Battery Pack and Underbody: Integration in the Structure Design for Battery Electric Vehicles—Challenges and Solutions

The evolution toward electric vehicle nowadays appears to be the main stream in the automotive and transportation industry. In this paper, our attention is focused on the architectural modifications that should be introduced into the car body to give a proper location to the battery pack. The required battery pack is a big, heavy, and expensive component to be located, managed, climatized, maintained, and protected. This paper develops some engineering analyses and shows sketches of some possible solutions that could be adopted. The possible consequences on the position of the vehicle center of gravity, which in turn could affect the vehicle drivability, lead to locate the battery housing below the passenger compartment floor. This solution is also one of the most interesting from the point of view of the battery pack protection in case of a lateral impact and for easy serviceability and maintenance. The integration of the battery pack’s housing structure and the vehicle floor leads to a sort of sandwich structure that could have beneficial effects on the body’s stiffness (both torsional and bending). This paper also proposes some considerations that are related to the impact protection of the battery pack, with particular reference to the side impacts against a fixed obstacle, such as a pole, which are demonstrated to be the most critical. By means of some FE simulation results, the relevance of the interplay among the different parts of the vehicle side structure and battery case structure is pointed out

Experiment based modeling of the mechanical expansion of tubes for the construction of heat exchangers

Tube heat exchangers are made by assembling metals tubes, which the fluid to be refrigerated is passed through, with fins where a refrigerating fluid (usually air) is flown over. The heat exchange between tubes and fins is obtained by exploiting their tight contact. This necessary very tight contact is obtained by means of brazing (typically in smaller equipment) or through the forced expansion of the tubes into the fins holes. The forced expansion can be hydraulic (by some fluid put in pressure in the assembly operation) or mechanic through the insertion of a sphere or an ogive with external diameter slightly larger than the internal diameter of the tube. The sphere or the ogive is pushed along the entire length of the tube so that the tube remains plastically forced into the fins holes. The process is then repeated for all the tubes of the heat exchanger. The present work concentrates on the mechanical expansion: to optimize the construction process it is necessary to have a model able to describe the mechanical phenomenon: that is, to evaluate the stress state in the tube during the insertion of the ogive, the residual stresses after the sphere/ogive passage, and the force required depending on the process and materials parameters (including the geometry of the tube, ogive, and fins, their material properties, friction, insertion speed etc.). The present work will describe an analytical model able to describe the process with a good level of predictability showing the effect of the main parameters involved in the process. The model is based and validated by means of experimental tests and numerical simulations at different levels and in different conditions and materials

Experimental investigation on the bending behaviour of hybrid and steel thin walled box beams—The role of adhesive joints

In the automotive design, nowadays there are two fundamental drivers. On one hand there are the environmental problems, on the other hand there are the safety matters. Within this contest, the weight reduction has become a key driver in the design of vehicles and it is necessary to consider and to study the use of nonconventional materials taking advantage from their high potential of weight reduction and energy absorption capability. In this perspective, the aim of this work is the study of the structural behaviour of box beams by means of a series of three points bending tests. The examined cross sections are those typically used in automotive construction. Different type of materials (steel, composite) and joining technologies (adhesive, spot weld) have been examined, considering different configurations. The work put in evidence the advantages coming from the use of adhesive, which allows structures with important weight reduction and better mechanical properties than traditional joining solution

experimental and numerical analysis of a thermoplastic lamina for composite material

Abstract Thermoplastic composites nowadays belong to an interesting class of materials for different type of industries. Those materials present a considerable number of advantages compared to the thermosetting composites. Their low density, low production cost, recyclability, are some of the positive aspects encouraging their usage. The numerical simulation is still an open research field due to the peculiar behaviour of the thermoplastic composites. According to that, this works starts a detailed numerical study in which the main deformation mechanisms are simulated using different modelling approaches. In this overview, the object of this study is a fully polypropylene composites made up of woven polypropylene laminas. These laminas are stacked and hot pressed. Previous research showed a ductile and plastic crush behaviour of this material, in which the main failure mode is governed by the delamination. Firstly, an experimental campaign is carried out, in order to define the constitutive properties of the single lamina. Woven laminas are orthotropic composites responding differently according to the direction of the load. Yarn test was executed to capture the tensile modulus and the strength, whereas the Bias-Extension test was carried out to examine the in-plane shear properties. The definition of those properties required several considerations and a detailed analysis because the load applied in the test is directed neither along the weft nor along the wrap direction. For this reason, geometrical approximations and hypothesis about the boundary condition are necessary to evaluate the shear stress and the shear angle parameters. Hence, three different FE models were developed in LS-DYNA and results were validated against the experimental tests. Two geometry discretization method and three material models were implemented. The first numerical model was developed for fabric materials and it represents a macro-mechanics approach with low computationally cost. The second model instead accounts for the fabric architecture, allowing to evaluate the weave geometry and the reorientation effect of the yarns during the deformation. The third model represents the discrete architecture of the fabric, modelling the specimen at the tape level. The numerical results showed a good approximation of the experimental evidence, especially considering the second numerical model. This material model confirmed the geometrical assumptions used to define the mechanical properties. This work gives a first important step for the simulation of components made of thermoplastic composites and with more complex geometry using a mesoscopic approach

