Upload
others
View
5
Download
0
Embed Size (px)
Citation preview
Page 1
RESEARCH: N. TRIANTAFYLLIDIS
RECENT WORK ON:
• Shape Memory Alloys (at different scales)
• Coupled Physics Problems (Mechanical -Magnetic - Electrical, at different speeds)
• Composites and Microstructured Media
RESEARCH: N. TRIANTAFYLLIDIS
Page 2
RESEARCH: N. TRIANTAFYLLIDIS Shape Memory Alloys (Atomic M-Lattices)
• Idea: Use atomistic models to find stablecrystal configurations at differenttemperatures and stresses
• Tools: Numerical calculations guided bysymmetry arguments and L(yapunov)-S(chmidt)-K(oiter) asymptotic techniques
• Collaborators: J. Shaw, R. Elliott
Page 3
RESEARCH: N. TRIANTAFYLLIDISShape Memory Alloys (NiTi)
Satellite Frangibolts
Page 4
RESEARCH: N. TRIANTAFYLLIDISShape Memory Alloys (Atomic M-Lattices)
Transformations under [110] stressStress-free Transformations
Page 5
RESEARCH: N. TRIANTAFYLLIDIS Shape Memory Alloys (Atomic M-Lattices)
Stress-stretch ratio for A-Mphase transformation
Energy-stress for A-Mphase transformation
Page 6
RESEARCH: N. TRIANTAFYLLIDIS Shape Memory Alloys (Honeycomb Structures)
• Idea: Use cellular architecture to increaserecoverable strain and decrease response time
• Tools: New experimental technique allowsbonding of NiTi strips. FEM calculations and useof Bloch wave theory predict interesting behavior
• Collaborators: J. Shaw, D. Grummon, P.Michailides
Page 7
RESEARCH: N. TRIANTAFYLLIDISShape Memory Alloys (Honeycomb Structures)
Isothermalresponse
Shapememoryresponse
Page 8
RESEARCH: N. TRIANTAFYLLIDISShape Memory Alloys (Honeycomb Structures)
Unit cell and finite structure response
Page 9
RESEARCH: N. TRIANTAFYLLIDISShape Memory Alloys (Honeycomb Structures)
Morphing effect in isothermal response (due to stability & phase transformation)
Page 10
RESEARCH: N. TRIANTAFYLLIDIS Coupled Physics (Magneto-Elasticity)
• Idea: Use iron particle-impregnated rubber tochange composite’s stiffness under externalmagnetic fields. Devices for sensors/actuators,vibration damping
• Tools: Developed theoretical framework formodeling these materials (direct and variationalapproach). Method is basis for FEM calculations.
• Collaborators: S. Kankanala
Page 11
RESEARCH: N. TRIANTAFYLLIDIS Coupled Physics (Magneto-Elasticity)
VNV A
V
NV
A
MRE torsional mounth
!
t
!
"#
!
t
Trac
tion
t (M
pa)
Stretch Ratio λ
Page 12
RESEARCH: N. TRIANTAFYLLIDIS Coupled Physics (Magneto-Elasticity)
Experimental set-up to determine constitutive properties
Displacement
MR Elastomer
Equipotential
Magnetic Plates
To Fluxmeter
(to measure B)
Gaussmeter(to measure H)
N S
Poles ofElectromagnet
Nonmagnetic
Yoke
Electromagnet
Load Cell
Displacement
Page 13
RESEARCH: N. TRIANTAFYLLIDIS Coupled Physics (Magneto-Elasticity)
• We solve the magnetoelasticbuckling of a rectangular blocksubjected to transverseuniform magnetic field.
• We use experiments to selectmaterial parameters.
• We use asymptotic analysis tocheck structural solutions ofthe corresponding beamproblem
SN
h0
Magnetoelastic beam buckling
Page 14
RESEARCH: N. TRIANTAFYLLIDIS Coupled Physics (Magneto-Elasticity)
Critical magnetic field as a function of aspect ratio (antis. & sym. modes).
Page 15
RESEARCH: N. TRIANTAFYLLIDIS Coupled Physics (Electro-Magnetic Forming)
• Idea: Use consistent formulation to model EMFprocesses and avoid current staggering schemesof solving independently and sequentially amechanics and an electromagnetic problem
• Tools: Developed theoretical framework formodeling these materials (direct andvariational approach). Method is basis for FEMcalculations using variational integratortechniques
• Collaborators: J. Bradley, G. Daehn, J. Thomas
Page 16
RESEARCH: N. TRIANTAFYLLIDIS Coupled Physics (Electro-Magnetic Forming)
EMF increases ductility overconventional methods (i.e. higherstrains attained before necking)
EMF used in aerospace andautomotive applications (i.e. fuel cells)
Page 17
RESEARCH: N. TRIANTAFYLLIDIS Coupled Physics (Electro-Magnetic Forming)
Page 18
RESEARCH: N. TRIANTAFYLLIDISShort Tube Simulations (free expansion)
R
Z
Page 19
RESEARCH: N. TRIANTAFYLLIDISLong Tube Simulations (free expansion)
R
Z
Page 20
RESEARCH: N. TRIANTAFYLLIDIS Composites and Microstructured Media
• Idea: Consistent derivation of “onset of failuresurfaces” (in stress or strain space) in solids withregular micro-structures
• Tools: Develop consistent nonlinear macroscopicmodels and check failure predictions againstmicroscopic case when failure starts as a localbuckling mode
• Collaborators: J.-C. Michel, D. Kosinsky, P.Ponte-Castaneda, O. Lopez-Pamies, W.Scherzinger
Page 21
RESEARCH: N. TRIANTAFYLLIDIS Composites and Microstructured Media
Macroscopic instability detected asloss of ellipticity in “averaged” moduli
Microscopic instability detected as firstbifurcation away from periodic solution
Page 22
RESEARCH: N. TRIANTAFYLLIDIS Composites and Microstructured Media
Page 23
RESEARCH: N. TRIANTAFYLLIDIS Composites and Microstructured Media
Macro and micro failure surfaces for finitely strained porous elastomers
Page 24
RESEARCH: N. TRIANTAFYLLIDISt
l
w
Reinforced composite
Room temperature collapse
High temperature collapseOnset of instabilities at 20% strain
Compressed reinforced honeycomb