Alessandro Scattina

Louver Finned Heat Exchangers for Automotive Sector: Numerical Simulations of Heat Transfer and Flow Resistance Coping With Industrial Constraints

Louvered fins perform better than any other geometry in accomplishing the task of enhancing heat transfer of compact heat exchangers without prohibitive costs and pressure drops. For this reason they are widely adopted for automotive applications. However, in order to improve louvered-fin compact heat exchangers, it is strongly required to understand how louvered fins behave regarding both heat transfer and pressure drop taking into account industrial constraints. For this purpose, numerical simulations based on the equations of thermo-fluid-dynamics have been developed for this study. In particular, boundary heat flux and pressure distributions have been analyzed along the louvered fin assembly and around the louvers, and even the effects of the flat portions (central and lateral louvers) have been investigated. In particular, the effects of the main geometrical parameters, such as fin pitch, louver pitch, and louver angle, have been evaluated by performing simulations on 40 different configurations. The results show that there is not one optimum configuration for the heat exchangers. Finally, a detailed procedure for the optimisation of louvered-fin compact heat exchangers, considering industrial constraints is suggested according to multiple regression technique of the numerical results

Numerical Analysis of Hybrid Joining in Car Body Applications

Nowadays, there are two fundamental issues in car body design. On the one hand, there is the need for weight reduction in order to reduce fuel consumption and, consequently, pollutant emissions, and on the other hand, there are ever more stringent safety requirements. To meet these targets, the trend is towards using hybrid structures made of unconventional materials, like aluminium, polymeric and composite materials. The use of these materials brings about some problems, one of them is associated with the joining techniques because the traditional resistance spot-welding, used in the assembly of a common steel chassis, cannot be used. Among the different alternative solutions, the most promising is the use of structural adhesives. From this perspective, this work aims to model the behaviour of simplified crash box elements made of different types of materials joined together by structural adhesives. In particular, the attention was focused on the adhesive joint modelling with a cohesive element formulation. Starting from experimental results for the characterization of the adhesive, the cohesive parameters were identified. The results were then applied to model the crushing of simplified crash boxes. The crushing axial compression of these components was investigated considering geometrical and loading conditions. The models were developed and verified by comparing the numerical with experimental results on these components. A good correlation was found in all loading conditions and with different geometries and substrate combinations.

Incidences of various passenger vehicle front-end designs on pedestrian lower limb injuries

The present study aims to investigate the influence of various passenger vehicle front-end designs on knee ligaments and tibia injuries of pedestrian lower limbs by finite element simulations. Using a detailed finite element model of the lower limb, this work was focused on tibia fractures and knee ligament ruptures of lower limbs during vehicle–pedestrian impacts. The influences of vehicle front-end structures on the risk of these two injury occurrences were investigated using super mini, small family car, executive car, and multipurpose vehicle passenger vehicle types. The overall results show that the bumper beam design play an important role in inducing pedestrian lower limb injuries. Its height to the road surface, width in the height direction, and the deformable depth between it and the bumper fascia should be all considered in the vehicle design to protect pedestrian lower limbs.

Structural Design and Experimental Investigation of a Carbon Fibre Wheel for Low Consumption Vehicle

Today, 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 presented.

Prediction of Cyclic Fatigue Life of Nickel-Titanium Rotary Files by Virtual Modeling and Finite Elements Analysis

INTRODUCTION The finite element method (FEM) has been proposed as a method to analyze stress distribution in nickel-titanium (NiTi) rotary instruments but has not been assessed as a method of predicting the number of cycles to failure (NCF). The objective of this study was to predict NCF and failure location of NiTi rotary instruments by FEM virtual simulation of an experimental nonstatic fatigue test. METHODS ProTaper Next (PTN) X1, X2, and X3 files (Dentsply Maillefer, Baillagues, Switzerland) (n = 20 each) were tested to failure using a customized fatigue testing device. The device and file geometries were replicated with computer-aided design software. Computer-aided design geometries (geometric model) were imported and discretized (numeric model). The typical material model of an M-Wire alloy was applied. The numeric model of the device and file geometries were exported for finite element analysis (FEA). Multiaxial random fatigue methodology was used to analyze stress history and predict instrument life. Experimental data from PTN X2 and X3 were used for virtual model tuning through a reverse engineering approach to optimize material mechanical properties. Tuned material parameters were used to predict the average NCF and failure locations of PTN X1 by FEA; t tests were used to compare FEA and experimental findings (P < .05). RESULTS Experimental NCF and failure locations did not differ from those predicted with FEA (P = .098). CONCLUSIONS File NCF and failure location may be predicted by FEA. Virtual design, testing, and analysis of file geometries could save considerable time and resources during instrument development.

