Role of Deformation Twinning in Strain Hardening and TextureRole of Deformation Twinning in Strain Hardening and Texture Evolution: Experiment and Numerical Simulation Evolution: Experiment and Numerical Simulation

S. R. Kalidindi & R. D. Doherty, Drexel University,S. R. Kalidindi & R. D. Doherty, Drexel University, MET MET DMR-0201382DMR-0201382Deformation twinning is the second most prevalent mode of plastic deformation in metals, and plays a dominant role in the strain hardening and underlying texture evolution in low temperature deformation of hcp metals. A combined experimental-modeling study was undertaken to incorporate deformation twinning and its associated hardening mechanisms in the crystal plasticity modeling framework. The model was found to provide good predictions of the anisotropic stress-strain response (Fig. 1) and texture evolution (Fig. 2) in a broad range of deformation modes.

0

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0 0.2 0.4 0.6 0.8 1 1.2 1.4

Equivalent strain

Eq

uiv

ale

nt

str

es

s (

MP

a)

Simple shear

simple compression in direction 2

simple compression in direction 3

E

PE

E

P

P

Fig.1. Comparison of measured (E) and predicted (P) true stress-strain curves for various deformation modes

Fig.2. Texture evolution at different strain levels during simple compression: (a) OIM measurement(b) Model prediction. ND is compression direction.

Role of Deformation Twinning in Strain Hardening and TextureRole of Deformation Twinning in Strain Hardening and Texture

Evolution: Experiments and Numerical SimulationsEvolution: Experiments and Numerical Simulations S. R. Kalidindi & R. D. Doherty, Drexel University,S. R. Kalidindi & R. D. Doherty, Drexel University, MET MET DMR-0201382DMR-0201382

Plastic deformation of -titanium is governed by both crystallographic slip and deformation twinning at low temperature. Twining plays an essential role in strain hardening and texture evolution, but is less well understood compared to slip.

Building on critical experimental observations, we have successfully developed a novel crystal plasticity model which incorporates deformation twinning and its associated hardening mechanisms for two different compositions of -titanium.

This model was found to provide good predictions of the anisotropic stress-strain response (Fig. 1) and texture evolution (Fig. 2) for both high purity and commercial purity -titanium in a broad range of deformation modes.

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0 0.5 1 1.5

Equivalent strain

Eq

uiv

ale

nt

str

ess(M

Pa

)

Simple compressionalong ND

Simple compression along TD

Simple shear

p

ppm

m

m

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0 0.5 1 1.5

Equivalent strain

Eq

uiv

ale

nt

str

ess(M

Pa

)

Simple compressionalong ND

Simple compression along TD

Simple shear

p

ppm

m

m

Fig.1. Comparison of measured (M) and predicted (P) true stress-strain curves in high purity -titanium.

RD

TD

0001

RD

TD

0001

RD

TD

0001

(a)

Initial Measured = -1.0 Predicted = -1.0

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ND

0001

RD

ND

0001

RD

ND

0001

(b)

Fig.2. Comparison of measured and predicted textures in simple compression along (a) ND and (b) TD in commercial purity -titanium.

Role of Deformation Twinning in Strain Hardening and TextureRole of Deformation Twinning in Strain Hardening and Texture Evolution: Experiment and Numerical Simulation Evolution: Experiment and Numerical Simulation

S. R. Kalidindi & R. D. Doherty, Drexel University,S. R. Kalidindi & R. D. Doherty, Drexel University, MET MET DMR-0201382DMR-0201382

Outreach:

A freshman from Washington State University, Jason Drexler, spent ten weeks working on this project with our research group during the summer 2005 as a part of an NSF funded REU experience. Through this program, this student now has a better appreciation of the role of the microstructure of in determining properties of a material and, more broadly, has been exposed to the scientific methods for innovations and discovery. Jason Drexler has shown a strong interest to pursue a graduate study in the area of materials science.

Education:

Gwenaelle Proust has successfully completed her PhD study and is continuing a post-doctoral training in a national lab. Xianping Wu is currently pursuing his PhD on this project and he is expected to complete his PhD in Spring 2006. Brendan Donohue, a senior student at Drexel University, has been working with our research group since Spring 2005. Exposure to cutting-edge research is expected to have a favorable impact on his future career plans.

Role of Deformation Twinning in Strain Hardening and TextureRole of Deformation Twinning in Strain Hardening and Texture

Evolution: Experiment and Numerical SimulationEvolution: Experiment and Numerical Simulation S. R. Kalidindi & R. D. Doherty, Drexel University,S. R. Kalidindi & R. D. Doherty, Drexel University, MET MET DMR-0201382DMR-0201382

Outreach:Several undergraduate students were exposed to this research. The list of students includes John Lloyd (now in the BS/MS program at Drexel University), Brendan Donohue (now in the PhD program at Drexel University), Jason Drexler (undergraduate student from Washington State University), Julio Nunez (minority undergraduate student from Pennsylvania State University), Robert Thomas (minority undergraduate student at Drexel University).

Education:Ayman Salem and Xianping Wu have completed their PhDs with support from this grant. Ayman is now employed at Air Force Research Laboratory in Dayton, OH. Xianping is scheduled to start employment at Exxon-Mobil in October 2006. Julio Nunez, working in our labs, as a participant

in the REU program at Drexel University.