1,720,999 research outputs found
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)
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
Thermal fluid-structure interaction by discontinuous Galerkin methods
Full text linkThis research study presents a novel high-order accurate computational framework for thermal fluid-structure interaction problems. The framework is based on the use of blockstructured Cartesian grids where level set functions are employed to define both the fluid and the solid regions. This leads to a mesh that consists of a collection of standard d-dimensional rectangular elements and a relatively smaller number of irregular elements at the fluid-solid interface. The embedded boundaries are resolved with high-order accuracy thanks to the use of high-order accurate quadrature rules for implicitly-defined regions. The fluid is assumed compressible and governed by the inviscid Navier-Stokes equations, whilst the solid region obeys the equations of thermo-elasticity within the small-strain regime. Numerical examples are provided to assess the capability of the proposed approach
Refined layer-wise models for nonlocal analysis of magneto-electro-elastic plates
No full textSize-dependent theories of continuum mechanics are an important tool for structural and material
modeling in engineering applications, with particular regard to those involving micro- and nano-scales.
Among various approaches proposed in the literature to account for the effect of the microstructure via
continuum models, the Eringen’s nonlocal elasticity model incorporates important features of material
behavior via a differential stress-strain relationship involving a scale coefficient, or characteristic length,
depending on the material microstructure [1]. In the framework of Eringen’s nonlocal elasticity, plate
theories have been reformulated for homogeneous and multilayered configurations also extending the
models to multifield problems. The literature review reveals that the proposed two-dimensional models
for multilayered plates are based on the equivalent single layer with some limitations. Indeed, the
equivalent single layer models do not allow to accurately capture the through-the-thickness distribution
of the unknown fields. Additionally, in the nonlocal material behavior framework, the proposed equivalent
single layer theories account for a unique value of the characteristic length common to all of the
layers, whereas this parameter can exhibit meaningful variability for layers of different materials. Here,
nonlocal layer-wise plate theories for the analysis of magneto-electro-elastic multilayered plates are presented.
They are obtained assuming Eringen’s nonlocal behavior for the layers. The plate governing
equations are obtained via the Reissner’s mixed variational theorem (RMVT), assuming the generalized
displacements and generalized out-of-plane stresses as primary variables. These are expressed as
through-the-thickness expansions of suitably selected functions, considering the expansion order as a
formulation parameter [2]. Different advanced high order nonlocal plate theories are then generated
using a layer-based assembly algorithm of the so-called fundamental nuclei associated with the variable
expansion terms. The use of the LW approach and RMVT allows for (i) the explicit fulfillment of the
transverse generalized stress interface equilibrium, which is crucial for a correct description of the plate
fields, (ii) the straightforward analysis of plates with layers exhibiting different nonlocality characteristic
lengths. To illustrate the features of the proposed nonlocal plate theories Navier solution results are
presented and discussed. Additionally, finite elements are developed basing on the proposed theories and
their performances discussed. References [1] A. Eringen, Nonlocal Continuum Field Theories, Berlin:
Springer, 2002. [2] E. Carrera, Developments, ideas, and evaluations based upon Reissner’s mixed
variational theorem in the modeling of multilayered plates and shells, Applied Mechanics Review, vol.
54, no. 4, pp.301–328, 2001
Buckling analysis of multilayered structures using high-order theories and the implicit-mesh discontinuous Galerkin method
No full textThis work presents a novel formulation for the linear buckling analysis of multilayered shells. The formulation
employs high-order Equivalent-Single-Layer (ESL) shell theories based on the through-the-thickness expansion
of the covariant components of the displacement field, whilst the corresponding buckling problem is derived
using the Euler’s method. The novelty of the formulation regards the solution of the governing equations, which
is obtained via implicit-mesh discontinuous Galerkin (DG) schemes. The DG method is a high-order accurate
numerical technique based on a discontinuous representation of the solution among the mesh elements and
on the use of suitably defined boundary integrals to enforce the continuity of the solution at the inter-element
interfaces as well as the boundary conditions. Owing to its discontinuous nature, the DG method may be
naturally employed with non-conventional meshes and is combined in this work with the implicitly-defined mesh
technique, whereby the mesh of the shell modelling domain is constructed by intersecting an easy-to-generate
background grid and a level set function that implicitly represents the cutouts. Several numerical examples are
considered. First, the buckling loads are computed for plates and cylindrical shells modelled by different ESL
theories and characterized by various materials, geometry and boundary conditions. Then, the buckling load of
a plate with a circular defined cutout is computed for different diameter-to-plate’s width ratios. The obtained
results are compared with those available in the literature or those obtained using finite-element analyses and
demonstrate the accuracy and the robustness of the proposed approach
A model for low-cycle fatigue in micro-structured materials
No full textA microscale formulation for low-cycle fatigue degradation in heterogeneous materials is presented. The interface traction-separation law is modelled by a cohesive zone model for low-cycle fatigue analysis, which is developed in a consistent thermodynamic framework of elastic-plastic-damage mechanics with internal variables. 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 static failure condition. A moving endurance surface, in the classic framework of kinematic hardening, enables a pure elastic behaviour without any fatigue degradation for low levels of cyclic traction. The developed model is then applied to micro-structured materials whose micromechanics is analysed using a boundary integral formulation. Preliminary results demonstrate the potential of the developed cohesive model. The future application of the proposed technique is discussed in the framework of multiscale modelling of engineering components and design of micro-electro-mechanical devices (MEMS)
Advanced models for nonlocal magneto-electro-elastic multilayered plates based on Reissner mixed variational theorem
No full textIn the present work, nonlocal layer-wise models for the analysis of magneto-electro-elastic multilayered plates are formulated.
