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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deformation energy absorbed by the bus door structure when subjected to an impact load from a virtual striker. Nowadays, heavy passenger vehicles are tested for their resilience when they are subjected to an impact at the vehicle´s front surface at a prescribed speed. The deployment of this process implies some investment, in terms of instrumentation and test rig kinematics. This test is performed as a preliminary task as part of the test regulation R-29, that specifically refers the side door of a bus as a deformable sub-system of the whole front structure. This regulation intends to evaluate the energy absorption capacity of heavy vehicles when subjected to a frontal impact and thus their validation. A test rig has been developed with a swinging pendulum that, once released, will impact the frontal area of the vehicle, with kinetic energy corresponding to the regulated amount ( 55 , for vehicles with a tare greater than 7.5 ), that is expected to be absorbed by the bus structure (J. O. d. U. Europeia, 20.11.2010). However, this regulation is indicated for heavy vehicles with a separate cabin, not being directly applied to buses, however, an adaptation will be made. The 1500 mass pendulum impacts the front surface of the bus as evenly as possible, at an approximate speed of 8.56 / . Considering that the door absorbs about 3% of the total mass of the impactor, it receives about 45 . Since the R-29 specifications refers to a typically dynamic test and more expensive than a static test, then, as alternative, a pseudo-dynamic method is performed. This type of test procedure presents results relatively close to a dynamic test at a lower cost. With an adequate number of increments, it is possible to accurately achieve virtually a dynamic test. In this work, the structural behavior of a vehicle door under an in-plane impact will be analyzed. The striker is then supposed to move in the door plane. For the pseudo-dynamic test, only a fraction of the striker mass is considered as a virtual equivalent mass, since real-time impact tests, recorded by high speed video, show that a small amount of deformation is exhibited by the vehicle body front-pillars and is propagated to the door structure. The door will be instrumented with 6 unidirectional strain gauges, having their location been previously studied using a numerical simulation tool. Additionally, the deformation fields of the main front panel were measured using 3D digital image correlation. A pseudo-dynamic test (PSD) is an experimental practice providing accurate and reliable results with the advantage of being quasi-statically performed. Given the structural simplicity of the door design, the associated dynamic model can be approached as a single degree of freedom (SDOF). The evolution of the deformation in time (virtual time) can provide useful information on the behavior of the structure due to its damage propagation modes. Nomenclature Mass of the impactor Current time instant ∆ Time step 0 Initial velocity of the impactor Velocity of the impactor at the instant +∆ Velocity of the impactor at the following instant Internal reaction of the deformable solid in the contact point at the instant +∆ Internal reaction of the deformable solid in the contact point at the following instant Displacement of impactor at instant (after = 0 , when the contact started) +∆ Displacement of impactor at the following instant 1.1. State of the art The automotive industry, at the most widespread point, demands the continuous improvement of its structural components. This way, it will be possible to improve the vehicle aesthetics and optimize the structure (Cavazzuti et al., 2012). The performance of several studies has shown that, among the different car manufacturers, safety is one of the crucial parameters of vehicle design (Porcu, Olivo, Maternini, & Barabino, 2020). Among the various authors who have dedicated themselves to these studies, Mayrhofer et al. (Mayrhofer, Steffan, & Hoschopf, 2005) devoted themselves to statistical studies of accidents, using numerical simulation to investigate the dynamic behavior of the bus. Additionally, proposals for its improvement were presented. Structural optimization goes through an iterative