José Meireles

Auxetic materials — A review

Auxetic materials are endowed with a behavior that contradicts common sense, when subjected to an axial tensile load they increase their transverse dimension. In case of a compression load, they reduce their transverse dimension. Consequently, these materials have a negative Poisson’s ratio in such direction. This paper reviews research related to these materials. It presents the theories that explain their deformation behavior and reveals the important role represented by the internal structure. Their mechanical properties are explored and some potential applications for these materials are shown.

The Rock Art of the Côa Valley (Portugal) and its Archaeological Context: First Results of Current Research

Abstract The Coa rock art covers 17 km of the river valley and extends along the banks of the Douro, downstream of the confluence between the two rivers. A total of 194 different panels with Palaeolithic zoomorphic motifs have already been identified. Later prehistoric and historic periods, especially the Iron Age, are also represented. Settlement of the valley in Upper Palaeolithic times is documented by residential sites dating to the Gravettian, the Solutrean and the Magdalenian periods. Results of stylistic analysis, whose chronological predictions have been independently confirmed by superposition patterns derived from the figurative stratigraphies observed in the numerous palimpsests known, indicate that all these periods are also represented in the art. The outdoor location of the Palaeolithic art, the size of the territory, the number and aesthetic quality of the motifs represented and the almost uninterrupted continuity to the present of the artistic use of the regions rock faces concur to the u...

Micromorphology of atlantic rankers on the coast of northern Portugal

Summary The micromorphological examination of atlantic rankers on the coast of northern Portugal shows the importance of alternating phases of landscape stability and instability during the genesis of the profiles. Archaeological artifacts and marine deposits allow the dating of these events. Recent pedogenesis is characterized by the formation of a microgranular structure and the illuviation of amorphous organic matter. Remnants of an older leached phase in the Gelfa section reflect an initial weakly base desaturation stage. During historical times the soil was buried under eolian sands.

Feasibility of Internally Reinforced Thin-Walled Beams for Industrial Applications

In this work, several types of reinforcement geometries of hollow-box beams for industrial applications are compared. A novel type of sandwich beams under bending and torsion uncoupled loadings is proposed as the best solution of all those that were studied. For the comparative analysis of the solutions, the models are modelled by the Finite Element Method (FEM) using the commercial software ANSYS Mechanical APDL. The feasibility of the novel beams was assessed by comparing the stiffness behavior of the beams with simple hollow-box beams in terms of deflection. An efficiency parameter was defined in order to determine the relative difference in terms of deflection. It is found that the novel geometries represent a great improvement under bending loadings, better than under torsion loadings. Nevertheless, for bending and torsion combined loadings, if bending stresses are predominant, the beams can still be interesting for some applications, mainly those with mobile parts.

A Global Optimization Approach Applied to Structural Dynamic Updating

In this paper, the application of stochastic global optimization techniques, in particular the GlobalSearch and MultiStart solvers from MatLab®, to improve the updating of a structural dynamic model, are presented. For comparative purposes, the efficiency of these global methods relatively to the local search method previously used in a Finite Element Model Updating program is evaluated. The obtained solutions showed that the GlobalSearch and MultiStart solvers are able to achieve a better solution than the local solver previously used, in the updating of a structural dynamic model. The results show also that the GlobalSearch solver is more efficient than the MultiStart, since requires less computational effort to obtain the global solution.

Effective Mechanical Behavior of Sandwich Beams under Uncoupled Bending and Torsion Loadings

Sandwich geometries, mainly panels and beams are widely used in several transportation industries, namely aerospace, aeronautic and automotive. Sandwich geometries are known for their advantages in structural applications: high specific stiffness, low weight, and possibility of design optimization prior to manufacturing. This study aims to know the influence of the number of reinforcements (ribs), and of the thickness on the mechanical behavior of sandwich panels subjected to bending and torsion loads separately. In this study, 3 geometries are compared: simple web-core beam, corrugated core, and honeycomb core. The last 2 are asymmetric, due to the use of odd number of ribs. The influence of the geometry on the results is discussed, by means of a parameter that establishes a relation between the stiffness behavior and the mass of the object. It is shown that the all relations are non-linear, despite the elastic nature of the analysis, by means of the application of loads with low intensity.

The use of traditional and computer-based visualization in archaeology: a user survey

Visualization methods are commonly used during the successive stages of the archaeological process. However, it is difficult to determine which methods are more intensively used in each stage and, also, which stage of the archaeological process is more demanding regarding visualization needs. Within a broader questionnaire regarding the use of computer tools, archaeologists were inquired about their use of traditional and computer-based visualization methods during the different stages of the archaeological process. The main survey results concerning visualization methods are presented and briefly analyzed.

Comparison of the Poisson's Ratio of Simulated Rigid and Elastic Auxetic Models Using Kinematic and Finite Element Analysis

Materials that possess a negative Poissons ratio are called Auxetics. They are characterized by the counterintuitive behavior of expanding in tension and contracting in compression. To justify this deformation behavior, there have been developed theoretical modelations like the reentrant and bowtie models. However, the most generalized models are based on geometries that possess rigid trusses and hinging nodes. This does not portrait the reality of the application of these models. In this study, there have been performed simulations, using kinematic analysis to characterize the auxetic behavior of the theoretical rigid/hinging models and finite element analysis to characterize elastic models that represent real bodies. There were determined and compared the Poissons ratios of the theoretical and elastic reentrant and bowtie. Additionally it was shown that there is a significant difference between the results. In conclusion the theoretical models predict lower values of Poissons ratio, while the elastic models that simulate a real body show less auxetic behavior.

Numerical Analysis of the Stress Distribution in Fillet Welds and Double Fillet Welds

Welding processes are extremely used in the metalworking industry all over the world. Sometimes the engineer has difficulties in finding solutions for the analytical calculation welded joints with eccentricity. In addition, calculations and analytical principles generally do not coincide with numerical results. In this work, analytically calculated stresses, are compared with numerical stresses for a double-fillet weld and the reasons for not having a complete agreement of results are clarified. In addition, an analytical method for fillet welds is compared, with numerical results.

A Thermomechanical Study of POM-Based Polymers

This work is focused on the study of thermomechanical behavior of a Polyoxymethylene-based gear at high temperatures using ANSYS16. The deformation of the gear teeth due to thermal loads was also studied through coupled thermal-structural analyses. The displacement results are obtained by numerical and experimental studies and compared with each other. It was concluded that the experimental and numerical results are in agreement.