PSI - Issue 19

Thorsten Voigt et al. / Procedia Structural Integrity 19 (2019) 4–11

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Dr.-Ing. Thorsten Voigt/ Structural Integrity Procedia 00 (2019) 000 – 000

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Figure 1: Urban EV vehicle

Figure 2: vehicle light weight design

Figure 3: foldable rear axle

The pulses generate a magnetic field and induce eddy currents in the tube. The interaction between both electrodynamic processes: magnetic field and current leads to strong Lorentz forces in the tube. These forces, which are directed inwards in the direction of the pipe longitudinal axis, are strong enough to crimp the tube material and to ensure that the two parts fit together positively. Note that applying this technology does not introduce thermal loads to the workpieces and therefore ensures the preservation of the aluminum tube ’s mechanical properties In the research project, the Fraunhofer Institute LBF was entrusted with the task of developing an integrated concept for fatigue evaluation of selected samples at component and subsystem level. This was intended to ensure the lifespan of the test specimens and to demonstrate the performance of the lightweight design concept. The further developed EMPT bonding as well as an EMPT crimped nodal element of the body frame were investigated (Lipp et al. (2017)). This paper addresses the experiments on the control arm of the pivoting rear axle and the investigations on a half-axle module of the rear axle. The challenge was that no load data from simulations or test drives were available in the run-up to the investigations. Therefore, efforts had first to be made to derive a variable amplitude load program that sufficiently reflects the stresses on the vehicle in daily use, and can thus be used as the basis for lifespan durability tests. In order to be able to ensure the durability of mechanical components, it is necessary to know the design basis (customer usage profile) for operational reliability of the components. This must be designed (Gudehus and Zenner (2004), Köhler et al. (2012)) so that it  includes all possible operational load cases,  reflects these load cases in the right proportion of their probability of occurrence,  also considers special load cases and  maps the entire lifespan of the component. Shortened load spectra for component tests can then be derived from the design spectrum. For these, the following premises apply: 2. Derivation of a load program with variable amplitudes In light small city vehicles such as the newly developed research vehicle, two problems are encountered in this regard. On the one hand, there is only little experience and measured data for this still young vehicle class L7e from which design spectra can be derived. On the other hand, the research vehicle is manufactured in extremely small numbers. During the development period and with the available budget, it was impossible to carry out test drives in order to determine realistic load spectra. Here, the use of standardized design spectra and synthetic load-time series for vehicle testing can be of help. In the past, extensive manufacturer-independent measurements were carried out on vehicles. The aim was to determine design spectra for the design of vehicle wheels (Grubisic (1973)). The investigations led to the conclusion that for basic driving maneuvers: straight driving, cornering, braking and acceleration, typical load spectra could be derived and standardized across all models. These can be adapted to a particular vehicle under consideration via the static wheel load and a few influencing parameters. Efforts were subsequently made to derive a synthetic load program from the standardized customer usage profile. The STAMAS collective ( ST Andardized M ulti A xial S imulation, Mueller et al. (1973)) includes four load channels: longitudinal force x , lateral force y , vertical force z and braking force brake , and takes into account the four load cases mentioned above. There are short load-time series for each of the load cases, each of which is normalized to the load range [1,-1]. For each load case, a set of impact parameters is to be determined, which reflects the influence of the vehicle type and the operating conditions of the vehicle on the loads occurring. With these parameter sets and the static wheel load, the standardized load-time series of all load cases are scaled to the load level expected for the vehicle under consideration. Table 1 shows impact parameters which were derived for the Ur ban EV-Vehicle with 230 kg static wheel load while Table 2 lists the corresponding maximum values for each load channel under consideration.  min/max values of the load channels must correspond to the values of the design basis  maintaining the correlation of the load channels with each other in typical operating load cases  maintaining the basic shape of the load spectra,  damage equivalence to the design spectrum.