• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2000.04a
• /
• pp.96-100
• /
• 2000

It is difficult to predict material behavior of forming process because the plastic instable flow phenomenon happens in practical forming process I. e. upsetting backward extrusion piercing indentation. In view of the direct relationship between instable material flow and quality defects of the products we should find out their phenomena, In this study we introduced the plastic spin and the kinematic hardening considering the kinematic hardening constitutive equation for rate-dependent material. Also analysis of upset forging is carried out using the rigid plastic FEM with Al7075

• Transactions of Materials Processing
• /
• v.3 no.3
• /
• pp.291-301
• /
• 1994

In the simultaneous forward-backward extrusion the effects of some process variables including area reduction, stroke advance, materials(Al 2024 and commercial pure copper) on the extrusion load, plastic flow and height ratio of upper to lower extruded parts are experimentally investigated and analyzed. Grid-marking technique is employed to visualize the plastic flow. The influence of using split and original specimen on the extrusion load and height ratio is evaluated by experiments. Experimental results show that the plastic flow if oriented to the part of lower area reduction in the begining but it is usually variated during the overall process. The configurations of plastic deformation and plastic flow are dependent on the working materials and the lubricational conditions.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.16 no.7
• /
• pp.1314-1321
• /
• 1992

In analyzing the plastic flow of axisymmetric tube extrusion a new method of formulation using the stream function approach and upper-bound theorem is proposed which permits the prediction of plastically deformed zone in analytic expression as well as metal flow. It is shown that the formulation proposed in this work covers the solid extrusion and tube extrusion in axisymmetric case. The effect of some process parameters such as area reduction, the ratio of radii(inner radius to outer radius) and friction factor on extrusion pressure, deformation zone and plastic flow through stream-lined dies has been studied. The presented theoretical analysis can be effectively used for the prediction of deformation zone and plastic flow.

• Structural Engineering and Mechanics
• /
• v.58 no.4
• /
• pp.719-729
• /
• 2016

The main objective of the present paper is to study the effect of the yield criterion on the magnitude of the strain rate and plastic work rate intensity factors in axisymmetric flow of isotropic incompressible rigid perfectly plastic material by means of a problem permitting a closed-form solution. The boundary value problem consisting of the axisymmetric deformation of a plastic tube is solved. The outer surface of the tube contracts. The radius of the inner surface does not change. The material of the tube obeys quite a general yield criterion and its associated flow rule. The maximum friction law is assumed at the inner surface of the tube. Therefore, the velocity field is singular near this surface. In particular, the strain rate and plastic work rate intensity factors are derived from the solution. It is shown that the strain rate intensity factor does not depend on the yield criterion but the plastic work rate intensity factor does.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.29 no.6
• /
• pp.279-288
• /
• 2017

Heat generation rate in a telecommunication cabinet increases due to the continued usage of mobile devices. Insufficient removal of heat intensifies the cabinet temperature, resulting in the malfunction of electronic devices. In this study, we assessed both aluminum and plastic heat exchangers used for cooling of the telecommunication cabinet, and compared the results against theoretical predictions. The aluminum heat exchanger was composed of counter flow parallel channels of 4.5 mm pitch, and the plastic heat exchangers were composed of cross flow triangular channels of 2.0 mm pitch. Samples were made by installing two plastic heat exchangers in both series and parallel. Results showed that the heat transfer rate was highest for the series cross flow heat exchanger, and was least for the aluminum heat exchanger. The temperature efficiency of the series cross flow heat exchanger was 59% greater than that of the aluminum heat exchanger, and was 4.3% greater than that of the parallel cross flow heat exchanger. In contrast, the pressure drop of the parallel cross flow heat exchanger was significantly lower than other samples. The heat exchange efficiency was also the largest for the parallel cross flow heat exchanger. The theoretical analysis predicted the temperature efficiency to be within 3.3%, and the pressure drop within 6.1%.

