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The present work investigates the mechanical and thermomechanical bending response of beam structures possessing a triangular lattice microarchitecture. The validity of generalized continuum models, in general, and the associated dimensionally reduced models for functionally step-wise-graded microarchitectural beams, in particular, is approved by full-field finite element simulations. Most importantly, the necessity of the temperature gradient in the Helmholtz free energy is substantiated. The corresponding strong and weak forms for the associated Bernoulli–Euler and Timoshenko models of functionally graded beams are derived. The effective classical thermoelastic properties of a metamaterial with a triangular lattice microarchitecture are defined by means of computational homogenization. The additional length scale parameter involved in the generalized beam models, and associated to the particular triangular microarchitecture, is calibrated by fitting the mechanical bending responses of a series of lattice beams to the analytical solutions of the corresponding theoretical models. Strongly size-dependent mechanical and size-independent thermal bending responses are observed for both thin and thick beams with triangular lattice microarchitectures. Finally, different lattice beams with varying microarchitectures are introduced and shown to behave as generalized functionally step-wise-graded beams with respect to the higher-order elastic modulus, i.e., the length scale parameter varying in the direction of the beam axis.

For oxide coatings, prepared by applying plasma electrolytic oxidation (PEO) to aluminium alloy Al6082, this conference contribution presents the finite element (FE) microstructural modeling of the PEO coatings. By utilizing the coating phase maps, obtained by electron back-scattered diffraction (EBSD) technique, the corresponding images have been converted into FE models with a detailed microstructure representation. By utilizing experimental data such as loading-unloading curves obtained upon micro-indentation using a Berkovich tip on the coatings cross-sections and surfaces, the material models representing the coating constituent phases have been calibrated.

For three-dimensional cellular beam- and plate-like structures with a triangular microarchitecture, this conference contribution presents a family of two-scale beam and plate models relying on the anisotropic form of Mindlin's strain gradient elasticity theory of form II. A computational homogenization method is adopted for determining the constitutive parameters of the related classical and higher-order constitutive tensors. Isogeometric conforming Galerkin methods are applied for solving the beam and plate problems. Numerical examples illustrate the reliability and efficiency of the dimensionally reduced structural models and numerical methods – in capturing the bending size effects induced by the microarchitecture, in particular.

A strain gradient elasticity model for shells of arbitrary geometry is derived for the first time. The Kirchhoff-Love shell kinematics is employed in the context of a one-parameter modification of Mindlin's strain gradient elasticity theory. The weak form of the static boundary value problem of the generalized shell model is formulated within an H-3 Sobolev space setting incorporating first-, second- and third-order derivatives of the displacement variables. The strong form governing equations with a complete set of boundary conditions are derived via the principle of virtual work. A detailed description focusing on the non-standard features of the implementation of the corresponding Galerkin discretizations is provided. The numerical computations are accomplished with a conforming isogeometric method by adopting C-P(-1)-continuous NURBS basis functions of order p >= 3. Convergence studies and comparisons to the corresponding three-dimensional solid element simulation verify the shell element implementation. Numerical results demonstrate the crucial capabilities of the non-standard shell model: capturing size effects and smoothening stress singularities. (C) 2018 Elsevier B.V. All rights reserved.

Technische Mechanik; 38; 1; 73-90; ISSN 2199-9244, We develop a numerical procedure for solving boundary value problems for elastic solids undergoing chemical transformations. The kinetic equation for the reaction front propagation is based on an expression for the chemical affinity tensor, which allows us to study the influence of stresses and strains on the chemical reaction rate and the normal component of the reaction front velocity. Isogeometric analysis provides a high accuracy when finding the normal to the reaction front, and it is applied with the use of Abaqus to a numerical simulation of the front propagation. In order to test and demonstrate the capabilities of the developed procedure a hollow cylinder undergoing a chemical transformation is considered. First, an axially-symmetric problem is solved and a good agreement between numerical simulations and analytical results is demonstrated. Then a case is considered where the initial front configuration does not have axial symmetry. Reaction front acceleration, retardation, and even reaction blocking due to mechanical stresses are investigated.