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INVESTIGATION OF HIGH VELOCITY IMPACT

PHENOMENA USING EXPLICIT AND IMPLICIT

MSC FEM CODES

Nicola Bonora, Andrew Ruggiero and Gianluca Iannitti

University of Cassino, I-03043 Cassino, Italy

www.cdm.unicas.itwww.cdm.unicas.it

1

The University of The University of CassinoCassino was funded in 1979. Today, offers graduation program was funded in 1979. Today, offers graduation program

and master degree in Engineering, Literature and Philosophy, Busand master degree in Engineering, Literature and Philosophy, Business and iness and

Administration, Law, Sport ScienceAdministration, Law, Sport Science

CassinoCassino

Outline

• Introduction

• Numerical codes for shock wave propagation

• Implicit vs Explicit Code formulation

• Application example: Dynamic extrusion test

• Application example: Pathogenesis of retina damage under impact

• Summary and conclusions

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IntroductionImpact phenomena: areas of interest and applications

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Armour/Anti Armour Blasting Aeronautics

Planetary and debris impact Oil and gas Explosive forming, welding, etc.

Introduction

• The understanding of high velocity impact

phenomena requires the knowledge of the

material response at high pressures, strain and

strain rates, as well as experimental and

numerical simulation advanced capabilities

• The higher the strain rate the more localized

the deformation processes are

• Understanding the correlation between the

material microstructure and the mechanical

behavior at the continuum scale becomes an

essential issue

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MA

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IntroductionShock compression R&D at the University of Cassino:

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Capabilities :

� constitutive modeling;

� failure, fracture and fragmentation;

� numerical simulation: hydrocodes (Autodyn, Epic) and

FEM (MSC.MARC, MSC.DYTRAN, LS-DYNA);

� design of experiment and testing;

Experimental facilities:

� Hopkinson bar;

� light gas-gun for instrumented

ballistic testing up to 1km/s;

� drop weight, max. vel. 22 m/s;

� high speed camera (500.000 fps);

� DIC, digital image correlation.

Type of test:

� Dynamic tractions and compressions test

�Taylor impact test;

� Flyer plate impact;

� Dynamic Extrusion Test;

� V50;

� STANAG 2920 assessment tests

Hydrocodes vs FEM

• Hydrocode modeling is most applicable to time-dependent, non-linear problems

• Hydrocode modeling rests on three pillars:

– the Newtonian laws of motion;

– the equation of state;

– and the constitutive model

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• Discretization (Lagrangian/Eulerian):

• Finite difference method

• FEM

• SPH

Hydrocodes vs FEM

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PROs CONTs

Computational time

Complex physics

EOS

Fracture and fragms

Transients

Inertia

Less sensitivity to

mesh distortion

Inaccuracy

Instability

No general hydrocode: Autodyn, Epic, Pronto, MESA, SALES_2, etc.

Uniaxial strain formulation

Hydrocodes

For some classes of problems solution may be too inaccurateFEM offers the possibility to investigate shock compression problems

MSC.MARC (Direct integration) MSC.DYNTRAN (fluid structure interaction)

DTE - DYNAMIC EXTRUSION TEST

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G.T. Gray III et al., Los Alamos National Laboratory , Proc. SCCM 2009

Scope of the test

Understand the correlation between microstructure and material response

Develop identification procedures for material constitutive modeling

Investigate the performances of the computational methods available and the constitutive

modeling needs

DTE - MATERIALS AND METHODS

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Material: 99.99% Cu

Three microstructures:

a) Annealed at 400°C, 65 mm

b) Annealed at 600°C, 118 mm

c ) Annealed at 800°C, 185 mm

Test type:

a)Quasi static tension, compression (Gray III et al. 2008,

Bonora et al. , 2005), torsion (Chiantoni and Bonora,

2009)

b)Taylor impact test (Gray III et al., 2008, House et al.

2006)

c)Flyer plate impact (Gray III et al., 2006)

d)DTE

ReferencesG.T. Gray III et al., LANL , Proc. SCCM 2009

N. Bonora et a.l, Unicas, Proc. SCCM 2009

N. Bonora et al., Unicas, Proc. SCCM 2005

DTE - MATERIALS AND METHODS

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� Traditional characterization tests did not reveal

substantial differences among the three microstructures

� Taylor impact tests showed only an increase of the

“orange-peel” feature with increasing grain size

microstructure

� DTE test showed an increased ductility for smaller

grain size microstructure

DTE - MODELING

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Constitutive modeling:

Flow curve: Voce type law + J&C correction for temperature and strain rate

Equation of state: linear

Ductile Damage: non linear CDM (Bonora, 1997)

( ) ( )( ) ( )( )( )*0, , 1 exp 1 ln / 1 m

y p y pT R b C Tσ ε ε σ ε ε ε∞

= + − − + −

& & &

0

Vp K

V=

( )

11

ln( / )cr

f thcr

dpdD R D D

D

p

aaa

uae e

-

= × × × - ×

DTE - MODELING

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Constitutive modeling cont. :

Microstructure evolution:

Rate of dislocation density

Rate of grain size

DTE - MODELING: coupling

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Constitutive modeling cont. :

Microstructure-strength coupling:

*y

d

λσ σ= +

Hall-Petch

0

( ) /2exp

3 / 1m vib

m c

T d S R

T d d

= − −

Grain size effect on melting temperature

DTE - COMPUTATIONAL MODELING

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Parametric analysis:

Dime: Rigid vs deformable

Strain hardeing vs thermal

softening

Constitutive modeling

Global remeshing options

Analysis features:

Automatic global remeshing

Thermal conversion of the plastic

strain work

Linear equation of state

Grain size evolution effect on

strength and melting temp

Same average mesh

size used as for MESA

calculation: 0,065 mm

DTE - RESULTS

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Max contact pressure ≈ 1.2 GPa

¼ of the estimated oblique

shock pressure (MESA)

Before the extrusion out of the

dime the average pressure in

the ball is 400 MPa

approximately

With the rigid dime the

calculated peak contact

pressure is higher

DTE - RESULTS

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DTE - RESULTS

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Evolution of

“tensile” pressure.