An Eringen non-local continuum behaviour is assumed for the layers material; in particular, as usual in plate theories, partial in-plane nonlocality is assumed whereas local constitutive behaviour is considered in the thickness direction.
The proposed plate theories are obtained via the Reissner Mixed Variational Theorem, assuming the generalized displacements and generalized out-of-plane stresses as primary variables, and expressing them as through-the-thickness expansions of suitably selected functions, considering the expansion order as a free parameter.
In the framework of the Carrera Unified Formulation, this allows the systematic generation of advanced high order plate theories via a layer-based assembly algorithm of the so-called fundamental nuclei associated with the variables exapansion terms.
The use of the layerwise approach and Reissner Mixed Variational Theorem allows for: i) the explicit fulfilment of the transverse generalized stress interface equilibrium, which is
crucial for a correct description of the plate fields, ii) the straightforward analysis of plates with layers exhibiting different characteristic lengths in their nonlocal behaviour.
A Navier solution for the developed models has been implemented and tested for the static bending and free vibrations analyses of rectangular simply-supported plates.
The obtained representative results favourably compare against available three-dimensional analytic results and demonstrate the features of the proposed theories
Morphing technology for gust alleviation: an UAS application
Full text linkAtmospheric turbulence can significantly affect aircraft missions in terms of
aerodynamic loads and vibration. These effects are particularly meaningful for MALE-HALE
UAS because of their high aspect ratios and because of their low speed, sometimes comparable
with that of the gust itself. Many studies have been conducted to reach the goal of efficient gust
alleviation. A viable solution appears the application of morphing technology. However, the design
of morphing aircraft is a strongly multidisciplinary effort involving different expertise from
structures to aerodynamics and flight control. In this study, a multidisciplinary wing-and-tail
morphing strategy is proposed for attaining gust attenuation in UAVs. The strategy is based on the
combined use of: i) an automatic detection system that identifies gust direction and entity and ii)
an aeroelastic model stemming from the coupling between a high-order structural model that is
able to resolve the motion and the strain and stress distributions of wings with complex internal
structures and a Vortex Lattice Method (VLM) model that accounts for the aerodynamics of the
wing-tail system. The gust alleviation strategy employs the information from the detection system
and the aeroelastic model to determine the modifications of the wing and the tail surfaces aimed
at contrasting wind effects, reducing induced loads and flight path errors. Numerical results are
presented to assess the capability of the framework
An implicit mesh discontinuous Galerkin formulation for higher-order plate theories
Full text linkIn this work, a discontinuous Galerkin formulation for higher-order plate theories is presented. The
starting point of the formulation is the strong form of the governing equations, which are derived in
the context of the Generalized Unified Formulation and the Equivalent Single Layer approach from
the Principle of Virtual Displacements. To express the problem within the discontinuous Galerkin
framework, an auxiliary flux variable is introduced and the governing equations are rewritten as a
system of first-order partial differential equations, which are weakly stated over each mesh element.
The link among neighboring mesh elements is then retrieved by introducing suitably defined numerical
fluxes, whose explicit expressions define the proposed Interior Penalty discontinuous Galerkin
formulation. Furthermore, to account for the presence of generally curved boundaries of the considered
plate domain, the discretisation mesh is built by combining a background grid and an implicit
representation of the domain. hp-convergence analyses and a comparison with the results obtained
using the Finite Element Method are provided to show the accuracy of the proposed formulation as
well as the computational savings in terms of overall degrees of freedom
Buckling and post-buckling of variable stiffness plates with cutouts by a single-domain Ritz method
Full text linkStructural components with variable stiffness can provide better performances with respect to classical ones and
offer an enlarged design space for their optimization. They are attractive candidates for advanced lightweight
structural applications whose functionalities often impose the presence of cutouts that requires accurate
and effective analysis for their design. In the present work, a single-domain Ritz formulation is proposed,
implemented and validated for the analysis of buckling and post-buckling behaviour of variable stiffness plates
with cutouts. The plate model is based on the first-order shear deformation theory with nonlinear von Karman
strain–displacement relationships. The plate generalized displacements are approximated with trial functions
built as products of one-dimensional Legendre orthogonal polynomials. The non linear governing equations
system is then deduced from the stationarity of the energy functional; the involved matrices are numerically
computed by a special integration algorithm based on the implicit description of the cutout via suitable level-set
functions. The formulation has been implemented in a computer code which has been used to validate the
method through comparison with literature solutions for variable angle tow laminates with circular cutouts.
Several investigations on buckling and post-buckling behaviour of variable angle tow composite plates with
cutouts having different shapes and dimensions are then presented to illustrate the approach capabilities,
provide benchmark results and point out features and design opportunities of the variable stiffness concept
for the buckling and post-buckling design of advanced lightweight structures
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