La suscettibilità all'ipnosi come possibile criterio per la selezione degli astronauti

Lo scopo della ricerca è studiare se alcune caratteristiche cognitive (suscettibilità all’ipnosi) sono correlate con risposte posturali (posizione e velocità del centro di pressione) e autonomiche (frequenza e variabilità cardiaca) alla stimolazione dell’apparato vestibolare e dei recettori del collo, e se, quindi, possono facilitare l’adattamento al volo spaziale e il recupero al ritorno sulla terra. Il tema della selezione dell’equipaggio viene affrontato come un problema di reverse engineering, . Si descrivono: la metodologia e il protocollo sperimentale, lo stato dell'arte della sperimentazione sull'uomo, le norme di sicurezza riguardanti le apparecchiature elettromedicali impiegate, la determinazione della stimolazione vestibolare efficace, l'apparecchiatura utilizzata e le procedure di elaborazione dei segnali e l’analisi statistica usata. Si presentano, infine, i risultati, che mostrano differenze tra soggetti di diversa suscettibilità ipnotica nella risposta agli stimoli descritti. La discussione riguarda l'interpretazione fisiologica dei risultati e la possibilità di includere la suscettibilità all’ipnosi tra i criteri per la selezione degli astronaut

Injury criteria for vehicles safety assessment: a review with a focus using Human Body Models

This paper aims at providing an overview of the most used injury criteria (IC) and injury metrics for the study of the passive safety of vehicles. In particular, the work is focused on the injury criteria that can be adopted when finite element simulations and Human Body Models (HBMs) are used. The HBMs will result a fundamental instrument studying the occupant’s safety of the Autonomous Vehicles (AVs), since they allow to analyze a larger variety of configurations compared to the limitations related to the traditional experimental dummies. In this work, the most relevant IC are reported and classified basing on the body segments. In particular, the head, the torso, the spine, the internal organs, and the lower limbs are here considered. The applicability of the injury metrics to the analyses carried out with the HBMs is also discussed. The paper offers a global overview on the injury assessment useful to choose the injury criteria for the study of the vehicle passive safety. To this aim, tables resuming the presented criteria are also reported to provide the available metrics for the considered body damage

A Numerical Method to Compute Brain Injury Associated to Concussion

This research proposes a new a numerical method to compute brain injury associated with concussion using the Peak Virtual Power method, using the THUMS 4.02 head model. The results indicate that mild and severe concussions could be prevented for lateral collisions and frontal impacts with PVP values lower than 0.928mW and 9.405mW, respectively, and no concussion would happen in the head vertical direction for a PVP value less than 1.184mW. This innovative method proposes a new paradigm to improve helmet designs, assess sports injuries and improve people's wellbeing.Comment: 12 page

Mechanical properties and impact behavior of a microcellular structural foam

Structural foams are a relatively new class of materials with peculiar characteristics that make them very attractive in some energy absorption applications. They are currently used for packaging to protect goods from damage during transportation in the case of accidental impacts. Structural foams, in fact, have sufficient mechanical strength even with reduced weight: the balance between the two antagonist requirements demonstrates that these materials are profitable. Structural foams are generally made of microcellular materials, obtained by polymers where voids at the microscopic level are created. Although the processing technologies and some of the material properties, including mechanical, are well known, very little is established for what concerns dynamic impact properties, for the design of energy absorbing components made of microcellular foams. The paper reports a number of experimental results, in different loading conditions and loading speed, which will be a basis for the structural modeling

A Numerical Method to Compute Brain Injury Associated to Concussion

This research proposes a new a numerical method to compute brain injury associated with concussion using the Peak Virtual Power method, using the THUMS 4.02 head model. The results indicate that mild and severe concussions could be prevented for lateral collisions and frontal impacts with PVP values lower than 0.928mW and 9.405mW, respectively, and no concussion would happen in the head vertical direction for a PVP value less than 1.184mW. This innovative method proposes a new paradigm to improve helmet designs, assess sports injuries and improve people's wellbeing.Comment: 12 page