Resistenza statica e dinamica di punti di saldatura in differenti condizioni di sollecitazione

Le saldature a punti sono il principale metodo di giunzione delle lamiere nelle scocche dei veicoli terrestri. Esiste un'ampia letteratura sulla resistenza statica ed a fatica dei punti e sulla loro modellazione statica. Per simulare fedelmente le strutture puntate occorre conoscere le proprietà dei punti in condizioni di sollecitazione dinamica. Su questo problema non esistono molti risultati per cui in questo lavoro si propone un metodo di prova che permette di studiare la resistenza a differenti velocità di impatto ed in diverse condizioni di sollecitazione. I risultati permettono di definire un criterio di rottura del punto in funzione del tipo di caric

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

A mechanical model of cellular solids for energy absorption

Cellular materials have a variety of applications in the fields of packaging and mitigation in the case of impact of vehicles, due to their ability to protect goods by absorbing energy. To design energy absorption systems, it is necessary to use predictive models of cellular materials. The models must describe the stress-strain behavior then energy absorption characteristics can be evaluated. Moreover, it must consider affecting factors like strain-rate. Modeling the influence of the density helps designer in selecting the best foam solution. In previous works the authors already presented models able to describe the quasistatic stress-strain behavior of several cellular materials. The current paper presents a general model able to describe the mechanical characteristic of a much larger variety of cellular materials including metal foams and considers the influence of strain-rate. Among the considered materials there are the Foaminal\uae foam and APM\uae aluminum foams. The model is fitted to experimental tests with parameters identified based on experimental data. Tests include quasi-static, dynamic, and impact tests in different loading conditions. It will be shown that the proposed model is fundamentally suitable for most materials, virtually any foamed material, and it is a useful tool for designers in the mentioned areas

Next Generation HEV Powertrain Design Tools: Roadmap and Challenges

Hybrid electric vehicles (HEVs) represent a fundamental step in the global evolution towards transportation electrification. Nevertheless, they exhibit a remarkably complex design environment with respect to both traditional internal combustion engine vehicles and battery electric vehicles. Innovative and advanced design tools are therefore crucially required to effectively handle the increased complexity of HEV development processes. This paper aims at providing a comprehensive overview of past and current advancements in HEV powertrain design methodologies. Subsequently, major simplifications and limits of current HEV design methodologies are detailed. The final part of this paper defines research challenges that need accomplishment to develop the next generation HEV architecture design tools. These particularly include the application of multi-fidelity modeling approaches, the embedded design of powertrain architecture and on-board control logic and the endorsement of multi-disciplinary optimization procedures. Resolving these issues may indeed remarkably foster the widespread adoption of HEVs in the global vehicle market

Hydraulic Brake Systems for Electrified Road Vehicles: A Down-sizing Approach

Down-sizing hydraulic brake systems can is made possible in electrified road vehicles thanks to the braking torque contribution provided by electric machines. Benefits in terms of weight and cost of the system can be ensured in this way. Nevertheless, appropriate care should be taken not to excessively deteriorate the overall electrical energy recovery capability of the electrified vehicle during braking maneuvers. For this reason, a multi-target optimization framework is developed in this paper to down-size hydraulic brake systems for electrified road vehicles while simultaneously maximizing the braking energy recovery capability of the electrified powertrain. Firstly, hydraulic brake system, electrified powertrain and vehicle chassis are modeled in a dedicated simulation platform. Subsequently, particle-swarm optimization is employed as search algorithm to identify optimal sizing parameters for the hydraulic brake system. Sizing variables particularly include diameter and stroke of the master cylinder, electrically assisted booster diameter, front brake piston diameter and rear brake piston diameter. The simulation of homologation tests for safety standards ensures that retained combinations of sizing parameters complies with regulatory requirements. A case study proves that the developed methodology is flexible and effective at rapidly producing several sub-optimal sizing options for both front-wheel drive and rear-wheel drive layouts for a retained battery electric vehicle

