J. Pinho-da-Cruz

Dynamic behaviour of cork and cork-filled aluminium tubes: Numerical simulation and innovative applications

Abstract Cork is a unique and complex natural cellular material with many industrial applications. The purpose of this paper is to explore a new application field for the use of micro-agglomerate cork as an energy-absorbing medium. A numerical study on the energy absorption capabilities of square and circular cork-filled aluminium tubes with a width or diameter of 80 mm, length of 300 mm and variable thickness was performed with the finite element method code LS-DYNA™. The tubes were impacted uniaxially at 10 and 15 m s-1. The same analysis was carried out on aluminium foam-filled tubes. The results demonstrate that cork filling leads to a considerable increase in the energy absorbed for both section geometries, and that tube thickness plays an important role in the deformation modes and energy absorption. The investigation revealed better results for aluminium foam-filled structures, but demonstrated that micro-agglomerate cork has high potential as an energy-absorbing medium in crash protection applications.

Prediction of mechanical properties of composite materials by asymptotic expansion homogenisation

Finite element (FE) simulation plays a crucial role in the analysis of the mechanical behaviour of structural elements built with complex microstructure composite materials. In order to define microstructural details, finite element analysis (FEA) often leads to the need for unstructured meshes and large numbers of finite elements. This fact frequently makes it impossible to perform numerical analyses on the mechanical behaviour of such structural components, due to the large amounts of required memory and CPU time. In this particular context, homogenisation methodologies lead to significant computational benefits.

Fatigue analysis of thin AlMgSi welded joints under constant and variable amplitude block loadings

Abstract This paper reports the fatigue behaviour of thin AlMgSi1 aluminium alloy weldments and the improvement in fatigue strength due to post-weld treatments. Several fatigue tests were performed using two distinct types of thin welded joints, T and single lap, manufactured using a 6xxx series aluminium alloy, and the efficiency of fatigue life improvement techniques, such as post-weld heat treatment and weld toe’s burr dressing, was studied. Both the post-weld heat treatment and the burr dressing produced a fatigue strength improvement. This fact is discussed, for both geometries, in the context of the initiation and propagation phases contribution to total fatigue life. Finally, several fatigue tests were performed under variable amplitude block loading using T6 post-weld heat-treated single lap joints, and the correspondent fatigue lives were compared with the predictions of Miner’s rule.

An Optimized Loading Path for Material Parameters Identification in Elastoplasticity

Presently, the need to characterize the constitutive parameters of materials has increased due to the manufacture of new materials and development of computational analysis software intending to reproduce the real behavior which depends on the quality of the models implemented and their material parameters. However, in order to identify all constitutive parameters of materials a large number of mechanical tests is required. Thus, only one mechanical test that could allow to characterize all the mechanical properties could be desired. Hence, the aim of this work is to propose a methodology that find the most informative loading path in the sense of display normal and shear strains as clear aspossible to warrantee that the solution is the most unique and distinguishable for the parameter identification process. To achieve this objective the proposed methodology uses Finite Element Analysis (FEA) and Singular Value Decomposition (SVD) coupled together with optimization strategies. Thismethodology is presented for elastoplasticity behavior.

Development of an Optimized Loading Path for Material Parameters Identification

Nowadays, the characterization of material is becoming increasingly important due to ma\-nu\-fac\-tu\-ring of new materials and development of computational analysis software intending to reproduce the real behaviour which depends on the quality of the models implemented and their material parameters. However, a large number of technological mechanical tests are carried out to characterize the mechanical properties of materials and similar materials may also have properties and parameters similar. Therefore, many researchers are often confronted with the dilemma of what should be the best set of numerical solution for all different results. Currently, such choice is made based on the empirical experience of each researcher, not representing a severe and objective criterion. Hence, via optimization it is possible to find and classify the most unique and distinguishable solution for pa\-ra\-me\-ters identification. The aim of this work is to propose a methodology that numerically designs the loading path of multiaxial testing machine to characterize metallic thin sheet behavior. This loading path has to be the most informative, exhibiting normal and shear strains as distinctly as possible. Thus, applying Finite Element Analysis (FEA) and Singular Value Decomposition (SVD), the loading path can be evaluated in terms of distinguishability and uniqueness. Consequently, the loading path that leads to the most distinguish and unique set of material parameters can be found using a standard optimization method and the approach proposed. This methodology has been validated to characterize the elastic moduli for an anisotropic material and extrapolated for an hyperelastic material.

Asymptotic Expansion Homogenisation and Multiscale Topology Optimisation of Composite Structures

Composite materials are among the most prominent materials today, both in terms of applications and development. Nevertheless, their complex structure and heterogeneous nature lead to difficulties, both in the prediction of its properties and on the achievement of the ideal constituent distributions. Homogenisation procedures may provide answers in both cases. With this in mind, the main focus of this chapter is to show the importance of computational procedures for this task, mainly in terms of the different applications of Asymptotic Expansion Homogenisation (AEH) to heterogeneous periodic media and, above all, composite materials. First of all, it is noteworthy that the detailed numerical modelling of the mechanical behaviour of composite material structures tends to involve high computational costs. In this scope, the use of homogenisation methodologies can lead to significant benefits. These techniques allow the simplification of a heterogeneous medium using an equivalent homogenousmedium andmacrostructural behaviour laws obtained from microstructural information. Furthermore, composite materials typically have heterogeneities with characteristic dimensions significantly smaller than the dimensions of the structural component itself. If the distribution of the heterogeneities is roughly periodic, it can usually be approximated by a detailed periodic representative unit-cell. Thus, the Asymptotic Expansion Homogenisation (AEH) method is an excellent methodology to model physical phenomena on media with periodic microstructure, as well as a useful technique to study the mechanical behaviour of structural components built with compositematerials. In terms of computational implementation, the main advantages of this method are (i) the fact that it allows a significant reduction of the number of degrees of freedom and (ii) the capability to find the stress and strain microstructural fields associated with a given macrostructural equilibrium state. In fact, unlike other common homogenisation methods, the AEH leads to explicit mathematical equations to characterise those fields, that is, to perform a localisation. On the other hand, topology optimisation typically deals with material distributions to achieve the best behaviour for a given objective. The common approach to structural topology optimisation uses a variety of compliance minimisation (stiffness maximisation) procedures and functions. When analysing composite materials, these strategies often lead to multiscale procedures, either as a way to relax the initial discrete problem or in an effort to attain both optimal global structure and optimal microstructure. In this sense, the integration of AEH 23