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Converting dynamic impact events to equivalent static loads in vehicle chassis

Vivek Ganeshan ; Sushanth Shandilya Dattakumar
Göteborg : Chalmers tekniska högskola, 2017. Diploma work - Department of Applied Mechanics, Chalmers University of Technology, Göteborg, Sweden, ISSN 1652-8557; 2017:55, 2017.
[Examensarbete på avancerad nivå]

The ever increasing need to simulate the complex dynamic events in vehicle chassis demands extensive computational resources. Due to the extreme nature of the peak load events, special attention needs to be given to the dynamic peak loads in order to understand the damage caused by them in the vehicle components and their effect on the design. To mitigate the difficulty of handling dynamic loads, structural engineers usually carry out the static simulations using a dynamic load factor. The dynamic load factors need to be reliable and determined logically by accounting for the inertial effects such that the equivalent static loads result in similar stress and strain patterns in the components. The explicit method has been used extensively in order to effectively replicate the complex events due to its ability to solve highly non-linear problems with very less convergence issues and unconditional stability. However, the limiting factor being the computational time to carry out such analysis being very high. For quasi-static based problems, implicit methods have proven to be a good solution, as the computational time required in this method is shorter and the calculations cycles involved are fewer, but with an implication of conditional stability. Thus, its very important to understand the pros and cons of each integration scheme and choose the suitable one based on the application. In the current study, a methodology has been devised utilising both the schemes to arrive at a reliable dynamic load factor. The methodology involves carrying out the dynamic simulation first to replicate the dynamic event, followed by a modal transient analysis to understand the active modes at each time instant. The equivalent static loads are calculated based on the modal transient analysis and applied in static or quasi static analysis to obtain similar stress and strain patterns in the components and thus the dynamic load factor. In the pre-study of the thesis, simple geometries such as the beams were tested for 2 configurations, namely, cantilever and simply supported. The physical and load impulse characteristics were investigated. In the main study, the project involved analysing the loading conditions from the multi-body dynamics model of the vehicle chassis components and developing an FE model to study the response of the sun-assembly to the applied dynamic and static loads. The equivalent static loads were adjusted to achieve the same damage (stress and strain distribution) in the components. The above procedure was adopted for 2 load cases, namely, the side kerb impact and the pothole load case. Parametric study was conducted to investiiv gate the effect of each parameter on the output response. The components studied in this work are the upper and the lower control arms of SLA type suspension system. Some of the key findings from the thesis work are : • Fundamental frequency of the sub-assembly governs the maximum displacement response. • For the various load curves studied, namely triangular,sinusoidal, and trapezoidal pulse load, the maximum response was found to be mainly influenced by the average impulse acting on the system. • The maximum displacement of the system is majorly governed by the ratio of the impulse duration to the fundamental time period of the system in case of isosceles triangular impulses. • The dynamic peak load has negligible effect on the dynamic load factors. Keywords: Impact events; Vehicle Chassis; Dynamic analysis; Equivalent static load.



Publikationen registrerades 2017-08-27. Den ändrades senast 2017-08-27

CPL ID: 251445

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