ballististen materiaalien mallinnusavusteinen kehittäminen

TEKNOLOGIAN TUTKIMUSKESKUS VTT OY

Ballististen Materiaalien

mallinnusavusteinen

kehittäminen - BalMa

MATINE Tutkimusseminaari 17.11.2016

Tomi Lindroos, Matti Lindroos, Anssi

Laukkanen

211.11.2016 2

Projektin perustiedot

Ballististen Materiaalien mallinnusavusteinen kehittäminen – BalMa,

projektikoodi 2500M-0047

Projekti on suunniteltu kaksivuotiseksi alkaen 1.1.2015 ja päättyen

31.11.2016.

Rahoitus 2016: MATINE 51 500 €, VTT 16 662 €, 68 162 €

Ohjausryhmä:

Tomi Lindroos, VTT

Paavo Raerinne, PVTUTKL

Jukka Kemppainen, Exote Oy

Pekka Lintula, Nammo Lapua Oy

311.11.2016 3

Tausta, lähtökohdat ja kytkennät aiempiin tutkimuksiin

Suojauskyvyn kasvattaminen ja samanaikainen painon alentaminen edellyttävät yhä

kehittyneempien ja suorituskykyisempien materiaalien ja materiaaliyhdistelmien käyttöä

Hyödyntämällä uusia, kehittyneitä mallinnus- ja simulointityökaluja on mahdollista

ymmärtää paremmin monimutkaistenkin materiaalien ja rakenteiden käyttäytymistä,

nopeuttaa kehitysprosessia ja päästä lähemmäs optimaalista ratkaisua.

Perinteisesti mallinnusaktiviteetit ovat rajoittuneet rakenteiden ja ballistisen iskun

karkeahkoon FE mallinnukseen. Makroskooppisilla rakennemalleilla ei kuitenkaan

pystytä kuvaamaan kaikkia vuorovaikutuksia, joista tutkittavan komponentin

suorituskyky muodostuu.

Monitasomallinnuksen (multi-scale modelling) avulla malliin voidaan luoda

yksityiskohtaisempia piirteitä aina elektroni- ja atomitasolle asti riippuen kuvattavan

ilmiön mittakaavasta.

411.11.2016 4

TAVOITTEET

Projektin kokonaistavoitteena on kehittää työkaluja, jotka mahdollistavat entistä

tehokkaampien (suorituskyky = suojaustaso + neliöpaino) suojausmateriaalien

ja rakenteiden kehittämisen nopeammin ja kustannustehokkaammin.

Projektissa luodaan perusteet materiaalien ja rakenteiden

mallinnusavusteiselle suunnittelulle ja lisätään tätä kautta ymmärtämystä

materiaalien käyttäytymisestä ballistisessa iskussa.

TEHTÄVÄT Selvittää monitasomallinnuksen tämän hetkiset mahdollisuudet ja rajoitukset

entistä tehokkaampien ballististen suojamateriaalien kehittämiseksi. (task 1)

Kehittää mikrorakennetason malleja, jotka mahdollistavat iskuenergian

jakautumisen visualisoinnin mikrorakenteessa ja tätä kautta ymmärtää miten

mikrorakennetta tulisi muokata suorituskyvyn kasvattamiseksi. (task 2)

Suorittaa kokeellista testausta (mekaaniset ominaisuudet, ampumakokeet)

mallien verifioimiseksi ja mallinnuksen materiaaliparametrien määrittämiseksi.

(task 3)

511.11.2016 5

Multi-scale modelling

611.11.2016 6

Material and Structure

Test structure for ballistic testing

against 7.62-51 FFV AP (M993) and

cross-section of structure after

impact

Microstructure informed modeling

Click to edit Master title style

Click to edit Master text styles

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88

Deformation at microscale

Computational microstructure

Loading axis

(compression)

strain rate�ε = 𝟏𝟏 𝟏

Simplified compression of the microstructure

to reveal local stress-strain behavior and its

relationship to failure



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99

Deformation at microscale Uniaxial deformation in compression, strain rate 𝟏𝟏 𝟏

Equivalent stress Strain Carbide damage

At damage

initiation

Stress relief after

material damage

(material stiffness

degraded)

Strain

localization in

matrix and

failed carbides

Damage network

inside carbides

(damage also prevails

in the matrix along the

shear bands)



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1010

Understanding the failure process

Damage

(local scale facture process)

Displacement field

(macroscopic understanding of the fracture)

Fragments

Fractured material

cannot withstand

tensile loads, but

resists compression

Degradiation of

strength chosen

for TiC

Strength of the matrix (Ni) rate-dependent

Strength degraded with JC-damage

because of more ductile nature of Ni

Tensile cut-off

JH-2



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1111

Deformation at microscale (visualization)

Peak strength

Damage initiates

throughout the

microstructure

Damage

developed

in RVE Damaged strength

(compression)

Intact material with

very little damage

Strain rate 20 000 1/s -- Homogenized curve (macroscopic behavior)



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1212

Strain, stress, carbide and matrix damage evolutions

Strain Carbide damage

Eqv. stress Matrix damage

Compression

axis

Shear bands

Damage

accumulation

in the matrix



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Upscaling the microstructure RVE

Larger scale allows to investigate the failure propagation in the

microstructure closer to the macroscopic scale

The transition from microscale (um) to mm, or even larger is

easier to establish when the microstructure is in mm-scale

256 µm

~17

0 µ

m

SEM-based model (green = TiC, light = Ni) Larger representative volume element (RVE)

