• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2000년도 춘계학술대회논문집
• /
• pp.9-12
• /
• 2000

The importance of the role of plastic spin in the rate-dependent response of materials at large deformations is the main objective of this work. After a brief presentation of a general consitutive framework for visco-rigid plasticity at large strains an isotropic/kinematic hardening and a visco-rigid plastic model are used to analyze the stress-strain response under simple shear. A clear understanding of the role of plastic spin is achieved by obtaining numerical analyzed results for different stress values in which the plastic spin consititutive parameters interrelaste with the strain rate and other more conventional model constants, Especially this paper is concerned with introducing behaviors of Al7075

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2004년도 추계학술대회논문집
• /
• pp.284-289
• /
• 2004

Since polymer materials at elevated temperatures are usually rate-sensitive, the analysis of RTP process requires considering the effect of the rate-dependent. The material behavior that exhibits rate-sensitivity is called visco-plastic. A two-dimensional visco-plastic finite element formulation which constitutive equation is based on the formulation proposed by Perzyna is presented. This Paper is purposed to calcuate pressure distribution on PMMA in compression process and to predict the relationship with defects after demolding process. This paper analyzes, both analytically and numerically, the pressure distributions on the surface of PMMA during open-die RTP process. In this research, PMMA is used to be simulated at $110^{\circ}C$ near the transition temperature.

• 소성∙가공
• /
• 제5권1호
• /
• pp.37-46
• /
• 1996

Superplastic forming/diffusion bonding (SPF/DB) processes were analyzed using a rigid visco-plastic finite element method. The optimum pressure-time relationship for a target strain rate and thickness distributions were predicted by two-node line elements based on the membrane approximation for plane strain. Material behavior during SPF/DB of the integral structures having complicated shapes was investigated. The tying condition is employed for the analysis of inter-sheet contact problems. A movement of rib structure is successfully predicted during the forming.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 1994년도 박판성형기술의 진보
• /
• pp.99-118
• /
• 1994

In recent years reduction in noise and vibration in automobile has been strongly required not only from the standpoint of environmental regulations but also for raising the commercial value and ride comfort. Vibration damping steel sheets, which are composites made by sandwitching a visco-elastic resin layer between two steel sheets, have been developed as effective noise-abating materials and have found a growth of use in automobile industries. Vibration damping steel sheets for commercial use must be excellent in vibration damping property, press formability and spot weldability, but are inferior to ordinary steel sheets. In this study, the mechanical properties of vibration damping steel are evaluated, and press formability is analysed on the basis of those properties and shear bonding strength. The development of engine oil pan using damping steel sheets are also reported, focusing on serious problems in oil pan drawing.

• Computers and Concrete
• /
• 제15권4호
• /
• pp.515-545
• /
• 2015

The paper presents results of FE simulations of the strain-rate sensitive concrete behaviour under dynamic loading at the macroscopic level. To take the loading velocity effect into account, viscosity, stress modifications and inertial effects were included into a rate-independent elasto-plastic formulation. In addition, a decrease of the material stiffness was considered for a very high loading velocity to simulate fragmentation. In order to ensure the mesh-independence and to properly reproduce strain localization in the entire range of loading velocities, a constitutive formulation was enhanced by a characteristic length of micro-structure using a non-local theory. Numerical results were compared with corresponding laboratory tests and available analytical formulae.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 1995년도 춘계학술대회논문집
• /
• pp.155-161
• /
• 1995

Superplastic forming/diffusion bonding(SPF/DB) processes are analyzed using a rigid visco-plastic finite element method. The optimum pressure-time relationship for a target strain rate and thickness distributions were predicted using two-node line element based on membrane approximation for plane strain shapes. Material behavior during SPF/DB of the integral structures with complicated shapes are investigated. The tying condition is employed for the analysis inter-sheet contact problems. A movement of rib structure is successfully prodicted during the forming.

