A finite strain beam formulation. The three-dimensional dynamic problem. I
In the context of a director type of approach, \textit{S. S. Antman} has developed a three-dimensional extension of the classical Kirchhoff-Love rod model including finite extension and finite shearing [Q. Appl. Math. 32, 221-240 (1974; Zbl 0302.73031)]. This paper should be regarded as a convenient parametrization of this extension, realized by constraining the 3-dimensional theory with the introduction of the kinematic assumption. In section 1, the formulation of the basic kinematics of the beam is given in terms of a 3-dimensional orthogonal moving frame defined so that one of its vectors, denoted by n, remains normal to a typical cross- section in any configuration. Corresponding expressions for the linear and angular momentum are obtained in section 2. The former is associated with the acceleration of the centroid and the latter with the time derivative of the vorticity vector of the moving frame. Next, the basic laws of motion are summarized in section 3, and the spatial and material descriptions of the resultant force acting on a cross-section are discussed. In section 4, starting with the general 3-dimensional expression for the internal power, the author develops spatial and material reduced expressions involvig the resultant force and torque and their conjugate strain rates. In the material description the reduced expression for the internal power enables one to identify the appropriate strain measures. In particular, the strain measure conjugate to the resultant torque has a simple geometric interpretation as the axial vector of a skew-symmetric tensor associated with the moving frame. In the spatial description, in addition to the appropriate strain measures, the reduced expression of the internal power determines the appropriate (objective) strain rate as the rate of change relative to an observer spinning with the moving frame. Finally, in section 5, i) it is shown that for the plane problem the present development reduces to that proposed by \textit{E. Reissner} [Z. Angew. Math. Phys. 23, 795-804 (1972; Zbl 0248.73022)]; ii) a remark is given on the significance of the parametrization employed in this paper in a finite element solution procedure. Issues concerning the resulting geometric stiffness and the numerical implementation of the formulation discussed here in the context of the finite element method will be addressed in a forthcoming paper.
reduced expression for the internal power
scientific article; zbMATH DE number 3934502