1,721,113 research outputs found
A Cohesive-frictional Grain-boundary Technique for Microstructural Analysis of Polycrystalline Materials
No full textThe development of a 3D microstructural model for the analysis of degradation and failure in polycrystalline materials is reviewed in the present chapter. The material is explicitly modelled at the grain level, using integral equations in conjunction with a phenomenological crystal plasticity framework for the bulk grains, and with cohesive-frictional laws to represent inter-granular micro-cracking processes. The method allows to capture the initiation, development and coalescence of damage or plasticity at the aggregate scale. The formulation’s key feature is the representation of the mechanical problem in terms of inter-granular variables only, which allows to reduce the computational cost of the analysis. In the present chapter, the building blocks of the technique are described and emphasis is given to the description of the adopted cohesive-frictional laws, which are the fundamental ingredient for the study of inter-granular degradation processes. The potential of the framework is illustrated through micro-cracking and crystal plasticity simulations. The effect of inter-granular friction on the macroscopic material properties is highlighted through micro-cracking simulations under compressive loading
An integral framework for computational thermo-elastic homogenization of polycrystalline materials
Full text linkA grain scale framework for thermo-elastic analysis and computational homogenization of polycrystalline materials is proposed. The morphology of crystal aggregates is represented employing Voronoi tessellations, which retain the main statistical features of polycrystalline materials. The behaviour of the individual grains is modelled starting from an integral representation for anisotropic thermo-elasticity, which is numerically addressed through a dual reciprocity boundary element method. The integrity of the aggregate is enforced through suitable intergranular thermo-elastic continuity conditions. By virtue of the features of the underlying formulation, the polycrystalline thermo-elastic problem is expressed in terms of grain boundary variables only, thus simplifying the subsequent task of meshing and reducing the overall computational cost of the analysis, ultimately providing an appealing tool for multiscale applications. The framework has been tailored for computational thermo-elastic homogenization of polycrystalline materials and it has been applied to the statistical computational homogenization of SiC and Al2O3 polycrystals, with accurate results confirming its robustness and effectiveness. The extension of the proposed framework to multiscale modelling of materials failure in thermally active environments is eventually discussed.(c) 2023 Elsevier B.V. All rights reserved
A Model for high-cycle fatigue in polycrystals
No full textA grain-scale formulation for high-cycle fatigue inter-granular degradation in polycrystalline aggregates is presented. The aggregate is represented through Voronoi tessellations and the mechanics of individual bulk grains is modelled using a boundary integral formulation. The inter-granular interfaces degrade under the action of cyclic tractions and they are represented using cohesive laws embodying a local irreversible damage parameter that evolves according to high- cycle continuum damage laws. The consistence between cyclic and static damage, which plays an important role in the redistribution of inter-granular tractions upon cyclic degradation, is assessed at each fatigue solution jump, so to capture the onset of macro-failure. Few polycrystalline aggregates are tested using the developed technique, which may find application in multiscale modelling of engineering components as well as in the design of micro-electro-mechanical devices (MEMS)
Mixed Finite Elements for multilayered smart plates nonlocal analysis
No full textA mixed finite element formulation for the Eringen’s nonlocal analysis of smart,
magneto-electro-elastic, multilayered plates is presented. Finite elements for different refined higher
order plate layerwise theories are systematically developed. They ensure interface continuity and
allow associating different values of the nonlocal parameter to the laminate layers. Standard 9-node
and 16-node isoparametric, quadrilateral finite elements have been implemented and tested, showing
the characteristics and limitations of the proposed approach
Automatic Wind Identification for UAS: a Case Study
No full textUAS applications are nowadays experiencing a tremendous development both in the civil and in military sector. One of the main issues for this kind of autonomous vehicles is induced by atmospheric turbulence, which may pose a severe problem especially for small size UAV. The present research extends previous investigations to a broader range of turbulence spectra and tests an innovative procedure based on Extended Kalman Filter (EKF) autotune for wind identificatio
A coupled plasticity-damage cohesive-frictional interface for low-cycle fatigue analysis
Full text linkA novel thermodynamically consistent cohesive-frictional model for the analysis of interface degradation and
failure under either monotonic quasi-static loading or cyclic loading in low-cycle fatigue problems is proposed.
