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

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Accordingly, the tensor α plays a role similar to the back-stress of the classicalplasticity and X is the relative stress.Introducing a yield function that is assumed to depend on the deviatoric part of thedevthermodynamic force f ( X ), the equation describing the associative normalityrule for the internal variable εtis given by:devdev∂f( X ) dev ∂f( X )ε t= ζ = ζI (6.32)dev∂X∂Xwith ζ the so-called plastic multiplier and ( dev = − 1)( : )X X X 1 1. From the3analysis of the flow rule form (6.28) it can be pointed out that the transformationstrain tensor ε tis a deviatoric tensor. This fact appears in a perfect agreement withthe experimental evidences indicating no volume variations during the phasetransition.Furhermore, between tension and compression pseudoelastic experiments, anasymmetric behavior is observed. In particular, at a given test temperature it is foundthat: (i) the stress level required to nucleate the martensitic phase from the austeniticphase is considerably higher in compression than in tension; (ii) the transformationstrain measured in compression is smaller than that in tension; (iii) the hysteresisloop generated in compression is wider (along the stress axis) than the hysteresisloop generated in tension. These major differences between the tension andcompression response of a Ni-Ti alloy in pseudoelastic experiments are shown inFig. 6.1.To catch the asymmetric behavior of SMA during tension-compression tests, theactivation of the phase transition, i.e. the evolution of the inelastic strain ε t, is102
assumed to be ruled by the limit function introduced by Auricchio and Petrini (2002;2004):J( X ) = 2 + −(6.33)3f J2m RJ2where J2and J3are the second and the third invariant of the deviatoric part of therelative stress X , defined, respectively, as:Jdevdev(( ) ) J ( )( )1 1X : 1 X : 1 (6.34)2 32 32=3=while R is the radius of the elastic domain in the deviatoric space and m is amaterial parameter, with m ≤ 0.46 to guarantee the yield surface convexity. Theparameters R and m are linked to the uniaxial critical transformation stresses intension σtand compression σc, respectively, through the following relations:2 σcσt 27 σc −σtR= 2 m=3 σ + σ 2 σ + σt c t c(6.35)103
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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
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applications are presented in order
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2 SHAPE MEMORY ALLOYS2.1 Introducti
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transformation (M→A), indicated r
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Fig. 2.2: SuperelasticityFig. 2.3:
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The Differential Scanning Calorimet
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2.3 Biocompatibility of Shape-Memor
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only in the angioplasty procedure,
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micropumps used to unblock blood ve
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introduction of a multi-well free-e
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spectral decomposition allowing the
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Fig. 3.1: Reference and deformed co
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δ δ = δ and δ δ = δ(3.6)iI iJ
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and it is a two-point tensor since
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Furthermore,( ) 2 2Jdet b= det F =
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3.2.3 Polar DecompositionThe deform
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which can now be interpreted as fir
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Fig. 3.2: Representation of the pol
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ecause, as time progresses, the spe
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It can be introduced the rotated ra
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traction vector. For the Cauchy’s
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Nt per unit area acting on the boun
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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 and 62: 3.4.2 Isotropic Hyperelasticity - M
Page 63 and 64: such phenomena as the Bauschinger e
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: T − Mf Tη = η0− ⎡⎣h( ω)
Page 111 and 112: ♦The limit function is assumed fu
Page 113 and 114: 6.3.1.1 Time Integration of the 3D
Page 115 and 116: ⎧∂f∂ ε⎪ C ⎡⎤⎣ ⎦⎪
Page 117 and 118: RRRRRRRR*( f )2 2 2Xd, X= I+ hΔ ζ
Page 119 and 120: If equation (6.42) is considered as
Page 121 and 122: 7 3D-1D Constitutive Model with 1D
Page 123 and 124: *∂f6 3σ9 3 2 2 T Ml− hϑ+mz β
Page 125 and 126: ⎡⎤⎢1 0 0 ⎥⎢⎥1ε t= ϑ
Page 127 and 128: (7.21)σ3 1.5R=− βc( T − Mf)+2
Page 129 and 130: It is interesting to evaluate how m
Page 131 and 132: It can be noted that equations (7.3
Page 133 and 134: The inelastic step is solved by the
Page 135 and 136: For brevity, only the saturated pha
Page 137 and 138: Fig. 7.2. Timoshenko’s beam theor
Page 139 and 140: NNNv1v2v3N θ1= ξξ ( − 1)21= ξ
Page 141 and 142: to analyze the two-dimensional elem
Page 143 and 144: 300 N . A regular mesh characterize
Page 145 and 146: 8.1.1.3 Superelastic and Shape-Memo
Page 147 and 148: 200180T=285 K160140120Force [N]1008
Page 149 and 150: 8.1.2 Comparison between 3D and 3D-
Page 151 and 152: PhLFig. 8.7: Geometry and boundary
Page 153 and 154: 250200150100Axial force [N]500-50-1
Page 155 and 156: 908070Bending moment [Nmm]605040302
Page 157 and 158: 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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Finite Strain Shape Memory Alloys Modeling - Scuola di Dottorato in ...

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