PSI - Issue 37

Behzad V. Farahani et al. / Procedia Structural Integrity 37 (2022) 668–675 Behzad V. Farahani et al./ Structural Integrity Procedia 00 (2021) 000 – 000

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They are also the most cost-efficient and flexible form of public transport, requiring minimal investments to launch new lines or routes. Medium-size buses for transportation of passengers become particularly popular because they provide more freedom, for both carriers and passengers; furthermore, they are environmentally friendly and economical. However, the growing number of used buses is accompanied by raising the traffic events where these vehicles are involved. Among all traffic events caused by buses, an event related to bus rollover constitutes the maximum damage because it may bring high fatality rate per event (Pravilonis, Eidukynas, and Sokolovskij 2020). Although in long vehicles and particularly buses, these type of crashes take place less frequently than passenger cars, if happen, these crashes bring a very high fatality (El-Hennawy et al. 2014). Nevertheless, in the case of bus rollover crashes, generally, the vehicle undergoes a multidirectional acceleration with multiple impacts, yielding a complex interaction between structural components and its occupants (Seyedi et al. 2019). It meant that the rollover test is a lateral tilting test in which the complete vehicle is standing on the tilting platform, with blocked suspension and is slowly tilted, from a height of 800 mm from the ground level, to its unstable equilibrium position. In this regard, for a single-deck rigid vehicle, the United Nations Economic Commission for Europe (UNECE) Regulation No. 66 (ECE R66) (En L 2011) suggests a residual space considered in the bus’s interior space. Hence, no part of the vehicle, which is outside the residual space at the beginning of the test, shall intrude into the residual space during the test. From crashworthiness point of view, the rollover crashes must be studied in terms of the vehicle’s ability to protect its occupants during an impact (C. C. Liang and Nam 2010). In this regard, Kongwa et al. (Kongwat, Jongpradist, and Hasegawa 2020) studied the crashworthiness of the bus body according to the ECE R66 regulation if the bus is subjected to a rollover test. They proposed a lightweight design for the bus body that can improve the energy consumption and operational cost in addition to the crashworthiness optimization. Bojanowski et al. (Bojanowski, Kwasniewski, and Wekezer 2013) carried out a computational study on the crashworthiness assessment of paratransit buses. It aimed to propose a verification and validation program for a bus rollover test simulation following the ECE R66 regulation. Lopes et al. (Lopes et al. 2021) studied the dynamic response of a passenger bus subjected to an impact loading and the modal behaviour of the bus has been analysed through numerical Finite Element Method (FEM) formulations. Bai et al. (Bai, Meng, and Zuo 2019; Li et al. 2020) deployed a rollover crashworthiness analysis to optimise the bus frame through beam and plastic joints. In the case of other vehicles, as an illustration, Baykasoğlu et al. (Baykasoglu et al. 2013; 2012; 2011) studied the crashworthiness of railroad vehicles subjected to rollover crashes through numerical and experimental analyses. Indeed, they carried out experiments to analyse the collision and to propose modifications improving crashworthiness of the studied vehicle. More research works dealing with the rollover crashworthiness can be found in (Zhu et al. 2020; Tao et al. 2019; C.-C. Liang and Le 2009). In this study, a segment of the whole bus structure, including the superstructure and chassis, is considered as the case study. The studied bus section was manufactured and it is experimentally tested in order to obtain the force/displacement curve upon loading and therefore the internal energy determination. According to real geometrical characteristics of the bus segment, numerical analyses have been performed through FEM formulations simulated in ABAQUS © . It tends at the structural safety assessment whether it possesses the sufficient strength to ensure that the residual space during and after the rollover test on complete vehicle remains unharmed. The ECE R66 regulation proposed a reference solution on internal energy respecting some conditions related to the residual space. This residual space is defined inside the bus section with the specific dimensions. The displacement of the lateral parts shall not be exceeded a certain value as recommended by the corresponding standard. This residual space must be considered in both numerical and experimental analyses. 2. Model definition A segment of a-12- m long bus is considered in this study to assess the ECE R66 regulation in terms of internal energy dissipated during loading condition. Figure 1 depicts the geometry of the studied bus section with the material definitions. As shown in the figure, the chassis structure was made of a steel alloy S420. The rest of the bus section (lateral sides and roof components) were made of Aluminum alloys including AA6005A-T6, AA6060-T6, AA6106 T6 and AA6082-T6. Table 1 reports the material properties considered for this study.