Marco Carrera

Numerical Analysis of Three-Dimensional Braided Composite by Means of Geometrical Modeling Based on Machine Emulation.

Three dimensional braided composite materials exhibit better performance in terms of structural integrity, through-thickness strength and impact resistance, than laminated composites. Other advantages regarding production are the ability to produce composite structures with intricate geometries close to the near-net-shape, and also with continuous changes in its cross-section. These properties are a consequence of the internal geometry of the 3D braided composites, in which yarns are interlaced following specific patterns programmed on a braiding machine. In this article, the operation of a typical rotary braiding machine is emulated in order to automatically obtain the geometry of a braiding unit cell. Once the geometrical description is obtained, a finite element model has been developed in order to carry out virtual testing of 3D composite materials. An AS4/epoxy braided material system has been virtually tested and a theory-experimental correlation has been performed for the longitudinal modulus and yield strength compression, using a failure criterion based on constituents and interface failures.

Development of an innovative concept of light semi-trailer by means of FEM and testing

A new light semi-trailer concept has been developed using numerical and experimental methods. In order to achieve this objective different types of light materials, such as high strength steels, aluminum alloys and sandwich compound materials, have been studied. The different semi-trailer models have been studied by means of a numerical model simulation based on F.E.M. (Finite Element Method) and subjected to whole loads and various boundary conditions. In testing whole strain values from critical points located in the semi-trailer have been obtained in order to correlate the numerical and the experimental results. Finally, some of the initial semi-trailer parts and areas were optimized by means of numerical methods. Results obtained in the numerical simulations were applied to the analyzed structure in order to design a second generation of semi-trailer structure in which weight is decreased.

Enhanced Impact Energy Absorption Characteristics of Sandwich Composites through Tufting

Sandwich structures are highly demanded where a high flexural stiffness per weight ratio is needed. The main limiting factor of these materials is the core/skin interface, which tends to delaminate. Tufting is one of the most promising technologies to reinforce this interface along the z-direction. In this article, the energy absorption of tufted sandwich structures under impact loads is evaluated. Six different types of tufted specimens were tested, including both carbon and glass fiber faces with three different tufting densities. The impact behavior of a sandwich panel is proved to be effectively improved by the tufting process.

Behaviour of Rear Underrun Protection System on Car-to-tank Vehicle Impact Used for Fuel Transportation

The European legislation for rear underrun protection systems on heavy vehicles, Commission Directive 2006/20/EC, specifies a series of criteria that must be fulfilled so that these devices can be homologated. The different models of devices used as rear underrun impact protection in tank vehicles for fuel transportation are an example of these criteria. Basically, the homologation tests based on this regulation consist in the quasi-static application of a load series at different points of the structure. In analysing the guidelines of Commission Directive 2006/20/EC, a number of questions about their validity may be raised with respect to, for instance, how efficient a homologated system of these characteristics is in real collision. The aim of this paper is to compare the behaviour of a rear underrun impact protection system, incorporated into a tank vehicle, to the behaviour of the same device when a car hits it at different collision speeds.

Response analyses of a two-phase cryogenic tank to longitudinal and lateral accelerations

The aim of this article is to present a methodology for calculating vehicle tankers by analysing the way baffle shape contributes to the movement of the fluid. This methodology could be used to optimise the geometry of these parts analysing different geometries. Four different lateral types of baffles used by different cryogenic tank manufacturers have been examined. Both the movement of the fluid and the forces transmitted by the latter to the tank during emergency braking manoeuvres are analysed and the principal conclusion is that the contribution of the geometry is very important. Besides, a longitudinal baffle meant to reduce the tendency of the tank to overturn while diminishing the moment generated by the load has been designed. The longitudinal baffle has been optimised, modifying the height and depending on the level of filling of the tanker the rollover moment can be reduced.

