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A Fractional Nonlinear Creep Damage Model for Transversely Isotropic Rock

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Abstract

Transversely isotropic layered rock is widely distributed in nature. To better describe the time-dependent entire creep characteristics for transversely isotropic rock, a simple nonlinear damage creep model is derived based on fractional order theory, which consists of a Hooke elastomer, a fractional Abel dashpot, a fractional nonlinear damage dashpot, and can effectively describe the characteristics of primary creep, steady-state creep and accelerating damage creep. Assuming that Poisson's ratio is constant, the creep equation of isotropic rock is extended to transversely isotropic rock, and the nonlinear damage creep model for transversely isotropic rock is established. Step-wise loading triaxial creep tests of phyllite specimens with three kinds of bedding angles (0°, 45° and 90°) are carried out, and it is found that there are significant differences in creep deformation and failure characteristics under different bedding angles. The parameters of the creep model at each bedding angle are identified using the Universal Global Optimization method. By comparing the Nishihara model, the modified Nishihara model and experimental data, it shows that the creep model in this paper are highly consistent with the experimental data under different bedding angles, load levels and creep stages, and the accuracy and rationality of the model are verified.

Highlights

  • A simple nonlinear damage creep model is derived based on fractional order theory.

  • By assuming that Poisson's ratio is constant, the creep equation of isotropic rock is extended to transversely isotropic rock, and the nonlinear damage creep model for transversely isotropic rock is established.

  • There are significant differences in creep deformation and failure characteristics of phyllite specimens with different bedding angles.

  • Parameters of the proposed creep model at each bedding angle are identified by using the Universal Global Optimization, and the accuracy and rationality of the model are verified.

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Abbreviations

D :

Damage variable

E :

Elastic modulus parallel to foliation plane

E′ :

Elastic modulus perpendicular to foliation plane

G′ :

Shear modulus perpendicular to foliation plane

μ :

Poisson's ratio parallel to foliation plane

μ :

Poisson's ratio perpendicular to foliation plane

m :

Smallest integer greater than β

n :

Ratio of E' to E

t :

Creep time

t a :

Accelerating creep time

θ :

Angle between loading direction and normal direction of bedding plane

β :

Derivative order of visco-elastic body

γ :

Derivative order of visco-plastic body

η :

Viscosity coefficient

η 1 :

Viscosity coefficient of visco-elastic body

η 2 :

Viscosity coefficient of visco-plastic body

η 3 :

Viscosity coefficient of the nonlinear viscous body

λ :

Damage parameter

σ :

Axial stress

σ s :

Yield stress

ε :

Axial strain

ε e :

Elastic strain

ε ve :

Visco-elastic strain

ε vp :

Visco-plastic strain

ε a :

Triggered strain of the accelerating creep stage

σ x, σ y, σ z :

Axial stresses in global coordinate system

τ yz, τ zx, τ xy :

Tangential stresses in global coordinate system

ε x, ε y, ε z :

Axial strains in global coordinate system

γ yz, γ zx, γ xy :

Tangential strains in global coordinate system

E ω,ξ (x):

Mittag–Leffler function

J(t):

Creep compliance

Г(β):

Gamma function

[A]:

Poisson's ratio matrix for isotropic rock

[U]:

Poisson's ratio matrix for transversely isotropic rock

[S]:

Flexibility matrix of global coordinate system

[S ]:

Flexibility matrix of local coordinate system

[ε]:

Strain tensor of global coordinate system

[ε′]:

Strain tensor of local coordinate system

[σ]:

Stress tensor of global coordinate system

[σ ]:

Stress tensor of local coordinate system

s ij :

Components of matrix [S]

u ij :

Components of matrix [U]

References

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Acknowledgements

This research was supported by the High Speed Railway and Natural Science United Foundation of China (No. U1734205), the Transportation Science and Technology Project of Sichuan Province, China (No. 2019ZL09), and CSCEC Technology R & D Plan of China (No. CSCEC-2021-Z-26).

Funding

This research was supported by the High Speed Railway and Natural Science United Foundation of China (No. U1734205), the Transportation Science and Technology Project of Sichuan Province, China (No. 2019ZL09), and CSCEC Technology R & D Plan of China (No. CSCEC-2021-Z-26).

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Correspondence to Wenbo Yang.

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Kou, H., He, C., Yang, W. et al. A Fractional Nonlinear Creep Damage Model for Transversely Isotropic Rock. Rock Mech Rock Eng 56, 831–846 (2023). https://doi.org/10.1007/s00603-022-03108-y

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  • DOI: https://doi.org/10.1007/s00603-022-03108-y

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