Dr. Gunjin Yun

Aerospace Structures and Materials Laboratory

3D Digital Image Correlation System

MTS Tester MachineClustered Super Computer

• KAIST BS (1994) / MS (1996)• University of Illinois Urbana-Champaign PhD (2006)• Washington University in St. Louis Post-Doc (2007)

• 1996-2002 Samsung Corporation Institute of Technology Researcher• 2008-2013 The University of Akron, Assistant Professor• 2013-2016 The University of Akron, Associate Professor• 2016-Present Seoul National University, Professor

• Air Force Summer Faculty Fellowship (2012, 2013)• NASA GRC Research Grants (2009-2012, 2014)

IN ASML

Aerospace Structural and Materials Laboratory has been

conducting cutting-edge research on m u l t i s c a l e a n d

multiphysics problems including thermal structural behavior,

life prediction, nonlinear deformation and damage models of

aircraft structures and composite materials used in extreme

loads, including complex loads and high temperature / high

pressures. We are working on both experimental and

simulation research on composite materials.

서울대학교 창의선도

신진 연구자 지원사업

ASML(Aerospace Structure & Material Lab.)Location : Building 300 Room 503

Tel : +82-2-880-7389

Homepage : asml.snu.ac.kr

3D Printer

Molecular Dynamics Simulation of Ablation

Thermal Protection System (TPS)

• Flight Vehicles with high speed are exposed to harsh environment in

earth’s atmosphere.

• Thermal Protection Systems are used to protect people and vehicles

from hot temperature.

Multiscale Approach with MD (Molecular Dynamics ) Simulation

• Using MD simulation, we can understand fundamental chemical

reactions and improve an accuracy of computational modeling

3C-SiC crystal structure

Deep Learning-based Joint Model for Hybrid FEA

A

Bolts

Bearings

X

Y

Z

Reference result Forwarding result @12500 epoch

Data acquisition Verification of the ANN-based FEA

Reference result UEL + ANN result (@20000 epoch)

Verification of the ANN-based FEA

x

y0.3 [mm]

2 beams

Data acquisition

ANN-based FEA : Forwarding result @ 25000 epoch

Reference result

Front-axle simulation

(scaled stress)

(scaled stress)

Molecular Dynamics Simulation of Nanocomposites

Nonlinear Micromechanics Analysis

Damage Plasticity Constitutive Model for CNT Nanocomposites

• Mori-Tanaka is one of the analytical homogenization scheme for predicting effective properties of composite materials• In order to express physical comprehensive material behaviors, nonlinear behaviors from plasticity & damage are considered

Ellipsoidal inclusion Cylinder fiber

Aspect ratio

Straight fiber with interfacial damage Wavy fiber with interfacial damage

Rotational

Transformation

Overall Scheme for Modified Mori-Tanaka Approach with Matrix Ductile Damage

• Taking account of interfacial/Matrix damage & effect of CNT waviness

+

Matrix ductile damage

Modified Mori-Tanaka Approach Results & Verifications with FE

Flowchart for modified Mori-tanaka Approach

• Describe the effective behaviors by changing the variables • Verification with FE model

Coarse grained MD with multi-objective optimization

Objective functions

2

,

1

1n

k k ref

k

fn MSD MSD

2 reffn

Deb, K., et al. (2002). IEEE transactions on evolutionary computation 6(2): 182-197.

NSGA-II (Non-dominated Sorting Genetic Algorithm)

VARTM(Vacuum Assisted Resin Transfer Molding) (Microscope Mechanical Test System)

FE Multiscale Analysis for Composites

FE2 Multiscale Anaylsis for Composite Materials• FE2 Multiscale Anaylsis is one of the numerical homogenization scheme for predicting

effective properties of composite materials by solving each scale problems

FE2 Multiscale Anaylsis Results• Profile of Macro- & Micro- FE model and results

• Identifing the plastic deformation distribution of RVE at point A from the anaylsis

Microstructure Topology Optimization by Targeting PrescribedNonlinear Stress-Strain Relationships