Axial crushing of metal-composite hybrid tubes: experimental analysis

In the automotive sector, special attention is paid to the study of the behavior of the structural components that make the car bodies. The continuous demands on the weight saving imply the car bodies to be assembled with components made in different materials and using different manufacturing processes. Considering the making of the sacrificial structures aimed to the energy absorption, composite materials are increasingly used to replace conventional metal materials. However, the use of composites is accompanied with a change in the type of deformation obtained during the impact phenomenon. Usually, with the conventional metal materials, the crushing behavior is a progressive buckling whereas the composite materials are characterized by a brittle fracture. The combination of the traditional metal materials with the composite ones can represent a good solution to obtain high levels of performance. In this context, the structural performance of metal-composite hybrid tubes subjected to quasi-static axial crushing is experimentally evaluated in this work. The specimens, with circular cross section, were obtained with tubes made in a fully thermoplastic composite internally reinforced with aluminum tubes. The composite material used were made in polypropylene both for the matrix and for the reinforcing fibers. This material has a good axial absorption capacity but irregular behavior during crushing. The addition of a conventional material as reinforcement allowed to increase the absorption capacity by ensuring a more progressive and controlled crush. The analysis was carried out by evaluating, for various geometric configurations, different parameters (mean load, average stress, specific energy, efficiency). The results, discussed in the work, showed how the energy absorption performance of a hybrid structure are higher than the sum of the performance of the single materials

Application of speed and separation monitoring method in human-robot collaboration: industrial case study

Application of human-robot-collaboration techniques in automotive industries has many advantages on productivity, production quality, and workers’ ergonomy, however workers’ safety aspects play the key role during this collaboration. In this paper, results of the ongoing research about the development of a manufacturing cell for the automotive brake disc assembly that is based on the human-robot collaboration are presented. Operational speed and worker-robot separation monitoring methodology (SSM) as one of the available method to reduce the risk of injury according to the ISO technical specification 15066 on collaborative robot in sharing space with human, has been applied. Virtual environment simulation has been used, considering different percentages of robot maximum speed, to determine the SSM algorithm parameters for estimating the minimum protective distance between the robot and operator. Using ISO/TS 15066 and virtual environment simulation, the minimum separation distance between operator and robot has been estimated. Using human-robot collaboration along with the safety issues specified by SSM system has increased the safety of operation and reduced the operator fatigue during the assembly process

Impact behavior of a fully thermoplastic composite

Composites are materials of choice for lightweight structures due to their excellent strength/weight/and stiffness/weight/properties. For several years, the application of composite materials with continuous fiber was limited to those with thermosetting matrix. Recently, interest in composites with thermoplastic matrix is growing thanks to their considerable advantages also in terms of recyclability. The thermoplastic composites appear to be the right alternative to the materials currently used, replacing not only the non-structural parts, but also the structural components located in areas potentially subject to impacts. This paper presents the results of an experimental campaign made on a fully thermoplastic composite, where both the reinforcement and the matrix are made in polypropylene. The target is to analyze its behavior under different impact loading conditions using a drop weight testing machine. The influence of the impact mass and of the velocity on the energy absorption capability of the material have been analyzed and discussed. During the tests, the material showed a ductile behavior and developed extended plasticity without a crack tip. The main observed damage mechanisms were the yarn sliding

Uncertainty in fatigue loading: Consequences on statistical evaluation of reliability in service

A design-by-reliability approach is ever more required and accurate design inputs are needed to meet reliability targets while reducing costs. Different models have been proposed in the literature to describe fatigue life variation with respect to the applied stress by assuming the applied stress as a deterministic independent variable and the fatigue life as a dependent random variable. In the paper also the applied stress is considered as a random variable with its own uncertainty and the procedure to valuate the error on the estimation of parameters usually adopted in service reliability assessment of structural components is shown. Exact equations are proposed for some special cases and an illustrative example showing the reliability errors originated by applying the ASTM recommendations is give