If ductile damage in

form of voids can

initiate and grow

under tensile

pressure states,

ductile damage is

expected to occur

only under tension,

damage seems to be

activated later in the

deformation process

at the exit of the

dime.

Interrupted tests may

planned in this sense

DTE - RESULTS

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Eulerian hydrocode2D, MESA, Los Alamos NationalLaboratory2D, CTH, AFRL WMW, Eglin AFB, USA

Lagrangian grid hydrocodeEPIC, AFRL WMW, Eglin AFB, USA

FEM, Direct integrationMSC.MARC, University of Cassino, Italy

DTE - RESULTS: time evolution and experiments

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Los Alamos National Lab. results. DTE specimen configuration (sphere with sabot). Simulated using MESA. Impact velocity = 400 m/s. Copper sphere –MTS material model. Steel die – JC material model.


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Grain size distribution in the segment in the dime

Damage

DTE - Summary and conclusions

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The DTE test offers interesting possibilities for enhancing the effects of material microstructural

on the macroscopic response

The proposed modeling seems to capture most of the features of the deformation and damage

process occurring in the DTE in copper

Standard Finite element method, in conjunction with automatic remeshing, can provide accurate

description of dynamic processes

Future work:

perform DTE at UNICAS DynaLAB;

improve the microstructure evolution modelingincorporating texture and grain

elongation;

explore new projectile configuration other than sphere;

parametric experimental study on velocity effects

PATHOGENESIS OF RETINA DAMAGE UNDER BLUNT

IMPACT

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60% of ocular damage is caused by blunt

impacts (non perforating)

Resulting damage: retinal tears and

detachment, macular holes, choroid rupture,

dyalisis,etc..

Although, clinic phenomenology is well

described, mechanisms resposnible for

retinal damage are not understood yet.

Posterior vitreous basePosterior vitreous base

Most frequent retinal damage type

PATHOGENESIS OF RETINA DAMAGE UNDER BLUNT IMPACT

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Actual theories:

�Internal Limiting Membrane Stiffness

� Differential Globe Layer Deformation

� Vitreous Chord Pulling / Traction


MOTIVATION/APPROACH

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MOTIVATION

54 y.o. adult white male patient who was

subjected to PPV( pars plana vitrectomy)

arrived at the emergency room consequently

to a blunt impact. Investigation showed the

presence of amcular hole.

Question: What caused the retinal damage?

Hypothesis :

Dynamic compression and shock wave

reflection

Literature:

Milestone paper by Delory et al. (1969), who

performed instrumented ballistic test on the

eye, excluded shock wave pathogenesis

mechanism

APPROACH

Develop a virtual model for the human eye

under impact

Calibrate the model based on the Delori et al.

results

Use the model to understand possible role of

shock wave propagation

Compare vitreous with aqueous


MOTIVATION/APPROACH

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COMPUTATIONAL ISSUES

Lack of data for soft tissues and organic

fluids (few data, dispersed, low strain

rate, uniaxial tension)

Critical aspects for constitutive

modeling: high strain rates, multiaxial

state of stress, visco-hyper-elasticity

Soft-hard contact interface

Fluid-structure interaction

Viscous damping

Artificial viscosity

Viscous adhesion between tissues

APPROACH

Occam’s razor: use the least number of

assumptions to reproduce the

phenomenon

Materials: linear elastic, linear equation

of state, all tissues/vitreous in contact,

viscous damping for the vitreous

(Maxwell model)


FEM MODEL

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FEM MODEL

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RESULTS: Delori et al. experiment

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t = 0 0.05 msec 0.30 msec 0.80 msec 1.50 msec



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0.01

0.05

0.05

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9 1

0.05 msec

0.30 msec

0.80 msec

compression rebound

Shock wavearrival

Paired t-test analysis showed significant pressure difference between vitreous and aqueous filled eyes at the macula



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Macula Equator Vitreous Base

Vitreous Aqueous Vitreous Aqueous Vitreous Aqueous

Mpa t-t0 Mpa t-t0 Mpa t-t0 Mpa t-t0 Mpa t-t0 Mpa t-t0Peak Negative Pressure -0,6 0,03 -0,6 0,53 -0,2 0,97 -0,6 0,46 -0,8 0,35 -1 0,35

Peak Positive Pressure 1,3 0,25 1,8 0,86 0,4 0,44 0,8 0,52 0,5 0,08 0,5 0,07


RESULTS - Summary and conclusions

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Shock wave physics seems to be the driver for retinal damage under blunt impact conditions

Vitreous seems not to have a role in the retinal damage development

Although the number of simplifications, FEM numerical simulation is a powerful tool to

investigate structural behavior of human organs

Multi-physics approach to biomechanics and medicine requires new tools to be developed

(special interfaces, efficient constitutive models, more efficient contact algorithms, element

distortion check, etc.)

In our experience, MSC.DYTRAN performed better than hydrocodes

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INVESTIGATION OF HIGH VELOCITY IMPACT …pages.mscsoftware.com/rs/mscsoftware/images... · Complex physics EOS Fracture and fragms Transients ... 99.99% Cu Three microstructures: