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A numerical calculation scheme for stress and its consistent tangent moduli with hyper-dual numbers(HDN) for Ogden-type hyperelastic material model was proposed. The main advantage of this scheme is that once the framework is coded, any Ogden-type hyperelastic material model can be implemented by only re-coding the strain energy density function. In this scheme, the new differentiation method for eigenvalue and eigenvector of the symmetric matrices with HDN were proposed. The proposed method can calculate the eigenvalue and eigenvector in non-real part analytically by using the eigenvalue and eigenvector in real part, in case that all eigenvalues in real part are not multiple root. We implemented the Neo-Hookean model and the Ogden model with the proposed scheme, to confirm the effectiveness and robustness of this method, and applied it to some examples. As the results, it was confirmed that the numerical results of the proposed method showed good agreement with analytical ones.

To diagnose hill-top branching and multiple bifurcation, which exhibit two critical eigenvalues of the tangent stiffness matrix in stability problems, a sophisticated computational asymptotic bifurcation theory is developed. The theory generally uses three modes which are composed of two homogeneous solutions (critical eigenvectors) and one particular solution of the singular stiffness equations. The first- and second-order derivatives of the stiffness matrix with respect to nodal degrees-of-freedom (DoF) are required to formulate the proposed computational asymptotic bifurcation theory. In two benchmark problems of hill-top branching and multiple bifurcation, the validation and performance of the proposed theory are discussed.

This paper presents a novel Formulated Alpha FEM with deviatoric / volumetric split, which is combination of standard FEM and Node-based Smoothed FEM (NS-FEM), to compute highly accurate deformation in mechanical problems using tetrahedral elements. The essential idea of the method is the use of a deviatoric alpha formulated on basis of the results of cantilever problem, and the volumetric alpha introduced NS-FEM. The features of this proposed method are: 1) immune from volumetric locking, 2) less sensitive to element distortion, and 3) to be carried out with the same preprocessing as standard FEM from user’s viewpoint. Several numerical examples show that the present method achieves higher accuracy compared to the standard FEM and Edge-based/NS-FEM which is known to be one of the best S-FEM formulations.

This paper proposes a novel implementation scheme of geometrically nonlinear finite element programs, which automatically compute exact internal force vectors and element stiffness matrices by numerically differentiating a strain energy function at each element. This method can significantly simplify the complex implementation procedure which is often observed in conventional finite element implementations, since it never requires B matrices, stress tensors, and elastic tensors by hand. The proposed method is based on a highly accurate numerical derivatives which use hyper-dual numbers and never suffer from any round-off and truncation errors. Several numerical examples are performed to demonstrate the effectiveness and robustness of the proposed method.

For error-free computation of high-derivatives of mathematical functions used in engineering applications, hyper-dual numbers (HDN) are receiving much attention in computational mechanics. Differently from classical finite differences, HDN provides a practically exact evaluation of higher-derivatives, such as the first and second derivatives of stiffness matrix with respect to nodal degrees-of-freedom (dof). As a preliminary step for introducing HDN in stability problems, the present paper formulates the theoretical basis of a 2-mode asymptotic bifurcation theory and examines its versatility on simple bench models. All obtained results in numerical examples well predict the stability behavior and agree with existing analytical solutions.