PSI - Issue 37

Rogério Lopes et al. / Procedia Structural Integrity 37 (2022) 115–122 R. F. Lopes et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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process in the development and design of new products that constitutes a progressive improvement in the stiffness/mass ratio. A highly effective method for studying this relationship is based on monitoring the natural frequency of components and/or structural assemblies. The aforementioned parameter is commonly used for structural optimization, as it is an extremely sensitive parameter to change both in mass and stiffness. The abovementioned observation contributes to the ultimate objectives of continually improving passenger safety and environmental sustainability (Chiandussi, Gaviglio, & Ibba, 2004). The focus of this work is mainly directed to heavy vehicles in the transport passengers, more specifically of bus type. While lightweight private vehicles are certified for their active and passive safety according to testing procedures included in objective standards, an equivalent certification is somewhat lacking and its setup needs further discussion by competent committees. This target can be technically improved (Jongpradist, Senawat, & Muangto, 2015). In the USA, there are about 55,000 accidents involving buses every year. A similar study in Europe, indicated that the number of road accidents involving buses has decreased by around 50% since 2005 (C. Europeia, 2016). As a result of the reduced research in this branch, more focus is devoted to the objectiveness in the design of upgraded standards for safety certification of heavy passenger vehicles. Such study has been awarded to UNECE (Commission for the Union of Economies of European Nations), who announced that one of its main objectives is to improve the design of vehicles discussed herein. The new focus of work implies the development and incorporation of technical solutions. Performance improvements should occur at the bus body level (UNECE, 2015). Road accidents can occur in the most diverse and varied ways, having different areas of impact. The author Mátyás Matolcsy (Matolcsy, 2016) in his study devoted himself to categorize the incidence of bus accidents, highlighting the frontal and combined impact (encompassing areas of incidence such as the lateral, the rear and / or overturning). The highest percentage of accidents tend to occur head-on (Jongpradist et al., 2015). Freight vehicle industry has regulations to validate their safety. Regulation-66 validates the vehicle tested for a rollover event, while Regulation-29 cares about the vehicle structural behavior when subjected to frontal shock. It should be noted, however, that the previously mentioned regulations are directly applied to heavy vehicles with a separate cabin (Cerit, Guler, Bayram, & Yolum, 2010). Other authors have directed their work towards the passenger safety level. In the studies of Matsumoto et al (Matsumoto, Driemeier, & Alves, 2012), it is concluded that the driver's safety is conditioned by the deformation level occurring in the compartment in the event of a crash. This is measured especially by the intrusion of materials and structures during the impact. Additionally, it is considered that the decelerations felt have a direct relationship with the time interval of the collision. Thus, it is intended that the body has structural components made of materials with the capability of absorbing in a controlled manner the energy dissipated in the collision. Thus, it is essential to optimize passive safety while safeguarding the life of the driver and passengers (Abramowicz, 2003; Jongpradist et al., 2015). Actual bus-type vehicle bodies have shown to be unable to absorb all the energy that is released in the collision, leading to hazardous intrusion of the components in the driver's compartment (Jongpradist et al., 2015). There are currently proposals for revising the regulations to be discussed by UNECE. Soon, it is expected, the issue of a regulation applicable to buses, more specifically to the tourism class, an opportune incentive to develop new models creating a new family of tour buses, breaking the technical frontiers. 1.2. Pseudo-dynamic test The experimental practice that is proposed in this chapter is less known and implemented; however, it is able to return precise and reliable results, provided that the dynamic behavior of the structure to be tested can be dynamically modelled by only one degree of freedom. With this technique, it is intended to obtain the evolution of the deformation that is directly related to time and will allow to assess the behavior of the structure when subjected to the virtual dynamic impact (Melo, Carneiro, Tavares, Camanho, & de Castro, 2006). In a pseudo-dynamic procedure, some entities must be numerically assumed (as the inertial properties of the model and velocity dependent damping forces, if existing), while other parameters are experimentally measured during the test, as is the case of the structure internal stiffness. This last parameter can be updated at each time increment of the test run, a procedure making the method to cope accurately with non-linear behavior of the structure in assessment (Aktan, 1986). This an hybrid (numerical-experimental) tool that is developed in loop, where at each time step, updated of values computed via a direct time integration algorithm, are input in a test rig equipped with displacement