저자명 조상순 
년도 2008 
A study about the dynamic response of materials under impact or blast load is a crucial research topic in many engineering applications such as crashworthiness of vehicles and explosive devices used in aerospace and military industry. When impact or blast load is imposed to a machine, the stress waves are propagated through a medium and fracture or damage occurs at the structural weak point by the crack or plastic deformation. Therefore, understanding of the stress wave propagation is very important for the reliable and safe design of machines.
Stress waves propagate through a medium rapidly when dynamic forces are applied for very short periods of time. Furthermore, if a pulse wave is transmitted to a material that has an exceeding the elastic limits, this pulse induces a plastic stress wave as well as a elastic stress wave. The analytical prediction of the propagation of stress waves is very difficult in practical problems since the governing equation is expressed by the hyperbolic differential equation and the solution may have discontinuities or singularities such as an elastic unloading, internal reflection and the crack. In spite of such difficulties, many researchers have been progressed valuable studies by various approaches since the early sixties. One remarkable effort is the numerical simulation using the finite element method. However, the conventional finite element method contains two typical problems currently during the simulation procedures: The first one is the difficulty of controlling dispersive and dissipative errors occurring at the discontinuous or singular domain; and the second difficulty is to resolving and preserving the short waves with discontinuities.
This paper proposed the numerical algorithm for the simulation of elasto-plastic stress waves using a time discontinuous variational integrator based in Hamiltonian. The proposed algorithm firstly adopts both the time-discontinuous variational integrator and the space-continuous Hamiltonian in order to reduce the dispersive and dissipative errors. The limited kinetic energy is introduced to enhance the stability problem in the discontinuities such as elastic unloading and internal reflection in plastic deformation.
This study also modified integration algorithm in the strain space for rate and temperature dependent elasto-plastic constitutive relations in order to obtain more accurate results in numerical implementation. Since most materials show their inherent rate and temperature dependent behaviors in various strain-rate, strain-rate and temperature dependent constitutive models are widely utilized in the numerical simulation for materials under dynamic loading conditions. Numerical implementations for the constitutive are typically carried out on the basis of theoretical results which are derived on the stress space formulation. The stress space formulation has the possibility of confusion in loading-unloading criteria when the plastic strain-rates are fluctuated or thermal softening takes place. However, the strain space formulation proposed by Il’yushin is attractive alternatives to eliminates confusion in the definition of the loading-unloading criterion and also provide a unified treatment for work-hardening or softening materials. The proposed integration algorithm of the constitutive model is integrated analytically using integration by part and chain rule based on the classical J2 elasto-plasticity and the strain space formulation and then is applied to the 2-stage Lobatto IIIA with second-order accuracy. The suggested algorithm enables to consider the convective stress rates on the yield surface of the strain space. Accuracy assessment using the isoerror maps indicates the result of the proposed algorithm is improved by 70% compared to the conventional backward-Euler return method. Numerical analysis of adiabatic shear band also demonstrates that the proposed algorithm is more accurate than the conventional method for rate and temperature dependent constitutive model.
Elastic and elasto-plastic numerical simulations for one and two dimensional stress wave propagation are carried out in order to evaluate the efficiency of the proposed algorithms. The results indicate that dispersive and dissipative errors, which appears in both a continuous Galerkin method and a discontinuous Galerkin method, are remarkably reduced using the time-discontinuous variational integrator of Hamiltonian with the proposed integration algorithm of the constitutive model.

번호 제목 저자명 날짜 조회 수
27 Study on Dynamic Tensile Tests of Auto-body Steel Sheet at the Intermediate Strain Rate for Material Constitutive Equations (차체강판의 중변형률 속도에서의 동적 인장시험 및 물성 구성방정식에 관한 연구) 임지호  2005.11.29 25430
» Analysis of Elasto-Plastic Stress Waves by a Time Discontinuous Variational Integrator of Hamiltonian with a Second-Order Integration Scheme of the Constitutive Model (해밀토니안의 시간 불연속 변분적분기와 구성방정식의 2차 정확도 적분법을 이용한 탄소 조상순  2008.12.15 21646
25 Forming Limit Diagram of Auto-body Steel Sheets at High Strain Rates for Sheet Metal Forming and Crashworthiness (박판성형 및 충돌성능 향상을 위한 고변형률속도에서의 차체강판 성형한계도) 김석봉  2010.07.13 21585
24 A New Ductile Fracture Criterion for the Formability Prediction of Steel Sheets and Its Application to Finite Element Analysis (강판의 성형성 예측을 위한 새로운 연성 파괴 조건 및 유한 요소 해석에의 응용) [1] Yanshan Lou  2012.12.10 20976
23 A Study on the Tension/Compression Hardening Behavior of Auto-body Steel Sheets Considering the Pre-strain and the Strain Rate (초기 변형률 및 변형률 속도를 고려한 차체 강판의 인장/압축 경화 거동에 관한 연구) [1] 배기현  2011.01.11 20274
22 A Study on Material Properties of OFHC Copper Film at High Strain Rates using High-Speed Micro Material Testing Machine (고속마이크로재료시험기를 이용한 무산소동 박판의 고변형률속도 재료물성치 연구) 김진성  2010.07.13 20156
21 Finite Element Inverse Approach and Initial Guess Generation for Sheet Metal Forming Analysis of Complicated Auto-body Members (복잡한 차체부재의 박판성형공정을 위한 유한요소 역해석 및 초기추측치 계산) 김승호  2005.11.29 19050
20 A Study on the Dynamic Failure Model of a Spot Weld under Combined Loading Conditions for Auto-body Crash Analyses (차체용 부재의 충돌해석을 위한 복합하중조건에서 점용접부의 동적 파단모델 연구) [1] 송정한  2008.07.24 18508
19 Optimum Process Design in Sheet Metal Forming Processes using Finite Element Sensitivity Analysis (유한요소 민감도해석을 이용한 박판금속성형에서의 공정변수 최적설계) [1] 김세호  2005.11.29 18448
18 Strain-Rate Dependent Anisotropic Yield Criteria for Auto-body Steel Sheets (자동차용 강판의 변형률속도 의존 이방성 항복함수에 관한 연구) 허지향  2012.12.11 17975
17 Evaluation of a cast-joining process of dual metal crankshafts for heavy-duty engines with ductile cast iron and high strength forged steel(구상흑연주철과 고강도 단조강의 주조접합 이종금속을 이용한 중대형 엔진 크랭크샤프트의 평가) 한 신  2010.07.13 17828
16 Dynamic Formulation of Finite Element Limit Analysis for Impact Simulation of Structural Members (구조부재의 충돌해석을 위한 유한요소 극한해석의 동적 수식화) 김기풍  2005.11.29 17725
15 Measurement Uncertainty Evaluation for High Strain Rate Tensile Properties of Auto-body Steel Sheet (자동차용 강판 고속인장물성 데이터의 측정불확도 산출) 정세환  2012.12.10 17703
14 Development of a Nonlinear Degenerated Shell Element with the Drilling Degree of Freedom by the Cubic Polynomial Interpolation and the Assumed Strain Method (드릴링 자유도의 삼차 근사법과 대체변형률법을 이용한 비선형 감절점 쉘 요소의 개발) 이형욱  2005.11.29 17662
13 Rate Dependent Hardening Model for Pure Titanium Considering the Effect of Deformation Twinning (쌍정의 영향을 고려한 티타늄의 변형률속도 의존 경화 모델) 안광현  2012.12.12 17136
12 Finite Element Simulation of 3-dimensional Superplastic blow forming with diffusion bonding (유한요소법을 이용한 초소성 재료의 삼차원 확산 접합 및 압력 성형 해석) 이기석  2005.11.29 16942
11 Microscopic investigation of the strain rate hardening for auto-body steel sheet(차체강판 변형률속도 경화의 미시적 관찰) 윤종헌  2010.07.13 16887
10 Crash Analysis of Auto-body Structures with an Explicit Finite Element Method ( 외연적 유한요소법을 이용한 차체 구조물의 충돌해석 ) 강우종  2005.11.29 16675
9 Shell Element Formulation for Limit Analysis of Thin-Walled Structures ( 박판부재의 붕괴거동해석을 위한 극한해석의 쉘요소 수식화 ) 김현섭  2005.11.29 14689
8 A Study on a Continuum Damage Yield Function to Predict Ductile Fracture of Materials (재료의 연성파단을 예측하기 위한 연속체 손상 항복 함수에 관한 연구) 고윤기  2012.12.10 14565