1,720,991 research outputs found
Electric conversion of a general aviation aircraft: a case study
Full text linkThis study analyses the process required to convert a conventional, air-breathing, pistonpowered, General Aviation (GA) airplane to fully electric propulsion. The work is configured as a feasibility study for such modifications with the intent of setting a path for similar electric conversion programs on GA airplanes. The motivation behind industries’ interest in alternative propulsion is examined and a full comprehension of the characteristics of the plane in question is achieved through the acquisition of transversal knowledge, examining the aircraft both from the engineering and real-world user points of view. Electric motor, batteries, auxiliary systems and implementation considerations were all made in accordance with regulatory authorities’ requirements, with the purpose of making the project to comply with EASA CS Part 23. The present work analyses the performances expected from the electric plane and compares them with the standard aircraft evaluating the project’s pros and cons. Considerations regarding typical mission profiles show how the electric powerplant will allow the airplane to outperform his conventional counterpart in terms of rate of climb, pollutant emission reduction, noise levels and operating costs. Such gains are however counterbalanced by the detriment of range and endurance performances, which might be deemed acceptable considering the specific plane’s intended use. The study shows how, even though close integration in electric GA aircrafts is desirable since the first stages of conceptual design, piston-to-electric conversions are possible and may indeed contribute to mitigate aviation climate impact
Modelling stress-corrosion microcracking in polycrystalline materials by the Boundary Element Method
Full text linkThe boundary element method is employed in this study in conjunction with the finite element method to build a multi-physics hybrid numerical model for the computational study of stress corrosion cracking related to hydrogen diffusion in polycrystalline microstructures. More specifically a boundary integral representation is used to represent the micro-mechanics of the aggregate while an explicit finite element method is used to model inter-granular hydrogen diffusion. The inter-granular interaction between contiguous grains is represented through cohesive laws, whose physical parameters depend on the concentration of inter-granular hydrogen, diffusing along the interfaces according to the Fick's second law. The model couples the effectiveness of the polycrystalline boundary element micro-mechanics model with the generality of the finite element representation of the inter-granular diffusion process. Few numerical tests are reported, to demonstrate the potential of the proposed technique
High-order accurate transient and free-vibration analysis of plates and shells
No full textThe limited availability of analytical solutions and the high cost associated with experimental testing motivate the use of computational tools to assess the dynamic behavior of load-bearing components, especially when a wide design space must be explored, as is often the case with composite structures. In this context, a novel high-order accurate discontinuous Galerkin formulation for transient and free-vibration analysis of multilayered plates and shells is presented and numerical validated. The starting point of the formulation is a generalized structural theory for multilayered shells with arbitrary curvature based on the expansion of the displacement covariant components throughout the shell thickness. The variational statement of three-dimensional elastodynamics allows deriving the strong form of the governing differential equations, which form the basis to obtain the corresponding discontinuous Galerkin weak statements. As the order of the through-the-thickness expansion and the order of the discontinuous Galerkin basis functions are free parameters, the proposed approach allows tuning the order of accuracy of the computed solution throughout both the shell thickness and the shell modeling domain. Numerical results are reported and discussed for several validation test cases in terms of h- and p-convergence analyses, demonstrating the high-order accuracy, robustness, and computational savings of the formulation
Virtual element method for damage modelling of two-dimensional metallic lattice materials
Full text linkAdditively-manufactured metallic lattice materials are a class of architectured solids that is becoming increasingly popular due to their unique cellular structure, which can be engineered to meet specific design requirements. Understanding and modelling the damage in these innovative materials is a significant challenge that must be addressed for their effective use in aerospace applications. The Virtual Element Method (VEM) is a numerical technique recently introduced as a generalisation of the FEM capable of handling meshes comprising an assemblage of generic polytopes. This advantage in creating domain discretisation has already been used to model the behaviour of materials with complex microstructures. This work employs a numerical framework based on a nonlinear VEM formulation combined with a continuum damage model to study the fracture behaviour of two-dimensional metallic lattice material under static loading. VEM's effectiveness in modelling lattice failure behaviour is assessed through several numerical tests. The influence of micro-architecture on the material's failure behaviour and macroscopic mechanical performance is discussed
