저자명 이기석 
년도 2000 
Superplasticity is the deformation behavior that produces essentially neck-free elongation of many hundreds of percent in metallic materials. The development of superplastic materials has provided new opportunities to produce complex components using forming techniques that are not possible with conventional metals and alloys. Superplastic forming (SPF) has been widely used in the aviation and the aerospace industry since it has great advantages to produce very complicated, light and strong components. The application of SPF today has expanded very quickly in the aerospace industry and it has been recently used to produce some consumer goods such as golf clubs and cookery-ware.
  Different types of SPF processes have been evolved for various superplastic materials. The simplest form of the superplastic sheet forming is the female forming. A number of superplastic forming processes have been developed and designed to avoid severe thickness deviation that is inevitable in simple female forming. Some of forming processes require tool movements for better thickness distribution than the simple female forming. On the other hand, superplastic forming/diffusion bonding (SPF/DB) process has been developed at Rockell, providing a means to inexpensively utilize a structurally efficient material heretofore inhibited by high fabrication and material costs.
I  n such processes, it is necessary to control the temperature and the strain rate for good stability of the plastic deformation and the large elongation less susceptible to localized necking. In order to successfully produce a complex sheet metal component by superplastic forming, the optimum condition of the pressure cycle to gain the maximum strain rate sensitivity has to be sought by numerical simulation. Although many effort has been made in the optimization of SPF processes with various methods, researches on the optimum forming condition of the moving-tool forming process and the SPF/DB process are still needed for successful application.  
  Computer simulations of three dimensional superplastic sheet forming processes have been carried out by the finite element method with a membrane element or a shell element. In general superplastic sheet forming processes, the bending effect due to the sheet thickness is not negligible since the sheet is not thin compare to the other dimensions. In the real process modeling, a membrane element is regarded as more preferable rather than a shell element because of the computing efficiency and the easy contact treatment. Nevertheless, a membrane element has a disadvantage of disregarding the bending effect during the deformation. To overcome such a deficit in using a membrane element, a modified membrane element may be required in the finite element formulation procedure to take the bending effect into account.
  In this dissertation, superplastic forming processes are simulated by the use of a finite element method in the convective coordinates system. The finite element formulation is derived from the equilibrium equations as a weak form of Lagrangian formulation for the incremental analysis. The inelastic behavior of the superplastic material is described as incompressible, nonlinear, viscous flow. The formulation derived has been implemented into a finite element code with a modified membrane finite element which approximates the bending energy term with the kink angle. The formulation is associated with an algorithm to consider properly contact between dies and materials and an algorithm to control the pressure cycle for the optimization of the forming time. The calculation deals with maximization of the stain rate sensitivity, protection of the localized deformation, and consistency of the desired strain rate. The code calculates the deformed shapes, the thickness distribution, and the strain rates as well as the optimum pressure cycle. The validity of the present code is demonstrated by comparing numerical results with experimental results in a simple female forming process.
  Analysis of moving-tool forming processes is carried out with the present finite element code. The result is compared with blow forming processes with a fixed female die to demonstrate that the thickness distribution with a moving die is different from that with a fixed die. Results show that the thickness distribution of a part can be improved by using a moving-tool forming process with the same part shape.
  Analysis of a superplastic forming / diffusion bonding (SPF/DB) process is also carried out for a 4-sheet sandwich part. The result shows that the deformed shape with the three dimensional analysis is different from that with the two dimensional plane strain analysis because of the end effect. The result demonstrates that three dimensional analysis is indispensable for simulation of SPF/DB to provide the accurate pressure cycle and deformed shapes. Remarkable deviation of the thickness distribution along the corridor direction also demonstrates the necessity of three dimensional analysis. The present analysis enables to predict accurate thickness distribution, which is necessary for good design of multi-sheet sandwich parts as an aircraft part.

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 27283
26 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 23122
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 23109
24 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 23079
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 22392
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 21868
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 20544
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 20401
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 20223
18 Strain-Rate Dependent Anisotropic Yield Criteria for Auto-body Steel Sheets (자동차용 강판의 변형률속도 의존 이방성 항복함수에 관한 연구) 허지향  2012.12.11 19939
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 19311
16 Measurement Uncertainty Evaluation for High Strain Rate Tensile Properties of Auto-body Steel Sheet (자동차용 강판 고속인장물성 데이터의 측정불확도 산출) 정세환  2012.12.10 19233
15 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 19131
14 Dynamic Formulation of Finite Element Limit Analysis for Impact Simulation of Structural Members (구조부재의 충돌해석을 위한 유한요소 극한해석의 동적 수식화) 김기풍  2005.11.29 19118
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 18888
12 Microscopic investigation of the strain rate hardening for auto-body steel sheet(차체강판 변형률속도 경화의 미시적 관찰) 윤종헌  2010.07.13 18516
» 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 18387
10 Crash Analysis of Auto-body Structures with an Explicit Finite Element Method ( 외연적 유한요소법을 이용한 차체 구조물의 충돌해석 ) 강우종  2005.11.29 18071
9 Shell Element Formulation for Limit Analysis of Thin-Walled Structures ( 박판부재의 붕괴거동해석을 위한 극한해석의 쉘요소 수식화 ) 김현섭  2005.11.29 16180
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 16067