Modelling of the effects of potholes on motor vehicle structures

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Matsika, Emmanuel
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The objective of this work was to investigate the effects of the impulses induced by potholes on motor vehicle structures. MATLAB computer package was used to develop a computer program to carry out the tasks. This was done with a view to make recommendations in the nature and frequency of maintenance or replacement of vulnerable parts of the vehicle structure. Further, recommendations were made that vehicle manufacturers should consider in the design of vehicles intended for areas where potholes exist. Mathematical models of the vehicle suspension systems were used to predict the dynamic forces induced. Stress analysis was performed on selected most susceptible parts of the vehicle. These included wheel bearings, linkage pins and associated bushings, springs and shock absorbers and related fastenings. The parts were chosen following verbal interviews with auto-mechanics in garages and indeed from the experience of the author while working in the transport section of a company. This study only considered stress analysis. In order to practically determine the vibration responses (acceleration and displacement) of the vehicle and the waveform that best approximates the exciting and excited motion when a wheel hits a pothole, on-vehicle vibration tests were carried out using a two-axle Toyota Corolla 1.5 GL saloon car. The experimental results were found to be lower than the simulated ones.Simulated results showed that for the car used as a case study, each wheel could be treated separately as a quarter car. The investigation on potholes showed that the pothole length determines the vehicle velocity at which resonance occurs while the magnitude of the induced force is influenced strongly by the pothole depth. In addition and to some extent, the velocity affects the force as it determines the value of the dynamic load factor. For the saloon car used, it was shown that the critical speed (resonance velocity) for both the sprung and unsprung masses fell within 4 to 10 km/h and 40 to 55 km/h for the sprung and unsprung masses, respectively. Since most driving is up to a maximum of 50 km/h around towns and residential areas, the issue of potholes has to be seriously addressed.The load on the unsprung mass was found to be much higher than that on the sprung mass.Therefore, in the design of suspension parts, emphasis should be put on the unsprung mass components. For the vehicle user, more frequent replacements of suspension parts was recommended, while for the manufacturer, redesigning of some suspension components was recommended.The results also showed that the suspension geometry, load path characteristics and components materials' mechanical properties dictate the failure mechanism of the vulnerable parts.
Motor vehicles--Zambia , Potholes(roads)--Zambia