle terminal used for 0.4mm pitch board to board connector among fine pitch connectors. When the material thickness is reduced by forging the receptacle terminal, the width change of the pin is checked. To reduce the thickness of the material by forging, pre-notching is applied in the first step, forging in the second step, and notching in the third step. After forming the width dimension of the pin to 0.28 mm in the pre-notching process, in the forging process, the material thickness 0.08 mm and 0.02 mm (25%) were forged and the thickness was changed to 0.06 mm and the width change amount of the pin was measured. The facility produced 10,000 pieces at 400 SPM using a Yamada Dobby (MXM-40L) press, and thirty pins were measured and the average value was shown. After forging by using C5210-H (HP) and NKT322-EH, which are frequently used in connectors, analyze the amount of change in each material. The effect of punching oil on forging is investigated by appling FM-200M, which is highly viscous, and FL-212, fast drying oil. This study aims to minimize mold modification by predicting the amount of material change after forging.

• Biomaterials and Biomechanics in Bioengineering
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• v.2 no.1
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• pp.23-32
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• 2015

Facile immobilization of growth factors in hyaluronic acid (HA) hydrogels using dual enzymes is reported in the paper. The hydrogels were formed by using horseradish peroxidase (HRP) and hydrogen peroxide ($H_2O_2$) and transforming growth factor-${\beta}3$ (TGF-${\beta}3$) was covalently conjugated on the hydrogels in situ using tyrosinase (Ty) without any modifications. For the preparation of hydrogels, HA was grafted with poly(ethylene glycol) (PEG), which was modified with a tyrosine. The gelation times of the HA hydrogels were ranging from 415 to 17 s and the storage moduli was dependent on the concentration of $H_2O_2$ and Ty (470-1600 Pa). A native TGF-${\beta}3$ (200 ng/mL) was readily encapsulated in the HA hydrogels and 17% of the TGF-${\beta}3$ was released over 1 month at the Ty concentration of 0.5 KU/mL, while the release was faster when 0.3 KU/mL of Ty was used for the encapsulation (27%). It can be suggested that the growth factors resident in the hydrogels for a long period of time may lead cells proliferating and differentiating, whereas the growth factors that are initially released from the hydrogels can induce the ingrowth of cells into the matrices. Therefore, the dual enzymatic methods as facile gel forming and loading of various native growth factors or therapeutic proteins could be highly promising for tissue regenerative medicines.