Sangyul Ha

Heterogeneous deformation of Al single crystal: Experiments and finite element analysis

This work combined experiments at the grain level with the constitutive modeling of a single crystal to investigate deformation behaviors of a pure aluminum single crystal oriented for a single slip. Simple compression of a [132] single crystal was conducted to obtain the macroscopic stress—strain response and observe the deformed shape of the sample. The evolution of the crystallographic orientation was measured by an electron backscattered diffraction system in a field emission scanning electron microscope. The heterogeneous in-plane surface deformation in a single crystal was calculated by using a digital image correlation technique. Finite element modeling based on a single crystal plasticity model agrees well with experimental results in an averaged sense, not at the individual dislocation level.

Experimental and numerical investigation of deformation behavior of aluminum multi-crystals during simple shear

In this study, experimental data is obtained and CPFEM analysis is performed to characterize the constitutive response of f.c.c. crystalline materials. Dislocation density based crystal plasticity model have been used to elucidate the deformation mechanism of the crystalline materials with limited number of grains. The simple shear experiment of multi crystal aluminum is analyzed for the first time. The results from initial orientation which affects the deformation of materials is predicted and analyzed. This research is expected to be a fundamental research about plastic deformation and anisotropy of materials.

Analysis for Fracture Characteristics of Porous Materials by using Cohesive Zone Models

The effect of porosity on the crack propagation is studied by using the cohesive zone model. Standard mode Ⅰ fracture test were done by using compact tension specimens with various porosities. Load-load line displacement curves and δ5-crack resistance curves for various porosities were obtained from experiments. The cohesive zone model proposed by Xu and Needleman was employed to describe the crack propagation in porous media, and the Gurson model is used for constitutive relation of porous materials. These models were implemented into user subroutines of a finite element program ABAQUS. The fracture mode changes from ductile fracture to brittle fracture as the porosity increases. Numerical calculations agree well with experimental results.

Finite Element Analysis for Die Compaction Process of Cemented Carbide Tool Parts

This paper reports on the finite elements analysis for die compaction process of cemented carbide tool parts. Experimental data were obtained under die compaction and triaxial compression with various loading conditions. The elastoplastic constitutive equations based on the yield function of Shima and Oyane were implemented into an explicit finite element program (ABAQUS/Explicit) and implicit finite element program (PMsolver/Compaction-3D) to simulate compaction response of cemented carbide powder during die compaction. For simulation of die compaction, the material parameters for Shima and Oyane model were obtained by uniaxial die compaction test. Explicit finite element results were compared with implicit results for cemented carbide powder.