2.048 mm

1.3

28m

m



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1414

Deformation and failure at larger scaleStress Strain

Carbide damage Strain (Failed material removed)2.048 mm



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Deformation and failure at larger scaleStress

Strain

Damage

At damage initiation Evolution Degraded/Failed

Stress

concentrations

assisting cracking

Strain localization

to failed regions

Secondary crack networks develop

Strength of the material mostly lost

(stress levels are decreased)

𝟏 ≤ 𝟏 ≤ 𝟏

2.048 mm



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1616

Material behavior at different strain rates ( Current material structure)

• Material strength increases as a function of strain rate

• Damage develops earlier due to high shock loading, but strain rate dependent

strength compensates damage process (ductility slightly increases)



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Deformation and failure at larger scaleMicroscale observations (direct SEM microstructure)

• Cracked carbides as a one source of failure,

but it absorbs energy in the process• Adibatic heating of the matrix has relatively little effect due to

rapid failure of the carbide structure at high loads



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The sources of failure during impact loading

(high strain rate conditions) – local behavior

Heavy fracture and

(slip line) network

in a carbideCrack propagation from

carbide-to-carbide’Closed’ loop

fracture in a carbide

Increasing

deformation

Fractured

material

Initiation of

local failure

• Carbides develop individual and joining

crack networks

• Strain concentrations localize damage

also in matrix (and increases its

temperature by ~100-200 C occasionally)

• Interface mistmatch between carbides

and matrix accelerates fracture initiation

(Blue=carbide)

(Light=matrix)



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Macroscopic strain ~0.013• Rate dependent model and coupling with damage, features:

• Strength is increased by viscous drag (towards shock conditions)

• The shock conditions at 100000 1/s are very different to 1000 1/s

• At lower strain rates, the local fractures develops earlier to macroscopic failure

The sources of failure during impact loading

(high strain rate conditions) – local behavior

Carbide

damage

Localized

strain

Fully developed to macroscopic fracture(s) Partially developed to macroscopic fracture(s) Early local fracture development



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2020

Microstructure design possibilities

Microstructure A Carbide content ~0.88 Carbide content ~0.71Microstructure B

• Lowering carbide content provides slightly better local ductility, however,

strength decreased by 20%

• The capability of the microstructure to absorb (impact) energy decreases

• Optimization of the microstructure in respect to design variables is possible

Microstructure BMicrostructure A



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Visualization of impact event (task 2)

Stresses at shock front Fracture along carbide (blue)

Strain localization,

including fracture



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2222

Stresses at shock front Fracture along carbide (blue)

Fracture process:• Material is crushed close to the

contact interface

• Circumferential crack pattern

develops, while its intensity

depends on the local strengths

• Shear develops also in the binder

phase, but carbide damage

prevails the process due to stress

concentrations generated by cracks

• Structure resists deformation under

compression relatively well

(excluding the crushed zone)

Material crushing zone

Energy absorption:• High strength carbides

temporarily store strain energy

• Cracking process consumes a

reasonable amount of energy

• Matrix is able store less strain

energy, but it retains its ability

withstand further deformation

until ductile failure

Multi-scale: From microstructure to

macroscopic material performance

Resist or

penetrate?



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Projectile deacceleration during the impact TiC-Ni

Damage of projectile and steelDamage of TiC-Ni

Stress

• TiC-Ni = 7 mm

• Steel = 4 mm

TiC-Ni

Steel

WC-Co



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Projectile deacceleration during the impact

TiC-Ni

• Nominal projectile velocity decreased by ~50

% before reaching the steel section

Energy loss = ~90%

• But, projectile degrades (fractures) during the

impact effectively when interacting with TiC-Ni

Only 10% of the original kinetic energy of the

projectile is absorbed by the steel

Residual

velocity

~50 %



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Performance at different thicknesses

Penetration

Fully blocked

Total

Thickness = 7mm

(Steel t = 4 mm)

Total

Thickness = 15mm

Total

Thickness = 11mm

Small energy

penetration possible

Residual energy

with 9mm, only ~5%



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Possibilities with multi-scale modeling

Microstructure informed modeling can be used to test alternative microstructures and establish a

relationship between structure and performance (MATERIAL DESIGN ASPECT)

Failure models acting at microstructure scale are able to produce the main damage and failure

properties of TiC-Ni material(s), such as carbide fracture, binder phase shear localization.

Distribution of (impact) energy introduced to the material by ballistic impacts can be visualized only by

microstructure based models, because of the different local behavior of phases (and interfaces).

Macroscopic impact models are able to provide a reasonable design tool for material thickness for

armouring application (COMPONENT DESIGN ASPECT)

Preliminary experiments verify that the numerical models can produce realistic material behavior and

assess the stopping-penetration ability of the composite structures

The experimental verification tests are required to adjust the final model parameters prior to wider use

of the simulation predictions



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High Speed Camera tests

Example

https://youtu.be/a5VMIvY2Uh8

Phantom v2511• 1280 x 800 resolution

• 280ns minimum exposure

with the FAST option

• 1 µs minimum exposure

standard

• Up to 677,000 fps standard or

1,000,000 fps with the FAST

• High-speed camera tests of ballistic impact 23.11.2016

Verification data for models

• Selected videos will be publishes ww.vtt.fi/powder



http://www.vtt.fi/powder

TEKNOLOGIASTA TULOSTA

www.vtt.fi/powder

www.vttresearch.com/propertune

http://www.vtt.fi/powder

http://www.vttresearch.com/propertune

ballististen materiaalien mallinnusavusteinen kehittäminen

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