저자명 김승호 
년도 2003 
The sheet metal forming process is an effective process widely used in industries for parts and bodies. There have been considerable efforts to optimize sheet metal forming processes and its progress has been remarkable with the aid of numerical simulation owing to amazingly increased computer capacity. Numerical simulation of sheet metal forming processes has become popular instead of the conventional trial-and-error or the expert-depending approach since the numerical analysis can easily deal with the nonlinear material properties in the plastic range, frictional conditions, complicated geometry of tools and material-die interaction. Recently, The finite element simulation has been actively applied to the initial and final design of vehicle structures to minimize design costs and time and automotive industries have made lots of efforts to reduce the weight of vehicle structures with increased safety to reduce fossil energy consumption as well as environment pollution. In most cases, forming simulation and crash simulation are usually carried out separately, although forming histories should be taken into account as the initial condition in the crash simulation for a robust design of the light vehicle structure. The design of vehicle structures to improve crash characteristics considering forming effects has been studied and attempted by several automotive companies, although it is not easy to apply for the actual structural design of vehicles due to the tremendous computing time to calculate forming histories.
  In this research, an inverse finite element method is employed for more capability to estimate formability from the desired final shape as well as to calculate forming histories such as thickness variation and plastic strain distributions which have great influences on the energy absorption of parts with small amount of computation time. The finite element inverse method adopts Henky's deformation theory, Hill's anisotropic yield criterion and simplified boundary conditions. The bending effect is considered by the modified membrane theory. Since the inverse analysis constructs a mesh system for the final stage of forming, crash simulation can be directly performed after the forming stage without a smoothing or remeshing. Although finite element inverse analysis is a quite effective scheme for those purposes in view of design cost and calculation time, it is extremely difficult to calculate an initial guess for the part with the large aspect ratio or the large angle of inclination. In this research, a direct mesh mapping scheme is newly proposed to estimate initial guesses for the finite element inverse analysis of arbitrary three-dimensional parts. Sliding constraint surfaces are described by finite element patches and constructed from the designed final shape or directly from the mesh system of the die and punch set that is used in the direct finite element analysis. An initial guess and a final shape are both calculated by the direct mesh mapping scheme from the sliding constraint surfaces of selected models.
  The present algorithm has been implemented in a finite element code and applied to several sheet metal forming processes to verify its validity and effectiveness. Multi-stage finite element inverse analysis is applied to multi-stage rectangular cup drawing processes with the large aspect ratio to calculate the initial and the intermediate shapes and the thickness strain distribution in each intermediate shape. The scheme can calculate deformed shapes and thickness strain distribution qualitatively for the initial tool design in the multi-stage deep drawing process. The design modification has been carried out to improve the uniform thickness distribution in each intermediate stage as well as the final stage. One-step inverse analysis is extended to the multi-step inverse analysis for the rectangular cup deep drawing process. The results are compared with the direct finite element method. The error induced by the one-step inverse analysis was reduced by the multi-step analysis, while reasonable analysis results still can be acquired with the one-step inverse analysis. The numerical example of an S-rail forming process demonstrates that the mapping scheme proposed is applicable to calculate an initial guess for a part with the large angle of inclination. The analysis result of the S-rail forming process is compared with that from a direct finite element analysis to evaluate the effectiveness of the mapping scheme proposed. In order to verify the validity and reliability of the inverse method in the crashworthiness simulation, crash analyses are simulated considering forming histories calculated by both the direct and inverse analysis. Analysis results demonstrate that energy absorption of structures is increased when simulation considers forming effects of thickness variation and work hardening. The total analysis time to estimate crashworthiness was significantly reduced when the inverse analysis is employed for the calculation of forming effects. Forming simulations for front frame members which have complicated geometry are also carried out to estimate formability and to calculate forming histories for the crash simulation without the die and punch set. Finally, crash simulation of front frame members is carried out considering forming effects from the inverse analysis to estimate crashworthiness. The results indicate that the inverse finite element can be applied to the optimum design of the light vehicle structures with enhanced reliabilities.
  The numerical results fully demonstrate that the finite element inverse analysis with the proposed direct mesh mapping scheme is greatly useful to estimate formability and to calculate forming histories in small amount of calculation time even with the complex geometry.

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 25431
26 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 20157
» 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 19051
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 17976
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 17829
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 17704
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 16890
10 Crash Analysis of Auto-body Structures with an Explicit Finite Element Method ( 외연적 유한요소법을 이용한 차체 구조물의 충돌해석 ) 강우종  2005.11.29 16676
9 Shell Element Formulation for Limit Analysis of Thin-Walled Structures ( 박판부재의 붕괴거동해석을 위한 극한해석의 쉘요소 수식화 ) 김현섭  2005.11.29 14690
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