• Transactions of Materials Processing
• /
• v.8 no.4
• /
• pp.393-398
• /
• 1999

The plastic instable flow phenomenon happens in practical forming process, I. e. upsetting, backward extrusion, piercing, indentation. And also, it is difficult to control precisely the shape and dimensions of forming process. It is found that instabilities of the process are mainly connected with imperfections in the lubrication, billet eccentricity, inclined punch alignment. In view of the direct relationship between instable material flow and quality defects of the products and for better control of forming operation, we should necessarily find out their phenomena. In this study, we introduced the friction disturbance due to inclined punch angle. Analysis of upset forging is carried out using the rigid plastic FEM and slab method with eccentricity. Also, we considered the buckling parameters of billet with the large aspect ratio in upset forging.

• Journal of Advanced Marine Engineering and Technology
• /
• v.28 no.3
• /
• pp.451-456
• /
• 2004

This present experimental study has dealt with the heat transfer characteristics of plastic particle slurry which flows in a circular tube. This type of slurry is suggested for heat transfer enhancement effect cause by random and vortex effect of plastic particle dispersed in water. As a result, the thermal boundary layer becomes thin so the heat transfer coefficient on the tube wall more increase compare to pure water flow. This experimental test section was composed with stainless pipe which has the length of 2000mm, inner pipe diameter of 14mm and outer pipe diameter of 60mm. The most effective and important parameter of this experiment is plastic packing factor(PPF). The focuses of these results are pressure drop and heat transfer coefficient. As results, the friction factor of plastic particle slurry becomes higher at laminar flow region than pure water because of buoyancy effect of plastic particle but the local heat transfer coefficient becomes higher.

• Tunnel and Underground Space
• /
• v.10 no.2
• /
• pp.173-179
• /
• 2000

The influence of the plastic flow rules on the elasto-plastic behaviour of a discrete joint element was investigated by performing the numerical direct shear tests under both constant normal displacement and normal displacement conditions. The finite interface elements obeying Plesha’s joint constitutive law was used to allow the relative motion of the rock blocks on the joint surface. Realistic results were obtained in the tests adopting the non-associated flow rule, while the associated flow rule overestimated the joint dilation. To overcome the computational drawbacks coming from the non-symmetric element stiffness matrix in the conventional non-associated plasticity, the symmetric formulation of the tangential stiffness matrix for a non-associated joint element was proposed. The symmetric elasto-plastic matrix it derived by assuming an imaginary equivalent joint with associated flow rule which shows the same plastic response as that of original Joint with non-associated flow rule. The validity of the formulation was confirmed through the numerical direct shear tests under constant normal stress condition.

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.10 no.2
• /
• pp.103-114
• /
• 2001

During a compression molding process of Unidirectional Fiber Reinforced Plastic Composites, control of filling patterns in mold and distribution of fiber is needed to predict the effects of molding parameters on the flow characteristics. To obtain an excellent product and decide optimum molding conditions, it is important to know the relationship between molding conditions and viscosity. In this study, the anisotropic viscosity of the Unidirectional Fiber Reinforced Plastic Composites is measured by using the parallel plastometer. The model for flow state has been simulated by using the viscosity. The composites is treated as an incompressible New-tonian fluid. The effects of longitudinal/transverse viscosity ration A and slip parameter $\alpha$ on buldging phenomenon and mold filling patterns, are also discussed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1999.03b
• /
• pp.98-101
• /
• 1999

The plastic instable flow phenomenon happens in practical forming process I. e. upsetting backward extrusion piercing indentation. And also it is difficult to control precisely the shape and dimensions of forming process. It is found that instabilities of the process are mainly connected with imperfection in the lubrication billet eccentricity inclined punch alignment. In view of the direct relationship between instable material flow and quality defects of the products and it is for better control of forming operation we should necessarily find out their phenomena. In this study we used the friction disturbance due to inclined punch angle and introduced the method considering kinematic hardening effect Analysis of upset forging is carried out using the rigid plastic FEM and slab method with eccentricity.