101 research outputs found
Numerical analysis of tube expansion process for heat exchangers production
No full textThis work analyses two different aspects of the mechanical process of tubes expansion used for the production of heat exchangers. In particular, the influences on the expansion process due to mandrel geometry and geometrical errors in tubes, caused by production tolerances, were studied and analyzed using finite element (FE) models. A 2D axisymmetric model was used to study the influence of mandrel geometry, whereas a 3D solid model was adopted to investigate the influence of geometrical errors in tubes. Experimental tests were carried out on actual materials in order to set up and validate the FE models. Force required for expansion, and variation in tube dimensions due to expansion were investigated and a good agreement was found between experimental and FE results. Additionally, the obtained results showed that the fillet radius is the most important geometrical factor of the mandrel in order to reduce the expansion force. A great influence of the tube geometrical errors was observed on the tube expansion process, which can compromise the performance of the heat exchanger. Finally, it is worth mentioning that the present study provides useful information that might be used to improve tubes expansion processes in general and heat exchangers production in particular
Some recent results of the Politecnico di Torino research in the field of vehicle passive safety
No full textEnergy absorption capability of laminated plates made of fully thermoplastic composite
No full textThe behaviour of composites materials, made of synthetic fibres embedded in a thermoplastic resin, subjected to low velocity impacts, was largely studied in the past. However, in the last years, the use of thermoplastic composites has been increased due to the considerable advantages in terms of recyclability of this family of materials. Thermoplastic composites are composed of polymers with different material’s structure if compared to the more traditional thermoset composite. Consequently, the behaviour of these materials can be different in some loading conditions. Moreover, considering the wide range of thermoplastic composites that have been developed in the last years, the study of the behaviour of these materials, in case of impact, has not been yet widely analysed, in particular considering materials where both the matrix and the reinforcement are made of thermoplastic. In this perspective, the goal of this work is to study the behaviour of a new thermoplastic composite (PURE thermoplastic) in conditions of low velocity impact. In this material, the matrix and the fibre reinforcement are made of polypropylene both. The paper presents the results of an experimental investigation. In particular, a series of impact tests with a drop dart equipment have been carried out on laminates made of PURE thermoplastic. Laminates with different thicknesses have been taken into consideration. The influence of the impact conditions on the material’s behaviour has been investigated and the capability of energy absorption has been studied. The PURE thermoplastic showed a different behaviour in terms of energy absorption and damage mechanisms if compared to the composites presented in the literature. The thickness of the laminate has had influence on the deformation and the damage mechanism of the specimens: with low thickness, the perforation of the specimen has been obtained, whereas, with the higher thickness, the specimens have shown a ductile behaviour and extended plasticity without crack tip. The contact force between the dart and the specimen has been influenced by the energy level of the impact, but with an opposite trend if compared to that of the composites studied in the literature
Analysis of the mechanical expansion process of thin-walled tubes for air heat-exchanger production
No full textFinned tube air heat-exchangers are built by joining the tubes to the fins by various techniques. A technique mostly used for large heat-exchangers consists of fitting the tubes into the holes of the fins by expanding the tubes using a mechanical process. The expansion is achieved by inserting an ogive of a larger diameter into the tube. The intimate contact of tubes and fins due to the press fitting ensures the proper thermal connection. This work tries to describe an experimental-numerical procedure useful to study and predict the mechanical process and the process parameters. The procedure, based on material properties obtained from tensile tests and the use of the inverse method to identify the material parameters, is based on bi-dimensional finite element (FE) models used to simulate the expansion process. The FE model is then used for process optimisation regarding such parameters as the ogive shape and ogive sizes, friction coefficient and speed of insertion of the ogive into the tube. Indeed, size and shape uncertainties strongly influence the process parameters and the process quality, as well as the heat-exchanger efficiency. The use of numerical models was proven highly effective in predicting and optimising the process by quickly analysing the influencing factors and optimising the production
Battery Pack and Underbody: Integration in the Structure Design for Battery Electric Vehicles—Challenges and Solutions
No full textThe 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
Structural design and experimental investigation of a carbon fibre wheel for low consumption vehicle
No full textToday, in the design of a new vehicle, one of the most important challenge is the weight reduction. This item is even more important in the design of prototype vehicles aimed to low consumption competitions, where it is necessary to minimize the weight of all components. For this reason the carbon fibre composite materials appear the best solution in terms of low density and mechanical properties. In this work the attention is focused on the wheel of the IDRA prototype, which participated in the Shell Eco Marathon competition. The wheel rim is a lenticular single part made of carbon fibre materials, without the use of structural adhesive. The different design steps, from the concept phase to structural analysis made by means of finite element code, are discussed. At the end the innovative manufacturing production process is presente
SVILUPPO DI UNA METODOLOGIA DI SIMULAZIONE DEL PROCESSO DI FORMATURA DEI TUBI PER I FASCI TUBIERI FORZATI NELLE PIASTRE FRONTALI
No full textIl fissaggio dei tubi sui pacchi alettati con cui sono realizzati i grandi scambiatori di calore può essere realizzato mediante un processo meccanico denominato mandrinatura, in cui una ogiva opportunamente sagomata viene spinta all’interno del tubo. L’obiettivo di questo lavoro è lo studio e la messa a punto di un modello agli elementi finiti in grado di simulare al meglio il processo di espansione. Il lavoro è suddiviso in una prima parte sperimentale, in cui vengono caratterizzati i materiali impiegati ed il processo di espansione, ed una seconda parte numerica in cui viene sviluppato il modello sulla base dei dati sperimentali raccolti. Il modello sviluppato permette di valutare l’influenza dei parametri che governano il processo
Experiment based modeling of the mechanical expansion of tubes for the construction of heat exchangers
No full textTube 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 of the structural behaviour of hybrid metal/composite thin walled box beams
No full textInvestigation on the energy absorption capability of composite crash-box with recyclable thermoplastic material
No full textNowadays the key points in the automotive design are the pollutant emissions and the safety. For these reasons, on one side, in the car design the tendency is to use innovative lightweight materials in order to reduce the weight of the vehicle and consequently the fuel consumption and the gas emissions. On the other side, to reach high level of safety, these materials have to be able to absorb high amount of energy in case of impact. For these reasons, in the last decades, the use of composites as design material for impact attenuators in automotive design is increased significantly. The ever-wider use of composite materials for automotive applications involves the need to predict their behaviour under various load conditions which they are subjected, for example with the use of finite element codes. Moreover, more recently, the strong emphasis on recyclability from the end-of-life vehicle directive seems to affect significantly the choice of materials in the design phase. In this overview, the use of thermoplastic composite based components for vehicle structure is investigated in this work. In particular a thermoplastic fibres combined with a thermoplastic matrix is considered. An experimental test campaign, in order to define the mechanical properties of this new material is carried out. Starting from the information obtained in the first experimental tests, the energy absorption capacity of impact attenuators made as thin wall tubes of circular cross section is investigated. The crushing sensitivity of these structures to the wall thickness and to the resistant section is studied. The experimental results and the failure mechanisms obtained in the tests are presented and discussed in the pape
- …
