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Crystal plasticity Wedge indentation and simulations of a Body Centered Cubic crystal.
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
2014 (English)Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Experiment and simulations of a wedge indenter into Body Centered Cubic (BCC) single crystal were performed. The indenter with included angle of 90 degrees was applied 200 _m in depth. The indentation was performed under plane strain conditions, resulting in seven in-plane slip system sets. The midsection of the single crystal was exposed by wire Electrical Discharge Machine (EDM) and the in-plane lattice rotation was calculated by measuring the crystallographic orientation with electron backscatter diffraction (EBSD). Lower bounds of Geometrically Necessary Dislocation (GND) densities were also calculated and plotted. Numerical simulations were performed in order to determine the plastic properties of tantalum and to understand the internal crystallographic interaction of a BCC single crystal. The inuence of latent to self hardening ratio between slip system sets in the same slip family and latent to self hardening between slip system sets in different slip families have been investigated. For Face Center Cubic (FCC) material latent to self hardening ratio between slip system sets in the same slip family has not been taken into account, since FCC material only consist of one slip family. However, materials with BCC crystal structure have two slip families and therefore, both ratios have to be taken into consideration. The simulations were performed with and without self to latent hardening between sets in different slip families. The comparison between the experimental lattice rotation and the lattice rotation given by the simulations are overall very good for both cases. In order to determine which case that describes the experimental behavior best additional experiments have to be performed.

Abstract [sv]

Experiment och numeriska simuleringar av en intryckning i en Body Centered Cubic (BCC) enkristall har utförts. En intryckare med vinkeln pa 90 applicerades på 200 m djup. Intryckningen utfördes under plan töjning, vilket resulterar i sju glidsystemset. Mittsektionen av enkristallen exponerades med hjälp av en trådgnistmaskin och gitterrotationen  beräknades genom att mäta den kristallograska orienteringen med "electron backscatter di raction" (EBSD). Lägre gränsen Geometriskt Nödvändig Dislokationer (GND) densiteter beräknades och plottades. Numeriska simuleringar utfördes för att bestämma de plastiska egenskaperna hos materialet tantalum och för att förstå den interna kristallina interaktionen hos en BCC enkristall. Inverkan av förhallandet mellan latent till självhårdnande mellan glidsystemset inom samma glidfamilj och forhallandet mellan latent till sjalvhardnande mellan glidsystemset inom olika glidfamiljer har undersökts. För Face Center Cubic (FCC) material har inte förhållandet mellan latent till självhårdnande mellan glidsystemset inom samma glidfamilj beaktats, da FCC material endast består av en glidfamilj. Material med BCC struktur har två glidfamiljer och därför måste båda förhållandena beaktas. Simuleringarna utfördes med och utan latent till självhårdnande mellan glidsystemset i olika glidfamiljer. Jämförelsen mellan den experimentella gitterrotation och gitterrotation för simuleringarna är överlag mycket bra för båda fallen. För att kunna bestämma vilket av fallen som beskriver det experimentella beteende bästa måste ytterligare experiment utforas.

Place, publisher, year, edition, pages
2014. , 52 p.
National Category
Applied Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-177186OAI: oai:DiVA.org:kth-177186DiVA: diva2:871850
Subject / course
Solid Mechanics
Supervisors
Available from: 2015-11-18 Created: 2015-11-17 Last updated: 2015-11-18Bibliographically approved

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