1,721,055 research outputs found
A 3D multi-physics boundary element computational framework for polycrystalline materials micro-mechanics
Full text linkA recently developed novel three-dimensional (3D) computational framework for the analysis of polycrystalline materials at the grain scale is described in this lecture. The framework is based on the employment of: i) 3D Laguerre-Voronoi tessellations for the representation of the micro-morphology of polycrystalline materials; ii) boundary integral equations for the representation of the mechanics of the individual grains; iii) suitable cohesive traction-separation laws for the representation of the multi-physics behavior of the interfaces (either inter-granular or trans-granular) within the aggregate, which are the seat of damage initiation and evolution processes, up to complete decohesion and failure. The lecture will describe the main features of the proposed framework, its main advantages, current issues and direction of potential further development. Several applications to the computational analysis of damage initiation and micro-cracking of common and piezoelectric aggregates under different loading conditions will be discussed. The framework could find profitable application in the multiscale analysis of polycrystalline components and in the design of micro-electromechanical devices (MEMS)
Inter-Element Crack Propagation with High-Order Stress Equilibrium Element
Full text linkThe present contribution proposes a formulation based on the use of hybrid equilibrium elements (HEEs), for the analysis of inter-element delamination and fracture propagation problems. HEEs are defined in terms of quadratic stress fields, which strongly verify both the homogeneous and inter-element equilibrium equations and they are employed with interfaces, initially exhibiting rigid behavior, embedded at the elements’ sides. The interface model is formulated in terms of the same degrees of freedom of the HEE, without any additional burden. The cohesive zone model (CZM) of the extrinsic interface is rigorously developed in the damage mechanics framework, with perfect adhesion at the pre-failure condition and with linear softening at the post-failure regime. After a brief review, the formulation is computationally tested by simulating the behavior of a double-cantilever-beam with diagonal loads; the obtained numerical results confirm the accuracy and potential of the method
Coupling BEM and VEM for the Analysis of Composite Materials with Damage
Full text linkNumerical tools able to predict and explain the initiation and propagation of damage at the microscopic level in heterogeneous materials are of high interest for the analysis and design of modern materials. In this contribution, we report the application of a recently developed numerical scheme based on the coupling between the Virtual Element Method (VEM) and the Boundary Element Method (BEM) within the framework of contin- uum damage mechanics (CDM) to analyze the progressive loss of material integrity in heterogeneous materials with complex microstructures. VEM is a novel numerical tech- nique that, allowing the use of general polygonal mesh elements, assures conspicuous simplification in the data preparation stage of the analysis, notably for computational micro-mechanics problems, whose analysis domain often features elaborate geometries. BEM is a widely adopted and efficient numerical technique that, due to its underlying formulation, allows reducing the problem dimensionality, resulting in substantial sim- plification of the pre-processing stage and in the decrease of the computational effort without affecting the solution accuracy. The implemented technique has been applied to an artificial microstructure, consisting of the transverse section of a circular shaped stiff inclusion embedded in a softer matrix. BEM is used to model the inclusion that is supposed to behave within the linear elastic range, while VEM is used to model the surrounding matrix material, developing more complex nonlinear behaviors. Numerical results are reported and discussed to validate the proposed method
A single-domain Ritz approach for buckling and post-buckling analysis of cracked plates
No full textA Ritz approach for the analysis of buckling and post-buckling of plates with through-the-thickness cracks is presented. The plate behavior is described by the first order shear deformation theory and von Kar- man’s geometric nonlinearity. The admissible functions used in the displacements approximation are se- ries of regular orthogonal polynomial supplemented with special functions able to decribe the diconti- nuity across the crack and the singularity at the crack tips; boundary functions are used to fullfill the homogeneous essential boundary conditions. Convergence studies and analysis results are presented for buckling and post-buckling of plates with a central through-the-thickness crack evidencing differences in the structural response between pre- and post-buckling regimes, which can substantially affect the plate residual strength. The performed analyses show the efficiency and potential of the method, which pro- vides accurate results in conjunction with a reduced number of degrees of freedom and simplified data preparation
An adaptive Ritz formulation for progressive damage modelling in variable angle tow composite plates
Full text linkIn this work, an adaptive Ritz model for the analysis of variable angle tow composite plates featuring damage initiation and evolution under progressive loading is proposed, developed, implemented and tested. The plate kinematics is represented employing a first-order shear deformation theory, while the plate equilibrium equations at a given load step are obtained by minimizing the structure potential energy. The constitutive behaviour is modelled within the framework of continuum damage mechanics. In particular the initiation and evolution of damage, up to failure, are tracked by defining irreversible damage indices related to both fibres and matrix, both in tensile or compression loading. The discrete equations are then obtained by assuming a polynomial Ritz approximation of the primary kinematic variables in the energy minimization. Preliminary tests show how the application of the method as a single-domain approach induces the emergence of problematic spurious effects, related to Gibbs artefacts due to the inability of the selected polynomial basis to represent damage localization. An adaptive multi-domain technique is thus proposed to circumvent such issues, which has been successfully validated by benchmark tests. Eventually, original results about variable angle tow plates featuring damage evolution under progressive loading are presented
