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Bristol, United Kingdom

Lanzi L.,IChrome Ltd | Airoldi A.,Polytechnic of Milan | Cacchione B.,Polytechnic of Milan | Astori P.,Polytechnic of Milan
Structural and Multidisciplinary Optimization | Year: 2012

The paper proposes a novel approach to identify the feasible region for a constrained optimisation problem. In engineering applications the search for the feasible region turns out to be extremely useful in the understanding of the problem as the feasible region defines the portion of the domain where design parameters can be ranged to fulfil the constraints imposed on performances, manufacturing and regulations. The search for the feasible region is not a trivial task as non-convex, irregular and disjointed shapes can be found. The algorithm presented in this paper moves from the above considerations and proposes a recursive feasible-infeasible segment bisection algorithm combined with Support Vector Machine (SVM) techniques to reduce the overall computational effort. The method is discussed and then illustrated by means of three simple analytical test cases in the first part of the paper. A real-world application is finally presented: the search for the survivability zone of a crashworthy helicopter seat under different crash conditions. A finite element model, including an anthropomorphic dummy, is adopted to simulate impacts that are characterised by different deceleration pulses and the proposed algorithm is used to investigate the influence of pulse shape on impact survivability. © 2012 Springer-Verlag.

Airoldi A.,Polytechnic of Milan | Di Landro L.,Polytechnic of Milan | Sirna M.,IChrome Ltd | Iavarone P.,Polytechnic of Milan | Sala G.,Polytechnic of Milan
Journal of Materials Science | Year: 2013

The article describes the development of a numerical material model of ceramic matrix composite (CMC) reinforced by bundles of thousands of short carbon fibres and produced by means of a liquid silicon infiltration process. The objective of the article is the development of a numerical mesoscale model that considers the material as a simple bi-phasic composite constituted by an isotropic matrix with differently sized inclusions. The distinctive material microstructure that complicates the development of such a model is presented and the issues represented by the generation of the finite element models and by the identification of the effective properties of the constituent phases are discussed. In the presented approach, models are generated by numerically simulating the packing of bundles and phases are identified by means of tests and numerical analyses, which are performed on long fibre-reinforced specimens and on specimens subjected to a thermal process for the elimination of carbon reinforcement. The approach is applied to find out the parameters of a homogenized orthotropic model for CMC plates. The obtained results show that the numerical packing simulations can generate models with a realistic distribution of size, shape and orientation of the bundles. The mesoscale model and the phase properties identified by the proposed numerical and experimental procedure are validated by considering the stiffness of standard CMC specimens obtained in three-point bending tests. According to the results, the developed methodologies can be considered as a promising approach for a reliable prediction of short fibre-reinforced CMC elastic properties. © 2012 Springer Science+Business Media New York.

Quaranta G.,Polytechnic of Milan | Lanzi L.,IChrome Ltd | Sima M.,IChrome Ltd
37th European Rotorcraft Forum 2011, ERF 2011 | Year: 2011

The paper presents a novel free mesh morphing technology based on Moving Least Square (MLS) applied to Structural Optimisation. The proposed approach moves from the field of surface reconstruction from 3D scattered data. From a more general standpoint, MLS methods seem promising methodologies to solve different morphing problems where existing meshes can be modified without specific needs to change their topology, i.e. their connectivity information. In this respect, MLS is a very effective and promising methodology for mesh morphing. The proposed MLS morphing methodology has been applied to the optimisation of composite stiffened panels. The goal of the optimisation is to reduce the overall panel weight finding the best layups (thickness and percentages) for skin and stringers as well as the optimal shape for the stringers via MLS morphing, considering stability and strength constraints. The optimisation process acts on the shape of the stringers, via the proposed MLS approach, without requiring any remeshing towards the optimisation process. Nonlinear Finite Element analyses are used to predict the overall behaviour of the panels in terms of force vs. shortening curve up to final failure, discriminate between local skin instabilities and global ones, eventually leading to the overall failure of the structure. Strength criteria are additionally accounted by monitoring the maximum Tsai-Wu failure index overall the structure.

Airoldi A.,Polytechnic of Milan | Bertoli S.,Polytechnic of Milan | Lanzi L.,IChrome Ltd | Sirna M.,IChrome Ltd | Sala G.,Polytechnic of Milan
Applied Composite Materials | Year: 2012

A study for the replacement of a metallic swing-arm of a high performance motorcycle with a composite part is presented. Considering the high structural effectiveness of the original metallic component, the case study evaluates the potential of composites in a challenging application. The FE model of the original component is developed to evaluate the structural performance in the most significant load conditions. A manufacturing process, based on a RTM technique, is proposed and analysed in order to develop realistic design hypotheses. The design approach is based on an optimisation process with 60 design variables. A constrained multi-objective genetic algorithm is applied to identify the solutions representing the best trade-off between mass reduction and improvement of torsional stiffness. Results show that composite materials can enhance the structural efficiency of the original metallic part, even considering technological limitations and damage tolerance requirements. © Springer Science+Business Media B.V. 2011.

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