• Korea-Australia Rheology Journal
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• v.16 no.4
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• pp.213-218
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• 2004

Linear high-density polyethylene (PE) was controlled to induce strain-hardening behavior by introducing a small amount of second component with an anisotropic structure. In order to form an anisotropic structure in the PE matrix, the polymer was extruded through a twin-screw extruder, and the structure was controlled by varying the extrusion conditions. Depending on conditions, the second component formed a film, thread and droplet structure. If the second component was kept rigid, the morphology evolution could be delayed and the second component could maintain its film or thread structure without further relaxation. In par­ticular, the second component of the thread structure made a physical network and gave rise to remarkable strain hardening behavior under high extension. This study suggests a new method that induces strain hard­ening behavior by introducing a physically networked second component into the linear polymer melt. This result is anticipated to improve the processibility of linear polymers especially when extensional flow is dominant, and to contribute to our understanding of strain hardening behavior.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.1299-1306
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• 2005

The introduction of geodetic methods of absolute displacement monitoring in tunnels has improved the value of the measurements significantly. By using this method, structurally controlled behavior and influences of an anisotropic rock mass can be determined and the excavation and support adjusted accordingly. In this study cases of tunnel monitoring in anisotropic/heterogeneous rock masses are analyzed, and various anisotrpic behavior of tunnel can be estimated. Because rock anisotropy and heterogeneity can have great influence on tunnel behavior, tunnel design considering rock anisotropy and heterogeneity is needed. Also under construction, feedback must be performed by using face mapping and monitoring to prevent over-deformation and tunnel collapse.

• Transactions of Materials Processing
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• v.23 no.5
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• pp.311-316
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• 2014

In the current study, the R-value behavior of a two-layer clad steel was investigated using finite element analysis. Hill's 1948 anisotropic yield equation was employed to characterize the anisotropic behavior of the steel with different assumed properties: isotropic (R=1) and anisotropic (R=2). Experimental R-values were determined by measuring the width and thickness ratios of tensile specimens. Finite element analysis results demonstrate a difference in strain behavior in the width and the thickness directions of the clad steel. The R-value behavior depends on the fraction of the clad materials and total elongation.

• Transactions of Materials Processing
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• v.20 no.5
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• pp.369-376
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• 2011

A non-quadratic anisotropic strain rate potential was introduced as a conjugate potential of the yield stress potential Yld2000-2d to describe anisotropic behavior of sheet metals, in particular, aluminum alloy sheets under plane stress state. This strain-rate potential takes into account the anisotropic yield stresses and R-values measured along the directions measured at 0, 45 and 90 degrees from the rolling direction, as well as the balanced biaxial yield stress and strain-rate ratio. The convexity of the strain-rate potential was completely proven. The strain-rate potential was applied for two anisotropic aluminum alloy sheets, AA6022-T4 and AA2090-T3. The results verified that the strain rate potential properly described the anisotropic behavior of aluminum alloy sheets and was closely conjugate of Yld2000-2d under the plane stress state.

• Journal of the Korean Society for Advanced Composite Structures
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• v.5 no.4
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• pp.1-10
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• 2014

A progressive failure analysis procedure for composite laminates is developed in here and in the companion paper. An anisotropic plastic constitutive model for fiber-reinforced composite material, is developed, which is simple and efficient to be implemented into computer program for a predictive analysis procedure of composites. In current development of the constitutive model, an incremental elastic-plastic constitutive model is adopted to represent progressively the nonlinear material behavior of composite materials until a material failure is predicted. An anisotropic initial yield criterion is established that includes the effects of different yield strengths in each material direction, and between tension and compression. Anisotropic work-hardening model and subsequent yield surface are developed to describe material behavior beyond the initial yield under the general loading condition. The current model is implemented into a computer code, which is Predictive Analysis for Composite Structures (PACS), and is presented in the companion paper. The accuracy and efficiency of the anisotropic plastic constitutive model are verified by solving a number of various fiber-reinforced composite laminates with and without geometric discontinuity. The comparisons of the numerical results to the experimental and other numerical results available in the literature indicate the validity and efficiency of the developed model.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.10a
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• pp.147-150
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• 2004

In order to describe the mechanical behavior of highly anisotropic and asymmetric materials such as fiber­reinforced composites, the elastic-plastic constitutive equations were used here based on the recently developed yield criterion and hardening laws. As for the yield criterion, modified Drucker-Prager yield surface was used to represent the orthotropic and asymetric properties of composite materials, while the anisotropic evolution of back­stress was accounted for the hardening behavior. Experimental procedures to obtain the material parameters of the hardening laws and yield surface are presented for 3D Circular Braided Glass Fiber Reinforced Composites. For verification purpose, comparisons of finite element simulations using the elastic-plastic constitutive equations, anisotropic elastic constitutive equations and experiments were performed for the three point bending tests. The results of finite element simulations showed good agreements with experiments, especially for the elastic-plastic constitutive equations with yield criterion considering anisotropy as well as asymmetry and anisotropic back stress evolution rule.

• Korean Journal of Computational Design and Engineering
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• v.2 no.2
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• pp.71-76
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• 1997

The deformations of polycrystalline materials are modelled by linking a constitutive equation for the crystallographic slip of a single crystal to the macroscopic behavior of the aggregate. In this study, anisotropic elasticity (lattice stretching) of a cubic crystal is incoporated into the anisotropic plasticity from crystallographic slip. The constitutive description for the aggregate, derived from a crystal plasticity theory, is used to formulate a Consistent Penalty Finite Element Method for the anisotropic elasto-viscoplastic deformation of polycrystalline materials. As an application, a plane-strain forging process is simulated and the effects of the initial textures on the deformation behavior of the workpiece are examined.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.144-147
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• 2003

In order to evaluate spring-back behavior in automotive sheet forming processes, a panel shape idealized as a SS-rail has been investigated. After spring-back kas been predicted fer SS-rails using the finite element analysis, results has been compared with experimental measurements for three automotive sheets. To account for hardening behavior such as the Bauschinger and transient effects in addition to anisotropic behavior, the combined isotropic-kinematic hardening law based on the Chaboche type single-surface model and a recently developed non-quadratic anisotropic yield function have been utilized, respectively.

• Fibers and Polymers
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• v.7 no.2
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• pp.123-128
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• 2006

The present study aims at characterizing and modeling the anisotropic creep behavior of coated textile membrane, a class of flexible textile composites that are used for moderate span enclosures (roofs and air-halls). The objective is to develop a creep model for predicting the lifetime of coated textile membrane. Uniaxial creep tests were conducted on three off-axis coupon specimens to obtain the directional creep compliance. A potential with three parameters is shown to be adequate for modeling the anisotropic creep behavior of coated textile membrane. Furthermore, a possibility of predicting the creep deformation of coated textile membrane in a multi-axial stress state is discussed using the three-parameter potential.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.6 no.6
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• pp.525-530
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• 2005

In this study, it is presented analysis results of bending problems in the anisotropic thick shell and the anisotropic thin shell bending problems. In the numerical analysis of various mechanical problems involving complex partial differential equations, finite element method is used. Both Kirchoffs assumptions and Mindlin assumptions are used as the basic governing equations of bending problems in the anisotropic shells. The analysis results are compared between the anisotropic thick shells and the anisotropic thin shells for the various width-thickness ratios. The numerical method of this study will be contributed not only to analysis the bending behavior of anisotropic shells but also to design the anisotropic shells.