A computational aeroelastic framework based on high-order structural models and high-fidelity aerodynamics
No full textA computational framework for high-fidelity static aeroelastic analysis is presented. Aeroelastic analysis traditionally employs a beam stick representation for the structure and potential, inviscid and irrotational flow assumptions for the aerodynamics. The unique contribution of this work is the introduction of a high-order structural formulation coupled with a high-fidelity method for the aerodynamics. In more details, the Carrera Unified Formulation coupled with the Finite Element Method is implemented to model geometrically complex composite, laminated structures as equivalent bi-dimensional plates. The open-source software SU2 is then used for the solution of the aerodynamic fields. The in-house fluid-structure coupling algorithm is based on the Moving Least Square technique. The paper contains a thorough validation of each disciplinary solver of the aeroelastic framework, and provides a few application test cases. For an unswept, untapered and isotropic wing, it was found that the method provides results in agreement with predictions from models based on potential flow theory for moderate freestream velocities. Departures were reported for very low speed and in the high-subsonic regime, alerting the need of adopting high-fidelity flow solutions at these flow conditions. The computational framework was then applied to the static aeroelastic tailoring of a composite wing. The paper concludes providing an overview of future implementation steps towards a tool for the seamless analysis of composite structures subject to different flow conditions, from low to high speed
X-Ritz Solution for Nonlinear Free Vibrations of Plates with Embedded Cracks
No full textThe analysis of large amplitude vibrations of cracked plates is considered in this study. The problem is addressed via a Ritz
approach based on the first-order shear deformation theory and von Kármán’s geometric nonlinearity assumptions. The
trial functions are built as series of regular orthogonal polynomial products supplemented with special functions able to
represent the crack behaviour (which motivates why the method is dubbed as eXtended Ritz); boundary functions are used
to guarantee the fulfillment of the kinematic boundary conditions along the plate edges. Convergence and accuracy are
assessed to validate the approach and show its efficiency and potential. Original results are then presented, which illustrate
the influence of cracks on the stiffening effect of large amplitude vibrations. These results can also serve as benchmark for
future solutions of the problem
A high-resolution layer-wise discontinuous Galerkin formulation for multilayered composite plates
Full text linkIn this work, a novel high-resolution formulation for multilayered composite plates is presented. The formulations
is referred to as high-resolution since it combines (i) Layer-Wise plate theories, which are based on a perlayer,
high-order expansion of the primary variables throughout the plate’s thickness, providing a detailed layerlevel
description of the sought solution; (ii) The discontinuous Galerkin method, a numerical approach based on
a discontinuous representation of the unknown fields over the mesh elements and on the introduction of
boundary integral operators enforcing inter-element continuity, which allow the natural treatment of high-order
mesh elements and provide high-resolution on the representation of the primary variables and their derivatives;
(iii) The implicitly-defined mesh technique, a meshing strategy based on an implicit representation of the plate
domain, which allows resolving the presence of curved boundaries with high-order accuracy.
Numerical tests are provided to investigate the effect of the penalty parameter and to show the optimal
convergence of the proposed formulation, which is subsequently employed in combination with an implicitlydefined
hierarchical quad-tree mesh to resolve the stress distribution in a rectangular plate and in a plate with a
circular hol
A hybrid virtual–boundary element formulation for heterogeneous materials
Full text linkIn this work, a hybrid formulation based on the conjoined use of the recently developed virtual element method (VEM) and the boundary element method (BEM) is proposed for the effective computational analysis of multi-region domains, representative of heterogeneous materials. VEM has been recently developed as a generalisation of the finite element method (FEM) and it allows the straightforward employment of elements of general polygonal shape, maintaining a high level of accuracy. For its inherent features, it allows the use of meshes of general topology, including non-convex elements. On the other hand, BEM is an effective technique for the numerical solution of sets of boundary integral equations, employed as the original model of the represented physical problem. For several classes of problems, BEM offers some advantages over more popular techniques, namely the reduction of the dimensionality of the problem, with associated computational savings. In this study, the inherent advantages of VEM and BEM are simultaneously employed for the study of heterogeneous material microstructures.
The method has been applied to i) the elastic analysis and ii) computational homogenization of fibre-reinforced composite materials and to iii) the analysis of composite unit cells exhibiting matrix isotropic damage. The discussed results show how the hybrid technique inherits the generality of VEM and the modelling simplification and accuracy of BEM, ensuring high accuracy and fast convergence and providing a versatile tool for the analysis of multiphase materials, also including non-linear behaviour such as material degradation. Further directions of research are identified and discussed after commenting on the presented results
A thermodynamically consistent CZM for low-cycle fatigue analysis
No full textA cohesive zone model for low-cycle fatigue analysis is developed in a consistent thermodynamic framework of elastic-plastic-damage mechanics with internal variable. A specific fatigue activation condition allows to model the material degradation related to the elastic-plastic cyclic loading conditions, with tractions levels lower than the damage activation condition. A moving endurance surface, in the classic framework of kinematic hardening, enables a pure elastic behavior without any fatigue degradation for low levels loading conditions
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