A general higher-order shell theory for compressible isotropic hyperelastic materials using orthonormal moving frame
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The aim of this study is three-fold: (i) to present a general higher-order shell theory to analyze large deformations of thin or thick shell structures made of general compressible hyperelastic materials; (ii) to utilize the orthonormal or Cartans moving frame in the formulation of shell theory in contrast to the classical tensorial covariant coordinate system; and (iii) to present the nonlinear weak-form Galerkin finite element model for the given shell theory. The displacement field of a point on the line normal to the shell reference surface is approximated by the Taylor series or Legendre polynomials. The kinematics of motion in the assumed coordinate system is derived using the tools of exterior calculus. The use of an orthonormal moving frame makes it possible to represent kinematic quantities, e.g., determinant of the deformation gradient, in a far more efficient manner than the classical tensorial representation of the same with covariant bases. The manipulation of the various tensor used in the kinematics and dynamics of the structures can be carried out with ease and a more computationally efficient manner. The governing equation of the shell has been derived in the general surface coordinates. The methodology developed herein is very much algorithmic, and hence it can also be applied for any arbitrary interpolated surfaces with equal ease. The higher-order nature of the approximation of the displacement field makes the theory suitable for analyzing thick and thin shell structures. The compressible hyperelastic material model used as the constitutive relation of the material. The formulation presented herein can be specialized for various nonlinear hyperelastic constitutive models suitable for use, for example, in bio-mechanics and other soft-material problems (e.g., neo-Hookean material, Mooney-Rivlin material, Generalized power-law neo-Hookean material, and so on).
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