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.

Multiscale Computational Fluid Dynamics Methodology for Predicting Thermal Performance of Compact Heat Exchangers

Computational Fluid Dynamics (CFD) is a powerful tool for analyzing the performance of heat exchangers. However, such an approach may be often limited by unaffordable computational time. In this paper, a multi-scale CFD capable of accurately and efficiently prediction of the heat transfer of compact heat exchanger is presented. This methodology is based on a small-scale CFD analysis of a single tube and a small element of the compact heat exchanger, and it is able to predict the thermal performance of an entire heat exchanger in a wide range of inlet conditions, with a reduced computational time. The proposed up-scaling procedure makes use of specific approximations and correlations derived from the CFD model and literature, in order to consider typical phenomena occurring in compact heat exchangers under laminar flow conditions. Results demonstrate an excellent accuracy when compared to experimental data (discrepancies <4.3%). This novel up-scaling method may have a strong impact on modelling and design strategy of compact heat exchangers in the industrial field.

Analysis of the influence of passenger vehicles front-end design on pedestrian lower extremity injuries by means of the LLMS model

ABSTRACT Objective: This work aims at investigating the influence of some front-end design parameters of a passenger vehicle on the behavior and damage occurring in the human lower limbs when impacted in an accident. Methods: The analysis is carried out by means of finite element analysis using a generic car model for the vehicle and the lower limbs model for safety (LLMS) for the purpose of pedestrian safety. Considering the pedestrian standardized impact procedure (as in the 2003/12/EC Directive), a parametric analysis, through a design of experiments plan, was performed. Various material properties, bumper thickness, position of the higher and lower bumper beams, and position of pedestrian, were made variable in order to identify how they influence the injury occurrence. The injury prediction was evaluated from the knee lateral flexion, ligament elongation, and state of stress in the bone structure. Results: The results highlighted that the offset between the higher and lower bumper beams is the most influential parameter affecting the knee ligament response. The influence is smaller or absent considering the other responses and the other considered parameters. The stiffness characteristics of the bumper are, instead, more notable on the tibia. Even if an optimal value of the variables could not be identified trends were detected, with the potential of indicating strategies for improvement. Conclusions: The behavior of a vehicle front end in the impact against a pedestrian can be improved optimizing its design. The work indicates potential strategies for improvement. In this work, each parameter was changed independently one at a time; in future works, the interaction between the design parameters could be also investigated. Moreover, a similar parametric analysis can be carried out using a standard mechanical legform model in order to understand potential diversities or correlations between standard tools and human models.

Energy absorption capability of laminated plates made of fully thermoplastic composite

The 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.

Repeated impact behaviour of fully thermoplastic laminates

The use of laminated composites are spreading in engineering applications, respect to heavier metallic materials, thanks to their excellent advantages of weight/strength and weight/stiffness ratio. Even if up to now the attention was focused on fibers reinforced with thermosetting matrix, in the last years composites made with thermoplastic matrix have gained consideration. This is mainly due to their advantages in terms of low density and, more important, recyclability. The use of thermoplastics composites are of interest not only for the replace of the non structural parts, but also for the structural components located in areas potentially subjected to impacts. Depending on the design geometry and the field of application, some composite components may be subjected to repeated impacts at localised sites either during fabrication, routine maintenance activities or during service conditions. Even though the impact damage associated to the single impact event maybe slight, the accumulation of the damage over time may seriously impair the mechanical performance of the structure. In this paper, experimental data of repeated impact tests performed on fully thermoplastic thick laminates are presented. Repeated impacts at different energy levels are considered. The experimental data are analyzed evaluting the damage index (DI). This parameter has been previously defined and used for thermosetting composites in order to overcome shortcomings of the damage degree (DD) in case of thick composite laminates. The rate of initial steady damage accumulation as well as the onset of severe damage modes are analyzed and discussed in the paper. When applied to repeated impact tests, the DI allows to distinguish between an initial steady phase of damage progression and the onset of severe damage mechanisms. For the initial damage, the damage index increases linearly with the impact number whereas the severe damage mechanisms lead to laminate performation in few impacts. In this work, the values of the DI at different stages are discussed: at first impact, in the steady phase and at the onset of the unsteady phase. Moreover, the total energy absorbed by the laminate in the steady phase is also computed for all the performed tests and compared with the results of other thermosetting composites previously tested by other researchers.