• 콘크리트학회논문집
• /
• 제20권3호
• /
• pp.317-323
• /
• 2008

본 연구에서는 굳지 않은 콘크리트 및 유동 콘크리트의 흐름 거동에 관한 해석 시뮬레이션 모델의 개발에 관한 것으로, 입자법의 일종인 MPS법 (moving particle semi-implicit method)을 적용하였다. 콘크리트의 유동 현상을 점소성의 흐름 문제로 고려하였으며, 콘크리트 입자의 운동에 관한 지배방정식은 라그랑지 정식화의 Navier-Stokes 방정식과 질량보존의 법칙에 기초하도록 하였다. 굳지 않은 콘크리트의 점소성 흐름 구성관계의 정식화를 위하여 콘크리트는 부동 상태인 경우 고점성체의 유체로, 유동상태인 경우 항복응력 이후 점소성체의 유체로 모델링하였다. 개발된 모델을 이용하여 L-형 박스의 콘크리트 유동 시험에 대해 시뮬레이션 하였으며, 그 결과 예측된 흐름량은 실험의 흐름량과 잘 일치하는 것으로 나타났다. 개발된 입자법의 해석 모델은 점소성 유체의 운동현상에 기초하여 정식화 되어 콘크리트 입자의 유동 및 운동 현상을 잘 묘사해 주는 것으로 평가된다.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 1997년도 고액공존금속의 성형기술 심포지엄
• /
• pp.5-15
• /
• 1997

It is the objective of this study that by conducting the serni-solid extrusion using A12024, the effect of various process variables on the quality of extruded product and extrusion force is understood. The results of experiment are compared with those of finite element simulation in order to verify the effectiveness of the developed FE-simulation code. In order to simulate densification in the deformation of serni-solid material, the semi-solid material is assumed to be composed of solid region as porous skeleton following compressible visco-plastic model and liquid region following Darcy's equation for the liquid flow saturated in the interstitial space. Then the flow and deformation of the semi-solid alloy are analyzed by coupling the deformation of the porous skeleton and the flow of the eutectic liquid. It is assumed that initial solid fraction is homogeneous. Yield and plastic potential function presented by Kuhn and constitutive model developed by Gunasekera are used for solid skeleton.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2008년도 춘계학술대회 논문집
• /
• pp.539-542
• /
• 2008

Recently, GMP(Glass Molding Press) process is mainly used to produce aspheric glass lenses. Because glass lens is heated at high temperature above Ty (yielding point) for forming glass, the quality of aspheric glass lens is deteriorated by residual stresses which are generated in a aspheric glass lens after forming. Before this study, as a fundamental study to develop forming conditions for progressive GMP process, compression, strain relaxation and thermal conductivity tests were carried out to obtain the visco-rigid plastic, the visco-elastic and thermal properties of K-PBK40 which is newly developed and applied for precision molding glass material, In this study, using the experimental results we obtained, a glass lens forming simulation in progressive GMP process was carried out and we could forecast the shape of deformed glass lenses and residual stresses contribution in the structure of deformed glass lenses after forming.

• 소성∙가공
• /
• 제9권1호
• /
• pp.59-65
• /
• 2000

Most studies of failure analysis in ductile metals have been based on the classical plasticity theory using the local constitutive relations. These frequently yields a physically unrealistic solution, in which a numerical prediction of the onset of a deformation localization shows an inherent mesh-size sensitivity. A one way to remedy the spurious mesh sensitivity resulted in the unreasonable results is to incorporate the non-local plasticity into the simulation model, which introduce an internal (material) length-scale parameter into the classical constitutive relations. In this paper, a non-local version of the modified Gurson constitutive relation has been introduced into the finite element formulation of the simulation for plane strain compression of the visco elastic-plastic void material. By introducing the non-local constitutive relations we could successfully removed the inherent mesh-size sensitivity for the prediction of the deformation localization. The effects of non-local constitutive relation are discussed in terms of the load-stroke curve and the strain distributions accross the shear band.