Comparative Analysis of Two Numerical Methods of Rollover Simulation of a Semitrailer for Hydrogen Transport

Nowadays, the use of the Finite Element Method [1] by means of simulation computer tools has made possible a substantial step forward in the field of calculation and optimization of vehicle structures. More specifically, these modern calculation tools are achieving great cost reductions corresponding to the experimental tests necessary to verify the appropriate performance of a vehicle in impact cases. On the other hand, great efforts will have to be done to develop correct numerical models for calculation. Once these numerical models have been validated with experimental tests, elimination of experimental costs compensates for these calculation efforts. A greater flexibility in decision making with respect to design and optimization alternatives will be achieved as well. The objective of this paper is to obtain an appropriate test simulation methodology for a specific vehicle and a specific impact case: There have been carried out the simulations of two different rollover test typologies in order to verify an adequate and safe behaviour of a semitrailer designed for hydrogen transport. After results of these two simulations are obtained, they will be compared in order to set which is the most restrictive and therefore the most appropriate. A lightened configuration has been also considered so as to carry out a sensibility analysis of material and thickness of some structural parts over numerical results in both test typologies in order to verify these simulations.Copyright

New Concept of Rollover Resistant Semitrailer for Hydrogen Transport

In this paper a new concept of semitrailer for hydrogen carriers is presented. It has been developed by means of numerical calculations carried out with the finite elements method. This new design of semitrailer incorporates several new functions. The first one is to achieve a rollover resistant vehicle. It has to be taken into account the absence of a specific regulation in Europe for this type of vehicles, so former vehicles were not enough rollover resistant. Nevertheless, in this development process it has been taken into account the European rollover regulation concerning large passenger vehicles “Regulation n° 66 of Geneva”, applied in this case to a vehicle having a much higher mass and a higher centre of gravity than a bus. Therefore a higher kinetic energy will be obtained in case of rollover. The second characteristic inherent to this new design of semitrailer is its lightness. It has achieved a mass reduction of 8500 kg in comparison with former designs, by means of lightening the structure, in charge of supporting the hydrogen cylinders, as well as making lighter these hydrogen cylinders themselves. Numerical models developed have been calculated by explicit integration of the dynamic balance equation. Very complex finite element models have been developed in order to include all geometric details. In these models, the elastic-plastic curves of involved materials have been included as well as its variation due to the strain rate influence. There have also been taken into account non-linear effects from contacts and from large strains that take place.Copyright

Application of Computational-Experimental Methods for Designing Optimized Semitrailer Axle Supports

Computational and experimental methods were applied to the design and optimization of a semitrailer axle support subjected to fatigue loads. Numerical results based on the finite element method (FEM) were correlated with extensometric tests to assess the accuracy of the computational method. This paper is focused on the “minimum radius manoeuvre.” This situation represents the highly critical load case occurring in a semitrailer operation where the tractor vehicle pulls the semitrailers kingpin at approximately 90° with respect to its longitudinal axis, and high stress and strain phenomena take place in the axle supports’ structure. Loads and boundary conditions that correspond to this load case were first adjusted by means of experimental tests and could be later applied to each semitrailer axle support in the numerical model. In this analysis, the stress-strain elastic-plastic curves of the base material, the welding, and the HAZ have been incorporated to the numerical models. Fatigue S-N curves combined with the maximum Von Mises equivalent stresses obtained in the computational analysis provided a maximum number of cycles that the semitrailer axle support could reach in case of the minimum radius manoeuvre being applied to the vehicle in a repeated manner. The initial design could then be optimized to improve its fatigue life.

Analysis of the torsional rigidity of a dump semi–trailer under unfavourable load conditions

The tipping operation of a dump semi-trailer increases the vehicle rollover risk. A higher centre of gravity, a transversal slope, varying compression degrees of the ground or an irregular unloading can lead to non-desirable lateral instability situations. Therefore it is interesting to analyse the torsional rigidity of the semi-trailer dump bed under unfavourable load conditions generating torsional compliance. By means of detailed finite element models, it has been possible to verify the correct performance of the articulated coupling between the semi-trailer dump bed and the hydraulic actuator in the presence of any unfavourable stability conditions that could occur.

Metallic Front Beam Design

In this paper, new advances in simulation of car frontal crash structure are presented. Experimental results have been used to calibrate constitutive material models and simulation procedures to obtain more accurate representation of material behavior under crash loading. These advanced computational techniques are then applied to the crash simulations of components. The front longitudinal beam studied in this paper is analyzed for frontal crash. Qualitative results on specific energy absorption, as well as the absolute energy absorbed by the structure, are especially relevant. Three designs are then proposed as potential solutions for the front side rail design. Through simulation of their impact into a wall the designs are compared on the basis of crush force and specific energy absorption and a preferred design is chosen.© 2007 ASME