Geometric effects on impact mitigation in architected auxetic metamaterials

Lightweight materials used for impact mitigation must be able to resist impact and absorb the maximum amount of energy from the impactor. Auxetic materials have the potential to achieve high resistance by drawing material into the impact zone and providing higher indentation and shear resistance. However, these materials must be artificially...

Topology optimization of geometrically nonlinear structures using reduced-order modeling

High computational costs are encountered in topology optimization problems of geometrically nonlinear structures since intensive use has to be made of incremental-iterative finite element simulations. To alleviate this computational intensity, reduced-order models (ROMs) are explored in this paper. The proposed method targets ROM bases...

Strain-rate based arclength model for nonlinear microscale analysis of unidirectional composites under off-axis loading

In this paper, a micromechanical framework for modeling the rate-dependent response of unidirectional composites subjected to off-axis loading is introduced. The model is intended for a thin slice representative volume element that is oriented perpendicular to the reinforcement of the composite material. The testing conditions from a uniaxial...

Buckling test of stiffened panels: Evaluation of post-buckling and failure by testing and layerwise models

The present paper deals with the buckling and post-buckling analysis of a multilayered composite reinforced panel. The panel, design for aeronautical applications, results in a complex stacking sequence, and the development of a refined model able to describe its geometrical nonlinear behavior is mandatory to avoid the usage of highly...

Numerical simulation of elastic buckling in 3D concrete printing using the lattice model with geometric nonlinearity

This paper explores buildability quantification of randomly meshed 3D printed concrete objects by considering structural failure by elastic buckling. The newly proposed model considers the most relevant printing parameters, including time-dependent material behaviors, printing velocity, localized damage and influence of sequential printing...

Topological synthesis of fluidic pressure-actuated robust compliant mechanisms

This paper presents a robust density-based topology optimization approach for synthesizing pressure-actuated compliant mechanisms. To ensure functionality under manufacturing inaccuracies, the robust or three-field formulation is employed, involving dilated, intermediate and eroded realizations of the design. Darcy's law in conjunction with a...

A modal derivatives enhanced Rubin substructuring method for geometrically nonlinear multibody systems

This paper presents a novel model order reduction technique for 3D flexible multibody systems featuring nonlinear elastic behavior. We adopt the mean-axis floating frame approach in combination with an enhanced Rubin substructuring technique for the construction of the reduction basis. The standard Rubin reduction basis is augmented with the...

A high-order model for in-plane vibrations of rotating rings on elastic foundation

A new high-order model for in-plane vibrations of rotating rings is developed in this paper. The inner surface of the ring is connected to an immovable axis through an elastic foundation (distributed springs), whereas the outer surface is traction free. The developed model enables the dynamic analysis of the rings on stiff elastic foundation...

Model order reduction and substructuring methods for nonlinear structural dynamics

Dynamic analysis of large-size finite element models has been commonly applied by mechanical engineers to simulate the dynamic behavior of complex structures. The ever-increasing demand for both detailed and accurate simulation of complex structures forces mechanical engineers to pursue a balance between two conflicting goals during the...

Nonlinear model order reduction for flexible multibody dynamics: A modal derivatives approach

An effective reduction technique is presented for flexible multibody systems, for which the elastic deflection could not be considered small. We consider here the planar beam systems undergoing large elastic rotations, in the floating frame description. The proposed method enriches the classical linear reduction basis with modal derivatives...

Modal Derivatives based Reduction Method for Finite Deflections in Floating Frame

Model order reduction techniques are widely applied in the floating frame of reference. The use of linear vibration modes, however, is not applicable when the elastic deformations become finite. In this paper, the non-linear elastic formulation, where the higher-order terms will be included in the strain energy expression to consider the bending...

A Koiter-Newton arclength method for buckling-sensitive structures

Thin-walled structures, when properly designed, possess a high strength-to-weight and stiffness-to-weight ratio, and therefore are used as the primary components in some weight critical structural applications, such as aerospace and marine engineering. These structures are prone to be limited in their load carrying capability by buckling, while...

Pushing the Boundaries: Level-set Methods and Geometrical Nonlinearities in Structural Topology Optimization

This thesis aims at understanding and improving topology optimization techniques focusing on density-based level-set methods and geometrical nonlinearities. Central in this work are the numerical modeling of the mechanical response of a design and the consistency of the optimization process itself. Concerning the first topic, we investigate...

A level-set based topology optimization using the element connectivity parameterization method

This contribution presents a novel and versatile approach to geometrically nonlinear topology optimization by combining the level-set method with the element connectivity parameterization method or ECP. The combined advantages of both methods open up the possibility to treat a wide range of optimization problems involving complex physical and/or...

A perturbation approach for geometrically nonlinear structural analysis using a general purpose finite element code

In this thesis, a finite element based perturbation approach is presented for geometrically nonlinear analysis of thin-walled structures. Geometrically nonlinear static and dynamic analyses are essential for this class of structures. Nowadays nonlinear analysis of thin-walled shell structures is often done using finite element based incremental...

Discontinious Galerkin formulations for thin bending problems

A structural thin bending problem is essentially associated with a fourth-order partial differential equation. Within the finite element framework, the numerical solution of thin bending problems demands the use of C^1 continuous shape functions. Elements using these functions are challenging and difficult to construct. A particular...

Finite element procedure for modelling fibre metal laminates