Engineering the crack path in lattice cellular materials through bio-inspired micro-structural alterations
No full textA computational study on the fracture behaviour of bio-inspired finite-size lattice configurations is performed in this work. The study draws inspiration from recent investigations aimed at increasing the fracture energy of some materials through small modifications of their microstructure. The main question here is whether it is possible, to some extent, to engineer the crack path in metallic cellular materials through such small micro-structural modifications and how to quantify the effect of alternative strategies. Nature provides several examples of strategies used to delay or arrest damage and crack propagation. One striking example is given by the micro-architecture of several kinds of wood, in which the crack propagation through a lignin cellular matrix is affected by density variations typical of the seasonal alternation between early-wood and late-wood and by the presence of sap channels. In this study, the effects on crack propagations induced by micro-structure alterations inspired by density variations and sap channels in wood are computationally investigated and some figures of merit are defined to assess the effect on the energy absorbed by alternative solutions. In an age in which tight control of the microarchitecture can be achieved, e.g. through high-resolution 3D printing, it is of interest to investigate whether, starting from a baseline cellular architecture, it is possible to achieve superior material performance by smart modifications of the microarchitecture
Nonlinear free vibrations analysis of cracked composite stiffened plates via X-Ritz approach
No full textThin and moderately thick composite multi-layered plates are widely employed in naval and aerospace
structures. They can experience the presence of cracks, generated for example by corrosion, fatigue
or accidental external causes, which aect their static and dynamic behaviour. As regard the dynamic
characteristics of plates, many studies have focused on the linear vibration analysis of both isotropic
and composite thin and thick plates, providing for a comprehensive knowledge of the plate dynamic
behaviour. However, for an accurate appraisal of the plate dynamics, in some applications it is needed
to investigate the nonlinear free vibration problem; a literature survey evidences that the large amplitude
vibrations have received considerable attention for single plate congurations. Dierent approaches have
been proposed to model cracked plates and, among others, the Ritz method shows adequate accuracy
and computational eciency. To apply the Ritz method to crack problems by using standard admissible
functions the sub-structuring or multi-domain strategy has been employed. More recently, the Ritz
approach has been proposed with special trial functions, which account for the presence of the crack by
describing the discontinuity of the solution across the crack and the tip singularity [1,2]. In the present
work, nonlinear free vibrations of cracked stiened composite plates are investigated by modelling the
problem by the X-Ritz formulation recently presented by the authors [3]. In the framework of the rst
order shear deformation theory, this formulation combines the features of both the Ritz method and the
X-FEM strategy, as it employs variables approximations obtained by enriching the Ritz series expansion
with suitably dened crack functions. This modelization applies to a single quadrangular plate and is
coupled with a multi-domain approach which open towards an ecient modelization of stiened panels
and thin-walled structures. Thus, the entire structure is modelled as individual, separated plates which
can contain cracks; these plates are then joined by enforcing the continuity conditions along the common
edges through penalty techniques. This approach has: (i) the advantage of a very simple pre-processing
stage, as it only requires the geometrical information on the plates that compose the structure and the
cracks locations; (ii) the feature to incorporate the singular behaviour at the crack tips. Convergence
and accuracy studies on linear and nonlinear free vibrations of uncracked congurations are carried out
on uncracked congurations to validate the approach by comparison with literature and nite elements
results. Cracked stiened panels nonlinear free vibrations results are then presented to discuss the
potential of the method.
References
1. Milazzo, A., Benedetti, I., Gulizzi, V. (2018). An extended
Ritz formulation for buckling and post-buckling analysis of cracked multilayered plates. Composite
Structures, 201, 980-994.
