TEKNOLOGIAN TUTKIMUSKESKUS VTT OY Ballististen Materiaalien mallinnusavusteinen kehittäminen - BalMa MATINE Tutkimusseminaari 17.11.2016 Tomi Lindroos, Matti Lindroos, Anssi Laukkanen
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 11.11.2016 2
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. 11.11.2016 3
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) 11.11.2016 4
Multi-scale modelling 11.11.2016 5
Material and Structure Test structure for ballistic testing against 7.62-51 FFV AP (M993) and cross-section of structure after impact 11.11.2016 6
Microstructure informed modeling
Deformation at microscale Computational microstructure Simplified compression of the microstructure to reveal local stress-strain behavior and its relationship to failure Loading axis (compression) strain rate ε = 11 1 8
At damage initiation Deformation at microscale Uniaxial deformation in compression, strain rate 11 1 Equivalent stress Strain Carbide damage 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) 9
Understanding the failure process Tensile cut-off Click to edit Master Degradiation title style of JH-2 strength chosen for TiC Fractured material cannot withstand tensile loads, but resists compression Strength of the matrix (Ni) rate-dependent Strength degraded with JC-damage because of more ductile nature of Ni Fragments Damage (local scale facture process) Displacement field (macroscopic understanding of the fracture) 10
Deformation at microscale (visualization) Strain rate 20 000 1/s -- Homogenized curve (macroscopic behavior) Click to edit Peak Master strength title style Damaged strength (compression) Damage developed in RVE Intact material with very little damage Damage initiates throughout the microstructure 11
Strain, stress, carbide and matrix damage evolutions Shear bands Click Strain to edit Master title style Carbide damage Eqv. stress Matrix damage Damage accumulation in the matrix Compression axis 12
Upscaling the microstructure RVE SEM-based model (green = TiC, light = Ni) Larger representative volume element (RVE) ~170 µm 1.328mm 256 µm 2.048 mm 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 13
Deformation and failure at larger scale Stress Strain Carbide damage 2.048 mm Strain (Failed material removed) 14
Stress Deformation and failure at larger scale Strain 2.048 mm Stress concentrations assisting cracking Strain localization to failed regions Strength of the material mostly lost (stress levels are decreased) Damage Secondary crack networks develop 1 1 1 At damage initiation Evolution Degraded/Failed 15
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) 16
Deformation and failure at larger scale Microscale observations (direct SEM microstructure) Adibatic heating of the matrix has relatively little effect due to rapid failure of the carbide structure at high loads Cracked carbides as a one source of failure, but it absorbs energy in the process 17
The sources of failure during impact loading (high strain rate conditions) local behavior Increasing deformation Initiation of local failure Crack propagation from carbide-to-carbide Closed loop fracture in a carbide Heavy fracture and (slip line) network in a carbide 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 Fractured material (Blue=carbide) (Light=matrix) 18
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 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 Macroscopic strain ~0.013 19
Microstructure design possibilities Microstructure A Carbide content ~0.88 Microstructure B Carbide content ~0.71 Microstructure A Microstructure 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 20
Visualization of impact event (task 2) Stresses at shock front Fracture along carbide (blue) Strain localization, including fracture 21
Material crushing zone Stresses at shock front 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) Fracture along carbide (blue) 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 22
Multi-scale: From microstructure to macroscopic material performance Resist or penetrate?
Projectile deacceleration during the impact TiC-Ni Stress TiC-Ni = 7 mm Steel = 4 mm WC-Co TiC-Ni Steel Damage of projectile and steel Damage of TiC-Ni 24
Projectile deacceleration during the impact TiC-Ni Residual velocity ~50 % Energy loss = ~90% Nominal projectile velocity decreased by ~50 % before reaching the steel section 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 25
Performance at different thicknesses Total Thickness = 11mm Fully blocked Small energy penetration possible Total Thickness = 15mm Penetration Residual energy with 9mm, only ~5% Total Thickness = 7mm (Steel t = 4 mm) 26
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 Fourth models level 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 27
High Speed Camera tests High-speed camera tests of ballistic impact 23.11.2016 Verification data for models Selected videos will be publishes ww.vtt.fi/powder 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 Example https://youtu.be/a5vmivy2uh8 28
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