• 소성∙가공
• /
• 제1권1호
• /
• pp.95-103
• /
• 1992

The plane strain analysis for simulating the stretch/draw forming operation with an arbitrarily-shaped tool profile is introduced. An implicit, incremental, updated Lagrangian formulation with a rigid-viscoplastic constitutive equation is employed. Contact and friction are considered through the mesh-normal, which compatibly describes arbitrary tool surfaces and FEM meshes without depending on the explicit spatial derivatives of tool surfaces. The linear line elements are used for depicting the formed sheet, based on membrane approximation. The FEM formulation is tested in the sections of automotive inner panel and two-side draw-in. Not only the excellent agreement between measured and computed strains is obtained in the stretched section, but also the numerical stability of formulation is verified in the draw-in section.

• 소성∙가공
• /
• 제16권4호
• /
• pp.276-281
• /
• 2007

The hardening and the constitutive equation based on the crystal plasticity are introduced for the numerical simulation of hemispherical sheet metal forming. For calculating the deformation and the stress of the crystal, Taylor's model of the crystalline aggregate is employed. The hardening is evaluated by using the Taylor factor, the critical resolved shear stress of the slip system, and the sum of the crystallographic shears. During the hemispherical forming process, the texture of the sheet metal is evolved by the plastic deformation of the crystal. By calculating the Euler angles of the BCC sheet, the texture evolution of the sheet is traced during the forming process. Deformation texture of the BCC sheet is represented by using the pole figure. The comparison of the strain distribution and punch force in the hemispherical forming process between the prediction using crystal plasticity and experiment shows the verification of the crystal plasticity-based formulation and the accuracy of the hardening and constitutive equation obtained from the crystal plasticity.

• 한국자동차공학회논문집
• /
• 제13권2호
• /
• pp.58-64
• /
• 2005

An infinite element for impact problem has been developed using ABAQUS/Standard UEL. 4-node plane strain element was considered, and the constitutive equation was derived from properties of propagation plane body waves. The element acts as unbounded domain to the plane waves generated by impact. The numerical method was tested for the simulation of plate impact. The results show the effectiveness of the infinite element.

• 소성∙가공
• /
• 제12권4호
• /
• pp.290-295
• /
• 2003

High temperature deformation behavior and prediction of final microstructure after forming of Ti-6Al-4V alloy were investigated in this study. Equiaxed and Widmanstatten microstructures of Ti-6Al-4V alloys were prepared as initial microstructures and compression tests were performed to obtain the flow curves at high temperatures (700∼110$0^{\circ}C$) and various strain rates (10$^{-4}$ ∼10$^2$/s). From the results of compression test, strain rate sensitivity (m) and activation energy (Q) were calculated and used to establish constitutive equation. To predict the final microstructure after farming, finite element analysis was performed considering the microstructural parameters such as grain size and volume fraction of second phase.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2003년도 추계학술대회 논문집(III)
• /
• pp.79-84
• /
• 2003

A fictitious crack model was used to analyze fatigue crack growth under the influence of residual stress. In the fictitious crack model, crack is represented in terms of the separation of two adjacent interfaces and the constitutive equation between the separation and traction is assumed. The effect of fatigue loading was included in the constitutive equation by considering damage accumulation in the cohesive zone. To investigate the effect of the residual stress on the fatigue crack growth, we calculated the residual stress distribution due to transient heat flux to the specimen by finite element method. Fatigue crack growth was simulated by the fictitious crack model with repeated loading. The mode-I crack growth rates were compared for the cases with and without the compressive residual stress around the crack tip. It was observed that the mode-I crack growth can be suppressed by compressive residual stress.

• Structural Engineering and Mechanics
• /
• 제5권6호
• /
• pp.679-689
• /
• 1997

The damage of concrete subjected to multiaxial complex loading involves strong anisotropy due to its highly heterogeneous nature and the geometrically anisotropic characteristic of the microcracks. A comprehensive description of concrete damage is proposed by introducing a fourth-order anisotropic damage tenser. The evolution of damage is assumed to be related to the principal components of the current states of stress and damage. The unilateral effect of damage due to the closure and opening of microcracks is taken into account by introducing projection tensors that are also determined by the current state of stress. The proposed damage model considers the different kinds of damage mechanisms that result in different failure modes and different patterns of microdefects that cause different unilateral effects. This damage model is embedded in a thermomechanically consistent constitutive equation in which hardening and the triaxial compression caused shear-enhanced compaction can also be taken into account. The validity of the proposed model is verified by comparing theoretical and experimental results of plain and steel fiber reinforced concrete subjected to complex triaxial stress histories.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2004년도 추계학술대회논문집
• /
• pp.287-290
• /
• 2004

A structure using the two-way shape memory effect (TWSME) returns to its initial shape by increasing or decreasing temperature under initial residual stress. Through the thermo-mechanical constitutive equation of shape memory alloy(SMA) proposed by Lagoudas et al., we simulate the behavior of a double actuator in which two SMA wires are attached to the tip of panel under the initially given residual stress. Through the numerical results conducted in the present study, the proposed actuator device is suitable for repeated actuation. The simulation algorithm proposed in the present study can be applied extensively to the analysis of the assembled .system of SMA-actuator and host structure in the practical applications.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
• /
• pp.120.2-120.2
• /
• 2005

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
• /
• pp.160.1-160.1
• /
• 2005

• 한국유변학회:학술대회논문집
• /
• 한국유변학회 2000년도 추계 학술발표회 논문집
• /
• pp.3-6
• /
• 2000