Finite Strain Shape Memory Alloys Modeling - Scuola di Dottorato in ...

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4 A FINITE STRAIN CONSTITUTIVE MODEL4.1 IntroductionA new phenomenological model for shape memory alloys in the framework of finitestrain is proposed.The model formulation is motivated by the well-understood micromechanicalanalysis of single-crystal metal plasticity (Fig. 4.1).Fig. 4.1: Kinematic model of elastoplastic deformation of a single crystalMetals in their usual form are polycrystalline aggregates, that is, they are composedof large numbers of grains, each of which has the structure of a simple crystal(Lubliner, 1990; Lubliner, 1991). A crystal is a three-dimensional array of atomsforming a regular lattice. The atoms vibrate about fixed points in the lattice but donot move away from them, being held more or less in place by the forces exerted byneighboring atoms. Because of the random orientation of individual grains in atypical metallic body, the overall behavior of the aggregate is largely isotropic, but56
such phenomena as the Bauschinger effect and preferred orientation, which occur asa result of different plastic deformation of grains with different orientations,demonstrate the effect of crystal structure on plastic behavior. In single crystals forwhich crystallographic slip is assumed to be the only mechanism of plasticdeformation, the material flows through the lattice via dislocation motion, while thelattice itself, with the material embedded to it, undergoes elastic deformation androtation. If the discrete dislocation substructure is ignored, the plastic deformationcan be considered to occur in the form of smooth shearing on the slip planes and inthe slip directions. This continuum slip model from the pioneering work of Taylor(1938) was employed and further developed by Hill (1950), Hill and Rice (1972) andAsaro (1983). For a crystal with a single slip system denoted by { sm , } withms ⋅ =0 and m = s = 1, this micromechanical description can be illustrated as inFig. 4.1. The unit vectors { sm , } are attached to the lattice, and the plastic flow ischaracterized by the tensor Fpdefined as:F = 1+ γs⊗m (4.1)pwhere γ is the plastic shearing on the crystallographic slip system defined by{ sm , }. Furthermore, the total deformation of the crystal is decomposed as:F= FF(4.2)epwhereFpis the part due to the slip only that moves the material through the latticevia dislocation motion, while Ferotates and distorts the crystal lattice.57
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University of CassinoFaculty of Eng
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Contents1. INTRODUCTION ...........
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5.2.1.2. Finite Element Approximati
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1 INTRODUCTIONScience and technolog
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The implementations of the model in
Page 11 and 12: applications are presented in order
Page 13 and 14: 2 SHAPE MEMORY ALLOYS2.1 Introducti
Page 16 and 17: transformation (M→A), indicated r
Page 18: Fig. 2.2: SuperelasticityFig. 2.3:
Page 21 and 22: The Differential Scanning Calorimet
Page 23 and 24: 2.3 Biocompatibility of Shape-Memor
Page 25 and 26: only in the angioplasty procedure,
Page 27 and 28: micropumps used to unblock blood ve
Page 29 and 30: introduction of a multi-well free-e
Page 31 and 32: spectral decomposition allowing the
Page 33 and 34: Fig. 3.1: Reference and deformed co
Page 35 and 36: δ δ = δ and δ δ = δ(3.6)iI iJ
Page 37 and 38: and it is a two-point tensor since
Page 39 and 40: Furthermore,( ) 2 2Jdet b= det F =
Page 41 and 42: 3.2.3 Polar DecompositionThe deform
Page 43 and 44: which can now be interpreted as fir
Page 45 and 46: Fig. 3.2: Representation of the pol
Page 47 and 48: ecause, as time progresses, the spe
Page 49 and 50: It can be introduced the rotated ra
Page 51 and 52: traction vector. For the Cauchy’s
Page 53 and 54: Nt per unit area acting on the boun
Page 55 and 56: transforms according to a= Qa. Velo
Page 57 and 58: ∂∂t=−∂F∂t−1 −1 −1F
Page 59 and 60: where the direct dependency upon X
Page 61: 3.4.2 Isotropic Hyperelasticity - M
Page 65 and 66: superposed to intermediate configur
Page 67 and 68: whereΨerepresents the elastic stra
Page 69 and 70: ( )( ) E 1 ( )Ψ = h ω β T − M
Page 71 and 72: 4.2.2 Clausius-Duhem InequalityIn o
Page 73 and 74: −1∂Ψe−TS− 2FtFt= 0∂Ce(4.
Page 75 and 76: qφ = T : dt− ⋅gradT≥0(4.30)T
Page 77 and 78: fact the values of ϕ andenergy usu
Page 79 and 80: 4.2.5 Final Format of the Constitut
Page 81 and 82: 1 ( C )*1t−1α = ( β T − M ( )
Page 83 and 84: 5 FINITE STRAIN CONSTITUTIVE MODEL:
Page 85 and 86: 2 3ζ 2 ζ 3exp( ζ g) = 1+ ζ g+ g
Page 87 and 88: where d is a user-defined parameter
Page 89 and 90: ⎡R R Rt⎢⎢RR Rt⎢⎣R R RtC C
Page 91 and 92: γ• R,Ct=12EEtt(5.28)• R γ ,
Page 93 and 94: The spatial virtual work equation s
Page 95 and 96: [ E E E 2 E 2 E 2 E ]δE = δ δ δ
Page 97 and 98: ˆNLB = B + B (5.51)a a ain whichBa
Page 99 and 100: Kirchhoff stress and converting int
Page 101 and 102: DF( φ)[ u]d=dεε = 0( φ εu)∂
Page 103 and 104: In terms of the linear strain tenso
Page 105 and 106: 6.2 3D Constitutive Model for Stres
Page 107 and 108: T − Mf Tη = η0− ⎡⎣h( ω)
Page 109 and 110: assumed to be ruled by the limit fu
Page 111 and 112: ♦The limit function is assumed fu
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6.3.1.1 Time Integration of the 3D
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⎧∂f∂ ε⎪ C ⎡⎤⎣ ⎦⎪
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RRRRRRRR*( f )2 2 2Xd, X= I+ hΔ ζ
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If equation (6.42) is considered as
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7 3D-1D Constitutive Model with 1D
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*∂f6 3σ9 3 2 2 T Ml− hϑ+mz β
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⎡⎤⎢1 0 0 ⎥⎢⎥1ε t= ϑ
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(7.21)σ3 1.5R=− βc( T − Mf)+2
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It is interesting to evaluate how m
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It can be noted that equations (7.3
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The inelastic step is solved by the
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For brevity, only the saturated pha
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Fig. 7.2. Timoshenko’s beam theor
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NNNv1v2v3N θ1= ξξ ( − 1)21= ξ
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to analyze the two-dimensional elem
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300 N . A regular mesh characterize
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8.1.1.3 Superelastic and Shape-Memo
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200180T=285 K160140120Force [N]1008
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8.1.2 Comparison between 3D and 3D-
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PhLFig. 8.7: Geometry and boundary
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250200150100Axial force [N]500-50-1
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908070Bending moment [Nmm]605040302
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The arch is subjected to tension-co
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10864Axial force [N]20-2-4-6-8beam
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Some parameters characterizing the
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9876Applied load [N]54321Numerical
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The proposed constitutive models se
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REFERENCESAdler P.H., Yu W., Pelton
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Auricchio F., Taylor R., A return-m
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Ciarlet P.G., The Finite Element Me
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Huang M.S., Brinson L.C., A multiva
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Raniecki B., Lexcellent Ch., Thermo
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Taylor G.I., Plastic strain in meta
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