Antonio Miravete

Effect of trigger geometry on energy absorption in composite profiles

This paper presents an experimental study on the energy absorption capability of two different composite profiles; both are realised in glass-polyester pultrusion. One of the profiles is a unidirectional box section, whilst the other, an I section, consists of alternating layers of mat and fabric. For each one of the two profiles, six different trigger geometries are analysed. The results show that the I profile is a good candidate for being considered for energy absorption applications. It is also concluded that when studying a trigger geometry, slight modifications (as the bevel angle of a bevel trigger) can result in important variations of the results.

Application of the Finite-Element Method to Predict the Onset of Delamination Growth

This paper deals with a basic methodology for the application of the finite element (FE) simulation and linear elastic fracture mechanics (LEFM) to predict the onset of delamination growth. The first step of the proposed methodology is the experimental characterisation of material interlaminar fracture in pure mode I (DCB test), pure mode II (ENF test) and mixed mode I+II (MMB test). In the second step, the results of the interlaminar fracture tests are translated from load/displacement data to strain energy release rates by means of test FE simulations; thus, the critical strain energy release rate (Gc), or fracture toughness are obtained as a function of mode ratio. The third step of the methodology consists of applying FE simulations to determine the strain energy release rate (G) and mode ratio for the delamination and then comparing the result to the values of the Gc curve. The main innovative aspect of the paper is that FE simulation is used as a part of the material characterisation process; in fact, data reduction of interlaminar fracture tests is carried out by means of FE simulations. In addition, regarding the practical details of FE application to the proposed methodology, some innovative aspects are introduced, such as the analysis is carried out as a non-linear geometric problem (taken into account large displacements) and considering inside each simulation different elastic properties for the material depending on whether it is under tension or compression. These aspects and the rest of the proposed methodology are validated by the experimental results presented in the paper.

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.

Strain and stress analysis in tapered laminated composite structures

Abstract Since laminated composite materials are composed of a number of layers, it is possible to make variable thickness composite structures in a simple way. If the design of a laminated composite structure accounts for the concept of variable thickness, a remarkable weight saving can be obtained. In the present work, a theoretical and experimental study dealing with the mechanical behavior of variable thickness composite structures is presented. The objective of the theoretical study is to evaluate longitudinal and interlaminar normal and shear strains in order to find out what happens inside the laminate when a transverse load is applied to a variable thickness laminated composite beam. A finite element model was used for calculating the strain components. Failure prediction was carried out by means of a quadratic failure criterion. The aim of the experimental analysis is to assess the accuracy of the theoretical model as well as study the different failure mechanisms that appear in a variable thickness composite beam when is subjected to a transverse load. AS4/3501-6 Graphite/Epoxy was used for this work. The type of testing performed was three point bending. Longitudinal and interlaminar strains were measured using strain gauges. An excellent agreement was found between the data and the prediction. The failure modes were also discussed.

Composite Bus Rollover Simulation and Testing

The present paper shows a simulation technique for the rollover test, based on the Geneva Regulation number 66, of complete steel or composite buses, which required a previous validation. A new concept of lightweight bus wholly made of composites is shown, owing to its outstanding advantages in the transportation, such as weight saving. This bus structure is able to meet the stiffness and strength requirements, which must be overcome by metallic buses. The rollover of the composite bus is studied by means of the developed simulation technique. A prototype of the composite bus was built and tested.

Advances in the Crash Simulation of Vehicle Frontal Crash Structures Made of Braided Composite Materials

In this paper, new advances in simulation of composite materials under crash loads are applied to the analysis of a car frontal crash structure. Experimental results are 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 crash simulations of components. The front longitudinal beam studied herein is analyzed for 2 load cases: frontal and lateral crash. Qualitative results on specific energy absorption, as well as the absolute energy absorbed by the structure, are especially relevant. Results of simulations of the structure in carbon and glass fibers are presented and compared, focusing on the absolute energy absorbed and specific energy absorption of the structure.

A new concept of a bus structure made of composite materials by using continuous transversal frames

In the transportation industry vehicles made of steel often have common problems which it can be feasible to solve using other materials or by improving the design, depending on the nature of the problem. Several types of pseudo-solutions can be applied so that nondesirable problems can be avoided at the present, but the trouble remains until new designs or acceptable solutions are discovered. One of the principal problems throughout the life of a vehicle made of metallic materials is the corrosion of some of its parts due to environmental exposure, therefore a maintenance service is necessary. Purely aesthetic damage or even weakening of the structure are also encountered during its life. The phenomenon of corrosion which tends to alter the mechanical characteristics of the materials which make up the vehicles and reduce its resistive capacity make necessary the establishment of periodical revisions which increase the total cost during the life of service. Much work has been done in order to obtain vehicles with optimum durability characteristics (aesthetics, functional, etc.) over a period of time, in most cases an increment of safety and low maintenance cost are recommended. Composite materials offer a wide spectra of possible solutions since corrosion is not considered as a problem, so typical parts of structures in machines (made of metallic materials) subjected to an environmental exposure have been replaced by pieces made of nonmetallic materials as bumpers, hub caps and bodywork components.

Development of a Simulation Tool for 3D Braiding Architectures

The usage of textile technologies for composites is widely extended in aeronautic applications. They provide an improvement on mechanical properties in the thickness direction, and offer some other advantages in comparison with prepreg technology regarding production. Nowadays 3D‐braiding machines do not only enable the production of solid profiles but enable also the production of complex near‐net‐shape reinforcement structures with changing cross section geometry. In order to attain a full understanding on structure of 3d braids to be able to predict mechanical properties, simulation tools including machine operation are needed. A simulation tool is being developed as a part of the EU project “Integrated Tool for Simulation of Textile Composites”, starting from 3d braiding machinery description and operation. This information is required to reproduce yarn paths in the produced unit cell, based on the interlacing pattern of the braid.

A micromechanical composite approach for finite element crashworthiness simulation

ABSTRACT The present article deals with micromechanical composite modeling. Both analytical and computational micromechanics approaches are described as well as micromechanical modeling of damage. Based on micromechanics of failure theory, a user subroutine including a progressive damage algorithm is programmed for finite element analysis. Three theory-experiment correlations of tubes under a three-point bending test have been carried out using the bi-phase material model developed along with this project. These studies include three-ply schedules.

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