• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.10a
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• pp.160-163
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• 2004

The hub hole in a wheel of vehicles usually formed with hole expansion process. Formability of material, especially the hole expansion ratio, is important to produce a fine hub hole. The hub hole expansion process is different from general forming process or bore expansion process in the viewpoint of forming a thick plate. In the hole expansion process of the plate with a hole, as the hole being expanded, the crack is occurred to outward direction at the boundary of a hole. Therefore, it is need to apply the fracture criterion in the hub hole expansion process. In this paper, the hub hole expansion process is simulated with commercial elasto-plastic finite element code, LS-DYNA3D considering some ductile fracture criteria. Fracture mode and hole expansion ratio is compared with respect to the fracture criteria. Analysis results demonstrate that only the effective plastic strain is not adequate to predict the fracture mode in the hub hole. And the analysis results also indicate that the ductile fracture criteria properly predict the fracture mode but hole expansion ratio is different with the result of each other because of their different characteristics.

• Journal of The Korean Society of Agricultural Engineers
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• v.46 no.1
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• pp.41-51
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• 2004

FRP re-bar in concrete structures could be used as a substitute of steel re-bars for that cases in which aggressive environment produce high steel corrosion, or lightweight is an important design factor, or transportation cost increase significantly with the weight of the materials. But FRP fibers have only linearly elastic stress-strain behavior; whereas, steel re-bar has linear elastic behavior up to the yield point followed by large plastic deformation and strain hardening. Thus, the current FRP re-bars are not suitable concrete reinforcement where a large amount of plastic deformation prior to collapse is required. The main objectives of this study in to evaluate the tensile behavior and the fracture mode of hybrid FRP re-bar. Fracture mode of hybrid FRP re-bar is unique. The only feature common to the failure of the hybrid FRP re-bars and the composite is the random fiber fracture and multilevel fracture of sleeve fibers, and the resin laceration behavior in both the sleeve and the core areas. Also, the result of the tensile and interlaminar shear stress test results of hybrid FRP re-bar can provide its excellent tensile strength-strain and interlaminar stress-strain behavior.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.1
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• pp.42-47
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• 2021

Recently, many structures using lightweight materials have been developed. This study was conducted by using Al6061-T6 and carbon fiber reinforced plastic (CFRP), two common lightweight materials. In addition, the failure characteristics of an interface bonded between a single material and a heterogeneous bonding material were analyzed. The specimens bonded with CFRP and Al6061-T6 were utilized by the combination of the heterogeneous bonding material. The specimens had a double cantilevered shape and the bonding between the materials was achieved by applying a structural adhesive. The experiments were conducted in opening mode: the lower part of the samples was fixed, while their upper part was subjected to a forced displacement of 3 mm/min by using a tensile tester. Under the tested amount of strength, energy release rate, and considering the specimens' fracture characteristics in opening mode, the specimen "CFRP-Al" presented the maximum stress, followed by "Al" and "CFRP". We can hence conclude that the inhomogeneous material "CFRP-Al" is useful for the construction of lightweight structures bonded with structural adhesive.

• Proceedings of the KWS Conference
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• 1998.10a
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• pp.317-320
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• 1998

• Geomechanics and Engineering
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• v.20 no.4
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• pp.275-285
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• 2020

Excavation usually induces considerable ground settlement in soft ground, which may result in damage of adjacent buildings. Generally, the settlement is predicted through elastic-plastic finite element method and empirical method with defects. In this paper, an analytical solution for predicting ground settlement induced by excavation is developed based on the definition of three basic modes of wall displacement: T mode, R mode and P model. A separation variable method is employed to solve the problem based on elastic theory. The solution is validated by comparing the results from the analytical method with the results from finite element method(FEM) and existing measured data. Good agreement is obtained. The results show that T mode and R mode will result in a downward-sloping ground settlement profile. The P mode will result in a concave-type ground settlement profile.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.263-266
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• 2008

This paper is concerned with the analysis of elasto-plastic stress waves in a mode I semi-infinite cracked solid subjected to Heaviside pulse load. This study adopts a time-discontinuous variational integrator based on Hamiltonian in order to reduce the numerical dispersive and dissipative errors. This also utilizes an integration scheme of the constitutive model with 2nd-order accuracy which is formulated on the strain space for a rate and temperature dependent material model. Finite element analyses of elasto-plastic stress waves are carried out in order to compare the accuracy between a conventional Galerkin method and the time- discontinuous variational integrator.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.6
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• pp.898-904
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• 2003

Using the modified Irwin model and the modified Dugdale model, the plastic zone size near the interface crack tip in a ductile layer bonding two dissimilar elastic substrates is predicted. Validity of the models is examined by finite element method. The effects of several factors such as the mode mixity, T-stress and material properties are explored. The plastic zone size significantly decreases with the Poisson's ratio of the ductile layer.

• Proceedings of the KWS Conference
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• 2004.05a
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• pp.246-248
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• 2004

It has been well known that ductile fracture of steels is accelerated by triaxial stresses. The characteristics of ductile crack initiation in steels are evaluated quantitatively using two-parameters criterion based on equivalent plastic strain and stress triaxiality. This study provides the fundamental clarification of the effect of strength mismatching, which can elevate plastic constraint due to heterogeneous plastic straining, loading mode and loading rate on critical condition to initiate ductile crack from notch root using equivalent plastic strain and stress triaxiality based on the two-parameter criterion obtained on homogeneous specimens under static tension. The critical condition to initiate ductile crack from notch root for strength mismatched bend specimens under both static and dynamic loading would be almost the same as that for homogeneous tensile specimens with circumferential sharp notch under static loading.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.85-88
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• 1995

Recently, the micro mold maching techining technology is developed by means of the mechanical and high energy beam process. It is possible to make the micro structure mold with high aspect ratio by the LIGA technology. This mode is used for mass production of plastic parts by the micro injection molding method. In this study, we intend to research on the basic technology of micro injection molding. As the result, we developed the injection molding technology for small column plastic parts which diameter is 500 .mu. m and 200 .mu. m respectively with wbout aspect ratio 20.

• Korean Journal of Optics and Photonics
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• v.22 no.1
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• pp.5-9
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• 2011

There are technical difficulties in measuring the numerical apertures of multi-mode gradient-index plastic optical fibers (GI-POFs) due to their strong speckle noise originating from dopants, non-uniformity of gradient-index profile, and multi-mode interference. Therefore, we propose a new method of obtaining the numerical aperture by controlling the size of the incident laser beam and measuring the numerical aperture of GI-POF. The results show that we can get a value for the numerical aperture of GI-POF very similar to that measured by the conventional method. We can also obtain the optimum launching condition of input beam and maximum coupling efficiency.