The aim of this study is to investigate the use of multi-body vehicle simulation models to predict the suspension forces acting on the chassis of the vehicle, in order to perform durability analyses. Traditionally, durability of vehicles is evaluated with proving ground tests. This implies that a physical prototype of the vehicle is required before its durability can be evaluated. If we were able to evaluate the durability of the vehicle without any physical part or a full prototype of the vehicle available, great cost and time savings may be gained. These possible gains have lead to the use of computer aided engineering (CAE) tools. These tools have supplemented the proving ground durability test by using historical measured data and/or predicted data from vehicle simulation models, as input to the durability analyses i.e. Finite Element Analyses (FEA). The usefulness of the historical test data is limited and many of the vehicle simulation models that are used to predict the input data, have not been validated. In this study a validated mathematical model of a 40 ton flat bed tri-axle semi-trailer, able to predict the suspension forces, is created. The validation of the full vehicle model includes correlations for displacements, velocities, accelerations and forces of various vehicle parameters. A validated mathematical model of the air springs, that includes mass transfer and flow effects for use in full vehicle dynamic simulations, is also developed. The results obtained indicate that the air spring model, integrated into the full vehicle model, is able to give relative accurate predictions of displacements, velocities, accelerations and forces of various vehicle parameters, over a discrete road event and over a rough road. / Dissertation (MEng)--University of Pretoria, 2009. / Mechanical and Aeronautical Engineering / Unrestricted

No abstract is provided. / Thesis / Master of Engineering (MEngr) / Scope and contents: This thesis describes an analytical study of the dynamics of a tractor-semitrailer vehicle. Two mathematical models; an articulated vehicle with self steering semitrailer and an articulated vehicle with a standard semitrailer, are developed to describe the longitudinal, lateral, vertical, pitching, rolling and yawing motions of the vehicle on a rough road surface. The natural frequencies of and the damped eigenvalues for both models are calculated. The steady state response of the vehicle components to the sinusoidal input profile of varying frequencies is calculated and the response curves are computer plotted in each case. For the self-steering semitrailer, the effect of varying the spring stiffness at the fifth wheel is studied. The dynamic loads imparted to the pavement due to the dynamic action of the vehicle in response to road irregularities, are also calculated. A discussion of the conclusions drawn from the analysis is given.