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서송원(Seo Songwon),민옥기(Min Oakkey) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.11
There is few research about contact problem in SPH because it is primarily suitable to analyze the large deformation problem. However, an elasto-plastic problem with small deformation need to be considered about contact characteristics. The numerical formulating methods for SPH is induced to be able to abtain solutions based on a varitional method in contact problem. The contact algorithm presented is applied to the elastic impact problem in ID and 2D. The results show that an imaginary tension and a numercal instability which happen in inpacting between different materials can be removed and contact forces which could not have been calculated are able to obtain.
양현모(Hyunmo Yang),민옥기(Oakkey Min) 대한기계학회 2007 大韓機械學會論文集A Vol.31 No.11
A compressive split Hopkinson pressure bar (SHPB) technique is used to investigate the dynamic behavior of SM45C at high temperature. A radiant heater, which consists of one ellipsoidal reflector and one halogen lamp, is used to heat the specimen. Specimens are tested from 600℃ to 1000℃ at intervals of 100℃ at a strain-rate ranging from 1100/s to 1150/s. A critical phenomenon occurs between 700℃ and 750℃ in SM45C. This phenomenon results in the drastic drop in a flow stress. In a modified Johnson-Cook constitutive equation, a reducer function is used to take into account for the effect of the drastic drop in a flow stress. A reducer function, which is dependant on the temperature as well as the strain, is introduced and the parameters of the modified Johnson-Cook constitutive equation are determined from test results.
서송원(Songwon Seo),민옥기(Oakkey Min) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.9
SPH is an appealing and valuable computational tool using no background mesh, especially for high deformation events such as impact. But, although research has widely done since invented in 1977, this method still have several problems-lacking consistency, tensile instability and especially boundary condition treatment. This paper review current works for the method of imposing boundary conditions and test several model to certify a validity of its methods. It is compared a method using a ghost particle with that using a boundary condition about a symmetric model. Numerical tests are shown a reasonable result when impose a traction or velocity constraint to the models by equations of boundary constraint condition.
양현모(Hyunmo Yang),민옥기(Oakkey Min) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11
High temperature SHPB(Split Hopkinson Pressure Bar) test system is used to investigate the dynamic behavior of SM45C at high temperature and high strain rate. In this work, one ellipsoidal reflectors with one halogen lamp is used to heat the test specimen. To determine the true stress-strain relationship, specimens are tested from room temperature to 1000℃ at intervals of 100 or 200℃ and at a strain-rate range of 1100/s ~ 1200/s. The parameters for a Johnson-Cook constitutive equation are evaluated from the test results.
이재훈(Jaehoon Lee),서송원(Songwon Seo),민옥기(Oakkey Min) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.11
This paper is concerned with numerical simulation of hypervelocity impacts(HVIs) of a projectile on laminated composite plate targets using SPH method. A one-parameter visco-plasticity model and damage model is used to describe the HVIs response of composite materials. The numerical simulation was carried out for a steel projectile striking to aluminum plate targets and for an aluminum projectile striking to laminated graphite/epoxy (Gr/Ep) composite plate targets. Through the numerical simulation, comparison with the HVIs response of isotropic materials and composite materials is discussed.
SPH에서 임의 형상의 강체면에 대한 탄소성 접촉 해석
서송원(Songwon Seo),이재훈(Jaehoon Lee),민옥기(Oakkey Min) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4
There is few research about contact problem for a rigid surface with an arbitrary shape in SPH. The variational equation based on the virtual work principle is derived and its solution is obtained by the penalty method. It is proposed a new method that can determine the parameters for a penetration and a penetration rate used in the penalty method. The reproducing condition is adopted to correct the deficiency of kernel on the boundary. In order to calculate a penetration of particles, after checking boundary particles for deformable body boundary normal vectors were determined on the rigid surface. Numerical simulations for models which have rigid surface with an arbitrary shape were conducted to validate the proposed method in 2D. The results of those analysis represent that the contact algorithm proposed in this study works properly.
SPH 기법을 이용한 고속충돌을 받는 복합 적층판의 해석
이재훈(Jaehoon Lee),서송원(Songwon Seo),이인규(Ingyu Lee),민옥기(Oakkey Min) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
This paper reports experimental results and numerical simulations of high velocity impact on laminated composite plates reinforced with graphite/epoxy. To describe material behavior under high velocity impacts, a 3-D anisotropic elasto-plasticity constitutive model, an equation of state and a failure criterion for unidirectional composites have been used. The above physics were incorporated into the SPH. The numerical simulation was carried out for a steel projectile striking to laminated graphite/epoxy composite plate targets with different layup configurations. Good correlation between numerical simulation and experimental results was achieved, both in terms of deformation and damage of the laminates.