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The early detection of failures in structures is a subject of great interest in engineering; several of these techniques are linked with the elastic wave propagation, using guided waves is one of these alternatives. Several structures of interest in engineering are laminar arrangements; the wave propagation in this type of structures depends not only on the material properties, but also on the geometric parameters, such as the plate thickness. Tubular structures, pressure vessels, tanks and also parts of ships hulls could be considered laminar. The elastic wave propagation in laminar structures could be considered as a sum of modal shapes that have its wave length and frequencies defined. These mode families are characteristics of each structure and could be represented through the dispersion curves. The definition of these dispersion curves is of crucial importance to understand the propagation of guided waves in the structure studied. In the present work the dispersion curves were generated using three different methodologies, specific for metallic rectangular stems that compound the strengthening armor in flexible riser duct. Each approach presented in the analysis were carried out using standard finite element commercial packages and an experimental verification, as well. The premise is to present the topics in the simplest way, not only to understand how the dispersion curves are built but also how these curves must be interpreted. [ABSTRACT FROM AUTHOR]

To improve the safety of the intercity bus structure against impact scenarios and to reduce the injuries and death in traffic accidents it is crucial in a country with continental dimensions like Brazil, where the road transport matrix is fundamental in the traffic of people and goods. In this context in the present article, a numerical model of an intercity bus was built with elastoplastic beam implemented in a commercial software Ls-Dyna. This model was submitted to different frontal and semi frontal impact crash scenarios. With this model were analyzed different accidents which happened in the Brazilian highways, it was also simulated a frontal impact test and the results obtained were compared with the experimental results. Finally two numerical approaches were compared, they are: a simple model made with lumped masses and non-linear springs series connected, and the elastoplastic beam model. The different comparisons carried out let us validate the intercity bus model created using elastoplastic beam elements and propose to use this model as an effective tool to search for more efficient bus structural configurations against impact scenarios. [ABSTRACT FROM AUTHOR]

The authors apply the so-called Discrete Element Method (DEM) to determine the dynamic response of concrete and rock plates of various sizes that fracture under the action of static and dynamic loading. When, on account of the size of the model, larger elements must be employed, the issue of mesh objectivity must be addressed. In response determinations of structures with initial cracks or high stress gradients, which result in fracture localization, well established procedures lead to results that appear to be mesh independent. However, in elements subjected to approximately uniform stress fields a hitherto unknown problem arises in the analysis of non-homogeneous materials: the need to know a priori the degree of fracturing of the element. This should also affect finite element analysis in cases in which there is no clear fracture localization. In order to provide additional evidence on fracture localization, plates of different sizes subjected to external uni-axial tensile loading under different levels of stress localization are investigated in this paper. The effective stress-strain relationship, ultimate tensile stress and strain, dissipated fracture energy and fracture patterns are determined for plates ranging in size from 0.25 to 15m. Difficulties associated to the prediction of the behavior of large nonlinear structural systems are discussed in connection with the available results. [ABSTRACT FROM AUTHOR]

The calculus of fractomechanic parameters using computational numerical methods is still an active area of investigation. Traditionally, the most employed methods are the Finite Element Method (FEM) and the Boundary Element Method (BEM). The Discrete Element Method (DEM) with bars is another alternative, although its usage is not so extended in the solid mechanic area. DEM success in the simulation of failure mechanisms and defect nucleation motivates its implementation in fracture mechanic problems. In order to explore its potentialities in this kind of problems, this work presents the static and dynamic calculus of fractomechanic parameters of a modeled plate with DEM. For this purpose the numerical methodologies used are the same as the ones employed in the traditional numerical methods, such as FEM and BEM, as well. The obtained results, compared with the numerical and analytical results published by other authors, allow the validation of DEM for such applications where the fracture process must be doubtlessly taken into account. [ABSTRACT FROM AUTHOR]

The collective intercity transportation by bus is currently a mean of locomotion much sought after by people. Security in accidents is a very important factor that must be taken into account in design of bus body structure, being the evaluation of passenger safety of this type of vehicle is an important subject that should be checked, because in many accidents occur disconnection between seats and fastening members causing serious passengers injury, often fatal. This work aims at evaluation the behavior of frame fixing of seats of intercity bus bodies, submitted to the frontal impact situation in a rigid wall of 100% offset, through evaluation by finite element method (FEM). This study uses a numerical model corresponding to the body structure and chassis, developed through flexible beam elements, combining with shell elements for the structure of the seats and its fastening members, with the objective of not missing the essential aspects of the problem, allowing the solution with a reduced computational time. The numerical model of bus body and seat was impacted against a rigid wall at a speed of 8.89 m/s, being its validation according to the deceleration curve established by Regulation 80. Then it was gotten the Von Mises stress in fastening members of the seat structure in bus body. It is also presented a proposal to improve the fastening of the seat structure, comparing the results of the stress gotten in the two types fastening submitted to the frontal impact. [ABSTRACT FROM AUTHOR]