• 한국지반공학회논문집
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• 제16권1호
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• pp.65-73
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• 2000

본 연구에서는 미소변형률에서 대변형률까지의 거동을 모델할 수 있는 탄소성 구성모델을 개발하였다. 제안된 구성모델은 일반 등방경화규칙에 근거한 비등방 경화규칙과 전응력 개념을 토대로 개발하였다. 그리고 제안된 구성관계가 기존의 대표적 구성모델을 포함하고 있음을 수학적으로 입증하였다. 국내 화강풍화토에 대한 공진주시험, 비틂전단시험, 삼축시험 등 일련의 실내시험 결과를 이용하여 검증한 결과, 쌍곡선 모델 및 Ramberg-Osgood모델과 비교하여 제안된 모델은 미소변형률에서 대변형률까지의 거동을 더욱 일관되고 정확하게 모델할 수 있다. 또한 비틂전단시험 결과와의 비교에서는, 미소변형률 조건에서 나타나는 비선형성을 적합하게 예측할 수 있었다.

• 소성∙가공
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• 제13권1호
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• pp.15-20
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• 2004

본 연구에서는 자동차용 판재 성형시 발생하는 스프링백을 정확히 예측하기 위하여, 수정된Chaboche형에 기초한 혼합형 등방-이동경화규칙이 개발되었다. 또한 판재의 이방성을 위하여 최근 개발된 Barlat의 YId2000-24 비이차 비이방성 항복 함수가 이용되었다. 단순인장실험과 인장/압축(압축/인장) 실험에 의하여 Bauschinger 및 transient 거동과 비이방성이 측정되었으며, 유한요소해석에 의한 구성방정식의 검증을 위해 실제 자동차 부품을 부분 변형시킨 double S-rail이 제작되었다. 수정된 Chaboche 형 조성방정식과 비등방 항복함수를 적용한 유한요소에 의한 수치해석의 결과는 굽힘에 의한 스프링백과 비틀림에 있어서 실험과 잘 일치함을 알 수 있었다.

• 소성∙가공
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• 제17권7호
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• pp.517-522
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• 2008

A visco-plastic self-consistent (VPSC) polycrystal model has been applied to simulate texture simulation and anisotropic properties of DP steels during deep drawing process. In order to evaluate the strain path during deep drawing, a steady state was assumed in the flange part of deep drawn cup. The final stable orientations were strongly dependent on the initial location in the blank. The evolution of anisotropy of DP steel sheets has been demonstrated through comparison of plastic strain rate vector at the different plastic strain levels.

• 소성∙가공
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• 제15권8호
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• pp.533-538
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• 2006

A simplified numerical procedure to predict drawbead restraining forces(DBRF) has been developed based on the hybrid membrane/bending method which superposes bending effects onto membrane solutions. As a semi-analytical method, the new approach is especially useful to analyze the effects of various constitutive parameters. The present model can accommodate general anisotropic yield functions along with non-linear isotropic-kinematic hardening under the plane strain condition. For the preliminary results, several sensitivity analyses for the process and material effects such as friction, drawbead depth, hardening behavior including the Bauschinger effect and yield surface shapes on the DBRF are carried out.

• 소성∙가공
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• 제18권4호
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• pp.329-335
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• 2009

In order to better predict the springback for friction stir welded DP590 steel sheet, the combined isotropic-kinematic hardening was formulated with considering the permanent softening behavior during reverse loading. As for yield function, the non-quadratic anisotropic yield function, Yld2000-2d, was used under plane stress condition. For the verification purposes, comparisons of simulation and experiments were performed here for the unconstrained cylindrical bending, the 2-D draw bending tests. For two applications, simulations showed good agreements with experiments.

• 소성∙가공
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• 제21권6호
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• pp.372-377
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• 2012

In this study, the plastic flow behaviors of extra deep drawing quality (EDDQ) steel subjected to non-proportional strain paths were investigated. Two-step uniaxial tension tests, in which the first step was performed in the rolling direction (RD) and the subsequent test in different directions in $15^{\circ}$ increments from the RD, were conducted. The experiments clearly showed that stress overshooting and strain hardening stagnation were the dominant features, which were captured reasonably well using a recently proposed distortional hardening model.

• 소성∙가공
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• 제4권3호
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• pp.222-232
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• 1995

The planar anisotripic FEM analysis for predicting earing profiles and draw-in amounts in the deep-drawing process is introduced. An implicit, incremental, updated Lagrangian formulation with a rigid-viscoplastic constitutive equation is employed. Contact and friction are considered through the mesh-based unit vector and normal contact pressure. The consistent full set of governing relations, which is comprising euilbrium and geometric constraint equations, is appropriately linearized. Barlat's strain-rate potential is employed, whose in-plane anisotropic properties are taken into account with anisotropic coefficients and potential parameters. The linear triangular membrane elements are used for depicting the formed sheet. In the numerical simulations of deep drawing processes of a flat-top cylindrical cup for 2090-T3 aluminum alloy sheet show good agreement with experiments, although some discrepancies were observed in the directional trend of cup height and thickness strains.

• 소성∙가공
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• 제8권3호
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• pp.252-261
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• 1999

The 3-dimensional finite element program is developed to analyze the non-isothermal forming processes of aluminum-alloy sheet metals. Bishop's method is introduced to solve the heat balance and force equilibrium equations. Also, Barlat's non-quadratic anisotropic yield function depicts the planar anisotropy of the aluminum-alloy sheet. To find an appropriate constitutive equation, four different forms are reviewed. For the verification of the reliability of the developed program, the computational try-outs of the non-isothermal cylindrical cupping processes of AL5052-H32 and Al1050-H16 are carried out. As results, the constitutive equation relating to strain and strain-rate, in which the constants are represented by the 5th-degree polynomials of temperature, is in good agreement with measurement. The computational try-outs can predict optimal forming conditions in non-isothermal forming processes.

• 소성∙가공
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• 제22권6호
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• pp.310-316
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• 2013

Recently, numerical predictions of surface deflection based on curvature analysis have been developed. In the current study, a measure of surface deflection is proposed as the maximum variation of curvature difference between the panel and the tool in order to account for surfaces that have high curvature. The current study focused on the assessment of accuracy for the surface deflection prediction with the consideration of planar anisotropy. As an example, a shallow rectangular drawn part with rectangular embossing was considered. In terms of the proposed surface deflection measure, the maximum variation of curvature difference, the prediction with a planar anisotropic model shows better correspondence with experiment than the one using a normal anisotropic model.

• 소성∙가공
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• 제7권6호
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• pp.594-602
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• 1998

The design analysis of axisymmetric, multi-stage deep drawing dies was performed using the rigid-viscoplastic finite element formulation. In the formulation the axisymmetric CFS algorithm was employed. Hill's non-quadratic normal anisotropic yield criterion and isotropic hardening rule were considered. For trial initial displacements and tool contact points. the geometric force equilibrium method was adopted. In order to see the validity of the formulation, the multi-stage deep drawing processes of shell-cylinder front part of hydraulic booster were simulated. The simulation showed good agreements with measurments and PAM-STAMP results.