2. Milazzo, A., Benedetti, I., Gulizzi, V. (2019). A single-domain Ritz
approach for buckling and post-buckling analysis of cracked plates. International Journal of Solids and
Structures, 159, 221-231.
3. Gulizzi, V., Oliveri, V., Milazzo, A. (2019), Buckling and post-buckling
analysis of cracked stiened panels via an X-Ritz method. Aerospace Science and Technology, in pres
Microcracking in piezoelectric materials by the Boundary Element Method
Full text linkA 3D boundary element model for piezoelectric polycrystalline micro-cracking is discussed in this contribution. The model is based on the boundary integral representation of the electro-mechanical behavior of individual grains and on the use of a generalized cohesive formulation for inter-granular micro-cracking. The boundary integral formulation allows to address the electro-mechanical boundary value problem in terms of generalized grain boundary and inter-granular displacements and tractions only, which implies the natural inclusion of the cohesive laws in the formulation, the simplification of the analysis pre-processing stage, and the reduction of the number of degrees of freedom of the overall analysis with respect to other popular numerical methods
Ritz Model for Damage Analysis in Variable Angle Tow Composite Plates
Full text linkIn this work, a Ritz method is developed for progressive damage analysis of multilayered variable angle tow (VAT) composite plates under geometrically non-linear strains. The proposed model adopts a first order shear deformation theory and considers geometric non-linearities through the von Karman assumptions. A meso-modelling approach based on Continuum Damage Mechanics is adopted for analysing the initiation and evolution of damage. The onset of damage is predicted using the Hashin’s criteria. Four damage indices are defined and computed for expressing the degradation of the mechanical properties of the material, both for fibers and matrix under either tension and compression loading. A set of numerical tests is carried out to validate the model, assess its convergence and show its capabilities, eventually presenting novel results for progressive non-linear damage in variable angle tow composite plates
Computational Homogenization of Heterogeneous Materials by a Novel Hybrid Numerical Scheme
Full text linkThe Virtual Element Method (VEM) is a recent numerical technique capable of dealing with very general polygonal
and polyhedral mesh elements, including irregular or non-convex ones. Because of this feature, the VEM ensures noticeable
simplification in the data preparation stage of the analysis, especially for problems whose analysis domain features complex
geometries, as in the case of computational micro-mechanics problems. The Boundary Element Method (BEM) is a well-known,
extensively used and effective numerical technique for the solution of several classes of problems in science and engineering. Due
to its underlying formulation, the BEM allows reducing the dimensionality of the problem, resulting in substantial simplification
of the pre-processing stage and in the reduction of the computational effort, without jeopardising the solution accuracy. In this
contribution, we explore the possibility of a coupling VEM and BEM for computational homogenisation of heterogeneous materials
with complex microstructures. The test morphologies consist of unit cells with irregularly shaped inclusions, representative e.g. of
a fibre-reinforced polymer composite. The BEM is used to model the inclusions, while the VEM is used to model the surrounding
matrix material. Benchmark finite element solutions are used to validate the analysis results
A discontinuous Galerkin formulation for variable angle tow composite plates higher-order theories
No full textA discontinuous Galerkin formulation for the mechanical behaviour of Variable
Angle Tow multi-layered composite plates is presented. The starting point of the
formulation is the strong form of the governing equations, which are obtained by means
of the Principle of Virtual Displacement, the Generalized Unified Formulation and the
Equivalent Single Layer assumption for the mechanical behaviour of the whole assembly.
To obtain the corresponding discontinuous Galerkin formulation, an auxiliary flux variable
is introduced and the governing equations are rewritten as a first-order system of
partial differential equations. To link neighbouring mesh elements, suitably defined numerical
fluxes are introduced and an Interior Penalty discontinuous Galerkin formulation
is obtained and presented. hp-convergence analyses for straight-fiber composite plates
and a comparison with the results available in the literature for variable angle tow plates
show the accuracy of the proposed formulation as well as the computational savings in
terms of overall degrees of freedom
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