Starting from the definition of a suitable Helmholtz energy density function, a phenomenological interface
model is developed in the framework of plasticity and damage mechanics. In particular, a coupled plasticitydamage
activation function is defined and employed together the consistent evolution rules to capture the
evolution of damage and plasticity under the action of the external loads. Due to the specific features of
such threshold and flow rules, the initiation and accumulation of damage under monotonic increasing loads
is captured and accompanied by negligible plastic evolution, allowing to approximate pure damage-based
cohesive laws. On the other hand, coupling associative plasticity and damage evolution allows linking the
interface degradation in low-cycle fatigue processes to plastic hysteresis, on the basis of the phenomenological
assumption that no infinite plastic flows may happen without microstructural transformation leading to loss of
load bearing capability. The model also embodies a smooth transition from an initially cohesive to a residual
frictional interface behaviour, governed by a Coulomb frictional activation function.
The developed formulation has been implemented and assessed for individual interfaces, highlighting
consistent phenomenological behaviour. It has been then applied to the analysis of delamination and
de-bonding in composite test cases, showing accuracy against experimental data and confirming its potential
A non-linear Ritz method for the analysis of low velocity impact induced dynamics in variable angle tow composite laminates
Full text linkVariable angle tow (VAT) laminates feature composite layers reinforced by fibres following continuous curved paths and offer a wide structural design space for the manufacturing of composite components. In this work, a formulation for the analysis of the impact-induced dynamics in VAT laminated plates is proposed, implemented and tested in this work. The method is based on the adoption of first order shear deformation kinematics and includes von Karman non-linear strains. The discrete system is obtained by employing a pb-2 Ritz series expansion into the Hamilton's variational statement, while the impact loading is modelled through Hertzian contact law. The resulting non-linear governing equations are solved using a Newmark time step integration algorithm, coupled with an iterative solution strategy. After validation against available literature data, several tests on different VAT configurations are performed, highlighting analogies and differences between different layups in terms of impact-induced dynamic response
Computational aeroelastic analysis of wings based on the structural discontinuous Galerkin and aerodynamic vortex lattice methods
Full text linkAn original computational framework for the aeroelastic analysis of wings featuring general transverse section is developed. The framework is based on the coupling between a novel discontinuous Galerkin structural model and an aerodynamic vortex lattice method, which is implemented in both the planar and non-planar version. The structural model, which constitutes the novelty of the present work, allows generalized kinematics and is thus able to capture higher-order structural deformation modes. With respect to other more used structural representations, the discontinuous Galerkin approach is based on the use of discontinuous basis functions and suitably-defined boundary terms to enforce the inter-element continuity and boundary conditions. Such features naturally enable high-order accuracy, ease of parallelization and, specifically for this work, straightforward coupling with the vortex lattice method. The framework is validated through benchmark tests, providing favourable matching with reference literature data
Evolution equations with nonlocal initial conditions and superlinear growth
Full text linkWe carry out an analysis of the existence of solutions for a class of nonlinear partial differential equations of parabolic type. The equation is associated to a nonlocal initial condition, written in general form which includes, as particular cases, the Cauchy multipoint problem, the weighted mean value problem and the periodic problem. The dynamic is transformed into an abstract setting and by combining an approximation technique with the Leray-Schauder continuation principle, we prove global existence results. By the compactness of the semigroup generated by the linear operator, we do not assume any Lipschitzianity, nor compactness on the nonlinear term or on the nonlocal initial condition. In addition, the exploited approximation technique coupled to a Hartman-type inequality argument, allows to treat nonlinearities with superlinear growth. Moreover, regarding the periodic case, we are able to show the existence of at least one periodic solution on the half line.(c) 2022 Elsevier Inc. All rights reserved
Differential equations with maximal monotone operators
Full text linkThe paper deals with multivalued differential equations in abstract spaces. Nonlocal conditions are assumed. The model includes an m-dissipative multioperator which generates an equicontinuous, not necessarily compact, semigroup. The regularity of the nonlinear term also depends on the Hausdorff measure of noncompactness. The existence of integral solutions is discussed, with a topological index argument. A transversality condition is required. The results are applied to a partial differential inclusion in a bounded domain in R n with nonlocal integral conditions. The model also includes an m-dissipative but not necessarily compact semigroup generated by a suitable subdifferential operator. (c) 2024 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http:// creativecommons .org /licenses /by -nc -nd /4 .0/)
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