Accelerated test for vehicle body durability basedon vehicle dynamics simulations using pseudodamage

Sammanfattning: Vehicle body durability evaluation strongly relies on the possibility of testing areal prototype on different testing surfaces, such as proving grounds, test rigsand real roads. Although many efforts have been made to reduce time requiredfor testing, this still remains one of the main resource-demanding phases in avehicle development. As direct consequence, more and more companies aim tooptimise and to improve vehicle development by means of CAE tools.This master thesis is a step towards virtual testing of a vehicle body, aimingto investigate and to select the most important measurements for a bodydurability evaluation and to reproduce an invariant excitation that could beapplied to other vehicle models for new durability assessments without theneed of real measurements from other models. Moreover, a comparison betweenfrequency-based methods and time-based methods and their differences werehighlighted and the validity of ISO8608:2016 discussed.The method relied on small sets of simple and easy-to-get internal measurements,called desired signal, that allowed back-calculation of wheel hubdisplacements and other excitations by means of the product of the model’stransfer function and desired signal. Then, the iteration procedure allowedto drastically reduce the error between the desired signal and the computedone and it proved to be essential in the process. Thanks to this procedure,damage information of also the not-measured signals could be computed andtheir damage assessed and thus available for durability purposes. Moreover, thechance of applying the same measurements taken from a real vehicle to a modelof a newer generation was investigated. This would avoid the need of buildinga running prototype, allowing a more accurate durability assessment alreadyavailable in the pre-design phase.As a result, using a specific set of 8 measurements, other 22 other forces,displacements and velocities of several components were precisely reproduced,showing that not all measurement are equally valuable in a durability evaluation.A method for the measurement selection, called Observability Method, wasthen developed and compared with a set of measurements selected by meansof experience, showing a better convergence of the pseudo damage and similarpseudo damage values. Eventually a small set of measures from an older carwas applied to a newer version. It was proved that a detailed knowledge ofthe car model is needed, in order to successfully back-calculate the relevantmeasurements.